355 MJO Phase Speed and Rainfall Variability Over the Congo Rainforest

Monday, 23 January 2017
4E (Washington State Convention Center )
Ajay Raghavendra, SUNY, Albany, NY; and L. Zhou, N. J. Schiraldi, and P. E. Roundy

Handout (2.0 MB)

A long-term reduction in precipitation over the Congo Basin has been observed for the past two decades. The well-documented gradual reduction of rainfall has important environmental implications, particularly over the Congo rainforest, the second largest rainforest on Earth. The influence of weather over the African rainforests is also important from a climate standpoint. While recent short-term droughts prompted numerous studies to look into the impacts of anomalously low rainfall over the Amazon rainforest, scientific literature on precipitation and rainfall variability over the Congo rainforest is sparse. Rainfall over Central African usually peaks around the months of April and October. Given the similar time scales of the Madden–Julian oscillation (MJO) cycle that varies between 30 – 60 days and the periods of heightened precipitation over central Africa, a possible correlation exists between the MJO phase speed and precipitation over the Congo rainforest. Monthly and seasonal periods of anomalous precipitation were identified from the National Centers for Environmental Prediction (NCEP) National Center for Atmospheric Research (NCAR) Reanalysis data. These precipitation anomalies were then studied using the MJO phases captured by the Wheeler-Hendon Diagram.  It was found that fast moving favorable i.e. wet MJO phases and slow moving unfavorable i.e. dry MJO phases for Africa results in anomalously low precipitation and subsequent drought. For example, Africa experienced a severe drought in 2005 (2005 was a weak ENSO year) and in the months of April and May, the MJO lasted 1.5 cycles. Suppressed precipitation over Africa during this time can be attributed to the MJO dry phase lasted 25 days and the wet phase lasting only 12 days for Africa.  More such case studies will be analyzed and relevant physical mechanisms for the drought-MJO teleconnection will be explored.
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