Lightning/percipitation relationships on a global basis

Abstract

Rainfall and lightning are measured and compared on a global basis using data gathered from the Tropical Rainfall Measuring Mission (TRMM) satellite, launched in November 1997. The satellite provides simultaneous lightning-precipitation measurements that allow for comprehensive relationships to be created for future rainfall monitoring utilizing unique electromagnetic methods. Precipitation and lightning comparisons using TPMM data showed that there is no unique relationship between lightning and near surface rainfall. No definite bimodality over land was found that indicated distinct regimes; however, maps of the mass of precipitation per flash showed a latitudinal dependence in both South America and Africa indicative of different regimes. Reflectivity-height distribution plots established reflectivity thresholds at 7 km and l O km where lightning over land completely dominates lightning over ocean. For reflectivity greater than 25 dBZ at 7 km altitude over land, there is 87% probability it will produce lightning. Ocean, on the other hand, requires higher than 35 dBZ at 7 km to generate lightning with a probability of 77%. Venn diagrams determined that lightning is not a good choice for measuring precipitation on a global scale when less than 6% of all precipitating clouds exhibit lightning. For precipitating clouds over land, lightning appears in 15% of the clouds at 2 km altitude. Lightning may be better suited for measuring rainfall over land. The mass of precipitation[kg] per lightning flash was found to be highly variable, with values ranging over four orders of magnitude. Correlation coefficients of scatter plots of mass of precipitation versus lightning rate confinned a non-unique relation between precipitation and lightning for rain measured near the surface (2km, 4 km), with numbers close to 0. The correlation coefficients increased to 0.5 for altitudes 7 km and above. The kg per flash values addressed the issue of an order of magnitude difference in lightning between continental and oceanic convection. This finding is consistent with the idea of mid-level updrafts being larger in continental than oceanic convective clouds.