Relationship between sea surface temperature, vertical dynamics, and the vertical distribution of atmospheric water vapor inferred from TOVS observations

Abstract

With the aim of better understanding the respective role of sea surface temperature (SST) and vertical dynamics on the vertical distribution of atmospheric water vapor, particularly in the tropics, global scale observations from NOAA 10, covering a 31−month period, have been processed using the improved initialization inversion ((3I) [Chédin and Scott, 1984]) retrieval method and interpreted in terms of tropospheric layered water vapor contents. The method of analysis uses the power law, which expresses the specific humidity q at pressure p as a function of their values at the surface, q0 and p0; q = q0(p/p0)λ. This description is applied independently to three layers giving three values of λ: λ1 for surface‐700 hPa, λ2 for 700–500 hPa, and λ3 for 500–300 hPa. It is shown that λ2 is a good indicator of the large‐scale vertical dynamics and gives results equivalent to those obtained using the vertical velocity at 500 hPa issued from a model. Consequently, the role of enhanced upward motion with increased SST for the “super greenhouse effect” situations is confirmed as well as the contribution of externally forced subsidence on the suppression of the deep convection for cases where SSTs exceed about 303 K. In addition, the influence of SST on the vertical distribution of water vapor is analyzed together with the large‐scale vertical dynamics contribution. The results show that the rate of change of water vapor content in the 700‐ to 500‐hPa and 500‐ to 300‐hPa layers with respect to SST increases with decreasing rate of change of λ2 with respect to SST, that is, with increasing rate of change of upward vertical dynamics with respect to SST.