Recent trends of the tropical hydrological cycle inferred from Global Precipitation Climatology Project and International Satellite Cloud Climatology Project data

Abstract

Scores of modeling studies have shown that increasing greenhouse gases in the atmosphere impact the global hydrologic cycle; however, disagreements on regional scales are large, and thus the simulated trends of such impacts, even for regions as large as the tropics, remain uncertain. The present investigation attempts to examine such trends in the observations using satellite data products comprising Global Precipitation Climatology Project precipitation and International Satellite Cloud Climatology Project cloud and radiation. Specifically, evolving trends of the tropical hydrological cycle over the last 20–30 years were identified and analyzed. The results show (1) intensification of tropical precipitation in the rising regions of the Walker and Hadley circulations and weakening over the sinking regions of the associated overturning circulation; (2) poleward shift of the subtropical dry zones (up to 2° decade−1 in June‐July‐August (JJA) in the Northern Hemisphere and 0.3–0.7° decade−1 in June‐July‐August and September‐October‐November in the Southern Hemisphere) consistent with an overall broadening of the Hadley circulation; and (3) significant poleward migration (0.9–1.7° decade−1) of cloud boundaries of Hadley cell and plausible narrowing of the high cloudiness in the Intertropical Convergence Zone region in some seasons. These results support findings of some of the previous studies that showed strengthening of the tropical hydrological cycle and expansion of the Hadley cell that are potentially related to the recent global warming trends.

Evolution and modulation of tropical heating from the last glacial maximum through the twenty-first century

“…But a number of studies have reached an opposite conclusion: that as SST increases the tropical circulations, especially the Walker Cell, reduces intensity (e.g., Vecchi et al 2006;Vecchi and Soden 2007). We will return to this issue later noting that a number of other papers (e.g., Zhou et al 2011;Meng et al 2011) support a more vigorous tropical circulation, in accord with the conclusions reached in the present study.…”

“…These differences in warming may explain differences in static stability that may help explain a reduction or acceleration of the large-scale tropical circulations. Zhou et al (2011) use data sets independent of the reanalysis products (the Global Precipitation Climatology Program: GPCP, Adler et al 2003, and the International Satellite Cloud Climatolgy Progrect: ISCCP, Rossow and Schiffer 1999) to determine the changes occurring in the Walker and Hadley cells. In agreement with Clement (2005, 2006) they find an intensification of the major tropical circulations.…”

“…During the last decade there has been a debate on whether the Hadley and Walker Circulation has decreased in intensity in the present era and will continue the same trend with further global warming (e.g., Vecchi et al 2006;Held and Soden 2006;Vecchi and Soden 2007) or has increased and perhaps will continue to increase in intensity in the future (e.g., Clement 2005, 2006;Meng et al 2011;Zhou et al 2011). These are fundamental questions that are addressed in this paper.…”

Regional‐scale rainfall projections: Simulations for the New Guinea region using the CCAM model

“…An analysis of the GCM results over the Western Pacific monsoon region by Smith et al [2012] suggested that these were reasonably consistent with a mechanism which causes relatively dry areas to become drier and relatively wet areas to become wetter, the so-called "rich-get-richer" mechanism [Chou et al, 2009]. Observations also indicate that this mechanism can also explain recent trends in large-scale rainfall patterns [Zhou et al, 2011;Wang et al, 2012]. The CCAM projections are consistent with this mechanism since, spatially, they indicate increases over the relatively wet mountain slopes during DJF (Figures 8 and 9) and decreases over the relatively dry mountains during JJA.…”

A steady-state analysis of the temperature responses of water vapor and aerosol lifetimes

“…We conclude that the influence of the ALTR on aerosol forcing may be significant, but it is probably small compared to other influences. Particularly important in this respect are changing spatial distributions of aerosol (precursor) emissions and transport routes (Bellouin et al, 2011;Zhang et al, 2007;Carslaw et al, 2010;Zhou et al, 2011), and changes in the aerosol activation efficiency. We present suggestions for model experiments involving idealized aerosol-like tracers that may help to quantify the separate influences on aerosol lifetime and assess their relevance for aerosol-climate simulations.…”