Diurnal variation of radar echoes and their possible role of preconditioning the atmospheric humidity

The effect of shallow convections is important as well as deep convections in the western Pacific Ocean for global climate and also for the onset of the MJO. Remarkable diurnal variations of isolated convections during a convectively undisturbed regime are focused. That is detected from three-dimensional radar observation in the western Pacific at the Republic of Palau (7 N, 134 E) from December 2004 to January 2005. The lower tropospheric humidity shows significant correlation with the number of isolated convection, but it shows less correlation with more organized convections in this regime. The lower tropospheric humidity increases day after day with superposed diurnal variation, coinciding with increase of organized convections. The recovery time is about five days in observed cases. This diurnal variation, on average, has maximum at 03 local time. The midnight maximum of the isolated convections initiates the moistening of lower troposphere in the convectively undisturbed regime.