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- Author or Editor: Anthony J. Schreiner x
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Abstract
This article describes the size, intensity, trajectory, lifetime and distribution of the GATE cloud clusters of West Africa and the eastern Atlantic Ocean and relates their distribution to the summer climate of the region. SMS-1 infrared and visible 3 h pictures for 85 days of GATE, starting 27 June 1974, were used. It was found that over 500 clusters occurred. Size averaged 2 × 105 km2; lifetime, one day. Although both were highly variable, in general, lifetime increased with maximum size. The clusters occurred in a band oriented west-southwest to east-northeast over the ocean and eastward over land. Nodes were observed at intervals of 5–7° along the axis of maximum frequency of occurrence. Clusters at all latitudes moved generally westward, having straighter tracks and faster speeds over land. From July to September the axis of the cluster band shifted northward 100–300 km, and tended to split over the ocean. Clusters on the northern flank of the band were associated with African easterly waves, especially during Phase III; however, most of the clusters of GATE occurred to the south of the surface pressure trough and surface confluence, apparently in association with convergence within the mean low-level monsoon circulation.
Abstract
This article describes the size, intensity, trajectory, lifetime and distribution of the GATE cloud clusters of West Africa and the eastern Atlantic Ocean and relates their distribution to the summer climate of the region. SMS-1 infrared and visible 3 h pictures for 85 days of GATE, starting 27 June 1974, were used. It was found that over 500 clusters occurred. Size averaged 2 × 105 km2; lifetime, one day. Although both were highly variable, in general, lifetime increased with maximum size. The clusters occurred in a band oriented west-southwest to east-northeast over the ocean and eastward over land. Nodes were observed at intervals of 5–7° along the axis of maximum frequency of occurrence. Clusters at all latitudes moved generally westward, having straighter tracks and faster speeds over land. From July to September the axis of the cluster band shifted northward 100–300 km, and tended to split over the ocean. Clusters on the northern flank of the band were associated with African easterly waves, especially during Phase III; however, most of the clusters of GATE occurred to the south of the surface pressure trough and surface confluence, apparently in association with convergence within the mean low-level monsoon circulation.
Abstract
To date, operational satellite temperature retrieves from the TIROS-N/NOAA A–G series of satellites and a large percentage of those produced for research purposes have used statistical techniques to estimate limb effects in satellite-observed radiances. In this study, temperature profiles were derived using the radiative transfer equation in a form which properly takes into account the angle of observation. These temperature profiles were then compared to those derived using the radiative transfer equation with “nadir radiances” produced by a statistical limb correction technique similar to those now used operationally. This comparison revealed significant differences in the derived temperature profiles at large viewing angles, particularly in the case of strong meridional temperature gradients. Overall, the results suggest that for the calculation of temperature profiles from nonnadir observations, the more proper physical solution is the preferred procedure for deriving temperature fields.
Abstract
To date, operational satellite temperature retrieves from the TIROS-N/NOAA A–G series of satellites and a large percentage of those produced for research purposes have used statistical techniques to estimate limb effects in satellite-observed radiances. In this study, temperature profiles were derived using the radiative transfer equation in a form which properly takes into account the angle of observation. These temperature profiles were then compared to those derived using the radiative transfer equation with “nadir radiances” produced by a statistical limb correction technique similar to those now used operationally. This comparison revealed significant differences in the derived temperature profiles at large viewing angles, particularly in the case of strong meridional temperature gradients. Overall, the results suggest that for the calculation of temperature profiles from nonnadir observations, the more proper physical solution is the preferred procedure for deriving temperature fields.
Abstract
Comparisons between geopotential analyses derived from rawinsondes (RAOB) and the VISSR Atmospheric Sounder (VAS) generally exhibit differences that are ultimately related to the horizontal density and placement of the respective observations and the vertical resolution inherent in the instruments. In order to overcome some of the inconsistencies that appear, two strategies have been developed which allow the analyses to communicate through the derived variable, geostrophic potential vorticity. The first incorporates the statistics of RAOB derived potential vorticity into the VAS vorticity analysis. This is accomplished by making a least-squares adjustment to VAS while constraining it to have first and second moments identical to the RAOB analysis. The other approach makes mutual least-squares adjustments to RAOB and VAS vorticity analyses subject to the dynamic constraint that forecast and hindcast of potential vorticity to the time midway between analyses are equal. The forecast and hindcast are made from a two-parameter baroclinic model. In both procedures, the heights are recovered from adjusted vorticities by inverting the elliptic operators that relate height to vorticity.
Data from the GOES-East satellite at 1430 GMT 6 March 1982 are used along with rawinsonde data at 1200 GMT to test the schemes. The statistical adjustment approach makes synoptically meaningful adjustments to the VAS analysis over the Gulf of Mexico and Gulf coast region, but fails to correct the obvious discrepancies over the continental United States. The dynamic scheme succeeds in making meaningful adjustments over both the Gulf of Mexico and the continent which result in improved vertical motion fields.
Abstract
Comparisons between geopotential analyses derived from rawinsondes (RAOB) and the VISSR Atmospheric Sounder (VAS) generally exhibit differences that are ultimately related to the horizontal density and placement of the respective observations and the vertical resolution inherent in the instruments. In order to overcome some of the inconsistencies that appear, two strategies have been developed which allow the analyses to communicate through the derived variable, geostrophic potential vorticity. The first incorporates the statistics of RAOB derived potential vorticity into the VAS vorticity analysis. This is accomplished by making a least-squares adjustment to VAS while constraining it to have first and second moments identical to the RAOB analysis. The other approach makes mutual least-squares adjustments to RAOB and VAS vorticity analyses subject to the dynamic constraint that forecast and hindcast of potential vorticity to the time midway between analyses are equal. The forecast and hindcast are made from a two-parameter baroclinic model. In both procedures, the heights are recovered from adjusted vorticities by inverting the elliptic operators that relate height to vorticity.
Data from the GOES-East satellite at 1430 GMT 6 March 1982 are used along with rawinsonde data at 1200 GMT to test the schemes. The statistical adjustment approach makes synoptically meaningful adjustments to the VAS analysis over the Gulf of Mexico and Gulf coast region, but fails to correct the obvious discrepancies over the continental United States. The dynamic scheme succeeds in making meaningful adjustments over both the Gulf of Mexico and the continent which result in improved vertical motion fields.
Abstract
Visible-Infrared Spin Scan Radiometer (VISSR) Atmospheric Sounder (VAS) moisture retrievals are compared to the National Meteorological Center Regional Analysis and Forecast System (RAFS) 12-h forecast and to 1200 UTC rawinsondes over the United States and the Gulf of Mexico on a daily basis for nearly 1.5 years. The principal objective is to determine what information the current moisture retrieval add to that available from the RAFS and surface data. The data are examined from the climatological perspective, that is, total precipitable water over the seasons for three geographical regions, and also for synoptic applications, that is, vertical and horizontal resolution. VAS retrievals are found to be systematically too moist at higher values. The variance of the VAS soundings more closely agrees with the rawinsonde at locations around the Gulf of Mexico than the RAFS. An examination of a case (6 June 1989) over the Gulf of Mexico region comparing three layers of VAS-derived moisture to the RAFS forecast shows the former capable of outperforming the latter in both the horizontal and, to some extent, the vertical frame of reference.
Abstract
Visible-Infrared Spin Scan Radiometer (VISSR) Atmospheric Sounder (VAS) moisture retrievals are compared to the National Meteorological Center Regional Analysis and Forecast System (RAFS) 12-h forecast and to 1200 UTC rawinsondes over the United States and the Gulf of Mexico on a daily basis for nearly 1.5 years. The principal objective is to determine what information the current moisture retrieval add to that available from the RAFS and surface data. The data are examined from the climatological perspective, that is, total precipitable water over the seasons for three geographical regions, and also for synoptic applications, that is, vertical and horizontal resolution. VAS retrievals are found to be systematically too moist at higher values. The variance of the VAS soundings more closely agrees with the rawinsonde at locations around the Gulf of Mexico than the RAFS. An examination of a case (6 June 1989) over the Gulf of Mexico region comparing three layers of VAS-derived moisture to the RAFS forecast shows the former capable of outperforming the latter in both the horizontal and, to some extent, the vertical frame of reference.
Abstract
The optimal nonlinear inversion or one-dimensional variational (1DVAR) method was used to retrieve the cloud-top height and effective cloud amount from Geostationary Operational Environmental Satellite (GOES) sounder longwave spectral-band cloudy radiance measurements. The cloud-top pressure and effective cloud amount derived from the carbon dioxide (CO2)–slicing technique served as the background or first guess in the 1DVAR retrieval process. The atmospheric temperature profile, moisture profile, and surface skin temperature from the forecast analysis were used for the radiative transfer calculation in both the CO2-slicing method and the 1DVAR retrieval processing. Simulation studies were made to investigate the accuracy (the retrievals were compared with truth) of the cloud-top pressures and the effective cloud amounts derived from both the CO2-slicing and 1DVAR algorithms. Significant improvement of 1DVAR over CO2-slicing cloud properties was found in the simulation studies; an improvement of 10–50 hPa for root-mean-square error was obtained in 1DVAR over the CO2-slicing-derived cloud-top pressures, depending on the cloud height (high, mid, or low). This improvement came largely from the reduction of the bias in the 1DVAR retrievals over the CO2-slicing cloud-top pressures. The 1DVAR approach was applied to process the GOES-8 sounder cloudy radiance measurements; consistent with the simulation results, CO2 slicing assigned high and low clouds to lower levels than 1DVAR did.
Abstract
The optimal nonlinear inversion or one-dimensional variational (1DVAR) method was used to retrieve the cloud-top height and effective cloud amount from Geostationary Operational Environmental Satellite (GOES) sounder longwave spectral-band cloudy radiance measurements. The cloud-top pressure and effective cloud amount derived from the carbon dioxide (CO2)–slicing technique served as the background or first guess in the 1DVAR retrieval process. The atmospheric temperature profile, moisture profile, and surface skin temperature from the forecast analysis were used for the radiative transfer calculation in both the CO2-slicing method and the 1DVAR retrieval processing. Simulation studies were made to investigate the accuracy (the retrievals were compared with truth) of the cloud-top pressures and the effective cloud amounts derived from both the CO2-slicing and 1DVAR algorithms. Significant improvement of 1DVAR over CO2-slicing cloud properties was found in the simulation studies; an improvement of 10–50 hPa for root-mean-square error was obtained in 1DVAR over the CO2-slicing-derived cloud-top pressures, depending on the cloud height (high, mid, or low). This improvement came largely from the reduction of the bias in the 1DVAR retrievals over the CO2-slicing cloud-top pressures. The 1DVAR approach was applied to process the GOES-8 sounder cloudy radiance measurements; consistent with the simulation results, CO2 slicing assigned high and low clouds to lower levels than 1DVAR did.
Abstract
A technique using the Geostationary Operational Environmental Satellite (GOES) sounder radiance data has been developed to improve detection of low clouds and fog just after sunrise. The technique is based on a simple difference method using the shortwave (3.7 μm) and longwave (11.0 μm) window bands in the infrared range of the spectrum. The time period just after sunrise is noted for the difficulty in being able to correctly identify low clouds and fog over land. For the GOES sounder cloud product this difficulty is a result of the visible reflectance of the low clouds falling below the “cloud” threshold over land. By requiring the difference between the 3.7- and the 11.0-μm bands to be greater than 5.0 K, successful discrimination of low clouds and fog is found 85% of the time for 21 cases from 14 September 2005 to 6 March 2006 over the GOES-12 sounder domain. For these 21 clear and cloudy cases the solar zenith angle ranged from 87° to 77°; however, the range of solar zenith angles for cloudy cases was from 85° to 77°.
The success rate further improved to 95% (20 out of 21 cases) by including a difference threshold of 5.0 K between the 3.7- and 4.0-μm bands, requiring that the 11.0-μm band be greater than 260 K, and limiting the test to fields of view where the surface elevation is below 999 m. These final three limitations were needed to more successfully deal with cases involving snow cover and dead vegetation. To ensure that only the time period immediately after sunrise is included the solar zenith angle threshold for application of these tests is between 89° and 70°.
Abstract
A technique using the Geostationary Operational Environmental Satellite (GOES) sounder radiance data has been developed to improve detection of low clouds and fog just after sunrise. The technique is based on a simple difference method using the shortwave (3.7 μm) and longwave (11.0 μm) window bands in the infrared range of the spectrum. The time period just after sunrise is noted for the difficulty in being able to correctly identify low clouds and fog over land. For the GOES sounder cloud product this difficulty is a result of the visible reflectance of the low clouds falling below the “cloud” threshold over land. By requiring the difference between the 3.7- and the 11.0-μm bands to be greater than 5.0 K, successful discrimination of low clouds and fog is found 85% of the time for 21 cases from 14 September 2005 to 6 March 2006 over the GOES-12 sounder domain. For these 21 clear and cloudy cases the solar zenith angle ranged from 87° to 77°; however, the range of solar zenith angles for cloudy cases was from 85° to 77°.
The success rate further improved to 95% (20 out of 21 cases) by including a difference threshold of 5.0 K between the 3.7- and 4.0-μm bands, requiring that the 11.0-μm band be greater than 260 K, and limiting the test to fields of view where the surface elevation is below 999 m. These final three limitations were needed to more successfully deal with cases involving snow cover and dead vegetation. To ensure that only the time period immediately after sunrise is included the solar zenith angle threshold for application of these tests is between 89° and 70°.
A processing scheme that determines cloud height and amount based on radiances from the Visible Infrared Spin Scan Radiometer Atmospheric Sounder (VAS) using a CO2 absorption technique has been installed on the National Environmental Satellite Data and Information Service VAS Data Utilization Center computer system in Washington, D.C. The processed data will complement the Automated Surface Observing System (ASOS). ASOS uses automated ground equipment that provides near-continuous observations of surface weather data that are currently manually obtained. Geostationary multispectral infrared measurements are available every hour with information on clouds above the ASOS laser ceilometer viewing limit of 12 000 ft. The combined ASOS/satellite system will be able to depict cloud conditions at all levels up to 50 000 ft. The error rate of combined ASOS and satellite observations is less than 4% of the total sample in a comparison test with manual observations performed by National Weather Service personnel during March and April 1992. An attempt to distinguish thin from opaque clouds, by using a satellite-determined effective cloud amount, resulted in a substantial reduction in the discrepancies.
A processing scheme that determines cloud height and amount based on radiances from the Visible Infrared Spin Scan Radiometer Atmospheric Sounder (VAS) using a CO2 absorption technique has been installed on the National Environmental Satellite Data and Information Service VAS Data Utilization Center computer system in Washington, D.C. The processed data will complement the Automated Surface Observing System (ASOS). ASOS uses automated ground equipment that provides near-continuous observations of surface weather data that are currently manually obtained. Geostationary multispectral infrared measurements are available every hour with information on clouds above the ASOS laser ceilometer viewing limit of 12 000 ft. The combined ASOS/satellite system will be able to depict cloud conditions at all levels up to 50 000 ft. The error rate of combined ASOS and satellite observations is less than 4% of the total sample in a comparison test with manual observations performed by National Weather Service personnel during March and April 1992. An attempt to distinguish thin from opaque clouds, by using a satellite-determined effective cloud amount, resulted in a substantial reduction in the discrepancies.
Since April 1994 a new generation of geostationary sounders has been measuring atmospheric radiances in 18 infrared spectral bands and thus providing the capability for investigating oceanographic and meteorological phenomena that far exceed those available from the previous generation of Geostationary Operational Environmental Satellites (GOES). Menzel and Purdom foreshadowed many of the anticipated improvements from the GOES-8/9 sounders. This article presents some of the realizations; it details the in-flight performance of the sounder, presents both validated operational as well as routinely available experimental products, and shows the impact on nowcasting and forecasting activities.
For the first time operational hourly sounding products over North America and adjacent oceans are now possible with the GOES-8/9 sounders. The GOES-8/9 sounders are making significant contributions by depicting moisture changes for numerical weather prediction models over the continental United States, monitoring winds over oceans, and supplementing the National Weather Service's Automated Surface Observing System with upper-level cloud information. Validation of many sounding products has been accomplished by comparison with radiosondes and aircraft measurements. Considerable progress has been made toward assimilation of soundings from clear skies and cloud properties in cloudy regions in operational as well as research forecast models; GOES-8/9 moisture soundings are now being used in the operational Eta regional forecast model.
Since April 1994 a new generation of geostationary sounders has been measuring atmospheric radiances in 18 infrared spectral bands and thus providing the capability for investigating oceanographic and meteorological phenomena that far exceed those available from the previous generation of Geostationary Operational Environmental Satellites (GOES). Menzel and Purdom foreshadowed many of the anticipated improvements from the GOES-8/9 sounders. This article presents some of the realizations; it details the in-flight performance of the sounder, presents both validated operational as well as routinely available experimental products, and shows the impact on nowcasting and forecasting activities.
For the first time operational hourly sounding products over North America and adjacent oceans are now possible with the GOES-8/9 sounders. The GOES-8/9 sounders are making significant contributions by depicting moisture changes for numerical weather prediction models over the continental United States, monitoring winds over oceans, and supplementing the National Weather Service's Automated Surface Observing System with upper-level cloud information. Validation of many sounding products has been accomplished by comparison with radiosondes and aircraft measurements. Considerable progress has been made toward assimilation of soundings from clear skies and cloud properties in cloudy regions in operational as well as research forecast models; GOES-8/9 moisture soundings are now being used in the operational Eta regional forecast model.
