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Because of the dominance of mesoscale convective systems (MCSs) over the Congo Basin (see Section 3.6), a fair amount of nocturnal rainfall is anticipated. Here the diurnal cycle is examined using three‐hourly data from TRMM 3B42 V7. April and October, peak rainy months in much of the region, are examined. These do indicate that the rainfall maximum is at night over large parts of the region.

Figure 3.14 shows the time of maximum rainfall averaged over the years 1998 to 2014. TRMM times are UTC, which is one hour earlier than local time in the west, two hours earlier in the east. Afternoon hours are indicated in yellow, nighttime hours in deep blue. Light blue is late afternoon/early evening. There is a clear pattern in which rainfall in the lowest area of the central basin tends to peak during the afternoon, but a nocturnal peak is evident in surrounding areas. The area with afternoon rains is markedly greatly in October than in April.

This pattern is to some extent consistent with the patterns of vertical shown in Figure 3.2. In the early evening hours there is a contrast in vertical motion, and presumably rainfall, between the central and basin and the highlands to the north and east. A strict correspondence is not to be expected, as Figure 3.2 represents a three‐month average and one time of day. However, the comparison hints at the role of topography in controlling the diurnal cycle.

Figure 3.14 The diurnal cycle of rainfall over the Congo Basin based on TRMM 3B42 for the years 1998 to 2014. TRMM is indicated in UCT (i.e., Z), with local time being roughly one hour later in western regions and two hours later in eastern regions. Afternoon hours are indicated in yellow, nighttime hours in deep blue. Light blue is late afternoon/early evening.

Source: Jackson et al., 2009. © American Meteorological Society. Used with permission.