Validation of the Upper Tropospheric Relative Humidity Determined from METEOSAT Data

Abstract

The purpose of this note is to ?validate? the upper tropospheric humidity (UTH) operationally extracted from the 6.3 ?m channel data of METEOSAT. The validation is carded out by comparing the satellite data with observed humidifies from the conventional network of radiosondes. The validation is not an absolute error assessment of the UTH, but rather an intercomparison, because the upper-tropospheric radiosonde humidities may not be very accurate. The results for three latitude belts indicate that the estimated humidity in the upper troposphere shows a fairly high linear correlation (coefficients 0.64?0.89) with the observed humidity and that the slope of the regression line ranges from 0.82?0.89. The rms-error of the UTH is generally less than 10%. The UTH tends to underestimate the observed humidity by about 4%. This relative bias is most pronounced in the midlatitude belts.