85th AMS Annual Meeting

Tuesday, 11 January 2005: 8:45 AM
TRMM evidence of a "weekend effect" for U.S. rainfall
Thomas L. Bell, NASA/GSFC, Greenbelt, MD; and M. Hahnenberger
Aerosols change the way precipitating clouds evolve, due to their effect on condensation and ice formation. The net effect of aerosols on precipitation varies depending on the local environment, the synoptic situation, and also on how far downstream one looks for effects. Repeated experiments with controlled release of aerosols would be helpful in unraveling how aerosols affect precipitation. The weekly variation in human activity may provide just such a set of experiments. Using the rainfall estimates from the passive microwave instrument on the Tropical Rainfall Measuring Mission (TRMM), which has been orbiting for over six years and can view areas as far north as 38 degs, we find that there is indeed a weekly variation in summer (JJA) precipitation (as measured by TRMM) over the southeastern U.S. land area, with the average rain rate peaking in the middle of the week (Tue-Thu). A bootstrap statistical test indicates that the variation is unlikely to be due to chance. The peak rainfall coincides with the well documented midweek peak in pollution around cities.

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