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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 113, D02209, doi:10.1029/2007JD008623, 2008

Midweek increase in U.S. summer rain and storm heights suggests air pollution invigorates rainstorms

Thomas L. Bell

Laboratory for Atmospheres, NASA/Goddard Space Flight Center, Greenbelt, Maryland, USA


Daniel Rosenfeld

Institute of Earth Sciences, The Hebrew University of Jerusalem, Jerusalem, Israel


Kyu-Myong Kim

Laboratory for Atmospheres, NASA/Goddard Space Flight Center, Greenbelt, Maryland, USA
Goddard Earth Sciences and Technology Center, Univ. Maryland Baltimore Cty., Baltimore, Maryland, USA


Jung-Moon Yoo

Department of Science Education, Ewha Womans University, Seoul, South Korea


Myong-In Lee

Laboratory for Atmospheres, NASA/Goddard Space Flight Center, Greenbelt, Maryland, USA
Goddard Earth Sciences and Technology Center, Univ. Maryland Baltimore Cty., Baltimore, Maryland, USA


Maura Hahnenberger

Meteorology Department, University of Utah, Salt Lake City, Utah, USA


Abstract

Tropical Rainfall Measuring Mission (TRMM) satellite estimates of summertime rainfall over the southeast U.S. are found on average to be significantly higher during the middle of the work week than on weekends, attributable to a midweek intensification of afternoon storms and an increase in area with detectable rain. TRMM radar data show a significant midweek increase in the echo-top heights reached by afternoon storms. Weekly variations in model-reanalysis wind patterns over the region are consistent with changes in convection implied by the satellite data. Weekly variations in rain gauge averages are also consistent with the satellite estimates, though possibly smaller in amplitude. A midweek decrease of rainfall over the nearby Atlantic is also seen. EPA measurements of surface particulate concentrations show a midweek peak over much of the U.S. These observations are consistent with the theory that anthropogenic air pollution suppresses cloud-drop coalescence and early rainout during the growth of thunderstorms over land, allowing more water to be carried above the 0°C isotherm, where freezing yields additional latent heat, invigorating the storms and producing large ice hydrometeors. The enhanced convection induces regional convergence, uplifting and an overall increase of rainfall. Compensating downward air motion suppresses convection over the adjacent ocean areas. Pre-TRMM-era data suggest that the weekly cycle only became strong enough to be detectable beginning in the 1980's. Rain-gauge data also suggest that a weekly cycle may have been detectable in the 1940's, but with peak rainfall on Sunday or Monday, possibly explained by the difference in composition of aerosol pollution at that time. This “weekend effect” may thus offer climate researchers an opportunity to study the regional climate-scale impact of aerosols on storm development and monsoon-like circulation.

Received 6 March 2007; accepted 16 November 2007; published 31 January 2008.

Keywords: Precipitation change; aerosols; anthropogenic climate change.

Index Terms: 3311 Atmospheric Processes: Clouds and aerosols; 3354 Atmospheric Processes: Precipitation (1854); 0345 Atmospheric Composition and Structure: Pollution: urban and regional (0305, 0478, 4251); 1803 Hydrology: Anthropogenic effects (4802, 4902); 3305 Atmospheric Processes: Climate change and variability (1616, 1635, 3309, 4215, 4513).

Subscriber Access to Full Article (Nonsubscribers may purchase for $9.00, Includes print PDF, file size: 2245858 bytes)

Citation: Bell, T. L., D. Rosenfeld, K.-M. Kim, J.-M. Yoo, M.-I. Lee, and M. Hahnenberger (2008), Midweek increase in U.S. summer rain and storm heights suggests air pollution invigorates rainstorms, J. Geophys. Res., 113, D02209, doi:10.1029/2007JD008623.