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Lanzhou University (2010)

Radiative Forcing Effect of Dust Aerosol over Northwestern China


Titre : Radiative Forcing Effect of Dust Aerosol over Northwestern China

Auteur : 苏婧;

Grade : Doctoral Dissertation 2010

Université : Lanzhou University

Dust aerosols hava strong absorption of solar radiation. They not only modulate the surface energy, but also affect the heating rate of atmosphere which would enhence cloud evaporation, and weaken and suppress regional precipitation. The investigation of the dust aerosol radiative forcing is therefore important to understand the dust aerosol effects on the regional energy balance and hydrological cycle, over Northwestern China with the arid climate. In this study, we quantify the dust direct radiative forcing, and its influence on atmospheric radiative heating rate by using the CERES, MODIS and CALIPSO satellite data, ground-based observation and radiative transfer model. We also examine the radiation energy budget change due to the interaction of dust and cloud, where we propose a comprehensive approach to separate the dust aerosol direct radiative effect and indirect/semi-direct radiative effect.There are large uncertainties in estimation of regional radiative forcing of dust over northwestern China because of lacking detailed and reliable observations of dust optical properties. Herein we use the dust aerosol optical properties, retrieved from ground-based observations at Zhangye site during the 2008 China-US Joint Field Experiment, to calculate the dust aerosol radiative forcing. After verifying the reliability of the retrieved dust aeosol optical and microphysical properties though the radiation closure experiment, we calculate the daily mean radiative forcing of dust aerosol at both the top of atmosphere and surface. It is shown that dust aerosol has a strong negative forcing at the surface, but the magnitude of dust ARF at the TOA is very small. The large ARF difference between TOA and surface means that solar radiation is kept within the atmosphere. This would reduce the vertical temperature gradient, enhace the stability of the atmosphere of the atmosphere, and thus slow down hydrological-cycle.The vertical profile of dust aerosols is important to estimate the atmospheric heating rate, and is also important to calculate the dust ARF. However, it is difficult to obtain the aerosol vertical profiles on the regional and globle spatial scales untile the active lidar observation become available from CALIPSO satellite. In this study, the CALIPSO lidar measurements are used to derive the vertical distribution of dust aerosols. We use the Fu-Liou radiation model along with the input of dust aerosol vertical profile to estimate the dust radiative forcing and atmospheric radiative heating rate. It is found that dust aerosols can maintain a large portion of solar energy in the atmosphere because of the strong absorption, thereby heating the atmosphere. During an evolution of a dust storm case, the dust aerosols heat the atmosphere (daily mean) by up to 1,2, and 3Kday-1, respectively. The maximum daily mean radiative heating rate reaches 5.5Kday-1.This work quantitatively estimates the warm effect of dust layer during a dust storm in the Taklimakan desert for the first time.In our study, four years of CERES data are also used to quantify the differences of cloud microphysical properties and radiative forcing between CLD (pure cloud) and COD (cloud over dust). We shown that the analysis of satellite observations, dust aerosols do change cloud microphysical properties. It is shown that when dust exists under a cloud it has a warming effect at TOA, which combines direct, indirect and semi-direct effect. However, it is difficult, using only satellite observations, to separate the dust aerosol direct effect from those caused by altered cloud properties. We propose a new simple method that uses the satellite observations along with the radiation model calculations to separate these effects. It is shown that the averaged direct, and the combined indirect and semi-direct instantaneous shortwave radiative forcing are 22.7 and 82.2Wm-2, respectively, which correspond to 21.6 and 78.4% of the total RF value. This method provides a new way to quantitatively study the interaction between clouds and aerosols

Mots clés : Northwest of China; Dust aerosol; direct radiation forcing; indirect radiation forcing; aerosol optical properties

Présentation (CNKI)

Page publiée le 17 mai 2018