John Marsham
School of Earth and Environment
University of Leeds, United Kingdom
The atmosphere of West Africa provides the setting for a unique
variety of convective phenomena: the Sahara in the north has the
deepest dry convective boundary layer in the world (reaching 6 km) and
to the south in the Sahel mesoscale convective systems embedded in the
West African monsoon provide the majority of the rainfall. The talk
will describe work centered on the GERB Intercomparison of Longwave
and Shortwave radiation (GERBILS) field campaign, which took place on
the southern border of the Sahara during June 2007.
Our current failure to represent the Saharan atmosphere accurately in
weather and climate models has important implications. The Saharan
Heat Low is a major control on regional dynamics,especially of the
West African monsoon. Hurricane precursors are also generated by the
African Easterly Jet. The Sahara is the world's largest source of
desert dust, and dust loadings have been linked to hurricane activity.
Dust is a key component of our climate, interacting with radiation
(affecting regional dynamics), nucleating ice clouds and providing
iron to the biosphere.
In the Sahara, observations show the common persistence of a split
boundary layer, with a residual layer above a convective boundary
layer. Complex layerings of dust and moisture and are frequently
observed in this residual layer. Dynamical mechanisms that allow
exchange between the convective and residual layers, and the
maintenance of the residual layers, will be discussed. Recent field
campaigns have also highlighted the role of convection in the uplift
of Saharan and Sahelian dust - through nocturnal low-level jets, the
diurnal cycle of the monsoon flow, and outflows from deep convective
storms. Results from GERBILS will be presented in the context of these
recent studies, focusing on the potential role of convective outflows
in the seasonal cycle of dust in the region.
Friday, 9 January 2009, 9:30 AM
Refreshments 9:15 AM
NCAR-Foothills Laboratory
3450 Mitchell Lane
Bldg 2 Auditorium (Rm1022)
For more information, contact Petter Weibring at ext. 2052, weibring@ucar.edu.
Fri, Dec 26, 2008 to Fri, Jan 9, 2009
