A23C-0807 1340h
Origins and Impacts of Arctic Soot: A GISS ModelE Experiment
The fragile Arctic is especially susceptible to the impacts of particles and other pollution. These may affect the radiative balance there, shifting temperature profiles, clouds and precipitation. Absorbing particles such as black carbon or soot may accelerate ice and snow melting. Studies of Arctic pollution typically implicate northern Eurasia, primarily Russia and Europe, as the primary sources of emissions that reach the Arctic. However, the predominant global source of industrial black carbon emissions is estimated to come from the Far East (20%). Another substantial but distant emission is from low latitude biomass burning (50%). We use the Goddard Institute for Space Studies (GISS) General Circulation Model (GCM) to investigate the origins of Arctic black carbon (BC) by isolating various source regions and types. We permit the BC to affect the model ice/snow albedo. The model suggests that the predominant sources of Arctic soot today are indeed these distant regions. The model's Arctic BC optical thickness is mostly from the Far East (30%) and from biomass (28%, with slightly more than 1/2 coming from north of 40N); North America, Russia and Europe each contribute 10-15%. Transport from the Far East and distant biomass regions involves lofting of BC aerosols to high altitudes where they may be transported pole-ward. Thus it differs from the classic `low altitude, winter-springtime Arctic haze' transport, presently believed to be the primary mechanism responsible for bringing pollution to the Arctic. The model does confirm the importance of Russian and European contributions to the low-altitude springtime Arctic haze transport, however it indicates that the Far East also contributes substantially (all 3 regions contribute 20-25%). In the Arctic upper troposphere/lower stratosphere during the springtime, we find that the Far East (30-50%) and low latitude biomass (20-30%) are dominant, with a significant aircraft contribution (10-20%). Substantial uncertainties result from the estimated sources, model vertical mixing and aerosol removal processes. Nevertheless, our results suggest that greater consideration of the distant sources and pathways of Arctic pollution is needed. We implement a scheme that allows model soot to affect ice and snow albedo and therefore ice/snow cover, radiation and climate. We will present the model radiative forcing due to BC in the atmosphere as well as the indirect ice/snow forcing.
A23C-0808 1340h
Monitoring Aerosol Optical Properties Over the Mediterranean From SeaWiFS Images Using a Neural Networks Inversion
The SeaWiFS archive provides a unique opportunity to study aerosol optical properties over oceans since October 1997. Standard SeaWiFS aerosol products are however not suitable because optical thicknesses are limited to 0.35 and Angstr\"om coefficient to 1.5. We developed an inversion based on neural networks to retrieve both optical thickness and Angstr\"om exponent from SeaWiFS read and near infrared channels. Neural networks are capable of approximating non-linear inverse functions and of processing efficiently large amounts of data. Neural networks were trained with radiative transfer computations for wide ranges of optical thickness and Angstr\"om exponent. All SeaWiFS images of the Mediterranean for years 1998, 1999 and 2000 were processed and monthly mean maps of aerosol optical thickness and Ansgtr\"om exponent were derived. A comparison with ground-based measurements at three AERONET stations in the Mediterranean for the year 2000 shows the good accuracy of the method, as well as the improvement compared to operational SeaWiFS aerosol products. The neural networks are able to retrieve high values of the optical tickness and of the Angstr\"om exponent.
A23C-0809 1340h
MSG Improved Capabilities for Marine Aerosol Characterization
Despite their significant contribution to the Earth radiative budget, aerosol spatial and temporal distributions are still insufficiently quantified at the global scale because of the variability of aerosol sources, particle size distributions and chemical compositions. Satellite observations are well suited to provide the climate community with the needed aerosol load distributions, even if most aerosol products suffer from a poor daily coverage. Compared to existing orbiting sensors such as MODIS or POLDER or to less sophisticated geostationary sensors such as METEOSAT or GOES, MSG multi-spectral measurements in the visible and near-infrared offer new opportunities to study aerosols at high temporal and spatial resolutions over oceans. The MSG field-of-view is particularly suitable for the monitoring of aerosol load and transport over the Atlantic and the Mediterranean, in particular Saharan dust from North Africa, biomass-burning aerosols from subtropical Africa and pollution plumes from Europe. We developed an inversion technique that relies on MSG bands at 0.6 and 0.8 m to estimate both aerosol optical thickness and Angström coefficient, a parameter characteristic of the particle size distribution. Spectral MSG measurements are compared to pre-computed values to find the best match. These theoretical values were computed using the 6S radiative transfer model (Vermote et al., 1997) for a set of aerosol models, which have been extrapolated from the Shettle and Fenn (1979) models to cover Angström coefficient values between 0 and 2.5. This inversion technique was applied to nine images per day between 09:00 and 16:00 UT for June 2003. A comparison with AERONET in-situ measurements performed in the tropical Atlantic and in the Mediterranean shows that MSG retrievals have a good accuracy in terms of both optical thickness and Angström coefficient. Monthly mean maps of both parameters are compared to that of the POLDER sensor for the same period, showing the benefit of using several images per day instead of one single orbit.
A23C-0810 1340h
Monte Carlo Approach to Estimating the Global Anthropogenic Aerosol Forcing: Sensitivity to Assumptions and Datasets
A preliminary estimate of the direct effects of the anthropogenic aerosols on the solar radiation is made. The approach is to use our Monte-Carlo Aerosol-Cloud Radiation (MACR) model to generate the global monthly climatology of the aerosol forcing at its recent level, say from 1995-2003. An earlier version of the MACR was developed and validated during INDOEX, and was updated for this study to include Monte Carlo integration of atmospheric fluxes in multidimensional parameter space. Additional update features include a) making the model global, b) using observed global ozone, precipitable water and surface albedo, c) accounting for the effect of the surface orography, and d) using observed cloud information from ISCCP D2. GOCART, MODIS and AERONET products were processed to obtain AOD, SSA and asymmetry parameter as inputs for the MACR. The global mean forcing in cloudy skies is -0.75 Wm-2 at the TOA, 3.0 Wm-2 in the atmosphere and -3.75 Wm-2 at the surface. The NH mean is -0.92 Wm-2 (TOA), 3.85 Wm-2 (atmosphere) and -4.76 Wm-2 (surface), and the SH mean -0.58 Wm-2 (TOA), 2.15 Wm-2 (atmosphere) and -2.73 Wm-2 (surface). These estimates are based upon certain assumptions and certain combination of the datasets. In case we use AOD, SSA and asymmetry parameter derived without AERONET, the forcing is -0.58 Wm-2 (TOA), 3.35 Wm-2 (atmosphere) and -3.93 Wm-2 (surface). We present various estimates by changing the assumption of aerosol mixing, making the sky clear, or changing the aerosol vertical profile.
A23C-0811 1340h
First Estimates of Anthropogenic Aerosol Radiative Forcing from Terra Satellite Measurements
Using the Single Scanner Footprint (SSF) data that combines the multi-spectral Moderate Resolution Imaging Spectroradiometer (MODIS) cloud and aerosol products with the Clouds and the Earth's Radiant Energy System (CERES) top of atmosphere broadband radiative fluxes, we first provide observational estimates of the instantaneous cloud-free shortwave aerosol radiative forcing (SWARF) over the global oceans. Different from our previous research, we corrected for both the sample biases and the diurnal cycle of SWARF and the cloud-free diurnally averaged SWARF is -5.3 +/- 1.7 Wm-2, a value that is consistent with previous studies. Furthermore, we partition the CERES shortwave flux as a function of MODIS aerosol optical thickness and the fraction of fine mode aerosol to the total aerosol optical depth (eta). Since eta is related to particle size and is a good surrogate for aerosol type, we present strategies for estimating the radiative forcing of anthropogenic aerosols from MODIS and CERES measurements that is important for quantifying the climate forcing of aerosols.
http://vortex.nsstc.uah.edu/~sundar/papers/2004/2004_grl_submit.pdf
A23C-0812 1340h
Use of Data Assimilation to Estimate the Aerosol Radiative Forcing
One of the major difficulties in assessing the aerosol radiative forcing is the interpretation and evaluation of a wide variety of satellite, aircraft, and surface measurements. In addition, the poor current state of knowledge of the global aerosol sources, sinks, and radiative properties makes relying on global climate models problematic. We are using data assimilation techniques to include measurements of atmospheric aerosols from many platforms in a global model, to improve the model simulations of the aerosol transport, and to assess the aerosol radiative forcing. We initially concentrate on the ACE-Asia and SAFARI 2000 campaigns for which there is much data, using the NCAR Community Atmosphere Model (CAM) to simulate the aerosol spatial distribution. Since radiances are the observables must closely related to our scientific goal of determining radiative forcing, we assimilate satellite-observed radiances directly---instead of the higher level data products that require assumptions about the aerosols and gases which may differ from instrument to instrument---using an adjoint of the radiative transport equation. (This technique has been successfully employed to assimilate data from the Mars Global Surveyor satellite.) We are also working on an adjoint of CAM that will allow full four-dimensional assimilation, with the prospect of improved determination of aerosol sources and sinks. With these tools, the assimilation of global satellite data can contribute to our knowledge of aerosol and tracer distributions, and particularly of aerosol radiative forcing.
A23C-0813 1340h
Modeling Aerosol Radiative Effects over Dust Source Regions in Western North China
To investigate the effects of aerosols on the radiation budget over Asian dust source regions in western north China, a synthetic numerical boundary layer model has been developed with respect to interactions of aerosols, heat, and wind fields. The model includes three sub-models, which are a 3-D non-stationary atmospheric boundary layer model, an atmospheric diffusion model and a radiation transmission model. The synthetic model has been validated with the measurement data of total suspended particles (TSP), temperature, wind, and radiation in atmospheric boundary layer obtained at Lanzhou (36N, 103E) and adjacent regions on the upper reaches of the Yellow River. The comparison shows that the simulated short and long wave radiation fluxes match the measured data fairly well. Testing of two modelling schemes with and without aerosols clearly brought up the importance of aerosol radiative effects on a regional scale. Preliminary results indicate an obvious heat increase in the boundary layer during daytime due to the effect of aerosol short radiative wave. The temperature increases more than 1 K in an hour. The corresponding variation of the wind speed is about 0.3m s-1. TSP concentrations on the lower layers tend to decline, but on the higher layers they tend to increase. At night, aerosol long wave radiative effect produces an increase in atmospheric temperature near the ground, but the temperature will drop in the lower layer (25m-300m) of the atmosphere, varying about 0.1-0.2 K h-1. Wind speed and TSP concentration tend to make corresponding variations.
A23C-0814 1340h
A new Idealized Global Climate Model and its Application to Dust-Climate Interactions
Airborne mineral dust can influence the climate by altering the radiative properties of the atmosphere. However, the sign and magnitude of climate forcing and response are not well known. An idealized global model is developed to study processes and feedbacks within the dust-climate system. The model is solved numerically for equilibrium climate states defined by zonal average surface and atmospheric temperatures as a function of latitude. Radiative, latent, and sensible heating are parameterized. The model includes a variable lapse rate, based on moist convection in the tropics and baroclinic eddies in high latitudes, and parameterizations of the major dynamical mechanisms responsible for meridional heat transport: the Hadley cell, midlatitude baroclinic eddies, and ocean circulation. The model determines the longwave and shortwave dust forcing, as well as the resulting climate change, based on the specified dust distribution and optical properties. The model reproduces both the observed mean variation of temperature with latitude and the global average heat budget. The model also produces realistic radiative forcing values for the present day dust distribution. Modeled radiative, temperature, and hydrological changes caused by the Mount Pinatubo eruption compare favorably to observations and general circulation model results. For a reference set of dust optical properties, the modeled global average top-of-atmosphere (TOA) shortwave dust forcing is -0.73 W/m$^2$, and the longwave forcing is 0.23 W/m$^2$. For plausible ranges in dust optical properties, the net forcing varies from -2.0 W/m$^2$ to +3.1 W/m$^2$. Studies which use a shortwave single scattering albedo corresponding to World Climate Program dust optical properties may be underestimating the effect of dust. Dust decreases the surface and atmospheric temperatures by about 0.1 K and reduces latent and sensible heat fluxes by 1%. Based on the range of optical property values used, the surface temperature change ranges from -0.3 K to 0.6 K. The latent heat change ranges from -1.9 W/m$^2$ to 0.5 W/m$^2$. In addition, temporal variations in dust concentration contribute to interannual climate variability.
A23C-0815 1340h
Comprehensive Characterization of Size-resolved Composition and Morphology of Mineral Dust Particles for Radiative Forcing Studies
Improved understanding of the properties of mineral aerosols is needed for both the interpretation of atmospheric radiation observations and for radiative forcing modeling. Complex shapes and source-dependent heterogeneous composition of mineral particles pose the main challenge in developing the reliable treatments of dust. We present the results of a comprehensive analysis of a unique data set of physicochemical properties of mineral dust representative of active dust production regions in the Sahel and China. Mineral dust aerosols were generated from natural soil samples in the laboratory wind-tunnel experiment in a way similar to saltation and sandblasting processes that are responsible for mineral dust emissions in natural conditions. Both soil and dust aerosol samples were analyzed for their size, morphology, elemental and mineralogical composition by a number of techniques. In addition, a new technique developed by Lafon et al. (2004) has been used to determine the amount and mineralogical speciation of iron oxides in the dust samples. This information is crucial for constraining the light absorption by dust particles. The data set enables us to reconstruct several classes of representative composition-shape-size distributions required for modeling the aerosol optical characteristics following the approach of Kalashnikova and Sokolik (2004). A detailed sensitivity study was performed to assess the range of changes in optical and radiative properties of dust due to the variability in method-dependent particle size distribution, assumptions on particle shapes, and varying amount of iron oxides.
A23C-0816 1340h
Comparison of an Aerosol Assimilation System of MODIS Radiances with AERONET retrievals.
We present results from a simple off-line assimilation system of the radiances from the 7 MODIS channels that sense atmospheric aerosols. We describe the assimilation cycle. The Goddard Chemistry and Aerosol Radiation Transport Model (GOCART), which is driven by assimilated meteorology, simulates five aerosol types: dust, seasalt, black carbon, organic carbon and sulfate. The forward model takes the aerosol information from the GOCART model and calculates radiances based on optical parameters of the aerosol type, satellite viewing angle and the particle growth from relative humidity. Because the GOCART model is driven by previously assimilated meteorology, these forward model radiances can be directly compared with the observed MODIS level2 radiances. The off-line assimilation system simply adjusts the aerosol loading in the GOCART model so that the observed minus forward model (O-F) radiances agree. Minimal change is made to the GOCART aerosol vertical distribution, size distribution and the ratio of the five different aerosol types. The loading in the GOCART model is updated with new MODIS observations every 6 hours. Since the previously assimilated meteorology provides surface wind speed, we account for radiance sensitivity to wind speed over rough ocean. Over land we use surface albedoes from the MODIS land team kindly provided by Eric Moody. Over ocean the assimilation aerosol optical depths (AOD) compare well with AERONET, over land less so. We compare our results with AERONET retrieved single scattering albedo and effective radius. We also investigate data retention issues in the assimilation. This research is part of an ongoing effort at NASA Goddard to integrate aerosols into the Goddard Modeling and Assimilation Office (GMAO) products.
A23C-0817 1340h
A New, Physically Based Algorithm, for Retrieving Aerosol Properties over Land from MODIS
The MODerate Imaging Spectrometer (MODIS) has been successfully retrieving aerosol properties, beginning in early 2000 from Terra and from mid 2002 from Aqua. Over land, the retrieval algorithm makes use of three MODIS channels, in the blue, red and infrared wavelengths. As part of the validation exercises, retrieved spectral aerosol optical thickness (AOT) has been compared via scatterplots against spectral AOT measured by the global Aerosol Robotic NETwork (AERONET). On one hand, global and long term validation looks promising, with two-thirds (average plus and minus one standard deviation) of all points falling between published expected error bars. On the other hand, regression of these points shows a positive y-offset and a slope less than 1.0. For individual regions, such as along the U.S. East Coast, the offset and slope are even worse. Here, we introduce an overhaul of the algorithm for retrieving aerosol properties over land, to include more physical, less empirical assumptions. The new algorithm will include surface type information, instead of assuming globally fixed ratios of visible to infrared surface reflectance. It will include updated aerosol optical properties to reflect the growing aerosol retrieved from eight-plus years of AERONET operation. The effects of polarization will be including during lookup table creation, using vector RT calculations. Most importantly, the new algorithm does not assume that aerosol is transparent in the infrared channel. This new formulation will invert reflectance observed in the three channels (blue, red, and infrared), rather than performing iterative single channel retrievals.
A23C-0818 1340h
Influences of biomass burning on land-atmosphere interactions and dry-to-wet transition over Amazonia
Observations have demonstrated that the dry-to-wet transition in Amazon basin is sensitive to small changes of the atmospheric thermodynamic conditions. It is thus reasonable to hypothesize that the wet-season onset can be influenced by smoke aerosols produced by the large-scale biomass burning. To test this hypothesis, a regional climate model (RegCM3) is forced with MODIS-retrieved aerosol optical depth in combination with GOCART simulations of aerosols during the dry-to-wet transition season (August-November). We examine the direct and semi-direct effects of smoke on the transition season. Our results show that the reduction of the solar flux is mainly responded by reduction of surface sensible flux. This consequently reduced the diurnal growth of the atmospheric boundary layer (ABL), and detrainment of dry air at the top of the ABL. The cloud formation is inhibited due to strong aerosol absorption. Such semi-direct effect can compensate the direct effect of aerosols on moist static instability and thus rainfall.We also found that these changes are sensitive to the prescribed vertical distribution of the aerosols. The simulations are also compared with MODIS aerosol-cloud and radiosonde measurement in 2002. The physical and dynamic processes key to determine the aerosols' influence on wet season onset will be discussed.
A23C-0819 1340h
Optical and Chemical Properties of Particles Generated by Traditional Wood Burning Cook Stoves
Some 2-3 billion people in the world use biofuel as their primary energy source for domestic fuel needs. It is estimated that the combustion of biofuel generates 20% of all carbonaceous aerosols. What are the characteristics of the particles emitted during biofuel use? How are these millions of small sources affecting the world around us, and are they adequately represented in today's climate models? Cooking fires have been replicated and measured in laboratory settings, but are the results representative of real-world combustion? Lack of knowledge about the characteristics and quantities of emissions from small combustion sources is a large contributor to uncertainties in global emission inventories of particulate matter. In the past, real-time field measurements at remote locations have been difficult to obtain for many reasons including limited access to sources, and the lack of power to operate measurement equipment. In order to facilitate measurements at a wide range of potential sampling sites, we designed and built a portable, battery-operated emission sampling cart. This sampling cart measures real-time data with a Particle Soot Absorption Photometer (PSAP), a Nephelometer, a CO sensor, and a CO2 sensor. Additionally, we captured the particles on filters for later analysis. We have developed working relationships with non-profit organizations in the United States and in developing countries, which afford us access to ongoing measurements of small sources, including traditional and improved wood burning cook stoves. With their help, we were able to obtain measurements from cook stove fires as operated. We present real-time measurements of optical properties including light absorption at three wavelengths (450, 550, and 700 nm), light scattering, and CO to CO2 ratio from cooking fires in Honduras. Fifteen sample data sets were measured over a two-week period. The data sets were collected from a variety of locations, over varying sample periods of at least two hours and from different wood fuels. We include a qualitative discussion of differences between the practices used in laboratory and real-world fires. From the real-time data, we derive emission factors for particle mass, elemental and organic carbon. From studies on open biomass burning, it is known that particle characteristics vary between "flaming" and "smoldering" combustion, with "flaming" combustion producing more elemental carbon. We discuss the differences in particle characteristics during different phases of combustion, as well as the relative quantities of particles produced during flaming and smoldering. We also include integrated samples of particle mass and chemistry (elemental and organic carbon and ions) taken concurrently with the optical measurements. We provide a comparison of predicted and measured optical properties of these particles. We examine how these measurements compare with previous results from laboratory studies. Finally, we discuss the implications of these data for the results of global climate modeling.
A23C-0820 1340h
3D Cloud Radiative Effects on Aerosol Optical Thickness Retrievals in Cumulus Cloud Fields in the Biomass Burning Region in Brazil
Aerosol amount in clear regions of a cloudy atmosphere is a critical parameter in studying the interaction between aerosols and clouds. Since the global cloud cover is about 50%, cloudy scenes are often encountered in any satellite images. Aerosols are more or less transparent, while clouds are extremely reflective in the visible spectrum of solar radiation. The radiative transfer in clear-cloudy condition is highly three-dimensional (3D). This paper focuses on estimating the 3D effects on aerosol optical thickness retrievals using Monte Carlo simulations. An ASTER image of cumulus cloud fields in the biomass burning region in Brazil is simulated in this study. The MODIS products (i.e., cloud optical thickness, particle effective radius, cloud top pressure, surface reflectance, etc.) are used to construct the cloud property and surface reflectance fields. To estimate the cloud 3D effects, we assume a plane-parallel stratification of aerosol properties in the 60 km x 60 km ASTER image. The simulated solar radiation at the top of the atmosphere is compared with plane-parallel calculations. Furthermore, the 3D cloud radiative effects on aerosol optical thickness retrieval are estimated.
A23C-0821 1340h
Cloud-Aerosol Interaction and its Impact on the Onset of the East Asian Summer Monsoon
Effect of aerosols from biomass burning on the early development of East Asian monsoon is investigated using various satellites and in situ observations including TOMS Aerosol Index (AI), GPCP precipitation, ISCCP cloud cover, and GISS surface air temperature. Based on TRMM fire produce and mean winds fields at 850mb, we identified the source and interaction regions of aerosols and investigated aerosol-cloud-precipitation characteristics in those regions. During March-April, northern Thailand, Myanmar, and Laos are major source of smoke from the combustion of agricultural waste. Excessive smoke, represented by high AI, is observed especially during dry and cloud-free year. On the other hand, there is no ground source of smoke in the interaction region. The most of aerosols in this area are believed to be transported from the source region. AI is appeared to be correlated with more clouds and less precipitation in interaction region. It suggests that the aerosol-cloud interaction can alter the distribution of cloud and the characteristics of regional hydrology. Aerosol-induced changes in atmospheric stability and associated circulation turns out to be very important to pre-monsoon rainfall pattern in southern China. Prolonged biomass burning is especially effective in changing rainfall pattern during April and May. Results suggest that excessive aerosol transported from source region may intensify pre-monsoon rain band over central China in May and lead to early monsoon onset.
A23C-0822 1340h
The impact of humidity above stratiform clouds on indirect aerosol climate forcing
Increases in concentrations of cloud condensation nuclei are consistently observed to enhance cloud droplet concentrations. For clouds with a fixed volume of condensed water, droplets become smaller as their numbers increase, thereby increasing cloud optical depth and albedo. The resulting increase in cloud reflectivity is expected to offset some of the global warming resulting from accumulation of greenhouse gases, but the magnitude of this indirect aerosol effect is highly uncertain. Smaller droplets are less efficient at producing precipitation, and decreased precipitation is expected to result in increased cloud water and cloud cover, further increasing cloud reflectivity. Yet polluted marine boundary-layer clouds are not generally observed to hold more water. Here we use model simulations of stratocumulus clouds to show that suppression of precipitation from increased droplet concentrations leads to increased cloud water only when sufficient precipitation reaches the surface, a condition favored when the overlying air is moist. Otherwise, suppression of precipitation from increased droplet concentrations enhances entrainment of overlying dry air, thereby reducing cloud water and diminishing the indirect aerosol effect.
A23C-0823 1340h
Importance of Spectral Shape in Cloud Parameterizations and Indirect Aerosol Effects
This work expands on our previous studies on the role that the relative dispersion of the cloud droplet size distribution has in improving cloud parameterizations and evaluating indirect aerosol effects. First we demonstrate the importance of the spectral shape in determining cloud radiative properties. Then we show that the relative dispersion changes when aerosol properties change. Especially, we present more observational evidence that an increase in the droplet concentration caused by increased aerosol loading results in an increase in the relative dispersion, leading to a dispersion effect that offsets the Twomey effect. The dispersion effect is further parameterized as a power-law function of the ratio of the liquid water content to the droplet concentration, leading to a new formalism that generalizes the commonly used equations in studies of cloud parameterizations and indirect aerosol effects. It is found that the dispersion effect significantly offsets the Twomey effect, and increases proportionally with the Twomey effect in magnitude. These results suggest that consideration of the dispersion effect, which has been largely ignored, (partially) resolves two fundamental problems confounding the study of indirect aerosol effects: the discrepancies between observations and those expected from the Twomey effect, and the large uncertainty in estimates of indirect aerosol effects. The effects of drizzle mode on the spectral shape and hence on the parameterization of cloud radiative properties are also discussed.
A23C-0824 1340h
Aerosol Versus Dynamic and Thermodynamic Control of Early Anvil Particle Size Over Subtropical and Tropical Regions
A major challenge of general circulation models is the correct prediction of cumulonimbus anvil crystal size, which may strongly influence the radiative impact of long-lived anvil shields. Here we divide the factors affecting early anvil development into aerosol versus dynamic and thermodynamic categories, and we first test a strategy for using observations to constrain conclusions regarding which exerts greater control over crystal size distributions. Global surveying satellite data from the MODIS instruments on the Aqua and Terra platforms now provide retrieved effective radius from anvil tops throughout the tropics and subtropics. While MODIS also provides some measures of column-integrated aerosol properties in cloud-free regions, there is no information on aerosol vertical distribution and no direct measurement of cloud dynamics (e.g., updraft strength). To fill in these missing pieces as robustly as possible, we begin our analysis using in situ aerosol data and ground-based radar data from the July 2002 CRYSTAL-FACE campaign, which is representative of regional subtropical convection (primarily continental). Considering the days for which CRYSTAL-FACE aerosol and radar data are available, Aqua data indicate marked differences in retrieved cloud-top effective radius. Radar data indicate large variability in fractional area exceeding a reflectivity threshold of 40 dBZ and the peak height of a 30 dBZ echo, which are indicators of the convective intensity of a system. In situ aerosol data also differ markedly in a manner not easily simplified owing to changes in both size and number within surface and elevated layers. To bridge this complex phase space (aerosol and thermodynamic and dynamic values all varying with elevation), we perform large-eddy simulations with size-resolved aerosol and cloud particles to test the expected sensitivity of anvil properties on each day to the variability of measured conditions, and then compare results with radar and MODIS observations. We finally consider possibilities for using MODIS data alone to extend this analysis to other regions, beginning with the tropical eastern Pacific, where the TCSP campaign will take place.
A23C-0825 1340h
Statistical Analysis of Cumulonimbus Anvil and Surrounding Aerosol Properties Retrieved by MODIS in Subtropical and Tropical Regions
In a contribution to a study of the factors controlling cumulonimbus anvil crystal size, here we present a statistical analysis of MODIS cloud and aerosol data from subtropical southern Florida (where the CRYSTAL-FACE field campaign took place in 2002) and the tropical eastern Pacific (where the TCSP field campaign will take place in 2005). We demonstrate algorithms that identify monolithic anvil shields and their more local likely core regions, where the youngest crystals are expected to be present, as well as aerosol data within a specified distance from the cloud edges. Choosing the July 2002 and June 2002 time periods for the two regions, respectively, we find that useful data from diurnal sea breeze convection over southern Florida is provided only by the Aqua platform, whereas both Aqua and Terra platforms can be used to study anvils over the eastern Pacific. Initial results indicate that predicted core regions do contain the smallest retrieved crystal effective radius over southern Florida, but not over the eastern Pacific, where the smallest retrieved effective radii in a given anvil are sometimes instead associated with the lowest optical depths. The significantly smaller anvils observed over southern Florida also exhibit a wider range of retrieved effective radius in the core regions. The greater anvil size and extent of low-cloud coverage limit successful aerosol retrievals over the eastern Pacific significantly more than over southern Florida, where aerosol data is often robust.
A23C-0826 1340h
The Impact of Aerosols on Cloud and Precipitation Processes: Cloud-Resolving Model Simulations
Cloud microphysics are inevitably affected by the smoke particle (CCN, cloud condensation nuclei) size distributions below the clouds. Therefore, size distributions parameterized as spectral bin microphysics are needed to explicitly study the effects of atmospheric aerosol concentration on cloud development, rainfall production, and rainfall rates for convective clouds. Recently, two detailed spectral-bin microphysical schemes were implemented into the Goddard Cumulus Ensemble (GCE) model. The formulation for the explicit spectral-bin microphysical processes is based on solving stochastic kinetic equations for the size distribution functions of water droplets (i.e., cloud droplets and raindrops), and several types of ice particles [i.e. pristine ice crystals (columnar and plate-like), snow (dendrites and aggregates), graupel and frozen drops/hail]. Each type is described by a special size distribution function containing many categories (i.e. 33 bins). Atmospheric aerosols are also described using number density size-distribution functions. A spectral-bin microphysical model is very expensive from a computational point of view and has only been implemented into the 2D version of the GCE at the present time. The model is tested by studying the evolution of deep cloud systems in the west Pacific warm pool region, in the sub-tropics (Florida) and in the mid-latitude using identical thermodynamic conditions but with different concentrations of CCN: a low "clean" concentration and a high "dirty" concentration. Besides the initial differences in aerosol concentration, preliminary results indicate that the low CCN concentration case produces rainfall at the surface sooner than the high CCN case but has less cloud water mass aloft. Because the spectral-bin model explicitly calculates and allows for the examination of both the mass and number concentration of species in each size category, a detailed analysis of the instantaneous size spectrum can be obtained for the two cases. It is shown that since the low CCN case produces fewer droplets, larger sizes develop due to greater condensational and collection growth, leading to a broader size spectrum in comparison to the high CCN case. Forward and backward trajectory calculation are performed to identify the origin of clouds; and retrieve the dynamics, thermo-dynamic and CCN characteristics along the trajectory.
A23C-0827 1340h
Maritime-continental contrasts of cloud condensation nuclei in the west coast of the Korean peninsula
Measurements of cloud condensation nuclei (CCN) were made at the Korea Global Atmospheric Watch (GAW) Observatory (KGAWO) (36.32 \deg N, 126.19 \deg E) on the west coast of the Korean Peninsula, south of Seoul, from April 30 to May 22, 2004. This location - 500 km distance from China across the Yellow Sea - provides a unique opportunity to monitor the influence of east China's rapidly growing industrial and human activities as well as the local Korean pollution. CCN were measured with the two Desert Research Institute (DRI) instantaneous CCN spectrometers. Condensation Nuclei (CN) were also measured with a TSI 3010 counter. On some foggy days fog droplets (2 - 50 micrometer diameter) were measured with an FSSP-100. For the whole period air masses were divided into 10 maritime and 12 continental regimes according to Hybrid Single Particle Lagrangian Integrated Trajectory model (HYSPLIT4) results. Preliminary analyses showed that the average CCN concentration at 1$%$ supersaturation of the continental air masses was 6573 cm$^{-3}$, which almost doubled the maritime average concentration of 2758 cm$^{-3}$. Average total particle (i.e., CN) concentration was higher and showed similar contrast between the continental and maritime air masses (8594 cm$^{-3}$ vs. 4872 cm$^{-3}$). These concentrations were significantly higher than those measured in some other parts of the earth atmosphere. For example, CCN measurements in marine environment but with continental influences showed 1411 cm$^{-3}$ in Florida and 1023 cm$^{-3}$ in northeast Atlantic. These are even lower than the maritime CCN concentrations in this study. Therefore, maritime in this study is only in a relative sense. An Asian Dust (AD) event occurred on May 4. CN and CCN concentrations on this day, 10880 and 8835 cm$^{-3}$, respectably, were higher than the average continental concentrations. However, one non-AD day also showed as high concentrations. Much more detailed analyses and comparisons will be made and presented at the conference.
A23C-0828 1340h
Regional and global CO and aerosol correlations: An integrated approach of surface, satellite, and aircraft measurements and model simulations
We investigate regional and global CO and fine mode aerosol correlations by combining GOCART model simulations with various measurements from surface (CMDL /CO and AERONET / aerosol), satellite (MOPITT / CO and MODIS / aerosol), and aircraft. CO mixing ratios and aerosol concentrations are examined using surface and aircraft measurements on several representative regions. Satellite observations provide the comparisons of CO column and aerosol fine model AOD at global scale. Numerical model simulation allows us to compare CO and aerosol properties without temporal and spatial limitations and with the capability to trace emissions by isolating different sources. Our zonal mean comparisons support the previous findings that the variations of CO and aerosol properties are out of phase by several months over northern hemisphere middle latitudes where anthropogenic emissions dominate. Over the biomass burning regions, such as southern hemisphere (SH) extra-tropics, the concentration and column properties of CO and aerosol show more agreement. Long-term transport and local chemistry drive the biggest phase shift of CO and aerosol properties over remote SH ocean regions. There are much more complicated relationships of CO and aerosol properties over stations and small regions due to emission, transport, and local chemistry.
A23C-0829 1340h
The Nature and Effects of Background Aerosols
Accurate, world-wide, long-term measurements of aerosol optical thickness (AOT) in continental and remote marine boundary layer reveal an absolute minimum in AOT ($\sim 0.02$ at 550 nm and an Angstrom exponent $\sim -1$) at most low-altitude locations but one. At this AOT magnitude the aerosols could have significant consequences on climate and remote sensing by the direct effect alone. For example, if all the optical thickness is due to aerosol absorption, as sometimes required for surface irradiance closure, an optical thickness of just 0.02 would increase atmospheric absorptance by about 4%, a significant fraction of the approximately 20% absorptance currently assumed for the shortwave. Likewise, satellite sensor calibration by ground-look methods would be severely affected. To better understand the nature of this background aerosol in the remote marine environment (i.e., sources, sinks, and lifetimes), Naval Research Laboratory's dynamic microphysical aerosol model MARBLES has been used with hourly meteorology input provided by COAMPS, the Navy's mesoscale meteorological model. Full specification of boundary layer profiles, including turbulent mixing, boundary layer height, wind speed, humidity, cloud cover, rain rates has been provided along COAMPS derived $\sim10$ day back trajectories from specified AERONET (NASA's sunphotometer network) sites. Calculated optical properties are compared with AERONET measurements for selected periods representative of remote background conditions and for several distinct aerosol events. Some comparisons show good agreement, indicating that marine aerosol sources, primarily sea-salt and sulfate, explain the AOT minimum well. Detailed results of calculated vertical aerosol concentration, composition and extinction profiles are provided. Implications will be discussed.