Clear-sky biases in satellite infrared estimates of upper tropospheric humidity and its trends

John, V.O., Holl, G., Allan, R. ORCID: https://orcid.org/0000-0003-0264-9447, Buehler, S.A., Parker, D.E. and Soden, B.J. (2011) Clear-sky biases in satellite infrared estimates of upper tropospheric humidity and its trends. Journal of Geophysical Research, 116. D14108. ISSN 0148-0227 doi: 10.1029/2010JD015355

Abstract/Summary

We use microwave retrievals of upper tropospheric humidity (UTH) to estimate the impact of clear-sky-only sampling by infrared instruments on the distribution, variability and trends in UTH. Our method isolates the impact of the clear-sky-only sampling, without convolving errors from other sources. On daily time scales IR-sampled UTH contains large data gaps in convectively active areas, with only about 20-30 % of the tropics (30 S­ 30 N) being sampled. This results in a dry bias of about -9 %RH in the area-weighted tropical daily UTH time series. On monthly scales, maximum clear-sky bias (CSB) is up to -30 %RH over convectively active areas. The magnitude of CSB shows significant correlations with UTH itself (-0.5) and also with the variability in UTH (-0.6). We also show that IR-sampled UTH time series have higher interannual variability and smaller trends compared to microwave sampling. We argue that a significant part of the smaller trend results from the contrasting influence of diurnal drift in the satellite measurements on the wet and dry regions of the tropics.

Item Type	Article
URI	https://centaur.reading.ac.uk/id/eprint/21843
Identification Number/DOI	10.1029/2010JD015355
Refereed	Yes
Divisions	Science > School of Mathematical, Physical and Computational Sciences > Department of Meteorology Science > School of Mathematical, Physical and Computational Sciences > NCAS Science > School of Mathematical, Physical and Computational Sciences > National Centre for Earth Observation (NCEO)
Publisher	American Geophysical Union
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