Abstract
AbstractAn idealized convectionâpermitting simulation is performed to investigate the physical mechanisms responsible for the nighttime offshore propagation of convection around tropical islands. An idealized island is placed in the middle of a long, nonrotating channel oceanic domain with constant sea surface temperature. A strong diurnal cycle typical of a tropical island is simulated, with a thermally forced sea breeze in daytime and the associated inland propagation of precipitation. Offshore propagation of a land breeze and its associated convection is simulated every night but with varying extent. Gravity waves of first and second baroclinic modes trigger convection far from the coast if the offshore conditions are favorable. This accelerates the propagation speed of the land breeze as it reduces the onshore wind associated with the lower branch of the overturning largeâscale circulation. Higherâorder modes may trigger convection or reinforce existing convection but less systematically. The distance of propagation is particularly sensitive to humidity and temperature at the top of the boundary layer, with occasional incursions of a dry anomaly at the top of the boundary layer near the island preventing convection from developing far from the island.
Highlights
Islands are focal points for the development of convection in the tropics
In order to understand what controls this offshore propagation, we study the movement of convection around an idealized tropical island
The solar forcing on these two contrasted surfaces results in a sea breeze circulation during the day when land warms rapidly and winds blow toward the island, followed by a smaller land breeze in the opposite direction at night (Mori et al, 2004; Qian, 2008)
Summary
Islands are focal points for the development of convection in the tropics If they are sufficiently far from the continent and sufficiently large, they can be seen as a fixed and localized forcing in the middle of a uniform ocean (Sobel et al, 2011). The solar forcing on these two contrasted surfaces results in a sea breeze circulation during the day when land warms rapidly and winds blow toward the island, followed by a smaller land breeze in the opposite direction at night (Mori et al, 2004; Qian, 2008). This is true over the main islands of the Maritime Continent: Sumatra (Mori et al, 2004; Yokoi et al, 2017), Borneo
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