Sea Breeze & Land Breeze: Thermal Circulation

Time & Conditions

Time of day 12:00

Land–sea thermal contrast 1.0×

Prevailing wind (sea→land +) 0.0 m/s

Live Readouts

Transition

Land temp

15.0°C

Sea temp

15.0°C

ΔT (land − sea)

0.0°C

Surface wind

0.0 m/s

How it works

Land has a much lower heat capacity than water, so it heats and cools far faster through the day. That temperature contrast drives a closed thermal-circulation cell — the same mechanism behind every coastal sea breeze and land breeze.

T_land(t) = 15°C + A_land·sin(2π(t−9)/24)
T_sea(t)  = 15°C + A_sea·sin(2π(t−12)/24)
A_land ≈ 8°C·contrast   A_sea ≈ 1.5°C·contrast (lags, damped by ocean heat capacity)

The circulating air follows a 2D streamfunction ψ(x,y) for a single closed convective cell spanning the coastline, with velocity components derived from it (guaranteeing the flow is divergence-free — air that rises must return):

ψ(x,y) = A·sin(kx·(x+X))·sin(ky·(y−y0))
u = ∂ψ/∂y   (horizontal wind)
v = −∂ψ/∂x  (vertical wind)
A ∝ −(T_land − T_sea)

When land is warmer (daytime) air rises over land and sinks over the sea, with a surface return flow blowing onshore — the sea breeze. After sunset the land cools faster than the sea, the cell reverses, and the surface flow blows offshore — the land breeze.

The displayed surface wind speed uses the gravity-current scaling from sea-breeze-front theory (Simpson, 1994):

g' = g·|ΔT| / T0        (reduced gravity)
U  = k·√(g'·h)          (k ≈ 0.35, h ≈ 1000 m mixed-layer depth)

The prevailing wind slider adds a uniform background flow on top of the thermal cell. Real sea breezes only develop when this synoptic wind is weak (roughly under 7–8 m/s); a strong opposing or reinforcing wind overwhelms the local thermal circulation, exactly as in this model.

12:00

Warm rising air Cool sinking air

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