期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2015
卷号：112
期号：12
页码：3630-3635
DOI：10.1073/pnas.1418682112
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：SignificanceIn spite of increasing research efforts, global warming signals of the Hadley Circulation (HC) and its dynamical linkages to water cycle changes remain largely unknown. Here, from model projections, we find robust signals of both strengthening and weakening components of the HC induced by CO2 warming. These changes in the HC drive a pattern of global dryness featuring widespread reduction of tropospheric humidity and increased frequency of dry months, particularly over subtropical and tropical land regions. We also find that global warming signal in increased dryness is the most detectable among numerous water-cycle quantities examined. Our results provide a scientific basis for inferring that greenhouse warming is likely to contribute to the observed prolonged worldwide droughts in recent decades. In this paper, we investigate changes in the Hadley Circulation (HC) and their connections to increased global dryness (suppressed rainfall and reduced tropospheric relative humidity) under CO2 warming from Coupled Model Intercomparison Project Phase 5 (CMIP5) model projections. We find a strengthening of the HC manifested in a "deep-tropics squeeze" (DTS), i.e., a deepening and narrowing of the convective zone, enhanced ascent, increased high clouds, suppressed low clouds, and a rise of the level of maximum meridional mass outflow in the upper troposphere (200-100 hPa) of the deep tropics. The DTS induces atmospheric moisture divergence and reduces tropospheric relative humidity in the tropics and subtropics, in conjunction with a widening of the subsiding branches of the HC, resulting in increased frequency of dry events in preferred geographic locations worldwide. Among various water-cycle parameters examined, global dryness is found to have the highest signal-to-noise ratio. Our results provide a physical basis for inferring that greenhouse warming is likely to contribute to the observed prolonged droughts worldwide in recent decades.
关键词：Hadley Circulation ; global dryness ; global warming ; drought
