Estimates of the tropospheric lapse rate γ 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 γ 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 γ decreases from 6.5 K/km at low latitudes to 4.5 K/km at polar latitudes. The values of
dγ/
dT s, the parameter of sensitivity of γ 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 γ of approximately 0.7% when the surface temperature of the NH is increased by 1 K. Estimates of
dγ/
dT s vary from about 0.05 km
?1 in the subtropics to 0.10 km
?1 at polar latitudes. When
dγ/
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 (
dγ/
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
dγ/
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 γ to increase with rising
T s, there are regional regimes with the opposite tendency, mainly over the ocean. The negative correlation of γ with
T s is found over the oceanic tropics and midlatitudes, in particular, over the oceanic belt around Antarctica.
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