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K. S. Nathan, P. W. Rosenkranz, and D. H. Staelin

Abstract

Satellite-borne radiometers have been used with increasing success to monitor geophysical parameters. The majority of the statistical retrieval schemes currently in use for estimating atmospheric temperature profiles are one-dimensional (1-D), that is, they consider correlations only in the dimension perpendicular to the surface. Here, a two-dimensional (2-D) spatial filter, optimum in the minimum-mean-square error sense, is used to retrieve atmospheric temperature profiles from Microwave Sounder Unit measurements. Horizontal correlations along the orbital track are taken into account. This additional statistical information results in lower mean-square errors for the 2-D filter compared to that of its 1-D counterpart. The previously unstudied behavior of retrieval errors as a function of spatial frequency along the orbital track is also investigated. A large part of the improved performance of the 2-D filter is due to the reduction of short spatial wavelength components in the error. In addition, retrievals were carded out over a severe cold front. The 2-D technique yielded substantially lower errors than the 1-D approach. The latter does not perform so well over fronts because of the loss in vertical correlation due to the presence of layers of air with different lapse rates.

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P. W. Rosenkranz, M. J. Komichak, and D. H. Staelin

Abstract

Simultaneous measurements of microwave emission from the earth, in the oxygen band near 60 GHz and the water vapor line near 183 GHz, permit inference of atmospheric temperature as a function of two variables: pressure and water vapor burden (integrated water vapor content above any level). Combination of these two profiles yields a profile of water vapor burden versus pressure. Occasional singularities in these retrievals can readily be identified and excluded. Numerical simulations have been made, using temperature and water vapor profiles from subtropical and midlatitude radiosonde stations, and assuming surface reflectivities typical of either land or ocean. Over a land surface, the residual rms errors in estimated water vapor burden profile between 300 and 1000 mb, range from 23 to 43% of the a priori standard deviation of water vapor burden for the corresponding climate. The relative humidity profile was also estimated with rms errors ranging from 4 to 17% of saturation. Over a seawater surface, using three additional channels at 18.5, 22.2 and 31.7 GHz, the corresponding results are 3–46% of a priori standard deviation for water vapor burden and 4–15% rms error for relative humidity.

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M. J. Schwartz, J. W. Barrett, P. W. Fieguth, P. W. Rosenkranz, M. S. Spina, and D. H. Staelin

Abstract

An imaging microwave radiometer with eight double-sideband channels centered on the 118-GHz oxygen resonance was flown on a high-altitude aircraft over a tropical cyclone in the Coral Sea. The measurements clearly resolved an eyewall of strong convection and a warm core within the eye. Brightness temperatures observed within the eye were approximately 10 K warmer than those observed in clear air 100 km or more away. This warming extended somewhat beyond the eyewall in the highest (most opaque) channel. The temperature profile in the eye, central pressure, and convective cell-top altitudes are inferred from the data.

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P. W. Rosenkranz, K. D. Hutchison, K. R. Hardy, and M. S. Davis

Abstract

Cross-track and conical scan microwave sounder designs are compared with respect to temperature profile retrieval accuracy in nonprecipitating atmospheres and with respect to the beamfilling effect of precipitation. The conical design shows slightly better accuracy at pressure levels of 3 hPa or less, while the cross-track design performs slightly better at pressure levels of 850 hPa or greater. Under the assumption that precipitation-contaminated fields of view would be rejected, consideration of beamfilling by rain cells indicates that retrieval yield would be higher for the cross-track design.

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D. H. Staelin, A. L. Cassel, K. F. Kunzi, R. L. Pettyjohn, R. K. L. Poon, P. W. Rosenkranz, and J. W. Waters

Abstract

The microwave spectrometer on the Nimbus 5 earth observatory satellite has been used to measure thermal radiation in five frequency bands between 22.235 and 58.8 GHz. Clouds were observed to affect less than 0.5% of the temperature profile soundings. Most such effects occur in the intertropical convergence zone and alter the inferred temperature profile by less than a few degrees Centigrade. These effects are evident as cold spots at 53.65 GHz and can be identified by virtue of their small spatial extent, in contrast to smooth variations characteristic of normal atmospheric temperature fields. These effects at 53.65 GHz are sufficiently well correlated with inferred liquid water abundances that they can be used for detecting major storm systems over both land and sea.

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