Tropospheric lapse rate and its relation to surface temperature from reanalysis data

Estimates of the tropospheric lapse rate gamma and analysis of its relation to the surface temperature T (s) in the annual cycle and interannual variability have been made using the global monthly mean data of the NCEP/NCAR reanalysis (1948-2001). The tropospheric lapse rate gamma is about 6.1 K/km in the Northern Hemisphere (NH) as a whole and over the ocean and about 6.2 K/km over the continents. The value of gamma decreases from 6.5 K/km at low latitudes to 4.5 K/km at polar latitudes. The values of d gamma/dT (s), the parameter of sensitivity of gamma to the variation of T-s for the NH in the interannual variability, are found to be about 0.04 km(-1) (0.041 km(-1) for the NH as a whole, 0.042 km(-1) over the ocean, and 0.038 km(-1) over the continents). This corresponds to an increase in gamma of approximately 0.7% when the surface temperature of the NH is increased by 1 K. Estimates of d gamma/dT (s) vary from about 0.05 km(-1) in the subtropics to 0.10 km(-1) at polar latitudes. When d gamma/dT (s) is positive, the surface and tropospheric warming means a temperature decrease above a certain critical level H (cr). The height of the level H (cr) with constant temperature, which is defined by the inverse value (d gamma/dT (s))(-1), is about 25 km for the NH as a whole, i.e., above the tropopause. In the subtropics, H (cr) is about 20 km. At polar latitudes, H (cr) decreases to about 10 km. Positive values of d gamma/dT (s) characterize a positive climatic feedback through the lapse rate and indicate a general decrease in the static stability of the troposphere during global warming. Along with a general tendency of gamma to increase with rising T (s), there are regional regimes with the opposite tendency, mainly over the ocean. The negative correlation of gamma with T (s) is found over the oceanic tropics and midlatitudes, in particular, over the oceanic belt around Antarctica.