A study of lightning activity over the warm pool western Pacific Ocean (TOGA-COARE region) for 1993

Abstract

The warm pool western Pacific Ocean is an area of the equatorial tropics characterized by strong and frequent convection, and vigorous lightning activity. However, it has been noted by various researchers that the vast oceanic expanses experience less lightning activity than adjacent land masses by as much as one order of magnitude. A report herein presents a look at the characteristics of lightning as recorded by three individual magnetic direction finders (DF's) at the Kapingamarangi Atoll, Rabaul, and Kavieng deployed to the Tropical Ocean Global Atmosphere Coupled Ocean-Atmosphere Response Experiment (TOGA-COARE). The lightning data recorded by each DF are azimuthally separated into "land" and ocean" sectors in an effort to assess each regimes similarities and differences. In addition to analyzing some of the more typical lightning parameters (e.g., percentage of positive lightning and positive and negative multiplicities), the thermodynamic relationships between convective available potential energy (CAPE), wet-bulb potential temperature, and flash rates are examined. Finally, the lightning data are run through time series methods in an attempt to both better describe the data and to appraise any possible link between lightning activity and the Madden-Julian Oscillation (MJO) through the use of an appropriately constructed band-pass filter. The results show that lightning activity in this region is remarkably biased towards land masses with land/ocean lightning ratios often exceeding 10. Figures on the percentage of positive lightning and positive/negative multiplicities agree well with results from United States studies in pattern though not in average values. Also, diurnal variation of lightning activity over the TOGA-COARE region is dramatically different from that of a typical United States locale with a pronounced maximum in activity that occurs between roughly 2000 and 0500 local standard time (LST). The relationship between CAPE and flash rate was not observed to be as well defined as previously suggested, pointing to possible limitations in the thermodynamic data, CAPE computation procedures and to parcel theory pitfalls. Finally, the construction of a band-pass filter to study the possible link between lightning activity and the MJO reveals a subtle link which is best seen during the Northern Hemisphere winter and spring months.