Strengthened tropical circulations in past three decades inferred from water vapor transport

By relating the water vapor flow from both reanalysis data and satellite observations to the lower branches of the Hadley and Walker circulations, it was shown that the strength of both north-south and east-west tropical circulations has intensified since 1979. Consistent with the expected water vapor climatology under the strengthened north-south Hadley circulation, satellite observations of upper tropospheric humidity and total water vapor show that the subsidence region has become drier because of the increased sinking motion. In the east-west direction, also consistent with the strengthened Walker circulation drawn from water vapor flux, the difference of the sea level pressure between the east Pacific and west Pacific has become larger over the past three decades.