If you are on the beach (or somewhere near the coast) you may have noticed that around noon a light wind starts to blow from the sea where there was none before. It is very likely that it is the sea breeze, a (pleasant) phenomenon that occurs due to the temperature difference between the sea surface and the land surface.
How is the sea breeze formed?
In spring and summer, during the day, the sun’s heat heats both surfaces, but for the same amount of heat received, it costs much more to raise the temperature of the sea water than that of the ground.
The ground heats up more quickly and efficiently, and the air that is in contact with it does too, losing density and pressure. It therefore becomes lighter, and is forced to rise (convective lift). In the inland areas where this occurs, a low thermal pressure is then created, while over the sea, which is colder, the air cannot rise and what is created is a high pressure.
Wind, which is air moving parallel to the surface, originates when a difference in pressure appears between two points. In a situation of coastal breezes, as on land the pressure is low, and on the sea the pressure is high, the air starts to move, always circulating from the areas where the pressure is higher to the areas where it is lower. In our case, from the sea to the land. The result is the sea breeze.
This phenomenon occurs during the day, because at night the sea surface can be warmer than the land surface, so that the pressure on the sea will be lower than that of the cold interior areas, where it will be higher. The wind then blows from land to sea. It is the terrestrial or terral breeze.
A respite for beaches and cities
The intensity of the breeze depends on how big the difference in temperature and pressure is between the two places.
The more the ground heats up on land – let us imagine the asphalt pavements and the majority of concrete materials in cities – the greater the tendency of the superheated air to rise, and the lower the atmospheric pressure in those areas. If the sea remains cold, the pressure on it will be higher and the maritime air – our breeze – will run faster towards the land, to try to fill as soon as possible the air gap that is created on the surface as it rises.
The breeze can reach tens of kilometers inland, where low pressure zones have been generated. To all this we must add that the breezes operate on a rather local geographical framework, and do not appear when there is a situation of moderate or strong general wind.
Effects on climatic comfort
An obvious impact of sea breezes is found in their moderating effect on maximum temperature values, relieving the suffocating summer heat. That is why they are a determining factor of climatic comfort, understood as a set of environmental parameters (temperature, humidity, radiation and wind) that, combined, do not generate stress in the human body.
If we suffer from stress due to high temperatures, the desired comfort can be achieved through the cooling effect of the breezes. Moreover, light winds like these provide climatic comfort that explains the tourist development of many coastal areas.
In the same way, in urban heat island conditions, the breezes cool the hot environment of the city during the summer, although this effect is obtained more in open areas near the sea, and in houses located on the upper levels of the buildings.
However, the less open paved streets and squares can contribute to warming the breeze along its route through the neighborhoods that are not strictly maritime. In addition, the layout of buildings and streets can decrease wind speed, increasing discomfort due to humid heat.
Summer breezes and storms
As an atmospheric phenomenon, sea breezes have been extensively studied by atmospheric sciences. They have been interested not only in characterizing the breeze regimes of the studied localities – their direction and intensity, as well as their hourly, daily, monthly and annual frequency and distribution – but also in exploring the repercussions of this wind in relation to other atmospheric phenomena, such as summer storms.
When the breeze moves inland, it carries air from the sea and therefore moisture. This means that in interior areas where the warmer air is rising –it is then said to be unstable–, it transports that humidity to slightly higher layers of the atmosphere, making the clouds grow and causing the typical summer storms, usually due to the late, albeit short-lived. These clouds are of the cumuliform type – they are cauliflower-shaped – and they grow so large that they are well captured by satellites.
Breezes in human activities
To the set of physical effects of the breezes we can add its human uses, and how this unique wind has been reflected in popular culture.
Historically, breezes have conditioned and continue to condition the territorial location of certain energy infrastructures, from modern wind turbines to old windmills – 629 flour mills and 2,445 water extraction mills have been inventoried in Mallorca.
In the past, they conditioned the work of winnowing and threshing the cereal in the old eras. They also condition not only the orientation of the runways of coastal airports, but also the runway time changes that regulate the direction of takeoff and landing of aircraft.
Finally, they also condition certain recreational activities related to coastal fishing, sun and beach tourism and sea sports (windsurfing, kitesurfing and light sailing in general).
These and other uses are of such magnitude that the phenomenon of the breezes comes to manifest itself in the dialect through the popular fixation of a proper name that describes it.
In the Catalan-speaking Mediterranean territories they receive the local name of marinade (Catalonia), embatà of migdia (Valencia) or embat (Majorca). In Western Australia they refer to the refreshing afternoon breeze with the vernacular term of Fremantle Doctor.
That the sea breezes, the marinadethe embatà of migdiathe embat or the Fremantle Doctor keep refreshing our summer afternoons.