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  • 1.
    Andersson, Tage
    et al.
    SMHI, Research Department.
    Gustafsson, Nils
    SMHI, Research Department, Meteorology.
    COAST OF DEPARTURE AND COAST OF ARRIVAL - 2 IMPORTANT CONCEPTS FOR THE FORMATION AND STRUCTURE OF CONVECTIVE SNOWBANDS OVER SEAS AND LAKES1994In: Monthly Weather Review, ISSN 0027-0644, E-ISSN 1520-0493, Vol. 122, no 6, p. 1036-1049Article in journal (Refereed)
    Abstract [en]

    A case with intense convective snowbands over the Baltic Sea is examined using the High-Resolution Limited Area Model. The intention is to gain a better insight into the importance of the shape of the cowta, the orography, and the surface roughness on the formation and evolution of the snowbands. Among the factors studied am the shape of the coast from which the air departs and that to which it arrives. These factors are so important that two new concepts-coast of departure and coast of arrival-are introduced.

  • 2. Ashcroft, Linden
    et al.
    Coll, Joan Ramon
    Gilabert, Alba
    Domonkos, Peter
    Brunet, Manola
    Aguilar, Enric
    Castella, Merce
    Sigro, Javier
    Harris, Ian
    Undén, Per
    SMHI, Research Department, Meteorology.
    Jones, Phil
    A rescued dataset of sub-daily meteorological observations for Europe and the southern Mediterranean region, 1877-20122018In: Earth System Science Data, ISSN 1866-3508, E-ISSN 1866-3516, Vol. 10, no 3, p. 1613-1635Article in journal (Refereed)
  • 3. Baron, P.
    et al.
    Murtagh, D. P.
    Urban, J.
    Sagawa, H.
    Ochiai, S.
    Kasai, Y.
    Kikuchi, K.
    Khosrawi, F.
    Körnich, Heiner
    SMHI, Research Department, Meteorology.
    Mizobuchi, S.
    Sagi, K.
    Yasui, M.
    Observation of horizontal winds in the middle-atmosphere between 30 degrees S and 55 degrees N during the northern winter 2009-20102013In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 13, no 12, p. 6049-6064Article in journal (Refereed)
    Abstract [en]

    Although the links between stratospheric dynamics, climate and weather have been demonstrated, direct observations of stratospheric winds are lacking, in particular at altitudes above 30 km. We report observations of winds between 8 and 0.01 hPa (similar to 35-80 km) from October 2009 to April 2010 by the Superconducting Submillimeter-Wave Limb-Emission Sounder (SMILES) on the International Space Station. The altitude range covers the region between 35-60 km where previous space-borne wind instruments show a lack of sensitivity. Both zonal and meridional wind components were obtained, though not simultaneously, in the latitude range from 30 degrees S to 55 degrees N and with a single profile precision of 7-9 ms(-1) between 8 and 0.6 hPa and better than 20 ms(-1) at altitudes above. The vertical resolution is 5-7 km except in the upper part of the retrieval range (10 km at 0.01 hPa). In the region between 1-0.05 hPa, an absolute value of the mean difference <2 ms(-1) is found between SMILES profiles retrieved from different spectroscopic lines and instrumental settings. Good agreement (absolute value of the mean difference of similar to 2 ms(-1)) is also found with the European Centre for Medium-Range Weather Forecasts (ECMWF) analysis in most of the stratosphere except for the zonal winds over the equator (difference >5 ms(-1)). In the mesosphere, SMILES and ECMWF zonal winds exhibit large differences (>20 ms(-1)), especially in the tropics. We illustrate our results by showing daily and monthly zonal wind variations, namely the semi-annual oscillation in the tropics and reversals of the flow direction between 50-55 degrees N during sudden stratospheric warmings. The daily comparison with ECMWF winds reveals that in the beginning of February, a significantly stronger zonal westward flow is measured in the tropics at 2 hPa compared to the flow computed in the analysis (difference of similar to 20 ms(-1)). The results show that the comparison between SMILES and ECMWF winds is not only relevant for the quality assessment of the new SMILES winds, but it also provides insights on the quality of the ECMWF winds themselves. Although the instrument was not specifically designed for measuring winds, the results demonstrate that space-borne sub-mm wave radiometers have the potential to provide good quality data for improving the stratospheric winds in atmospheric models.

  • 4.
    Bengtsson,, Lennart
    et al.
    SMHI.
    Gustafsson, Nils
    SMHI, Research Department, Meteorology.
    Döös, Bo
    SMHI.
    Söderman, Daniel
    Helsinki University in Finland.
    Moen, Lars
    SMHI, Research Department, Climate research - Rossby Centre.
    Thompson, Thomas
    SMHI.
    Jakobsson, Paul
    SMHI.
    Bleckert, Gunnar
    SMHI.
    Henriksson, Ann-Beate
    SMHI.
    Lindgren, Bo
    SMHI.
    Kållberg, Per
    SMHI, Research Department, Meteorology.
    The Meteorological Auto Code (MAC) and Numerical Weather Prediction (NWP) at SMHI2016Report (Other academic)
    Abstract [en]

    Sweden was a pioneering country in the development of NumericalWeather Prediction (NWP). The worlds first operational numerical forecast was produced already in 1954 by the International Meteorological Institute in Stockholm. SMHI started a bit later, but in 1961 a long term program for development of NWP was initiated. The activities grew gradually during the 1960’s and resulted in a core component for the SMHI forecast services. An early challenge was to overcome the limited computational resources with slow computational speed, small memory size and primitive software support. It was necessary to compensate for these limitations with dedicated work and creativity. A core component in this work was the software system MAC (Meteorological Auto Code) that was developed by the NWP group at SMHI. The MAC system is described in detail in this report and it included all computational software needed for the weather service, for example numerical models, objective analysis techniques, automatic data extraction, quality control of observations as well as forecast products in graphical or digital form.

    We hope that this report will provide the younger generation with some insight into the conditions for development of NWP during the 1960’s.

  • 5.
    Bengtsson, Lisa
    et al.
    SMHI, Research Department, Meteorology.
    Andrae, Ulf
    SMHI, Research Department, Meteorology.
    Aspelien, Trygve
    SMHI.
    Batrak, Yurii
    Calvo, Javier
    de Rooy, Wim
    Gleeson, Emily
    Hansen-Sass, Bent
    Homleid, Mariken
    Hortal, Mariano
    Ivarsson, Karl-Ivar
    SMHI, Core Services.
    Lenderink, Geert
    Niemelza, Sami
    Nielsen, Kristian Pagh
    Onvlee, Jeanette
    Rontu, Laura
    SMHI.
    Samuelsson, Patrick
    SMHI, Research Department, Climate research - Rossby Centre.
    Santos Munoz, Daniel
    Subias, Alvaro
    Tijm, Sander
    Toll, Velle
    Yang, Xiaohua
    Koltzow, Morten Odegaard
    The HARMONIE-AROME Model Configuration in the ALADIN-HIRLAM NWP System2017In: Monthly Weather Review, ISSN 0027-0644, E-ISSN 1520-0493, Vol. 145, no 5, p. 1919-1935Article in journal (Refereed)
  • 6.
    Bengtsson, Lisa
    et al.
    SMHI, Research Department, Meteorology.
    Körnich, Heiner
    SMHI, Research Department, Meteorology.
    Impact of a stochastic parametrization of cumulus convection, using cellular automata, in a mesoscale ensemble prediction system2016In: Quarterly Journal of the Royal Meteorological Society, ISSN 0035-9009, E-ISSN 1477-870X, Vol. 142, no 695, p. 1150-1159Article in journal (Refereed)
    Abstract [en]

    A stochastic parametrization for deep convection, based on cellular automata, has been evaluated in the high-resolution (2.5 km) ensemble prediction system Hirlam Aladin Regional Mesoscale Operational NWP Ensemble Prediction System (HarmonEPS). We studied whether such a stochastic physical parametrization, whilst implemented in a deterministic forecast model, can have an impact on the performance of the uncertainty estimates given by an ensemble prediction system. Various feedback mechanisms in the parametrization were studied with respect to ensemble spread and skill, in both subgrid and resolved precipitation fields. It was found that the stochastic parametrization improves the model skill in general, by reducing a positive bias in precipitation. This reduction in bias, however, led to a reduction in ensemble spread of precipitation. Overall, scores that measure the accuracy and reliability of probabilistic predictions indicate that the net impact (improved skill, degraded spread) of the ensemble prediction system is improved for 6 h accumulated precipitation with the stochastic parametrization and is rather neutral for other quantities examined.

  • 7.
    Bengtsson, Lisa
    et al.
    SMHI, Research Department, Meteorology.
    Körnich, Heiner
    SMHI, Research Department, Meteorology.
    Kaellen, Erland
    Svensson, Gunilla
    Large-Scale Dynamical Response to Subgrid-Scale Organization Provided by Cellular Automata2011In: Journal of Atmospheric Sciences, ISSN 0022-4928, E-ISSN 1520-0469, Vol. 68, no 12, p. 3132-3144Article in journal (Refereed)
    Abstract [en]

    Because of the limited resolution of numerical weather prediction (NWP) models, subgrid-scale physical processes are parameterized and represented by gridbox means. However, some physical processes are better represented by a mean and its variance; a typical example is deep convection, with scales varying from individual updrafts to organized mesoscale systems. This study investigates, in an idealized setting, whether a cellular automaton (CA) can be used to enhance subgrid-scale organization by forming clusters representative of the convective scales and thus yield a stochastic representation of subgrid-scale variability. The authors study the transfer of energy from the convective to the larger atmospheric scales through nonlinear wave interactions. This is done using a shallow water (SW) model initialized with equatorial wave modes. By letting a CA act on a finer resolution than that of the SW model, it can be expected to mimic the effect of, for instance, gravity wave propagation on convective organization. Employing the CA scheme permits the reproduction of the observed behavior of slowing down equatorial Kelvin modes in convectively active regions, while random perturbations fail to feed back on the large-scale flow. The analysis of kinetic energy spectra demonstrates that the CA subgrid scheme introduces energy backscatter from the smallest model scales to medium scales. However, the amount of energy backscattered depends almost solely on the memory time scale introduced to the subgrid scheme, whereas any variation in spatial scales generated does not influence the energy spectra markedly.

  • 8.
    Bengtsson, Lisa
    et al.
    SMHI, Research Department, Meteorology.
    Magnusson, Linus
    Källén, Erland
    Independent Estimations of the Asymptotic Variability in an Ensemble Forecast System2008In: Monthly Weather Review, ISSN 0027-0644, E-ISSN 1520-0493, Vol. 136, no 11, p. 4105-4112Article in journal (Refereed)
    Abstract [en]

    One desirable property within an ensemble forecast system is to have a one-to-one ratio between the root-mean-square error (rmse) of the ensemble mean and the standard deviation of the ensemble (spread). The ensemble spread and forecast error within the ECMWF ensemble prediction system has been extrapolated beyond 10 forecast days using a simple model for error growth. The behavior of the ensemble spread and the rmse at the time of the deterministic predictability are compared with derived relations of rmse at the infinite forecast length and the characteristic variability of the atmosphere in the limit of deterministic predictability. Utilizing this methodology suggests that the forecast model and the atmosphere do not have the same variability, which raises the question of how to obtain a perfect ensemble.

  • 9.
    Bengtsson, Lisa
    et al.
    SMHI, Research Department, Meteorology.
    Steinheimer, Martin
    Bechtold, Peter
    Geleyn, Jean-Francois
    A stochastic parametrization for deep convection using cellular automata2013In: Quarterly Journal of the Royal Meteorological Society, ISSN 0035-9009, E-ISSN 1477-870X, Vol. 139, no 675, p. 1533-1543Article in journal (Refereed)
    Abstract [en]

    A cellular automaton (CA) is introduced to the deep convection parametrization of the high-resolution limited-area model Aire Limitee Adaptation/Application de la Recherche a l'Operationnel (ALARO). The self-organizational characteristics of the CA allow for lateral communication between adjacent numerical weather prediction (NWP) model grid boxes and add additional memory to the deep convection scheme. The CA acts in two horizontal dimensions, with finer grid spacing than the NWP model. It is randomly seeded in regions where convective available potential energy (CAPE) exceeds a threshold value. Both deterministic and probabilistic rules, coupled to the large-scale wind, are explored to evolve the CA in time. Case studies indicate that the scheme has the potential to organize cells along convective squall lines and enhance advective effects. An ensemble of forecasts using the present CA scheme demonstrated an ensemble spread in the resolved wind field in regions where deep convection is large. Such a spread represents the uncertainty due to subgrid variability of deep convection and could be an interesting addition to an ensemble prediction system.

  • 10.
    Bengtsson, Lisa
    et al.
    SMHI, Research Department, Meteorology.
    Tijm, Sander
    Vana, Filip
    Svensson, Gunilla
    Impact of Flow-Dependent Horizontal Diffusion on Resolved Convection in AROME2012In: Journal of Applied Meteorology and Climatology, ISSN 1558-8424, E-ISSN 1558-8432, Vol. 51, no 1, p. 54-67Article in journal (Refereed)
    Abstract [en]

    Horizontal diffusion in numerical weather prediction models is, in general, applied to reduce numerical noise at the smallest atmospheric scales. In convection-permitting models, with horizontal grid spacing on the order of 1-3 km, horizontal diffusion can improve the model skill of physical parameters such as convective precipitation. For instance, studies using the convection-permitting Applications of Research to Operations at Mesoscale model (AROME) have shown an improvement in forecasts of large precipitation amounts when horizontal diffusion is applied to falling hydrometeors. The nonphysical nature of such a procedure is undesirable, however. Within the current AROME, horizontal diffusion is imposed using linear spectral horizontal diffusion on dynamical model fields. This spectral diffusion is complemented by nonlinear, flow-dependent, horizontal diffusion applied on turbulent kinetic energy, cloud water, cloud ice, rain, snow, and graupel. In this study, nonlinear flow-dependent diffusion is applied to the dynamical model fields rather than diffusing the already predicted falling hydrometeors. In particular, the characteristics of deep convection are investigated. Results indicate that, for the same amount of diffusive damping, the maximum convective updrafts remain strong for both the current and proposed methods of horizontal diffusion. Diffusing the falling hydrometeors is necessary to see a reduction in rain intensity, but a more physically justified solution can be obtained by increasing the amount of damping on the smallest atmospheric scales using the nonlinear, flow-dependent, diffusion scheme. In doing so, a reduction in vertical velocity was found, resulting in a reduction in maximum rain intensity.

  • 11. Berner, Judith
    et al.
    Achatz, Ulrich
    Batte, Lauriane
    Bengtsson, Lisa
    SMHI, Research Department, Meteorology.
    de la Camara, Alvaro
    Christensen, Hannah M.
    Colangeli, Matteo
    Coleman, Danielle R. B.
    Crommelin, Daaaan
    Dolaptchiev, Stamen I.
    Franzke, Christian L. E.
    Friederichs, Petra
    Imkeller, Peter
    Jarvinen, Heikki
    Juricke, Stephan
    Kitsios, Vassili
    Lott, Francois
    Lucarini, Valerio
    Mahajan, Salil
    Palmer, Timothy N.
    Penland, Cecile
    Sakradzija, Mirjana
    von Storch, Jin-Song
    Weisheimer, Antje
    Weniger, Michael
    Williams, Paul D.
    Yano, Jun-Ichi
    STOCHASTIC PARAMETERIZATION Toward a New View of Weather and Climate Models2017In: Bulletin of The American Meteorological Society - (BAMS), ISSN 0003-0007, E-ISSN 1520-0477, Vol. 98, no 3, p. 565-587Article in journal (Refereed)
  • 12. Berntell, Ellen
    et al.
    Zhang, Qiong
    Chafik, Leon
    Körnich, Heiner
    SMHI, Research Department, Meteorology.
    Representation of Multidecadal Sahel Rainfall Variability in 20th Century Reanalyses2018In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 8, article id 10937Article in journal (Refereed)
  • 13. Blazica, V.
    et al.
    Gustafsson, Nils
    SMHI, Research Department, Meteorology.
    Zagar, N.
    The impact of periodization methods on the kinetic energy spectra for limited-area numerical weather prediction models2015In: Geoscientific Model Development, ISSN 1991-959X, E-ISSN 1991-9603, Vol. 8, no 1, p. 87-97Article in journal (Refereed)
    Abstract [en]

    The paper deals with the comparison of the most common periodization methods used to obtain spectral fields of limited-area models for numerical weather prediction. The focus is on the impact that the methods have on the spectra of the fields, which are used for verification and tuning of the models. A simplified model is applied with random fields that obey a known kinetic energy spectrum. The periodization methods under consideration are detrending, the discrete cosine transform and the application of an extension zone. For the extension zone, three versions are applied: the Boyd method, the ALADIN method and the HIRLAM method. The results show that detrending and the discrete cosine transform have little impact on the spectra, as does the Boyd method for extension zone. For the ALADIN and HIRLAM methods, the impact depends on the width of the extension zone - the wider the zone, the more artificial energy and the larger impact on the spectra. The width of the extension zone correlates to the modifications in the shape of the spectra as well as to the amplitudes of the additional energy in the spectra.

  • 14. Bojarova, Jelena
    et al.
    Gustafsson, Nils
    SMHI, Research Department, Meteorology.
    Johansson, Åke
    SMHI, Research Department, Meteorology.
    Vignes, Ole
    The ETKF rescaling scheme in HIRLAM2011In: Tellus. Series A, Dynamic meteorology and oceanography, ISSN 0280-6495, E-ISSN 1600-0870, Vol. 63, no 3, p. 385-401Article in journal (Refereed)
    Abstract [en]

    The ETKF rescaling scheme has been implemented into the HIRLAM forecasting system in order to estimate the uncertainty of the model state. The main purpose is to utilize this uncertainty information for modelling of flow-dependent background error covariances within the framework of a hybrid variational ensemble data assimilation scheme. The effects of rank-deficiency in the ETKF formulation is explained and the need for variance inflation as a way to compensate for these effects is justified. A filter spin-up algorithm is proposed as a refinement of the variance inflation. The proposed spin-up algorithm will also act to prevent ensemble collapse since the ensemble will receive 'fresh blood' in the form of additional perturbation components, generated on the basis of a static background error covariance matrix. The resulting ETKF-based ensemble perturbations are compared with ensemble perturbations based on targeted singular vectors and are shown to have more realistic spectral characteristics.

  • 15. Bolin, Karl
    et al.
    Almgren, Martin
    Olsson, Esbjörn
    SMHI, Research Department, Meteorology.
    Karasalo, Ilkka
    Long term estimations of low frequency noise levels over water from an off-shore wind farm2014In: Journal of the Acoustical Society of America, ISSN 0001-4966, E-ISSN 1520-8524, Vol. 135, no 3, p. 1106-1114Article in journal (Refereed)
    Abstract [en]

    This article focuses on computations of low frequency sound propagation from an off-shore wind farm. Two different methods for sound propagation calculations are combined with meteorological data for every 3 hours in the year 2010 to examine the varying noise levels at a reception point at 13 km distance. It is shown that sound propagation conditions play a vital role in the noise impact from the off-shore wind farm and ordinary assessment methods can become inaccurate at longer propagation distances over water. Therefore, this paper suggests that methodologies to calculate noise immission with realistic sound speed profiles need to be combined with meteorological data over extended time periods to evaluate the impact of low frequency noise from modern off-shore wind farms. (C) 2014 Acoustical Society of America.

  • 16. Boone, Aaron
    et al.
    Samuelsson, Patrick
    SMHI, Research Department, Climate research - Rossby Centre.
    Gollvik, Stefan
    SMHI, Research Department, Meteorology.
    Napoly, Adrien
    Jarlan, Lionel
    Brun, Eric
    Decharme, Bertrand
    The interactions between soil-biosphere-atmosphere land surface model with a multi-energy balance (ISBA-MEB) option in SURFEXv8-Part 1: Model description2017In: Geoscientific Model Development, ISSN 1991-959X, E-ISSN 1991-9603, Vol. 10, no 2, p. 843-872Article in journal (Refereed)
  • 17. Borsche, M.
    et al.
    Kaiser-Weiss, A. K.
    Undén, Per
    SMHI, Research Department, Meteorology.
    Kaspar, F.
    Methodologies to characterize uncertainties in regional reanalyses2015In: Advances in Science and Research, ISSN 1992-0628, E-ISSN 1992-0636, Vol. 12, p. 207-218Article in journal (Refereed)
    Abstract [en]

    When using climate data for various applications, users are confronted with the difficulty to assess the uncertainties of the data. For both in-situ and remote sensing data the issues of representativeness, homogeneity, and coverage have to be considered for the past, and their respective change over time has to be considered for any interpretation of trends. A synthesis of observations can be obtained by employing data assimilation with numerical weather prediction (NWP) models resulting in a meteorological reanalysis. Global reanalyses can be used as boundary conditions for regional reanalyses (RRAs), which run in a limited area (Europe in our case) with higher spatial and temporal resolution, and allow for assimilation of more regionally representative observations. With the spatially highly resolved RRAs, which exhibit smaller scale information, a more realistic representation of extreme events (e.g. of precipitation) compared to global reanalyses is aimed for. In this study, we discuss different methods for quantifying the uncertainty of the RRAs to answer the question to which extent the smaller scale information (or resulting statistics) provided by the RRAs can be relied on. Within the European Union's seventh Framework Programme (EU FP7) project Uncertainties in Ensembles of Regional Re-Analyses (UERRA) ensembles of RRAs (both multi-model and single model ensembles) are produced and their uncertainties are quantified. Here we explore the following methods for characterizing the uncertainties of the RRAs: (A) analyzing the feedback statistics of the assimilation systems, (B) validation against station measurements and (C) grids derived thereof, and (D) against gridded satellite data products. The RRA ensembles (E) provide the opportunity to derive ensemble scores like ensemble spread and other special probabilistic skill scores. Finally, user applications (F) are considered. The various methods are related to user questions they can help to answer.

  • 18.
    Bringfelt, Björn
    et al.
    SMHI, Research Department, Climate research - Rossby Centre.
    Heikinheimo, M
    Gustafsson, Nils
    SMHI, Research Department, Meteorology.
    Perov, Veniamin
    SMHI, Research Department, Meteorology.
    Lindroth, A
    A new land-surface treatment for HIRLAM - comparisons with NOPEX measurements1999In: Agricultural and Forest Meteorology, ISSN 0168-1923, E-ISSN 1873-2240, Vol. 98-9, p. 239-256Article in journal (Refereed)
    Abstract [en]

    In order to improve the accuracy of forecasting near-surface atmospheric variables over a heterogeneous landscape, a framework of subgrid surface types and the ISBA parameterisation scheme for land surfaces have been tested in the operational weather forecast model HIRLAM, using a 5.5 km grid resolution. Surface energy fluxes measured during a single summer day at six fixed sites in the NOPEX area, representing agricultural fields, boreal forests and lakes, were used for verification. Both, in-situ field measurements and the HIRLAM simulation indicated that the Bowen ratio over forests was about twice as large as that of adjacent agricultural fields. This difference could be explained by the more effective turbulent mixing and larger surface resistance associated with the forest, thus making the sensible heat flux relatively large there. The use of initial soil moisture from a routine hydrological model gave improved agreement with measured surface fluxes and radiosonde temperature and humidity profiles compared to initialising from routine HIRLAM surface data. The differences in heat fluxes between the various surface types were also demonstrated by airborne flux measurements flown along a track at a height of ca. 100 m above the terrain. Modelled heat fluxes along the flight track were considerably smoothed due to the grid resolution used, e.g. the effect of a lake in reducing grid-averaged sensible heat flux could only be weakly detected, because the lake surface represented only 10% of the grid area. When the proportion of a contrasting surface type (lake) was altered from 10 to 100%, the surface fluxes calculated for the lake surface were almost unchanged; the results of the comparison did not provide evidence that more complex aggregation schemes for heat fluxes than straightforward area-weighted averaging would be required. The hourly variation of the modelled and simulated heat fluxes during the day studied could not be directly compared, because the simulated cloudiness did not exactly match that observed at the field sites. When the simulated net radiation was replaced with direct measurements, the model-based estimates of sensible and latent heat fluxes were closer to the corresponding field measurements. The divergence of sensible heat flux with height, as inferred from the tower measurements made over the forest, were supported by the aircraft measurements and the HIRLAM simulations. (C) 1999 Elsevier Science B.V. All rights reserved.

  • 19. Chen, Hans W.
    et al.
    Zhang, Qiong
    Körnich, Heiner
    SMHI, Research Department, Meteorology.
    Chen, Deliang
    A robust mode of climate variability in the Arctic: The Barents Oscillation2013In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 40, no 11, p. 2856-2861Article in journal (Refereed)
    Abstract [en]

    The Barents Oscillation (BO) is an anomalous wintertime atmospheric circulation pattern in the Northern Hemisphere that has been linked to the meridional flow over the Nordic Seas. There are speculations that the BO has important implications for the Arctic climate; however, it has also been suggested that the pattern is an artifact of Empirical Orthogonal Function (EOF) analysis due to an eastward shift of the Arctic Oscillation/North Atlantic Oscillation (AO/NAO). In this study, EOF analyses are performed to show that a robust pattern resembling the BO can be found during different time periods, even when the AO/NAO is relatively stationary. This BO has a high and stable temporal correlation with the geostrophic zonal wind over the Barents Sea, while the contribution from the AO/NAO is small. The surface air temperature anomalies over the Barents Sea are closely associated with this mode of climate variability.

  • 20. Cuxart, J
    et al.
    Holtslag, A A M
    Beare, R J
    Bazile, E
    Beljaars, A
    Cheng, A
    Conangla, L
    Ek, M
    Freedman, F
    Hamdi, R
    Kerstein, A
    Kitagawa, H
    Lenderink, G
    Lewellen, D
    Mailhot, J
    Mauritsen, T
    Perov, Veniamin
    SMHI, Research Department, Meteorology.
    Schayes, G
    Steeneveld, G J
    Svensson, G
    Taylor, P
    Weng, W
    Wunsch, S
    Xu, K M
    Single-column model intercomparison for a stably stratified atmospheric boundary layer2006In: Boundary-layer Meteorology, ISSN 0006-8314, E-ISSN 1573-1472, Vol. 118, no 2, p. 273-303Article in journal (Refereed)
    Abstract [en]

    The parameterization of the stably stratified atmospheric boundary layer is a difficult issue, having a significant impact on medium-range weather forecasts and climate integrations. To pursue this further, a moderately stratified Arctic case is simulated by nineteen single-column turbulence schemes. Statistics from a large-eddy simulation intercomparison made for the same case by eleven different models are used as a guiding reference. The single-column parameterizations include research and operational schemes from major forecast and climate research centres. Results from first-order schemes, a large number of turbulence kinetic energy closures, and other models were used. There is a large spread in the results; in general, the operational schemes mix over a deeper layer than the research schemes, and the turbulence kinetic energy and other higher-order closures give results closer to the statistics obtained from the large-eddy simulations. The sensitivities of the schemes to the parameters of their turbulence closures are partially explored.

  • 21.
    Dahlgren, Per
    et al.
    SMHI, Research Department, Meteorology.
    Gustafsson, Nils
    SMHI, Research Department, Meteorology.
    Assimilating host model information into a limited area model2012In: Tellus. Series A, Dynamic meteorology and oceanography, ISSN 0280-6495, E-ISSN 1600-0870, Vol. 64, article id 15836Article in journal (Refereed)
    Abstract [en]

    We propose to add an extra source of information to the data-assimilation of the regional HIgh Resolution Limited Area Model (HIRLAM) model, constraining larger scales to the host model providing the lateral boundary conditions. An extra term, J(k), measuring the distance to the large-scale vorticity of the host model, is added to the cost-function of the variational data-assimilation. Vorticity is chosen because it is a good representative of the large-scale flow and because vorticity is a basic control variable of the HIRLAM variational data-assimilation. Furthermore, by choosing only vorticity, the remaining model variables, divergence, temperature, surface pressure and specific humidity will be allowed to adapt to the modified vorticity field in accordance with the internal balance constraints of the regional model. The error characteristics of the J(k) term are described by the horizontal spectral densities and the vertical eigenmodes (eigenvectors and eigenvalues) of the host model vorticity forecast error fields, expressed in the regional model geometry. The vorticity field, provided by the European Centre for Medium-range Weather Forecasts (ECMWF) operational model, was assimilated into the HIRLAM model during an experiment period of 33 d in winter with positive impact on forecast verification statistics for upper air variables and mean sea level pressure.

  • 22.
    Dahlgren, Per
    et al.
    SMHI, Research Department, Meteorology.
    Landelius, Tomas
    SMHI, Research Department, Atmospheric remote sensing.
    Kållberg, Per
    SMHI, Research Department, Meteorology.
    Gollvik, Stefan
    SMHI, Research Department, Meteorology.
    A high-resolution regional reanalysis for Europe. Part 1: Three-dimensional reanalysis with the regional HIgh-Resolution Limited-Area Model (HIRLAM)2016In: Quarterly Journal of the Royal Meteorological Society, ISSN 0035-9009, E-ISSN 1477-870X, Vol. 142, no 698, p. 2119-2131Article in journal (Refereed)
  • 23. Dee, D. P.
    et al.
    Uppala, S. M.
    Simmons, A. J.
    Berrisford, P.
    Poli, P.
    Kobayashi, S.
    Andrae, U.
    Balmaseda, M. A.
    Balsamo, G.
    Bauer, P.
    Bechtold, P.
    Beljaars, A. C. M.
    van de Berg, L.
    Bidlot, J.
    Bormann, N.
    Delsol, C.
    Dragani, R.
    Fuentes, M.
    Geer, A. J.
    Haimberger, L.
    Healy, S. B.
    Hersbach, H.
    Holm, E. V.
    Isaksen, L.
    Kållberg, Per
    SMHI, Research Department, Meteorology.
    Koehler, M.
    Matricardi, M.
    McNally, A. P.
    Monge-Sanz, B. M.
    Morcrette, J. -J
    Park, B. -K
    Peubey, C.
    de Rosnay, P.
    Tavolato, C.
    Thepaut, J. -N
    Vitart, F.
    The ERA-Interim reanalysis: configuration and performance of the data assimilation system2011In: Quarterly Journal of the Royal Meteorological Society, ISSN 0035-9009, E-ISSN 1477-870X, Vol. 137, no 656, p. 553-597Article, review/survey (Refereed)
    Abstract [en]

    ERA-Interim is the latest global atmospheric reanalysis produced by the European Centre for Medium-Range Weather Forecasts (ECMWF). The ERA-Interim project was conducted in part to prepare for a new atmospheric reanalysis to replace ERA-40, which will extend back to the early part of the twentieth century. This article describes the forecast model, data assimilation method, and input datasets used to produce ERA-Interim, and discusses the performance of the system. Special emphasis is placed on various difficulties encountered in the production of ERA-40, including the representation of the hydrological cycle, the quality of the stratospheric circulation, and the consistency in time of the reanalysed fields. We provide evidence for substantial improvements in each of these aspects. We also identify areas where further work is needed and describe opportunities and objectives for future reanalysis projects at ECMWF. Copyright (C) 2011 Royal Meteorological Society

  • 24. Fortelius, C
    et al.
    Andrae, Ulf
    SMHI, Research Department, Meteorology.
    Forsblom, M
    The BALTEX regional reanalysis project2002In: Boreal environment research, ISSN 1239-6095, E-ISSN 1797-2469, Vol. 7, no 3, p. 193-201Article in journal (Refereed)
    Abstract [en]

    The BALTEX regional reassimilation project uses meteorological data assimilation for quantifying the climatic energy and water cycles over the catchment basin of the Baltic Sea during the course of one annual cycle, Sep. 1999-Oct. 2000. This report presents the data assimilation system used, the available products, and a sample of preliminary results. The latter demonstrate that the system is capable of simulating the essential features of the energy and water cycles of the Baltic drainage basin. We find this encouraging, because the model has not been tuned to reproduce these cycles, but mainly to predict the atmospheric state.

  • 25. FRANZEN, LG
    et al.
    HJELMROOS, M
    Kållberg, Per
    SMHI, Research Department, Meteorology.
    BRORSTROMLUNDEN, E
    JUNTTO, S
    SAVOLAINEN, AL
    THE YELLOW-SNOW EPISODE OF NORTHERN FENNOSCANDIA, MARCH-1991 - A CASE-STUDY OF LONG-DISTANCE TRANSPORT OF SOIL, POLLEN AND STABLE ORGANIC-COMPOUNDS1994In: Atmospheric Environment, ISSN 1352-2310, E-ISSN 1873-2844, Vol. 28, no 22, p. 3587-3604Article in journal (Refereed)
    Abstract [en]

    The present paper describes a vast dustfall with snow in northern Fennoscandia, 10 March 1991. The area affected by dust deposition was at least 320,000 km(2). and the particulate mass received amounted to between 50 and 200 mg m(-2). The total amounts of dust deposited in the investigated area sum up to approximately 50,000 tonnes. The dust consisted of soil particles, i.e. single mineral grains and loose ferric aggregates of mineral grains in addition to pollen and spores. Mineralogically, the dust was dominated by small rounded quartz grains. Median size of the dust particles was 2.72 mu m. The total pollen concentration varied from 327 to 1172 pollen cm(-2). The pollen types identified were divided in ''Nordic/Central European'' taxa and ''Exotic'' taxa. Pollen from the former group, e.g. Betula, Alnus and Corylus were believed to originate in the Alps and in the northern parts of Central Europe where these species were flowering. The latter category was considered to originate in more remote areas, many of them belonging to the taxa growing only around the Mediterranean. From a paleo-ecological point of view, long-distance transport such as this would count for an important potential source of error whenever interpreting Holocene pollen diagrams. The content of stable organic compounds showed that the dust was relatively clean, compared to other episodes, when the dust deposited had originated in heavily polluted regions. The small amounts of chlorinated hydrocarbons, polychlorinated biphenyles (PCB), polyaromated hydrocarbons (PAH) and other hydrocarbons found, are believed to have been adsorbed by the particle surfaces during transportation. The results of the study, along with meteorological data, lead to the conclusion that the material originated in North Africa. Dust mobilization was reported in Tunisia as well as in Algeria. This means that the dust was transported at least 7000 km before deposition.

  • 26. Garstang, M
    et al.
    Tyson, P D
    Swap, R
    Edwards, M
    Kållberg, Per
    SMHI, Research Department, Meteorology.
    Lindesay, J A
    Horizontal and vertical transport of air over southern Africa1996In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 101, no D19, p. 23721-23736Article in journal (Refereed)
    Abstract [en]

    Tropospheric air trajectories that occurred during the Southern African Fire-Atmosphere Research Initiative (SAFARI) in August-October 1992 are described in terms of a circulation classification scheme and the vertical stability of the atmosphere. Three major and frequently occurring stable discontinuities are found to control vertical transport of aerosols in the subtropical atmosphere at the end of the dry season. Of these, the main subsidence-induced feature is a spatially ubiquitous and temporally persistent absolutely stable layer at an altitude of about 5 km (3.5 km above the interior plateau elevation). This effective obstacle to vertical mixing is observed to persist without break for up to 40 days. Below this feature an absolutely stable layer at 3 km (1.5 km above the surface) prevails on and off at the top of the surface mixing layer for up to 7 days at a time, being broken by the passage of regularly occurring westerly wave disturbances. Above the middle-level discontinuity a further absolutely stable layer is frequently discerned at an altitude of about 8 km. It is shown that five basic modes can be used to describe horizontal aerosol transportation fields over southern Africa. Dominating these is the anticyclone mode which results in frequent recirculation at spatial scales varying from hundreds to thousands of kilometers. In exiting the anticyclonic circulation, transport on the northern periphery of the system is to the west over the Atlantic Ocean via a semistationary easterly wave over the western part of the subcontinent. On the southern periphery, wave perturbations in the westerly enhance transports which exit the subcontinent to the east into the Indian Ocean. Independently derived data suggest that during SAFARI only 4% of the total transport of air from three locations south of 18 degrees 8 was into the Atlantic Ocean. Over 90% of the transport was into the Indian Ocean across 35 degrees E. This result reflects circulation fields typical of the extremely dry conditions prevailing in 1992. The integrated effect of the control exerted by atmospheric stability on vertical mixing, on the one hand, and the nature of the horizontal circulation fields, on the other, is to produce a distinctive suite of transport patterns that go a long way to explain the observed high concentrations of tropospheric aerosols and trace gases observed over the subcontinent in winter and spring, as well as over the tropical South Atlantic and southwestern Indian Oceans.

  • 27.
    Gollvik, Stefan
    SMHI, Research Department, Meteorology.
    On the effects of horizontal diffusion, resolution and orography on precipitation forecasting in a limited area model1999In: Meteorological Applications, ISSN 1350-4827, E-ISSN 1469-8080, Vol. 6, no 1, p. 49-58Article in journal (Refereed)
    Abstract [en]

    Precipitation forecasting experiments have been carried out with HIRLAM, a numerical weather prediction model. The model has been run with three different horizontal gridlengths: 22, 11 and 5.5 Km. An attempt has been made to estimate the appropriate magnitude of the horizontal diffusion, which is used to control small-scale noise in the model, by looking at Kinetic energy spectra. It is shown that, for the higher resolutions, smoothing the orography gives smoother precipitation patterns. The small-scale precipitation resulting from runs with the original orography has negligible extra skill compared to the smoothed orography runs. The results show that the model is able to forecast good precipitation amounts, even with 22 Km gridlengths. No significant improvements occur when the higher horizontal resolutions are used. Experiments have been performed using the tendencies of the physical parameterisations computed on a coarser grid than that of the dynamics. The resulting precipitation patterns are very similar and this indicates a more economical way of integrating the model.

  • 28.
    Gustafsson, Nils
    SMHI, Research Department, Meteorology.
    Control of lateral boundary conditions in four-dimensional variational data assimilation for a limited area model2012In: Tellus. Series A, Dynamic meteorology and oceanography, ISSN 0280-6495, E-ISSN 1600-0870, Vol. 64, article id 17518Article in journal (Refereed)
    Abstract [en]

    The limited area model forecasting problem is a lateral boundary condition (LBC) problem in addition to the initial condition problem. The data assimilation has traditionally been considered as a process for estimation of the initial condition only, while for the limited area data assimilation this estimation may be extended to include also the LBCs, at least during the data assimilation time window when observations are available. A procedure for such a control of the LBCs has been included in the four-dimensional variational data assimilation (4D-Var) scheme for the HIgh Resolution Limited Area Model (HIRLAM) forecasting system. A description of this procedure is provided together with results from idealised as well as real data experiments. The results indicate that control of LBCs may be important with small forecast domains and in particular for weather disturbances moving quickly into and through the forecast domain.

  • 29.
    Gustafsson, Nils
    SMHI, Research Department, Meteorology.
    Discussion on '4D-Var or EnKF?'2007In: Tellus. Series A, Dynamic meteorology and oceanography, ISSN 0280-6495, E-ISSN 1600-0870, Vol. 59, no 5, p. 774-777Article in journal (Other academic)
  • 30.
    Gustafsson, Nils
    SMHI, Research Department, Meteorology.
    Statistical issues in weather forecasting2002In: Scandinavian Journal of Statistics, ISSN 0303-6898, E-ISSN 1467-9469, Vol. 29, no 2, p. 219-239Article in journal (Refereed)
    Abstract [en]

    Research and operational applications in weather forecasting are reviewed, with emphasis on statistical issues. It is argued that the deterministic approach has dominated in weather forecasting, although weather forecasting is a probabilistic problem by nature. The reason has been the successful application of numerical weather prediction techniques over the 50 years since the introduction of computers. A gradual change towards utilization of more probabilistic methods has occurred over the last decade; in particular meteorological data assimilation, ensemble forecasting and post-processing of model output have been influenced by ideas from statistics and control theory.

  • 31.
    Gustafsson, Nils
    et al.
    SMHI, Research Department, Meteorology.
    Berre, Loik
    SMHI, Research Department, Atmospheric remote sensing.
    Hörnquist, Sara
    SMHI, Research Department, Atmospheric remote sensing.
    Huang, X Y
    Lindskog, Magnus
    SMHI, Research Department, Meteorology.
    Navascues, B
    Mogensen, K S
    Thorsteinsson, S
    Three-dimensional variational data assimilation for a limited area model Part I: General formulation and the background error constraint2001In: Tellus. Series A, Dynamic meteorology and oceanography, ISSN 0280-6495, E-ISSN 1600-0870, Vol. 53, no 4, p. 425-446Article in journal (Refereed)
    Abstract [en]

    A 3-dimensional variational data assimilation (3D-Var) scheme for the HIgh Resolution Limited Area Model (HIRLAM) forecasting system is described. The HIRLAM 3D-Var is based on the minimization of a cost function that consists of one term J(b). which measures the distance between the resulting analysis and a background field, in general a short-range forecast. and another term J(o). which measures the distance between the analysis and the observations. This paper is concerned with the general formulation of the HIRLAM 3D-Var and with Jb. while the companion paper by Lindskog and co-workers is concerned with the handling of observations, including the J(o) term, and with validation of the 3D-Var through extended parallel assimilation and forecast experiments. The 3D-Var minimization requires a pre-conditioning that is achieved by a transformation of the minimization control variable. This change of variable is designed as an operator approximating an inverse square root of the forecast error covariance matrix in the model space. The main transformations are the Subtraction of the geostrophic wind increment, the bi-Fourier transform, and the projection on vertical eigenvectors. The spectral bi-Fourier approach allows one to derive non-separable structure functions in a limited area model. in the form of vertically dependent horizontal spectra and scale-dependent vertical correlations. Statistics have been accumulated from differences between +24 h and +48 h HIRLAM forecasts valid at the same time. Results from single observation impact studies as well as results from assimilation cycles using operational observations are presented. It is shown that the HIRLAM 3D-Var produces assimilation increments in accordance with the applied analysis structure functions, that the fit of the analysis to the observations is in agreement with the assumed error statistics. and that assimilation increments are well balanced. It is also shown that the particular problems associated with the limited area formulation have been solved. These results, together with the results of the companion paper, indicate that the 3D-Var scheme performs significantly better than the statistical interpolation scheme.

  • 32.
    Gustafsson, Nils
    et al.
    SMHI, Research Department, Meteorology.
    Bojarova, J.
    Four-dimensional ensemble variational (4D-En-Var) data assimilation for the HIgh Resolution Limited Area Model (HIRLAM)2014In: Nonlinear processes in geophysics, ISSN 1023-5809, E-ISSN 1607-7946, Vol. 21, no 4, p. 745-762Article in journal (Refereed)
    Abstract [en]

    A four-dimensional ensemble variational (4D-EnVar) data assimilation has been developed for a limited area model. The integration of tangent linear and adjoint models, as applied in standard 4D-Var, is replaced with the use of an ensemble of non-linear model states to estimate four-dimensional background error covariances over the assimilation time window. The computational costs for 4D-En-Var are therefore significantly reduced in comparison with standard 4D-Var and the scalability of the algorithm is improved. The flow dependency of 4D-En-Var assimilation increments is demonstrated in single simulated observation experiments and compared with corresponding increments from standard 4D-Var and Hybrid 4D-Var ensemble assimilation experiments. Real observation data assimilation experiments carried out over a 6-week period show that 4D-En-Var outperforms standard 4D-Var as well as Hybrid 4D-Var ensemble data assimilation with regard to forecast quality measured by forecast verification scores.

  • 33.
    Gustafsson, Nils
    et al.
    SMHI, Research Department, Meteorology.
    Bojarova, J.
    Vignes, O.
    A hybrid variational ensemble data assimilation for the HIgh Resolution Limted Area Model (HIRLAM)2014In: Nonlinear processes in geophysics, ISSN 1023-5809, E-ISSN 1607-7946, Vol. 21, no 1, p. 303-323Article in journal (Refereed)
    Abstract [en]

    A hybrid variational ensemble data assimilation has been developed on top of the HIRLAM variational data assimilation. It provides the possibility of applying a flow-dependent background error covariance model during the data assimilation at the same time as full rank characteristics of the variational data assimilation are preserved. The hybrid formulation is based on an augmentation of the assimilation control variable with localised weights to be assigned to a set of ensemble member perturbations (deviations from the ensemble mean). The flow-dependency of the hybrid assimilation is demonstrated in single simulated observation impact studies and the improved performance of the hybrid assimilation in comparison with pure 3-dimensional variational as well as pure ensemble assimilation is also proven in real observation assimilation experiments. The performance of the hybrid assimilation is comparable to the performance of the 4-dimensional variational data assimilation. The sensitivity to various parameters of the hybrid assimilation scheme and the sensitivity to the applied ensemble generation techniques are also examined. In particular, the inclusion of ensemble perturbations with a lagged validity time has been examined with encouraging results.

  • 34.
    Gustafsson, Nils
    et al.
    SMHI, Research Department, Meteorology.
    Huang, S Y
    Sensitivity experiments with the spectral HIRLAM and its adjoint1996In: Tellus. Series A, Dynamic meteorology and oceanography, ISSN 0280-6495, E-ISSN 1600-0870, Vol. 48, no 4, p. 501-517Article in journal (Refereed)
    Abstract [en]

    The tangent-linear and the adjoint of the spectral High Resolution Limited Area Model (HIRLAM) have been derived as a first step in the development of a 4-dimensional variational data assimilation system for HIRLAM. The adjoint of the spectral HIRLAM was applied successfully to test the sensitivity of short-range forecast errors to initial conditions. These sensitivity experiments were carried out for a particular case study in addition to a full 5-day period. The results of the sensitivity experiments indicate an ability of the adjoint model to improve the assimilation of baroclinically developing systems and this may open possibilities for application of the adjoint model in a ''Poor mans 4-dimensional variational data assimilation'' in advance of the implementation of the full 4-dimensional variational data assimilation.

  • 35.
    Gustafsson, Nils
    et al.
    SMHI, Research Department, Meteorology.
    Huang, Xiang-Yu
    Yang, Xiaohua
    Mogensen, Kristian
    Lindskog, Magnus
    SMHI, Research Department, Meteorology.
    Vignes, Ole
    Wilhelmsson, Tomas
    Thorsteinsson, Sigurdur
    SMHI, Research Department, Meteorology.
    Four-dimensional variational data assimilation for a limited area model2012In: Tellus. Series A, Dynamic meteorology and oceanography, ISSN 0280-6495, E-ISSN 1600-0870, Vol. 64, article id 14985Article in journal (Refereed)
    Abstract [en]

    A 4-dimensional variational data assimilation (4D-Var) scheme for the HIgh Resolution Limited Area Model (HIRLAM) forecasting system is described in this article. The innovative approaches to the multi-incremental formulation, the weak digital filter constraint and the semi-Lagrangian time integration are highlighted with some details. The implicit dynamical structure functions are discussed using single observation experiments, and the sensitivity to various parameters of the 4D-Var formulation is illustrated. To assess the meteorological impact of HIRLAM 4D-Var, data assimilation experiments for five periods of 1 month each were performed, using HIRLAM 3D-Var as a reference. It is shown that the HIRLAM 4D-Var consistently out-performs the HIRLAM 3D-Var, in particular for cases with strong mesoscale storm developments. The computational performance of the HIRLAM 4D-Var is also discussed.

  • 36.
    Gustafsson, Nils
    et al.
    SMHI, Research Department, Meteorology.
    Janjić, Tijana
    Schraff, Christoph
    Leuenberger, Daniel
    Weissmann, Martin
    Reich, Hendrik
    Brousseau, Pierre
    Montmerle, Thibaut
    Wattrelot, Eric
    Bučánek, Antonĺn
    Mile, Máté
    Hamdi, Rafiq
    Lindskog, Magnus
    SMHI, Research Department, Meteorology.
    Barkmeijer, Jan
    Dahlbom, Mats
    Macpherson, Bruce
    Ballard, Sue
    Inverarity, Gordon
    Carley, Jacob
    Alexander, Curtis
    Dowell, David
    Liu, Shun
    Ikuta, Yasutaka
    Fujita, Tadashi
    Survey of data assimilation methods for convective‐scale numerical weather prediction at operational centres2018In: Quarterly Journal of thte Royal Meteorology Society, ISSN 1350-4827, Vol. 144, no 711Article in journal (Other academic)
  • 37.
    Gustafsson, Nils
    et al.
    SMHI, Research Department, Meteorology.
    Källén, Erland
    SMHI, Research Department, Meteorology.
    Thorsteinsson, Sigurdur
    SMHI, Research Department, Meteorology.
    Sensitivity of forecast errors to initial and lateral boundary conditions1998In: Tellus. Series A, Dynamic meteorology and oceanography, ISSN 0280-6495, E-ISSN 1600-0870, Vol. 50, no 2, p. 167-185Article in journal (Refereed)
    Abstract [en]

    The adjoint of a limited area model has been used to study the sensitivity of 12 h forecast errors to initial and lateral boundary conditions. Upper troposphere potential vorticity and mean sea level pressure verification scores for 1 month of operational forecasts from the Swedish Meteorological and Hydrological Institute were used to select 2 cases with particularly poor forecast performance. The sensitivity experiments show that errors in initial data is the most likely explanation for one of the forecast failures, while errors in initial as well as lateral boundary data can explain the 2nd forecast failure. Results from the sensitivity experiments with respect to the lateral boundary conditions indicate that poor quality lateral boundary conditions may be improved by utilizing subsequent downstream observations within the model integration area. This result is of great significance with regard to the possibilities for applying 4-dimensional variational data assimilation (4DVAR) for limited area forecast models. Results from the sensitivity experiments also reveal, however, that the lateral boundary treatment in operational limited area models needs to be improved with regard to the mathematical formulation. It is furthermore shown that modifications to be applied to the lateral boundary conditions need to be determined with appropriate time resolution and that some filtering of these lateral boundary modifications has to be introduced to avoid enhanced high-frequency gravity wave noise in the vicinity of the lateral boundaries.

  • 38.
    Gustafsson, Nils
    et al.
    SMHI, Research Department, Meteorology.
    Lonnberg, P
    Pailleux, J
    Data assimilation for high-resolution limited-area models1997In: Journal of the Meteorological Society of Japan, ISSN 0026-1165, Vol. 75, no 1B, p. 367-382Article in journal (Refereed)
    Abstract [en]

    The present status of development of data assimilation techniques for high resolution limited area models is reviewed and various candidates for a new generation of a data assimilation system are compared. It is concluded that data assimilation based on 3-dimensional or 4-dimensional variational techniques is the most promising approach. Further investigations are needed, however, to find out whether variational data assimilation is feasible over "limited" model integration areas or whether global/hemispheric model integration areas have to be introduced for high resolution limited area data assimilation purposes. The main problem in this connection is the rapid propagation of forecast errors on a global or at least hemispheric atmospheric scale within a time-scale of a few days.

  • 39.
    Gustafsson, Nils
    et al.
    SMHI, Research Department, Meteorology.
    McDonald, A
    A comparison of the HIRLAM gridpoint and spectral semi-Lagrangian models1996In: Monthly Weather Review, ISSN 0027-0644, E-ISSN 1520-0493, Vol. 124, no 9, p. 2008-2022Article in journal (Refereed)
    Abstract [en]

    A comparison of two semi-Lagrangian limited area models, one spectral, and the other grid point, is described. Forecasts from both models are compared and contrasted, first on a 55-km horizontal mesh and subsequently an a 22-km horizontal mesh. The weaknesses in the respective models exposed by these tests, and the corrections made to overcome them are described. The final models arrived at are shown to be accurate and more efficient than the Eulerian counterpart for the test dataset. It is also found that the spectral model is as accurate as the gridpoint model and is also computationally competitive. It is concluded that with sufficient thought and effort the gridpoint and spectral models can be made to produce equally good forecasts at comparable computer costs. Finally. a reassessment of the relative merits and drawbacks of the spectral and gridpoint schemes is attempted taking into account the fact that the advection terms are integrated by the semi-Lagrangian scheme.

  • 40.
    Gustafsson, Nils
    et al.
    SMHI, Research Department, Meteorology.
    Nyberg, Leif
    SMHI.
    Omstedt, Anders
    SMHI, Research Department, Oceanography.
    Coupling of a high-resolution atmospheric model and an ocean model for the Baltic Sea1998In: Monthly Weather Review, ISSN 0027-0644, E-ISSN 1520-0493, Vol. 126, no 11, p. 2822-2846Article in journal (Refereed)
    Abstract [en]

    The coupling between a high-resolution weather forecasting model and an ocean model is investigated. It is demonstrated by several case studies that improvements of short-range weather forecasting in the area of the Baltic Sea require an accurate description of the lower boundary condition over sea. The examples are taken from summer situations without sea ice as well as from winter situations with extreme sea ice conditions. It is shown that the sea state variables used in the model influence the weather forecast both directly on the local scale due to the local impact of surface fluxes of latent and sensible heat and on regional and larger scales. The convective snowbands during winters with cold airmass outbreaks over the open water surfaces of the Baltic Sea are extreme examples of the influence of sea state variables on a regional scale, It is furthermore demonstrated that the sea state conditions may change considerably within forecasting periods up to 48 h. This implies the necessary application of ocean models, two-way interactively coupled to the weather forecasting model. The coupling of an advanced 2.5-dimensional ice-ocean model to the operational Swedish Meteorological and Hydrological Institute (SMHI) weather forecasting model HIRLAM is described. The ice-ocean model includes two-dimensional, horizontally resolved ice and storm surge models and a one-dimensional, vertically resolved ocean model applied to 31 Baltic Sea regions. The coupled model system is applied operationally in a data assimilation system at the SMHI. No data assimilation is applied in the operational ocean component: manual modifications to the sea state variables are introduced a few times every winter season. The application of this operational coupled model data assimilation system to the mesoscale reanalysis for the Baltic Sea Experiment (BALTEX) shows that it is necessary to apply data assimilation fur the sea state variables in order to avoid drift of the coupled model system toward less realistic model states. A successful application of a simple assimilation of SST observations is presented. The observed SSTs are first subject to a horizontal filter in order to minimize the effects of observational errors and to restrict the influence to a larger horizontal scale. Then the differences between these filtered temperature observations and the model SSTs are used to construct a modified sensible heat Aux that is applied as a form of a "nudging" term to the ocean model. It turns out that this "nudging" is successful in avoiding the drift away from realistic sea state conditions. The described atmosphere and ocean data assimilation scheme has been applied in a rerun of the BALTEX mesoscale reanalysis for the cold winter 1986/87. The quality of this reanalysis was assessed through the successful simulation of the convective snowbands in January 1987.

  • 41.
    Gustafsson, Nils
    et al.
    SMHI, Research Department, Meteorology.
    Thorsteinsson, S.
    Stengel, M.
    Holm, E.
    Use of a nonlinear pseudo-relative humidity variable in a multivariate formulation of moisture analysis2011In: Quarterly Journal of the Royal Meteorological Society, ISSN 0035-9009, E-ISSN 1477-870X, Vol. 137, no 657, p. 1004-1018Article in journal (Refereed)
    Abstract [en]

    We present a reformulation of the humidity part of the HIRLAM (HIgh-Resolution Limited-Area Model) variational data assimilation. The purpose is to rectify some of the shortcomings of the present formulation which uses specific humidity, q, as an assimilation control variable with homogeneous and static covariances. One problem is that specific humidity forecast errors tend to have a non-Gaussian probability distribution, in particular near saturation and near zero humidity. In addition, the variance of the distribution tends to change in space and time due to the dependency of the water vapour saturation pressure on temperature. A modified pseudo-relative humidity variable has been adapted to the statistical balance background constraint, including the associated moisture balance formulation. Background-error statistics for the new moisture control variable and the moisture-related balances were derived, taking differences between forecasts valid at the same time as a proxy for background forecast errors. The background-error statistics were compared with the corresponding statistics for specific humidity as the moisture assimilation control variable. In connection with the nonlinearity of the change of the variable, it was noted that specified background-error standard deviations were chosen to be substantially reduced for nearly dry and saturated states, which can raise difficulties. The impact of the new moisture assimilation control variable is illustrated with simulated observation experiments as well as data assimilation experiments using real observations, for one summer month and one winter month in a 4D-Var assimilation cycle using two outer loop iterations in the 4D-Var minimization. The impact of the new formulation on forecast verification scores is small and essentially neutral, while using the second outer loop in the old formulation has a small positive impact. Copyright (C) 2011 Royal Meteorological Society

  • 42. HAUGEN, JE
    et al.
    MACHENHAUER, B
    Gustafsson, Nils
    SMHI, Research Department, Meteorology.
    A Spectrial Limited-Area Formulation with Time-Dependent Boundary-Conditions Applied to the Shallow-Water Equations - Reply1995In: Monthly Weather Review, ISSN 0027-0644, E-ISSN 1520-0493, Vol. 123, no 10, p. 3124-3124Article in journal (Refereed)
  • 43. Hazeleger, Wilco
    et al.
    Severijns, Camiel
    Semmler, Tido
    Stefanescu, Simona
    Yang, Shuting
    Wang, Xueli
    Wyser, Klaus
    SMHI, Research Department, Climate research - Rossby Centre.
    Dutra, Emanuel
    Baldasano, Jose M.
    Bintanja, Richard
    Bougeault, Philippe
    Caballero, Rodrigo
    Ekman, Annica M. L.
    Christensen, Jens H.
    van den Hurk, Bart
    Jimenez, Pedro
    Jones, Colin
    SMHI, Research Department, Climate research - Rossby Centre.
    Kållberg, Per
    SMHI, Research Department, Meteorology.
    Koenigk, Torben
    SMHI, Research Department, Climate research - Rossby Centre.
    McGrath, Ray
    Miranda, Pedro
    Van Noije, Twan
    Palmer, Tim
    Parodi, Jose A.
    Schmith, Torben
    Selten, Frank
    Storelvmo, Trude
    Sterl, Andreas
    Tapamo, Honore
    Vancoppenolle, Martin
    Viterbo, Pedro
    Willén, Ulrika
    SMHI, Research Department, Climate research - Rossby Centre.
    EC-Earth A Seamless Earth-System Prediction Approach in Action2010In: Bulletin of The American Meteorological Society - (BAMS), ISSN 0003-0007, E-ISSN 1520-0477, Vol. 91, no 10, p. 1357-1363Article in journal (Other academic)
  • 44. Heygster, Georg
    et al.
    Melsheimer, Christian
    Mathew, Nizy
    Toudal, Leif
    Saldo, Roberto
    Andersen, Soren
    Tonboe, Rasmus
    Schyberg, Harald
    Tveter, Frank Thomas
    Thyness, Vibeke
    Gustafsson, Nils
    SMHI, Research Department, Meteorology.
    Landelius, Tomas
    SMHI, Research Department, Atmospheric remote sensing.
    Dahlgren, Per
    SMHI, Research Department, Meteorology.
    Integrated Observation and Modeling of the Arctic Sea Ice and Atmosphere2009In: Bulletin of The American Meteorological Society - (BAMS), ISSN 0003-0007, E-ISSN 1520-0477, Vol. 90, no 3, p. 293-297Article in journal (Refereed)
  • 45.
    Häggmark, Lars
    et al.
    SMHI, Core Services.
    Ivarsson, Karl-Ivar
    SMHI, Core Services.
    Gollvik, Stefan
    SMHI, Research Department, Meteorology.
    Olofsson, R O
    Mesan, an operational mesoscale analysis system2000In: Tellus. Series A, Dynamic meteorology and oceanography, ISSN 0280-6495, E-ISSN 1600-0870, Vol. 52, no 1, p. 2-20Article in journal (Refereed)
    Abstract [en]

    A system for mesoscale analyses of selected variables has been developed. The analysed parameters are of general interest in operational weather forecasting, but normally not available from NWP systems, or available, but with a significantly lower quality than achieved by the mesoscale analysis system. A supplementary objective is to produce initial information to be used for now-casting techniques. Examples of parameters are precipitation, temperature, humidity, visibility, wind and clouds. The basis of the analysis system is the optimal interpolation technique (OI). The use of observations from automatic stations, radars and satellites have been investigated. The investigation indicates that a dense network of ordinary precipitation gauge measurements can produce more accurate analyses than more elaborate systems like radar that suffers from anomalous echoes and other errors.

  • 46. Jacob, D
    et al.
    Van den Hurk, B J J M
    Andrae, Ulf
    SMHI, Research Department, Meteorology.
    Elgered, G
    Fortelius, C
    Graham, Phil
    SMHI, Research Department, Climate research - Rossby Centre.
    Jackson, S D
    Karstens, U
    Kopken, C
    Lindau, R
    Podzun, R
    Rockel, B
    Rubel, F
    Sass, B H
    Smith, R N B
    Yang, X
    A comprehensive model inter-comparison study investigating the water budget during the BALTEX-PIDCAP period2001In: Meteorology and atmospheric physics (Print), ISSN 0177-7971, E-ISSN 1436-5065, Vol. 77, no 1-4, p. 19-43Article in journal (Refereed)
    Abstract [en]

    A comparison of 8 regional atmospheric model systems was carried out for a three-month late summer/early autumn period in 1995 over the Baltic Sea and its catchment area. All models were configured on a common grid using similar surface and lateral boundary conditions, and ran in either data assimilation mode (short term forecasts plus data assimilation), forecast made (short term forecasts initialised daily with analyses) or climate mode (no re-initialisation of model interior during entire simulation period). Model results presented in this paper were generally post processed as daily averaged quantities, separate for land and sea areas when relevant. Post processed output was compared against available analyses or observations of cloud cover, precipitation, vertically integrated atmospheric specific humidity, runoff, surface radiation and near surface synoptic observations. The definition of a common grid and lateral forcing resulted in a high degree of agreement among the participating model results for most cases. Models operated in climate mode generally displayed slightly larger deviations from the observations than the data assimilation or forecast mode integration, but in all cases synoptic events were well captured. Correspondence to near surface synoptic quantities was good. Significant disagreement between model results was shown in particular for cloud cover and the radiative properties, average precipitation and runoff. Problems with choosing appropriate initial soil moisture conditions from a common initial soil moisture field resulted in a wide range of evaporation and sensible heat flux values during the first few weeks of the simulations, but better agreement was shown at later times.

  • 47. Jarvinen, H.
    et al.
    Salonen, K.
    Lindskog, Magnus
    SMHI, Research Department, Meteorology.
    Huuskonen, A.
    Niemela, S.
    Eresmaa, R.
    Doppler radar radial winds in HIRLAM. Part I: observation modelling and validation2009In: Tellus. Series A, Dynamic meteorology and oceanography, ISSN 0280-6495, E-ISSN 1600-0870, Vol. 61, no 2, p. 278-287Article in journal (Refereed)
    Abstract [en]

    An observation operator for Doppler radar radial wind measurements is developed further in this article, based on the earlier work and considerations of the measurement characteristic. The elementary observation operator treats radar observations as point measurements at pre-processed observation heights. Here, modelling of the radar pulse volume broadening in vertical and the radar pulse path bending due to refraction is included to improve the realism of the observation modelling. The operator is implemented into the High Resolution Limited Area Model (HIRLAM) limited area numerical weather prediction (NWP) system. A data set of circa 133 000 radial wind measurements is passively monitored against the HIRLAM six-hourly background values in a 1-month experiment. No data assimilation experiments are performed at this stage. A new finding is that the improved modelling reduces the mean observation minus background (OmB) vector wind difference at ranges below 55 km, and the standard deviation of the radial wind OmB difference at ranges over 25 km. In conclusion, a more accurate and still computationally feasible observation operator is developed. The companion paper (Part II) considers optimal super-observation processing of Doppler radar radial winds for HIRLAM, with general applicability in NWP.

  • 48.
    Johansson, Åke
    et al.
    SMHI, Research Department, Meteorology.
    Barnston, A
    Saha, S
    van den Dool, H
    On the level and origin of seasonal forecast skill in northern Europe1998In: Journal of Atmospheric Sciences, ISSN 0022-4928, E-ISSN 1520-0469, Vol. 55, no 1, p. 103-127Article in journal (Refereed)
    Abstract [en]

    This study examines the level and origin of seasonal forecast skill of surface air temperature in northern Europe. The forecasts are based on an empirical methodology, canonical correlation analysis (CCA), which is a method designed to find correlated patterns between predictor and predictand fields. A modified form of CCA is used where a prefiltering step precedes the CCA as proposed by T.P. Barnett and R. Preisendorfer. The predictive potential of four fields is investigated, namely, (a) surface air temperature (i.e., the predictand field itself), (b) local sea surface temperature (SST) in the northern European area on a dense grid, (c) Northern Hemisphere 700-hPa geopotential height, and (d) quasi-global SST on a coarse grid, The design is such that four contiguous predictor periods (of 3 months each) are followed by a lead time and then a single predictand period (3 months long). The shortest lead time is 1 month and the longest is 15 months. The skill of the CCA based forecasts is estimated for the 39-yr time period 1955-93, using cross-validated hindcasting. Skill estimates are expressed as the temporal correlation between the forecasts and the respective verifying observations. The forecasts are most skillful in the winter seasons with a secondary weaker skill maximum during summer. During winter the geopotential height field produces the highest skill scores of the four predictor fields. The dominant predictor pattern of the geopotential height field is confined to the predictor period that is closest to a preceding core winter season and resembles the North Atlantic Oscillation (NAG) teleconnection pattern. The time series of the expansion coefficients of this dominant predictor pattern correlates well with a low-pass filtered rime series of an NAO index. The obtained skill is similar to what is found in the United States, both with regard to seasonal distribution and level of skill. The origin of skill is however different. In the United States it is the El Nino-Southern Oscillation (ENSO) with its predominantly interannual character that is the main source of skill in winter. In northern Europe it is instead the NAO that contributes the most, and especially the lower frequency part of the NAO (periods between 4 and 10 yr). Spatially sparse station data of surface pressure extending back to the middle of the nineteenth century suggests a nonstationarity in the NAO behavior. The implications of this nonstationarity for the obtained results of this study is briefly discussed. Because finely resolved field data are not readily available for this earlier period, the level of skill realizable for that period using a pattern relationship technique such as CCA remains an open question.

  • 49.
    Kållberg, Per
    et al.
    SMHI, Research Department, Meteorology.
    Montani, A.
    A case study carried out with two different NWP systems2006In: Natural hazards and earth system sciences, ISSN 1561-8633, E-ISSN 1684-9981, Vol. 6, no 5, p. 755-760Article in journal (Refereed)
    Abstract [en]

    A model intercomparison between two atmospheric models, the non-hydrostatic Lokal Modell (LM) and the hydrostatic HIgh Resolution Limited Area Model (HIRLAM) is carried out for a one-week period, including a case of cyclogeneis leading to heavy precipitation over Northern Italy. The two models, very different in terms of data-assimilation and numerics, provide different results in terms of forecasts of surface fields. Opposite diurnal biases for the two models are found in terms of screen level temperatures. HIRLAM wind speed forecasts are too strong, while LM precipitation forecasts have larger extremes. The intercomparison exercise identifies some systematic differences in the weather products generated by the two systems and sheds some light on the biases of the two numerical weather prediction systems.

  • 50.
    Kållberg, Per
    et al.
    SMHI, Research Department, Meteorology.
    Uppala, Sakari
    Simmons, Adrian
    The real first weather satellite picture2010In: Weather, ISSN 0043-1656, E-ISSN 1477-8696, Vol. 65, no 8, p. 211-213Article in journal (Refereed)
12 1 - 50 of 96
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