Diurnal Variation of TRMM/LIS Lightning Flash Radiances

This study provides, for the first time, detailed climatological diurnal variations in lightning flash optical energetics observed from the Tropical Rainfall Measuring Mission Lightning Imaging Sensor (TRMM/LIS). The analysis of 13 years (2002-2014) of LIS global-scale (~38°S-38°N) flash radiances (ε) as a function of the local solar time (LST) reveals remarkably consistent regional and seasonal patterns. 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. In particular, 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 only about 15% for oceanic ε. The study confirms that the results are not affected by diurnal biases associated with instrument detection characteristics, 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 diurnal 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, few tentative hypotheses about the underlying physical mechanism(s) are discussed.