A11E-0175
Appling 3.9 μm Channels to AOD Retrieval Algorithm for Geostationary Satellite, MTSAT-1R
Aerosol optical depth (AOD) retrieval algorithms utilizing a single visible channel have been used for geostationary earth orbit (GEO) satellites. In these algorithms, surface reflectance is obtained from the clear- sky composite with the assumptions that there is at least one clear sky condition and surface conditions do not changed for the previous certain number of days. This method to retrieve surface reflectance, however, has limitations for its validity due to assumptions, and single visible channel algorithm also has larger retrieval error in AOD than other multiple-channel algorithms due to errors in estimating surface reflectance. In this study, to overcome limitations in surface reflectance retrieval, possibility to utilize mid-infrared (MID-IR) channel at 3.9 μm was investigated, and AODs are retrieved from two channels of visible and 3.9 μm channel onboard a GEO satellite, MTSAT-1R by using look up table (LUT) approach. Utilization of 3.9 μm channel provides additional information on the surface reflectance with its insensitivity to the presence of aerosol in the atmosphere. The retrieved AODs are compared with AERONET values (within ¢®¨ú30 minutes) at Anmyon site during March, 2006. The application of 3.9 μm channel over restricted surface area shows potentials in retrieving more accurate AODs from GEO satellites. With the aid of 3.9 μm channel, correlation coefficient(R) as good as earlier one, and the RMSE and BIAS are improved from 0.30 to 0.16 and 0.23 to 0.06 respectively. One should note that the signals for MID-IR channel are affected by terrestrial radiation. Therefore, the channel can be utilized when MID-IR reflectance is properly corrected for surface temperature changes.
A11E-0176
Correlation between Black Carbon and CO on Urban and Wildfire Area in East Asia From Satellite Remote Sensing
Recent development in satellite remote sensing, with its global coverage now enables us to investigate correlation between aerosols and pollutant gases. MOPITT (Measurement of Pollution in the Troposphere) onboard the Terra satellite launched in 1999 has observed CO(carbon monoxide) density, and MODIS(Moderate Resolution Imaging Spectroradiometer) has observed AOD(Aerosol Optical Depth). Increases of CO, a very important gas in tropospheric chemistry, in atmosphere can reduce the self- purification ability of atmosphere, thus modifies atmospheric chemical, physical, and climatological properties. Direct radiative forcing of black carbon aerosol has been regarded as a potential factor causing global warming(IPCC, 2007). MODIS-OMI algorithm is used to investigate correlation between CO and black carbon AOD. This algorithm uses OMI's AI(Aerosol Index) to determine radiative absorption of aerosol and MODIS's AE(Angstrom Exponent) to determine size of aerosol (Kim et al., 2007). Using this algorithm, we can classify the aerosol into 4 types – black carbon, soil dust, sulfate, and seasalt(Higurashi and Nakajima, 2002; Kim et al., 2007). Main sources of both CO and black carbon are related to incomplete combustion which results from wildfires and urban industrial emissions, but sinks are different. This research investigates how the correlation between CO and black carbon varies according to these two sources in East Asia. We use the MODIS Land cover, MODIS fire counts, sulfate by MODIS-OMI algorithm, and OMI's nitrogen dioxide data to distinguish urban and wildfires region. To scrutinize how the correlation between CO and black carbon varies in relation to urban and wildfires, East Asia is divided into 2 areas – A (urban industrial emissions are dominant) and B (wildfires are dominant). The density of black carbon and CO in both A and B region is high, but that in A region is higher than that in B region.
A11E-0177
Relationship between Visibility and Relative Humidity, PM in terms of Hygroscopicity
Meteorological range can alternate visibility which is function of extinction coefficient by using Kochsmeider equation. Extinction coefficient is related with various variables. Among them, particle mass concentration and relative humidity has higher correlation. But they are not independent variables. Hygroscopicity plays a key role connecting those three variables. And constituent of aerosol is important factor in terms of hygroscopicity. Many experiments have been performed to find features of hygroscopicity with diverse kinds of constituents. Based on those preceding studies, we investigated how dominantly hygroscopicity influences on visibility. Mega-city Air Quality Monitoring Facility managed by Yonsei University and Gwangju Institute of Science and Technology has made observation in Seoul, Korea since ARP 2007. To observe extinction coefficient and PM, We used Transmissiometer LPV-3 and Dust Monitor(Grimm inc.). And we analyzed relationship between extinction coefficient per particle mass concentration and RH. In high RH (> 80%) Coarse ( PM10 - PM2.5 ) mode had strong influence whole period while in low RH(< 80%) fine mode ( PM2.5 ) had dominant effects in portion of period that might caused by NH4 or H2SO4, NaCl.
A11E-0178
Direct Radiative Effect of Major Aerosol Types Derived From MODIS Over Ocean
Accurate calculation of direct radiative effect of aerosol (DREA) at the top of atmosphere (TOA) is important to understand climate effect of aerosol. It is thought that the DREA is cooling effect at TOA in global average, however, DREA efficiency defined by DREA of unit aerosol optical thickness (AOT) is different for aerosol optical properties and even the sign could be opposite depending on aerosol optical properties and underlying surface albedo. To quantify accurately these effects from nadir-viewing satellite observation, aerosol classification algorithm should be taken into account in aerosol remote sensing algorithm. In this study, aerosol remote sensing algorithm including aerosol type classification procedure is proposed and DREA of major aerosol types, that is dust, black carbon, seasalt, and sulfate, at TOA is derived from Moderate Resolution Imaging Spectroradiometer (MODIS) over ocean. The derived annual mean DREAs show distinctly large negative value over west coast of Africa, the circumference of the Asian continent and the Antarctic continent. The west coast of Africa is affected by dust and black carbon aerosol from Sahara Desert and biomass burning from South Africa, the circumference of the Asian continent is affected by dust, black carbon, and sulfate from desert, biomass burning, and huge anthropogenic activity, and near the Antarctic continent is affected by enhanced seasalt by strong wind in boreal winter. The DREA efficiency show seasonal variation due to different fraction of aerosol types in each season. The DREA of major aerosol types derived in this study could help to understand more the climate effect of each aerosol type.
A11E-0179
Chemical Characterization and Single Scattering Albedo of Atmospheric Aerosols Measured at Amami-Oshima, Southwest Japan, During Spring Seasons
An intensive field program was performed to measure atmospheric aerosols at Amami-Oshima, a small island located at southwest Japan, in the spring season of 2001, 2003, and 2005 under the ACE-Asia, APEX and ABC-EAREX2005 projects. Chemical analysis of the fine and coarse aerosols was made for elemental carbon (EC) and organic carbon, water soluble ions, and trace elements. Single scattering albedo (SSA) of aerosols was independently estimated by two methods. The one (SSAc) is by chemical compositions assuming a half internal mixture between EC and non sea-salt sulfate, and the other (SSAo) is by optical measurements of scattering coefficient and absorption coefficient. The backward trajectory analysis showed that the aerosol concentrations in the air masses arrived at Amami, were much higher from the Asian Continent than from other regions, and two types of aerosol enhancement were observed. The one was caused by polluted air masses from the urban-industrial area of east-coast China, the other was by high mineral dusts due to large- scale dust storms in the desert regions of northwest China. The SSAc was in a range of 0.87-0.98, and in good agreement with the SSAo after some corrections for original scattering and absorption coefficients. The SSAc showed no significant difference between the air masses from the polluted area and the desert regions. The negative correlation between the SSAc and EC was divided into two groups depending on the concentration of non sea-salt sulfate, while the increase in mineral dusts did not show any correlation with the SSAc.
A11E-0180
Combined Microwave Radiometer and Micro Rain Radar Analysis of Cloud Liquid Water
The cloud liquid water is a parameter of vital interest in both modeling and forecasting weather. In meso- scale models, the magnitude of latent heat effects corresponds to the amount of cloud liquid water, which is important in the development of a certain weather system. The purpose of this study is to obtain the combined cloud liquid water from a 21.8 and 31.4 GHz ground based microwave radiometer (MWR) and the micro rain radar (MRR), because each instrument has the limitation of observation; it is widely known that the measurements of MWR and MRR are not meaningful with and without rainfall, respectively. The cloud liquid water of the two instruments has been measured at the Cloud Physics Observation System (CPOS) site, located at 37.41¢¥ N, 128.45¢¥ E and 842 m from mean sea level. To examine the performance of instruments, the precipitable water vapor (PWV) measured by the MWR was compared with the calculated PWV of nearest radiosonde from December 2003 to July 2008, and MRR was compared with the several accumulated precipitation observed by AWS. The PWV of MWR gives good agreement with that of radiosonde: R-square = 0.82 for spring, 0.78 for summer, 0.83 for fall, but 0.25 for winter. This bad performance in the winter season seems from the heavy snow on the radome, and then the winter data of MWR has been not considered in the combining algorithm. The comparison of MRR and AWS a correlation coefficient: 30min accumulated precipitation was R-square = 0.84. To combine the MRR and MWR cloud liquid water, firstly we estimate the cloud physical thickness from the difference between the MTSAT-1R cloud top height and cloud base height of visual observation of Daegwallyeong weather station, and the cloud liquid water path of MRR is obtained by multiplying the LWC of MRR and the estimated cloud physical thickness. The trend of MWR liquid water path agrees with that of the MRR during small precipitation. We study these characteristics of MRR and MWR for small precipitation to obtain the combined cloud water content of MRR and MWR, constantly operated regardless to the rainfall.
A11E-0181
An Experimental Study of Different Hygroscopic Material Seeding Paths to Dissipate Warm Advection Fog
A series of warm-fog dissipation experiments have been conducted on Daegwallyeong Plateau in South Korea during the spring of 2005-2008. The experiments were to examine the effects of two different hygroscopic substances (mainly CaCl2) seeding paths - circulating around the target (the circle seeding method) and crossing the advection fog flow incoming into the target (the line seeding method): 9 line seeding and 7 circle seeding experiments. Most of experiments showed the broadening of the FSSP- measured fog droplet distribution and the raindrops were detected in some experiments by disdrometer. The OPC (optical particle counter) measurements showed that the CaCl2 nuclei remained somewhat long time (more than 1 hour) around the target, probably by the aerial drag. Comparison between two seeding experimental results showed that the line seeding method had slower seeding impact time, defined as the time from the finish of seeding to the first peak of visibility improvement, but longer visibility improvement period and higher visibility improvement than those of the circle seeding. On average, two methods showed the 1.23-times improvement of visibility during about 23 minutes after the seeding. Most of experimental results gave a good agreement with Trabert's approximation theory, though slightly smaller. Further simulation approaches are needed to understand the effects of different seeding paths.
A11E-0182
Absorption of Visible and Long-wave Radiation by Primary and Secondary Biogenic Aerosols.
Field results for the 14C content of carbonaceous aerosols are presented that indicate significant biogenic sources of both primary and secondary aerosols in urban and regional environments. Samples collected in Mexico City and downwind of the urban area during the MILAGRO field study are compared with results reported previously in the literature indicating a significant amount of biogenic aerosols from both biomass burning and secondary photochemical production (e.g. terpene oxidations) are contributing to the overall carbonaceous aerosols in the optically active region of 0.1 to 1.0 micron. Samples in this size range collected on quartz fiber filters were also examined using an integrating sphere and FTIR diffuse reflectance techniques to obtain absorption spectra from 280 to the mid-IR. These data clearly indicate that the biogenic derived primary aerosols from agricultural and trash-burning, as well as secondary organic aerosols from isoprene and terpene oxidations will produce both UV-Visible (short-wave) absorbing substances as well as IR (long-wave) absorbing compounds including humic-like-substances (HULIS). With the anticipated increases in growing seasons (i.e. earlier springs and longer summers) the likely hood of increased fires (forest and grassland) as well as the continuing growth in agricultural burning activities, these primary sources are expected to increase and may play a role in heating of the atmosphere. The compound effects of these primary and secondary biogenic sources of absorbing aerosols to the total aerosol loading and regional climate will be discussed. This work was supported by the Office of Science (BER), U.S. Department of Energy, Grant No. DE-FG02-07ER64328 as part of the Atmospheric Science Program.
A11E-0183
Shortwave Aerosol Radiative Forcing over East-Asia Determined from Satellite and Ground based observations
Despite of heavy loading and strong absorbing characteristics, the aerosol radiative effect (ARE) over East Asian region is largely unknown. In this study, we attempt to estimate the ARE by using integrated data from ground-based measurement, satellite observation, radiative transfer model (RTM) calculation, and discuss its implications. The uncertainties of the radiative flux calculations used in this study are investigated due to the uncertainties in the RTM input parameters, such as aerosol optical depth (AOD), Angstrom exponent, single scattering albedo (SSA), surface reflectance, ozone, and relative humidity (RH). It is found that the anticipated overall uncertainty in radiative flux calculation is 8.56±3.24W/m2. The calculation results are consistent with AERONET inversion products and fluxes measured by the broadband radiometer and CERES. ARE is estimated as the difference in flux calculations with and without aerosols. The diurnal-mean aerosol radiative forcing efficiency, the slope of the linear fit line through the diurnal-mean ARE versus AOT plot, was found to be -35.1W/m2/τ550 (surface), -0.5 W/m2/τ550 (TOA), and 34.5 W/m2/τ550 (atmosphere). The national and annual mean aerosol radiative forcing values is - 15.7±8.9 W/m2 (surface), 0.3±1.6 W/m2 (TOA), and 16.0±9.2 W/m2 (atmosphere). Atmospheric aerosol forcing is highly responsible for negative forcing at surface. The maximum heating rate for hazy conditions (AOT>0.2) was 5.16°K/day, which is almost double the value in clean days (AOT<0.2) during the spring 2005. Furthermore, absorbing aerosols increased by 3 times larger during hazy conditions with respect to the integrated heating rate estimated during clean periods.
A11E-0184
Inter-Annual Variability of Radiative Forcing over the Northern Plains of Indian Sub- Continent using AERONET Sun-photometer, MODIS Terra, Aqua and CERES
Recent short term studies over the northern plains of the Indian sub-continent show very high aerosol optical depth (AOD) and high degree of seasonal and inter-annual variability of aerosols. Availability of relatively long term daily data (2001-2007), collocated over the same spatial (10km grid) and temporal (±30min) dimensions, from the ground (AERONET sun-photometer, level 2) and space platform (MODIS Terra and Aqua, level 2) provide a unique opportunity to study seasonal dependency and bias in satellite data for both late morning (Terra) and early afternoon (Aqua). Seasonal variability of AOD, COD (cloud optical depth) and validation of AOD (2001-2007) has been studied over the city of Kanpur, located centrally in the northern plains of the Indian sub-continent. We show quantitative seasonal and monthly dependency of bias, root mean square error and correlation coefficients. The observed aerosol optical parameters (AOD and Angström coefficient) and aerosol characteristics (fine mode fraction, effective radius and soot mass) vary with season (summer, winter and monsoon period). The seasonal and monthly variability of the associated aerosol radiative effect (ARE) based on AERONET sun-/sky-photometer and cloud radiative effect (CRE) from CERES for shortwave, and longwave at the surface, top-of-the-atmosphere (TOA) and net atmospheric for the period 2001-2007 will be presented in view of the observed dust events during summer, fog conditions during winter and poor or good monsoon conditions during monsoon season. The inter-seasonal variability is also evident in radiative forcing (TOA ARE is found to vary in the range -8.06 to -4.33 and -10.4 to -7.25 during summer and winter, respectively). We will discuss relations between MODIS Terra derived AOD, COD and CERES Terra CRF, during various seasons over the northern plains.
A11E-0185
Light Absorbing Aerosols in Mexico City
The direct effects of aerosol radiative forcing has been identified by the IPCC as a major uncertainty in climate modeling. The DOE Megacity Aerosol Experiment-Mexico City (MAX-Mex), as part of the MILAGRO study in March of 2006, was undertaken to reduce these uncertainties by characterization of the optical, chemical, and physical properties of atmospheric aerosols emitted from this megacity environment. Aerosol samples collected during this study using quartz filters were characterized in the uv-visible-infrared by using surface spectroscopic techniques. These included the use of an integrating sphere approach combined with the use of Kubelka-Munk theory to obtain aerosol absorption spectra. In past work black carbon has been assumed to be the only major absorbing species in atmospheric aerosols with an broad band spectral profile that follows a simple inverse wavelength dependence. Recent work has also identified a number of other absorbing species that can also add to the overall aerosol absorption. These include primary organics from biomass and trash burning and secondary organic aerosols including nitrated PAHs and humic-like substances, or HULIS. By using surface diffuse reflection spectroscopy we have also obtained spectra in the infrared that indicate significant IR absorption in the atmospheric window-region. These data will be presented and compared to spectra of model compounds that allow for evaluation of the potential importance of these species in adding strength to the direct radiative forcing of atmospheric aerosols. This work was supported by the Office of Science (BER), U.S. Department of Energy, Grant No. DE-FG02-07ER64327 as part of the Atmospheric Science Program.
A11E-0186 [WITHDRAWN]
Instrument Development for Single-Particle Albedo Measurements
The ASTER (Aerosol Scattering To Extinction Ratio) instrument simultaneously measures scattering and extinction by single aerosol particles from which the albedo for each particle can be determined. ASTER employs a high-Q laser cavity to amplify loses in the cavity caused by individual particles to produce measurable extinction signals. The instrument collects light in three separate channels representing backward, forward, and wide-angle scattering. The ratio of forward to total scattering provides a proxy measurement for particle size that Mie scattering calculations show to be largely independent of particle refractive index for diameters below about 2 micrometers. Laboratory measurements on particles of known sizes and scattering properties have been used to assess the performance of the instrument and as a guide for ongoing modifications for eventual field deployment. Results from the current version of the instrument will be presented and compared to previous ASTER data to demonstrate improved performance. Data taken from ambient air have shown modes of highly absorbing particles that would not have been evident from bulk measurements. The single-particle nature of the measurements will provide additional information to complement existing methods for measuring aerosol albedos in the atmosphere.
A11E-0187
Using MISR data to estimate TOA albedo change by aerosols based on land surface types
Using internally-consistent albedo, aerosol, cloud and surface data from the Multi-angle Imaging SpectroRadiometer (MISR) instrument onboard the Terra satellite, top-of-atmosphere (TOA) spectral albedo change ( dα ) in the presence of aerosols over land is estimated and its dependence on aerosol and surface properties is analyzed. Linear regressions between spectral TOA albedo and aerosol optical depth (AOD) for different surface types are examined to derive the aerosol-free TOA albedo. MISR surface BiHemispherical Reflectance (BHR) values are used to differentiate surface types. We find relatively high correlations between spectral TOA albedo and AOD for BHR-stratified data in 2° × 2° grid cells. The global mean values of cloud-free dα over land for June-September 2007 are estimated to be 0.018±0.003 (blue), 0.010±0.003 (green), 0.007±0.003 (red), and 0.008±0.006 (NIR). Individual regions show large variations from these values. Global patterns of dα are determined mainly by AOD and aerosol radiative efficiency. Large positive values of dα are observed over regions with high aerosol loading and large single-scattering albedo (SSA), where the aerosol scattering effect is dominant. The presence of light absorbing aerosols reduces aerosol radiative efficiency and dα. Surface reflectance influences both aerosol scattering and absorbing effects. Generally, the aerosol radiative efficiency decreases with increasing BHR. We also examined dα–AOD correlations over different vegetation types. We find the smallest dα values are over needleleaf forests and shrublands, whereas the largest values are over cropland and barren regions. The aerosol radiative efficiencies are lowest over needleleaf forests and barren regions, and highest over grasslands and croplands.
A11E-0188
Equatorial Superrotation on Earth Induced by Optically Thick Dust Clouds
How does the Earth's atmosphere respond to exceptional aerosol events, and what is the mechanism leading to consequent past and possible future climate shifts? One possible mechanism leading to aerosol-induced climate shifts is the striking atmospheric dynamics phenomenon of equatorial superrotation, such as that found on Venus and Saturn's moon Titan, with its enhanced meridional transport. Recently, a significant breakthrough has been made in our theoretical understanding of atmospheric superrotation on Venus and Titan. Extending this result regarding superrotation in planetary atmospheres to the concept of superrotation in Earth's atmosphere serves not only to shed insight into long-standing and seemingly disparate questions of Earth's climate (such as the mechanism of mass extinction and geo-engineering mitigation of global warming) but also to develop a common theoretical framework to address the impacts of profound changes of atmospheric aerosols and their consequences. The three-dimensional Goddard Institute for Space Studies (GISS) modelE GCM and Johns Hopkins University Applied Physics Laboratory (JHU/APL) two-dimensional radiative-dynamical model are used to investigate the induction of equatorial superrotation in Earth's stratosphere, as well as its effect on meridional transport of dust and aerosols in association with the supervolcano eruptions. Preliminary results show that an equatorial superrotational wind in the upper troposphere was initiated and lasted for more than two years following the Mt Toba eruption near the equator about 71,000 years ago. The circulation structure at mid-latitude was also altered, indicating a global impact of an equatorial injection of an aerosol layer.
A11E-0189
Diagnosing the Effects of Aerosol and Cloud Droplet Aging on Microphysical and Optical Variations in Warm Clouds
Enhanced aerosol concentrations have a number of impacts on clouds, includnig higher droplet concentrations, changed cloud droplet dispersion, and effects on cloud dynamics. While there have been extensive field observations focused on simultaneously measuring aerosol and cloud physicochemical properties as well as measures of cloud dynamics and thermodynamics, it is difficult to disentangle the variability associated with the aerosol effects from those of large-scale forcing of the cloud system and small- scale effects associated with cloud dynamics and evolution. In this paper, we use a number of statistical and filtering techniques, including principle components analysis and spectral-domain filtering, to try to ascribe observed variability in cloud microphysics to the aerosol and dynamical factors that force that variability. The primary source of data used are observations from ONR's CIRPAS Twin Otter aircraft.
A11E-0190
Observations of marine stratocumulus microphysics and implications for processes controlling droplet spectra: results from the Marine Stratus/Stratocumulus Experiment (MASE)
During the Marine Stratus/Stratocumulus Experiment (MASE), cloud and aerosol microphysics were measured in the eastern Pacific off the coast of Northern California onboard Department of Energy Gulfstream-1 in July 2005. Three cases with uniform aerosol concentration and minimal drizzle concentration were examined to study the cloud microphysical behavior. For these three cases, the average droplet number concentration increased with increasing altitude, while the average interstitial aerosol concentration decreased with altitude. The data show enhanced growth of large droplets and spectral broadening in cloud parcels with low liquid water mixing ratio. Three mixing models, including inhomogeneous mixing, entity type entrainment mixing, and circulation mixing proposed in this study, are examined with regard to their influences on cloud microphysics. The observed cloud microphysical behavior is most consistent with the circulation mixing, which describes the mixing between cloud parcels with different lifting condensation levels during their circulations driven by evaporative and radiative cooling. The enhanced growth and spectrum broadening resulting from the circulation mixing reduce cloud albedo at the same liquid water path and facilitate the formation of precipitation embryos.
A11E-0191
Cloud radiative properties derived from the Solar Spectral Flux Radiometer (SSFR) during recent airborne field campaigns
The Solar Spectral Flux Radiometer (SSFR) has flown on several airborne campaigns in the last few years (e.g. PACDEX, TC4, ARCTAS). From the measurement of spectral irradiance, cloud optical properties are derived including: optical depth, spectral albedo, flux divergence (cloud absorption) and particle effective radius. Most of these important parameters for radiative budget studies are derived from satellite radiance measurements (e.g. MODIS), others such as flux divergence are not. Aircraft spectral irradiance measurements offers the possibility to validate satellite retrievals and to examine the relationship between radiance measurements (made by satellites) to those of irradiance, the fundamental quantity of the radiative energy budget. We test the ability of radiative transfer models (both 1 and 3-D) and asymptotic theory to recreate spectral cloud albedo measurements from radiance measurements. Finally, spectral flux divergence, is compared to model calculations for both low level liquid water clouds and for high level ice clouds. The possible influence of aerosols on cloud radiative properties is highlighted.
A11E-0192
Design and Characterization of the 4STAR Sun-Sky Spectrometer with Results from 4- Way Intercomparison of 4STAR, AATS-14, Prede, and Cimel Photometers at Mauna Loa Observatory.
Uncertainties in radiative forcing of climate are still dominated by uncertainties in forcing by aerosols. Aerosols impact the radiation balance in three primary ways: the direct effect through scattering and absorption of radiation, the indirect effect by acting as cloud condensation nuclei affecting cloud optical depth and longevity, and the semi-direct effect affecting cloud formation and longevity through heating and thermodynamics. An active collaboration between the Pacific Northwest National Laboratory (PNNL), National Aeronautics and Space Administration (NASA) Ames Research Center (ARC), and NASA Goddard Space Flight Center (GSFC) is advancing new instrument concepts with application to reducing these aerosol uncertainties. The concept of 4STAR (Spectrometer for Sky-Scanning, Sun-Tracking Atmospheric Research) combines airborne sun tracking capabilities of the Ames Airborne Tracking Sun Photometer (AATS-14) and Aeronet-like sky scanning capability with state-of-the-art monolithic spectrometry. The overall science goal for the new instruments is to improve knowledge of atmospheric constituents and their links to climate. The high-resolution spectral capability will improve retrievals of gas constituents (e.g., H2O, O3, and NO2) and thereby improve determination of aerosol properties as residual components of the total optical depth. The sky scanning capability will enable retrievals of aerosol type (via complex refractive index and shape) and aerosol size distribution extending to larger sizes than attainable by direct-beam sun photometry alone. Additional technical goals are to reduce instrument size, weight, and power requirements while increasing autonomy and component modularity to permit operation on a wide range of aircraft including unmanned aerial vehicles (UAVs). To investigate techniques to accomplish these goals, we developed a ground-based prototype, 4STAR-Ground. The 4STAR-Ground operating performance has been characterized in many tests including field of view (FOV) scans, repeatability testing of the fiber optic coupler, calibration of diffuse sky radiance with integrating sphere, and calibration of solar irradiance via Langley retrievals. Recent results from an intercomparison on Mauna Loa Observatory involving 4STAR, AATS-14, AERONET Cimel sun-sky photometers, and a Prede sun-sky photometer will be presented.
A11E-0193
Examining the Effect of Future Sulfate Emissions Controls in the U.S. on Photolysis Rates
An online photolysis module has been developed and implemented within the Community Multiscale Air Quality (CMAQ) model. The module uses clouds predicted by the meteorological model and modeled nitrogen dioxide (NO2), ozone (O3), and aerosol concentrations to calculate actinic fluxes and photolysis rates at every vertical level in each of seven wavelength intervals from 291 to 850 nm, as well as the total surface irradiance and aerosol optical depth within each interval. The module is computationally efficient, requiring approximately 7.5% additional runtime compared to the offline lookup table method employed in standard CMAQ. The vertical profiles of summertime photolysis rates and ozone concentrations computed by the online and offline modules will be compared. Preliminary results indicate significant decreases in ozone over urban areas due to either enhanced absorption by NO2 and O3 or increased aerosol scattering. We will also present a sensitivity study with emission controls mandated by the U.S. Environmental Protection Agency's Clean Air Interstate Rule (CAIR) to examine the effect of reduced sulfate emissions on predicted photolysis rates and ozone concentrations.
A11E-0194
Cloud and aerosol retrieval methods with scattered surface-based radiance measurements
The Shortwave Spectrometer (SWS) has been operating continuously for 2.5 years at the Southern Great Plains facility of the Department of Energy's Atmospheric Radiation Measurement Program. The SWS measures ground based zenith radiance with a field of view of 1.4°. We will demonstrate a new method of retrieving cloud properties, specifically cloud optical depth and, with additional observations, the cloud particle effective radius. This retrieval method will be compared to an existing surface radiance based retrieval method. Though the primary focus of the SWS is cloud remote sensing, some of the more intriguing data has been observed under cloudless skies. On nearly every cloudless day when the solar elevation was sufficiently large, the SWS measured preferential scattering not visible to the eye at angles near 25°. In addition to the zenith measurements taken daily by the SWS, recent measurements were taken at different observation angles under cloudless skies using a solar tracker/positioner. The spectral information in these measurements indicates that this is a corona feature, as opposed to a halo, similar to that of Bishop's Ring. This corona feature will be used to derive the properties of the aerosol responsible for the angular scattering behavior.
A11E-0195
The effect of nonsphericity on the scattering and radiative properties of mineral dust aerosols: An application to the deep blue aerosol retrieval algorithm
The scattering and radiative properties of mineral dust aerosols at the MODIS bands involved in the deep blue algorithm are investigated. The response functions are considered in calculating the bulk optical properties of dust aerosols. A spheroid model is assumed to account for the nonsphericity effect of mineral dust particles on their scattering and radiative properties. For comparison, Mie theory is also used to calculate the scattering properties of spherical dust particles. To simulate the single-scattering properties of spheroidal dust particles, a combination of the T-matrix method and an approximate method is employed in the present study. Difference in the phase functions of mineral dusts between spheroid and sphere shape assumption leads to significant inconsistency in the computation of radiative properties of mineral dust aerosols. Furthermore, the sensitivity study regarding the nonsphericity effect on the retrieved optical depth in the deep blue algorithm indicates the importance of particle nonsphericity in the retrieval of mineral dust aerosol properties.
A11E-0196
Low Cloud Cover Increase by Absorbing Soil (Mineral) Dust Aerosols - A Counterexample to the Classic Semi-direct Aerosol Effect
The semi-direct aerosol effect is defined as a change in cloud cover due to changes in column temperature and humidity by aerosol radiative heating. In the classic example, heating within the aerosol layer increases temperature, thereby reducing relative humidity and cloud cover. Here we show a counterexample from simulations with an atmosphere general circulation model, where low cloud cover is increased during Northern Hemisphere summer by absorbing aerosols. Dust aerosol radiative forcing heats the column. The anomalous temperature increase is highest in the upper troposphere and smallest near the surface. This temperature change by itself would reduce relative humidity and cloud cover, with the largest decrease at upper levels. However, the absorbing aerosols increase column moisture, and this increases relative humidity near the surface. Thus, in this example, aerosols increase low cloud cover while decreasing cloud cover at upper levels. These anomalies increase with aerosol absorption. The cloud cover increase results from dynamical changes to column temperature and moisture rather than aerosol changes to cloud micro-physics.
A11E-0197
Sensitivity of cloud droplet number concentration, cloud fraction, and precipitation to nucleation
New particle formation by nucleation is an important source of atmospheric particles under some conditions. Particle formation rates predicted by competing nucleation theories vary by many orders of magnitude, and this creates uncertainty in model predictions of cloud condensation nuclei (CCN) concentrations and cloud droplet number concentration (CDNC). Our previous work evaluated the sensitivity of CCN concentrations at a fixed supersaturation to nucleation using a global aerosol microphysics model (Pierce and Adams, 2008). The sensitivity of cloud microphysics properties, e.g. CDNC, spectral dispersion and precipitation, to nucleation rates is very important for aerosol indirect effects, but it has not been investigated using the global aerosol microphysics model. To evaluate nucleation impacts on CDNC, it is necessary to have an advanced aerosol activation algorithm in the global model. The aerosol activation parameterization developed by Nenes and Seinfeld (2003) accounts for kinetic limitations using the "population splitting" method. This parameterization had been continuously developed by Fountoukis and Nenes (2005) and can account complex chemical effects, e.g. surfactant effects. Newly formed particles, typically a few nanometers in diameter, exist in the nucleation mode (Kulmala et al, 2004). Often, nucleation mode particles are not simulated explicitly in global models due to the high computational burden from the additional size range of particles (Kerminen et al., 2004a) and their fast dynamics. As a substitute, global models use a parameterization developed by Kerminen et al. (2004b) (hereafter, Kerminen parameterization) that takes into account the nuclei growth by vapor condensation as well as the coagulational scavenging of the growing nuclei by pre-existing particles. Applying the Kerminen parameterization in a global model may introduce biases in indirect effect calculations. In this work, we evaluate the ability of the Kerminen parameterization to reproduce nucleation mode dynamics by comparing against the global aerosol microphysics model with an explicit nucleation mode. With the more reasonable configuration of the global aerosol model based on the evaluation result of Kerminen parameterization, we investigate how much CDNC, cloud fraction, and precipitation are changed with different nucleation mechanisms using the GISS GCM II-prime (Hansen et al, 1983) with online aerosol microphysics (Adams and Seinfeld, 2002) and aerosol activation parameterization based on Nenes and Seinfeld (2003) with the mass transfer coefficient correction of Fountoukis and Nenes (2005). (1) Pierce, J. R. and P. J. Adams, Atmos. Chem. Phys. Discuss., 8, (2008) (2) Nenes, A. and J. H. Seinfeld, J. Geophys. Res., 108, (2003) (3) Fountoukis, C. and A. Nenes, J. Geophys. Res., 110, (2005) (4) Kulmala, M. et al., Aerosol Science, 35, (2004) (5) Kerminen, V., et al., Tellus, 56B, (2004a) (6) Kerminen, V., et al., Aerosol Sci. Technol., 38, (2004b) (7) Hansen, J. et al., Mon. Weather Rev., 111, (1983) (8) Adams, P. J. and J. H. Seinfeld., J. Geophys. Res., 107, (2002)
A11E-0198
ICARE: Data And Services In Support Of Cloud And Aerosol Research
The ICARE Thematic Center was created in 2003 at the University of Lille to provide data and services to the
science community in research fields such as aerosols, clouds, water cycle, radiation, and their interactions.
ICARE is sponsored by CNES, CNRS/INSU, the University of Lille, and the Nord-Pas-De-Calais Regional
Council. One primary objective is to help the science community access and exploit the huge data volumes
derived from the A-train satellites, combine them with products derived from other satellite missions, including
meteorological satellites, or compare them to ground-based measurements to support validation activities.
ICARE is in charge of the production and distribution of PARASOL science products. In addition, many data
sets such as Calipso, CloudSat, Aqua, and Aura products are routinely acquired by ICARE from other data
providers, then made available to the ICARE community through the ICARE website or ftp server. ICARE
develops expertise with satellite data and operational processing, and offers various support services to the
users community, such as development of operational processing codes using algorithms provided by
scientists, development of specific tools based on users requests, and development of web interfaces to help
users browse, select and analyze data from the ICARE archive. In particular, ICARE favors multisensor
approaches and aims at developing and implementing combined products (e.g., PARASOL-MODIS,
CALIPSO-PARASOL, CALIPSO-Cloudsat...). Examples of ICARE achievements will be shown, with emphasis
on the A-train related activities.
http://www.icare.univ-lille1.fr
A11E-0199
Comparison of near-surface and column-integrated atmospheric optical properties at Bermuda
Many long term records of atmospheric optical and chemical properties are based on near-surface measurements. Interpreting and extending climatologies of near-surface observations in the context of column-averaged properties such as aerosol optical depth (e.g., the AERONET network) requires information concerning the structure and distribution of aerosols within the overlying atmospheric column. As part of a 3-year, NSF-sponsored project, light scattering and spectral absorption by near-surface aerosols at Bermuda were measured with a scattering nephelometer and from the reflectance of filter samples, respectively. Recently these measurements have been augmented by a Micropulse Lidar (MPL) operated through MPLNET, and an AERONET CIMEL sun/sky photometer. The LIDAR observations provide the link with which to extend the optical properties of near-surface aerosols to the aerosol optical depth of the overlying column. We will present and interpret coincident data ensembles generated during summer 2008.
A11E-0200
Direct-to-diffuse UV Solar Irradiance Ratio for a UV rotating Shadowband Spectroradiometer and a UV Multi-filter Rotating Shadowband Radiometer
Abstract. Two spectroradiometers reside that measure direct and diffuse UV solar irradiance are located at the Table Mountain Test Facility, 8 km north of Boulder, CO. The UV- Rotating Shadowband Spectrograph (UV-RSS) measures diffuse and direct solar irradiance from 290 – 400 nm. The UV Multi-Filter Rotating Shadowband Radiometer (UV-MFRSR) measures diffuse and direct solar irradiance in seven 2-nm wide bands, i.e. 300, 305, 311, 317, 325, and 368 nm. The purpose of the work is to compare radiative transfer model calculations (TUV) with the results from the UV-Rotating Shadowband Spectroradiometer (UV-RSS) and the UV-MFRSR to estimate direct-to-diffuse solar irradiance ratios (DDR) that are used to evaluate the possibility of retrieving aerosol single scattering albedo (SSA) under a variety of atmospheric conditions: large and small aerosol loading, large and small surface albedo. For the radiative transfer calculations, total ozone measurements are obtained from a collocated Brewer spectrophotometer.
A11E-0201
Infrared cloud imaging for diurnal remote sensing of cloud statistics including cloud type
Clouds are a critical component in determining weather and climate. Spatial and temporal statistics of cloudiness are needed in applications ranging from climate research to precision agriculture. Ground-based cloud remote sensing is particularly useful in applications requiring high spatial and temporal resolution. Thermal infrared imaging allows continuous detection of clouds from their thermal emission, with no interruption during sunrise, sunset, or night. In addition to detecting clouds continually during day and night,the third-generation Infrared Cloud Imager (ICI-3) is capable of classifying thin clouds according to their optical depth. This added capability is provided by a rigorous radiometric calibration and compensation of atmospheric emission from the infrared sky images. Data are shown that illustrate the importance of cloud- type classification in determining the radiative effect of variable cloudiness.