Radiative Cooling by Stratospheric Water Vapor: GCM Treatment vs. Observations
Lacis, A.A. (a) and Oinas, V. (b), NASA Goddard Institute for Space Studies
Eleventh Atmospheric Radiation Measurement (ARM) Science Team Meeting
The stratosphere has been cooling over the past two to three decades by about 1-2 K/decade. Recent attempts to reconcile decadal trends in climate data and climate model simulations suggest that stratospheric water vapor is potentially an important contributor to the observed decadal stratospheric cooling. However, there are surprisingly large differences among recent GCM simulations for prescribed changes in stratospheric water vapor, which point to problems with current treatment of absorption and emission by stratospheric water vapor. Forster and Shine [1999], using a wideband infrared radiation scheme, obtain an equilibrium cooling of about 0.8?C for a stratospheric water vapor increase of 0.7 ppmv. However, with a high-resolution correlated k-distribution treatment that is capable of accurately simulating the cooling by stratospheric water vapor, we obtain a stratospheric cooling of 0.3?C. This brings closer agreement between global climate data and model simulations of stratospheric temperature change over the past several decades.
Note: This is the poster abstract presented at the meeting; an extended version was not provided by the author(s).
