Quasi-Biennial Oscillation Impacts on Lightning in the Tropics

The Quasi-Biennial Oscillation (QBO) is a 24 to 36-month oscillation of the zonal wind in the tropical stratosphere, typically between 50 and 70 hPa. In the east phase, the tropopause is higher and colder at the equator and 200-100 hPa wind shear decreases, with opposite conditions in the west phase. Previous studies have investigated the influence of the QBO on convection, but limited studies have explored the relationship of the QBO to lightning. This study hopes to aid in this void by looking at how these environmental parameters during the QBO affect lightning in the tropics.

Monthly, 2.5 degree lightning data is obtained from the Lightning Imaging Sensor (LIS) onboard the Tropical Rainfall Measuring Mission (TRMM) satellite from 1998 to 2013. Environmental parameters are obtained or derived from monthly European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis Interim (ERA-Interim) and regridded to match the spatial resolution of the LIS data. In addition to the 16-year annual averages, this study looks at seasonal and regional variations of 200-100 hPa wind shear and tropopause temperatures by QBO phase to evaluate their potential influence on lightning. The highest correlation between flash rates and shear is in southern Central Africa (r= -0.776) in boreal winter, indicating that as shear increases, lightning decreases, as expected. The highest correlation between tropopause temperature and flash rates is in India (r= -0.810) in boreal summer, indicating that there is an inverse relationship between lightning and tropopause temperature, also as expected. These preliminary results support the hypothesis that lightning is enhanced in the east phase and suppressed in the west phase along the equator, and provides further insight on lightning production and convection in the tropics.