Relation Between the Madden Julian Oscillation with Wet and Dry Spells During Belg Season Over Ethiopia

Abstract

The main objective of this study is to explore seasonal impacts of the Madden–Julian oscillation (MJO) on tropospheric circulations affecting Ethiopia during Belg (March–May) rains and associated variability in precipitation. The data used daily rainfall, daily Madden-Julian (MJO) indices, daily Outgoing Longwave Radiation (OLR) and zonal and meridional wind data. The methods used for this study is Correlation and composite analyses are used to establish the association and the relationship between the MJO and rainfall over Ethiopia. A non-significant declining trend in annual rainfall across Ethiopia has been observed over the past three decades trend change per year over by -0.602 mm and P-Value 0.338. The mean length of wet spells 90 days over SNNPR and Southern Oromia Region, and with a least mean length of wet spell is 10 days over Afar, Tigray and western Amhara Region. The results reveals that there is a strong correlation between Ethiopian rainfall and MJO to the west of the region especially around Central and Southeastern parts of the Country. Out of phase (opposite) relationship between the west and the east is also indicating different rain causing mechanisms for the two regions. The rainfall amount also shown to depend on the configuration of the winds at lower and upper levels. Based on composite analysis extreme rainfall events shown to occur during preferential phases of the MJO. Phase 2 coincides with enhanced rainfall, high negative anomaly OLR values as well as westerly and easterly winds configuration at 200hpa and 850hpa while phase 5, 6 and 7 are associated with deficit of rainfall. The inclusion of other modes of variability such as Sea surface Temperatures (SSTs) and the Indian Ocean Dipole (IOD), as predictors recommended in predicting interaseasonal rainfall.