Sea breeze front velocity

Vsbf : knots

Criteria for sea breezes:
  • Inland temperatures greater than temperature of coastal waters;
  • A moderate depth of dry convection to, say, between 750 and 900 m (2500 to 3000 ft) is required before the sea breeze can become established;
  • If the air is so stable that the convection is confined to a very shallow layer there will be little or no penetration of the sea-breeze regardless of the temperature difference between land and sea;
  • Only a weak offshore wind component of <14 knots at 3000 ft initially;
  • Convection to 1500 m (4000 ft) favours deep inland penetration (deep convection, leading to shower or thundery activity, tends to halt the sea-breeze);
  • Significant inland penetration is only likely if offshore 3000 ft wind is <10 knots.

Calculation method:
The calculator applies the density current equation from Simpson’s Sea Breeze and Local Winds and subsequent research by David Jameson (Operational Meteorologist, Wattisham Met. Office). $$v_{sbf} = 0.87 \left(\sqrt{gD \frac{\bigtriangleup \rho}{\rho}} \right) - 0.59U_g - \tau$$ The constants 0.87 and 0.59 were derived through experimentation along the south coast of England. D = depth of sea breeze circulation (usually 350 m). The fraction is the density excess of the post sea breeze front air, g = 9.81 and τ is a resultant action working against the sea breeze front inland propagation, a direct result of turbulent mixing at the frontal boundary. This is at a maximum at max diurnal heating, but wanes during the evening.