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

Jean K Kigotsi,Serge Soula,Jean-François Georgis

doi:10.5194/nhess-18-479-2018

Abstract

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 09:00 UTC and between 16:00 and 17:00 UTC, 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.

Highlights

According to several studies about the lightning climatology around the Earth, the Congo Basin is considered as the most active region with either a large maximum or two distinct ones (Christian et al, 2003; Williams and Sátori, 2004; Albrecht et al, 2011, 2016; Cecil et al, 2014; Soula et al, 2016)
The features of the maximum area depend on the spatial resolution considered in the calculation of the flash rate density (FRD) and the scale resolution in the graphic representation
This difference can be understood since the maximum value is very localized and can change substantially from one year to the and the spatial density resolution used in the study is very high, with a value of 0.05◦

Summary

Introduction

According to several studies about the lightning climatology around the Earth, the Congo Basin is considered as the most active region with either a large maximum or two distinct ones (Christian et al, 2003; Williams and Sátori, 2004; Albrecht et al, 2011, 2016; Cecil et al, 2014; Soula et al, 2016). Albrecht et al (2016) performed a very detailed analysis of FRD thanks to Lightning Imaging Sensor (LIS) data around the Earth by using several spatial resolutions. They showed the features of the maxima FRD strongly depend on the spatial resolution and on the duration of the period considered for the study. With the better resolution (0.1◦) used in Albrecht et al (2016), the second-ranked hotspot is always located around [28◦ E, 2◦ S] from 5 years of data They showed most of the first 10 lightning hotspots over the entire African continent, including the strongest ones, are located in Democratic Republic of Congo (DRC). By considering the maps of FRD in Albrecht et al (2016), the existence of two regions of maximum activity in DRC is displayed, but the non-linear scale does not allow a quantitative comparison of the maximum values

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Conclusion