a coastline due to turbulent surface fluxes, turbulent mixing effects are frontolytical once a well-developed sea-breeze front is formed. Table 2.4 summarizes the effects of offshore and onshore geostrophic flow on sea breezes. Most numerical studies with a non-zero background flow have focused on the impact of offshore geostrophic flow. If the offshore geostrophic wind speed is above some critical value, then sea breezes do not form as the synoptic pressure gradient effectively cancels the local pressure gradient. The critical value of the offshore geostrophic wind above which sea breezes are likely to be absent has been found to be 11 m s-1, depending on the strength of the land-water temperature gradient (Biggs and Graves 1962; Arritt 1993; Porson et al. 2007c). For small and medium-sized lakes, the critical value is unknown, but likely ranges between 3-5 m s-1 (Segal et al. 1997). For offshore winds greater than 4-8 m s-1 but less than 6-10 m s-1, the sea-breeze front may stall at the coastline where shear instabilities help to retard its inland penetration (Grisogono et al. 1998). Offshore geostrophic flow also shifts sea breezes so that they are no longer symmetric about the shoreline (Finkele et al. 1995) and may then not be closed circulations (Banta et al. 1993). For offshore geostrophic flows of 1-2 m s-1, is l on the order of 50 km, while is on the order of km for offshore geostrophic flows of l 4-5 m s-1 and onshore penetration occurs later in the afternoon (Arritt 1993; Tijm et al. 1999b; Porson et al. 2007c). Inland penetration speed of the sea-breeze front is likewise Table 2.4: Summary of key results from numerical studies pertaining to geostrophic wind (Vg). Study focus Findings References Offshore (OFF) OFF > 6-11 m s-1 no SB forms (smaller Vg Estoque 1962; ambient for lakes) Vg Physick Geostrophic OFF > 4-8 m s-1 but < 6-10 m s-1 SBF 1976, 1980; Vg
11 a coastline due to turbulent surface fluxes, turbulent mixing effects are frontolytical once a well-developed sea-breeze front is formed. Table 2.4 summarizes the effects of offshore and onshore geostrophic flow on sea breezes. Most numerical studies with a non-zero background flow have focused on the impact of offshore geostrophic flow. If the offshore geostrophic wind speed is above some critical value, then sea breezes do not form as the synoptic pressure gradient effectively cancels the local pressure gradient. The critical value of the offshore geostrophic wind above which sea breezes are likely to be absent has been found to be m s-1, depending on the strength of the land-water temperature gradient (Biggs and Graves 1962; Arritt 1993; Porson et al. 2007c). For small and medium-sized lakes, the critical value is unknown, but likely ranges between 3-5 m s-1 (Segal et al. 1997). For offshore winds greater than 4-8 m s-1 but less than 6-10 m s-1, the sea-breeze front may stall at the coastline where shear instabilities help to retard its inland penetration (Grisogono et al. 1998). Offshore geostrophic flow also shifts sea breezes so that they are no longer symmetric about the shoreline (Finkele et al. 1995) and may then not be closed circulations (Banta et al. 1993). For offshore geostrophic flows of 1-2 m s-1, l is on the order of 50 km, while l is on the order of km for offshore geostrophic flows of 4-5 m s-1 and onshore penetration occurs later in the afternoon (Arritt 1993; Tijm et al. 1999b; Porson et al. 2007c). Inland penetration speed of the sea-breeze front is likewise Table 2.4: Summary of key results from numerical studies pertaining to geostrophic wind (Vg). Study focus Findings References Offshore (OFF) ambient Geostrophic OFF Vg > 6-11 m s-1 no SB forms (smaller Vg for lakes) OFF Vg > 4-8 m s-1 but < 6-10 m s-1 SBF Estoque 1962; Physick 1976, 1980;
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