Differences in the Evolution of Convection and Lightning between Land and Ocean: A Study Using TRMM and Ground-based Data

In this study we examine the structural and evolutionary differences between land and ocean thunderstorms and their respective capabilities of becoming convectively intense enough to develop lightning.

In earlier work we found that in archetypal land and ocean regions, convective systems with lightning tended to be large (contiguous precipitation area over 2,000 km2) and with a substantial fraction of precipitation classified as stratiform, a result that applies throughout the global tropics, to varying extents.

We note that, on the whole, while the tropical oceanic environment is not conducive to updrafts strong enough to develop graupel and thereby lightning, larger convective systems are more likely to have lightning; the question is why. We argue that the majority of oceanic systems with lightning occur in the presence of some kind of forcing, be it synoptic, a gust front, an outflow boundary, or any other externally imposed boundary on which to focus convection. Unlike most continental regions, small storms over tropical oceans are unlikely to have lightning.

In order to identify the role played by forcing and convective evolution in the development of lightning, we analyze ground S-band radar and soundings from the Southeast United States and the Kwajalein Atoll as representative locations for land and ocean (respectively). We use World Wide Lightning Location Network (WWLLN) data to determine the timing and location of flashes within the convective systems as they evolve.