Diurnal variation of upper tropospheric humidity and its relations to convective activities over tropical Africa
Diurnal variations of upper tropospheric humidity\n\n(UTH) as well as middle tropospheric humidity (MTH) were\n\nexamined in conjunction with the diurnal cycle of convection\n\nover tropical Africa and the adjacent tropical Atlantic Ocean\n\nusing Meteosat-8 measurements. Cloud and humidity features\n\nwere also tracked to document the diurnal variations of\n\nhumidity and clouds in the Lagrangian framework.\n\nA distinct diurnal variation of UTH (and MTH) is noted\n\nover regions where tropical deep convective cloud systems\n\nare commonly observed. The amplitude of the UTH diurnal\n\nvariation is larger over land, while its variations over\n\nconvectively inactive subtropical regions are much smaller.\n\nThe diurnal variation of UTH tends to reach a maximum\n\nduring nighttime over land, lagging deep convection and\n\nhigh cloud whose maxima occurred in the late afternoon\n\nand evening, respectively. It was revealed that these diurnal\n\nvariations over the African continent are likely associated\n\nwith continental-scale daytime solar heating and topography,\n\nin which topographically-induced signals develop earlier\n\naround the mid-afternoon and merge into stronger and\n\nbroader continental-scale convection clusters later, forming a\n\nprecipitation maximum in the late afternoon. It was also revealed\n\nthat advection effect on the diurnal variation appears\n\nto be insignificant.