Abstract
Abstract. This study investigates the diurnal evolution of sea-breeze (SB) rotation over an island at the middle latitudes. Earlier research on sea breezes in Sardinia shows that the onshore winds around various coasts of the island exhibit both the theoretically predicted clockwise rotation as well as seemingly anomalous anticlockwise rotation. A non-hydrostatic fully compressible numerical model (WRF) is used to simulate wind fields on and around the island on previously studied sea-breeze days, and is shown to capture the circulation on all coasts accurately. Diurnal rotation of wind is examined, and patterns of clockwise and anticlockwise rotation are identified. A dynamical analysis is performed by extracting individual forcing terms from the horizontal momentum equations. Analysis of several regions around the island shows that the direction of rotation is a result of a complex interaction between near-surface and synoptic pressure gradient, Coriolis and advection forcings. An idealized simulation is performed over an artificial island with dramatically simplified topography yet similar dimensions and latitude to Sardinia. Dynamical analysis of the idealized case reveals a rather different pattern of hodograph rotation to the real Sardinia, yet similar underlying dynamics. The research provides new insights into the dynamics underlying sea-breeze hodograph rotation, especially in coastal zones with a complex topography and/or coastline.
Highlights
Sea-breeze (SB) circulation is a mesoscale phenomenon driven by a mesoscale, horizontal pressure gradient resulting from the differential heating of land and water
The primary goal was to demonstrate that the model captures the SB circulation and hodograph rotation on all coasts, and we focused on comparing the winds and associated diurnal evolution of wind hodographs at each of the station locations
This study examined the dynamics of SB rotation in a region of complex topography, with known occurrence of both theoretically expected clockwise hodograph rotation (CR) as well as “anomalous” counterCoriolis anticlockwise hodograph rotation (ACR)
Summary
Sea-breeze (SB) circulation is a mesoscale phenomenon driven by a mesoscale, horizontal pressure gradient resulting from the differential heating of land and water. The switch to ACR occurs at a critical value, which is a function of friction and latitude They employed a simple two-dimensional model with artificial topography and found that the dominant term inducing the rotation was a combination of pressure and surface pressure gradient. In contrast to primarily analytical and idealized work, Steyn and Kallos (1992) used a three-dimensional numerical mesoscale model to study the issue in the Attic Peninsula, Greece Their findings were in agreement with Kusuda and Alpert (1983) as well as local observations. The study demonstrates using averaged wind hodographs that both CR and ACR are known to occur along the coast of the island
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