Diana BOU KARAM » abstract

Sharav dust storm

admin — Sat, 30 Jan 2010 09:42:02 +0000

Bou Karam D., C. Flamant, J. Cuesta, J. Pelon, E. Williams (2010):

Dust emission and transport associated with Saharan depressions: The February 2007 case.

Abstract

The dust activity over North Africa associated with the Saharan depression event in February 2007 is investigated by mean of spaceborne observations and ground based measurements. The main characteristics of the cyclone as well as the meteorological conditions during this event are described using the European Centre for Medium-range Weather Forecasts (ECMWF). The dust storm and cloud cover over North Africa is thoroughly described combining for the first time Spinning Enhanced Visible and Infra-Red Imager (SEVIRI) images for the spatio-temporal evolution and Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) and CloudSat observations for the vertical distribution.

The Saharan depression formed over Algeria in the lee of the Atlas Mountain on the afternoon of February 20 in response to midlatitude trough intrusion. It migrated eastward with a speed of 11 m s^-1 and reached Libya on February 22 before exiting the African continent toward the Mediterranean Sea on February 23. The horizontal scale of the cyclone at the surface varied between 800 km and 1000 km during its lifetime. On the vertical the cyclone extended over 8 km and a potential vorticity of 2 PVU was reported on its centre at 3km in altitude. The cyclone was characterised by a surface depth of 9 hPa, a warm front typified at the surface by an increase in surface temperature of 5°C, and a sharp cold front expressed by a drop in surface temperature of 8°C and an increase in 10m wind speed of 15 m s^-1.

The cyclone provided a dynamical forcing that led to strong near-surface winds and produced a major dust storm over North Africa. Heavy dust load was seen along the cold front and the southeastern edge of the cyclone accompanied by a deep cloud band along its northwestern edge. The dust was transported all around the cyclone leaving a clear eye on its centre. On the vertical, slanted dust layers were consistently observed during the event over North Africa. Furthermore, the dust was lofted to altitudes as high as 7 km, becoming subject to long range transport.

Key Words: Mediterranean cyclone, CloudSat, ECMWF, North Africa, Sharav cyclone, CALIPSO.

Bou Karam D., C. Flamant, J. Cuesta, J. Pelon, E. Williams (2010): Dust emission and transport associated with a Saharan depression: The February 2007 case , J. Geophys. Res., doi:10.1029/2009JD012390.

Model inter-comparisons of dust emission over the Bodélé Depression

admin — Sat, 30 Jan 2010 09:45:14 +0000

M.C. Todd, D. Bou Karam, C. Cavazos, C. Bouet, B. Heinold, G. Cautenet, P. Tulet, C. Perez, I. Tegen, and R. Washington: “Quantifying uncertainty in estimates of mineral dust flux: an inter-comparison of model performance over the Bodélé Depression, Northern Chad”, J. Geophys. Res., 113, D24107, 2008, doi:10.1029/2008JD010476.

Abstract

Mineral dust aerosols play an important role in the climate system. Coupled climate aerosol models are an important tool with which to quantify dust fluxes and the associated climate impact.

In recent years, numerous models have been developed but to date there have been few attempts to compare the performance of these models. In this paper a comparison of five regional atmospheric models with dust modules is made, in terms of their simulation of meteorology, dust emission and transport.

The inter-comparison focuses on a 3-day dust event over the Bodélé depression in Northern Chad, the world’s single most important dust source. Simulations are compared to satellite data and in-situ observations from the Bodélé Dust Experiment (BoDEx 2005).

Overall, the models reproduce many of the key features of the meteorology and the large dust plumes that occur over the study domain. However, there is at least an order of magnitude range in model estimates of key quantities including, dust concentration, dust burden, dust flux and AOT.

As such, there remains considerable uncertainty in model estimates of the dust cycle and its interaction with climate. The paper discusses the likely sources of this model uncertainty.

Biomass burning aerosol characterisctics over Benin

admin — Sat, 30 Jan 2010 09:46:27 +0000

Pelon, J., M. Mallet, A. Mariscal, P. Goloub, D. Tanré, D. Bou Karam, C. Flamant, J. Haywood, B. Pospichal, S. Victori: “Characterisation of biomass burning aerosol from microlidar observations at Djougou (Benin) during AMMA-SOP0/DABEX”, J. Geophys. Res., 113, D00C18, doi:10.1029/2008JD009976.

Abstract:

Microlidar observations performed at the Djougou-Nangatchori site in northern Benin, have been performed during the AMMA-SOP 0/DABEX intensive observation period of AMMA in the dry season, from mid-January to mid-February 2006. During the dry season, the Djougou area is a region where biomass burning aerosols are heavily produced from agriculture fires.

The aerosol vertical distribution is also controlled by dynamics, as the penetration of the winter monsoon flux to the north, and northern winds bring mineral dust leads to a frontal discontinuity location close to Djougou latitude. During the early dry season, the aerosol vertical distribution was observed to be structured in two layers, the lower being the boundary layer reaching altitudes up to 2 km, and an upper layer reaching 4 to 5 km.

Lidar data are used to retrieve the time evolution and vertical profile of extinction, and discuss transport processes during the period analyzed. As the monsoon flux during the dry season is steadily progressing to the north, but also moving back and forth according to shorter time scale forcings, biomass burning particles are transported from the boundary layer into the upper troposphere. This transport has a strong impact on the distribution of aerosol particles on the vertical, and extinction values larger than 0.3 km-1 have been retrieved at altitudes close to 3 km.

A particular event of biomass burning air mass outbreak associated with a synoptic forcing is studied, where satellite observations are used to discuss observations of biomass burning particles over Djougou and at the regional scale.