Tropical cirrus and water vapor: an effective Earth infrared iris feedback? Q. Fu, M. Baker, and D. L. Hartmann Department of Atmospheric Sciences, University of Washington, Seattle, Washington, USA
Abstract. We revisit a model of feedback processes proposed by Lindzen et
al. (2001), in which an assumed 22% reduction in the area of tropical high clouds per degree increase in sea
surface temperature produces negative feedbacks associated with upper tropospheric
water vapor and cloud radiative effects. We argue that the water vapor feedback is
overestimated in Lindzen et al. (2001) by at least 60%, and that the high cloud feedback is small.
Although not mentioned by Lindzen et al. (2001), tropical low clouds make a significant
contribution to their negative feedback, which is also overestimated. Using more realistic
parameters in the model of Lindzen et al. (2001), we obtain a feedback factor in the range of
-0.15 to -0.51, compared to their larger negative feedback factor of -0.45 to
-1.03. It is noted that our feedback factor could still be overestimated due to the assumption of
constant low cloud cover in the simple radiative-convective model.
Citation: Fu, Q., Baker, M., and Hartmann, D. L.: Tropical cirrus and water vapor: an effective Earth infrared iris feedback?, Atmos. Chem. Phys., 2, 31-37, doi:10.5194/acp-2-31-2002, 2002.