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2020) studied the interannual variability of MCS characteristics over the Congo Basin during the period 1984 to 2015. Some of the variables considered were total number, mean duration, minimum cloud‐top temperature (CTT, a measure of MCS intensity), and area. Hartman’s calculations for the latitudes of 0° to 5°N (region 1) and 0° to 5°S (region 2) are shown in Figure 3.25. For both regions there is a slight tendency for the number of MCSs to increase over time. The increase is largest in MAM in region 2, the area with strongest MCS activity. In region 1 there is a tendency for increasing/decreasing duration and area in MAM/SON. Minimum CTT decreases over time in both seasons, suggesting more intense MCSs. In region 2, the duration generally increases and the area generally decreases over time in both seasons. As in region 1, CCT decreases over time in both seasons. In both regions the decrease is greater in MAM than in SON.

Schematic illustration of interannual variability of select characteristics of MCSs over the Congo Basin during the period 1984 to 2015.

      As mentioned earlier, one of the open questions concerning the Congo Basin is why rainfall is relatively low compared to other equatorial areas, such as the Amazon. Here a brief comparison is made between the Congo Basin and the Amazon, in order to examine some aspects of that question.

Schematic illustration of mean rainfall (mm/mo)over the Amazon based on TRMM 3B43 V7 for the period 1998 to 2014. Schematic illustration of the diurnal cycle of rainfall over the Amazon, as in Figure 3.14.

      The drier conditions over the Congo Basin might provide some explanation for the more intense convective activity compared to the Amazon. Hamada et al. (2015) underscored the contrast between factors enhancing convection (i.e., MCSs) and those enhancing rainfall. Lower relative humidity and lower moisture flux convergence favor the convection. Notably, the atmospheric moisture content over the Congo Basin is similar to that in the area of most extreme MCSs over South America.

      3.8.1. Controls on the Rainfall Regime

      The rainfall regime over the Congo Basin is shaped by a number of factors on both global and local scales. Over‐riding factors are orographic effects, which appear to produce a local and shallow Walker‐type circulation over the Congo Basin, the Walker cells over the Indian and Atlantic Oceans, tropical sea‐surface temperatures, and a mid‐level easterly jet stream that is present only during the SON rainy season.

      Most of the rainfall, as much as 60–70%, is associated with intense MCSs. These systems include a layer of ice and a large anvil cloud, and produce both stratiform and convective rainfall. The stratiform component is strongest at night. The systems over the Congo appear to be the strongest in the world and are associated with the world’s highest frequency of lightning.

      3.8.2. Mean Rainfall and the Seasonal Cycle

      The

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