Impact of anthropogenic aerosols on climate variability over Central Africa by using a regional climate model

In the present study, we have investigated the impacts of anthropogenic aerosols on some relevant atmospheric parameters such as temperature, precipitation, wind and shortwave radiation. For this aim, we use the International Centre for Theoretical Physics (ICTP) regional climate model version 4 named RegCM4. Two sets of simulations with 1 year of spin-up, from 2001 to 2006, identical in their structure have been conducted: one includes the interactions of anthropogenic aerosols (ExpA) and another simulation which does not (Exp). In this regard, it should be noted that discrepancies between ExpA and Exp estimate the impact of the aerosol direct effect. The shortwave radiative forcing associated with the anthropogenic aerosols is negative throughout the entire domain with more negative values up to −6 W m-2 over the latitudinal band 0°–10°N during DJF accordingly to the main sources region. This induces cooling at surface higher than 0.4 °C. Elsewhere over the raining area, the effect on precipitation is largely negative and the reduction can reach up to 1 mm day−1. Moreover, the atmospheric circulation is not systematically affected even though we note a variation of wind speed in the vicinity of the latitudinal band 6°–10°N resembling a dipole pattern. The results also highlight that irrespective of the season, aerosols lead to enhance the moisture divergence mostly over the Guinea Gulf around Nigerian and Cameroonian coasts. This study provides evidence that anthropogenic aerosols influence climate variability and hydrological cycle mostly during dry season.

[1]  Wayne Howard Schubert.  The Interaction of a Cumulus Cloud Ensemble with the Large Scale Environment. , 1973 .

[2]  B. Briegleb.  Delta‐Eddington approximation for solar radiation in the NCAR community climate model , 1992 .

[3]  Christopher S. Bretherton,et al.  A New Parameterization for Shallow Cumulus Convection and Its Application to Marine Subtropical Cloud-Topped Boundary Layers. Part I: Description and 1D Results , 2004 .

[4]  Robert E. Dickinson,et al.  Intercomparison of Bulk Aerodynamic Algorithms for the Computation of Sea Surface Fluxes Using TOGA COARE and TAO Data , 1998 .

[5]  Ann Henderson-Sellers,et al.  Biosphere-atmosphere Transfer Scheme (BATS) for the NCAR Community Climate Model , 1986 .

[6]  G. Grell.  Prognostic evaluation of assumptions used by cumulus parameterizations , 1993 .

[7]  M. Ha-Duong,et al.  Climate change 2014 - Mitigation of climate change , 2015 .

[8]  P. Jones,et al.  Representing Twentieth-Century Space-Time Climate Variability. Part II: Development of 1901-96 Monthly Grids of Terrestrial Surface Climate , 2000 .

[9]  Jeffrey T. Kiehl,et al.  Twentieth century climate model response and climate sensitivity , 2007 .

[10]  C. Willmott,et al.  A refined index of model performance , 2012 .

[11]  A. Arakawa,et al.  Interaction of a Cumulus Cloud Ensemble with the Large-Scale Environment, Part I , 1974 .

[12]  P. J. Rasch,et al.  Radiative forcing due to sulfate aerosols from simulations with the National Center for Atmospheric Research Community Climate Model, Version 3 , 2000 .

[13]  F. Giorgi,et al.  Indirect vs. Direct Effects of Anthropogenic Sulfate on the Climate of East Asia as Simulated with a Regional Coupled Climate-Chemistry/Aerosol Model , 2003 .

[14]  Raquel V. Francisco,et al.  Regional Climate Modeling for the Developing World: The ICTP RegCM3 and RegCNET , 2007 .

[15]  Ivan Güttler,et al.  RegCM4 : model description and preliminary tests over multiple CORDEX domains , 2012 .

[16]  F. Giorgi,et al.  Regional simulation of anthropogenic sulfur over East Asia and its sensitivity to model parameters , 2001 .

[17]  K. Prather,et al.  Direct observations of the atmospheric processing of Asian mineral dust , 2006 .

[18]  Christopher S. Bretherton,et al.  A Moist PBL Parameterization for Large-Scale Models and Its Application to Subtropical Cloud-Topped Marine Boundary Layers , 2001 .

[19]  V. Ramanathan,et al.  Aerosols, Climate, and the Hydrological Cycle , 2001, Science.

[20]  F. Giorgi,et al.  Modeling of sea salt in a regional climate model: Fluxes and radiative forcing , 2008 .

[21]  Yu Gu,et al.  Dust aerosol impact on North Africa climate: a GCM investigation of aerosol-cloud-radiation interactions using A-Train satellite data , 2011 .

[22]  P. Zanis,et al.  Regional climate feedback of anthropogenic aerosols over Europe using RegCM3 , 2012 .

[23]  F. Giorgi,et al.  The Effects of Domain Choice on Summer Precipitation Simulation and Sensitivity in a Regional Climate Model , 1998 .

[24]  W. Pokam,et al.  Atmospheric water vapor transport and recycling in Equatorial Central Africa through NCEP/NCAR reanalysis data , 2012, Climate Dynamics.

[25]  C. Tchawoua,et al.  Sensitivity experiments of RegCM4 simulations to different convective schemes over Central Africa , 2017 .

[26]  F. Giorgi,et al.  Direct radiative forcing and regional climatic effects of anthropogenic aerosols over East Asia: A regional coupled climate‐chemistry/aerosol model study , 2002 .

[27]  J. Peixoto,et al.  Physics of climate , 1984 .

[28]  L. Ruby Leung,et al.  Radiative impact of mineral dust on monsoon precipitation variability over West Africa , 2010 .

[29]  Christian Mätzler,et al.  MATLAB Functions for Mie Scattering and Absorption , 2002 .

[30]  J. Hansen,et al.  Radiative forcing and climate response , 1997 .

[31]  C. Willmott,et al.  An Empirical Method for the Spatial Interpolation of Monthly Precipitation within California , 1980 .

[32]  A. Holtslag,et al.  A High Resolution Air Mass Transformation Model for Short-Range Weather Forecasting , 1990 .

[33]  Alessandra Giannini,et al.  A global perspective on African climate , 2008 .

[34]  P. Zanis.  A study on the direct effect of anthropogenic aerosols on near surface air temperature over Southeastern Europe during summer 2000 based on regional climate modeling , 2009 .

[35]  Thomas S. Pagano,et al.  Prelaunch characteristics of the Moderate Resolution Imaging Spectroradiometer (MODIS) on EOS-AM1 , 1998, IEEE Trans. Geosci. Remote. Sens..

[36]  S. Dey,et al.  Impacts of aerosols on dynamics of Indian summer monsoon using a regional climate model , 2015, Climate Dynamics.

[37]  C. Liousse,et al.  Aerosol modelling for regional climate studies: application to anthropogenic particles and evaluation over a European/African domain , 2006 .

[38]  R. Arritt,et al.  Sensitivity studies of the RegCM3 simulation of summer precipitation, temperature and local wind field in the Caribbean Region , 2006 .

[39]  Y. Xue,et al.  The WAMME regional model intercomparison study , 2010 .

[40]  D. Tanré,et al.  Remote sensing of aerosol properties over oceans using the MODIS/EOS spectral radiances , 1997 .

[41]  Stefano Schiavon,et al.  Climate Change 2007: The Physical Science Basis. , 2007 .

[42]  J. Penner,et al.  Precipitation changes in a GCM resulting from the indirect effects of anthropogenic aerosols , 2000 .

[43]  Rosenfeld,et al.  Suppression of rain and snow by urban and industrial air pollution , 2000, Science.

[44]  J. Haywood,et al.  On summing the components of radiative forcing of climate change , 2001 .

[45]  F. Giorgi,et al.  Progress in regional downscaling of west African precipitation , 2011 .

[46]  J. Penner,et al.  A global three‐dimensional model study of carbonaceous aerosols , 1996 .

[47]  F. Giorgi,et al.  Precipitation Climatology in an Ensemble of CORDEX-Africa Regional Climate Simulations , 2012 .

[48]  T. McMahon,et al.  Updated world map of the Köppen-Geiger climate classification , 2007 .

[49]  F. Giorgi,et al.  Development of a Second-Generation Regional Climate Model (RegCM2). Part I: Boundary-Layer and Radiative Transfer Processes , 1993 .

[50]  Kyu-Myong Kim,et al.  Influence of aerosol-radiative forcings on the diurnal and seasonal cycles of rainfall over West Africa and Eastern Atlantic Ocean using GCM simulations , 2010 .

[51]  C. Liousse,et al.  Long-term simulations (2001–2006) of biomass burning and mineral dust optical properties over West Africa: comparisons with new satellite retrievals , 2011 .

[52]  F. Giorgi,et al.  Regional climate effects of aerosols over China: modeling and observation , 2003 .

[53]  O. Boucher,et al.  Estimates of the direct and indirect radiative forcing due to tropospheric aerosols: A review , 2000 .

[54]  H. Rodhe,et al.  Regional temperature response due to indirect sulfate aerosol forcing: impact of model resolution , 2003 .

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

[56]  Jens Debernard,et al.  Response of the climate system to aerosol direct and indirect forcing: Role of cloud feedbacks , 2005 .

[57]  John H. Seinfeld,et al.  Climate response of direct radiative forcing of anthropogenic black carbon , 2005 .

[58]  C. Tchawoua,et al.  Evaluation of Vapor Pressure Estimation Methods for Use in Simulating the Dynamic of Atmospheric Organic Aerosols , 2013 .

[59]  Ann Henderson-Sellers,et al.  Biosphere-atmosphere transfer scheme(BATS) version 1e as coupled to the NCAR community climate model , 1993 .

[60]  F. Giorgi,et al.  Development of a Second-Generation Regional Climate Model (RegCM2). Part II: Convective Processes and Assimilation of Lateral Boundary Conditions , 1993 .

[61]  M. Mallet,et al.  Radiative and climatic effects of dust over West Africa, as simulated by a regional climate model , 2012 .

[62]  U. Lohmann,et al.  Nonlinear Aspects of the Climate Response to Greenhouse Gas and Aerosol Forcing , 2004 .

[63]  Leon D. Rotstayn,et al.  Tropical Rainfall Trends and the Indirect Aerosol Effect , 2002 .

[64]  A. Jones,et al.  The response of the climate system to the indirect effects of anthropogenic sulfate aerosol , 2001 .

[65]  O. Boucher,et al.  A satellite view of aerosols in the climate system , 2002, Nature.

[66]  S. Emori,et al.  Simulation of climate response to aerosol direct and indirect effects with aerosol transport‐radiation model , 2005 .

[67]  D. Lüthi,et al.  Implementation and evaluation of aerosol and cloud microphysics in a regional climate model , 2011 .

[68]  J. Hack,et al.  Description of the NCAR Community Climate Model (CCM1) , 1987 .

[69]  F. Giorgi,et al.  Implementation and testing of a desert dust module in a regional climate model , 2006 .

[70]  P. Huszár,et al.  Interactive coupling of a regional climate model and a chemical transport model: evaluation and preliminary results on ozone and aerosol feedback , 2012 .

[71]  V. Salomonson,et al.  MODIS: advanced facility instrument for studies of the Earth as a system , 1989 .

[72]  Amin K. Dezfuli,et al.  The Relationship of Rainfall Variability in Western Equatorial Africa to the Tropical Oceans and Atmospheric Circulation. Part II: The Boreal Autumn , 2013 .

[73]  M. Katz.  Validation of models , 2006 .

[74]  F. Giorgi,et al.  Dust aerosol impact on regional precipitation over western Africa, mechanisms and sensitivity to absorption properties , 2008 .

[75]  C. Willmott.  ON THE VALIDATION OF MODELS , 1981 .

[76]  V. Ramaswamy,et al.  A general circulation model study of the global carbonaceous aerosol distribution , 2002 .