The Tropical Rainfall Measurement Mission (TRMM) Lightning Imaging Sensor (LIS) has been in low earth orbit for approximately 10 years. During this decade of lightning sampling, climate markers such as surface temperature, sea level temperature and tropospheric temperature have continued to indicate a general warming trend. Based on previous studies of intraseasonal, interseasonal, annual and interannual trends in lightning and/or lightning proxies, it is expected that net global or regional changes in any underlying control on convective intensity or frequency (e.g. temperature, or tropospheric temperature structure), should result in subsequent changes in lightning distribution and frequency. Given a decade of LIS sampling and a continually warming climate in the tropics, we ask the question: Has the behavior of global tropical and/or regional lightning flash frequency (one proxy for the character of convective intensity) in the tropical and sub-tropical latitudes changed in tandem with other climate markers or hypothesized manifestations of climate change (i.e., increased tropical cyclone frequency/intensity?

To answer these questions we make use of TRMM-LIS lightning flash data to compute global tropical and regional annual total lightning flash density trends for the decade of 1998-2007. A preliminary analysis of these trends indicates that despite surface temperature increases the annual lightning flash density for the global tropics has remained essentially unchanged (i.e., lightning trends are flat) over the past decade. However, the flat trend in global tropical annual mean flash density does not necessarily hold regionally. Collectively, the tropical oceanic regions of the equatorial Indian and western Pacific Oceans, and the northern sub-tropical Pacific indicate marked upward trends in lightning flash density. Interestingly, while the tropical Atlantic Basin has exhibited anomalously warm sea-level temperatures, and has been increasingly active from a tropical cyclone perspective over the last 10 years, the LIS data indicate no associated increases (or decreases) in lightning flash density- on the contrary the trend is flat. Over three broad regions of ascent in the tropics, tropical continental Africa, South America, and Australia, Africa and Australia have exhibited no detectable change in flash density while that of South America has decreased by 11%. The Maritime Continent oceanic region has exhibited a slight decrease in flash density (9%) but there has been no detectable change in flash rate over Maritime Continent land masses.

We are currently investigating changes in other dominant climate modes of lightning variability (e.g., diurnal cycle changes) and will report on further correlations and trends noted between tropical lightning activity as detected by the LIS and other associated climate parameters.