6.1
Changes in global ocean cloud cover and related radiation flux since 1952
Joel R. Norris, SIO/Univ. Of California, La Jolla, CA
A recent study documented large changes in satellite-measured tropical mean reflected SW and outgoing LW radiation during 1985-1999, attributing them to cloud changes. Using surface synoptic reports of oceanic cloud cover, I estimate the impact of cloud variability on reflected SW and outgoing LW and find high correlations between estimated and measured time series. These high correlations suggest that synoptic cloud reports may be used to reliably estimate the impact of cloud cover variability on radiation in the pre-satellite era. Results show that upper-level cloud cover decreased between 1952 and 1997 over both the tropics and extratropics, causing a corresponding increase in global ocean mean outgoing LW radiation. SW reflection by clouds decreased in the tropics and increased in the extratropics, resulting in little global ocean mean change. Cloud-related net upward radiation increased by 1.7 watts per square meter from 1952 to 1997, indicating that changes in oceanic cloud cover during the past five decades have acted to substantially reduce the rate of global warming. Examination of the geographical distribution of cloud and radiation trends suggests the atmospheric circulation has become more El Nino-like over the past several decades.
Session 6, Radiative Forcing of the Climate: Modeling (Room 609/610)
Tuesday, 13 January 2004, 3:30 PM-5:30 PM, Room 609/610
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