Tropical climate variations and their impacts on circulation and precipitation in the Northwest Indian Ocean - Northeast Africa - Southwest Asia region

We have examined the relationships between intraseasonal and interannual climate variations occurring in and affecting the tropical eastern hemisphere, from the tropical Atlantic to the maritime continent. The variations of primary interest are El Nino-La Nina (ENLN), the Indian Ocean Zonal Mode (IOZM), and the Madden-Julian Oscillation (MJO). Our focus region is the northwest Indian Ocean, northeast Africa, and southwest Asia. Our goals are to determine: (1) how tropical climate variations alter circulations in our focus region; and (2) how these altered circulations contribute to fall-winter precipitation anomalies in the focus region. Our primary data sets are NCEP reanalysis fields, several satellite based water vapor and precipitation fields, and indices of ENLN, IOZM, and MJO activity.

We have identified several upper and lower level circulation anomaly patterns that are directly linked to tropical climate variations and to anomalous precipitation in the focus region. The circulation anomalies associated with positive and negative precipitation anomalies are similar for ENLN, IOZM, and MJO periods. The mechanisms for these circulation anomalies involve equatorial Rossby-Kelvin wave dynamics and related alterations of the southwesterly and northeasterly monsoon flows, tropical easterly jet, and subtropical jet in our focus region. Much of the impact on precipitation occurs through: (1) anomalous moisture advection over the tropical northwest Indian Ocean and tropical and subtropical north Africa; and (2) anomalous moisture convergence. We have developed a new climate index to characterize and monitor the circulation anomalies associated with periods of anomalously high and low precipitation. ENLN, IOZM, and MJO occur at intraseasonal to interannual scales, and are relatively predictable once initiated. Thus, the potential for intraseasonal and longer forecasts of related circulation and precipitation anomalies in the northwest Indian Ocean, northeast Africa, and southwest Asia may be relatively high.