The Land-Sea Breeze Circulation Over the West Coast of Sumatra

Characteristics of the land and sea breeze near the west coast of Sumatra are studied using hourly 10-m wind observations from the Bengkulu Airport for the year 2018, with an emphasis on the properties of the land breeze. Spectral analysis shows that the land-sea breeze cycle is a dominant part of the overall circulation in the region, with disturbances at the diurnal frequency accounting for roughly half the overall disturbance kinetic energy. A method is presented for isolating the near-diurnal parts of the flow through a combination of high- and low-pass filtering, with land and sea breezes defined in terms of the shore-perpendicular component of the filtered winds. By this definition, a land breeze occurs each day, with a median onset time of 19 LT, a median duration of 15 hours, and a median maximum speed of 1.8 ms −1 occurring near 2 LT. The characteristics of the land breeze are found to depend strongly on the phase of the Madden-Julian Oscillation. A dependence was also found during the Asian and Australian monsoons, particularly for the onset time and maximum speed. Sea breezes occur almost every day but are much shorter (about 8.5 hours) and stronger (> 3 ms −1 ) than land breezes. Comparisons between airport observations and ERA5 surface winds show that while ERA5 accurately captures the onset time, duration, and timing of the maximum speed for sea breezes, it only captures the onset time and duration for land breezes. For both, the maximum speed is significantly underestimated.