Sea breeze what is

What are sea breezes and why do they occur? Return to Science Education Home U. Disclaimer Information Quality Glossary. The return current aloft carries the excess of air towards the sea. Cloud development frequently occurs in the ascending part of the circulation, while clouds tend to dissipate over the sea, where the air is sinking. When the air is very dry, as often is the case in spring and early summer, the cumulus clouds may not appear at all. In these cases the use of satellite imagery is clearly problematic for the detection of Sea-Breezes, while it may still be detectable using other remote sensing means, such as sensitive weather radars.

In the afternoon, when the boundary layer heating over land is at its maximum, the Sea-Breeze is normally at its most intense, and can penetrate tens of kilometres - in some cases, even over a hundred kilometres - inland. If the large-scale flow is weak, the direction of the Sea-Breeze often veers with time. This is a result of the Coriolis force having an impact on the air current. The return current is about twice as thick as the Sea-Breeze, leaving for the total vertical dimension of the Sea-Breeze circulation typically about 1 to 3 km.

In the return current almost the same amount mass of air is returned to the sea, compared with the mass of air transported inland by the Sea-Breeze wind. The scheme in the image above presents all horizontal and vertical processes.

Later in the day, as solar radiation decreases, the Sea-Breeze dies out, the thermals weaken and the cumuliform clouds gradually disappear. Sufficient temperature contrast between the land and sea surfaces is needed for the initiation of the Sea-Breeze. In this respect the physical background differs for Coastal Convergence see Coastal Convergence in which the differential friction over land and over the sea is the main component for the development.

The coastline shape can either enhance or inhibit Sea-Breeze development. For example, merging of two Sea-Breezes originating from both sides of a peninsula enhances convection. On the other hand, over land areas adjoining bays the Sea-Breezes tend to diverge, which enhances low-level descent of air. The image below shows a case over Finland, in which Sea-Breezes barely visible as a line of cumulus merge along the Finnish west and south coasts, producing some intensive, local Cb Clouds in the south-western corner of Finland.

Meanwhile, along the coast adjacent to the eastern Gulf of Finland the wind field is more divergent and no clouds are produced. The low-level gradient wind steers the development of a Sea-Breeze: If the large-scale flow is weak, the Sea-Breeze circulation dominates. If opposing offshore large-scale wind exists, it can either inhibit the Sea-Breeze totally or slow down the development of the Sea-Breeze. Under these circumstances the Sea-Breeze may develop late in the afternoon moving inland very slowly.

The most intensive Sea-Breeze fronts develop in association with an opposing light large-scale flow. Strong low-level convergence within the Sea-Breeze front may result in strong convection restricted to a narrow line along the front. If moderate or strong large-scale onshore winds exist, the Sea-Breeze circulation often has no possibilities to develop, as the large-scale flow advects the cool sea air over land, reducing the temperature and pressure gradients. Some of this heat is transported to higher levels in the atmosphere through convection.

On the other hand, since the temperature of the water remains relatively constant throughout the day, the air over the water is not heated from below as over land , resulting in lower air temperatures over the water. Forces, Winds. Terms for using data resources.