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  • 101. Rossa, A.
    et al.
    Haase, Gunther
    SMHI, Forskningsavdelningen, Atmosfärisk fjärranalys.
    Keil, C.
    Alberoni, P.
    Ballard, S.
    Bech, J.
    Germann, U.
    Pfeifer, M.
    Salonen, K.
    Propagation of uncertainty from observing systems into NWP: COST-731 Working Group 12010Ingår i: Atmospheric Science Letters, ISSN 1530-261X, E-ISSN 1530-261X, Vol. 11, nr 2, s. 145-152Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The COST-731 Action is focused on uncertainty propagation in hydrometeorological forecasting chains. The goals and activities of the Action Working Group 1 can be subdivided by (1) describing and studying the impact of imperfect observations, mostly from radar, (2) exploiting radar data assimilation as a promising avenue for improved short-range precipitation forecasts and (3) high-resolution ensemble forecasting. Activities of Working Group 1 are presented along with their possible significance for hydrological applications. Copyright (C) 2010 Royal Meteorological Society and Crown Copyright

  • 102.
    Devasthale, Abhay
    et al.
    SMHI, Forskningsavdelningen, Atmosfärisk fjärranalys.
    Willén, Ulrika
    SMHI, Forskningsavdelningen, Klimatforskning - Rossby Centre.
    Karlsson, Karl-Göran
    SMHI, Forskningsavdelningen, Atmosfärisk fjärranalys.
    Jones, Colin
    SMHI, Forskningsavdelningen, Klimatforskning - Rossby Centre.
    Quantifying the clear-sky temperature inversion frequency and strength over the Arctic Ocean during summer and winter seasons from AIRS profiles2010Ingår i: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 10, nr 12, s. 5565-5572Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Temperature inversions are one of the dominant features of the Arctic atmosphere and play a crucial role in various processes by controlling the transfer of mass and moisture fluxes through the lower troposphere. It is therefore essential that they are accurately quantified, monitored and simulated as realistically as possible over the Arctic regions. In the present study, the characteristics of inversions in terms of frequency and strength are quantified for the entire Arctic Ocean for summer and winter seasons of 2003 to 2008 using the AIRS data for the clear-sky conditions. The probability density functions (PDFs) of the inversion strength are also presented for every summer and winter month. Our analysis shows that although the inversion frequency along the coastal regions of Arctic decreases from June to August, inversions are still seen in almost each profile retrieved over the inner Arctic region. In winter, inversions are ubiquitous and are also present in every profile analysed over the inner Arctic region. When averaged over the entire study area (70 degrees N-90 degrees N), the inversion frequency in summer ranges from 69 to 86% for the ascending passes and 72-86% for the descending passes. For winter, the frequency values are 88-91% for the ascending passes and 89-92% for the descending passes of AIRS/AQUA. The PDFs of inversion strength for the summer months are narrow and right-skewed (or positively skewed), while in winter, they are much broader. In summer months, the mean values of inversion strength for the entire study area range from 2.5 to 3.9 K, while in winter, they range from 7.8 to 8.9 K. The standard deviation of the inversion strength is double in winter compared to summer. The inversions in the summer months of 2007 were very strong compared to other years. The warming in the troposphere of about 1.5-3.0K vertically extending up to 400 hPa was observed in the summer months of 2007.

  • 103.
    Thomas, Manu Anna
    et al.
    SMHI, Forskningsavdelningen, Luftmiljö.
    Suntharalingam, P.
    Pozzoli, L.
    Rast, S.
    Devasthale, Abhay
    SMHI, Forskningsavdelningen, Atmosfärisk fjärranalys.
    Kloster, S.
    Feichter, J.
    Lenton, T. M.
    Quantification of DMS aerosol-cloud-climate interactions using the ECHAM5-HAMMOZ model in a current climate scenario2010Ingår i: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 10, nr 15, s. 7425-7438Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The contribution of ocean dimethyl sulfide (DMS) emissions to changes in cloud microphysical properties is quantified seasonally and globally for present day climate conditions using an aerosol-chemistry-climate general circulation model, ECHAM5-HAMMOZ, coupled to a cloud microphysics scheme. We evaluate DMS aerosol-cloud-climate linkages over the southern oceans where anthropogenic influence is minimal. The changes in the number of activated particles, cloud droplet number concentration (CDNC), cloud droplet effective radius, cloud cover and the radiative forcing are examined by analyzing two simulations: a baseline simulation with ocean DMS emissions derived from a prescribed climatology and one in which the ocean DMS emissions are switched off. Our simulations show that the model realistically simulates the seasonality in the number of activated particles and CDNC, peaking during Southern Hemisphere (SH) summer coincident with increased phyto-plankton blooms and gradually declining with a minimum in SH winter. In comparison to a simulation with no DMS, the CDNC level over the southern oceans is 128% larger in the baseline simulation averaged over the austral summer months. Our results also show an increased number of smaller sized cloud droplets during this period. We estimate a maximum decrease of up to 15-18% in the droplet radius and a mean increase in cloud cover by around 2.5% over the southern oceans during SH summer in the simulation with ocean DMS compared to when the DMS emissions are switched off. The global annual mean top of the atmosphere DMS aerosol all sky radiative forcing is -2.03 W/m(2), whereas, over the southern oceans during SH summer, the mean DMS aerosol radiative forcing reaches -9.32 W/m(2).

  • 104.
    Devasthale, Abhay
    et al.
    SMHI, Forskningsavdelningen, Atmosfärisk fjärranalys.
    Fueglistaler, S.
    A climatological perspective of deep convection penetrating the TTL during the Indian summer monsoon from the AVHRR and MODIS instruments2010Ingår i: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 10, nr 10, s. 4573-4582Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The impact of very deep convection on the water budget and thermal structure of the tropical tropopause layer is still not well quantified, not least because of limitations imposed by the available observation techniques. Here, we present detailed analysis of the climatology of the cloud top brightness temperatures as indicators of deep convection during the Indian summer monsoon, and the variations therein due to active and break periods. We make use of the recently newly processed data from the Advanced Very High Resolution Radiometer (AVHRR) at a nominal spatial resolution of 4 km. Using temperature thresholds from the Atmospheric Infrared Sounder (AIRS), the AVHRR brightness temperatures are converted to climatological mean (2003-2008) maps of cloud amounts at 200, 150 and 100 hPa. Further, we relate the brightness temperatures to the level of zero radiative heating, which may allow a coarse identification of convective detrainment that will subsequently ascend into the stratosphere. The AVHRR data for the period 1982-2006 are used to document the differences in deep convection between active and break conditions of the monsoon. The analysis of AVHRR data is complemented with cloud top pressure and optical depth statistics (for the period 2003-2008) from the Moderate Resolution Imaging Spectroradiometer (MODIS) onboard Aqua satellite. Generally, the two sensors provide a very similar description of deep convective clouds. Our analysis shows that most of the deep convection occurs over the Bay of Bengal and central northeast India. Very deep convection over the Tibetan plateau is comparatively weak, and may play only a secondary role in troposphere-to-stratosphere transport. The deep convection over the Indian monsoon region is most frequent in July/August, but the very highest convection (coldest tops, penetrating well into the TTL) occurs in May/June. Large variability in convection reaching the TTL is due to monsoon break/active periods. During the monsoon break period, deep convection reaching the TTL is almost entirely absent in the western part of the study area (i.e. 60 E-75 E), while the distribution over the Bay of Bengal and the Tibetan Plateau is less affected. Although the active conditions occur less frequently than the break conditions, they may have a larger bearing on the composition of the TTL within the monsoonal anticyclone, and tracer transport into the stratosphere because of deep convection occurring over anthropogenically more polluted regions.

  • 105.
    Karlsson, Karl-Göran
    et al.
    SMHI, Forskningsavdelningen, Atmosfärisk fjärranalys.
    Dybbroe, Adam
    SMHI, Forskningsavdelningen, Atmosfärisk fjärranalys.
    Evaluation of Arctic cloud products from the EUMETSAT Climate Monitoring Satellite Application Facility based on CALIPSO-CALIOP observations2010Ingår i: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 10, nr 4, s. 1789-1807Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The performance of the three cloud products cloud fractional cover, cloud type and cloud top height, derived from NOAA AVHRR data and produced by the EUMETSAT Climate Monitoring Satellite Application Facility, has been evaluated in detail over the Arctic region for four months in 2007 using CALIPSO-CALIOP observations. The evaluation was based on 142 selected NOAA/Metop overpasses allowing almost 400 000 individual matchups between AVHRR pixels and CALIOP measurements distributed approximately equally over the studied months (June, July, August and December 2007). Results suggest that estimations of cloud amounts are very accurate during the polar summer season while a substantial loss of detected clouds occurs in the polar winter. Evaluation results for cloud type and cloud top products point at specific problems related to the existence of near isothermal conditions in the lower troposphere in the polar summer and the use of reference vertical temperature profiles from Numerical Weather Prediction model analyses. The latter are currently not detailed enough in describing true conditions relevant on the pixel scale. This concerns especially the description of near-surface temperature inversions which are often too weak leading to large errors in interpreted cloud top heights.

  • 106. Kärner, O.
    et al.
    Karlsson, Karl-Göran
    SMHI, Forskningsavdelningen, Atmosfärisk fjärranalys.
    Climate Monitoring SAF - Cloud products feasibility study in the inner Arctic region: Part II: Evaluation of the variability in radiation and cloud data2009Rapport (Övrigt vetenskapligt)
  • 107. Kokhanovsky, Alexander A.
    et al.
    Naud, Catherine M.
    Devasthale, Abhay
    SMHI, Forskningsavdelningen, Atmosfärisk fjärranalys.
    Intercomparison of Ground-Based Radar and Satellite Cloud-Top Height Retrievals for Overcast Single-Layered Cloud Fields2009Ingår i: IEEE Transactions on Geoscience and Remote Sensing, ISSN 0196-2892, E-ISSN 1558-0644, Vol. 47, nr 7, s. 1901-1908Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The objective of this paper is to assess the accuracy of the Semi-Analytical CloUd Retrieval Algorithm (SACURA) that retrieves cloud-top heights (CTHs) using hyperspectral SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY (SCIAMACHY) onboard Environmental Satellite measurements for overcast single-layer cloud fields. Intercomparisons with ground-based 35-GHz millimeter wave cloud radar CTHs were performed for 14 dates during 2003-2007 at the US. Atmospheric Radiation Measurement (ARM) program Southern Great Plains site (36.6 degrees N, 97.5 degrees W). In addition, for some of these dates, European Space Agency MEdium Resolution Imaging Spectrometer (MERIS) and the NASAL-TERRA Moderate Resolution Imaging Spectroradiometer (MODIS) cloud-top pressure retrievals were also collected, transformed into CTHs using nearby ARM radiosonde profiles, and compared with the SACURA SCIAMACHY and radar retrievals. The accuracy of the SACURA-SCIAMACHY CTH retrievals is better than 0.34 km for low-level clouds and 2.22 km for high-level clouds with an underestimate in CTH on average for all clouds. The average bias in SCIAMACHY CTHs was about 0.07 km for low clouds and about 0.5 km for high-level clouds. Both MODIS and MERIS slightly overestimated the CTHs of low-level clouds by MO m, with an uncertainty better than 1 km. However, although MODIS accuracy for high-level clouds is close to SCIAMACHY, MERIS CTHs were significantly underestimated for these fairly optically thick cases.

  • 108. Salonen, K.
    et al.
    Jarvinen, H.
    Haase, Gunther
    SMHI, Forskningsavdelningen, Atmosfärisk fjärranalys.
    Niemela, S.
    Eresmaa, R.
    Doppler radar radial winds in HIRLAM. Part II: optimizing the super-observation processing2009Ingår i: Tellus. Series A, Dynamic meteorology and oceanography, ISSN 0280-6495, E-ISSN 1600-0870, Vol. 61, nr 2, s. 288-295Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Doppler radar radial wind observations are modelled in numerical weather prediction (NWP) within observation errors which consist of instrumental, modelling and representativeness errors. The systematic and random modelling errors can be reduced through a careful design of the observation operator (Part I). The impact of the random instrumental and representativeness errors can be decreased by optimizing the processing of the so-called super-observations (spatial averages of raw measurements; Part II). The super-observation processing is experimentally optimized in this article by determining the optimal resolution for the super-observations for different NWP model resolutions. A 1-month experiment with the HIRLAM data assimilation and forecasting system is used for radial wind data monitoring and for generating observation minus background (OmB) differences. The OmB statistics indicate that the super-observation processing reduces the standard deviation of the radial wind speed OmB difference, while the mean vector wind OmB difference tends to increase. The optimal parameter settings correspond at a measurement range of 50 km (100 km) to an averaging area of 1.7 km(2) (7.3 km(2)). In conclusion, an accurate and computationally feasible observation operator for the Doppler radar radial wind observations is developed (Part I) and a super-observation processing system is optimized (Part II).

  • 109. 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, Forskningsavdelningen, Meteorologi.
    Landelius, Tomas
    SMHI, Forskningsavdelningen, Atmosfärisk fjärranalys.
    Dahlgren, Per
    SMHI, Forskningsavdelningen, Meteorologi.
    Integrated Observation and Modeling of the Arctic Sea Ice and Atmosphere2009Ingår i: Bulletin of The American Meteorological Society - (BAMS), ISSN 0003-0007, E-ISSN 1520-0477, Vol. 90, nr 3, s. 293-297Artikel i tidskrift (Refereegranskat)
  • 110. Haley, P. J., Jr.
    et al.
    Lermusiaux, P. F. J.
    Robinson, A. R.
    Leslie, W. G.
    Logoutov, O.
    Cossarini, G.
    Liang, X. S.
    Moreno, P.
    Ramp, S. R.
    Doyle, J. D.
    Bellingham, J.
    Chavez, F.
    Sheldon, Johnston, Marston
    SMHI, Forskningsavdelningen, Atmosfärisk fjärranalys.
    Forecasting and reanalysis in the Monterey Bay/California Current region for the Autonomous Ocean Sampling Network-II experiment2009Ingår i: Deep-sea research. Part II, Topical studies in oceanography, ISSN 0967-0645, E-ISSN 1879-0100, Vol. 56, nr 3-5, s. 127-148Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    During the August-September 2003 Autonomous Ocean Sampling Network-II experiment, the Harvard Ocean Prediction System (HOPS) and Error Subspace Statistical Estimation (ESSE) system were utilized in real-time to forecast physical fields and uncertainties, assimilate various ocean measurements (CTD, AUVs, gliders and SST data), provide suggestions for adaptive sampling, and guide dynamical investigations. The qualitative evaluations of the forecasts showed that many of the surface ocean features were predicted, but that their detailed positions and shapes were less accurate. The root-mean-square errors of the real-time forecasts showed that the forecasts had skill out to two days. Mean one-day forecast temperature RMS error was 0.26 degrees C less than persistence RMS error. Mean two-day forecast temperature RMS error was 0.13 degrees C less than persistence RMS error. Mean one- or two-day salinity RMS error was 0.036 PSU less than persistence RMS error. The real-time skill in the surface was found to be greater than the skill at depth. Pattern correlation coefficient comparisons showed, on average, greater skill than the RMS errors. For simulations lasting 10 or more days, uncertainties in the boundaries could lead to errors in the Monterey Bay region. Following the real-time experiment, a reanalysis was performed in which improvements were made in the selection of model parameters and in the open-boundary conditions. The result of the reanalysis was improved long-term stability of the simulations and improved quantitative skill, especially the skill in the main thermocline (RMS simulation error 1 degrees C less than persistence RMS error out to five days). This allowed for an improved description of the ocean features. During the experiment there were two-week to 10-day long upwelling events. Two types of upwelling events were observed: one with plumes extending westward at point Ano Nuevo (AN) and Point Sur (PS); the other with a thinner band of upwelled water parallel to the coast and across Monterey Bay. During strong upwelling events the flows in the upper 10-20 m had scales similar to atmospheric scales. During relaxation, kinetic energy becomes available and leads to the development of mesoscale features. At 100-300 m depths, broad northward flows were observed, sometimes with a coastal branch following topographic features. An anticyclone was often observed in the subsurface fields in the mouth of Monterey Bay. (C) 2008 Elsevier Ltd. All rights reserved.

  • 111. Schulz, J.
    et al.
    Albert, P.
    Behr, H. -D
    Caprion, D.
    Deneke, H.
    Dewitte, S.
    Durr, B.
    Fuchs, P.
    Gratzki, A.
    Hechler, P.
    Hollmann, R.
    Sheldon, Johnston, Marston
    SMHI, Forskningsavdelningen, Atmosfärisk fjärranalys.
    Karlsson, Karl-Göran
    SMHI, Forskningsavdelningen, Atmosfärisk fjärranalys.
    Manninen, T.
    Mueller, R.
    Reuter, M.
    Riihela, A.
    Roebeling, R.
    Selbach, N.
    Tetzlaff, Anke
    SMHI, Forskningsavdelningen, Atmosfärisk fjärranalys.
    Thomas, W.
    Werscheck, M.
    Wolters, E.
    Zelenka, A.
    Operational climate monitoring from space: the EUMETSAT Satellite Application Facility on Climate Monitoring (CM-SAF)2009Ingår i: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 9, nr 5, s. 1687-1709Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The Satellite Application Facility on Climate Monitoring (CM-SAF) aims at the provision of satellite-derived geophysical parameter data sets suitable for climate monitoring. CM-SAF provides climatologies for Essential Climate Variables (ECV), as required by the Global Climate Observing System implementation plan in support of the UNFCCC. Several cloud parameters, surface albedo, radiation fluxes at the top of the atmosphere and at the surface as well as atmospheric temperature and humidity products form a sound basis for climate monitoring of the atmosphere. The products are categorized in monitoring data sets obtained in near real time and data sets based on carefully intercalibrated radiances. The CM-SAF products are derived from several instruments on-board operational satellites in geostationary and polar orbit as the Meteosat and NOAA satellites, respectively. The existing data sets will be continued using data from the instruments on-board the new joint NOAA/EUMETSAT Meteorological Operational Polar satellite. The products have mostly been validated against several ground-based data sets both in situ and remotely sensed. The accomplished accuracy for products derived in near real time is sufficient to monitor variability on diurnal and seasonal scales. The demands on accuracy increase the longer the considered time scale is. Thus, interannual variability or trends can only be assessed if the sensor data are corrected for jumps created by instrument changes on successive satellites and more subtle effects like instrument and orbit drift and also changes to the spectral response function of an instrument. Thus, a central goal of the recently started Continuous Development and Operations Phase of the CM-SAF (2007-2012) is to further improve all CM-SAF data products to a quality level that allows for studies of interannual variability.

  • 112. Reuter, M.
    et al.
    Thomas, W.
    Albert, P.
    Lockhoff, M.
    Weber, R.
    Karlsson, Karl-Göran
    SMHI, Forskningsavdelningen, Atmosfärisk fjärranalys.
    Fischer, J.
    The CM-SAF and FUB Cloud Detection Schemes for SEVIRI: Validation with Synoptic Data and Initial Comparison with MODIS and CALIPSO2009Ingår i: Journal of Applied Meteorology and Climatology, ISSN 1558-8424, E-ISSN 1558-8432, Vol. 48, nr 2, s. 301-316Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The Satellite Application Facility on Climate Monitoring (CM-SAF) is aiming to retrieve satellite-derived geophysical parameters suitable for climate monitoring. CM-SAF started routine operations in early 2007 and provides a climatology of parameters describing the global energy and water cycle on a regional scale and partially on a global scale. Here, the authors focus on the performance of cloud detection methods applied to measurements of the Spinning Enhanced Visible and Infrared Imager (SEVIRI) on the first Meteosat Second Generation geostationary spacecraft. The retrieved cloud mask is the basis for calculating the cloud fractional coverage (CFC) but is also mandatory for retrieving other geophysical parameters. Therefore, the quality of the cloud detection directly influences climate monitoring of many other parameters derived from spaceborne sensors. CM-SAF products and results of an alternative cloud coverage retrieval provided by the Institut fur Weltraumwissenschaften of the Freie Universitat in Berlin, Germany (FUB), were validated against synoptic measurements. Furthermore, and on the basis of case studies, an initial comparison was performed of CM-SAF results with results derived from the Moderate Resolution Imaging Spectrometer (MODIS) and from the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP). Results show that the CFC from CM-SAF and FUB agrees well with synoptic data and MODIS data over midlatitudes but is underestimated over the tropics and overestimated toward the edges of the visible Earth disk.

  • 113.
    Devasthale, Abhay
    et al.
    SMHI, Forskningsavdelningen, Atmosfärisk fjärranalys.
    Grassl, H.
    A daytime climatological distribution of high opaque ice cloud classes over the Indian summer monsoon region observed from 25-year AVHRR data2009Ingår i: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 9, nr 12, s. 4185-4196Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A daytime climatological spatio-temporal distribution of high opaque ice cloud (HOIC) classes over the Indian subcontinent (0-40 degrees N, 60 degrees E-100 degrees E) is presented using 25-year data from the Advanced Very High Resolution Radiometers (AVHRRs) for the summer monsoon months. The HOICs are important for regional radiative balance, precipitation and troposphere-stratosphere exchange. In this study, HOICs are sub-divided into three classes based on their cloud top brightness temperatures (BT). Class I represents very deep convection (BT < 220 K). Class II represents deep convection (220 K <=BT < 233 K) and Class III background convection (233 K <=BT < 253 K). Apart from presenting finest spatial resolution (0.1x0.1 degrees) and long-term climatology of such cloud classes from AVHRRs to date, this study for the first time illustrates on (1) how these three cloud classes are climatologically distributed during monsoon months, and (2) how their distribution changes during active and break monsoon conditions. It is also investigated that how many deep convective clouds reach the tropopause layer during individual monsoon months. It is seen that Class I and Class II clouds dominate the Indian subcontinent during monsoon. The movement of monsoon over continent is very well reflected in these cloud classes. During monsoon breaks strong suppression of convective activity is observed over the Arabian Sea and the western coast of India. On the other hand, the presence of such convective activity is crucial for active monsoon conditions and all-India rainfall. It is found that a significant fraction of HOICs (3-5%) reach the tropopause layer over the Bay of Bengal during June and over the north and northeast India during July and August. Many cases are observed when clouds penetrate the tropopause layer and reach the lower stratosphere. Such cases mostly occur during June compared to the other months.

  • 114.
    Devasthale, Abhay
    et al.
    SMHI, Forskningsavdelningen, Atmosfärisk fjärranalys.
    Grassl, H.
    Comparison of low brightness temperatures derived from the AVHRR thermal channels with in situ measurements in Antarctica2009Ingår i: International Journal of Remote Sensing, ISSN 0143-1161, E-ISSN 1366-5901, Vol. 30, nr 2, s. 525-532Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Data from the National Oceanic and Atmospheric Administration (NOAA) satellites' Advanced Very High Resolution Radiometers (AVHRRs) represent the longest record (more than 25 years) of continuously available satellite-based thermal measurements, and have well-chosen spatial and spectral resolutions. As a consequence, these data are used extensively to develop cloud climatologies. However, for such applications, accurate calibration and intercalibration of both solar and thermal channels of the AVHRRs is necessary so as to homogenize the data obtained from the different AVHRR sensors. AVHRR thermal channels 4 and 5 are routinely used in threshold-based hierarchical decision-tree cloud detection and classification algorithms, and therefore an evaluation of the stability of these channels at low temperatures is important. In this letter, the AVHRR channel 4 and 5 brightness temperatures (BTs) are compared at five stations in Antarctica. The data for the period of June, July and August (the coldest months of every year and with minimal atmospheric influence) from 1982 to 2006 were used for the evaluations. The calibration and intercalibration of the thermal channels are found to be very robust. The root mean square errors (RMSEs) range from 2.2 to 3.4K and the correlation coefficients from 0.84 to 0.95. No apparent artefacts or artificial jumps in the BTs are visible in the data series after changes of sensors. The BTs from the thermal channels of the AVHRRs can be used for preparing cloud climatologies, as their intercalibration is found to be consistent across different afternoon satellites.

  • 115.
    Trolez, Matthieu
    et al.
    SMHI.
    Karlsson, Karl-Göran
    SMHI, Forskningsavdelningen, Atmosfärisk fjärranalys.
    Johnston, Sheldon
    SMHI, Forskningsavdelningen, Klimatforskning - Rossby Centre.
    Albert, Peter
    SMHI.
    The impact of varying NWP background information on CM-SAF cloud products: Visiting Scientist Report Climate Monitoring SAF (CM-SAF)2008Rapport (Övrigt vetenskapligt)
    Abstract [en]

    The purpose of this study was to quantify the impact of using ancillary data from Numerical Weather Prediction (NWP) models in the derivation of cloud parameters from satellite data in the Climate Monitoring Satellite Application Facility (CM-SAF) project. In particular, the sensitivity to the NWP-analysed surface temperature parameter was studied.A one-year dataset of satellite images over the Scandinavian region from the Advanced Very High Resolution Radiometer (AVHRR) on the polar orbiting NOAA satellites was studied. Cloud products were generated by use of the Polar Platform System (PPS) cloud software and the sensitivity to perturbations of the NWP-analysed surface temperature was investigated. In addition, a study on the importance of the chosen NWP model was also included. Results based on three different NWP models (ECMWF, HIRLAM and GME) were analysed.It was concluded that the NWP model influence on the results appears to be small. An interchange of NWP model analysis input data to the PPS cloud processing method did only lead to marginal changes of the resulting CM-SAF cloud products. Thus, the current CM-SAF cloud algorithmsproduce robust results that are not heavily dependent on NWP model background information. Nevertheless, the study demonstrated a natural high sensitivity to the NWP-analysed surface skin temperature. This parameter is crucial for the a priori determination of the thresholds used for the infrared cloud tests of the PPS method. It was shown that a perturbation of the surface skin temperature of one K generally resulted in a change of cloud cover of about 0.5-1 % in absolute cloud amount units. However, if perturbations were in the range 5-10 K the change in cloud cover increased to values between 1 to 2 % per degree, especially for positive perturbations. Important here is that a positive surface temperature perturbation always leads to an increase in the resulting cloud amounts and vice versa.

  • 116.
    Karlsson, Karl-Göran
    et al.
    SMHI, Forskningsavdelningen, Atmosfärisk fjärranalys.
    Willen, Ulrika
    SMHI, Forskningsavdelningen, Klimatforskning - Rossby Centre.
    Jones, Colin
    SMHI, Forskningsavdelningen, Klimatforskning - Rossby Centre.
    Wyser, Klaus
    SMHI, Forskningsavdelningen, Klimatforskning - Rossby Centre.
    Evaluation of regional cloud climate simulations over Scandinavia using a 10-year NOAA advanced very high resolution radiometer cloud climatology2008Ingår i: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 113, nr D1, artikel-id D01203Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A satellite-derived (NOAA Advanced Very High Resolution Radiometer) cloud climatology over the Scandinavian region covering the period 1991 - 2001 has been used to evaluate the performance of cloud simulations of the Swedish Meteorological and Hydrological Institute Rossby Centre regional climate model (RCA3). Several methods of adapting the satellite and model data sets to allow a meaningful comparison were applied. RCA3-simulated total cloud cover was shown to agree within a few percent of the satellite-retrieved cloud amounts on seasonal and annual timescales. However, a substantial imbalance between the respective RCA3 contributions from low-, medium- and high-level clouds was seen. The differences from satellite-derived contributions were +2.4% for high-level clouds, -5.2% for medium-level clouds and +4.0% for low- level clouds. In addition, an overrepresentation of cloud categories with high optical thicknesses was seen for all vertical cloud groups, particularly during the summer season. Some specific features of the geographical distribution of cloudiness were also noticed. Most pronounced were the excess of cloud amounts over the Scandinavian mountain range and a deficit leeward of the mountains. The overall results imply problems with the RCA3-modeled surface radiation budget components by causing reduced incoming solar radiation and increased downwelling longwave radiation.

  • 117.
    Eliasson, Salomon
    et al.
    SMHI, Forskningsavdelningen, Atmosfärisk fjärranalys.
    Tetzlaff, Anke
    SMHI, Forskningsavdelningen, Atmosfärisk fjärranalys.
    Karlsson, Karl-Göran
    SMHI, Forskningsavdelningen, Atmosfärisk fjärranalys.
    Prototyping an improved PPS cloud detection for the Arctic polar night2007Rapport (Övrigt vetenskapligt)
    Abstract [sv]

    under noll grader och snö och regn är vanligt förekommande, vilket bl.a. skapar hala vägar och behov av

  • 118.
    Johnston, Sheldon
    et al.
    SMHI, Forskningsavdelningen, Klimatforskning - Rossby Centre.
    Karlsson, Karl-Göran
    SMHI, Forskningsavdelningen, Atmosfärisk fjärranalys.
    METEOSAT 8 SEVIRI and NOAA AVHRR Cloud Products: A Climate Monitoring SAF2007Rapport (Övrigt vetenskapligt)
    Abstract [sv]

    åtgärder för att minska halka, såsom användning av vinterdäck (med eller utan dubb), sandning och

  • 119.
    Johansson, Barbro
    et al.
    SMHI, Affärsverksamhet.
    Lindström, Göran
    SMHI, Forskningsavdelningen, Hydrologi.
    Olsson, Jonas
    SMHI, Forskningsavdelningen, Hydrologi.
    Yacoub, Tahsin
    SMHI, Samhälle och säkerhet.
    Haase, Günther
    SMHI, Forskningsavdelningen, Atmosfärisk fjärranalys.
    Jacobsson, Karin
    SMHI, Affärsverksamhet.
    Sanner, Håkan
    SMHI, Samhälle och säkerhet.
    Översvämningsprognoser i områden med ofullständiga data: Metodutveckling och utvärdering2007Rapport (Övrigt vetenskapligt)
    Abstract [sv]

    Rapporten redovisar slutresultat från projektet ”Översvämningsprognoser Utveckling av metoder för ett rikstäckande system för vattenförings- och vattenståndsprognoser”. Projektet har i huvudsak varit finansierat av Räddningsverket, numera MSB, (Myndigheten för Samhällsskydd och Beredskap), men har även utnyttjat resultat från näraliggande projekt finansierade av Elforsk, SMHI och EU.I ett rikstäckande system måste prognoser göras för vattendrag där det saknas detaljerad information om avrinningsområdets och älvfårans egenskaper. Modeller kan inte tillämpas och verifieras på samma sätt som i områden med god datatillgång och tillgång till tidsserier med observerad vattenföring. Eftersom beräkningarna inte kan verifieras mot observationer blir det extra viktigt med bra nederbördsinformation och att kunna ge ett mått på osäkerheten i prognosen. Projektet har dels arbetat med metodutveckling, dels med en omfattande utvärdering av data och beräkningsresultat. En pilotstudie gjordes för flödet sommaren 2004 i Lagan/Ljungby. Fokus har varit på följande områden:- Utveckling och utvärdering av en metodik för att utnyttja meteorologiska och hydrologiska sannolikhetsprognoser- Utvärdering och minimering av osäkerheten i hydrologiska (vattenföring) och hydrauliska (vattenstånd) prognosmodeller.- Utveckling och utvärdering av metoder för att utnyttja radarobservationer av nederbörd.Projektet har visat att det är möjligt att göra vattenståndsprognoser med rimlig noggrannhet, utgående från data som finns tillgängliga i ett rikstäckande system. Tillgång till bra nederbördsinformation för dagarna före prognosen är viktig, speciellt i sjörika system med ett långsamt förlopp. För att kunna göra sannolikhetsprognoser räcker det inte att ta hänsyn till osäkerheten i den meteorologiska prognosen genom att direkt utnyttja meteorologiska ensembleprognoser. Spridningen i de meteorologiska nederbördsprognoserna är inte tillräcklig och osäkerheten i den hydrologiska modellen måste beaktas.De projektresultat som inom det närmaste året kommer att utnyttjas i ett rikstäckande system är de som är relaterade till hydrologisk modellering och sannolikhetsprognoser. Arbetet med att utveckla metoder för att utnyttja radarinformation i operationell skattning av arealnederbörd fortgår. Fallstudier har visat att vattenståndsprognoser kan göras med modeller baserad på översiktlig information om topografi och tvärsektioner i vattendragen. Däremot är det tidsödande att sätta upp en hydraulisk modell för en godtycklig älvsträcka. Tills vidare är det realistiskt att anta att vattenståndsprognoser främst kommer att göras i vattendrag som ingått i den översiktliga översvämningskarteringen.

  • 120. Zhang, Jianzhong
    et al.
    Kuenzer, Claudia
    Tetzlaff, Anke
    SMHI, Forskningsavdelningen, Atmosfärisk fjärranalys.
    Oertel, Dieter
    Zhukov, Boris
    Wagner, Wolfgang
    Thermal characteristics of coal fires 2: Results of measurements on simulated coal fires2007Ingår i: Journal of Applied Geophysics, ISSN 0926-9851, E-ISSN 1879-1859, Vol. 63, nr 3-4, s. 135-147Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this paper we present thermal characteristics of coal fires as measured during simulated fires under an experimental setting in Germany in July 2002. It is thus a continuation of the previously published paper "Thermal surface characteristics of coal fire 1: Results of in-situ measurement", in which we presented temperature measurements of real subsurface coal fires in China [Zhang, J., Kuenzer, C., accepted for publication. Thermal Surface Characteristics of Coal Fires 1: Results of in-situ measurements. Accepted for publication at Journal of Applied Geophysics.]. The focus is on simulated coal fires, which are less complex in nature than fires under natural conditions. In the present study we simulated all the influences usually occurring under natural conditions in a controllable manner (uniform background material of known thermal properties, known ventilation pathways, homogeneous coal substrate), creating two artificial outdoor coal fires under simplified settings. One surface coal fire and one subsurface coal fire were observed over the course of 2 days. The set up of the fires allowed for measurements not always feasible under "real" in-situ conditions: thus compared to the in-situ investigations presented in paper one we could retrieve numerous temperature measurements inside of the fires. Single temperature measurements, diurnal profiles and airborne thermal surveying present the typical temperature patterns of a small surface-and a subsurface fire under undisturbed conditions (easily accessible terrain, 24 hour measurements period, homogeneous materials). We found that the outside air temperature does not influence the fire's surface temperature (up to 900 degrees C), while fire centre temperatures of up to 1200 degrees C strongly correlate with surface temperatures of the fire. The fires could heat their surrounding up to a distance of 4.5 m. However, thermal anomalies on the background surface only persist as long as the fire is burning and disappear very fast if the heat source is removed. Furthermore, heat outside of the fires is transported mainly by convection and not by radiation. In spatial thermal line scanner data the diurnal thermal patterns of the coal fire are clearly represented. Our experiments during that data collection also visualize the thermal anomaly differences between covered (underground) and uncovered (surface) coal fires. The latter could not be observed in-situ in a real coal fire area. Subsurface coal fires express a much weaker signal than open surface fires and contrast only by few degrees against the background. In airborne thermal imaging scanner data the fires are also well represented. Here we could show that the mid-infrared domain (3.8 mu m) is more suitable to pick up very hot anomalies, compared to the common thermal (8.8 mu m) domain. Our results help to understand coal fires and their thermal patterns as well as the limitations occurring during their analysis. We believe that the results presented here can practicably help for the planning of coal fire thermal mapping campaigns - including remote sensing methods and the thermal data can be included into numerical coal fire modelling as initial or boundary conditions. (c) 2007 Elsevier B.V. All rights reserved.

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