[Eoas-seminar] EOAS Colloquium Firday Nov 13 at 3:30pm

[eoas-seminar at lists.fsu.edu]

Please join us Friday at 3:30 on zoom for this week's EOAS Colloquium 
speaker:


Dr. Sharon Nicholson of EOAS at FSU


Time: Nov 13, 2020 03:30 PM Eastern Time (US and Canada)

Join Zoom Meeting
https://fsu.zoom.us/j/93321272960

Meeting ID: 933 2127 2960

*RAINFALL ENHANCEMENT OVER THE EAST AFRICAN LAKES*

The numerous lakes of the East African Rift Valley are a major resource 
for the countries of the region.The largest, Lake Victoria, sustains the 
livelihood of some 30 million people and its level determines the flow 
the Nile, the lifeblood of Egypt, Sudan and South Sudan.Rainfall over 
the lake occurs mainly at night and in the early morning and is known to 
be enhanced by some 50% compared to rainfall in its catchment.The 
enhancement is a combined result of lake/land breezes and 
mountain/valley winds. The nocturnal rainfall is coupled with intense 
thunderstorms, which result in some 5,000 deaths annually.

This talk presents an in-depth view of the lake-effect rains over Lake 
Victoria and a brief overview of the enhancement by other East African 
lakes.Both the seasonal and diurnal cycles over Lake Victoria are 
analyzed in the context of meteorological parameters that might control 
rainfall.These include winds and wind divergence, vertical motion, 
convective available potential energy (C.A.P.E.) and Mesoscale 
Convective Systems (MCSs).The meteorological analysis is based on 
ERA5.Several satellite rainfall products were evaluated and TRMM 3B43 
and 3B42 were determined to perform best in this region and utilized for 
the analyses.

Several new conclusions about the lake-effect rains have emerged.For 
one, there is substantial enhancement of rainfall over Lake Victoria in 
all months, even during the two dry seasons.Rainfall enhancement is also 
apparent over numerous other lakes in the region, even small ones.Some 
of the enhancement occurs during the dry season when the catchment is 
rainless.The magnitude of the enhancement is driven by large-scale 
meteorological factors as opposed to local conditions over the lakes.For 
example, the patterns of low-level divergence over the lake are similar 
in dry season and wet season months. Most of the rainfall over Lake 
Victoria is from MCSs that develop in situ at night.

A surprising conclusion that emerged is that the relatively new IMERG 
data of the Global Precipitation Measurement (GPM) mission vastly 
overestimates rainfall over inland water bodies, such as Lakes Victoria, 
Malawi, and Tanganyika.This appears to be related to the passive 
microwave sources incorporated into the final product.

Victoria_satellite.jpg




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