Prior knowledge-supported aerosol optical depth retrieval over land surfaces at 500 m spatial resolution with MODIS data

Aerosol optical depth (AOD) values at a spatial resolution of 500 m were retrieved over terrain areas by applying a time series of Moderate resolution Imaging Spectroradiometer (MODIS) 500 m resolution data in the Heihe region (36–42° N, 97–104° E) of Gansu Province, China; in the Pearl River Delta (18–30° N, 108–122° E), China; and in Beijing (39–41° N, 115–118° E), China. A novel prior knowledge scheme was used in the algorithm that performs cloud screening, simultaneous AOD and surface reflectance retrieval from the MODIS 500 m Level 1B data. This prior knowledge scheme produced a new Ångström exponent α, utilizing a Terra pass time α and an Aqua pass time α to better satisfy the invariant α assumption. The retrieved AOD data were compared with AOD data observed with the ground-based, automatic Sun-tracking photometer CE318 at corresponding bands in the Heihe region and with Aerosol Robotic Network (AERONET) data in the Pearl River Delta and in Beijing. Validation experiments demonstrated the potential of applying the algorithm to MODIS 500 m AOD retrieval on land; validation showed the uncertainty of Δτ = ±0.1±0.2τ over various types of underlying land surface, including cities, where τ is the aerosol optical depth. The root mean square errors (RMSEs) were around 0.1 for inland regions and up to 0.24 for cities by the sea, such as Hong Kong and Zhongshan, China.     

Comparing MODIS and AERONET aerosol optical depth over China

The newest daily and monthly Moderate Resolution Imaging Spectroradiometer (MODIS) aerosol optical depths (AOD or τ) dataset over land, C005, retrieved using the second-generation operational algorithm, were evaluated using a ground-based Aerosol Robotic Network (AERONET) dataset from 13 sites over China. The dataset covers the period 2003–2006. Daily MODIS C005 AODs over China were found to have a positive bias with a relationship of τ_MODIS?=?0.135?+?1.022τ_AERONET, for which the offset is larger than reported global validation results. However, the relationship τ_MODIS?=?0.021?+?0.929τ_AERONET showed that monthly MODIS C005 AODs were an overestimation for small AOD and underestimation for high AOD. Both daily and monthly MODIS AOD retrievals showed poor performance in extreme aerosol conditions, e.g. under dust events or heavy urban/industrial haze. Nevertheless, both daily and monthly MODIS C005 AOD datasets can be used for investigation of aerosol spatial distribution and temporal variation over China.     

Study on spatial-temporal variation of aerosol optical depth over the Yangtze Delta and the impact of land-use/cover

Aerosol optical depth (AOD) is a principal indicator used to describe the atmospheric condition and effect of aerosols on radiative transfer in the Earth’s atmosphere. In this study, the spatial-temporal variation of AOD of the Yangtze Delta during 2000–2011 and the impact of land cover were studied. The results show that Moderate Resolution Imaging Spectroradiometer (MODIS) AOD was in good agreement with data obtained from six ground-based Aerosol Robotic Network (AERONET) sun photometers (R > 0.75). The AOD over the Yangtze Delta presented an obvious one year cycle variation from 2000 to 2011. The largest value often appeared in May or June, and the smallest often appeared in December or January. The AOD over main cities has increased gradually over the years. The AOD over urban areas increased faster than that in rural areas. A change of land-use/cover leads to a change of AOD. Areas of land-use/cover with increased intense human activity leads to changes in higher AOD whereas an increase in forested areas leads to an AOD change to a lower value. Forest land has a purification effect against atmospheric aerosols.     

Intercomparison of CALIOP,MODIS, and AERONET aerosol optical depth over China during the past decade

ABSTRACT

Aerosol optical depth (AOD) data from Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) were intercompared and validated against ground-based measurements from Aerosol Robotic Network (AERONET) as well as space-based Moderate Resolution Imaging Spectroradiometer (MODIS) over China during June 2006 to December 2015. This article aims to evaluate CALIOP daytime AOD using MODIS and AERONET AODs. Comparing the AOD between CALIOP and AERONET in different regions over China using quality control flags to screen the AOD data, we find that CALIOP AOD is generally lower than AERONET AOD especially at optical depths over 0.4 likely due to differences in the cloud screening algorithms and general retrieval uncertainty. Comparison between CALIOP AOD and MODIS AOD results show that the overall spatio-temporal distribution of CALIOP AOD and MODIS AOD is basically consistent. As for the spatial distribution, both data sets show several high-value regions and low-value regions in China. CALIOP is systematically lower than MODIS over China, especially over high AOD value regions for all seasons. As for the temporal variation, both data sets show a significant seasonal variation: AOD is largest in spring, then less in summer, and smallest in winter and autumn. A long-term linear trend analysis based on the domain averaged monthly mean CALIOP and MODIS AOD shows agreement among CALIOP and MODIS for the trends over the 10-year period in four regions examined. The trends in AOD derived from CALIOP and MODIS indicate a decline in aerosol loading in China since 2006. It is found from frequency comparison that CALIOP and MODIS AOD generally exhibit a degree of correlation over China. Statistical frequency analysis shows that CALIOP AOD frequency distribution shows a higher peak than MODIS AOD when AOD < 0.4. For the most part, mean MODIS AOD is higher than mean CALIOP AOD. Evaluation of CALIOP AOD retrievals provides the prospect for application of CALIOP data. The intercomparison suggests that CALIOP has systematically underestimated daytime AOD retrievals, especially deteriorating with increasing AOD, and therefore, CALIOP daytime AOD retrievals should be treated with some degree of caution when the AOD is over 0.4.     

Aerosol characteristics over Delhi national capital region: a satellite view

Multi-sensor aerosol data sets are analysed to examine the aerosol characteristics over the Delhi national capital region. Both the Multiple-angle Imaging Spectroradiometer (MISR) and Moderate Resolution Imaging Spectroradiometer (MODIS) capture the seasonal cycle of aerosol optical depth (AOD) as observed by ground-based measurements. However, AOD from MISR shows a low bias relative to AOD from MODIS, which increases linearly at high AOD conditions. A large difference (by >25 W m^–2 per unit AOD) in the top-of-atmosphere direct radiative forcing efficiency derived from MODIS and MISR-retrieved AOD is observed during the winter and pre-monsoon seasons relative to the other seasons. The ubiquitous presence of dust (as indicated by non-spherical particle fraction to AOD and linear depolarization ratio values) is observed throughout the year. The aerosol layer is mostly confined to within 2 km of surface in the winter and post-monsoon seasons, while it expands beyond 6 km in the pre-monsoon and monsoon seasons. Columnar AOD is found to be highly sensitive to aerosol vertical distribution. The applicability of multi-sensor data sets and climatic implications are discussed.     

Aerosol characteristics during the coolest June month over New Delhi,northern India

June 2008, which is also the transition month between two major seasons for Indo-Gangetic Basin (IGB), has been identified the coolest June over New Delhi during the past century, showing mean temperature of 31.6 ± 1.7°C, which was found to be ～2°C less than its climatological mean (33.9°C). Aerosol optical properties for this month and thus obtained physical parameters have been studied using data from the CIMEL sun/sky radiometer, installed in New Delhi under the Aerosol Robotic Network (AERONET) programme. Results reveal bimodal aerosol volume size distribution. The monthly mean values for aerosol optical depth (AOD) at 500 nm (0.96 ± 0.31) and Ångström exponent at the wavelength pair of 440–870 nm (0.79 ± 0.42) show significant lower values whereas single scattering albedo at 675 nm shows a significantly larger value (0.94 ± 0.04) compared with previous measurements over the station. Results suggest dominance of scattering-type particles such as water-soluble aerosols from anthropogenic sources and dust aerosols from natural sources with higher relative humidity over the station. Radiative forcing caused due to the aerosols for the month of June 2008, which have been computed using the radiative-transfer model, informs low forcing at the top of atmosphere (TOA,?+14 W m^?2) as well as at surface (?33 W m^?2). The resultant atmospheric forcing (+47 W m^?2) indicates warming effect that caused heating of lower atmosphere at the rate of 0.89 K day^?1.     

Ground-, satellite- and simulation-based analysis of a strong dust event over Abastumani,Georgia, during May 2009

A strong dust event over Abastumani, Georgia, during May 2009 was studied using light detection and ranging (lidar), satellite and sun photometric measurements. High aerosol optical depth (AOD) values (0.45–0.57) at 500 nm were measured over the closest Aerosol Robotic Network (AERONET) site (Erdemli, Turkey), whereas over Georgia, the AOD measured by the Moderate Resolution Imaging Spectroradiometer (MODIS) was about 0.9 at 550 nm. The AERONET data analysis showed a mean aerosol effective radius of about 2.5 μm, whereas the mean value of the Ångström exponent (α) (wavelength pair 440/870 nm) was smaller than 1, indicating the dominance of large aerosols. The aerosol lidar over Abastumani showed the existence of a strong particle load from the near ground up to a height of 3.5 km. The BSC-DREAM8b forecast model showed that the dust aerosols travelled from the Saharan and the Arabic deserts to the studied area, even reaching southern Russia, covering a total distance of about 5500 km, in the height region from about 2 to 11.5 km.     

Lidar and spectroradiometer measurements of atmospheric aerosol optical characteristics over an urban area in Sofia,Bulgaria

A series of campaigns involving a systematic investigation of the atmosphere over an urban area of Sofia city were carried out. A European Aerosol Research Lidar Network (EARLINET) scanning aerosol lidar, a spectroradiometer, a standard sun photometer and a ground meteorological station were used in the observations. Multiple aerosol layers of variable thickness (200–600 m) were observed systematically in the planetary boundary layer (PBL) over the study area and the experimental data were compared with theoretical data. A study of the optical characteristics of the atmospheric aerosol, including the extinction coefficient, aerosol optical depth (AOD) and Angstrom parameters α and β, was performed and their variations followed during the convective boundary layer (CBL) formation. Values of the AOD obtained using the different instruments during simultaneous measurements were compared. Preliminary results show that the AOD values recorded by the sun photometer and those calculated on the basis of the spectroradiometer data are higher than those retrieved from the lidar data. Determination of the atmospheric optical depth and extinction coefficient using a ground-based spectral instrument is a relatively simple and inexpensive method of monitoring the total aerosol content in the atmosphere as well as the air quality over the region.     

MATCH对中国地区2006年气溶胶光学厚度分布特征的模拟研究

利用2006年NCEP/NCAR再分析资料驱动大气化学传输模式MATCH （Model of Atmospheric Transport and Chemistry）,模拟了中国地区气溶胶光学厚度的分布及其季节变化特征,并与MODIS（MODerate resolution Imaging Spectro-radiometer）卫星产品MOD08_M3和中国太阳分光观测网CSHNET（the Chinese Sun Hazemeter Network）的观测资料进行了对比和验证。在此基础上,研究得出,2006年中国的华北、华中和华南地区是气溶胶光学厚度的高值区,青藏高原和东北地区是低值区。在中国的华北、华中、华南和西南等大部分地区,硫酸盐气溶胶产生的光学厚度所占的比重较大,其次为有机碳气溶胶,黑碳气溶胶和海盐气溶胶所占比重较小。     

Seasonal variability in aerosol optical depth over India: a spatio-temporal analysis using the MODIS aerosol product

Aerosols are one of the key components of climate systems. They absorb and scatter both solar and terrestrial radiation and produce strong surface as well as atmospheric radiative forcing effects. Aerosol climatology includes the measurement of light extinction by aerosol scattering and absorption, by procedures such as aerosol optical depth (AOD), angstrom exponent (α), single-scattering albedo (ω), and size distribution. This article analyses the dynamics of seasonal AOD over the Indian subcontinent from 2001 to 2009 using the MODIS level 2 data set. The analysis carried out for winter, pre-monsoon, monsoon, and post-monsoon seasons is based on 8 days’ composite AOD data for selected months representative of each season. The spatial variability of AOD has been shown to be 0.47 μm and 0.66 μm for fine- and coarse-mode aerosols, respectively, which illustrates the principle of relative difference. The dynamics of seasonally averaged AOD over the period under study represent an increasing tendency from 0.20 to 0.37 at 0.47 μm and from 0.16 to 0.26 at 0.66 μm during winter (2003–2009), whereas AOD in the pre-monsoon season ranged from 0.24 to 0.16 at 0.47 μm and from 0.24 to 0.16 at 0.66 μm (2005–2009). The monsoon season yielded an AOD of less than 0.15 throughout the study period, and the post-monsoon season recorded an increasing tendency from 0.18 to 0.29 at 0.47 μm and from 0.16 to 0.19 at 0.66 μm (2005–2009), reflecting a similar trend to that of the winter AOD curve. The spatial distribution of AOD shows that the northern part of India – especially the Indo-Gangetic plain – remains most affected by high AOD throughout the year. Such high AOD can be attributed to increasing anthropogenic emission due to an ever-increasing population, and urban, industrial, and other economic activities causing high concentrations of fine-mode organic and inorganic aerosol particles, along with coarse soil and mineral dust over the Indo-Gangetic plain.     

Verification of dust forecast over the Indian region with satellite and ground based observations

This article presents the verification results of the dust forecast by a numerical model over India and neighbouring regions. National Centre for Medium Range Weather Forecasting Unified Model (NCUM) is a global numerical weather prediction (NWP) model with a prognostic dust scheme. Evaluation of the performance of dust forecast by NCUM is carried out in this study. Model forecast of dust optical depth (DOD) at 550 nm is validated against ground-based and satellite observations since optical depth measurements in mid-visible wavelength are easily available. Daily 5-day forecast based on 00 UTC initial condition during dust dominated pre-monsoon season (April–May) of 2014 is used in this study. Location specific and geographical distribution of dust forecast is validated against Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) satellite retrieved DOD observation at 532 nm, Moderate Resolution Imaging Spectroradiometer (MODIS) aerosol optical depth (AOD), Ozone Monitoring Instrument (OMI), aerosol index, and Aerosol Robotic Network (AERONET) station data of total and coarse mode AOD. The verification results indicate that NCUM dust forecast generally gives good representation of large scale geographical distribution of dust over the western region of India. DOD forecasts show good correlation with co-located CALIPSO DOD over the western part (0.71) compared to central (0.58) and eastern (0.61) part of India in April while it show similar trend in May with slightly improved correlation (0.68) over the eastern part of India. Results also show that DOD forecasts are better correlated to AERONET coarse mode AOD observations over Jaipur in April and over Kanpur in May. Vertical distribution of dust concentrations in the forecast show reasonably good agreement with attenuated backscatter and depolarization ratio from CALIPSO observations. The model is also able to simulate spatiotemporal distribution of dust during a major dust event as observed by CALIPSO, MODIS, and OMI.     

Himawari-8气溶胶产品的验证及应用

为准确分析中国地区气溶胶空间分布与时间变化特征规律,首先利用中国地区9个AERONET（Aerosol Robotic Network）地基站点观测资料对新一代静止气象卫星Himawari-8气溶胶光学厚度（Aerosol Optical Depth, AOD）产品数据进行一致性验证,并在此基础上选取2015年7月至2018年4月Himawari-8逐小时AOD数据分析了中国地区气溶胶光学厚度时空变化特征。结果表明：①Himawari-8 AOD与AERONET AOD之间相关性很高,9个站点的相关系数R在0.64 ~ 0.91之间,拟合曲线斜率k的范围为0.57 ~ 0.68。②Himawari AOD产品与AERONET AOD的相关性在中午时段较其他时段相对较低;北方地区Himawari-8 AOD冬季反演效果与夏季相比较差,南方地区则相反。③中国地区年平均AOD呈东高西低分布,春、夏两季AOD明显高于秋、冬两季,其中夏季最高,春季次之;地区间AOD月变化差异也较大;大部分地区AOD日变化呈现先下降后上升再下降的趋势,AOD最高值出现在午后14 ~ 16时,最低值出现在18时。研究结果为了解中国地区大气气溶胶的时空变化规律和全天时的大气污染监测方法提供新的参考。     

Seasonal variations in aerosol optical thickness over eastern China determined from VIIRS data and ground measurements

Two-year records of Visible Infrared Imaging Radiometer Suite (VIIRS) Intermediate Product (IP) data on aerosol optical thickness (AOT) at 550 nm were evaluated by comparing them to sun-sky radiometer measurements from the Chinese Sun Hazemeter Network (CSHNET) and the Aerosol Robotic Network (AERONET). The monthly and seasonal variations in the aerosol optical properties over eastern China were then investigated using collocated VIIRS IP data and CSHNET and AERONET measurements. Between 59.2 and 62.1% of the retrieved VIIR IP values fell within the range defined for MODIS (Moderate Resolution Imaging Spectroradiometer) and had similar values for the correlation coefficient (0.880–0.909). The performances of the current VIIRS IP AOT retrievals at the provisional stage were consistent with ground measurements. However, over urban areas, the VIIRS exhibits more scatter and therefore less precision than observed over marine and rural areas. Similar characteristics of seasonal and monthly variations were found among the measurements, though the observational methodologies were different, showing maxima in the summer and spring and minima in the winter and autumn. Although the intensities vary from season to season, the spatial AOT distribution patterns did not change. High-AOT centres were situated in the industrialized coastal regions of China and were related to the distribution of urban areas.     

Himawari-8气溶胶产品的验证及应用

为准确分析中国地区气溶胶空间分布与时间变化特征规律，首先利用中国地区9个AERONET（Aerosol Robotic Network）地基站点观测资料对新一代静止气象卫星Himawari-8气溶胶光学厚度（Aerosol Optical Depth, AOD）产品数据进行一致性验证，并在此基础上选取2015年7月至2018年4月Himawari-8逐小时AOD数据分析了中国地区气溶胶光学厚度时空变化特征。结果表明：①Himawari-8 AOD与AERONET AOD之间相关性很高，9个站点的相关系数R在0.64 ~ 0.91之间，拟合曲线斜率k的范围为0.57 ~ 0.68。②Himawari AOD产品与AERONET AOD的相关性在中午时段较其他时段相对较低；北方地区Himawari-8 AOD冬季反演效果与夏季相比较差，南方地区则相反。③中国地区年平均AOD呈东高西低分布，春、夏两季AOD明显高于秋、冬两季，其中夏季最高，春季次之；地区间AOD月变化差异也较大；大部分地区AOD日变化呈现先下降后上升再下降的趋势，AOD最高值出现在午后14 ~ 16时，最低值出现在18时。研究结果为了解中国地区大气气溶胶的时空变化规律和全天时的大气污染监测方法提供新的参考。     

Satellite and surface-based remote sensing of Saharan dust aerosols

The spatial and temporal characteristics of dust aerosols and their properties are assessed from satellite and ground-based sensors. The spatial distribution of total column aerosol optical depth at 550 nm (AOD) from the Moderate Resolution Imaging SpectroRadiometer (MODIS) coupled with top of atmosphere Clouds and the Earth's Radiant Energy System (CERES) shortwave fluxes are examined from the Terra satellite over the Atlantic Ocean. These data are then compared with AOD from two Aerosol Robotic Network (AERONET) ground-based sun photometer measurement sites for nearly six years (2000-2005). These two sites include Capo Verde (CV) (16°N, 24°W) near the Saharan dust source region and La Paguera (LP) (18°N, 67°W) that is downwind of the dust source regions. The AOD is two to three times higher during spring and summer months over CV when compared to LP and the surrounding regions. For a unit AOD value, the instantaneous TOA shortwave direct radiative effect (DRE) defined as the change in shortwave flux between clear and aerosol skies for CV and LP are − 53 and − 68 Wm^− 2 respectively. DRE for LP is likely more negative due to fall out of larger particles during transport from CV to LP. However, separating the CERES-derived DRE by MODIS aerosol effective radii was difficult. Satellite and ground-based dust aerosol data sets continue to be useful to understand dust processes related to the surface and the atmosphere.     

Validation of MODIS retrieval aerosol optical depth and an investigation of aerosol transport over Mohal in north western Indian Himalaya

This study deals with the optical properties of aerosols during 2007 over Mohal (31.9º N, 77.12º E) in north western Indian Himalaya, investigated using ground-based measurements and multi-satellite data. The daily average (mean ± standard deviation) aerosol optical depth (AOD) at 500 nm, Ångström exponent and turbidity coefficient values were 0.2 ± 0.1, 1.1 ± 0.3 and 0.1 ± 0.1, respectively. About 84% of AOD values retrieved from satellites were found to be within an uncertainty limit with a significant correlation coefficient around 0.70. The present study suggests that AOD retrieval using the Moderate Resolution Imaging Spectroradiometer (MODIS) is able to characterize AOD distribution over Mohal. However, to eliminate systematic errors, the existing MODIS algorithm needs to be modified in view of the changing aerosol optical properties, especially during the biomass-burning period. To investigate the influence of aerosol transport, a multi-sensor approach in conjunction with back-trajectory analysis was used. The observed higher values of AOD during dust-loading days with simultaneous study of the space-borne lidar measurements as well as back-trajectory analysis suggest the influx of desert aerosols. Transport of dust aerosols on 12 April, 27 April and 1 June caused a significant reduction in surface-reaching solar irradiance by 43, 40 and 39 W m^–2, respectively. Atmospheric forcing during these days increased by 33.8, 33.0 and 33.2 W m^–2, which translates into atmospheric heating rates of 0.95, 0.93 and 0.93 K day^–1, respectively. This indicates significant climatic implications due to arriving aerosols in north-western Indian Himalaya.     

Ozone Monitoring Instrument aerosol products: a comparison study with ground-based airborne sun photometer measurements over Europe

Airborne sun photometer measurements are used to evaluate retrievals of extinction aerosol optical depth (AOD). These data are extracted from spatially coincident and temporally near-coincident measurements by the Ozone Monitoring Instrument (OMI) aboard the Aura satellite taken during 2005. OMI-measured top of atmosphere (TOA) reflectances are routinely inverted to yield aerosol products such as AOD using two different retrieval techniques: the Aura OMI Near-Ultraviolet Aerosol Data Product, OMAERUV, and the multi-wavelength Aura OMI Aerosol Data Product, OMAERO. In this work, we propose a study that specifically compares the instantaneous aerosol optical thicknesses retrieved from OMI at several locations containing sites and those of the Aerosol Robotic Network (AERONET). The result of the comparison shows that, just over Europe, OMI aerosol optical thicknesses are better retrieved in the multi-wavelength retrieval than in the near-ultraviolet. Correlations have been improved by applying a simple criterion to avoid scenes probably contaminated by thin clouds, and surface scattering. The ultraviolet irradiance positive bias in the OMI data is corrected using a procedure based on global climatological fields of aerosol absorption optical depth. The results generally show a bias significantly reduced by 5–20%, a lower variability and an unchanged, high correlation coefficient.     

Correcting MODIS aerosol optical depth products using a ridge regression model

Aerosol optical depth (AOD) is an important metric for the concentration of aerosols in the atmosphere. Dark target (DT) algorithm is a widely used physical model to retrieve AOD over land from Moderate Resolution Imaging Spectroradiometer (MODIS) data. However, due to the limitation of surface ‘dark-target’ in some regions and over certain surface types, it does not work very well. In this paper, we propose two hybrid frameworks based on ridge regression (RR) to improve the retrieval accuracy. They are serial and parallel approaches. In both frameworks, the DT algorithm is used as a baseline to derive an initial result, and the bias between the derived AOD and the ground-truth is corrected by the RR model. To validate the effectiveness of the proposed methods, we apply them on 3093 collocated MODIS and Aerosol Robotic Network (AERONET) observations, covering 10 stations at all available time in China. The obtained results demonstrate that the proposed methods can improve retrieval performance compared to the corresponding DT algorithm and the RR model.     

Climatic oscillations in aerosol optical depth over tropical oceanic regions pertaining to genesis of the Indian Ocean Dipole

Data on aerosol optical depth (AOD) derived from the ocean colour sensor of the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) from September 1997 to December 2010 over the western tropical Indian Ocean (WTIO) (10° S to 10° N; 50° E to 70° E) and southeastern tropical Indian Ocean (SETIO) (10° S to equator; 90° E to 110° E) were analysed with a view to understanding its response to climatic oscillations in regard to the El Niño–Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD). This study demonstrates the existence of a bimodal distribution pattern of AOD in the atmosphere over both WTIO and SETIO, with the highest values being around 1.1 during the period of primary maximum during August over the WTIO and during October over the SETIO. A secondary maximum (～0.9) appeared during March over both areas. In addition, the existence of a see-saw oscillation in the distribution of AOD between the atmospheric columns over the study regions was revealed, with higher values during August–December over the SETIO. AOD data over the SETIO captured very well the influence of these atmospheric modes, whereas the influence was not as significant over the WTIO. Stronger El Niño (Niño index > 0.80) events produced a significantly positive (more than +0.03) anomaly in AOD values over the SETIO during October, whereas the lone mode of IOD events and La Niña were not sufficient to induce any significant change in the aerosol distribution over the area. The mode of El Niño co-occurring with a positive IOD (PIOD) strengthens this anomalous behaviour. A significantly negative anomaly (≤0.03) in AOD was observed with concurrent La Niña (Niño index < ?1.1) and negative IOD (NIOD) (dipole mode index ≤ 1.1) events. The Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model and National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) winds were utilized to verify these observations.     

双通道算法与MODIS算法反演中国近海气溶胶光学特性的对比研究

利用双通道和IMAPP气溶胶反演算法处理TERRA/MODIS L1B数据得出中国近海气溶胶的光学厚度,与AERONET太阳光度计的反演结果作对比分析,验证了反演方法的可行性。同时,对各海域的反演结果及表征粒子谱宽度的Angstrom指数(α)的变化情况进行了分析,结果表明：在东海和日本以南等广阔海域,两种反演算法的结果同AERONET太阳光度计的观测结果基本一致,相关性较好;在渤海和黄海近海岸一带两者气溶胶光学厚度的反演值均偏高,其原因主要是由这些海域的二类水体的影响导致的。探讨分析了这些海域的水域特征及光学特性,为研究发展适合中国近海气溶胶特性的反演算法提供了依据。