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Research objectives |
Effects on the Environment |
How measurements are made |
Measurement-based Assessments
How measurements are made
Over the last decade aerosol science has attracted growing attention from the scientific
community due to the realization that climate change cannot be understood accurately enough to predict future climates without taking aerosol into account. This realization was further enhanced by finding new processes in which aerosol and in particular black carbon absorption can influence climate and the hydrological cycle.
Among climate changing agents, aerosol is much more complex than greenhouse gases
and requires new tools to study it. Global heterogeneity of aerosol sources and aerosol short
lifetime causes heterogeneity in the aerosol distribution and variability of their properties. In
contrast to the single ground based instrument that already in the 1950's showed that the
concentration of carbon dioxide is increasing around the world, describing the global aerosol requires precise global daily measurements, achievable mainly from space
[NACIP, 2002].
Tools:
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Dust and mass burning in Central Africa, as taken by MODIS-Terra
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We have several new tools at our disposal to study the global aerosol system:
- Satellites systems designed with aerosol remote sensing in mind: MODIS and MISR on Terra and Aqua, as well as GLAS and CALIPSO lidars.
- Other satellite instruments that were found to be useful after the fact (TOMS, AVHRR, ATSR), producing retrospective records, and adding information from the UV (TOMS).
- Since 1993, the Aerosol Robotic Network (AERONET) provides continuously critical information on aerosol distribution, seasonal variation and properties.
- Aerosol chemical
transport models, using realistic meteorological parameters and source characterization
developed a realistic picture of the global aerosol, yet not accurate enough to determine their
forcing of regional and global climate.
The retrieved data:
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AERONET data retrived showing Aerosol optical thickness at different pressures , per hour of a day
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These data sources have different information content on the aerosol properties and
different error sensitivities.
The accuracy of the data sets varies with the aerosol concentration, surface properties etc. Fusing these new data sources together is required to derive the aerosol effect on the environment and climate. Therefore an integrated data set that accounts for the advantages and disadvantaged of the specific data sources in specific conditions will be an asset
to the community and enable derivation of the aerosol forcing of climate.
For example, the integrated data set will heavily rely on AERONET measurements in remote locations with low and homogeneous aerosol [Kaufman et al 2001], while downwind of pollution or dust sources it will rely on MODIS characterization of the aerosol spatial distribution over the ocean and dark surfaces [Remer et al., 2002b] and on TOMS (with GOCART described heights) over bright surfaces [Torres et al 2002b]. The launch of new geostationary sensors with several channels in the solar spectrum can enhance the information by adding to the AERONET description of the diurnal cycle.
Measuring black carbon absorbtion:
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GOCART model of global black carbon distribution
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The problem of black carbon absorption of sunlight is most urgent. The uncertainty in
black carbon source characterization, uncertainty in atmospheric processes that affect black
carbon lifetime, and uncertainty in its absorption efficiency determined by its mixing with the
nonabsorbing part of aerosol and with clouds, causes a factor 5 uncertainty in the BC absorption of sunlight [Martins et al 1998; Jacobson et al 2000]. Yet satellite measurements of aerosol absorption are just now emerging [Kaufman, 1987; Kaufman et al 2001b, Torres et al 2002a] and in situ measurements of the last decades are sparse [Clarke & Charlson, 1985] and not always accurate [Kaufman et al 2001b].We need to develop new techniques to measure aerosol absorption from satellites and in situ and to use the new AERONET measurements of aerosol absorption and the new satellite measurements to improve aerosol absorption characterization in GOCART and climate models.
Integrating the data:
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GOCART model of global monthly aerosol distribution
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In this project we integrate a variety of observational data, model simulated/assimilated data, adding new analysis of satellite data for aerosol absorption, and generate a measurement based description of the global aerosol system - description of the spatial and seasonal variation of aerosol concentration and properties. We investigate the direct and indirect radiative forcing at the top of the atmosphere and at the surface, as well as
the climate and weather responses to these forcings.
The improvement in the GOCART characterization of sources and aerosol processes, along with assimilation of aerosol observations into an integrated climate/chemical transport model helps to provide a description of the global aerosol field, including the cloudy areas where satellite measurements are not available. These cloudy area estimates enable the study of the aerosol effect on clouds, and determine the composition of the aerosol, and the anthropogenic fraction.
In the present study it is our goal to determine the global direct forcing by aerosol within ±0.05 W/m2 at the top of the atmosphere and ±0.1 W/m2 at the surface, generating in the process the heating rates in the atmosphere. Measurements of the aerosol effects on cloud properties, on atmospheric circulation and on precipitation are more difficult, mainly due to the difficulty of distinguishing the aerosol effects from natural variability of clouds and atmospheric circulation of energy and moisture.
Our goal is to determine these processes in preferred locations, and to simulate them using models so that parameterization of the effect over the globe will be possible.
Research objectives |
Effects on the Environment |
How measurements are made |
Measurement-based Assessments
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