Diurnal Variation of TRMM/LIS Lightning Flash Radiances

Abstract

his study provides, for the first time, an analysis of the climatological diurnal variations in the lightning flash radiance data product (ε) from the Tropical Rainfall Measuring Mission Lightning Imaging Sensor (TRMM/LIS). The ε values over 13 years (2002-2014), and over a global scale (~38°S-38°N), reveal remarkably consistent regional and seasonal patterns as a function of the local solar time (LST). In particular, the diurnal variation of ε (over both continental and oceanic regions) is characterized by a monotonic increase from late afternoon (~20:00 LST), attaining a maximum around 09:00 LST, followed by a decreasing trend. The continental (oceanic) ε values reach a broader minimum spanning from ~15:00-19:00 LST (~18:00-20:00). The relative diurnal amplitude variation in continental ε is about 45%, compared to about 15% for oceanic ε. This study confirms that the results are not affected by diurnal biases associated with instrument detection or other statistical artifacts. A notable agreement is shown between the diurnal variations of ε and the global scale (~38°S-38°N) Mesoscale Convective Systems areal extent. Comparisons with recently published diurnal variations of cloud-to-ground lightning peak current over the US also exhibit a marked similarity. Given the novelty of these findings, a few tentative hypotheses about the underlying physical mechanism(s) are discussed.