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  • 1. 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.

  • 2. Jeong, Jee-Hoon
    et al.
    Walther, Alexander
    Nikulin, Grigory
    SMHI, Research Department, Climate research - Rossby Centre.
    Chen, Deliang
    Jones, Colin
    SMHI, Research Department, Climate research - Rossby Centre.
    Diurnal cycle of precipitation amount and frequency in Sweden: observation versus model simulation2011In: Tellus. Series A, Dynamic meteorology and oceanography, ISSN 0280-6495, E-ISSN 1600-0870, Vol. 63, no 4, p. 664-674Article in journal (Refereed)
    Abstract [en]

    This study investigated the diurnal cycle of precipitation in Sweden using hourly ground observations for 1996-2008. General characteristics of phase and amplitude for the diurnal cycle of precipitation, both in amount and frequency, were identified. In the warm season (April-September), the 'typical' afternoon (14-16 LST) peaks are dominant over inland Sweden, whereas late night to early morning (04-06 LST) peaks with relatively weak amplitude are discernable in the east coast along the Baltic Sea. The diurnal variation is almost negligible in the cold season (October-March), due to the weak solar radiation at high latitudes. The variations of convective activity forced by solar heating and modulated by geographical characteristics were suggested as primarily factors to invoke the cycles and spatial variation identified. The observed cycle was compared with the cycle simulated by a regional climate model. The model fairly well captures the spatial pattern of the phase of the diurnal cycle. However, the warm season afternoon peak is simulated too early and too uniformly across the stations, associated with too frequent occurrences of convective rainfall events with relatively light intensity. These discrepancies point to the need to improve the convection parametrization and geographic representation of the model.

  • 3. Johansson, Mattias
    et al.
    Galle, Bo
    Zhang, Yan
    Rivera, Claudia
    Chen, Deliang
    Wyser, Klaus
    SMHI, Research Department, Climate research - Rossby Centre.
    The dual-beam mini-DOAS technique-measurements of volcanic gas emission, plume height and plume speed with a single instrument2009In: Bulletin of Volcanology, ISSN 0258-8900, E-ISSN 1432-0819, Vol. 71, no 7, p. 747-751Article in journal (Refereed)
    Abstract [en]

    The largest error in determining volcanic gas fluxes using ground based optical remote sensing instruments is typically the determination of the plume speed, and in the case of fixed scanning instruments also the plume height. We here present a newly developed technique capable of measuring plume height, plume speed and gas flux using one single instrument by simultaneously collecting scattered sunlight in two directions. The angle between the two measurement directions is fixed, removing the need for time consuming in-field calibrations. The plume height and gas flux is measured by traversing the plume and the plume speed is measured by performing a stationary measurement underneath the plume. The instrument was tested in a field campaign in May 2005 at Mt. Etna, Italy, where the measured results are compared to wind fields derived from a meso-scale meteorological model (MM5). The test and comparison show that the instrument is functioning and capable of estimating wind speed at the plume height.

  • 4. Miao, J F
    et al.
    Chen, D
    Wyser, Klaus
    SMHI, Research Department, Climate research - Rossby Centre.
    Modelling subgrid scale dry deposition velocity of O-3 over the Swedish west coast with MM5-PX model2006In: Atmospheric Environment, ISSN 1352-2310, E-ISSN 1873-2844, Vol. 40, no 3, p. 415-429Article in journal (Refereed)
    Abstract [en]

    A mesoscale meteorological model (MM5) coupled with an advanced land surface model (PX LSM) is used in this study to model high-resolution (2 km) dry deposition velocity of ozone over the Swedish west coast, together with a newly revised dry deposition parameterization for air-quality models with emphasis on non-stomatal resistance. The important air-surface exchange processes for air quality (surface fluxes of heat, moisture and momentum) are also simulated by this model. The modelled subgrid scale variability of the dry deposition velocity and its dependence on land use, terrain height and synoptic conditions are investigated. It is found that a systematic difference in the deposition velocity modelled by different resolutions exists, and the difference varies diurnally and daily. The subgrid scale variation is significant, which has a clear impact on the area-averaged deposition velocity. The deposition velocity depends strongly on land use and weather conditions, but not on topography for the area studied. Meteorological conditions at subgrid scales play an important role in determining the deposition velocity. It is also concluded that the dry deposition velocity simulated in this study is reasonable, and that a 6-km resolution would be practically good enough to resolve the inhomogeneity of the surface properties for dry deposition studies in this area. The variation range of dry deposition velocity over different land use categories and the corresponding resistances are outlined. Moreover, the difference in the estimated dry deposition velocitiy between the methods using fractional land use and using dominant land use is compared. (c) 2005 Elsevier Ltd. All rights reserved.

  • 5. Moberg, Anders
    et al.
    Jones, Philip D.
    Lister, David
    Walther, Alexander
    Brunet, Manola
    Jacobeit, Jucundus
    Alexander, Lisa V.
    Della-Marta, Paul M.
    Luterbacher, Juerg
    Yiou, Pascal
    Chen, Deliang
    Tank, Albert M. G. Klein
    Saladie, Oscar
    Sigro, Javier
    Aguilar, Enric
    Alexandersson, Hans
    SMHI.
    Almarza, Carlos
    Auer, Ingeborg
    Barriendos, Mariano
    Begert, Michael
    Bergstroem, Hans
    Boehm, Reinhard
    Butler, C. J.
    Caesar, John
    Drebs, Achim
    Founda, Dmitra
    Gerstengarbe, Friedrich-Wilhelm
    Micela, Giusi
    Maugeri, Maurizio
    Osterle, Hermann
    Pandzic, Kreso
    Petrakis, Michael
    Srnec, Lidija
    Tolasz, Radim
    Tuomenvirta, Heikki
    Werner, Peter C.
    Linderholm, Hans
    Philipp, Andreas
    Wanner, Heinz
    Xoplaki, Elena
    Indices for daily temperature and precipitation extremes in Europe analyzed for the period 1901-20002006In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 111, no D22, article id D22106Article in journal (Refereed)
    Abstract [en]

    We analyze century-long daily temperature and precipitation records for stations in Europe west of 60 degrees E. A set of climatic indices derived from the daily series, mainly focusing on extremes, is defined. Linear trends in these indices are assessed over the period 1901-2000. Average trends, for 75 stations mostly representing Europe west of 20 degrees E, show a warming for all temperature indices. Winter has, on average, warmed more (similar to 1.0 degrees C/100 yr) than summer (similar to 0.8 degrees C), both for daily maximum (TX) and minimum (TN) temperatures. Overall, the warming of TX in winter was stronger in the warm tail than in the cold tail (1.6 and 1.5 degrees C for 98th and 95th, but similar to 1.0 degrees C for 2nd, 5th and 10th percentiles). There are, however, large regional differences in temperature trend patterns. For summer, there is a tendency for stronger warming, both for TX and TN, in the warm than in the cold tail only in parts of central Europe. Winter precipitation totals, averaged over 121 European stations north of 40 degrees N, have increased significantly by similar to 12% per 100 years. Trends in 90th, 95th and 98th percentiles of daily winter precipitation have been similar. No overall long-term trend occurred in summer precipitation totals, but there is an overall weak (statistically insignificant and regionally dependent) tendency for summer precipitation to have become slightly more intense but less common. Data inhomogeneities and relative sparseness of station density in many parts of Europe preclude more robust conclusions. It is of importance that new methods are developed for homogenizing daily data.

  • 6. Walther, Alexander
    et al.
    Jeong, Jee-Hoon
    Nikulin, Grigory
    SMHI, Research Department, Climate research - Rossby Centre.
    Jones, Colin
    SMHI, Research Department, Climate research - Rossby Centre.
    Chen, Deliang
    Evaluation of the warm season diurnal cycle of precipitation over Sweden simulated by the Rossby Centre regional climate model RCA32013In: Atmospheric research, ISSN 0169-8095, E-ISSN 1873-2895, Vol. 119, p. 131-139Article in journal (Refereed)
    Abstract [en]

    This study examines the diurnal cycle of precipitation over Sweden for the warm season (April to September) both in hourly observational data and in simulations from the Rossby Centre regional climate model (RCA3). A series of parallel long-term simulations of RCA3 with different horizontal resolutions - 50, 25, 12, and 6 km - were analyzed to investigate the sensitivity of the model's horizontal resolution to the simulated diurnal cycle of precipitation. Overall, a clear distinction between an afternoon peak for inland stations and an early morning peak for stations along the Eastern coast is commonly found both in observation and model results. However, the diurnal cycle estimated from the model simulations show too early afternoon peaks with too large amplitude compared to the observation. Increasing horizontal model resolution tends to reduce this bias both in peak timing and amplitude, but this resolution effect seems not to be monotonic; this is clearly seen only when comparing coarser resolution results with the 6 km resolution result. As the resolution increases, the peak timing and amplitude of the diurnal cycle of resolved large-scale precipitation become more similar to the observed cycle of total precipitation while the contribution of subgrid scale convective precipitation to the total precipitation decreases. An increase in resolution also tends to reduce too much precipitation of relatively light intensity over inland compared to the observation, which may also contribute to the more realistic simulation of the afternoon peak in convective precipitation. (C) 2011 Elsevier B.V. All rights reserved.

  • 7.
    Wetterhall, Fredrik
    et al.
    SMHI, Research Department, Hydrology.
    Bardossy, Andras
    Chen, Deliang
    Halldin, Sven
    Xu, Chong-Yu
    Daily precipitation-downscaling techniques in three Chinese regions2006In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 42, no 11, article id W11423Article in journal (Refereed)
    Abstract [en]

    [ 1] Four methods of statistical downscaling of daily precipitation were evaluated on three catchments located in southern, eastern, and central China. The evaluation focused on seasonal variation of statistical properties of precipitation and indices describing the precipitation regime, e. g., maximum length of dry spell and maximum 5-day precipitation, as well as interannual and intra-annual variations of precipitation. The predictors used in this study were mean sea level pressure, geopotential heights at 1000, 850, 700, and 500 hPa, and specific humidity as well as horizontal winds at 850, 700, and 500 hPa levels from the NCEP/NCAR reanalysis with 2.5 degrees x 2.5 degrees resolution for 1961 - 2000. The predictand was daily precipitation from 13 stations. Two analogue methods, one using principal components analysis (PCA) and the other Teweles-Wobus scores (TWS), a multiregression technique with a weather generator producing precipitation (SDSM) and a fuzzy-rule-based weather-pattern-classification method (MOFRBC), were used. Temporal and spatial properties of the predictors were carefully evaluated to derive the optimum setting for each method, and MOFRBC and SDSM were implemented in two modes, with and without humidity as predictor. The results showed that ( 1) precipitation was most successfully downscaled in the southern and eastern catchments located close to the coast, ( 2) winter properties were generally better downscaled, ( 3) MOFRBC and SDSM performed overall better than the analogue methods, ( 4) the modeled interannual variation in precipitation was improved when humidity was added to the predictor set, and ( 5), the annual precipitation cycle was well captured with all methods.

  • 8.
    Wetterhall, Fredrik
    et al.
    SMHI, Research Department, Hydrology.
    Bardossy, Andras
    Chen, Deliang
    Halldin, Sven
    Xu, Chong-yu
    Statistical downscaling of daily precipitation over Sweden using GCM output2009In: Journal of Theoretical and Applied Climatology, ISSN 0177-798X, E-ISSN 1434-4483, Vol. 96, no 1-2, p. 95-103Article in journal (Refereed)
    Abstract [en]

    A classification of Swedish weather patterns (SWP) was developed by applying a multi-objective fuzzy-rule-based classification method (MOFRBC) to large-scale-circulation predictors in the context of statistical downscaling of daily precipitation at the station level. The predictor data was mean sea level pressure (MSLP) and geopotential heights at 850 (H850) and 700 hPa (H700) from the NCEP/NCAR reanalysis and from the HadAM3 GCM. The MOFRBC was used to evaluate effects of two future climate scenarios (A2 and B2) on precipitation patterns on two regions in south-central and northern Sweden. The precipitation series were generated with a stochastic, autoregressive model conditioned on SWP. H850 was found to be the optimum predictor for SWP, and SWP could be used instead of local classifications with little information lost. The results in the climate projection indicated an increase in maximum 5-day precipitation and precipitation amount on a wet day for the scenarios A2 and B2 for the period 2070-2100 compared to 1961-1990. The relative increase was largest in the northern region and could be attributed to an increase in the specific humidity rather than to changes in the circulation patterns.

1 - 8 of 8
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