Boundary layer development over a tropical island during the maritime continent thunderstorm experiment

Data collected during the Maritime Continent Thunderstorm Experiment (MCTEX ) (10 November-10 December 1995) have been used to analyze boundary layer d evelopment and circulations over two almost flat, tropical islands. The two adjacent islands have a combined length of about 170 km from east to west and 70 km from north to south. Intense thunderstorms formed over these isla nds every day of the field campaign. The boundary layer depth, temperature, and circulation over the island have been measured over the full diurnal c ycle using a multiple radar analysis combined with surface and radiosonde m easurements. On average, the island boundary layer depth reaches 1.5 km by early to midafternoon coinciding with the development of the deep convectio n. Thus, the island boundary layer is significantly deeper than the typical tropical oceanic boundary layer. In the midafternoon, thunderstorm outflow s and their associated cold pool stabilize the lower boundary layer, suppre ssing late convection. This is followed by a period of partial boundary lay er recovery for 1-2 h. After sunset, cooling leads to a deepening ground-ba sed inversion below a residual mixed layer. Near the island center, the res idual mixed layer of island-modified air is replaced by air of oceanic orig in by about 2300 LST (local standard time) that then persists until sunrise the next day. The advection of boundary layer air of oceanic origin over t he islands every evening resets the boundary layer development cycle. It is shown that much of the variation in the diurnal temperature profile is a r esult of thunderstorm activity, radiative processes, and the advection of i sland and oceanic boundary layer air.