Oceanic climate

World map showing oceanic climate zones, as defined by the Köppen climate types "Cfb", "Cfc", "Cwb" and "Cwc".

An oceanic climate (also known as marine, west coast and maritime) is the climate typical of the west coasts at the middle latitudes of most continents, and generally features warm, but not hot summers and cool, but not cold winters, and a relatively narrow annual temperature range. It typically lacks a dry season, as precipitation is more evenly dispersed throughout the year. It is the predominant climate type across much of Europe, in coastal northwestern North America, portions of southwestern South America and small areas of Africa, in southeast Australia, and New Zealand, as well as isolated locations elsewhere.

Under the Köppen climate classification, the typical zone associated with the Oceanic climate is Cfb, although it includes subtropical highland zones not usually associated with marine climates. Often, parts of the Csb Mediterranean or Dry-Summer subtropical zones are not associated with a typical Mediterranean climate, and would be classified as Temperate Oceanic (Cfb), except dry-summer patterns meet Koeppen's minimum Cs thresholds. Other climate classification systems, such as Trewartha, place these areas firmly in the Oceanic zone (Do).^[1]

Properties

Climates near the ocean generally have warm (but not hot) summers, and cool (but not cold) winters. They are characterized by a narrower annual range of temperatures than are encountered in other places at a comparable latitude, and generally do not have the extremely dry summers of Mediterranean climates.^[2] Oceanic climates are most dominant in Europe, where they spread much farther inland than in other continents.^[3]

Oceanic climates can have much storm activity as they are located in the belt of the stormy westerlies. The annual range of temperatures is smaller than typical climates at these latitudes due to the constant stable marine air masses that pass through oceanic climates, which lack both very warm and very cool fronts.

Similar climates in thermal range are also found in tropical highlands even at considerable distance from any coastline. Generally, they fall into Köppen climate classification Cfb or Cwb.^[4][5] The narrow range of temperatures results from the slight thermal range of temperatures between seasons characteristic of tropical lowlands. Altitudes are high enough that some places have at least one month cooler than 18 °C (64 °F) and do not qualify for grouping in the true tropical climates. This variation of the oceanic climate is termed “subtropical highland climate”. Unlike the norm in true oceanic climates, subtropical highland climates may have a marked winter drought. Agricultural potential in both oceanic climates and subtropical highland climates is similar.

Precipitation

Seattle, a city with an oceanic climate

Precipitation is both adequate and reliable throughout the year in oceanic climates, except in certain tropical highland areas, which would have tropical or humid subtropical climates (with a dry season in winter) if not for the high altitude making them cooler (Koppen Cwb). Under some variations of the Koppen classification system, parts of the Pacific Northwest and south-central Chile are classified as having a Mediterranean climate (Koppen "Csb") due to a markedly drier summer months. Despite the "Csb" designation, these areas are generally considered Oceanic, rather than "Mediterranean", due to the generally extended months of rain and cloudy conditions that these locations experience outside the summer months. Seattle is an example of this. Between October and May, Seattle experiences high rainfall and is mostly or partly cloudy six out of every seven days.^[6]

In most areas with an oceanic climate, for the majority of the year precipitation comes in the form of rain. However during the winter, despite its C classification, the majority of areas with this climate see some snowfall annually. Outside of Australia, South Africa, the majority of New Zealand and tropical highland locations, most areas with an oceanic climate experiences at least one snowstorm 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 vary among oceanic climates; those at the lowest latitudes are nearly subtropical from a thermal standpoint, but more commonly a mesothermal regime prevails, with cool, but not cold, winters and warm, but not hot, summers. Summers are also cooler (often much cooler) than in areas with a humid subtropical climate. Average temperature of warmest month must be less than 22 °C (72 °F) and that of the coldest month warmer than −3 °C (27 °F) although American scientists prefer 0 °C (32 °F) in the coldest month. Poleward of the latter is a zone of the aforementioned subpolar oceanic climate (Köppen Cfc),^[5] with long but relatively mild 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 in the Northern Hemisphere and extreme southern Chile and Argentina in the Southern Hemisphere.

Locations

Ireland and Great Britain experience a typical maritime climate, with prevailing south-westerly winds from the Atlantic Ocean. The annual average temperature range in the British Isles is only about 14°C (57°F).^[7] Although the west coast of Alaska experiences a maritime climate, the absence of an equally significant warm Pacific current in the upper-mid latitudes means that these regions are generally colder in winter, with more precipitation falling as snow. The oceanic climate is prevalent in a good portion of western Europe and the European part of northern Turkey.

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 Boone, North Carolina, Block Island, and Cape Cod, have a similar climate.^[8] A significant portion of oceanic climate exhibited in North America features a drying trend in the summer, thus falling under the dry-summer subcategory explained below.

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, with additional pockets of this climate inland of the Eastern Cape and KwaZulu-Natal coast. Interior southern Africa, elevated portions of eastern Africa, and Mozambique also share this climate type. It is usually warm most of the year with no pronounced rainy season, but slightly more rain in autumn and spring. The only significant areas where this climate is found at or near sea level in Asia is on the Black Sea coast in northern Turkey, in small pockets along or near the Caspian Sea in Azerbaijan and in small pockets along or near the Tsugaru Strait in northern Japan. The oceanic climate is prevalent in the more southerly locations of Oceania. A mild Maritime climate is in existence in New Zealand. In Australia, the island of Tasmania, southern parts of Victoria and New South Wales, also exhibit a mild Maritime climate. It can also be found along the western areas of the south coast of Western Australia. The oceanic climate is found in isolated pockets in South America. It exists in southeast-central and southwest Argentina and southern Chile.

Under Koeppen-Geiger, many areas generally considered to have Oceanic climates are classified as cool summer, dry-summer subtropical (Csb) climates. These areas are not usually associated with a typical Mediterranean climate, and include much of the Pacific Northwest, southern Chile, parts of southeastern-central Argentina, and northwest of the Iberian Peninsula.^[8] Many of these areas would be classified as Cfb climates, except dry-summer patterns meet Koeppen's Cs thresholds, and cities such as Concepción, Chile; Seattle, Washington; Portland, Oregon; and Victoria, British Columbia can be classified as Csb.

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 mild steppe or desert climates. This milder version of steppe and desert climates are found in Washington and Oregon to the east of the Cascade Range in the United States, Patagonia in southern Argentina, the Atacama Desert in northern Chile and coastal areas in the southeastern portion of Western Australia.

Varieties

Subtropical highland variety

The subtropical highland variety of the oceanic climate 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 also tends to experience noticeably drier weather during the "low-sun" season.

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 tends to feature 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 the elevation, many of these regions would likely feature either tropical or humid subtropical climates. These regions usually carry a Cwb or Cfb designation, though very small areas in Yunnan, Sichuan and parts of Argentina and Bolivia may have summers sufficiently short to be Cwc with fewer than four months over 10 °C (50 °F), though no records exist for such stations.^[9]

This type of climate exists in parts of east, south and south-eastern Africa, some mountainous areas across southern Europe, sections of mountainous North (including higher elevations of the Southern Appalachians), Central and South America, some mountainous areas across Southeast Asia, and parts of the Himalayas. It also occurs in a few areas of Australia, although average high temperatures during summers there tend to be higher and the climate drier than is typical of subtropical highland climates, with summer maxima sometimes exceeding 40 °C (104 °F).^[10]

Subpolar variety (Cfc)

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 humid 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°C (26.6°F). It typically carries a Cfc designation. This variant of an oceanic climate is found in parts of coastal Iceland, the Faroe Islands, small sections of the Scottish Highlands, northwestern coastal areas of Norway such as Lofoten and reaching to 70°N on some islands,^[11] uplands near the coast of southwestern Norway, southern islands of Alaska and northern parts of the Alaskan Panhandle, the far south of Chile and Argentina, and a few highland areas of Tasmania, and the Australian and Southern Alps.^[12] The classifications used to this regime are Cfc.^[5]

Dry summer variety (Csb)

Despite the fact that dry summers are a feature which differentiate Csb areas from oceanic climates, some areas of Csb climate are typically considered "oceanic" as opposed to "Mediterranean" (see Mediterranean climate). Technically, this version of the Oceanic climate meets Koppen's minimum precipitation threshold limit of 30 millimetres (1.2 in) (or 40 millimetres (1.6 in) under Koppen-Geiger), resulting in a Csb designation. Nevertheless, due to the higher annual accumulation of precipitation and generally cloudier conditions that these regions experiences in comparison to other areas with Csb climates, a number of scientists consider this climate oceanic. This is especially the case in the Pacific Northwest region of the United States and Canada, some sections of coastal Chile, in Galicia in northwestern Spain and in northern Portugal, where conditions are wetter and generally cloudier during the course of the year than typical Csb climates.^{[citation needed][13]} Nevertheless, those regions have several Mediterranean features :

• Greater annual hours of sunshine than the typical oceanic domain, especially during the drier summer months, sometimes unbroken sunny stretches for weeks at a time under the dominating influence of stable high pressure. For example, cities such as A Coruña or Seattle have at least 2000 hours of sunshine, while the values of the typical Cfb regions are almost always below 2000 hours.^[14][15]
• Vegetation which is partially adapted to xeric conditions. So the cork oak, a typically acidophilus Mediterranean species, and which is widely distributed in Portugal and in southern-half of Galicia.^[16] In contrast, beech or birch, widely distributed in the Cfb area, are not common in Iberia, mostly confined to the Pyrenees and the Cantabrian mountains. In addition, Garry oak, typical of California, can be found as far north as Vancouver Island.^[17][18] Douglas fir, which is the typical species of the Pacific Northwestern forests, is very well adapted to the summer drought.^[19]
• Forest fires are regular in those regions due to the summer drought.^[20][21]

See also

• Climate classification
• Temperate climate
• Humid subtropical climate
• Subtropical climate
• Continental climate
• Polar climate

References

External links

• University of Wisconsin–Stevens Point: Marine (Humid) West Coast Climate
• EPIC Data Collection On-line ocean observational data collection
• NOAA In-situ Ocean Data Viewer Plot and download ocean observations
• http://www.ace.mmu.ac.uk/eae/Climate/Older/Maritime_Climate.html