An algorithm for improving the retrieval of cloud liquid water andwater vapor using effective radiating temperature of clouds

摘要

An algorithm is discussed which can significantly lower the rmsnerrors in integrated cloud liquid water and water vapor retrieval fromnradiometric brightness temperature. This algorithm makes use of theneffective radiating temperature of the atmosphere which is estimatednfrom surface temperature, cloud base temperature, and cloud base height.nThe surface temperature is easily measured, while the cloud basentemperature and the cloud base height may be measured by use of anpyrometer and a ceilometer, respectively. The effective radiatingntemperature T_eff is estimated at two separate frequenciesncorresponding to the two frequencies used to measure radiometricnbrightness temperature, and these estimates are then used to modify thenbrightness temperatures. For a data base compiled at University Park,nPennsylvania, the estimates of effective radiating temperature reducednthe rms error in retrieving cloud liquid water content from 37 to 21nμm, and reduced the rms error in retrieving water vapor under cloudynconditions from 0.20 to 0.11 cm. The reduction in the uncertainty innretrieved liquid water content was consistent with that achieved by Hannand Thomson (1) for tropical conditions. Han and Thomson usednmeasurements of cloud base height and cloud base temperature, along withna climatological mean effective radiating temperature to improve theirnretrievals