Abstract:
Data collected during the Maritime Continent Thunderstorm Experiment (MCTEX) (10 November-10 December
1995) have been used to analyze boundary layer development 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 islands every day of the field campaign. The
boundary layer depth, temperature, and circulation over the island have been measured over the full diurnal
cycle using a multiple radar analysis combined with surface and radiosonde measurements. On average, the
island boundary layer depth reaches 1.5 km by early to midaftemoon coinciding with the development of the
deep convection. Thus, the island boundary layer is significantly deeper than the typical tropical oceanic boundary
layer. In the midaftemoon, thunderstorm outflows and their associated cold pool stabilize the lower boundary
layer, suppressing late convection. This is followed by a period of partial boundary layer recovery for 1-2 h.
After sunset, cooling leads to a deepening ground-based inversion below a residual mixed layer. Near the island
center, the residual mixed layer of island-modified air is replaced by air of oceanic origin 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 the islands every evening resets the boundary layer development cycle. It is shown that much of
the variation in the diurnal temperature profile is a result of thunderstorm activity, radiative processes, and the
advection of island and oceanic boundary layer air.
