ESP GUEST SEMINAR - Wednesday, 29 January 10:00

[Earth System Physics Section]

Earth System Physics
SPECIAL GUEST SEMINAR
Wednesday, 29 January - 10:00
Central Area, 2nd Floor, ex-SISSA Bldg.

Giovanni A. Dalu

Studying monsoonal flows with Gill’s model with an Ekman layer


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.