Synoptic-scale dust emissions over the Sahara Desert initiated by a moist convective cold pool in early August 2006

Diana Bou Karam, Earle Williams, Matthew Janiga, Cyrille Flamant, Michael Mcgraw-Herdeg, Juan Cuesta, Antoine Auby, Chris Thorncroft

Research output: Contribution to journalArticlepeer-review

Abstract

This article is concerned with a dust-raising cold pool over the Sahara desert that occurred on 3-5 August 2006. Both the quantity of the uplifted dust and its spatio-temporal evolution are examined using satellite observations and a numerical simulation. The dust emission during this event was initiated by a mesoscale cold pool emanating from mesoscale convective systems (MCSs) that developed over northern Niger and Mali on 3 August. This event is one of several exceptional northward surges of the West African Monsoon (WAM) during the 2006 wet season. We examine the propagation of the cold pool and associated dust lofting using high temporal resolution false-colour dust product images from the Meteosat Second Generation Spinning Enhanced Visible and InfraRed Imager (MSG-SEVIRI). Observations from Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) are used to characterize the vertical structure of the dust cloud as it spreads over the Sahara and across the Atlantic coast. The European Centre for Medium-range Weather Forecasts African Monsoon Multidisciplinary Analysis (ECMWF-AMMA) special reanalysis was used to describe the synoptic conditions that accompanied this event. Furthermore, a numerical simulation using the mesoscale model MesoNH was performed to estimate the emissions and the westward transport of dust during this event. MODIS aerosol optical depth (AOD) satellite imagery has then been used to track the dust plume across the Atlantic Ocean to Barbados, where comparisons are made with the local dust record there. The dusty cold pool covered southern Algeria and a large part of northern Mali and western Niger attaining a total area close to 2 × 106 km2. It extended over 2-3 km in altitude and had an AOD on the order of 1.5 and an estimated total dust load of about 1.5 Tg on average. Following daytime heating, the dusty cold pool and associated northward surge of moisture favoured the development of new convection and additional precipitation over the Sahara. The northward extension of the dusty cold pool was accompanied by a collapse of the Saharan heat-low, a characteristic feature of monsoon surges. A model-estimated quantity of 0.4 Tg of the dust produced during this event was subjected to westward transport toward the Atlantic Ocean after being mixed upward in the thickening boundary layer by the daytime heating over the Sahara to altitudes as high as 5-6 km. The arrival of the dust plume in Barbados in the Caribbean Sea 9 days after its departure from the west coast of Africa was characterized by a peak in dust concentration of 48.5 μg m-3.

Original languageEnglish (US)
Pages (from-to)2591-2607
Number of pages17
JournalQuarterly Journal of the Royal Meteorological Society
Volume140
Issue number685
DOIs
StatePublished - Oct 1 2014

Keywords

  • Cold pool
  • Density current
  • MesoNH
  • Mesoscale convective systems
  • Mineral dust
  • Monsoon surge
  • Saharan Heat-Low (SHL)
  • West African Monsoon

ASJC Scopus subject areas

  • Atmospheric Science

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