The airborne dust has been well recognized to have a significant impact on the climate system at varying spatial scales (through direct, indirect, and semi-direct effects), on biochemistry (providing marine phytoplankton with iron nutrient), and on human health (causing severe disease) during the past decades. However, current estimations of these effects are still very uncertain because the dust cycle involves many complex physical and chemical processes in the atmosphere at different spatial and temporal scales, as well as the state of surfaces prone to the dust emission. It becomes further complicated if feedbacks and interactions within different components of the Human-Environment-Climate system is taken into account. The goal of this thesis is to quantitatively investigate the spatiotemporal variability of dust aerosols in Central Asia and estimates the regional direct radiative impact with a synergy between satellite observations and model simulations. The specific objectives are as follows: 1) examining the spatiotemporal variability of dust aerosols from the satellite perspective by using widely used aerosol products in a coherent fashion; 2) developing a dust climatology in Central Asia to determine the dust trend and variability, explicitly considering land cover and land use changes; 3) estimating the direct radiative impact of mineral dust by incorporating several in-common compositions into a coupled regional dust modeling framework.
We are unaware of any significant trend during the research period in the dust aerosol optical depth and the dust occurrence. Our analysis on the vertical structure of dust plumes, the layer-integrated color ratio and the depolarization ratio indicates varying climate effects (e.g., different direct radiative impacts) by mineral dust, dependent on the event being observed in Central Asia. According to the simulation for a “perfect” dust storm case that occurred on May 7, 2007, the net instantaneous direct forcing (solar + infrared) averaged over the Aral Sea basin are approximately in a range of (-8.05, -0.47) W m-2 at the top of the atmosphere. In comparison to the forcing estimated based on the default complex index, incorporation of dust minerals induced a less cooling effect at the top of the atmosphere. For a given clay-to-silt ratio, the net instantaneous forcing and the forcing in the solar band are sensitive to the surface albedo and the hematite variation in the silt fraction. In the infrared band, the forcing, however, is insensitive to these parameters, but more depends on calcite and quartz amounts in the silt fraction. Our results highlight the importance of accurately predicting the size-resolved content of hematite and the surface albedo change to quantify the radiative forcing of mineral dust.