Scientific Calendar Event

Starts 29 Jan 2020 10:00
Ends 29 Jan 2020 11:00
Central European Time
ExSISSA Central Area
Via Beirut 2-4

The west African monsoon (WAM) originates in the gulf of Guinea, when the intertropical convergence zone (ITCZ) makes its landfall. The south Asian monsoon (SAM) originates in the Indian ocean when the ITCZ crosses the equator. Historically, these monsoons as been seen as giant sea breezes; but now days, it has been recognized that the low-level convergence due to the increased friction after landfall plays an important role in monsoonal flows. Thus, in this study we have implanted an Ekman frictional layer (EFL) in Gill’s tropospheric model for studying the mutual influence between WAM and SAM. Results show that WAM has an influence on SAM via Kelvin modes by driving a Walker-like circulation with the lower-level westerlies and he upper-level easterlies over the Tropical Indian ocean, and that SAM has an influence over WAM via long planetary modes by driving the subsidence over the north African deserts. In the upper-layer, air particles spiral-out anticyclonically away from SAM and from WAM, reaching the Tropical Atlantic and the Tropical Indian ocean, or transiting into the southern hemisphere by crossing the equator. In the absence of orography, marine air particles spiral-in cyclonically towards WAM or SAM, the latter been a preferred ending destination. The Somali mountains (SM), introduced as a barrier to the Ekman winds, split the lower cyclonic circulation in two cyclones, separating the ketch basin of WAM from that of SAM. Thus, marine air particles originated to the west of SM stay in the ketch basin of WAM; whilst, marine air particles, originated over the Indian ocean, stay in the ketch basin of SAM. The Indian Ghats (IG), introduced as a semi-impermeable barrier to the Somali jet, lift the marine air particles carried by this jet into SAM; whilst, particles originated in the eastern Indian ocean reach the eastern flank of SAM.