Land-Sea Contrast in the Lightning Diurnal Variation as Observed by the WWLLN and LIS/OTD Data

Data from the World Wide Lightning Location Network （WWLLN） for the period 2005-2011 and data composite of the Lightning Imaging Sensor/Optical Transient Detector （LIS/OTD） for 1995-2010 are used to analyze the lightning activity and its diurnal variation over land and ocean of the globe. The Congo basin shows a peak mean annual flash density of 160.7 fl km-2 yr-1 according to the LIS/OTD. The annual mean land to ocean flash ratio is 9.6：1, which confirms the result from Christian et al. in 2003 based on only 5-yr OTD data. The lightning density detected by the WWLLN is in general one order of magnitude lower than that of the LIS/OTD. The diurnal cycle of the lightning activity over land shows a single peak, with the maximum activity occurring around 1400-1900 LT （Local Time） and a minimum in the morning from both datasets. The oceanic diurnal variation has two peaks： the early morning peak between 0100 and 0300 LT and the afternoon peak with a stronger intensity between 1100 and 1400 LT over the Pacific Ocean, as revealed from the WWLLN dataset; whereas the diurnal variation over ocean in the LIS/OTD dataset shows a large fluctuation.

Response of global lightning activity to air temperature variation

It is an issue of great attention but yet not very clear whether lightning activities increase or decrease on a warmer world. Reeve et al. presented that lightning activities in global land and the Northern Hemisphere land have posi- tive response to the increase of wet bulb temperature at 1000hPa. Is this positive response restricted only to wet bulb temperature or in land? What is the response of global light- ning activities (in both land and ocean) to the global surface air temperature variation like? This paper, based on the 5-year or 8-year OTD/LIS satellite-based lightning detecting data and the NCEP reanalysis data, makes a reanalysis of the response of the global and regional lightning activities to temperature variations. The results show that on the inter- annual time scale the global total flash rate has positive re- sponse to the variation in global surface air temperature, with the sensitivity of 17±7% K?1. Also, the seasonal mean flash rate of continents all over the world and that of conti- nents in the Northern Hemisphere have sensitive positive response to increase of global surface air temperature and wet bulb temperature, with the sensitivity of about 13±5% K?1, a bit lower than estimation of 40% K?1 in Reeve et al. However, the Southern Hemisphere and other areas like the tropics show no significant correlation.