Possible Causes of the Interdecadal Transition of the Somali Jet Around the Late 1990s

This observational study demonstrates that the Somali jet (SMJ) experienced a notable interdecadal transition in not only its lower-level parts ( 850 hPa) but also its higher-level parts (850-600 hPa) in the late 1990s. The results also show that the jet at higher level is more significantly related to East Asian monsoon rainfall than that at lower level. Thus, a new whole-layer SMJ (WSMJ) index which includes variations of the higher-level jet is defined based on the average meridional wind speed at five levels (1000-600 hPa). The interdecadal transition of the SMJ can be mainly attributed to the meridional thermal contrast anomalies near the equator which are associated with the three-pole pattern of the southern Indian Ocean.