Statistical comparison of meteorological parameters between gigantic jet-producing thunderstorms and null cases in northern Colombia using ERA-5

Abstract:

Since 2009, low-light cameras have been operated in the Caribbean region of Colombia, one of the regions with the highest lightning activity in the world, to study the occurrence of (in particular) gigantic jets in the tropics. The best results have been obtained from Santa Marta city at the north coast of Colombia since 2016, and during intensive observation campaigns in 2017 and 2018. The total number of nights with observations of gigantic jets is 29, counting also those recorded by the San Andres island camera from 2009-2014.

Gigantic jets have been discovered at two locations in the tropics in 2002, and subsequent observations have also been reported (often by photographers) in similar climate regions such as Caribbean Sea, eastern China, Japan, India, Brazil, northern Australia and even beyond, in the southern United States. There have been indications that factors as high vertical wind shear and turbulence in the upper levels may play a role in producing a favorable electrical charge distribution, or the overshooting top (which relate to convective available potential energy).

We compared vertical profiles extracted from ERA-5 reanalysis data for 15 gigantic jet nights over northern Colombia (land) against 39 null cases in the same monitored area, selected for their prolonged clear views over active thunderstorms from Santa Marta without detected jets, as well as 14 gigantic jet nights combining maritime cases around San Andres and cases closer to the Colombia and Panama coast. Representative profiles were taken in proximity in time (up to a few hours) and space (0.5 degree) relative to the real-world occurrence, avoiding convective disruption in the reanalysis fields.

The results reveal differences in other parameters than expected. None of the parameters regarding the upper levels of the storm were statistically significant at the 99% level. While gigantic jet cases often had moderate vertical shear in the mid-upper levels (usually between 400 and 200 hPa), so have null cases. Instead, gigantic jet cases over land had less CAPE, cooler low levels, weaker 1-2.5 km shear, greater warm cloud depth, as well as higher relative humidity and weaker lapse rate above the cloud base than null cases in the same geographical area (Welch’s t-test p<<0.01).