Sea breeze

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Sea breeze moving across the water (towards theviewer) in Hobart, Tasmania, Australia

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Lake/sea breeze and atmosphericdepth

A sea breeze or onshore breeze is a wind that blows in the afternoon from a large bodyof water toward or onto a landmass. By contrast, a landbreeze or offshore breeze is a wind that blows in the night from a landmass toward or onto a large bodyof water. Seabreezes and landbreezes are both important factors in coastal regions' prevailing winds.

Sea breeze and land breeze develop due to differences in Template:Nowr created by the differing heat capacities of water and dryland. As such, seabreezes and landbreezes are more localised than prevailing winds. Since land heats up much faster than water under solar radiation, a seabreeze is a common occurrence along coasts after sunrise. On the other hand, dryland also cools faster than water without solar radiation, so the wind instead flows from the land towards the sea when the seabreeze dissipates after sunset.

The land breeze at nighttime is usually shallower than the seabreeze in daytime. Unlike the daytime seabreeze, which is driven by convection, the nighttime landbreeze is driven by convergenceTemplate:Definition needed.

The term offshore wind refers to any wind over open water, which is related to but not synonymous with offshore breeze.

Causes

Sea breeze

The sea has a greater heat capacity than land, so the surface of the sea warms up more slowly than the surface of the land. As the temperature of the surface of the land rises, the land heats the air above it by convection. The hypsometric equation states that the hydrostatic pressure depends on the temperature. Thus, the hydrostatic pressure over the land decreases less at higher altitude. As the air above the coast has a relatively higher pressure, it starts moving towards the sea at high altitude. This creates an inverse airflow near the ground. The strength of the seabreeze is directly proportional to the temperature difference between the land and the sea. If a strong offshore wind is present (that is, a wind greater than ) and opposing the direction of a possible seabreeze, the seabreeze is not likely to develop.

Land breeze

The land forces the dying of seabreeze so the temperature of the land approaches that of the ocean. If the land becomes cooler than the adjacent sea surface temperature, the airpressure over the water will be lower than that of the land, setting up a landbreeze blowing from the land to the sea, as long as the environmental surface wind pattern is not strong enough to oppose it.

Effects

Sea breeze

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Schematic cross-section through a Template:Nowr front. If the air inland is moist, cumulus often marks the front.

A sea-breeze front is a weather front created by a seabreeze, also known as a convergence zone. The coldair from the sea meets the warmer air from the land and creates a boundary like a shallow Template:Nowr. When powerful, this front creates cumulus clouds, and if the air is humid and unstable, the front can sometimes trigger thunderstorms. If the flow aloft is aligned with the direction of the seabreeze, places experiencing the seabreeze frontal passage will have benign, or fair, weather for the remainder of the day. At the front warmair continues to flow upward and coldair continually moves in to replace it, and so the front moves progressively inland. Its speed depends on whether it is assisted or hampered by the prevailing wind, and the strength of the thermal contrast between land and sea. At night, the seabreeze usually changes to a landbreeze, due to a reversal of the same mechanisms.

Sea breezes in Florida

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Sea breeze convergence in Cuba is very similar to that in Florida. The northern seabreeze meets the southern seabreeze, creating a sharp convergence line in the cumulus field.

Thunderstorms caused by powerful sea breeze fronts frequently occur in Florida, a peninsula bounded on the east and west by the Atlantic Ocean and Gulfof Mexico, respectively. During the Template:Nowr, which typically lasts from June through SeptemberTemplate:Wbr/Template:WbrOctober, any direction that the winds are blowing would always be off the water, thus making Florida the place most often struck by lightning in the UnitedStates, and one of the most on Earth. These storms can also produce significant hail due to the tremendous updraft it causes in the atmosphere, especially during times when the upper atmosphere is cooler such as during the spring or fall.

On calm summer afternoons with little prevailing wind, seabreezes from both coasts may collide in the middle, creating especially severe storms down the center of the state. These thunderstorms can drift towards either the west or eastcoast depending on the relative strengths of the seabreezes, and sometimes survive to move out over the water at night, creating spectacular cloud-to-cloud lightning shows for hours after sunset. Due to its large size, Template:Nowr may also contribute to this activity by creating its own lakebreeze which collides with the east and westcoast seabreezes.

In Cuba, similar seabreeze collisions with the northern and southern coasts sometimes lead to storms.

Sea breezes in Southeast Australia

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A sailing skiff during an afternoon seabreeze in the Template:Nowr

In the southeast Australian states of NewSouth Wales and Victoria, an intense seabreeze called the southerly buster causes an abrupt, squally southerly wind change, with gusts in excess of , in coastal cities such as Sydney in NewSouth Wales, south to Mallacoota, Victoria and Melbourne, as it approaches from the southeast, mainly on a hot day, bringing in cool, usually severe weather and a dramatic temperature drop, thus ultimately replacing and relieving the prior hot conditions. Marking the boundary between hot and cool air masses, the southerly buster is sometimes represented by a Template:Nowr perpendicular to the coast.

The southerly buster is caused by the interaction of a shallow cold front with the blocking GreatDividing Range that aligns with the coast, as the coolair becomes trapped against the ranges. The mountains create a channelling effect as the southerly gale winds move across the NewSouth Wales coast, and frictional contrasts over the mainland and the ocean that disconnect the flow. Temperature changes can be dramatic, with falls of often occurring in a fewminutes.

Land breeze

Land breeze, which consists of coolair coming from the land, pushes the warmerair upwards over the sea. If there is sufficient moisture and instability available, the landbreeze can cause showers, or even thunderstorms, over the water. Overnight thunderstorm development offshore due to the landbreeze can be a good predictor for the activity on land the following day, as long as there are no expected changes to the weather pattern over the following Template:Nowr. This is mainly because the strength of the landbreeze is weaker than the seabreeze. The landbreeze will die once the land warms up again the next morning.

Utilisation

Wind farms can be situated near a coast to take advantage of the normal daily fluctuations of wind speed resulting from sea or landbreezes. While many onshore and offshore windfarms do not rely on these winds, a nearshore windfarm is a type of offshore windfarm located on shallow coastal waters to take advantage of both sea and landbreezes. For practical reasonsTemplate:Explain, other offshore windfarms are situated further out to sea and rely on prevailing winds rather than seabreezes.

See also

• Fremantle Doctor, the local name for the seabreeze in and around Perth, WesternAustralia
• Southerly buster, a sea breeze, though usually a storm, which is experienced in the southeast coast of NewSouth Wales, southern coast of Victoria and Template:Nowr
• Template:Anl