High cloud variations with surface temperature from 2002 to 2015: Contributions to atmospheric radiative cooling rate and precipitation changes

摘要

The global mean precipitation is largely constrained by atmospheric radiative cooling rates (Qr), which are sensitive to changes in high cloud fraction. We investigate variations of high cloud fraction with surface temperature (Ts) from July 2002 to June 2015 and compute their radiative effects on Qr using the Fu-Liou-Gu plane-parallel radiation model. We find that the tropical mean (30 degrees S-30 degrees N) high cloud fraction decreases with increasing Ts at a rate of about -1.0 +/- 0.34% K-1 from 2002 to 2015, which leads to an enhanced atmospheric cooling around 0.86 W m(-2) K-1. On the other hand, the northern midlatitudes (30 degrees N-60 degrees N) high cloud fraction increases with surface warming at a rate of 1.85 +/- 0.65% K-1 and the near-global mean (60 degrees S-60 degrees N) high cloud fraction shows a statistically insignificant decreasing trend with increasing Ts over the analysis period. Dividing high clouds into cirrus, cirrostratus, and deep convective clouds, we find that cirrus cloud fraction increases with surface warming at a rate of 0.32 +/- 0.11% K-1 (0.01 +/- 0.17% K-1) for the near-global mean (tropical mean), while cirrostratus and deep convective clouds decrease with surface warming at a rate of -0.02 +/- 0.18% K-1 and -0.33 +/- 0.18% K-1 for the near-global mean and -0.64 +/- 0.23% K-1 and -0.37 +/- 0.13% K-1 for the tropical mean, respectively. High cloud fraction response to feedback to Ts accounts for approximately 1.9 +/- 0.7% and 16.0 +/- 6.1% of the increase in precipitation per unit surface warming over the period of 2002-2015 for the near-global mean and the tropical mean, respectively.