Upper-Tropospheric Winds Derived from Geostationary Satellite Water Vapor Observations (original) (raw)
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Bulletin of the American Meteorological Society, 1995
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°W to 50°E. The wind fields are derived from tracking features in successive images of upper-tropospheric water vapor (WV) as depicted in the 6.5-JI 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 10-6 and 5 x 10-6 sec 1 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 threedimensional 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.
Satellite observations of upper tropospheric relative humidity, clouds and wind field divergence
… to atmospheric physics, 1995
This paper presents / an observational study of upper level wind field divergence, upper tropospheric relative humidity (UTH) and high level cloud from satellite. Wind fields are derived from successive half-hourly images of the METEOSAT-4 water vapour (WV: 5.7-7.1 (im) channel. The UTH is inferred from the WV image data with a physical retrieval scheme based on radiative forward calculations. Upper tropospheric cloud amounts are based on the C0 2 -slicing technique applied to bi-spectral radiance observations from the High Resolution Infrared Sounder (HIRS) aboard the NOAA-11 and 12 polar orbiting satellites. The previous UTH retrieval has been simplified such that two radiative forward calculations define a linear relationship between observed WV brightness temperature and the UTH for each retrieval. The new approach is computationally more efficient, however, it retains the important dependency of the UTH on local mean temperature and lapse rate. The WV wind vectors provide a dense spatial coverage of the upper tropospheric flow and, thus, can be used to estimate monthly mean wind fields and associated large-scale divergence. Inferred values of the wind field divergence over a scale of 1500 km are between -5xl0 _6 s _1 and 5xl0~6s _1 which is consistent with other observations. The spatial patterns of monthly means of wind field divergence and UTH closely resemble each other although the quantitative relationship is non-linear. A comparison of the UTH with high-level cloud amounts from the HIRS instrument aboard the NOAA polar orbiting satellites also features a high spatial coherence between both data sets. This suggests that largescale dynamics is the governing factor for both the upper tropospheric relative humidity field and the cloud formation processes associated with the humidity fields. Some implications for largescale models are discussed.
A comparison of water vapor derived from GPS occultations and global weather analyses
Journal of Geophysical Research, 2001
Despite its fundamental importance in radiative transfer, atmospheric dynamics, and the hydrological cycle, atmospheric water is inadequately characterized particularly at a global scale. Occultation measurements from the Global Positioning System (GPS) should improve upon this situation. Individual occultations yield profiles of specific humidity accurate to 0.2 to 0.5 g/kg providing sensitive measurements of lower and middle tropospheric water vapor with global coverage in a unique, all-weather, limbviewing geometry with several hundred meters to a kilometer vertical resolution. We have derived water vapor profiles from June 21 to July 4, 1995, using GPS occultation data combined with global temperature analyses from the European Center for Medium-Range Weather Forecasts (ECMWF) and reanalyses from the National Centers for Environmental Prediction (NCEP). The zonal mean structure of the profiles exhibits basic climatological features of tropospheric moisture. Specific humidity biases between the GPS results and the ECMWF global humidity analyses in the middle to upper troposphere are ϳ0.1 g/kg or less. Occultation results below 6 km altitude are generally drier than those of ECMWF with the bias generally increasing toward warmer temperatures. Near the height of the trade wind inversion, the ECMWF analyses are significantly moister than the occultation results due to vertical smoothing and overextension of the boundary layer top in the analyses. Overall, the occultation results are drier than the NCEP reanalyses with a marked exception near the Intertropical Convergence Zone (ITCZ) where occultation results are wetter by more than 10%. The occultation results are significantly wetter near the ITCZ and drier in the subtropics than the classical moisture climatology of Peixoto and Oort. Similarities between the NCEP and the Peixoto and Oort near-ITCZ differences suggest that a common analysis/model problem may be responsible. The generally wetter Peixoto and Oort results in the subtropics are due in part to moist radiosonde biases. Discrepancies between these data sets are significant and limit our ability to resolve uncertainties in moisture control and feedbacks in a changing climate.
RELATIONSHIP BETWEEN MONTHLY MEAN WATER VAPOUR WIND FIELDS AND THE UPPER TROPOSPHERIC HUMIDITY
The paper describes first results of a pilot study investigating the relationship between the monthly mean fields of wind and humidity in the upper troposphere. The wind fields are derived from successive METEOSAT images in the water vapour channel (WV: 5.7 -7.1 μm) and the up-per tropospheric relative humidity (UTH) is inferred from water vapour image data with a physical retrieval scheme. Quantitative information on the large scale circulation in the upper troposphere can be derived from WV wind fields, since the WV wind vectors are numerous enough to provide a dense spatial coverage, and thus clearly depict the atmospheric flow in the upper troposphere. The monthly mean wind field of January 1992 is employed to estimate the large scale divergence; values are within a range of about – 5⋅ 10 –6 s –1 and 5⋅ 10 –6 s –1 for a scale of about 1500 km. The spatial pattern ofthe UTH field closely resembles the divergence of the wind field suggesting that the UTH fields are principally det...
2002
Wind products from geostationary satellites have been generated for over 20 years, and are used in numerical weather prediction systems. However, because geostationary satellites do not provide useful wind information poleward of the midlatitudes, and because the high-latitude rawinsonde network is sparse, the polar regions remain data poor. This study demonstrates the feasibility of deriving tropospheric wind information at high latitudes from polar-orbiting satellites. The methodology employed is based on the algorithms currently used with geostationary satellites, modified for use with the Moderate Resolution Imaging Spectroradiometer (MODIS). The project presents some unique challenges, including the irregularity of temporal sampling, different viewing geometries in successive orbits, uncertainties in wind vector height assignment as a result of low atmospheric water vapor amounts and thin clouds typical of the Arctic and Antarctic, and the complexity of surface features. A 30-d...
Atmospheric Research, 2008
Past studies using a variety of satellite instruments have demonstrated the possibility of detecting lower stratospheric water vapor against a cold background of deep convective storm tops. The method is based on the brightness temperature difference (BTD) between the water vapor absorption and infrared window bands, assuming a thermal inversion above the cloud top level. This paper confirms the earlier studies, documenting positive BTD values between the 6.2 μm and 10.8 μm bands in Meteosat Second Generation (MSG) Spinning Enhanced Visible and InfraRed Imager (SEVIRI) imagery above tops of deep convective storms over Europe. The observed positive BTD values for a case from 28 June 2005 are compared to calculations from a radiative transfer model, and possible reasons for their existence are discussed. A localized increase in positive BTD is observed at the later stages of storm evolution, and this increase is likely a signal of water vapor being transported by this particular storm from the troposphere into the lower stratosphere.
Estimating Upper-Tropospheric Water Vapor from SSM/T-2 Satellite Measurements
Journal of Applied Meteorology, 2003
A method and a passive microwave retrieval algorithm have been developed to retrieve upper-tropospheric water vapor (UTW) from Special Sensor Microwave Water Vapor Profiler (SSM/T-2) measurements taken at three discrete frequencies near the 183-GHz water vapor line. The algorithm is based on physical relaxation utilizing statistical covariance information to provide initial-guess profiles and to constrain the updating step in the relaxation process. The scheme incorporates a method to remove SSM/T-2 brightness temperature bias in comparison with collocated simulated brightness temperatures. Correction functions are designed for the three SSM/T-2 183-GHz channels. The algorithm is validated against radiosonde observations and collocated SSM/ T-2 brightness temperatures. Under clear-sky and nonprecipitating-cloud conditions, the UTW retrievals exhibit an rms error of 0.68 kg m Ϫ2 with integrated water vapor biases below 5% for the upper-tropospheric layers of 700-500 and 500-200 hPa. The retrieval provides an independent source of satellite-derived water vapor information in the upper troposphere, distinct from upper-tropospheric humidity information retrieved from thermal infrared (IR) measurements around the 6.3-m water vapor absorption band. The microwave retrievals can then be used to cross-check IR retrievals and/or to augment IR retrievals, dependent upon the problem at hand.
The Role of GOES Satellite Imagery in Tracking Low-Level Moisture
Weather and Forecasting, 2006
This note provides examples of how geostationary satellite data can be applied to augment other data sources in tracking warm, moist air masses as they move northward from the Gulf of Mexico. These so-called returning air masses are often a key ingredient in bringing about severe weather outbreaks in the central and southeastern United States. The newer NOAA–GOES imagery provides high spatial and temporal resolution. Together, surface observations, upper-air soundings, and high-resolution satellite imagery provide a comprehensive picture of the returning moist air mass.