A comparison of SSM /I‐derived global marine surface‐specific humidity datasets

Satellite‐based microwave sensors have, since the 1980s, provided a means to retrieve near‐surface marine specific humidity ( q a ), accurate estimation of which is necessary for climate and air–sea interaction applications. Seven satellite measurement‐derived monthly mean humidity datasets are compared with one another and with a dataset constructed from in situ measurements. The means, spatial and temporal structures of the datasets are shown to be markedly different, with a range of yearly, global mean q a of ∼1 g kg –1 . Comparison of the datasets derived using the same satellite measurements of brightness temperature reveals differences in q a that depend on the source of satellite data; the processing and quality control applied to the data; and the algorithm used to derive q a from the satellite measurements of brightness temperature. Regional differences between satellite‐derived q a due to the choice of input data, quality control and retrieval algorithm can all exceed the accuracy requirements for surface flux calculation of ∼0.3 g kg –1 and in some cases can be several g kg –1 in monthly means for some periods and regions.