Indian Ocean Dipole

The Indian Ocean Dipole ( IOD) (hence german sea -surface- temperature and short SST anomaly ) refers to a naturally occurring anomaly of sea surface temperature in the equatorial eastern and western end of the Indian Ocean ( Indian Ocean ). It accounts for about 12 % of the total temperature anomalies in the Indian Ocean.

From a strong IOD event is created when the western equatorial region near the Indiks warmer and the eastern part of the equator near Indiks is cooler than normal, which in the coupled ocean-atmosphere system has far-reaching consequences. Was first discovered this phenomenon in 1999. It is this system be based on a cycle duration of about 30 years in which alternating positive, negative, and neutral phases in six-month cycles. Similar systems are in the other two oceans, the Atlantic Ocean ( Atlantic Multi- decadal oscillation ) and Pacific ( Pacific Decadal Oscillation ) are also known.

Effects

The effects of this sea temperatures anomaly are quite different, especially in relation to the Indian monsoon. A positive IOD event falls on the west side of the Indian subcontinent less rainfall due to the reduced sea - land temperature and hence pressure difference, which is on the east coast now is again more pronounced and more precipitation falls here.

The IOD divides the Indian Ocean into two regions, in the Indonesian- Australian which should be considered as belonging together and the east coast of Africa. In these two regions, respectively always arises in a non-neutral phase one opposite the other region with low precipitation or precipitation rich phase. The precipitation patterns, but do not hang out here to the monsoonal winds as in India, and thus not on the land-sea Temperatur-/Druckunterschied, Australia and Indonesia and the equatorial part of East Africa are located so close to the equator that the existing pressure conditions (see Hadley cell and Intertropical convergence Zone ) temperature differences are not of the land-sea -dependent and the precipitate is simply controlled by the evaporation and convection over the sea, thus it comes with a regional decrease of SST in each case to less convection over the sea and therefore less rainfall and the probability of increasing drought. With a positive event so we have ahead of Australia and Indonesia lower SST and thus to less rainfall, while in the Middle East increased equatorial SST and therefore be accompanied more precipitation. A negative event always has exactly the opposite consequences.

Interaction with El Niño - Southern Oscillation

Since the (short ENSO ) index is usually defined by the difference in air pressure between the Indonesia area of ​​low pressure and the high pressure of the Peruvian El Niño - Southern Oscillation interactions are not surprising, since the Indonesian Deep is also a sub-element of the IOD. A positive IOD event can be triggered by a positive ENSO event, but also a IOD event can trigger a positive ENSO event, but the internal variability of the system also allows one occurrence of different phases without external influences. The existing teleconnections work on the atmosphere, so a positive IOD phase can produce a negative SST anomaly (due to upwelling ) off Indonesia and the associated pressure drop, an occurrence of a positive ENSO event.