19th Conference on Climate Variability and Change


Diurnal variations of upper and middle tropospheric humidity and their relations to convective activities over tropical Africa from Meteosat-8 measurements

B. J. Sohn, Seoul National University, Seoul, South Korea; and E. S. Chung, J. Schmetz, and M. Koenig

Diurnal variations of upper tropospheric humidity (UTH) and middle tropospheric humidity (MTH) are studied in conjunction with deep convection proxy (precipitation index) and high cloud amount (deep convective cloud plus cirrus anvil cloud) over tropical Africa and the adjacent tropical Atlantic Ocean using Meteosat-8 measurements. Analyses were done both on the Eulerian and Lagrangian frameworks.

Like deep convection proxies and cloudiness, smaller but distinct diurnal variations of UTH (and MTH) are noted over tropical convective regions in which deep convective clouds are frequently observed. The amplitudes appear larger over land while convectively inactive subtropical regions do not show meaningful diurnal variation of UTH. The land-sea contrast is also found in diurnal phases. UTH tends to peak during the nighttime over land, lagging deep convection (late afternoon) and high cloud (evening). In contrast, considering that deep convection and high cloud maximums over the ocean exist around the early morning and around the late afternoon, respectively, the time lag of maximum UTH (nighttime) appears larger in comparison to those over land.

Meanwhile, cirrus anvil cloud shows a nearly identical peak to those of UTH and MTH, implying insignificant moistening effect from the evaporation of cirrus anvil cloud. On the other hand, EOF analysis indicates that higher (and colder) clouds evolve to lower (and warmer) clouds during the nighttime in particular over land. From those results, it was inferred that water vapor and cirrus anvil clouds are evolved from the dissipation of deep convective clouds.

Session 5A, The diurnal cycle
Wednesday, 17 January 2007, 11:15 AM-5:30 PM, 214B

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