Effects on the West Coasts
The northern portions of the west coasts ofcontinents generally have cool summers and warm winters. The summers are cool because of the presence of cold northern waters along their shores. However, the winters are generally mild because of the transport of warm ocean waters to these latitudes. For example, the south and southeast coasts of Alaska and the west coasts of Canada, Washington, and Oregon have relatively warm currents flowing along their shores. These currents are the Aleutian and North Pacific cur-rents, which are branches of the warm northward-flowing Kuroshio current. The currents flow along the west side of the Pacific high and bring warm water into southern Alaska and the Pacific Northwest.
As these currents merge and flow southwardalong the British Columbia coast, they move into warmer waters and become the cold California current.
The southern portions of the west coasts ofcontinents generally have cooler climates than do the east coasts of the same latitude. For exam-ple, during summer, the cold California current flows southward along the shores of California. Due to the Pacific high, the winds normally flow either across the cold current toward shore (on-shore) or parallel to the coastline. This results in cool air being advected inland allowing cities such as San Francisco and Seattle to enjoy relatively cool summers. Unfortunately, when the warm, moist air from the Pacific high does move over the underlying cold current, extensive fog and stratus develop which also move inland. This situation is typical along the southern portions of the west coasts in both hemispheres.
Another factor affecting west coasts is upwell-ing.Upwelling is the process by which cold subsurface waters are brought to the surface by wind. It occurs in areas where the wind causes the surface water to be transported away from the coast. The surface water is then replaced by the colder subsurface water. In the Northern Hemisphere, upwelling is common where the wind blows parallel to the coast and the surface water is transported away from the coast. In the process of upwelling, the exchange of water takes place only in the upper layers.
Generally, the following statements are trueregarding the effects of ocean currents along the west coasts of continents:
. The west coasts of continents in middleand higher latitudes are bordered by warm waters which cause a distinct maritime climate characterized by cool summers and relatively mild winters with small annual range of temperatures (upper west coasts of the United States and Europe).
. The west coasts of continents in tropicaland subtropical latitudes (except close to the equator) are bordered by cool waters, and their average temperatures are relatively low with small diurnal and annual ranges. There are fogs, but generally the areas (southern California, Morocco, etc.) are arid (dry).
Effects on the East Coasts
The effects of currents along the eastern coastsof continents are less dramatic than those of the west coasts because of the west-to-east flow of weather. The effects, however, are just as significant.
In the tropical and subtropical regions, warmocean currents introduce warm, rainy climates, especially on the windward sides of mountainous land masses. As the warm currents progress northward into middle latitudes, warm, moist air produces a hot, humid climate with frequent rain showers during the summer. Winters are relatively moderate (but still cold) along the coast due to the transport of warm water. The higher latitudes along eastern shores normally have cold waters flowing southward from the polar region; warm ocean currents rarely extend very far north. The regions where the two currents meet have cool summers and cold winters with extensive fogs. This is especially true along the Grand Banks of Newfoundland and the Kamchatka Peninsula of eastern Asia.
The following general statements are trueregarding the effects of ocean currents along the eastern coasts of continents:
l The east coasts in the tropics and sub-tropicallatitudes are paralleled by warm currents and have resultant warm and rainy climates. These areas lie in the western margins of the subtropical anticyclone regions (Florida, Philippines, and Southeast Asia).
l The east coasts in the lower middlelatitudes (leeward sides of land masses) have ad-jacent warm waters with a modified continental-type climate. The winters are fairly cold, and the summers are warm and humid.
l The east coasts in the higher middlelatitudes typically experience cool summers with cool ocean currents paralleling the coasts.
Ocean currents also affect the location ofprimary frontal zones and the tracks of cyclonic storms. Off the eastern coast of the United States in the winter, two of the major frontal zones are located in areas where the temperature gradient is strong and where a large amount of warm water is being transported into the middle latitudes. The fact that these frontal zones are located near large amounts of energy suggests that cyclones develop-ing in these regions along the primary front may be of thermodynamic origin. The main hurricane tracks in the Atlantic and Pacific also appear to follow warm waters. Extratropical cyclones also tend to occur in warm waters in fall and early winter.