USING TRMM PRECIPITATION RADAR TO INVESTIGATE THE TROPICAL TGF PARADOX

Abstract:

With the advent of different satellite missions in the last decade, it has been possible to observe worldwide Terrestrial Gamma-ray Flash (TGF) and advance our knowledge on how thunderstorms can produce these sub-millisecond pulse-like emissions of MeV energetic gamma ray photons. For example, several studies have identified an asymmetric behavior on the TGF to lightning ratio over the 3 tropical chimneys (America, Africa and Southeast Asia). Basically, African thunderstorms produce the most lightning but yield the lowest fraction of TGFs when compared to American and Southeast Asian thunderstorms. According to one of such studies (Fabro et al., 2019), the intra-cloud (IC) lightning activity might be responsible to control such behavior that is ruled by the distance of separation between the electrical charge center in addition of the respective height. To understand the physical insights into this asymmetry, this study combines TRMM Precipitation Radar (PR) and Lightning Imaging Sensor (LIS) measurements with TGF occurrences detected by AGILE, Fermi-GBM and RHESSI sensors during the period of 1998 and 2014. TRMM PR and LIS lightning flashes measurements are used to characterize the vertical precipitation structure of the observed thunderstorms in the 3 regions. AGILE, Fermi-GBM and RHESSI observations are used to identify the thunderstorms that might be associated with TGFs. Based on such database, more than 41 thousand thunderstorms, African thunderstorms are taller, smaller and have higher concentration of super-cooled water droplets above the freezing level. TGF thunderstorms are taller and more intense (0.5-1.5 dBZ), besides presenting similar radar reflectivity decay with height independent of the region. These storms show thicker electrical charge layers separated by 4.7-5.2 km, a positive charge fraction reduction between -20^oC and -40^oC and enhancement above -50^oC when compared to the overall thunderstorms.