AMS Forum: Climate Change Manifested by Changes in Weather


An aerosol climatology from MODIS observations and products

Lorraine A. Remer, NASA/GSFC, Greenbelt, MD; and R. Kleidman and Y. Kaufman

One of Yoram Kaufman's passions was the unraveling of the scientific puzzle of how aerosols affect climate, weather and the hydrological cycle. He attacked this passion from many fronts, including being the instigator and driving force behind the development of several important tools that now make it possible to better describe the global aerosol system and aerosol effects on other systems. One of these tools is the MODIS (MODerate resolution Imaging Spectroradiometer) aerosol product.

MODIS was launched on the Terra satellite at the end of 1999 and on the Aqua satellite in May 2002. A MODIS instrument observes the Earth in 36 bands 4 times a day. The MODIS aerosol product is based on 7 MODIS bands and the 2 day light overpasses, with cloud clearing algorithms making use of additional channels. The standard MODIS aerosol algorithm includes spectral aerosol optical depth (AOD) 0.47 to 2.13 m over ocean and 0.47 to 0.66 m over land, the fraction of aerosol optical depth attributed to fine mode aerosols, and aerosol effective radius over ocean only. The MODIS product has been evaluated extensively against well-calibrated ground and airborne sunphotometers and the accuracy and limitations of the products are well-characterized. We have 6 years of well-characterized MODIS global aerosol observations, and 4 years of MODIS aerosol observations twice a day. A climatology of the global and regional aerosol climatology is beginning to emerge.

The emerging climatology includes global and regional time series of aerosol loading, divided into fine and coarse modes. We see the recurring seasonal fluctuations of the aerosol and the interannual deviations that we can attribute to specific causes such as extensive biomass burning in Siberia. We see the overall relationship between aerosol loading and aerosol size, globally and regionally. We can also determine total column aerosol mass concentration. The differences between global results and regional results accentuate the complexity of the aerosol system and the need for continued global monitoring of the system by satellites. Comparisons between Terra and Aqua results highlight that diurnal differences in aerosol properties are small over open ocean, and that comparing the results from the two sensors provides a determination of the precision of the overall product.

We find that the global aerosol optical depth over the oceans at 0.55 m is 0.129, the fine mode mass concentration is 0.063 g-cm-2 and the coarse mode mass concentration is 0.26 g-cm-2. Terra and Aqua global mean AOD over the oceans agree to approximately 1%. As these results are finalized we will post them to so that the entire community can benefit. We plan to present these findings, and similar ones calculated for the land. Creating and presenting such a climatology was one of Yoram Kaufman's last projects. We feel that such a climatology will become a significant building block for future studies that continue Yoram Kaufman's passionate attempts to unravel the role of aerosols in influencing weather and climate.

Session 6, Impacts of Aerosols on Weather and Climate
Thursday, 18 January 2007, 1:30 PM-5:45 PM, 214D

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