The North Atlantic Oscillation describes pressure fluctuations between the Icelandic low and the Azores high. This parameter is computed with the sea level pressures of Ponta Delgada on the Azores Islands and Reykjavík. A positive NAOI implies that increased westerlies are present, which result in cool and contrary weather conditions. If the NAOI is negative, then the westerlies are suppressed and blocking situations can occur, which are responsible for stable weather conditions. The index changes daily.
The Southern Oscillation is the atmospheric contributor to El Niño. The oscillation describes a reversal of surface pressure over Indonesia and the eastern Pacific. This index is used as an indicator for the strength of the southern oscillation and to assess the relative strength of the trade winds. If the Index is positive, the pressure over Indonesia is higher than over the eastern Pacific. This situation is referred to as El Niño. If the index is negative, the pressure over the eastern Pacific is higher. This situation is then referred to as La Niña. If the index is equal to zero, then neutral conditions are prevailing. The index changes daily.