Comment on "variations of tropical upper tropospheric clouds with sea surface temperature and implications for radiative effects" by H. Su et al.

Abstract

Using TRMM VIRS data, we attempt to replicate the analysis made by Su et al. (2008) to quantify the effect of methodological choices on the magnitude of the observed correlations between upper-level cloud cover and SST. Using brightness temperature thresholds to identify upper-level cloud, we recover a relatively small change in the normalized area of cirrus clouds with SST (∼-6%/K compared to ∼-2%/K found by Su et al. (2008)). We discuss the effect of several methodological choices on the magnitude of the signal, namely, the classification of cloudy regions into convective updrafts and anvil, the use of cloud weighted SST, and the truncation and sampling error of the orbital satellite data with respect to the evolution of mesoscale convective systems. Accounting for some of these methodological differences could resolve the discrepancy between the weak signal documented by Su et al. (2008) and the stronger signal documented originally by Lindzen et al. (2001) and others, including the results reported in this comment. Copyright 2010 by the American Geophysical Union.