Abstract

Focusing on three dust storms occurring in spring 2001, we developed a detailed aerosol parameterization scheme and integrated it in a radiative transfer model to characterize possible impacts of solar altitude angle on dust direct radiative effects over China desert regions and the North Pacific, using actual daily solar altitude angles. Increasing solar altitude angle from early spring (or winter) to late spring (or summer) leads to increase of positive clear sky radiative forcing, and decrease of negative radiative forcing due to dust aerosols at the top of the atmosphere. Because solar altitude angle increases from early to late spring, dust-clear sky radiative forcing may change from negative to positive at the top of atmosphere, showing a change from cooling to heating of the earth-atmosphere system over high-albedo deserts and nearby regions. Over low-albedo ocean negative clear sky radiative forcing by dust may decrease, suggesting a change from strong to weak cooling on the earth-atmosphere system. The impacts of solar altitude angle on cloudy sky radiative forcing due to dust are similar to those of clear sky. Impacts of low cloud on dust radiative forcing are the same as increasing surface albedo. This causes the transition of dust cooling effects into heating effects over deserts to occur earlier, and causes decrease of negative radiative forcing over the ocean and even cause a change from weak negative radiative forcing to weak positive forcing over local areas. Even in the same East Asian desert regions and nearby areas, the strength and sign of the radiative forcings depend on storm dates and thus solar altitude angle. The nearer to early spring (or winter) a dust storm occurs, the easier it leads to negative radiative forcing at the top of atmosphere, which indicates cooling effects on the earth-atmosphere system. In contrast, the nearer to late spring (or summer) a dust storm occurs, the easier it leads to positive radiative forcing at the top of atmosphere, showing heating effects. Over East Asian deserts and nearby regions, dust layers may be regarded as cooling sources in early spring (winter) and warming sources in late spring (summer).

Highlights

  • Focusing on three dust storms occurring in spring 2001, we developed a detailed aerosol parameterization scheme and integrated it in a radiative transfer model to characterize possible impacts of solar altitude angle on dust direct radiative effects over China desert regions and the North Pacific, using actual daily solar altitude angles

  • Because dust aerosols can both absorb and scatter solar radiation, and dust particles vary in absorption and scattering ability in different places [7], the impacts of solar altitude angle on dust direct radiative forcing at the top of the atmosphere and the atmospheric radiative heating rates are even more complicated than sulfate and soot, as demonstrated by studies on Saharan dusts

  • What differences will be made on the earth-atmosphere system radiation effect by dusts of the dust storms occurring in the early spring, or late spring? We further investigate this

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Summary

Data and model description

Data used in this analysis were dust concentration, complex refractive indices of dust aerosols, meteorological data such as temperature, atmospheric pressure and humidity, and surface conditions such as land cover type and desert distribution. Albedo 0.12 0.12 0.17 0.17 0.12 0.21 0.20 0.25 0.24 0.17 0.14 0.67 0.08 0.08 0.20 scheme including instant dust forecasting concentration and latest dust optical performance into the model, which rapalces the climate values of key radiative parameters including optical thickness, single scattering albedo and dust asymmetry factors with temporal and special changing values on-line calculated by the dust model It successfully calculated the radiative forcing of aerosols in the East Asia-North Pacific region in northern spring 2001, and evaluated the impact of optical performance of east Asian dust particles on direct radiative forcing and radiative heating rates. On the basis of this prior research, we further assess the impact of seasonal and annual variation in sinζ on dust radiative forcing and earth-atmosphere radiative effect in the East Asia-North Pacific region. What differences will be made on the earth-atmosphere system radiation effect by dusts of the dust storms occurring in the early spring (or winter), or late spring (or early summer)? We further investigate this

Effect of solar altitude angle on clear-sky dust radiative forcing
Clouds diagnostics scheme
Findings
Discussion
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