Dr. Jun Wang

Goals:

Some of the goals of this project include a) Detecting dust aerosols using satellite remote sensing data, b) Using insitu and ground based data to examine microphysical properties, c) Retrieve aerosol optical depth from satellite data and
radiative transfer calculations and d) estimate the radiative forcing on regional climate.  With the high temporal resolution of GOES8, the diurnal change of dust aerosol forcing can be derived, and more accurate estimation of aerosol forcing on regional climate can be achieved.

Methods:

• Using all available in situ measurements to characterize aerosol optical and radiative proprieties. The data used in this study includes aerosol size distribution measurements, light scattering/absorbing coefficients (from Nephelometer), and vertical aerosol profile (aerosol concentration and optical thickness from air-borne instruments).

• Create look-up table in which the reflectance at the top of atmosphere is calculated as a function of different surface reflectance, aerosol optical thickness, and different satellite-earth geometries.

• A multi-channel threshold method is developed to remove the cloud, and detect dust pixels.

• For a cloud-free pixel, the AOT is retrieved by finding the best bit between GOES8 reflectance and the pre-calculated reflectance in the look-up table. The validation is performed by comparing GOES8 with ground-based and air-borne Sunphotometer measured AOTs.  A good agreement was found.

• To calculate the dust radiative forcing, the broad-band dust optical properties are further derived from the mutli-spectral aerosol optical thickness inferred from AERONET Sunphtometer.

• Using derived dust optical properties and a house-modified delta four stream radiative transfer model, we found an excellent agreement between calculated and measured downward shortwave fluxes (including global, direct, and diffuse components), which ensure the reliability of further using GOES8 AOT to calculate dust forgings. 

 Results:

Good agreement between GOES8 AOT and ground-based and air-borne Sunphotomter infered AOT
Diurnal radiative forcing of dust aerosols. Left figure shows that calculated downward shorwave irradiance (DSWI) have a good agreement with measured quantities.  Right panel shows the derived monthly mean shortwave radiative forcing based on the GOES AOT calculations.
GOES-8 aerosol optical thickness (AOT670) and dust short wave aerosol radiative forcing (SWARF) at the top of atmosphere and the surface for a selected dust event (July 19-July23) during PRIDE. Clouds are shown in black and land areas are in white.