Oceanic climate

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.

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.

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),[1] 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 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.

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.[2] 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.

Oceanic climates in Europe occur mostly in northwest 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[4]), 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 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.[5] 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.

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.

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).[7] 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.[8]

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).

The subtropical highland is the variety of the oceanic climate that exists in elevated portions of the world that are within either the tropics or subtropics, though it is typically found in mountainous locations in some tropical countries. Despite the latitude, the higher altitudes of these regions mean that the climate tends to share characteristics with oceanic climates, though it can experience noticeably drier weather during the lower-sun "winter" season, and it usually has warmer winters than most oceanic climates.

In locations outside the tropics, other than the drying trend in the winter, subtropical highland climates tend to be essentially identical to an oceanic climate, with mild summers and noticeably cooler winters, plus, in some instances, some snowfall. In the tropics, a subtropical highland climate typically features spring-like weather year-round. Temperatures there remain relatively constant throughout the year and snowfall is seldom seen.

Areas with this climate feature monthly averages below 22 °C (72 °F) but above −3 °C (27 °F) (or 0 °C (32 °F) using American standards). At least one month's average temperature is below 18 °C (64 °F). Without their elevation, many of these regions would likely feature either tropical or humid subtropical climates.

This type of climate exists in parts of east, south and southeastern Africa, interior southern Africa and elevated portions of eastern Africa as far north as Ethiopia and of western Africa (west region of Cameroon) up to the southwestern Angola highlands also share this climate type. The exposed areas of High Atlas, some mountainous areas across southern Europe, mountainous sections of North America, including parts of the southern Appalachians, Central and parts of South America in the states of Minas Gerais, Rio Grande do Sul, Santa Catarina, Paraná, São Paulo, Rio de Janeiro and Espírito Santo in Brazil, most of Yunnan and mountainous areas across Southeast Asia, parts of the Himalayas, parts of Sri Lanka, and parts of the Hawaiian Islands of Maui and Hawaii (island).

Small areas in Yunnan, Sichuan and parts of Bolivia have summers sufficiently short to be Cwc with fewer than four months over 10 °C (50 °F).[9] However due to the high altitudes at these locations, these areas feature Cwc climates. This is the cold variant of Subtropical Highland Climate. El Alto, Bolivia, is one of the few confirmed towns that features this variation of the subtropical highland climate.

Temperate oceanic climates, also known as "marine mild winter" climates[10] or simply oceanic climates, are found either at middle latitudes. They are often found on or near the west coast of continents; hence another name for Cfb, "marine west coast climates". In addition to moderate temperatures year-round, one of the characteristics is the absence of a dry season. Except for western Europe, this type of climate is confined to narrow bands of territory, largely in mid or high latitudes, although it can appear in elevated areas of continental terrain in low latitudes, e.g. plateaus in the subtropics.[11] It exists in both hemispheres between 35° and 60°: at low altitudes between Mediterranean, humid continental, and subarctic climates.[12]

Western sea breezes ease temperatures, especially if warm sea currents are present, and cause cloudy weather to predominate. Precipitation is constant, especially in colder months, when temperatures are warmer than elsewhere at comparable latitudes. This climate can occur farther inland if no mountain ranges are present.[13] As this climate causes sufficient moisture year-round without permitting deep snow cover, vegetation typically prospers in this climate. Deciduous trees are predominant in this climate region. However, conifers such as spruce, pine, and cedar are also common in few areas, and fruits such as apples, pears, and grapes can often be cultivated here.

In the hottest month, the average temperature is below 22 °C (72 °F), and at least four months feature average temperatures higher than 10 °C (50 °F). The average temperature of the coldest month must not be colder than −3–0 °C (27–32 °F), or the climate will be classified as continental.[11][14] The average temperature variations in the year are between 10–15 °C (50–59 °F), with average annual temperatures between 6–13 °C (43–55 °F). Rain values can vary from 50–500 cm (20–197 in), depending on whether mountains cause orographic precipitation. Frontal cyclones can be common in marine west coast regions, with some areas experiencing more than 150 rainy days annually, but strong storms are rare.[12]

Cfb climates are predominant in most of Europe except the northeast, as global temperature became warmer towards late 20th and early 21st century. However, just few decades ago, oceanic climate was only present in parts of Western Europe, including northern Spain, Northwestern Portugal (mountains), Belgium, Britain, France, Ireland, and the Netherlands. They are the main climate type in New Zealand and the Australian states of Tasmania, Victoria, and southeastern New South Wales (starting from the Illawarra region). In North America, they are found mainly in Washington, Oregon, Vancouver Island, and neighbouring parts of British Columbia, as well as many coastal areas of southwest Alaska. There are pockets of Cfb in most South American countries, including many parts of Southern Brazil, parts of the provinces of Chubut, Santa Cruz, and southeast Buenos Aires province in Argentina. In Western Asia, small pockets are found close to sea level on the Black Sea coast of northern Turkey and Georgia. While Cfb zones are rare in Africa, one dominates the coastline of the Eastern Cape in South Africa.

The climate subtype can also be found in Nantucket, Massachusetts (in the immediate west and northwest in transition for humid continental, the remainder of Cape Cod[15])[16]

Areas with subpolar oceanic climates feature an oceanic climate but are usually located closer to polar regions. As a result of their location, these regions tend to be on the cool end of oceanic climates. Snowfall tends to be more common here than in other oceanic climates. Subpolar oceanic climates are less prone to temperature extremes than subarctic climates or continental climates, featuring milder winters than these climates. Subpolar oceanic climates feature only one to three months of average monthly temperatures that are at least 10 °C (50 °F). As with oceanic climates, none of its average monthly temperatures fall below -3.0 °C (26.6 °F) or 0 °C depending on the isotherm used. Typically, these areas in the warmest month experience daytime maximum temperatures below 17 °C (63 °F), while the coldest month features highs near or slightly above freezing and lows just below freezing. It typically carries a Cfc designation, though very small areas in Argentina and Chile have summers sufficiently short to be Cwc with fewer than four months over 10 °C (50 °F).[19]

This variant of an oceanic climate is found in parts of coastal Iceland, the Faroe Islands, parts of Scotland, northwestern coastal areas of Norway (most of Lofoten, Vesterålen, warmest part of Tromsø reaching to 71°N on some islands),[20] uplands/highlands in western Norway, the Aleutian Islands of Alaska and northern parts of the Alaskan Panhandle, the southwest of Argentina, and a few highland areas of Tasmania, and the Australian and Southern Alps.[21] This type of climate is even found in very remote parts of the New Guinea Highlands. The classification used for this regime is Cfc.[1] In the most marine of those areas affected by this regime, temperatures above 20 °C (68 °F) are extreme weather events, even in the midst of summer. Temperatures above 30 °C (86 °F) have been recorded on rare occasions in some areas of this climate, and in winter temperatures down to −20 °C (−4 °F) have seldom been recorded in some areas.