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Zhe Wang
,
Zhenhui Wang
,
Xiaozhong Cao
,
Jiajia Mao
,
Fa Tao
, and
Shuzhen Hu

Abstract

An improved algorithm to calculate cloud-base height (CBH) from infrared temperature sensor (IRT) observations that accompany a microwave radiometer was described, the results of which were compared with the CBHs derived from ground-based millimeter-wavelength cloud radar reflectivity data. The results were superior to the original CBH product of IRT and closer to the cloud radar data, which could be used as a reference for comparative analysis and synergistic cloud measurements. Based on the data obtained by these two kinds of instruments for the same period (January–December 2016) from the Beijing Nanjiao Weather Observatory, the results showed that the consistency of cloud detection was good and that the consistency rate between the two datasets was 81.6%. The correlation coefficient between the two CBH datasets reached 0.62, based on 73 545 samples, and the average difference was 0.1 km. Higher correlations were obtained for thicker clouds with a larger echo intensity. A low-level thin cloud cannot be regarded as a blackbody because of its high transmittance, which results in higher CBHs derived from IRT data. Because of a smaller cloud radiation effect for high-level thin cloud above 8 km, the contribution of the atmospheric downward radiation below the cloud base to the IRT cannot be ignored, as it results in lower CBHs derived from IRT data. Owing to the seasonal variation of atmospheric downward radiation reaching the IRT, the difference between the two CBHs also has a seasonal variation. The IRT CBHs are generally higher (lower) than the cloud radar CBHs in winter (summer).

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Ed R. Westwater
,
Wang Zhenhui
,
Norman C. Grody
, and
Larry M. McMillin

Abstract

Temperature profiles are derived from ground- and satellite-based microwave radiometric observations. Data taken by the NOAA Profiler during December 1981 to December 1982, at Stapleton International Airport, Denver, Colorado, are combined with NOAA 6/7 Microwave Sounding Unit (MSU) observations over Denver. The results of 460 retrievals by the Profiler, the MSU, and the Profiler + MSU are compared with soundings by National Weather Service radiosondes (RAOBs). From the surface to 300 mb, maximum rms differences between the combined retrievals and RAOBs are less than about 2 K. For 17 cases in March 1981, radiometric data from the Profiler and MSU were combined with tropopause height measurements obtained from a VHF radar. The combined retrievals using the tropopause height information were improved in the vicinity of the tropopause by about 2 K rms relative to the pure passive ones.

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