Mineral dust emission from the Bodélé Depression, northern Chad, during BoDEx 2005

Mineral dust in the atmosphere is an important component of the climate system but is poorly quantified. The Bodele depression of Northern Chad stands out as the world’s greatest source region of mineral dust into the atmosphere. Frequent dust plumes are a distinguishing feature of the region’s climate. There is a need for more detailed information on processes of dust emission/transport and dust optical properties to inform model simulations of this source. During the Bodele Dust Experiment (BoDEx) in 2005 instrumentation was deployed to measure dust properties and boundary layer meteorology. Observations indicate that dust emission events are triggered when near surface wind speeds exceed 10ms-1, associated with synoptic scale variability in the large-scale atmospheric circulation. Dust emission pulses in phase with the diurnal cycle of near surface winds. Analysis of dust samples shows that the dust consists predominantly of fragments of diatomite sediment. The particle size distribution of this diatomite dust estimated from sun photometer data, using a modified Aeronet retrieval algorithm, indicate a dominant coarse mode (radius centred on 1-2?m) similar to other Saharan dust observations. Single scattering albedo values are high, broadly in line with other Saharan dust even though the diatomite composition of dust from the Bodele is likely to be unusual. The radiative impact of high dust loadings results in a reduction in surface daytime maximum temperature of around 7°C in the Bodele region. Using optical and physical properties of dust obtained in the field we estimate the total dust flux emitted from the Bodele to be 1.18±0.45Tg per day during a substantial dust event. We speculate that the Bodele depression (~10,800km2) may be responsible for between 6-18% of global dust emission, although the uncertainty in both the Bodele and global estimates remain high.

[1]  Dale A. Gillette,et al.  Fine Particulate Emissions Due to Wind Erosion , 1977 .

[2]  Michael Garstang,et al.  Saharan dust in the Amazon Basin , 1992 .

[3]  Nick Middleton,et al.  The changing frequency of dust storms through time , 1992 .

[4]  J. Dudhia.  A Nonhydrostatic Version of the Penn State–NCAR Mesoscale Model: Validation Tests and Simulation of an Atlantic Cyclone and Cold Front , 1993 .

[5]  I. Fung,et al.  Modeling of mineral dust in the atmosphere: Sources, transport, and optical thickness , 1994 .

[6]  G. Grell,et al.  A description of the fifth-generation Penn State/NCAR Mesoscale Model (MM5) , 1994 .

[7]  P. Bhartia,et al.  Global distribution of UV-absorbing aerosols from Nimbus 7/TOMS data , 1997 .

[8]  Mian Chin,et al.  Contribution of different aerosol species to the global aerosol extinction optical thickness: Estimates from model results , 1997 .

[9]  P. Formenti,et al.  Optical properties of Saharan dust during ACE 2 , 1998 .

[10]  A. Smirnov,et al.  AERONET-a federated instrument network and data archive for aerosol Characterization , 1998 .

[11]  Ina Tegen,et al.  Climate Response to Soil Dust Aerosols , 1998 .

[12]  Alexander Smirnov,et al.  Cloud-Screening and Quality Control Algorithms for the AERONET Database , 2000 .

[13]  Michael D. King,et al.  A flexible inversion algorithm for retrieval of aerosol optical properties from Sun and sky radiance measurements , 2000 .

[14]  K. Shine.  Radiative Forcing of Climate Change , 2000 .

[15]  W. Collins,et al.  Simulating aerosols using a chemical transport model with assimilation of satellite aerosol retrievals: Methodology for INDOEX , 2001 .

[16]  M. Chin,et al.  Sources and distributions of dust aerosols simulated with the GOCART model , 2001 .

[17]  B. Holben,et al.  A dust outbreak episode in sub‐Sahel West Africa , 2001 .

[18]  Yoram J. Kaufman,et al.  Absorption of sunlight by dust as inferred from satellite and ground‐based remote sensing , 2001 .

[19]  T. Eck,et al.  Variability of Absorption and Optical Properties of Key Aerosol Types Observed in Worldwide Locations , 2002 .

[20]  M. Heimann,et al.  Impact of vegetation and preferential source areas on global dust aerosol: Results from a model study , 2002 .

[21]  O. Torres,et al.  ENVIRONMENTAL CHARACTERIZATION OF GLOBAL SOURCES OF ATMOSPHERIC SOIL DUST IDENTIFIED WITH THE NIMBUS 7 TOTAL OZONE MAPPING SPECTROMETER (TOMS) ABSORBING AEROSOL PRODUCT , 2002 .

[22]  N. C. Hsu,et al.  Radiative Forcing of Saharan Dust: GOCART Model Simulations Compared with ERBE Data , 2002 .

[23]  Oleg Dubovik,et al.  Non‐spherical aerosol retrieval method employing light scattering by spheroids , 2002 .

[24]  Paul Ginoux,et al.  A Long-Term Record of Aerosol Optical Depth from TOMS Observations and Comparison to AERONET Measurements , 2002 .

[25]  R. Washington,et al.  Dust-Storm Source Areas Determined by the Total Ozone Monitoring Spectrometer and Surface Observations , 2003 .

[26]  Jonathan P. Taylor,et al.  Radiative properties and direct effect of Saharan dust measured by the C‐130 aircraft during Saharan Dust Experiment (SHADE): 2. Terrestrial spectrum , 2003 .

[27]  P. Formenti,et al.  Measurement and modeling of the Saharan dust radiative impact: Overview of the Saharan Dust Experiment (SHADE) , 2003 .

[28]  Peter J. Lamb,et al.  African Droughts and Dust Transport to the Caribbean: Climate Change Implications , 2003, Science.

[29]  P. Formenti,et al.  Radiative properties and direct radiative effect of Saharan dust measured by the C-130 aircraft during SHADE: 1. Solar spectrum , 2003 .

[30]  B. Holben,et al.  Comparison of aerosol size distributions, radiative properties, and optical depths determined by aircraft observations and Sun photometers during SAFARI 2000 , 2003 .

[31]  C. Timmreck,et al.  Monthly Averages of Aerosol Properties: A Global Comparison Among Models, Satellite Data, and AERONET Ground Data , 2003 .

[32]  C. Zender,et al.  Mineral Dust Entrainment and Deposition (DEAD) model: Description and 1990s dust climatology , 2003 .

[33]  Sundar A. Christopher,et al.  Longwave radiative forcing of Saharan dust aerosols estimated from MODIS, MISR, and CERES observations on Terra , 2003 .

[34]  Didier Tanré,et al.  Modeling the radiative impact of mineral dust during the Saharan Dust Experiment (SHADE) campaign , 2003 .

[35]  Soon-Ung Park,et al.  Parameterization of dust emission for the simulation of the yellow sand (Asian dust) event observed in March 2002 in Korea , 2003 .

[36]  C. Zender,et al.  Quantifying mineral dust mass budgets:Terminology, constraints, and current estimates , 2004 .

[37]  Yoram J. Kaufman,et al.  Direct wind measurements of Saharan dust events from Terra and Aqua satellites , 2004 .

[38]  Steven Platnick,et al.  Spatially complete global spectral surface albedos: value-added datasets derived from Terra MODIS land products , 2005, IEEE Transactions on Geoscience and Remote Sensing.

[39]  Richard Washington,et al.  Atmospheric controls on mineral dust emission from the Bodélé Depression, Chad: The role of the low level jet , 2005 .

[40]  J. Giles.  Climate science: The dustiest place on Earth , 2005, Nature.

[41]  Nicolas Clerbaux,et al.  Can desert dust explain the outgoing longwave radiation anomaly over the Sahara during July 2003 , 2005 .

[42]  Yoram J. Kaufman,et al.  Dust transport and deposition observed from the Terra‐Moderate Resolution Imaging Spectroradiometer (MODIS) spacecraft over the Atlantic Ocean , 2005 .

[43]  Jean-François Léon,et al.  Application of spheroid models to account for aerosol particle nonsphericity in remote sensing of desert dust , 2006 .

[44]  O. Dubovik,et al.  Modelling soil dust aerosol in the Bodélé depression during the BoDEx campaign , 2006 .

[45]  Y. Kaufman,et al.  The Bodélé depression: a single spot in the Sahara that provides most of the mineral dust to the Amazon forest , 2006 .

[46]  Richard Washington,et al.  Dust and the low‐level circulation over the Bodélé Depression, Chad: Observations from BoDEx 2005 , 2006 .