Middle East and Southwest Asia Daily Precipitation Characteristics Associated with the Madden−Julian Oscillation during Boreal Winter

While previous research has shown a robust relationship between the Madden Julian Oscillation (MJO) and Middle East and Southwest Asia (MESW) precipitation during the region’s November-April rainy season, how the relationship changes over the course of the season and how the relationship is expressed through changes in precipitation frequency and intensity has so far only received limited attention. Closing this knowledge gap will provide insights into potential MESW subseasonal precipitation prediction skill, and ultimately the region’s water and agricultural resources, given the importance of infrequent storms to the annual precipitation.

Therefore, the spatial and temporal evolution of MESW precipitation characteristics and the associated atmospheric circulation during times in which tropical eastern Indian Ocean precipitation is either enhanced or reduced associated with the MJO is assessed. Using multiple estimates of both the observed precipitation and the MJO during 1981-2016, the evolution of MESW precipitation characteristics throughout November-April is examined in terms of monthly precipitation accumulation on precipitation days, the number of precipitation days and the number of extreme precipitation days.

MJO phases 2-4, during which eastern Indian Ocean precipitation is enhanced, and MJO phases 6-8, during which eastern Indian Ocean precipitation is reduced, are related with significant decreases and increases in the number of precipitation days across MESW, respectively. The patterns of precipitation day changes between MJO phases undergo noteworthy spatial and temporal evolutions across the boreal cold season that are influenced by the interaction between Rossby wave forcing by the MJO and seasonal changes in both the upper-level jet and low-level moisture over the region. During December-January, the changes in precipitation days are found primarily over northern MESW, while during February-March, the changes in precipitation days are found primarily over southern MESW. Although the results identify an important sensitivity in the number of precipitation days over the MESW related to the MJO, the same sensitivity is not apparent in terms of the number of extreme precipitation days and, in particular, the amount of precipitation on a precipitation day.