新疆地区不同下垫面气溶胶光学特性的分析

利用太阳光度计CE318资料,对新疆地区3个观测站点（阿克达拉、乌鲁木齐、塔中）所代表的草场、城市和沙漠下垫面的440 nm波长处气溶胶光学厚度（AOD）和440~870 nm之间的Angstrom波长指数（AE）进行了统计分析,结果表明：三个站点的AOD年均值塔中站最大、乌鲁木齐站次之、阿克达拉站最小。其中阿克达拉站点的AOD全年变化不大,其月均值均小于0.3;乌鲁木齐站点AOD则表现出明显的季节性变化,冬春季的AOD月均值是夏秋季节的2.17倍;塔中站全年的AOD表现为单峰型,大值时段主要集中在3-7月。三个站点的AE年均值阿克达拉站最大、乌鲁木齐站次之、塔中站最小。阿克达拉和乌鲁木齐站点的AOD以人为排放等小粒径气溶胶为主,塔中站的AOD主要为沙尘等大粒径气溶胶。从年际变化来看,乌鲁木齐站AOD总体呈下降趋势,塔中站和阿克达拉站AOD总体呈上升趋势。乌鲁木齐霾天气的AOD日均值分布在0.35~1.21之间,塔中站沙尘天气的AOD日均值范围为0.30~2.05。     

Trends in aerosol optical properties over Eastern Europe based on MODIS-Aqua

This study provides characteristics of aerosol columnar properties, measured over ten countries in Eastern Europe from 2002 to 2019. Aerosol optical depth (AOD) and Ångström exponent (AE) were obtained with the Moderate Resolution Imaging Spectroradiometer (MODIS) Collection 6.1 merged Dark Target and Deep Blue aerosol product. The product is validated using ground-based Aerosol Robotic Network (AERONET) situated at Minsk, Belsk, Moldova and Kyiv. The results showed that 76.15% of retrieved AOD data are within the expected error. It was established that 64.2% of AOD points are between 0 and 0.2 and 79.3% of all AE points are over 1. Mean AOD values in the region vary from 0.130 ​± ​0.04 (Moldova) to 0.193 ​± ​0.03 (Czech Republic) with mean value in the region 0.162 ​± ​0.05. Seasonal mean AOD (AE) values were at the maximum during the summer from 0.231 ​± ​0.05 (1.482 ​± ​0.09 in winter) to minimum 0.087 ​± ​0.04 during the winter (1.363 ​± ​0.17 in summer). Gradual AOD reduction is observed in all countries with annual trend from −0.0050 (Belarus) to −0.0029 (Russia). Finally, the relationship between AOD and AE was studied to classify various aerosol types and showed seasonal non-uniformity of their contribution depending on variation in sources. The entire region is under significant impact of various aerosol types, including clean continental (СС), mixed (MX) and anthropogenic/burning (AB) aerosols types that are at 59.77%, 24.72%, and 12.97% respectively. These results form an important basis for further regional studies of air quality and distribution of sources of pollution.     

Latitudinal and longitudinal variation in aerosol characteristics from Sun photometer and MODIS over the Bay of Bengal and Arabian Sea during ICARB

Spatial variations in aerosol optical properties as function of latitude and longitude are analysed over the Bay of Bengal and Arabian Sea during ICARB cruise period of March–May 2006 from in situ sun photometer and MODIS (Terra, Aqua) satellite measurements. Monthly mean 550 nm aerosol optical depths (AODs) over the Bay of Bengal and Arabian Sea show an increase from March to May both in spatial extent and magnitude. AODs are found to increase with latitude from 4°N to 20°N over the Bay of Bengal while over Arabian Sea, variations are not significant. Sun photometer and MODIS AODs agree well within ±1σ variation. Bay of Bengal AOD (0.28) is higher than the Arabian Sea (0.24) latitudinally. Aerosol fine mode fraction (FMF) is higher than 0.6 over Bay of Bengal, while FMF in the Arabian Sea is about 0.5. Bay of Bengal α(～1) is higher than the Arabian Sea value of 0.7, suggesting the dominance of fine mode aerosols over Bay of Bengal which is corroborated by higher FMF values over Bay of Bengal. Air back trajectory analyses suggest that aerosols from different source regions contribute differently to the optical characteristics over the Bay of Bengal and Arabian Sea.     

Optical and radiative properties of aerosols over Abu Dhabi in the United Arab Emirates

The present study is on the aerosol optical and radiative properties in the short-wave radiation and its climate implications at the arid city of Abu Dhabi (24.42 ^°N, 54.61 ^°E, 4.5 m MSL), in the United Arab Emirates. The direct aerosol radiative forcings (ARF) in the short-wave region at the top (TOA) and bottom of the atmosphere (BOA) are estimated using a hybrid approach, making use of discrete ordinate radiative transfer method in conjunction with the short-wave flux and spectral aerosol optical depth (AOD) measurements, over a period of 3 years (June 2012–July 2015), at Abu Dhabi located at the south-west coast of the Arabian Gulf. The inferred microphysical properties of aerosols at the measurement site indicate strong seasonal variations from the dominance of coarse mode mineral dust aerosols during spring (March–May) and summer (June–September), to the abundance of fine/accumulation mode aerosols mainly from combustion of fossil-fuel and bio-fuel during autumn (October–November) and winter (December–February) seasons. The monthly mean diurnally averaged ARF at the BOA (TOA) varies from ?13.2 Wm^?2 (～?0.96 Wm^?2) in November to ?39.4 Wm^?2 (?11.4 Wm^?2) in August with higher magnitudes of the forcing values during spring/summer seasons and lower values during autumn/winter seasons. The atmospheric aerosol forcing varies from + 12.2 Wm^?2 (November) to 28.2 Wm^?2 (June) with higher values throughout the spring and summer seasons, suggesting the importance of mineral dust aerosols towards the solar dimming. Seasonally, highest values of the forcing efficiency at the surface are observed in spring (?85.0 ± 4.1 W m^?2 τ ^?1) followed closely by winter (?79.2 ± 7.1 W m^?2 τ ^?1) and the lowest values during autumn season (?54 ± 4.3 W m^?2 τ ^?1). The study concludes with the variations of the atmospheric heating rates induced by the forcing. Highest heating rate is observed in June (0.39 K day ^?1) and the lowest in November (0.17 K day ^?1) and the temporal variability of this parameter is linearly associated with the aerosol absorption index.     

Relationship between MODIS based Aerosol Optical Depth and PM10 over Croatia

This study analyzes the relationship between Aerosol Optical Depth (AOD) obtained from Terra and Aqua Moderate Resolution Imaging Spectroradiometer (MODIS) and ground-based PM10 mass concentration distribution over a period of 5 years (2008–2012), and investigates the applicability of satellite AOD data for ground PM10 mapping for the Croatian territory. Many studies have shown that satellite AOD data are correlated to ground-based PM mass concentration. However, the relationship between AOD and PM is not explicit and there are unknowns that cause uncertainties in this relationship. The relationship between MODIS AOD and ground-based PM10 has been studied on the basis of a large data set where daily averaged PM10 data from the 12 air quality stations across Croatia over the 5 year period are correlated with AODs retrieved from MODIS Terra and Aqua. A database was developed to associate coincident MODIS AOD (independent) and PM10 data (dependent variable). Additional tested independent variables (predictors, estimators) included season, cloud fraction, and meteorological parameters — including temperature, air pressure, relative humidity, wind speed, wind direction, as well as planetary boundary layer height — using meteorological data from WRF (Weather Research and Forecast) model. It has been found that 1) a univariate linear regression model fails at explaining the data variability well which suggests nonlinearity of the AOD-PM10 relationship, and 2) explanation of data variability can be improved with multivariate linear modeling and a neural network approach, using additional independent variables.     

Evaluation and comparison of CMIP6 models and MERRA-2 reanalysis AOD against Satellite observations from 2000 to 2014 over China

Rapid industrialization and urbanization along with a growing population are contributing significantly to air pollution in China. Evaluation of long-term aerosol optical depth (AOD) data from models and reanalysis, can greatly promote understanding of spatiotemporal variations in air pollution in China. To do this, AOD (550 nm) values from 2000 to 2014 were obtained from the Coupled Model Inter-comparison Project (CIMP6), the second version of Modern-Era Retrospective analysis for Research, and Applications (MERRA-2), and the Moderate Resolution Imaging Spectroradiometer (MODIS; flying on the Terra satellite) combined Dark Target and Deep Blue (DTB) aerosol product. We used the Terra-MODIS DTB AOD (hereafter MODIS DTB AOD) as a standard to evaluate CMIP6 Ensemble AOD (hereafter CMIP6 AOD) and MERRA-2 reanalysis AOD (hereafter MERRA-2 AOD). Results show better correlations and smaller errors between MERRA-2 and MODIS DTB AOD, than between CMIP6 and MODIS DTB AOD, in most regions of China, at both annual and seasonal scales. However, significant under- and over-estimations in the MERRA-2 and CMIP6 AOD were also observed relative to MODIS DTB AOD. The long-term (2000–2014) MODIS DTB AOD distributions show the highest AOD over the North China Plain (0.71) followed by Central China (0.69), Yangtse River Delta (0.67), Sichuan Basin (0.64), and Pearl River Delta (0.54) regions. The lowest AOD values were recorded over the Tibetan Plateau (0.13 ± 0.01) followed by Qinghai (0.19 ± 0.03) and the Gobi Desert (0.21 ± 0.03). Large amounts of sand and dust particles emitted from natural sources (the Taklamakan and Gobi Deserts) may result in higher AOD in spring compared to summer, autumn, and winter. Trends were also calculated for 2000–2005, for 2006–2010 (when China introduced strict air pollution control policies during the 11th Five Year Plan or FYP), and for 2011–2014 (during the 12th FYP). An increasing trend in MODIS DTB AOD was observed throughout the country during 2000–2014. The uncontrolled industrialization, urbanization, and rapid economic development that mostly occurred from 2000 to 2005 probably contributed to the overall increase in AOD. Finally, China's air pollution control policies helped to reduce AOD in most regions of the country; this was more evident during the 12th FYP period (2011–2014) than during the 11th FYP period (2006–2010). Therefore this study strongly advises the authority to retain or extend these policies in the future for improving air quality.     

Atmospheric aerosol characteristics retrieved using ground based solar extinction studies at Mohal in the Kullu valley of northwestern Himalayan region,India

Aerosol parameters are measured using a ground-based Multi-wavelength Radiometer (MWR) at Mohal (31.90°N, 77.11°E, 1154 m amsl) in the Kullu valley during clear sky days of a seasonal year. The study shows that the values of spectral aerosol optical depths (AODs) at 500 nm and the Ångstrom turbidity coefficient ‘β’ (a measure of columnar loading in atmosphere) are high (0.41 ± 0.03, 0.27 ± 0.01) in summer, moderate (0.30 ± 0.03, 0.15 ± 0.03) in monsoon, low (0.19 ± 0.02, 0.08 ± 0.01) in winter and lowest (0.18 ± 0.01, 0.07 ± 0.01) in autumn, respectively. The Ångstrom wavelength exponent ‘α’ (indicator of the fraction of accumulation-mode particles to coarse-mode particles) has an opposite trend having lowest value (0.64 ± 0.06) in summer, low (0.99 ± 0.10) in monsoon, moderate (1.20 ± 0.15) in winter and highest value (1.52 ± 0.03) in autumn. The annual mean value of AOD at 500 nm, ‘α’ and ‘β’ are 0.24 ± 0.01, 1.06 ± 0.09 and 0.14 ± 0.01, respectively. The fractional asymmetry factor is more negative in summer due to enhanced tourists’ arrival and also in autumn months due to the month-long International Kullu Dussehra fair. The AOD values given by MWR and satellite-based moderate resolution imaging spectro-radiometer have good correlation of 0.76, 0.92 and 0.97 on diurnal, monthly and seasonal basis, respectively. The AODs at 500 nm as well as ‘β’ are found to be highly correlated, while ‘α’ is found to be strongly anti-correlated with temperature and wind speed suggesting high AODs and turbidity but low concentration of fine particles during hot and windy days. With wind direction, the AOD and ‘β’ are found to be strongly anti-correlated, while ‘α’ is strongly correlated.     

Impact of dust events on aerosol optical properties over Iraq

The spatial and temporal characteristics of aerosol optical properties (AOP) were analyzed in order to find out the hotspot aerosol sources over Iraq and surrounding regions. The correlation of AOP with the frequency of dust events (dust storm (DS), rising dust (RD), suspended dust (SD)) over 12 Iraqi stations is evaluated during the study period (January 2005–December 2014). The AOP: aerosol absorption optical depth (AAOD), aerosol extinction optical depth (AOD), and aerosol single scattering albedo (SSA) at 388 and 500 nm and aerosol index (AI), are derived from the Ozone Monitoring Instrument (OMI) on board the Aura satellite. Three well-known spatial interpolation techniques: inverse distance weighting, radial basis function with three sub-types, and kriging with three sub-types, are examined in ArcGIS software. Statistical analysis is applied to compute the station probability of dust events and its correlation with AOP. Results showed that the spline with the lowest RMSE and MPE near zero is the optimum method for estimating AOP. The spatial mean of AAOD, AOD, and AI (SSA) have the same pattern with high (low) mean values over the south and northwest of Iraq, Kuwait, and the northeast of Saudi Arabia. The seasonal variability of AAOD and AOD over the Iraqi stations showed that high (low) values occurred during spring and summer (winter) and concluded that AAOD is a responsible component for variation in AOD. DS and RD probability is higher over stations in the middle and south of Iraq than the stations in the north. High SD probability is over Mosul, Baghdad, and Nasiriya stations. The correlation of AOP with dust events suggests that the AAOD component is more important in the study of DS than SSA and AI while AI is a good index for the study of RD and SD in the study region.     

Spatiotemporal characteristics of TOMS-based dust aerosol optical depth in northern China during 1978–2005

Using the Total Ozone Mapping Spectrometer (TOMS) data from the National Aeronautics and Space Administration (NASA) earth satellites, the Aerosol Optical Depth (AOD) as indicated by AOD Index (AI) for the period 1978–2005 is analyzed for northern China. The spatial distribution of annual mean AI has the largest values in the desert regions of northwestern China, such as southern Xinjiang Taklimakan Basin, western Gansu and Qinghai’s Qaidam Basin. Large values are found in western Inner Mongolia, the Jogger Basin, and north of the Loess Plateau, as well as in the North China and Northeast China Plains. In Northern China, the AI of spring and summer is larger than in other seasons. The large AI values in spring register the most extensive coverage, but the AI values in regions affected by the Asian monsoon experience a significant decrease during the summer season. The lowest AI values generally occur in autumn in North and Northeast China, but they appear in winter in the northwestern arid region. Overall, the analysis results using TOMS AI data well reflect the spatiotemporal characteristics of dust aerosol as reported previously based on the dust weather observation data, with greater consistency seen in northwestern arid and semi-arid regions. It is also realized that the TOMS AI data are potentially useful for estimating atmospheric mineral aerosol deposition flux in northern China in order to better understand the formation and evolution of China loess in the Quaternary.     

Spatio-temporal variability of dust aerosols over the Sistan region in Iran based on satellite observations

Satellite remote sensing provides important observational constraints for monitoring dust life cycle and improving the understanding of its effects on local to global scales. The present work analyzes the dust aerosol patterns over the arid environment of the Sistan region in southeastern Iran, by means of multiple satellite platforms aiming to reveal the spatio-temporal distribution and trends. The dataset includes records of Aerosol Index (AI) from Total Ozone Mapping Spectrometer (TOMS) (1978–2001) and 6-year AI records from the Ozone Monitoring Instrument (OMI) aboard Aura. Moreover, the aerosol optical depth is analyzed through 11-year records from Multi-angle Imaging Spectroradiometer (MISR) aboard Terra (2000–2010) and from Moderate-resolution Imaging Spectroradiometer (MODIS) onboard Terra (2000–2007) and Aqua (2002–2011). The main focus is to determine the similarities and differences in dust variability over southwest Asia, in general, and the Sistan region, in particular. The results show a marked seasonal cycle with high aerosol loading during summer and lower in winter, while MISR, MODIS, and TOMS/OMI observations agree in both terms of monthly and seasonally mean spatial and temporal patterns. The higher aerosol concentrations during summer are interpreted as a result of the combined effect of the seasonal drying of the Hamoun lakes and the strong northerly Levar winds favoring dust erosion from the alluvial deposits in Sistan. After prolonged drought period, the dust aerosol load over the area has increased in the beginning of the 2000 s and decreased after 2004, thereby leading to an overall declining trend during the last decade. Such a trend is absent during the winter period when dust emission over the region is minimal.     

Surface water and aerosol spatiotemporal dynamics and influence mechanisms over drylands

Under the background of global warming and excessive human activities, much surface water in drylands is experiencing rapid degradation or shrinkage in recent years. The shrinkage of surface water, especially the degradation of lakes and their adjacent wetlands in drylands, may lead to the emergence of new salt dust storm hotspots, which causes greater danger. In this paper, based on high spatial resolution global surface water (GSW) and multiangle implementation of atmospheric correction (MAIAC) AOD data, we systematically analyze the dynamic characteristics of surface water and aerosols in typical drylands (Central Asia, CA) between 2000 and 2018. Simultaneously, combined with auxiliary environment variables, we explore the driving mechanisms of surface water on the regional salt/sand aerosols on different spatial scales. The results show that the seasonal surface water features an increasing trend, especially a more dramatic increase after 2015, and the permanent surface water indicates an overall decrease, with nearly 54.367 % at risk of receding and drying up. In typical lakes (Aral Sea and Ebinur Lake), the interannual change feature of the surface water area (WA) is that a continuous decrease during the study period occurs in Aral Sea area, yet a significant improvement has occurred in Ebinur Lake after 2015, and the degradation of Ebinur Lake takes place later and its recovery earlier than Aral Sea. The aerosol optical depth (AOD) in CA shows obvious seasonal variation, with the largest in spring (0.192 ± 0173), next in summer (0.169 ± 0.106), and the smallest in autumn (0.123 ± 0.065). The interannual variation of AOD exhibits an increase from 2000 to 2018 in CA, with high AOD areas mainly concentrated in the Taklamakan Desert and some lake beds resulting from lake degradation, including Aral Sea and Ebinur Lake. The AOD holds a similar trend between Aral Sea and Ebinur Lake on an interannual scale. And the AOD over Ebinur Lake is lower than that over Aral Sea in magnitude and lags behind in reaching the peak compared with Aral Sea. The WA change can significantly affect aerosol variation directly or indirectly on the aerosol load or mode size, but there are obvious differences in the driving mechanisms, acting paths, and influence magnitude of WA on aerosols on different spatial scales. In addition, the increase of WA can significantly directly suppress the increase of Ångström exponent (AE), and the effects of WA on AOD are realized majorly by an indirect approach. From the typical lake perspective, the effects of WA on aerosol in Aral Sea are achieved via an indirect path; and the decrease of WA can indirectly promote the AOD rise, and directly stimulate the AE growth in Ebinur Lake.     

Characteristics of spectral aerosol optical depths over India during ICARB

Spectral aerosol optical depth (AOD) measurements, carried out regularly from a network of observatories spread over the Indian mainland and adjoining islands in the Bay of Bengal and Arabian Sea, are used to examine the spatio-temporal and spectral variations during the period of ICARB (March to May 2006). The AODs and the derived Ångström parameters showed considerable variations across India during the above period. While at the southern peninsular stations the AODs decreased towards May after a peak in April, in the north Indian regions they increased continuously from March to May. The Ångström coefficients suggested enhanced coarse mode loading in the north Indian regions, compared to southern India. Nevertheless, as months progressed from March to May, the dominance of coarse mode aerosols increased in the columnar aerosol size spectrum over the entire Indian mainland, maintaining the regional distinctiveness. Compared to the above, the island stations showed considerably low AODs, so too the northeastern station Dibrugarh, indicating the prevalence of cleaner environment. Long-range transport of aerosols from tshe adjoining regions leads to remarkable changes in the magnitude of the AODs and their wavelength dependencies during March to May. HYSPLIT back-trajectory analysis shows that enhanced long-range transport of aerosols, particularly from the west Asia and northwest coastal India, contributed significantly to the enhancement of AOD and in the flattening of the spectra over entire regions; if it is the peninsular regions and the island Minicoy are more impacted in April, the north Indian regions including the Indo Gangetic Plain get affected the most during May, with the AODs soaring as high as 1.0 at 500 nm. Over the islands, the Ångström exponent (α) remained significantly lower (～1) over the Arabian Sea compared to Bay of Bengal (BoB) (～1.4) as revealed by the data respectively from Minicoy and Port Blair. Occurrences of higher values of α, showing dominance of accumulation mode aerosols, over BoB are associated well with the advection, above the boundary layer, of fine particles from the east Asian region during March and April. The change in the airmass to marine in May results in a rapid decrease in α over the BoB.     

Analysis of marine aerosol optical depth retrieved from IRS-P4 OCM sensor and comparison with the aerosol derived from SeaWiFS and MODIS sensor

Aerosol optical depth is regularly derived from SeaWiFS and MODIS sensor and used by the scientific community in various climatic studies. In the present study an attempt has been made to retrieve the aerosol optical depth using the IRS-P4 OCM sensor data and a comparison has been carried out using few representative datasets. The results show that the IRS-P4 OCM retrieved aerosol optical depth is in good agreement with the aerosols retrieved from SeaWiFS as well as MODIS. The RMSE are found to be ±0.0522 between OCM and SeaWIFS and ±0.0638 between OCM and MODIS respectively. However, IRS-P4 OCM sensor retrieved aerosol optical depth is closer to SeaWiFS (correlation = 0.88, slope = 0.96 and intercept = ?0.013) compared to MODIS (correlation = 0.75, slope = 0.91 and intercept = 0.0198). The mean percentage difference indicates that OCM retrieved AOD is +12% higher compared to SeaWiFS and +8% higher compared to MODIS. The mean absolute percentage between OCM derived AOD and SeaWiFS is found to be less (16%) compared to OCM and MODIS (20%).     

2001-2015年天山山区积雪时空变化及其与温度和降水的关系

采用2001-2015年MODIS积雪和陆表温度数据、中国高时空分辨率降水数据,基于趋势分析和相关分析方法,分析了天山山区积雪时空变化及其与温度和降水的关系。结果表明：（1）年内积雪面积变化受海拔影响,海拔≤4 000 m,呈单峰型分布,积雪面积冬季大,夏季小;海拔介于4 000~≤5 000 m,积雪面积分别在春季和秋季出现两次峰值;海拔>5 000 m,积雪面积变化与低海拔相反,在夏季达到最大,冬季最小。就年际变化而言,全区积雪面积呈略微减少趋势,其中秋季略微增加,春季变化不大,冬季和夏季明显减少。（2）积雪覆盖频率受水汽来向和地形影响,呈西高东低、北高南低分布格局,与海拔呈正相关。山区大部分区域积雪覆盖频率呈减少趋势,其中海拔介于3 600~≤4 600 m的积雪覆盖频率减少最为显著。（3）在春、夏季,温度是决定积雪面积变化的主要因素,与积雪面积呈负相关;在秋、冬季,降水对积雪面积变化的贡献大于温度,与积雪面积呈正相关。（4）积雪覆盖频率整体上与年均温度呈负相关,与降水呈低度正相关,相关程度及显著性水平在空间分布上存在差异,温度对积雪覆盖频率变化的贡献大于降水。     

Influence of circulation parameters on the AOD variations over the Bay of Bengal during ICARB

MODIS (Moderate Resolution Imaging Spectroradiometer) level-3 aerosol data, NCEP (National Centers for Environmental Prediction) reanalysis winds and QuikSCAT ocean surface winds were made use of to examine the role of atmospheric circulation in governing aerosol variations over the Bay of Bengal (BoB) during the first phase of the ICARB (Integrated Campaign for Aerosols, gases and Radiation Budget) campaign (March 18–April 12, 2006). An inter-comparison between MODIS level-3 aerosol optical depth (AOD) data and ship-borne MICROTOPS measurements showed good agreement with correlation 0.92 (p < 0.0001) and a mean MODIS underestimation by 0.01. During the study period, the AOD over BoB showed high values in the northern/north western regions, which reduced towards the central and southern BoB. The wind patterns in lower atmospheric layers (> 850 hPa) indicated that direct transport of aerosols from central India was inhibited by the presence of a high pressure and a divergence over BoB in the lower altitudes. On the other hand, in the upper atmospheric levels, winds from central and northern India stretched south eastwards and converged over BoB with a negative vorticity indicative of a downdraft. These wind patterns pointed to the possibility of aerosol transport from central India to BoB by upper level winds. This mechanism was further confirmed by the significant correlations that AOD variations over BoB showed with aerosol flux convergence and flux vorticity at upper atmospheric levels (600–500 hPa). AOD in central and southern BoB away from continental influences displayed an exponential dependence on the QuikSCAT measured ocean surface wind speed. This study shows that particles transported from central and northern India by upper atmospheric circulations as well as the marine aerosols generated by ocean surface winds contributed to the AOD over the BoB during the first phase of ICARB.     

Aerosol optical depths at Mohal-Kullu in the northwestern Indian Himalayan high altitude station during ICARB

First time observations of spectral aerosol optical depths (AODs) at Mohal (31.9°N, 77.11°E; altitude 1154 m amsl) in the Kullu valley, located in the northwestern Indian Himalayan region, have been carried out during Integrated Campaign for Aerosols, gases and Radiation Budget (ICARB), as a part of the Indian Space Research Organisation-Geosphere Biosphere Program (ISRO-GBP). AODs at six wavelengths are obtained using Microtops-II Sunphotometer and Ozonometer. The monthly mean values of AOD at 500 nm are found to be 0.27 ± 0.04 and 0.24 ± 0.02 during March and April, 2006 respectively. However, their monthly mean values are 0.33 ± 0.04 at 380 nm and 0.20 ± 0.03 nm at 870 nm during March 2006 and 0.31 ± 0.3 at 380 nm and 0.17 ± 0.2 at 870 nm during April 2006, showing a gradual decrease in AOD with wavelength. The Ångstrom wavelength exponent ‘α’ had a mean value of 0.72 ± 0.05, implying reduced dominance of fine particles. Further, the afternoon AOD values are higher as compared to forenoon values by ～ 33.0% during March and by ～ 9.0% during April 2006 and are attributed to the pollutant lifted up from the valley by the evolving boundary layer. Besides the long-range transportation of aerosol particles by airmass from the Great Sahara and the Thar Desert regions to the observing site, the high values of AODs have also been influenced by biomass burning and frequent incidents of forest fire at local levels.     

新疆山区低层云水资源时空分布特征

采用云与地球辐射能量系统(CERES)2003～2007年的CERESSSF Aqua MODIS云资料,选取新疆阿尔泰山、天山和昆仑山三大山区,通过考察云量和云液态水柱含量分析了低层云水资源的多年空间分布和季节变化特征。结果表明,三大山区多年平均的云量年平均区域值在24.4%～27.5%之间,云液态水柱含量在51～56.3g/m2之间。三大山区低层云量和云液态水柱含量有明显的季节变化特征。综合云量和云水柱含量来看,春季是三大山区低层云量资源最丰富的季节,冬季是三大山区低层云中的含水量最丰富的季节。     

基于多源数据的西藏地区积雪变化趋势分析

利用1980—2009年气象台站的观测数据、 北半球NOAA周积雪产品和2001—2010年500 m分辨率的EOS/MODIS积雪产品等多源资料, 从不同角度对近30 a来西藏区域积雪变化趋势进行了分析. 结果表明: 不同资料分析均显示, 近30 a来西藏地区积雪不断减少, 尤其以近些年较为明显. 近30 a积雪日数、 最大积雪深度总体上呈现下降趋势, 尤其是进入21世纪以来, 下降趋势非常明显. 从秋冬春季节的积雪变化趋势来看, 冬、 春两季的积雪在减少, 而秋季在增多, 这些变化趋势都与各季节的气温和降水密切相关. NOAA资料显示, 近30 a来西藏地区的积雪覆盖面积正在逐步减少; 季节变化略有不同, 春、 秋两季略呈上升趋势, 冬、 夏两季在减少, 且夏季减少趋势较明显. MODIS资料分析表明, 近10 a来西藏地区的积雪总体呈下降趋势, 尤其是2007年下半年开始下降明显. 秋季的积雪在增加, 冬、 春、 夏三季的积雪趋于减少, 且春季的下降趋势最明显, 其次为冬季, 夏季的减少幅度最小. 不同海拔的积雪都有减少趋势, 最明显的是海拔4 000~5 000 m的积雪, 其次是海拔5 000~6 000 m段. 按地理区域分析, 近10 a来西藏东、 西、 中3个区域的积雪都呈减少趋势, 其中西部的下降趋势最明显, 其次为中部, 东部相对较稳定.     

Trend analysis and change point detection of annual and seasonal precipitation and temperature series over southwest Iran

This paper presents results of trend analysis and change point detection of annual and seasonal precipitation, and mean temperature (TM), maximum temperature (TMAX) and minimum temperature (TMIN) time series of the period 1950–2007. Investigations were carried out for 50 precipitation stations and 39 temperature stations located in southwest Iran. Three statistical tests including Pettitt’s test, Sequential Mann–Kendall test (SQ-MK test) and Mann–Kendall rank test (MK-test) were used for the analysis. The results obtained for precipitation series indicated that most stations showed insignificant trends in annual and seasonal series. Out of the stations which showed significant trends, highest numbers were observed during winter season while no significant trends were detected in summer precipitation. Moreover, no decreasing significant trends were detected by statistical tests in annual and seasonal precipitation series. The analysis of temperature trends revealed a significant increase during summer and spring seasons. TMAX was more stable than TMIN and TM, and winter was stable compared to summer, spring and autumn seasons. The results of change point detection indicated that most of the positive significant mutation points in TM, TMAX and TMIN began in the 1990s.     

撒哈拉地区沙尘气溶胶南北空间型分布特征及其成因

本次研究利用MODIS、CALIPSO等卫星观测资料以及MERRA-2再分析资料分析了2007–2017年撒哈拉地区气溶胶光学厚度的空间分布特征.结果表明,撒哈拉地区气溶胶光学厚度的空间分布具有明显的季节变化,夏季沙尘气溶胶光学厚度高值区位于撒哈拉北部地区,高达0.6以上;而冬季沙尘气溶胶光学厚度高值区位于撒哈拉南部地...