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Hai-Tien Lee
and
Robert G. Ellingson

Abstract

This paper develops a nonlinear statistical method that uses satellite radiance observations directly to estimate the downward longwave radiation (DLR) at the earth's surface, a necessary component of the surface energy budget. The proposed technique has rms regression errors of about 9 W m–2 for clear-sky conditions, and about 4 to 8 W m–2 for overcast conditions, depending on the cloud levels. It is shown that this technique can produce unbiased estimates over a large range of meteorological conditions, which is crucial for climate studies.

Sensitivity studies show that the DLR is most sensitive to errors in the cloud amount on average. Overall, the combined errors for an instantaneous DLR estimate, excluding the effects of the surface pressure errors, range from about 7 to 12 W m–2 when there is a ±10% uncertainty in cloud amount and a ±100 hPa uncertainty in cloud-base pressure. When the cloud amount uncertainty rises to 30%, the combined DLR error ranges from about 10 to 25 W m–2.

This clear-sky DLR estimation technique was validated preliminarily by using simulated radiation data. The DLR differences between estimated and calculated values have a standard deviation of about 9 W m–2 and are unbiased in most conditions.

The validity of the DLR estimation technique has been demonstrated; however, validation for cloudy conditions, comparison with surface observations, and improvements related to surface pressure dependence and skin temperature discontinuity are left for future study.

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Robert G. Ellingson
,
Hai-Tien Lee
,
David Yanuk
, and
Arnold Gruber

Abstract

Simultaneous observations by the Earth Radiation Budget Experiment (ERBE) scanning radiometer and the High-Resolution Infrared Sounder (HIRS) on board the NOAA-9 spacecraft have been used to validate a multispectral technique for estimating the outgoing longwave radiation (OLR) from the earth-atmosphere system. Results farm approximately 100 000 collocated observations show that the HIRS technique provides instantaneous OLR estimates that agree with the ERBE observations just as well as different ERBE scanners agree with each other—about 5 W m−2 rms. Although there are differences between the HIRS and ERBE estimates that depend upon the scene type and time of day, the HIRS technique explained more than 99% of the variance of the ERBE observations for both day and night observations. The results suggest that the HIRS OLR technique is a suitable replacement for the Advanced Very High Resolution Radiometer technique now used by the National Oceanic and Atmospheric Administration for operational estimates of the OLR.

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Kenneth R. Knapp
,
Steve Ansari
,
Caroline L. Bain
,
Mark A. Bourassa
,
Michael J. Dickinson
,
Chris Funk
,
Chip N. Helms
,
Christopher C. Hennon
,
Christopher D. Holmes
,
George J. Huffman
,
James P. Kossin
,
Hai-Tien Lee
,
Alexander Loew
, and
Gudrun Magnusdottir

Geostationary satellites have provided routine, high temporal resolution Earth observations since the 1970s. Despite the long period of record, use of these data in climate studies has been limited for numerous reasons, among them that no central archive of geostationary data for all international satellites exists, full temporal and spatial resolution data are voluminous, and diverse calibration and navigation formats encumber the uniform processing needed for multisatellite climate studies. The International Satellite Cloud Climatology Project (ISCCP) set the stage for overcoming these issues by archiving a subset of the full-resolution geostationary data at ~10-km resolution at 3-hourly intervals since 1983. Recent efforts at NOAA's National Climatic Data Center to provide convenient access to these data include remapping the data to a standard map projection, recalibrating the data to optimize temporal homogeneity, extending the record of observations back to 1980, and reformatting the data for broad public distribution. The Gridded Satellite (GridSat) dataset includes observations from the visible, infrared window, and infrared water vapor channels. Data are stored in Network Common Data Format (netCDF) using standards that permit a wide variety of tools and libraries to process the data quickly and easily. A novel data layering approach, together with appropriate satellite and file metadata, allows users to access GridSat data at varying levels of complexity based on their needs. The result is a climate data record already in use by the meteorological community. Examples include reanalysis of tropical cyclones, studies of global precipitation, and detection and tracking of the intertropical convergence zone.

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