Issues in the Integration of Research and Operational Satellite Systems for Climate Research Part I. Science and Design (2000) / Chapter Skim
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Aerosols
Aerosols
Pages 82-98
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From page 82... ...
. For the purpose of behavioral description and modeling, tropospheric aerosols are commonly classified according to their composition and source, because they vary significantly in concentration and composition by region (source)
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From page 83... ...
Other significant sources of natural tropospheric aerosols are volcanic eruptions and windblown dust from arid and semiarid regions. While the direct and indirect radiative effects of sulfates are important, other tropospheric aerosols may contribute significantly to the global radiative balance.
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From page 84... ...
They are present globally between the tropopause and about 30 km, undergo seasonal variations, and are greatly influenced by large volcanic eruptions. During volcanically quiescent periods, the vertical distribution of the stratospheric aerosol particles relative to tropopause height is very similar at all latitudes, with mass mixing ratios and number densities on the order of 1 ppbm and 10 particles cm-3, respectively.
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From page 85... ...
Figure 7.1 shows the climate forcings by several different agents (Hansen et al., 1998~. GHG forcing is estimated at 2.3+0.25 Wm-2, while tropospheric aerosols are estimated to force climate on a global scale -0.4+0.3 Wm-2.
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From page 86... ...
Whereas the stratospheric aerosol is more homogeneous in composition and controlled primarily by episodic volcanic eruptions, the tropospheric aerosol is more heterogeneous in composition and location and is controlled by the myriad of aerosol sources in each region. Global data on tropospheric aerosol are sparse.
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From page 87... ...
The global tropospheric aerosol measurements, however, depend primarily on the success of the satellite-borne MODIS instrument and the ESSP PICASSO-CENA mission and their ability to retrieve aerosol optical depth in Earth's boundary layer (the first few kilometers of altitude)
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From page 88... ...
on September 12,1991, by the space shuttle Discovery into a 585-km, near-circular orbit with a 57-degree inclination. Like SAGE, the HALOE instrument uses the solar occultation technique to measure vertical profiles of O3, HC1, HE, CH4, H2O, NO, and NO2, extinction due to aerosols, and temperature versus pressure.
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From page 89... ...
It is designed as a simpler SAGE II instrument to measure vertical profiles of aerosols, O3, NO2, and H2O in nine channels between approximately 0.35 and 1.06,um, with 1 km vertical resolution (Glaccum et al., 1996~. The instrument performs 14 sunrise and 14 sunset measurements each day; because it is in a Sun-synchronous orbit like ILAS, all sunrise events occur entirely at high northern latitudes (55 to 71 degrees N)
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From page 90... ...
both temperature and molecular density profiles from O2 A-band measurements near 0.760 ,um (McCormick et al., 1999~. The SAGE III instrument will also have a channel centered near 1.54,um to improve the size discrimination of larger aerosol particles and to separate cloud and aerosol signals.
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From page 91... ...
Since current spacecraft instruments cannot make tropospheric aerosol measurements over land, on a global scale, the uncertainties are large. Table 7.2 lists the expected optical depth measurement uncertainties for MODIS, MISR, and a number of other spaceborne sensors.
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From page 92... ...
Similarly, it will be difficult for spaceborne instruments to quantify indirect aerosol forcing. Again, a combination of instruments like PICASSO-CENA and EOS PM flying
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From page 93... ...
troposphere, both of which must be taken into account in order to understand aerosol climate forcing. The currently planned and funded satellite instruments described above have the potential to yield information on tropospheric and stratospheric aerosols.
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From page 94... ...
Uncertainties in funding and in the long-term availability of aircraft and other forms of support require that the validation plan be a working document, periodically updated to reflect necessary changes. Because there is no accepted technique for calibrating atmospheric aerosol extinction measurements, previous validation programs (e.g., SAM II and SAGE I and II)
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From page 95... ...
used empirical relationships between the 0.525, 0.940, and 1.02 ,um extinction measurements to seek a size distribution parameterization that gave the best water vapor retrieval at 0.940 ,um. He showed that the SAGE II measurements of the pre-Pinatubo stratospheric aerosol could be modeled with size distributions in the form of a segmented power law while preserving the wavelength dependence of the measured extinction.
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From page 96... ...
1999. Tropospheric aerosol climate forcing in clear-sky satellite observations over the oceans.
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From page 97... ...
1998. Aerosol size distributions obtained from HALOE spectral extinction measurements.
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From page 98... ...
1999. Aerosol properties and radiative effects on atmospheric radiation in the United States East Coast haze plume: an overview of the Tropospheric Aerosol Radiative Forcing Observational Experiment (TARFOX)
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