Evolution of maritime continent thunderstorms under varying meteorological conditions over the Tiwi Islands

Abstract

The development of tropical island thunderstorms in the maritime continent were investigated over the Tiwi Islands to the north of the Australian continent. A satellite cloud climatology was developed to examine these island thunderstorms, locally known as Hectors. During the pre-monsoon period of 1990 and 1991 Hectors were observed on 70% of days. These Hectors were observed to occur under two distinct environmental flow regimes. Under easterly flow, development occurred on the western end of the island and conversely under westerly flow, development occurred to the east. Hectors were also observed to have three distinct modes of development (Hector, suppressed and late developing) and one mode of non-development (non-Hector). Satellite cloud climatologies were developed and mean atmospheric characteristics were determined for each of these development modes. Hectors developed under conditions of moderate convective available potential energy, moderate shear and high moisture availability. Sub-cloud layer winds were also thought to contribute to the structure of the storm. Non-Hector and suppressed Hector days usually occurred after a previous convective disturbance such as a monsoon low or squall line and had typically low convective available potential energy and high values of convective inhibition. Conditions for late developing Hectors appeared to be conducive for thunderstorm development with high convective available potential energy and low values of convective inhibition. However, early initiation was suppressed by high shear conditions. Development in the late developing mode could be more intense than in other modes.

NO<sub>x</sub> production by lightning in Hector: first airborne measurements during SCOUT-O3/ACTIVE

“…2). The latter finding was confirmed by Beringer et al (2001) and Brunner et al (2009) who typically observed Hector developments over the eastern (western) end of the island during westerly (easterly) flow. Many of the strongest Hector systems develop when gust fronts from separate areas over the Bathurst and Melville Islands collide.…”

“…During the pre-monsoon period in NovemberDecember, Hector systems over the Tiwi Islands are detected on at least 2/3 of the days and the mean lifetime is 2-5 h (Keenan et al, 1990;Beringer et al, 2001). The convection develops in an environment with low to moderate shear, moderate convective available potential energy (CAPE) and high moisture availability.…”

“…In contrast, it is known that Hector develops in an environment with moderate shear (Sect. 2) and can last several hours (Keenan et al, 1990;Beringer et al, 2001). …”

Surface energy exchanges and interactions with thunderstorms during the Maritime Continent Thunderstorm Experiment (MCTEX)

“…However the Tiwi Islands are not complicated by significant mountainous terrain that is a feature of some maritime continent islands. Maritime continent island thunderstorms occur with regularity and consistency over islands within the region and are strongly diurnally modulated [ Beringer et al , 2001]. See Tapper [2002] for a detailed meteorology of islands of the maritime continent region.…”

Delineation of surface energy exchanges variations during thunderstorm and non-thunderstorm days during pre-monsoon season

“…Raman et al, 1998;Venalainen et al, 1998;Beringer and Tapper, 2002;Rouse et al, 2003;Schuttemeyer et al, 2006;Jun et al, 2007;Bhat and Arunchandra, 2008;Xufeng and Mingguo, 2009). SEB studies are helpful in understanding the link between the land surface and atmosphere, which have great influence on regional climate and water cycle as well as for the global climate (Moncrieff and Green, 1972;Keenan et al, 1989;Beringer et al, 2001;Arya, 2001).…”