Dust aerosol optical properties retrieval and radiative forcing over northwestern China during the 2008 China‐U.S. joint field experiment

Abstract

The Atmosphere Radiation Measurements Program's Ancillary Facility (AAF/SMART‐COMMIT) was deployed to Zhangye (39.082°N, 100.276°E), which is located in a semidesert area of northwest China, during the period of late April to mid June in 2008. We selected 11 cases to retrieve dust aerosol optical depth (AOD), Angstrom exponent, size distribution, single‐scattering albedo (SSA) and asymmetry parameter (ASY) from multifilter rotating shadowband radiometer (MFRSR) measurements. These cases are dominated by large particles with Angstrom exponent values ranging from 0.34 to 0.93. The values of AOD at 0.67 μm range from 0.07 to 0.25. The mean SSA value increases with wavelength from 0.76 ± 0.02 at 0.415 μm to 0.86 ± 0.01 at 0.870 μm, while the mean ASY value decreases from 0.74 ± 0.04 to 0.70 ± 0.02. Before estimating dust aerosol direct radiative forcing, a radiative closure experiment was performed to verify that the retrieved aerosol optical properties and other input parameters to the radiative transfer model appropriately represent atmospheric conditions. The daytime‐averaged differences between model simulations and ground observations are −8.5, −2.9, and −2.1 W m−2 for the total, diffuse, and direct normal fluxes, respectively. The mean difference in the instantaneous reflected solar fluxes at the top of atmosphere (TOA) between the model and CERES observations is 8.0 W m−2. The solar aerosol direct radiative forcing (ARF), averaged over a 24 h period, at the surface is −22.4 ± 8.9 W m−2, while the TOA ARF is small and has an average value of only 0.52 ± 1.69 W m−2. The daily averaged surface aerosol radiative forcing efficiency at 0.5 μm is −95.1 ± 10.3 W m−2τ−1. Our results illustrate that the primary role of dust aerosol is to alter the distribution of solar radiation within the climate system rather than to reflect solar energy to space. We assess the satellite aerosol optical depth products from Mutiangle Imaging Spectroradiometer (MISR) and Moderate Resolution Imaging Spectroradiometer (MODIS) observations by comparing them with our ground‐based retrievals. Reasonable agreements with the ground‐based observations are found for the MISR product and MODIS Deep Blue product.

Dust aerosol effect on semi-arid climate over Northwest China detected from A-Train satellite measurements

“…Huang et al (2009) found that the single scattering albedo (SSA) of Taklamakan dust aerosols is about 0.89 at 0.67 µm which is about 6% less than for Saharan dust. Ge et al (2010) also confirmed that the SSA shows an increasing trend with wavelength, indicating stronger dust aerosol absorption at shorter wavelengths. The values of SSA, which range from 0.76 ± 0.02 to 0.86 ± 0.01, are much lower than those derived in Africa and also relatively smaller than earlier results obtained over East Asia.…”

Aerosol optical properties and radiative effect determined from sky-radiometer over Loess Plateau of Northwest China

“…The relative difference in the mean SSA between adjusted and unadjusted value is about 4 % in MAM. Compared with the SSA observed at the other observatory over the Loess Plateau (Ge et al, 2010), the values of the SSA (adjusted) are larger in this study. The adjusted ASY at 500 nm ranges from 0.65 to 0.74 in MAM (not shown in figure).…”

“…Bi et al (2010) analyzed the aerosol optical properties measured at Semi-Arid Climate and Environment Observatory of Lanzhou University over Loess Plateau of Northwestern China obtained through a CIMEL Sun photometer of the ground-based Aerosol Robotic Network for the period of August 2006-October 2008. However, there are some difference between the results of Ge et al (2010) and Bi et al (2010). This study will use another measurement (sky-radiometer) to calculate and check the optical and radiative properties of the dust aerosol at SACOL over Loess Plateau of Northwest China.…”

“…Such event causes not only the serious damage to agriculture, economics, environment and human health in this region but also a climatic impact on the global scale. Ge et al (2010) retrieved dust aerosol optical properties from Multi-filter Rotating Shadowband Radiometer (MFRSR) and estimated the dust aerosol direct radiative forcing over Northwestern China during the 2008 China-US Joint Field Experiment. Bi et al (2010) analyzed the aerosol optical properties measured at Semi-Arid Climate and Environment Observatory of Lanzhou University over Loess Plateau of Northwestern China obtained through a CIMEL Sun photometer of the ground-based Aerosol Robotic Network for the period of August 2006-October 2008.…”

Nighttime AOT Retrieval for Asian Dusts from MODIS IR Measurements: An Artificial Neural Network Approach

“…The estimated retrieval error of MODIS aerosol products are known to be = ±0.03 ± 5% over the ocean and = ±0.05 ± 15% over the land (Remer et al 2005). However, over the land, instead of the MODIS standard product of "dark-target" approach (Kaufman et al 1997), we used the "Deepblue" product (Hsu et al 2004) claimed to be in better agreement with ground-based observations (Ge et al 2010). Meanwhile, CALIPSO AOT shows a systematic underestimation compared with MODIS AOT (Royer et al 2010;Kacenelenbogen et al 2011;Yumimoto et al 2008).…”