Impact of improved near-infrared water vapor line data in simulations with the ECHAM4 general circulation model

Abstract

Recently, two new water vapor line absorption data sets have become available. First, the HITRAN 2000 data set provides updated information on several water vapor absorption lines in the near infrared. Second, an independent study initiated by the European Space Agency (ESA) created a new line data set for the spectral range between 8592 and 20000 cm-1. We investigate the impact of these new data in the near infrared as compared to HITRAN-92 on the absorption of solar radiation in the ECHAM4 general circulation model. Owing to the increased water vapor absorption in the new parameterizations, the global annual mean atmospheric absorption of solar radiation in ECHÅ M4 is increased under all skies between 3.2 and 3.7 W m-2 and between 5.0 and 5.7 W m-2 under clear skies for the different data sets. While the dynamics barely change, the hydrological cycle is slightly weaker, the cloud cover has decreased by 0.4% and the precipitation by 0.06 to 0.08 mm d-1 when the new data sets are used. Copyright 2002 by the American Geophysical Union.