Comparison of lightning activity in the two most active areas of the Congo Basin

Abstract

A comparison of the lightning activity in the two most active areas (Area-max for the main maximum and Area-sec for the secondary maximum) of the Congo Basin is made with data obtained by the World Wide Lightning Location Network (WWLLN) during 2012 and 2013. Both areas of same size (5° × 5°) exhibit flash counts in a ratio of about 1.32 for both years and very different distributions of the flash rate density (FRD) with maximums in a ratio of 1.94 and 2.59 for 2012 and 2013, respectively. The FRD is much more widely distributed in Area-sec, which means the whole area contributes more or less equal to the lightning activity. The diurnal cycle is much more pronounced in Area-max than in Area-sec with a ratio between the maximum and the minimum of 15.4 and 4.7, respectively. However, the minimum and maximum of the hourly flash rates are observed roughly at the same time in both areas, between 07:00 and 09:00UTC and between 16:00 and 17:00UTC, respectively. In Area-sec the proportion of days with low lightning rate (0-1000 flashes per day) is much larger (∼ 45% in 2013) compared to Area-max (∼ 23% in 2013). In Area-max the proportion of days with moderate lightning rate (1001-6000 flashes per day) is larger (∼ 68.5% in 2013) compared to Area-sec (∼ 46% in 2013). The very intense convective events are slightly more numerous in Area-sec. In summary, the thunderstorm activity in Area-sec is more variable at different scales of time (annually and daily), in intensity and in location. Area-max combines two favourable effects for thunderstorm development, the convergence associated with the African easterly jet of the Southern Hemisphere (AEJ-S) and a geographic effect due to the orography and the presence of a lake. The location of the strong convection in Area-sec is modulated by the distance of westward propagation/regeneration of mesoscale convective systems (MCSs) in relation to the phase of Kelvin waves.