Trade winds | Revolvy
Atmospheric circulation is the large-scale movement of air, and together with ocean circulation Part of the air rising at 60° latitude diverges at high altitude toward the poles The easterly Trade Winds and the polar easterlies have nothing over which to A strong high, moving polewards may bring westerly winds for days. When clear of Terra del Fuego, I should recommend stretching to the that the south-westerly winds, which they will afterwards be certain to meet, and This was made in the summer, when the trade-wind extends further south Plate; they are generally preceded by strong N.W. winds, and a low altitude of the barometer. The westerlies, anti-trades, or prevailing westerlies, are prevailing winds from the west toward the east in the middle latitudes between 30 and 60 degrees latitude. They originate from the high-pressure areas in the horse latitudes and trend.
Wind-induced upwelling is generated by temperature differences between the warm, light air above the land and the cooler denser air over the sea. In temperate latitudesthe temperature contrast is greatly seasonably variable, creating periods of strong upwelling in the spring and summer, to weak or no upwelling in the winter. For example, off the coast of Oregon, there are four or five strong upwelling events separated by periods of little to no upwelling during the six-month season of upwelling.
In contrast, tropical latitudes have a more constant temperature contrast, creating constant upwelling throughout the year. The Peruvian upwelling, for instance, occurs throughout most of the year, resulting in one of the world's largest marine fisheries for sardines and anchovies. The Peruvian upwelling system is particularly vulnerable to ENSO events, and can cause extreme interannual variability in productivity.
For example, a submarine ridge that extends out from the coast will produce more favorable upwelling conditions than neighboring regions. Upwelling typically begins at such ridges and remains strongest at the ridge even after developing in other locations.
While studying the trophic levels and patterns typical of upwelling regions, researchers have discovered that upwelling systems exhibit a wasp-waist richness pattern. In this type of pattern, the high and low trophic levels are well-represented by high species diversity.
SAGE Reference - Winds, Westerlies
However, the intermediate trophic level is only represented by one or two species. This trophic layer, which consists of small, pelagic fish usually makes up about only three to four percent of the species diversity of all fish species present.
The lower trophic layers are very well-represented with about species of copepodsspecies of gastropodsand species of crustaceans on average. At the apex and near-apex trophic levels, there are usually about species of marine mammals and about 50 species of marine birds. The vital intermediate trophic species however are small pelagic fish that usually feed on phytoplankton.
In most upwelling systems, these species are either anchovies or sardines, and usually only one is present, although two or three species may be present occasionally. These fish are an important food source for predators, such as large pelagic fish, marine mammals, and marine birds.
Although they are not at the base of the trophic pyramid, they are the vital species that connect the entire marine ecosystem and keep the productivity of upwelling zones so high  Threats to upwelling ecosystems[ edit ] A major threat to both this crucial intermediate trophic level and the entire upwelling trophic ecosystem is the problem of commercial fishing. Since upwelling regions are the most productive and species rich areas in the world, they attract a high number of commercial fishers and fisheries.
On one hand, this is another benefit of the upwelling process as it serves as a viable source of food and income for so many people and nations besides marine animals. However, just as in any ecosystem, the consequences of over-fishing from a population could be detrimental to that population and the ecosystem as a whole. In upwelling ecosystems, every species present plays a vital role in the functioning of that ecosystem.
If one species is significantly depleted, that will have an effect throughout the rest of the trophic levels.
For example, if a popular prey species is targeted by fisheries, fishermen may collect hundreds of thousands of individuals of this species just by casting their nets into the upwelling waters. As these fish are depleted, the food source for those who preyed on these fish is depleted.
Therefore, the predators of the targeted fish will begin to die off, and there will not be as many of them to feed the predators above them. This system continues throughout the entire food chainresulting in a possible collapse of the ecosystem. It is possible that the ecosystem may be restored over time, but not all species can recover from events such as these.
Even if the species can adapt, there may be a delay in the reconstruction of this upwelling community. Fisheries may target a variety of different species, and therefore they are a direct threat to many species in the ecosystem, however they pose the highest threat to the intermediate pelagic fish. Since these fish form the crux of the entire trophic process of upwelling ecosystems, they are highly represented throughout the ecosystem even if there is only one species present.
Unfortunately, these fish tend to be the most popular targets of fisheries as about 64 percent of their entire catch consists of pelagic fish.
Among those, the six main species that usually form the intermediate trophic layer represent over half of the catch. The animals higher in the trophic levels may not completely starve to death and die off, but the decreased food supply could still hurt the populations.
If animals do not get enough food, it will decrease their reproductive viability meaning that they will not breed as often or as successfully as usual. This can lead to a decreasing population, especially in species that do not breed often under normal circumstances or become reproductively mature late in life.
Another problem is that the decrease in the population of a species due to fisheries can lead to a decrease in genetic diversity, resulting in a decrease in bio-diversity of a species. If the species diversity is decreased significantly, this could cause problems for the species in an environment that is so variable and quick-changing; they may not be able to adapt, which could result in a collapse of the population or ecosystem. The coastal upwelling zones diminish as well since they are wind driven systems, and the wind is no longer a very strong driving force in these areas.
As a result, global upwelling drastically decreases, causing a decrease in productivity as the waters are no longer receiving nutrient-rich water. Without these nutrients, the rest of the trophic pyramid cannot be sustained, and the rich upwelling ecosystem will collapse.
- Trade winds
A KYR record of upwelling off Oman during the late quaternary: Upwelling mechanisms in the northwestern Alboran Sea. Journal of Marine Systems, Biological-Physical Interactions in the Oceans. Global climate change and intensification of coastal ocean upwelling.
Satellite measurements reveal persistent small-scale features in ocean winds. Save The westerlies blue arrows and trade winds yellow and brown arrows The trade winds are the prevailing pattern of surface winds from the east toward the west easterly found in the tropicswithin the lower portion of the Earth's atmospherein the lower part of the troposphere near the Earth's equator. The trade winds blow predominantly from the northeast in the Northern Hemisphere and from the southeast in the Southern Hemispherestrengthening during the winter and when the Arctic oscillation is in its warm phase.
Trade winds have been used by captains of sailing ships to cross the world's oceans for centuries, and enabled colonial expansion into the Americas and trade routes to become established across the Atlantic and Pacific oceans. In meteorologythe trade winds act as the steering flow for tropical storms that form over the Atlantic, Pacific, and southern Indian Oceans and make landfall in North America, Southeast Asia, and Madagascar and eastern Africa, respectively.
Trade winds also transport African dust westward across the Atlantic Ocean into the Caribbean Seaas well as portions of southeastern North America. Shallow cumulus clouds are seen within trade wind regimes, and are capped from becoming taller by a trade wind inversion, which is caused by descending air aloft from within the subtropical ridge.
The weaker the trade winds become, the more rainfall can be expected in the neighboring landmasses. History A Spanish galleon The term trade winds originally derives from the early fourteenth century late Middle English word "trade," meaning "path" or "track.
Atmospheric circulation - Wikipedia
They could then turn northeast, to the area around the Azores islands, and finally east to mainland Europe. Following the African coast southbound means upwind in the Southern hemisphere. In the Pacific ocean, the full wind circulation, which included both the trade wind easterlies and higher-latitude Westerlieswas unknown to Europeans until Andres de Urdaneta 's voyage in For example, Manila galleons could not sail into the wind at all.