Monthly mean large-scale analyses of upper-tropospheric humidity and wind field divergence derived from three geostationary satellites

This paper describes the results from a collaborative study between the European Space Operations Center, the European Organization for the Exploitation of Meteorological Satellites, the National Oceanic and Atmospheric Administration, and the Cooperative Institute for Meteorological Satellite Studies investigating the relationship between satellite-derived monthly mean fields of wind and humidity in the upper troposphere for March 1994. Three geostationary meteorological satellites GOES-7, Meteosat-3, and Meteosat-5 are used to cover an area from roughly 160 deg W to 50 deg E. The wind fields are derived from tracking features in successive images of upper-tropospheric water vapor (WV) as depicted in the 6.5-micron absorption band. The upper-tropospheric relative humidity (UTH) is inferred from measured water vapor radiances with a physical retrieval scheme based on radiative forward calculations. Quantitative information on large-scale circulation patterns in the upper-troposphere is possible with the dense spatial coverage of the WV wind vectors. The monthly mean wind field is used to estimate the large-scale divergence; values range between about-5 x 10(exp -6) and 5 x 10(exp 6)/s when averaged over a scale length of about 1000-2000 km. The spatial patterns of the UTH field and the divergence of the wind field closely resemble one another, suggesting that UTH patterns are principally determined by the large-scale circulation. Since the upper-tropospheric humidity absorbs upwelling radiation from lower-tropospheric levels and therefore contributes significantly to the atmospheric greenhouse effect, this work implies that studies on the climate relevance of water vapor should include three-dimensional modeling of the atmospheric dynamics. The fields of UTH and WV winds are useful parameters for a climate-monitoring system based on satellite data. The results from this 1-month analysis suggest the desirability of further GOES and Meteosat studies to characterize the changes in the upper-tropospheric moisture sources and sinks over the past decade

Measuremnts of the radiation budget components over the North Sea

On board of the German research vessels "Meteor" and "Anton Dohrn" the components of shortwave and longwave radiation budgets have been measured over the Fladenground area during a short period in 1975 (13.-19. August) and the Fladenground-Experiment (FLEX, 25 March 1976-13 June 1976). The data show that in spring and in the beginning of summer, when the ocean water is still cool, the daily incident solar radiation exceeds the net thermal radiation loss of the water to the atmosphere. In August, however, the water emission has increased to such a level that on disturbed days the daily mean radiation balance is negative. The monthly averages of the radiation budget and the global radiation derived from the shipborn measurements agree surprisingly well with those derived by several authors from climatological data. A simple scheme has been developed to parameterize the global radiation with respect to the observed cloudiness

Model‐simulated humidity bias in the upper troposphere and its relation to the large‐scale circulation

The depiction of water vapor in the upper troposphere in Geophysical Fluid Dynamics Laboratory (GFDL) climate model and ERA‐40 reanalysis is evaluated through a model‐to‐radiance approach. Brightness temperatures of High‐Resolution Infrared Radiation Sounder (HIRS) 6.7 μm channel, Special Sensor for Microwave Water Vapor Profiler (SSM/T‐2) 183.31 ± 1 GHz channel, and Microwave Sounding Unit (MSU) 60 GHz channel simulated with data from the GFDL climate model and ERA‐40 reanalysis show a distinct cold and moist bias in the upper troposphere compared to satellite observations, particularly over the subtropics. Temperature biases are a common feature in many climate models and complicate the interpretation of radiance‐based comparisons with satellite data. We introduce a new method for evaluating the water vapor distribution which combines both HIRS 6.7 μm and SSM/T‐2 183.31 ± 1 GHz channels and is much less sensitive to tropospheric temperature biases. Using this method, we show that GFDL climate model has a more humid upper troposphere over dry subtropical area than ERA‐40 reanalysis. The geographical distribution of the humidity bias is found to exhibit a close association with differences in the 500 hPa vertical pressure velocity, suggesting that much of the bias in tropical upper tropospheric relative humidity can be attributed to errors in simulating the intensity of large‐scale tropical circulation. Given the strong dependence of upper tropospheric water vapor on the large‐scale circulation, these results suggest that long‐term monitoring of upper tropospheric water vapor from satellites may also offer insight into variations in the large‐scale atmospheric circulation. Key Points Investigation of the depiction of upper tropospheric water vapor in models Model‐simulated humidity bias in the upper troposphere Relation of model‐simulated humidity bias to large‐scale circulatio

Observations depuis l'orbite géostationnaire avec Meteosat troisième génération (MTG)

Meteosat troisième génération (MTG), la prochaine génération de satellites météorologiques géostationnaires européens, disposera de capacités largement accrues, comparées à celles des autres missions actuellement en orbite géostationnaire. C'est un système à deux satellites, avec deux instruments différents sur chaque satellite. Le nouvel imageur, dénommé FCI (Flexible Combined Imager), possède 16 bandes spectrales et apporte à la fois la continuité et des améliorations aux données actuelles d'imagerie pour leurs applications en prévision immédiate (PI) et en prévision numérique du temps (PNT). Il est accompagné d'un imageur d'éclairs (LI pour Lightning Imager), qui effectue des mesures optiques à la longueur d'onde de 777,4 nm. Les satellites emportant ces deux instruments sont dénommés MTG-I (imageur). Les satellites compagnons sont dénommés MTG-S (sondeur) et emportent un sondeur infrarouge hyperspectral (IRS), qui mesurera la température, l'humidité, les gaz trace et les nuages, et fournira, grâce à sa haute répétitivité temporelle, des informations sur la circulation atmosphérique. Le second instrument de MTG-S est un sondeur à haute résolution dans l'ultraviolet, le visible et le proche infrarouge (UVN) pour mesurer la composition atmosphérique, et correspondant à la mission Sentinel-4 de Copernicus. La flotte MTG comprendra six satellites, quatre satellites MTG-I et deux satellites MTG-S pour fournir respectivement 20 et 15 ans et demi de service opérationnel. Le lancement du premier satellite MTG-I est prévu en 2021 et celui du premier satellite MTG-S en 2022.Meteosat Third Generation (MTG), the next generation of European geostationary meteorological satellites, will have greatly enhanced capabilities in comparison to other current meteorological satellite missions in geostationary orbit. It is a twinsatellite system with two different instruments on each satellite. The new imager, called the Flexible Combined Imager (FCI), has 16 spectral channels and provides continuity and improvements for established imager observations and applications in nowcasting and numerical weather prediction. The companion payload to the FCI is the Lightning Imager (LI) measuring optically at a wavelength of 777.4 nm. The satellites carrying these two instruments are referred to as the MTG-I (imager) satellites. The twin-satellites are denoted MTG-S (sounder) and carry an InfraRed hyper-spectral Sounder (IRS) that will measure temperature, humidity, trace gases and clouds and, by utilising the high temporal repeat cycle, will provide information on the atmospheric flow. The second instrument on MTG-S is a high resolution Ultraviolet Visible Nearinfrared (UVN) sounder for atmospheric composition measurements, which corresponds to Copernicus Sentinel-4 mission. The MTG fleet will comprise of six satellites, four MTG-I and two MTG-S satellites providing 20 and 15.5 years of operational service, respectively. The launch of the first MTG-I is expected in 2021 and the first MTG-S is currently planned for 2022