Seasonal Indian Ocean Rim Drought in the Absence of La Niņa and the Indian Ocean Dipole

Rainfall extremes during March-May over East Africa and Central-Southwest Asia are often closely related with the phase of El Niņo Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD). La Niņa, the cold phase of ENSO, and a negative phase of the Indian Ocean Dipole, characterized by warm sea surface temperatures (SSTs) over the southeastern tropical Indian Ocean and cold SSTs over the northwestern Indian Ocean, are linked to widespread regional drought over continental areas of the northwest Indian Ocean Rim. However, the 1980 and 2004 March-May seasons over both East Africa and Central Asia experienced strongly reduced precipitation in the absence of La Niņa and the Indian Ocean Dipole. Here, we examine the forcing of drought over the northwest Indian Ocean Rim for the 1980 and 2004 March-May seasons with an emphasis on the potential predictability of future droughts of this nature.

The regional circulations over the northwest Indian Ocean Rim during MAM 1980 and 2004 were very similar. Both were dominated by a strong middle tropospheric cyclone centered over the Arabian Peninsula. These cyclones were responsible for strong regional precipitation-reducing subsidence and moisture flux divergence over East Africa and Central Asia. During the MAM 1980 and 2004 seasons, the regional circulations over the northwest Indian Ocean Rim were linked to increases in middle tropospheric diabatic forcing over the south-central Indian Ocean.