Browsing by Author "Ryder, Claire L."
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Item Net radiative effects of dust in the tropical North Atlantic based on integrated satellite observations and in situ measurements(Copernicus Publications, 2018-08-13) Song, Qianqian; Zhang, Zhibo; Yu, Hongbin; Kato, Seiji; Yang, Ping; Colarco, Peter; Remer, Lorraine A.; Ryder, Claire L.In this study, we integrate recent in situ measurements with satellite retrievals of dust physical and radiative properties to quantify dust direct radiative effects on shortwave (SW) and longwave (LW) radiation (denoted as DRE(SW) and DRE(LW), respectively) in the tropical North Atlantic during the summer months from 2007 to 2010. Through linear regression of the CERES-measured top-of-atmosphere (TOA) flux versus satellite aerosol optical depth (AOD) retrievals, we estimate the instantaneous DRE(SW) efficiency at the TOA to be −49.7±7.1Wm⁻²AOD⁻¹ and −36.5±4.8Wm⁻²AOD⁻¹ based on AOD from MODIS and CALIOP, respectively. We then perform various sensitivity studies based on recent measurements of dust particle size distribution (PSD), refractive index, and particle shape distribution to determine how the dust microphysical and optical properties affect DRE estimates and its agreement with the above-mentioned satellite-derived DREs. Our analysis shows that a good agreement with the observation-based estimates of instantaneous DRE(SW) and DRE(LW) can be achieved through a combination of recently observed PSD with substantial presence of coarse particles, a less absorptive SW refractive index, and spheroid shapes. Based on this optimal combination of dust physical properties we further estimate the diurnal mean dust DRE(SW) in the region of −10Wm⁻² at TOA and −26Wm⁻² at the surface, respectively, of which ∼ 30% is canceled out by the positive DRE(LW). This yields a net DRE of about −6.9 and −18.3Wm⁻² at TOA and the surface, respectively. Our study suggests that the LW flux contains useful information on dust particle size, which could be used together with SW observations to achieve a more holistic understanding of the dust radiative effect.Item Observation and modeling of the historic “Godzilla” African dust intrusion into the Caribbean Basin and the southern US in June 2020(EGI, 2021-08-18) Yu, Hongbin; Tan, Qian; Zhou, Lillian; Zhou, Yaping; Bian, Huisheng; Chin, Mian; Ryder, Claire L.; Pradhan, Yaswant; Shi, Yingxi; Song, Qianqian; Zhang, Zhibo; Colarco, Peter R.; Kim, Dongchul; Remer, Lorraine; Yuan, Tianle\; Mayol-Bracero, Olga; Brent N. Holben, Brent N.This study characterizes a massive African dust intrusion into the Caribbean Basin and southern US in June 2020, which is nicknamed the “Godzilla” dust plume, using a comprehensive set of satellite and ground-based observations (including MODIS, CALIOP, SEVIRI, AERONET, and EPA Air Quality network) and the NASA GEOS global aerosol transport model. The MODIS data record registered this massive dust intrusion event as the most intense episode over the past 2 decades. During this event, the aerosol optical depth (AOD) observed by AERONET and MODIS peaked at 3.5 off the coast of West Africa and 1.8 in the Caribbean Basin. CALIOP observations show that the top of the dust plume reached altitudes of 6–8 km in West Africa and descended to about 4 km altitude over the Caribbean Basin and 2 km over the US Gulf of Mexico coast. The dust intrusion event degraded the air quality in Puerto Rico to a hazardous level, with maximum daily PM10 concentration of 453 µg m−3 recorded on 23 June. The dust intrusion into the US raised the PM2.5 concentration on 27 June to a level exceeding the EPA air quality standard in about 40 % of the stations in the southern US. Satellite observations reveal that dust emissions from convection-generated haboobs and other sources in West Africa were large albeit not extreme on a daily basis. However, the anomalous strength and northern shift of the North Atlantic Subtropical High (NASH) together with the Azores low formed a closed circulation pattern that allowed for accumulation of the dust near the African coast for about 4 d. When the NASH was weakened and wandered back to the south, the dust outflow region was dominated by a strong African easterly jet that rapidly transported the accumulated dust from the coastal region toward the Caribbean Basin, resulting in the record-breaking African dust intrusion. In comparison to satellite observations, the GEOS model reproduced the MODIS observed tracks of the meandering dust plume well as it was carried by the wind systems. However, the model substantially underestimated dust emissions from haboobs and did not lift up enough dust to the middle troposphere for ensuing long-range transport. Consequently, the model largely missed the satellite-observed elevated dust plume along the cross-ocean track and underestimated the dust intrusion into the Caribbean Basin by a factor of more than 4. Modeling improvements need to focus on developing more realistic representations of moist convection, haboobs, and the vertical transport of dust.Item Quantifying the response of the ORAC aerosol optical depth retrieval for MSG SEVIRI to aerosol model assumptions(AGU, 2011-03-15) Bulgin, Claire E.; Palmer, Paul I.; Merchant, Christopher J.; Siddans, Richard; Gonzi, Siegfried; Poulsen, Caroline A.; Thomas, Gareth E.; Sayer, Andrew; Carboni, Elisa; Grainger, Roy G.; Highwood, Eleanor J.; Ryder, Claire L.We test the response of the Oxford-RAL Aerosol and Cloud (ORAC) retrieval algorithm for Meteosat Second Generation Spinning Enhanced Visible and InfraRed Imager (MSG SEVIRI) to changes in the aerosol properties used in the dust aerosol model, using data from the Dust Outflow and Deposition to the Ocean (DODO) flight campaign in August 2006. We find that using the observed DODO free tropospheric aerosol size distribution and refractive index increases simulated top of the atmosphere radiance at 0.55 μm assuming a fixed aerosol optical depth of 0.5 by 10–15%, reaching a maximum difference at low solar zenith angles. We test the sensitivity of the retrieval to the vertical distribution of the aerosol and find that this is unimportant in determining simulated radiance at 0.55 μm. We also test the ability of the ORAC retrieval when used to produce the GlobAerosol data set to correctly identify continental aerosol outflow from the African continent, and we find that it poorly constrains aerosol speciation. We develop spatially and temporally resolved prior distributions of aerosols to inform the retrieval which incorporates five aerosol models: desert dust, maritime, biomass burning, urban, and continental. We use a Saharan Dust Index and the GEOS-Chem chemistry transport model to describe dust and biomass burning aerosol outflow and compare AOD using our speciation against the GlobAerosol retrieval during January and July 2006. We find AOD discrepancies of 0.2–1 over regions of intense biomass burning outflow, where AOD from our aerosol speciation and GlobAerosol speciation can differ by as much as 50–70%.