Multi-decadal Changes in the Vertical Temperature Structure of the Tropical Troposphere

Global atmospheric temperature trends based on satellite-borne Microwave Sounding Unit observations since 1979 show less warming than trends based on surface meteorological observations. Both the validity and possible source of this discrepancy have engendered controversy in the scientific community, the news media, and public policy forums.

We have analyzed independent radiosonde observations of surface and tropospheric temperature, which confirm the pattern of greater surface warming since 1979 in the tropics. Analysis of temperatures and lower-tropospheric lapse rates, computed from individual radiosoundings, indicates that the differential temperature trends are associated with lapse-rate changes. Spatially coherent decreases in the static stability of the tropical atmosphere are observed during 1979-97. These trends exceed unforced static stability variability simulated by state-of-the-art coupled ocean- atmosphere climate models.

Radiosonde observations are available for a longer period than the MSU data and so afford the opportunity to examine multi-decadal variability in the vertical temperature structure of the atmosphere. The differential temperature trends and lapse-rate changes seen during the satellite era are not sustained back to 1960, which suggests a different mechanism was operating in the recent period than in earlier decades.