The climatology of dust aerosol over the arabian peninsula

49 Pages·2015·3.74 MB·English

Atmos.Chem.Phys.Discuss.,15,1523–1571,2015 D
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doi:10.5194/acpd-15-1523-2015 s
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©Author(s)2015.CCAttribution3.0License. io 15,1523–1571,2015
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Thisdiscussionpaperis/hasbeenunderreviewforthejournalAtmosphericChemistry e The climatology of
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andPhysics(ACP).PleaserefertothecorrespondingfinalpaperinACPifavailable. dust aerosol over the
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arabian peninsula
The climatology of dust aerosol over the D
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A. Shalaby1, B. Rappenglueck2, and E. A. B. Eltahir3 pe
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1TheInternationalCentreforTheoreticalPhysics,Trieste,Italy |
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2DepartmentofEarthandAtmosphericSciences,UniversityofHouston,Texas77004,USA
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3MassachusettsInstituteofTechnology,Cambridge,Massachusetts,USA is Tables Figures
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Received:25September2014–Accepted:19December2014–Published:19January2015 s
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Correspondenceto:A.Shalaby([email protected])
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PublishedbyCopernicusPublicationsonbehalfoftheEuropeanGeosciencesUnion. p
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Dust storms are considered to be a natural hazard over the Arabian Peninsula, since s
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theyoccurallyearroundwithmaximumintensityandfrequencyinSpringandSummer. io 15,1523–1571,2015
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TheRegionalClimateModelversion4(RegCM4)hasbeenusedtostudytheclimatol- P
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5 ogy of atmospheric dust over the Arabian Peninsula from 1999 to 2012. This relatively pe The climatology of
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long simulation period samples the meteorological conditions that determine the cli- dust aerosol over the
matology of mineral dust aerosols over the Arabian Peninsula. The modeled Aerosol | arabian peninsula
Optical Depth (AOD) has been compared against ground-based observations of three D
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Aerosol Robotic Network (AERONET) stations that are distributed over the Arabian c A.Shalabyetal.
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10 Peninsula and daily space based observations from the Multi-angle Imaging Spec- sio
troRadiometer (MISR), the Moderate resolution Imaging SpectroRadimeter (MODIS) n
and Ozone Monitoring Instrument (OMI). The large scale atmospheric circulation and Pa TitlePage
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the land surface response that lead to dust uplifting have been analyzed. While the e
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modeledAODshowsthatthedustseasonextendsfromMarchtoAugustwithtwopro-
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nouncedmaxima,oneoverthenorthernArabianPeninsulainMarchwithAODequalto Conclusions References
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0.4andoneoverthesouthernArabianPeninsulainJulywithAODequalto0.7,theob- is Tables Figures
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servationsshowthatthedustseasonextendsfromApriltoAugustwithtwopronounced u
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maxima, one over the northern Arabian Peninsula in April with AOD equal to 0.5 and sio (cid:74) (cid:73)
oneoverthesouthernArabianPeninsulainJulywithAODequalto0.5.Inspringahigh n
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pressure dominates the Arabian Peninsula and is responsible for advecting dust from a (cid:74) (cid:73)
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southernandwesternpartoftheArabianPeninsulatonorthernandeasternpartofthe r Back Close
Peninsula. Also, fast developed cyclones in northern Arabian Peninsula are responsi-
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ble for producing strong dust storms over Iraq and Kuwait. However, in summer the FullScreen/Esc
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main driver of the surface dust emission is the strong northerly wind (“Shamal”) that is
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transport dust from the northern Arabian Peninsula toward south parallel to the Ara- u Printer-friendlyVersion
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bian Gulf. The AERONET shortwave Top of Atmosphere Radiative Forcing (TOARF) io InteractiveDiscussion
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andattheBottomofAtmosphereRadiativeForcing(BOARF)havebeenanalyzedand P
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comparedwiththemodeleddirectradiativeforcingofmineraldustaerosol.Theannual p
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−2 D
modeledTOARFandBOARFare−3.3and−12Wm ,respectively.However,thean-
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nual observed TOARF and BOARF are significantly different at −10 and −52Wm−2, cu ACPD
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respectively.TheanalysisofobservedandmodeledTOARFagreeswithpreviousstud- s
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ies in highlighting the need for more accurate specification of surface albedo over the n
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region. Due to the high surface albedo of the central Arabian Peninsula, mineral dust a
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aerosols tend to warm the atmosphere in summer (June–August). r
dust aerosol over the
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arabian peninsula
1 Introduction D
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Atmospheric mineral dust is a natural aerosol and is ubiquitous in the Earth’s atmo- s
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sphere, despite that it is emitted from hyper-arid, arid and semi-arid regions on the ion
globe. About 2000Mt is emitted annually to the atmosphere, 1500Mt is deposited to P TitlePage
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the land and 500Mt is deposited onto the ocean surface (Shao et al., 2011). It affects pe
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radiationbyabsorptionandscatteringthatinturnaffectssurfaceandatmospherictem-
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perature, also it acts as ice cloud condensation nuclei (ICCN) that impacts the micro- Conclusions References
physics of the clouds and its radiative properties (IPCC, 2013). The transported dust D
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also carries nutrients and bacteria, which may affect the marine life and land surface c
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life. For instance, 20Mt of nutrients rich Saharan dust is transported to the Amazon s
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basin in South America each year (Koren et al., 2006). Atmospheric mineral dust, es- n
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pecially fine dust (smaller than 2.5µm) may cause cardiopulmonary disease and lung a (cid:74) (cid:73)
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cancer (Giannadaki et al., 2014). It also affects many of human activities like aviation, e
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real estate construction, agriculture, and water resource management (Stefanski and
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Sivakumar, 2009). FullScreen/Esc
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Dust particles are emitted from major deserts on the globe (e.g., Sahara, the Ara- is
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bianPeninsula,TaklamakanandGobidesertsinChina,AustraliadesertsandAtacama u Printer-friendlyVersion
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desertinChile).Themineraldustemissionprocesses(i.e.,saltationandsandblasting) sio InteractiveDiscussion
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are determined by meteorological conditions (e.g., atmospheric instability, soil mois-
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ture). Large-scale wind systems may carry coarse and fine dust particles horizontally a
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for thousands of kilometers (e.g., Koren et al., 2006) and vertically up 6 to 10km (e.g., r
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Gobbi et al., 2004). Depending on dust particle size and atmospheric conditions dust D
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particles may remain airborne between 1.5 to 7.4 days and will then deposit to the c ACPD
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surface by gravitational settling or rain washout (Shao et al., 2011). s
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This paper focuses on atmospheric mineral dust over the Arabian Peninsula, a re- n
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5 gion,whichhasbeenlessstudiedoverthelastdecadescomparedtoSaharanregions. a
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In an early study Wilkerson (1991) described the onset and evolution of dust storms e The climatology of
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overIraqandKuwaitanalyzingsatelliteimagesandvisbilityrecords.Wilkerson’sstudy dust aerosol over the
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categorizedthetypesofduststormsaspre-frontal,post-frontalandShamaltypes,the arabian peninsula
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latter being a regional northwesterly wind that typically occurs in summer (“Shamal”
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10 denotes “northerly wind” in Arabic). Mashat et al. (2008) used meteorological obser- u
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vationsfromSaudiArabiatoanalyzethemeteorologicalconditionswhichfavoreddust s
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storms and their spatial and seasonal distribution. They found that dust storms most n
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frequently occur in the eastern part of the Arabian Peninsula in spring and extend a
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towards the southern part of the Arabian Peninsula in summer. Alharbi (2009) and Al- r Abstract Introduction
harbi et al. (2013) explored dust storms generation over the Arabian Peninsula, dust
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source regions and atmospheric conditions that promote dust storms, which include
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large-scale atmospheric instability, high surface winds, and dry, rich dust sources. The is Tables Figures
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quantification and characterization of mineral dust aerosol (e.g., dust concentrations u
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profile and mineral dust optical properties) became possible after the installation of io (cid:74) (cid:73)
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TheAErosolROboticNETwork(AERONET)inBahrainandSaudiArabiaaround1998.
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Smirnovetal.(2002)usedaoneyeardatarecord(July1998–July1999)oftheBahrain p
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siteintheArabianGulftodeducetheclimatologyofaerosolopticalproperties(i.e.,the r Back Close
AerosolOpticalDepth(AOD)andtheÅngströmparameter).In2004anintensivemea- |
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surement campaign was held in the United Arab Emirates (UAE), which led to the
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installation of various AERONET stations. Among them only the Mezaira site is fully is
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operationaluptodate.Thiscampaigncharacterizedthenatureofatmosphericaerosol s
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over the UAE and validated satellite aerosol products over a bright surface such as io InteractiveDiscussion
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desert (Reid et al., 2005; Eck et al., 2008). Kim et al. (2011) studied AERONET data P
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records from North Africa and the Arabian Peninsula and derived the seasonal behav- p
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ior of mineral dust aerosol optical properties in these regions. This study showed that D
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theArabianPeninsuladustismoreabsorbingintheshortwaverangethantheSaharan c ACPD
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dust does. García et al. (2012) analyzed most of the AERONET stations on the globe s
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includingtheArabianPeninsulaandfoundthatatmosphericaerosolsoverhighsurface n
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5 albedo regions, as deserts, lead to a warming of the Earth’s atmosphere. a
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Using a regional climate model offers the advantage to investigate meso-scale phe- e The climatology of
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nomena such as surface dust emission processes, transportation, deposition and its dust aerosol over the
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radiative impact on the regional climate at a higher spatial resolution (e.g., ≤50km) arabian peninsula
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than global models with coarse spatial resolution (e.g., ≥100km). The Regional Cli-
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10 mate Model Version 3 (RegCM3) (Pal et al., 2007) and RegCM4 (Giorgi et al., 2012) u
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havebeenusedtoinvestigatemineraldustaerosolsanditsradiativeimpactonregions s
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in North and West Africa (Zakey et al., 2006; Solmon, 2008; Konarè et al., 2008; Na- n
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pat et al., 2012; Steiner et al., 2014), but studies on the Middle East area are rare. a
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Marcella and Eltahir (2010, 2011) used RegCM3 for the first time over the Northern r Abstract Introduction
Arabian Peninsula, to explore the impact of dust on climate and found that the im-
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plementation of subgrid wind variability and dust aerosol lateral boundary conditions
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couldenhancethedustsimulation.NazrulIslamandAlmazroui(2012)usedRegCM4, is Tables Figures
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showed that the direct radiative effect of mineral dust results in a decrease of surface u
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temperatureandincreaseinprecipitationovertheArabianPeninsulainthewetseason io (cid:74) (cid:73)
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(November–April).
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The first objective of this study is to define and identify the dust season by means of p
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available observations (e.g. through AERONET and satellite data bases) and regional r Back Close
climate modeling. As the uncertainties of aerosol radiative forcing are large (IPCC, |
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2013), more investigation on the sources of such uncertainties, especially on regional
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scales,isneeded.Thus,thesecondobjectiveofthisstudyistoestimatetheBottomOf is
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AtmosphereRadiativeForcing(BOARF)andtheTopofAtmosphereRadiativeForcing s
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(TOARF) of mineral dust aerosols using AERONET products and the model. These io InteractiveDiscussion
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objectives integrate observations and modeling to obtain a better assessment of the P
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atmospheric behavior of mineral dust aerosol. p
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2 Methods D
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2.1 Observational datasets s
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The observation of atmospheric dust from space has become very vital to the under- P
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standing of this phenomenon. Space-borne observations provide global information p
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of the spatial distribution (horizontal and vertical) and the temporal evolution of the r
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AerosolOpticalDepth(AOD).However,comparisonofmodeleddust(AOD)withsatel- |
arabian peninsula
litemeasurementsmaybeproblematic,sincesatelliteobservationsapplyassumptions D
about the nature of the aerosol, which is different from approaches in numerical mod- isc A.Shalabyetal.
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els (Woodward, 2001). On the other hand, ground-based observation is needed to s
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provide more details of atmospheric dust characteristics such as high frequency mea- io
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surements of near ground concentration (e.g., PM10) and AOD. Also ground-based P TitlePage
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measurements include physical and chemical analysis of aerosols, such as its geo- e
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metrical shape, size distribution and chemical composition. The ground-based mea-
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surements are also used to validate the space-borne observations. For instance, the Conclusions References
AOD from AERONET stations has been used to validate satellite AOD products (Mar- D
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tonchik et al., 2004; Abdou et al., 2005). In the following subsections we will briefly c
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discuss the characteristics of AERONET and satellite datasets. s
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2.1.1 AERONET Pa (cid:74) (cid:73)
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The AErosol RObotic NETwork (AERONET) provides valuable measurements of at- r Back Close
mospheric aerosol optical properties. AERONET stations comprise an automatic sun |
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photometer.Ithasitsownalgorithmtoevaluatedataqualityandinstrumentfunctional- D
ity.AERONETmeasuresAODfordifferentwavelengths,fromnearIR(1064nm)tonear isc
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UV(340nm).AERONETsunphotometerprovidesinformationaboutaerosolsizedistri- s
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bution,aerosolradiativeforcing,andaerosolshape(spherical/non-spherical).Detailed ion InteractiveDiscussion
description of the instrument and its function can be found in Holben et al. (1998). P
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The measurements pass multilevel quality assurance (QA): level 1 without cloud D
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screening, level 1.5 has cloud screened but may be without final calibration. Level 2 c ACPD
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has cloud screened and quality assured calibrations. The AOD accuracy of calibrated s
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AERONET station is wavelength dependent and varies from root mean square error n
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5 of ±0.012 (UV band) to root mean square error of ±0.006 (IR band) at overhead sun a
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(airmass=1) (Schmid et al., 1999). e The climatology of
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The AERONET stations are widely used over the globe. However there are only few dust aerosol over the
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AERONETstationsintheArabianPeninsulawithrelativelylongmeasurementrecords. arabian peninsula
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AmongthemistheSolar-VillagestationinSaudiArabia,theKuwaitUniversitystationin
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about the site and their locations see Table 1 and Fig. 1. s
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Each station has its unique features; the Kuwait station is downwind of major dust n
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sourcesinSouthernIraq.Solar-VillageislocatedinthecenterofSaudiArabiaanditis a
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atarelativelyhighaltitude(764ma.s.l.)comparedtoothersites,whichcouldreflectthe r Abstract Introduction
transportationofdusttohighaltitudes.MezairainUnitedArabEmirate(UAE)isinland
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site and could be considered a receptor site for dust coming from southern Arabian
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Peninsula. is Tables Figures
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2.1.2 MISR sio (cid:74) (cid:73)
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Most satellite instruments looks down to the earth (0 degrees Nadir angle), or toward a (cid:74) (cid:73)
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the edge of the planet and receive the reflected sunlight. The Earth’s surface, clouds e
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and aerosols reflect sunlight in different direction, which requires an instrument that
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accounts for such different reflected angle. The Multiangle Imaging Spectroradiometer FullScreen/Esc
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(MISR) is a unique instrument flown in the space since late 1998. It has nine cameras is
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corresponding to nine view angles, the middle one pointing toward the nadir, four of u Printer-friendlyVersion
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25 theminaforwarddirectionwith(26.1,45.6,60.0and70.0◦,respectively)relativetothe sio InteractiveDiscussion
nadir camera and the other four in the rearward direction with (−26.1, −45.6, −60.0 n
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and −70.0◦ respectively). Each direction measures four individual wavelength (443, a
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555, 670 and 865nm). Therefore, MISR has 36 channels (Diner et al., 1998). MISR r
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has been used in many fields including studies on, clouds (Marchand et al., 2010), D
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aerosols (Martonchik et al., 2004; Abdou et al., 2005; Marey et al., 2011) and Earth c ACPD
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surface (Pinty et al., 2011). For our purpose, we will focus on the aerosol facilities of s
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MISR. The MISR global aerosol retrieval is used to obtain AOD values to characterize n
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5 thetypesofaerosolbasedontheirphysicalandopticalproperties,andaerosolparticle a
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shape (spherical or non-spherical). The aerosol retrieval algorithm strategy has many e The climatology of
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steps.First,itutilizesalookuptablethatcontainsasuiteofanaturalaerosoltypesand dust aerosol over the
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calculatedaerosolopticalpropertiesbyaradiativetransfermodel.Second,theretrieval arabian peninsula
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of theaerosol overdark surfaceslike theocean dependson red andnear infrared(IR)
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10 channels (Martonchik et al.,1998). The most difficult retrieval is above bright surface cu A.Shalabyetal.
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like deserts. This latter retrieval needs special treatment and is therefore associated s
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with large uncertainties (Diner, 1998; Martonchik, 1998; Abdou et al., 2005). n
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In this work we concentrate only on the MISR AOD dataset and its comparison with a
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the model output. The MISR data used in our study spans 6 years from 2006 to 2012. r Abstract Introduction
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The data resolution is 0.5 ×0.5 . Data has been retrieved from the Giovanni website
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(http://Giovanni.gsfc.nasa.gov/giovanni).
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2.1.3 MODIS (Deepblue) u
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The Moderate Resolution Imaging Spectroradiometer (MODIS) instrument is aboard n
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the NASA EOS (Earth Observing System) Terra and Aqua satellites and began trans- a (cid:74) (cid:73)
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mitting date in 2000. The instruments have high spatial resolution (10km resolu- e
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tion) and almost global coverage. Like MISR, MODIS aerosol retrievals are based on
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a lookup table procedure in which the satellite measured radiances are matched to FullScreen/Esc
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pre-calculated values in the lookup table. The values of the aerosol properties used to is
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create the calculated radiances are retrieved (Remer et al., 2005; Abdou et al., 2005). u Printer-friendlyVersion
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25 The MODIS data set spans from January 2008 to December 2011. Data has been sio InteractiveDiscussion
retrieved from the Giovanni website (http://Giovanni.gsfc.nasa.gov/giovanni). n
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2.1.4 OMI D
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TheOzoneMonitoringInstrument(OMI)hasbeenorbitingtheEarthononeoftheEOS s
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mission “Aura spacecraft” since July 2004. OMI is a high spatial resolution (13km× io 15,1523–1571,2015
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24km) ground pixel size ultraviolet/visible (UV/VIS) backscatter spectrometer (Levelt P
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5 et al., 2006). The OMI aerosol retrieval algorithm is the same as for the Total Ozone pe The climatology of
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Mapping spectrometer (TOMS) near-UV method of aerosol absorption sensing from dust aerosol over the
space (Torres et al., 2005). The accuracy of the OMI retrieval of aerosol optical depth | arabian peninsula
is around 30% relative to AERONET measurements (Torres et al., 2005). D
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10 from Giova◦nni◦site portal (http://Giovanni.gsfc.nasa.gov/giovanni). From that data we sio
selected 2 ×2 box around the three AERONET stations (see Fig. 1) for comparison n
purposes with the observations. The time span of this data is from January 2008 to Pa TitlePage
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December 2011. e
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2.2 Model description and experimental design Conclusions References
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15 2.2.1 General model description cu
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The International Centre for Theoretical Physics (ICTP) Regional Climate Model io (cid:74) (cid:73)
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(RegCM) was built upon the National Center for Atmospheric Research (NCAR) P
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Mesoscale Model version 4 (MM4) (Giorgi and Bates, 1989; Giorgi et al., 1993a, b). p
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oftheRegCMcoreafterRegCM3(Paletal.,2007).Thecodingstructureiscompletely |
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changed.IthasbecometotallyFORTRAN90compliantandmodularstructuredandits D
parallelizationandmemorymanagementhasbecomemoreefficient.TheRegCM4has isc
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morephysicsoptions,whichincludetheCommunityLandsurfaceModel(CLM3.5)land s
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surfaceparameterization,theTiedtkeconvectionscheme,theUniversityofWashington ion InteractiveDiscussion
(UW)planetaryboundarylayer(PBL)scheme,andtheRapidRadiativeTransferModel P
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(RRTM) (Giorgi et al., 2012). e
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RegCM4 is an online climate-chemistry model and has an online gas-phase chem- D
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istry scheme (CBMZ) (Shalaby et al., 2012). It has various aerosol components such c ACPD
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as,foursizebindust,twosizebinseasalt,sulphate,blackcarbonandorganiccarbon. s
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Sulphate, black carbon and organic carbon (Solmon et al., 2006), as well as dust and n
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5 sea-salt are radiatively active (Zakey et al., 2006, 2008). a
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2.2.2 Dust parameterization dust aerosol over the
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Sand particles are affected by many forces that determine their fate. Dust particles D
havethreedynamicmodes:(a)saltation:smallparticlesmovebyjumpinglikeleap-frog, isc A.Shalabyetal.
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Onceliftedbywinditwilldriftdownwindandreturntohitthegroundagainandtransfer s
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energy and momentum to other soil aggregates (soil particles). (b) Creeping: large io
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Suspension:iftheupwarddraftisstrongenoughtocompensatethegravitationalforce e
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of the dust particles, dust will remain airborne and be transported by the wind over
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longer distances until its gravitational force overcome the uplifting force. It is believed Conclusions References
that saltation is the main mechanism for surface dust emission (Shao et al., 1993; D
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Marticorena and Bergametti, 1995). c
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FollowingMarticorenaandBergametti(1995)andAlfaroandGomes(2001),acom- s
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plex dust emission scheme has been implemented in RegCM3 (Zakey et al., 2006). n
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This emission scheme is based on parameterization of soil aggregate saltation and a (cid:74) (cid:73)
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sandblasting processes. According to this scheme, a critical parameter for the dust e
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saltationprocessisthethresholdfrictionvelocityu∗,whichisafunctionofparticlesize
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D (Eq. 1), such that, u∗ represents an ideal minimum threshold friction velocity, f is FullScreen/Esc
p ts eff
acorrectionfactoraccountingfortheeffectofsurfaceroughnessandfw isafactorthat Dis
accounts for the effect of soil moisture content on the threshold friction velocity. The cu Printer-friendlyVersion
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25 particle size is determined by the land surface soil texture. Calculating the threshold sio InteractiveDiscussion
frictionvelocityisrequiredtocalculatethehorizontaldustflux(dH )(Eq.2),suchthat, n
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E is the ratio of erodible to total surface, dS is the relative surface of soil aggregate a
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of diameter D to the total aggregate surface and R(D ) is the ratio of the threshold r
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