Donghai Xie

Dust Identification over Arid and Semiarid Regions of Asia Using AIRS Thermal Infrared Channels

Asia dust generated in northern China exerts significant influences on regional air quality, weather, and climate. In this study, a dust identification algorithm over arid and semiarid regions of Asia was proposed based on the thermal observations of atmospheric infrared sounder (AIRS). Firstly, a combination of the line-by-line (LBL) and discrete ordinates radiative transfer (DISORT) model was utilized to investigate the thermal infrared signatures of dust and cloud in 800–1250 cm−1 region. Secondly, six channels in the thermal infrared region were selected from AIRS to monitor dust from space, and a further sensitivity analysis for dust and cloud under different conditions was also performed. Then, the description of the detailed identification method was provided based on distinct thermal infrared signature of dust. At last, several dust events that observed in northern China between the period of 2008 and 2012 were analyzed, and the usefulness of monitoring the outbreaks of Asian dust was emphasized through the comparison with moderate resolution imaging spectroradiometer (MODIS) visible observations and cloud aerosol lidar with orthogonal polarization (CALIOP) data in this study.

Spatiotemporal variability in dust observed over the Sinkiang and Inner Mongolia regions of Northern China

This study presents a detailed analysis of the spatiotemporal variability in dust observed over Sinkiang and Inner Mongolia in Northern China from 2005 to 2008. The relationships between airborne dust (observed by OMI–AI and MODIS–AOD), the normalized difference vegetation index (NDVI), monthly total precipitation (MTP) and surface wind speed (SWS) are investigated. The results show that the spatial distribution of airborne dust distinctly decreases from west to east across Northern China; this pattern is opposite to that of the NDVI and MTP. Both Sinkiang and Inner Mongolia experience high amounts of airborne dust in spring, with the highest values in April. The two regions also had different dust variabilities. In Sinkiang, three major dust regions were identified, with airborne dust mainly distributed in regions with NDVI values between 0 and 0.1, SWS values between 2 and 5 m/s, and a MTP of less than 5 mm. In addition, the temporal variation in airborne dust exhibits both positive and negative correlations with the NDVI, MTP and SWS. However, over Inner Mongolia, five high–dust regions were confirmed, with airborne dust generally distributed in the areas with NDVI values between 0 and 0.4, SWS values between 3 and 6 m/s, and a MTP of less than 10 mm. The time series of airborne dust is negatively correlated with the NDVI and MTP but strongly and positively correlated with the SWS. In addition, the temporal pattern of the AOD in Sinkiang is essentially controlled by dust activity, whereas it may be influenced by anthropogenic emissions in Inner Mongolia. Overall, the spatiotemporal variabilities in dust over Sinkiang and Inner Mongolia are not identical, although both regions are important sources of dust in East Asia.

Trend analysis of the aerosol optical depth over China using fusion of MODIS and MISR aerosol products via adaptive weighted estimate algorithm

Atmospheric aerosol play an important role in the climate change, though direct and indirect processes1. To evaluate the effects of aerosols on climate it is necessary to estimate their spatial and temporal distributions2. Since 2000, the Moderate Resolution Imaging Spectroradiometer (MODIS) and Multi-angle Imaging Spectroradiometer (MISR) have been providing global aerosol products3. However, the uncertainties still exist in current satellite aerosol products attributable to the complex surface, cloud contamination, and aerosol models used in the retrieving process5. Comparing to AERONET AOD, the larger magnitude and different variation tendency in AOD for both sensors indicate that either individual aerosol product may not be good application over China. Combing multiple sensors is a method to reduce uncertainties and improve observational accuracy. An adaptive weighted estimate algorithm of multi-sensor data fusion was presented, which could adjust the fused sensor’s weight in time according to the variation in sensor’s variance. The combined AOD product using the fusion method is in better agreement with corresponding AOD from AERONET than single sensor, which illustrate the fusion method performs better applicability in China. The fusion method can reduce uncertainties both sensors and expand the scope of the distribution in AOD. Using the latest ten-year (2002-2010) fusion product, we study the trend analysis of the aerosol optical depth over typical regions in China. The increasing trend is found over Jingjintang and Yangtze River Delta, which are highly associated with human activities.

Latest decade's spatial-temporal properties of aerosols over China

Aerosols are one of the most important parameters affecting the Earths energy balance and hydrological cycle1. They can arouse uncertainties effects on climates. To narrow the uncertainties associated with the direct and indirect aerosol effects on climates, the spatial-temporal properties of aerosol over China are investigated using the radiance measurements performed by the Moderate Resolution Imaging Spectroradiometer (MODIS) instrument on board the Terra and Aqua satellites from 2002 to 2010. The most prominent variational regions are the northern, eastern China. The high AOD values occur in 2004, 2006 and 2007 year, respectively. The tendencies of AOD are in good agreement with corresponding AOD tendencies based on data from Aerosol Robotic Network (AERONET) stations in the study regions2. Seasonal AOD maxima are obtained in spring (March to May) and summer (June to August) seasons, due to large humidity and biomass burning, respectively. Dust activities in spring are frequent occurrences that also lead to high aerosol loading. AOD minima are obtained in winter (December to February) seasons. The result of our analysis reveal significant trend of seasonal AOD in the Northern and Southern China.

Latest decade’s spatial–temporal properties of aerosols over China based on Multiangle Imaging SpectroRadiometer observations

Abstract The analysis of the spatial–temporal variability and trends of aerosols over China based on ∼ 11 years (February 2000 to December 2010) of Terra-Multiangle Imaging SpectroRadiometer (MISR) Level 3 aerosol products is the focus. The study shows that the MISR aerosol optical depth (AOD) is in good agreement with corresponding AOD from AERONET stations and suggests that MISR aerosol products have higher applicability compared with MODIS AOD products over China. The spatial–temporal distribution and trends for annual and seasonal AOD values over the middle and eastern regions of China are the main focus. The results of our analysis show the significant characteristics and seasonal variation of the aerosol distribution over the study areas. The seasonal distribution in AOD over the study areas is not consistent with the MODIS data. An insignificant trend (5.3%) is observed over the whole study area during the study period. The larger positive tendencies are found in the Yangtze River Delta and the Pearl River Delta (PRD); the values increased by 24.4% and 18% and are considered to be significant with a confidence level of > 95 % . However, in contrast to the recently reported negligible AOD trends of 0.002 per decade using MODIS data over Sichuan, significant increasing trends of 0.046 per 11 years for MISR over the same areas have been measured. The analysis of seasonal variation revealed the seasonal trend in the AOD and the main types of aerosols. During spring, the largest increasing trend (30.2%) is observed in the PRD with a stable composition of fine and coarse aerosols. A pronounced decreasing trend is found over Shanxi and decreased by − 18.7 % in spring during the period, which has not been previously reported. MODIS-Terra currently shows artificial negative AOD trends over land. Therefore, trends derived from MODIS-Terra may not reflect the realistic decadal aerosol changes and variability. The study shows that seasonal distribution and trend analyses are inconsistent when using MISR AOD products and MODIS AOD products over study areas, which indicates that the analysis of aerosol variation using MISR sensors is necessary.

Regional trend analysis of the aerosol optical depth comparing to MODIS and MISR aerosol products

This paper analyzes the Moderate Resolution Imaging Spectroradiometer (MODIS) and the Multiangle Imaging Spectroradiometer (MISR) AOD products to study aerosol distribution and regional trends during 2002 to 2010. Firstly, we compared MODIS and MISR AOD with AERONET station AOD. MISR has been found the better correlation (R= 0.93), which dominate MISR perform better than MODIS over eastern China. Our study found that the spatial distribution of aerosol for both sensors is highly associated with human activities. The trend analysis shows that increasing trends are found over study areas and MISR has better applicable over eastern China is evidenced using method of trend evaluation.