Evidence for Strengthening of the Tropical General Circulation in

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the 1990s

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stron

2360

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NASA Goddard Institute for Space Studies

2005

rok

Satellite observations suggest that the thermal radiation emitted by Earth to space increased by

more than 5 watts per square meter, while reflected sunlight decreased by less than 2 watts per

square meter, in the tropics over the period 1985–2000, with most of the increase occurring after

1990. By analyzing temporal changes in the frequency of occurrence of emitted thermal and

reflected solar fluxes, the effects of El Nino–Southern Oscillation are minimized, and an

independent longer-time-scale variation of the radiation budget is identified. Similar analyses of

upper tropospheric humidity, cloud amount, surface air temperature, and vertical velocity confirm

that these flux changes are associated with a decadal-time-scale strengthening of the tropical

Hadley and Walker circulations. Equatorial convective regions have intensified in upward motion

and moistened, while both the equatorial and subtropical subsidence regions have become drier and

less cloudy.