The Kwinana Coastal Fumigation Study: II - Growth of the thermal internal boundary layer

Aircraft measurements of potential temperature and turbulent kinetic energy are used to examine the growth of the thermal internal boundary layer (TIB L) in sea-breeze flows on four selected days of a coastal fumigation study performed in 1995 at Kwinana in Western Australia. The aircraft data, toget her with radiosonde measurements taken on the same days, show a multi-layer ed low-level onshore flow in the vertical with a superadiabatic layer exten ding to about 50 m above the water surface on all four days. On the first t hree days the layer above the superadiabatic layer was neutral, typically 2 00 m deep, capped by a stably stratified region, whereas on the remaining d ay it was fully stable. The occurrence of the neutral layer on most experim ental days contrasts with the more usual situation involving an entirely st able onshore flow. A composite approach based on both temperature and turbu lence data is used to provide a pragmatic but self-consistent definition of the TIBL height. The data for the first three days indicate that the TIBL grows rapidly into the neutrally stratified region to the top of the region within about 2 km from the coast, with a very slow subsequent growth into the stable stratification aloft. On the other hand, the TIBL grows only to about 200 m within a distance of 7 km from the coast on the fourth day due to a strong stable stratification. An existing numerical TIBL model based on the slab approach, capable of des cribing the TIBL growth in both neutral and stable environments, and a rece nt analytical model, more efficient for operational use, are used to simula te the aircraft TIBL observations. The predictions by both models agree rea sonably well with the data.