Basic Answers
1) The sea and land breezes are proportional to the magnitude of the land/sea
temperature difference and are dependent on synoptic flow. For example, onshore
synoptic flow favors the sea breeze, while offshore synoptic flow impedes
the sea breeze. The opposite is true for the land breeze. For this example,
there is weak synoptic flow since there isn’t much of a pressure gradient
near Florida. This allows the land/sea breezes to form unimpeded.
2) The sea breeze usually penetrates inland about 25 miles without onshore synoptic flow, but can reach 200 miles inland with onshore synoptic flow. The sea and land breezes reach a peak at the leading edge of the temperature gradient which resembles a shallow cold front and is a favored location for convection. This cold front is referred to as the sea breeze front during the day and appears over land. Overnight, the cold front is referred to as the land breeze front and appears over water.
3) The sea breeze forms during the mid to late morning hours when the land temperature exceeds the water temperature by 6-10 degrees Fahrenheit due to the larger heat capacity of water. The circulation intensifies as daytime solar heating reaches its maximum because the solar heating increases the temperature gradient by decreasing the pressure over land.
4) Around noon, the surface winds associated with the sea breeze normally reach 10-20 knots up to 500 vertical feet. The afternoon hours are the most active time of day because the sea breeze penetration reaches a maximum and the winds are strongest. This is shown in Figure 3.
5) By late afternoon the sea breeze diminishes and then dies out 1-2 hours after sunset. At this time, the land cools and the process reverses itself (temperatures over land are cooler than over water) with the formation of the land breeze circulation. The land breeze is shown in Figure 2.
6) The land breeze is weaker than the sea breeze, yet nocturnal convection occasionally fires up along the land breeze front over the ocean during the nighttime hours when the circulation is strongest.
7) The topography of the coastline is the primary factor in the direction of the land and sea breezes. The land and sea breezes are perpendicular to the coastline and oriented along the surface pressure gradient. The direction can then affect local weather along coastal towns. For example, during a sea breeze event, a coastline with a concave shape will lead to divergent winds. On the contrary, a coastline with a convex shape will cause convergent winds, which can lead to convection.
8) The presence of coastal mountains also affects the land and sea breeze circulations. Coastal mountains affect the location of surface heating and the mountain/valley breezes associated with the mountains can reinforce the sea breeze or converge with the sea breeze. This can also impact the local weather.
9) The presence and strength of low-level inversions play an important role in the strength of the sea breeze circulation. An inversion tends to limit the vertical extent of the heating to a shallow layer, which reduces the strength of the sea breeze. An inversion may also provide significant convective inhibition and the lift induced by the sea breeze may not break the inversion, preventing the sea breeze from strengthening.
10) A conditionally unstable environment (up to 850 mb) will allow for a stronger sea breeze than a shallow inversion (surface to 950 mb). In Fort Lauderdale, we see a conditionally unstable environment up to about 850 mb and a strong sea breeze circulation at 1PM in Figure 5.
11) The sea breeze can be a key component to the local weather of coastal towns during the spring and fall months. The afternoon is the most active time of day because the sea breeze penetrates farther inland and is strongest at this time. In areas where winds converge, convection is favored and cumulus clouds frequently are observed. Also, vertical motion and thunderstorms occur in regions where the sea breeze front interacts with outflow boundaries and other sea breeze fronts.
12) In Florida the collision between the sea breeze fronts of the Atlantic coast and the Gulf coast often occur, creating convection and thunderstorms on the peninsula during afternoon hours. This module is a textbook example of this phenomenon. The Pacific coast of the U.S. also is affected by sea breezes. In this region, strong gusty winds lead to the onshore advection of marine stratus clouds and fog.
13) The influence of the land/sea breeze is more pronounced in the tropics than the mid-latitudes. This is mostly due to the fact that the inland or offshore extent of the land/sea breeze is greater in the tropics compared with the mid-latitudes (about 100 km compared to about 10 km). The difference in extent is explained by the weaker Coriolis acceleration in the tropics.
14) Land breeze interaction with the trade
winds has been documented as producing enhanced rainfall at night and early
morning on the east coasts of Brazil and the Ivory Coast. Also, large mountainous
islands (such as Puerto Rico) often have a clear ring of suppressed cloudiness
surrounding them in the afternoon. This is due to the compensating subsidence
from the convection and thunderstorms over the interior.