Oceanic climate

Encyclopedia

An oceanic climate, also known as a maritime climate or marine climate, is the Köppen classification of climate typical of west coasts in higher middle latitudes of continents, generally featuring mild summers (relative to their latitude) and cool but not cold winters, with a relatively narrow annual temperature range and few extremes of temperature. Oceanic climates can be found in both temperate and subtropical areas, notably in Western Europe, parts of central and Southern Africa, North America, South America, parts of Asia, and as well as parts of Australia and New Zealand.

Precipitation

Locations with oceanic climates tend to feature cloudy conditions with precipitation, though it can experience clear, sunny days. London is an example of an oceanic climate. It experiences reliable and constant precipitation throughout the entire year. Despite this, thunderstorms are quite rare since hot and cold air masses meet infrequently in the region. In most areas with an oceanic climate, precipitation comes in the form of rain for the majority of the year. However, some areas with this climate see some snowfall annually during winter. Most oceanic climate zones, or at least a part of them, experience at least one snowfall per year. In the poleward locations of the oceanic climate zone (“subpolar oceanic climates”, described in greater detail below), snowfall is more frequent and commonplace.

Temperature

Overall temperature characteristics of the oceanic climates feature cool temperatures and infrequent extremes of temperature. In the Köppen climate classification, Oceanic climates have a mean temperature of 0 °C (32 °F) or higher (or −3 °C (27 °F) or higher in the coldest month), compared to continental climates where the coldest month has a mean temperature of below 0 °C (32 °F) (or −3 °C (27 °F) in the coldest month). Summers are cool, with the warmest month having a mean temperature below 22 °C (72 °F). Poleward of the latter is a zone of the aforementioned subpolar oceanic climate (Köppen Cfc), with long but relatively mild (for their latitude) winters and cool and short summers (average temperatures of at least 10 °C (50 °F) for one to three months). Examples of this climate include parts of coastal Iceland, the coast of Norway north of Bodø, the Scottish Highlands, the mountains of Vancouver Island, and Haida Gwaii in Canada, in the Northern Hemisphere and extreme southern Chile in the Southern Hemisphere (examples include Punta Arenas), the Tasmanian Central Highlands, and parts of New Zealand.

The Trewartha climate classification considers climates averaging above freezing in all months and four to seven months of at least 10 °C (50 °F) to be oceanic. Under this standard there is no upper monthly average limit so that some climates that Koeppen may consider humid subtropical are considered oceanic by Trewartha.

The cause

Oceanic climates are not necessarily found in coastal locations on the aforementioned parallels; however, in most cases oceanic climates parallel higher middle latitude oceans. The polar jet stream, which moves in a west to east direction across the middle latitudes, advances low pressure systems, storms, and fronts. In coastal areas of the higher middle latitudes (45–60° latitude), the prevailing onshore flow creates the basic structure of most oceanic climates. Oceanic climates are a product and reflection of the ocean adjacent to them. In the autumn, winter, and early spring, when the polar jet stream is most active, the frequent passing of marine weather systems creates the frequent fog, cloudy skies, and light drizzle often associated with oceanic climates. In summer, high pressure often pushes the prevailing westerlies north of many oceanic climates, often creating a drier summer climate (for example in the Northwest coast of North America, bathed by the Pacific Ocean).

The North Atlantic Gulf Stream, a tropical oceanic current that passes north of the Caribbean and up the East Coast of the United States to North Carolina, then heads east-northeast to the Grand Banks of Newfoundland, is thought to greatly modify the climate of Northwest Europe. As a result of the North Atlantic Current, west-coast areas located in high latitudes like Ireland, the UK, and Norway have much milder winters (for their latitude) than would otherwise be the case. The lowland attributes of western Europe also help drive marine air masses into continental areas, enabling cities such as Dresden, Prague, and Vienna to have maritime climates in spite of being located well inland from the ocean.

Locations

London, United Kingdom
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Source: Met Office

Europe

Oceanic climates in Europe occur mostly in Western Europe. It starts in northwestern Europe, from Ireland and Great Britain eastward to central Europe. Most of France (away from the Mediterranean), Belgium, the Netherlands, Austria, Luxembourg, Denmark, western Germany, south coast and western areas of Norway north to Skrova Lofoten, several parts of Czech Republic, the north coast of Spain (Asturias, Basque Country, Cantabria, Galicia and north of Navarre, Aragon and Catalonia), the western Azores off the coast of Portugal, the north of Serbia and southern portions of Sweden, also have oceanic climates.

Examples of oceanic climates are found in Glasgow, London, Bergen, Amsterdam, Dublin, Berlin, Hamburg, Vienna, Bilbao, Oviedo, Biarritz, A Coruña, Bayonne, Zürich, Copenhagen, Prague, Skagen, and Paris. With decreasing distance to the Mediterranean Sea, the oceanic climate of northwest Europe gradually changes to the subtropical dry-summer or Mediterranean climate of southern Europe. The line between Oceanic and Continental climate’s in Europe runs in a generally west to east direction. For example, western Germany is more impacted by milder Atlantic air masses than is eastern Germany. Thus, winters across Europe become colder to the east, and (in some locations) summers become hotter. The line between oceanic Europe and Mediterranean Europe normally runs north to south and is related to changes in precipitation patterns and differences to seasonal temperatures.

The Americas

Vancouver, Canada
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Source: Environment Canada
Valdivia, Chile
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The oceanic climate exists in an arc spreading across the north-western coast of North America from the Alaskan panhandle to northern California, in general the coastal areas of the Pacific Northwest. It includes the western parts of Washington and Oregon, the Alaskan panhandle, western portions of British Columbia, and north-western California. In addition, some east coast areas such as Block Island, Cape Cod, Martha’s Vineyard, and Nantucket have a similar climate. An extensive area of oceanic climates distinguishes the coastal regions of southern Chile and extends into bordering Argentina.

All mid-latitude oceanic climates are classified as humid. However, some rainshadow climates feature thermal régimes similar to those of oceanic climates but with steppe-like (BSk) or even desert-like (BWk) scarcity of precipitation. Despite the oceanic-like thermal regimes, these areas are generally classified as steppe or desert climates. These arid versions of oceanic climates are found in eastern Washington and Oregon to the east of the Cascade Range in the United States, in the Okanagan Valley in British Columbia in Canada, Patagonia in southern Argentina, and the Atacama Desert in northern Chile.

Africa

The only noteworthy area of Maritime Climate at or near sea-level within Africa is in South Africa from Mossel Bay on the Western Cape coast to Plettenberg Bay (the Garden Route), with additional pockets of this climate inland of the Eastern Cape and KwaZulu-Natal coast. It is usually warm most of the year with no pronounced rainy season, but slightly more rain in autumn and spring. The Tristan da Cunha archipelago in the South Atlantic also has an oceanic climate.

Asia and Oceania

Melbourne, Australia
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Average max. and min. temperatures in °C
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The oceanic climate is prevalent in the more southerly parts of Oceania. A mild maritime climate is in existence in New Zealand. It occurs in a few areas of Australia, namely in the southeast, although average high temperatures during summers there tend to be higher and the summers drier than is typical of oceanic climates, with summer maxima sometimes exceeding 40 °C (104 °F). The climate is found in Tasmania, southern half of Victoria and southeastern New South Wales (southwards from Wollongong).

In Asia, the coastal part of northwestern Turkey, from Karadeniz Ereğli to Inebolu, features this climate. Additionally parts of the northeastern coast of Honshu, from Mutsu, Aomori towards Miyako, Iwate in Japan, feature this climate.

Indian Ocean

Île Amsterdam and Île Saint-Paul, both part of the French Southern and Antarctic Lands, are located in the subtropics and have an oceanic climate (akin to Tristan da Cunha; see above).

Varieties

Subtropical highland variety (Cfb, Cwb, Cwc)

Mexico City
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