Effects of Ocean Currents

Introduction

Ocean currents have a large number of direct and indirect effects. Western margins of the continents within the tropics (except near the equator) are washed by cold currents which do not cause much rainfall. As such, these are areas of hot deserts with low humidity and high range temperature. In the middle and high latitudes, the west coasts of the continents are washed by warm currents and enjoy distinct marine climate. The mixing of warm and cold currents help to replenish the oxygen and favour the growth of planktons, the primary food for ship population. The best shing grounds of the world exist mainly in these mixing zones. Important ocean highways follow the favourable current, whenever possible.

Straits and Isthmuses

A strait is a narrow channel of water that connects two large bodies of water and at the same time separates two neighbouring land masses. For example, strait of Gibraltar connects Atlantic Ocean to the Mediterranean Sea and separates southern Spain in Europe from northern Morocco in Africa. The Bering Strait lies between Cape Dezhnev in Russia and Cape Prince of Wales in Alaska. Similarly, Palk Strait is situated between Tamil Nadu in India and Mannar district of Northern Province of Sri Lanka.

An isthmus is just an opposite of a strait because it represents a narrow strip of land connecting two large land masses and separating two large water bodies. Isthmus of Panama and that of Suez are the best examples of an isthmus. An isthmus is often cut to build a canal for providing short route for navigation. Panama Canal a cross the Panama Isthmus and Suez Canal a cross the Suez Isthmus are examples of international canals which provide short route facilities for navigating ships. Teleconnections, the Southern Oscillation, EI Nino and La Nina

Recent studies have revealed that there seems to be a link between meteorological events which are separated by long distances and large intervals of time. They are called meteorological teleconnections. The phenomena which have arouse considerable interest among the meteorologists are EI Nino, Southern Oscillation and La Nina.

El Nino

Is a warm subsurface current wing between 36°S and 3°S latitudes at a distance of about 180 km from the Peruvian coast. It comes into being as a result of southward shifting of the counter equatorial warm current during the southern winter. It replaces the northward wing Peru Current and its associated cold upwelling southward. Fisherman of Spanish descendants called this event as EI Nino. In Spanish, it means “The child Christ” because it usually appears around Christmas in late December. EI Nino was shift reported in 1541 and has been reported to occur frequently since then. EI Nino reduces monsoon rainfall in India.

Southern Oscillation (S.O.)

Southern Oscillation is the name ascribed to the curious phenomena of sea-saw pattern of meteorological changes observed between the Pacific and Indian oceans. This great discovery was made by Sir Gilbert Walker in 1920. While working as the head of the Indian Meteorological service, he noticed that when the pressure was high over equatorial south Pacific was low over the equatorial south Indian Ocean and vice versa. When there is low pressure over the Indian Ocean in winter, the chances are that the coming monsoon will be good and will cause rainfall. Due to the close association between and EI Nino (E.N.) and the Southern Oscillation (S.O.), the two are jointly referred to as an ENSO event.

La Nina

After an El-Nino, weather conditions return to normal. However, sometimes trade winds become so strong that they cause abnormal accumulation of cold water in the central and eastern Pacific region. This event is called La Nina (Spanish for “the girl”), which in effect is the complete reversal of EI Nino. The name was applied to the phenomena for the first time in 1986. A La Nina also marks an active hurricane season. But in India, the presence of La Nina brings exceptionally good news. It is the harbinger of heavy monsoon showers in India.

El Nino Modoki

It is a new type of El Nino which is more or less similar to El Nino but also differs from the original (from Japanese meaning similar but different). It has been recently observed in the Central Pacific rather than the Eastern Pacific as the normal El Nin o does. It is associated with warming of the Central Pacific Ocean which is caused by high frequency of storms. Some scientists believe that it is caused by global warming though no convincing evidence has been gathered till now. However, scientist feel that its prediction is much easier than the typical El Nino.

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