High Aerosol Optical Thickness Research Articles

Remote sensing of eruptions and transport of Taal volcano in January 2020

The eruption and transport of the Taal volcano (14 N, 121 E) in January 2020 have been investigated using remote sensing measurements of several satellites, including the Moderate Resolution Imaging Spectroradiometer, Ozone Monitoring Instrument (OMI), Ozone Mapping and Profiler Suite, and Himawari-8. The aerosol optical thickness (AOT), angstrom exponent (AE), and column densities of sulfur dioxide (SO2) derived from satellites are analyzed in this study. The ground-based AERONET data of Manila city and OMI SO2 are studied to validate high AOT events. Our findings indicate that ash and gases followed opposite transport paths. This differential transport is consistent with various wind data, HYSPLIT back and forward trajectory calculations, and emission dispersion models. The potential influences of deposition on ocean biology and climate are also discussed.

Spatiotemporal Evolution and Prediction of AOT in Coal Resource Cities: A Case Study of Shanxi Province, China

As aerosols in the air have a great influence on the health of residents of coal resource-based cities, these municipalities are confronting the dilemma of air pollution that is caused by the increase of suspended particles in the atmosphere and their development process. Aerosol optical thickness could be used to explore the aerosol temporal and spatial variations and to develop accurate prediction models, which is of great significance to the control of air pollution in coal resource-based cities. This paper explored the temporal spatial variation characteristics of aerosols in coal resource-based regions. A total of 11 typical coal-resource prefecture-level cities in the Shanxi Province were studied and inverted the aerosol optical thickness (AOT) among these cities based on MODIS (Moderate Resolution Imaging Spectroradiometer) data and analyzed the significant factors affecting AOT. Through inputting significant correlation factors as the input variables of NARX (nonlinear auto regressive models with exogenous inputs) neural network, the monthly average AOTs in the Shanxi Province were predicted between 2011 and 2019. The results showed that, in terms of time series, AOT increased from January to July and decreased from July to December, the maximum AOT was 0.66 in summer and the minimum was 0.2 in autumn, and it was related to the local monsoon, temperature, and humidity. While as far as the space alignment is concerned, the figure for AOT in Shanxi Province varied significantly. High AOT was mainly concentrated in the centre and south and low AOT was focused on the northwestern part. Among the positively correlated factors, the correlation coefficient of population density and temperature exceeded 0.8, which was highly positive, and among the negatively correlated factors, the correlation coefficient of NDVI exceeded -0.8, which was highly negative. After improving the model by adding the important factors that were mentioned before, the error between the predicted mean value and the actual mean value was no more than 0.06. Considering this charge, the NARX neural network with multiple inputs can contribute to better prediction results.

The Bistatic Radar as an Effective Tool for Detecting and Monitoring the Presence of Phytoplankton on the Ocean Surface

A massive dust storm formed over the Sahara Desert in June 2020. The African dust cloud, which traveled over the tropical Atlantic’s main development region for hurricanes, resulted in the highest aerosol optical thickness (AOT) for the past two decades. Dust particles contained in dust clouds are at some point deposited on the ocean surface, impacting the ocean biogeochemistry through the supply of nutrients. Although there are remote sensing systems that can map the AOT, the locations of the aerosol particles deposited on the ocean surface remain unknown quantities with remote sensing measurements. In addition, the supplied nutrients are not static and are displaced by ocean currents. Nutrients trigger the phytoplankton (algae) blooms, which form a film on the ocean surface and affect the ocean surface tension. The change in ocean surface tension causes a local decrease of ocean surface roughness over the areas covered with phytoplankton. Bistatic radar data from the CYclone Global Navigation Satellite System (CYGNSS) mission can detect changes in the ocean surface roughness, expressed as an increase in reflectivity when the surface becomes smoother. Therefore, decreased ocean surface roughness correlated with a recent dust storm represents a key indicator of the presence of phytoplankton. In this paper, we present for the first time the capability of bistatic radar measurements to provide an effective tool to map information of areas covered with phytoplankton, establishing bistatic radar as the most reliable remote sensing tool for detecting phytoplankton blooms and monitoring their presence across the ocean surface. We present the analysis of low ocean roughness signatures in the bistatic radar measurements from the CYGNSS mission observed in the Gulf of Mexico after the Sahara’s dust storm circulation from Africa to the American continent from May to July 2020. CYGNSS data offer an unprecedented spatial and temporal coverage that allows for the analysis of those signatures at time scales of 1-day, robust to the presence of clouds and dust clouds. The described capability benefits the improvement of models, promoting a better constraint of the supply of dust into the ocean surface and a better understanding of the excess of nutrients that triggers the phytoplankton blooms. This new bistatic radar application enhances our understanding on the role of dust storms on ocean biogeochemistry and the global carbon cycle.

Extending XBAER Algorithm to Aerosol and Cloud Condition

The retrieval of cloud optical properties for aerosol contaminated water cloud is challenging because of the complexity of physical processes in such situations. Conventionally, cloud optical data products are typically derived, ignoring the aerosol impacts on radiative transfer in the retrieval process. This is potentially a significant source of error. In this paper, the eXtensible Bremen Aerosol Retrieval (XBAER) algorithm has been optimized for the retrieval of aerosol/cloud properties for the aerosol contaminated cloud (ACC) scenarios. This version of XBAER delivers cloud optical thickness (COT) and cloud effective radius (CER) for ACCs and simultaneously retrieves aerosol optical thickness (AOT). The surface parameterization and aerosol types used in the standard XBAER algorithm have been adapted in this retrieval to account for the ACC conditions. Aerosol types in XBAER for the retrieval of ACC scenarios have been parameterized to comprise weak and strong absorptions. The comparisons of COT, CER, and AOT retrieved using this adapted XBAER algorithm and two new NASA algorithms show good agreements, especially for biomass burning aerosol. The correlation coefficients are >0.9 for AOT, ~0.8 for CER, and ~0.7 for COT. There is also a good agreement for dust plume contaminated cloud scene. The XBAER derived AOT values for dust aerosols are systematically smaller than the NASA retrieval, but both products have the same spatial distribution patterns. The comparison of COT retrieved using the adapted XBAER algorithm and that retrieved from ground-based microwave radiometer (MWR) measurements shows much better agreement for ACC conditions with high AOT.

Long-term measurements of aerosol optical and physical properties over the Eastern Mediterranean: Hygroscopic nature and source regions

Long-term aerosol optical and physical properties such as aerosol optical thickness and angstrom exponent were obtained from AERONET ground based sun sky radiometer located at the rural coastal Erdemli (36.6°N, 34.3°E) site in the Eastern Mediterranean from January 2000 to December 2014. Aerosol Optical Thickness (AOT) and Angstrom Exponent (α) exhibited a great short-term variability, varying up to couple of fold from day to day. The lowest AOT values was found in winter due to the removal of particles by wet deposition. Elevated AOT values with low α440-870 was observed in spring owing to sporadic mineral dust transport from North Africa and the Middle East. High AOT at 440 nm and α440-870 were characterized in summer because of high gas-to-particle conversion, sluggish air masses and absence of rain. Enhanced AOT and low α (0.7) and fine mode fraction (47%) were associated with air flow from North Africa and the Middle East with a slight decrease from 440 nm to 1020 nm, showing importance of coarse particles. Air flow from Mediterranean Sea, Eastern Europe, Western Europe and Turkey, on the other hand, showed comparatively higher α (>1.1) and fine mode fraction (>62%). Three classes of aerosol were identified namely non-hygroscopic dominated, moderately hygroscopic and hygroscopic dominated. Non-hygroscopic particles were dust dominated aerosol population originated from North Africa (Southern Tunisia, Western Libya, Libya/Chad border, southern Egypt northeastern Mauritania, north Mali, southern Algeria, Northwestern Niger) and the Middle East (extending from Iraq to eastern Saudi Arabia). Moderately hygroscopic particles were a mixture of mineral dust and anthropic aerosols when the dust reached receptor site after passing through industrialized and populated sites (such as Spain, France and Italy). Hygroscopic particles, however, were ascribed to nearly mesoscale formation of secondary aerosols under the prevailing summer conditions.

Characterization of Eastern Mediterranean dust storms by area of origin; North Africa vs. Arabian Peninsula

The Eastern Mediterranean (EM) Basin is exposed to frequent dust storms during all seasons but summer. The dust is originating from two large sources: a western source, namely North African (mainly Sahara Desert) and an eastern source, the Arabian Peninsula.The characteristics of 53 dust storms (2007–2013) were examined in relation to their origin – western (30) vs. eastern (23). Analysis was done using ground monitoring stations, satellite data and subjective synoptic classification. Significantly higher ground concentration (722 μg/m3 for western events vs 242 μg/m3 for eastern events), higher Aerosol Optical Thickness (AOT) levels (0.50 for western events vs 0.32 for eastern events), longer duration (25 h for western events vs 15 h for eastern events) and stronger surface wind speed (6 m/s for western events vs 4 m/s for eastern events) were found for western origin dust storms. Dust top height was higher for eastern origin events (1.7 km for western events vs 2.3 km for eastern events, non significant). The associated synoptic circulation types dominant during the western origin dust storms are winter cold-core cyclones while for the eastern origin events the Red Sea Trough is the dominant type and occur mainly during fall.The main assumed reasons for these distinguished characteristics (higher ground concentration, AOT levels, longer duration, and surface wind speed) are that western origin cyclones can induce both mobilization and transport of dust. Together with longer dust path and local sources contribution will create a potential for high concentration and long-lasting event as compared to eastern origin events where there is a separation between main mobilization process that occur during summer and the transport westwards necessary to deliver dust to the EM and occurs during non-summer events.

Round-the-clock measurements of aerosol optical thickness over Antarctica made using a Dual Imager System during January-February 2017

ABSTRACTAntarctica provides an opportunity to study natural forcing and background values of various constituents in the atmosphere, in particular, aerosols. In a recent effort during the 36th Indian Scientific Expedition to Antarctica (36th ISEA), a Dual Imager System was installed at Indian station Bharati (69.4°S, 76.18°E) to study round-the-clock variations of aerosol optical thickness (AOT). The data reveal a weak diurnal pattern in the AOT variability and the values vary from 0.07 to 0.10 during daytime while they reach ~ 0.12 during nighttime. The daytime (solar zenith angle < 70°) results compare well with collocated sun photometer as well as space based estimates, while the higher solar zenith angle (> 70°) AOT values are reported for the first time over Antarctica. The observed higher AOT values at higher zenith angles, i.e. during nighttime are suggested to be due to variations in wind speed and temperature.

Seasonal and Regional Characteristics of Aerosol Pollution in East and Southeast Asia

The atmospheric aerosol distribution in Asia is complex because it is influenced by both natural phenomena and human activities. In this article, multifaceted approach using satellite observations and numerical model simulation shows seasonal and regional variations of the aerosol distribution over Asia. Asia covers a large area; however, this article is limited to East and Southeast Asia. The aerosol optical thickness (AOT) in the inland desert area is normally high in spring and dusty aerosols are widely spread with the wind. The AOT values are high in summer over East Asia. A high AOT caused by biomass burning plumes is observed in autumn over Southeast Asia and in spring over Siberia and heavy air pollution occurs in Beijing in winter, a very well-known phenomenon. These phenomena caused by heavy aerosol concentration were determined based on Aqua/MODIS data and aerosol characteristics retrievals and estimated the aerosol characteristics. Furthermore, the impact of aerosols on the climate assessed by numerical model simulations suggest that aerosols reduce solar radiation and therefore the Earth’s surface temperature. In addition to these influences on the radiation budget, aerosols have a significant potential to change the circulation fields.

The Saharan Air Layer as an Early Rainfall Season Suppressant in the Eastern Caribbean: The 2015 Puerto Rico Drought

AbstractEastern Puerto Rico and the surrounding Caribbean experienced a severe drought in 2015 that resulted in record‐low reservoir and river levels. Rainfall deficits in April and May, which represent the period when the drought began, were more severe in 2015 than recent droughts of record. While El Niño has been associated with drought in the Caribbean, onset of the 2015 drought was strongly associated with lower‐than‐average values of a recently developed tool used by weather forecasters in San Juan, the Gálvez‐Davison Index (GDI), which is used to measure the potential for thunderstorm development and rainfall. Persistently low GDI values indicate strong and frequent intrusions of hot, dry air in the low to middle troposphere, suppressing convection, both locally and in development regions for tropical waves that impact Puerto Rico. The Saharan Air Layer (SAL) is largely responsible for this anomalously hot, dry air, which produced thermodynamically stable conditions and limited thunderstorms and rainfall. Moreover, higher‐than‐normal aerosol concentrations, typically associated with SAL intrusion over the Caribbean, were recorded in April and May 2015. A comparison to advanced very high resolution radiometer aerosol optical thickness demonstrates that higher Caribbean aerosols in the early rainfall season, particularly June, are associated with decreased rainfall in eastern Puerto Rico. Results here demonstrate a direct link between the early and more pronounced SAL intrusions into the Caribbean and the suppression of the early rainfall season. More broadly, a reduction in the GDI and increase in the trade wind inversion was associated with reduced early season rainfall in the eastern Caribbean.

Assimilation of AERONET and MODIS AOT observations using variational and ensemble data assimilation methods and its impact on aerosol forecasting skill

AbstractData assimilation of Aerosol Robotic Network (AERONET) and Moderate Resolution Imaging Spectroradiometer (MODIS) aerosol optical thickness (AOT) for aerosol forecasting was tested within the Navy Aerosol Analysis Prediction System (NAAPS) framework, using variational and ensemble data assimilation methods. Navy aerosol forecasting currently makes use of a deterministic NAAPS simulation coupled to Navy Variational Data Assimilation System for aerosol optical depth, a two‐dimensional variational data assimilation system, for MODIS AOT assimilation. An ensemble version of NAAPS (ENAAPS) coupled to an ensemble adjustment Kalman filter (EAKF) from the Data Assimilation Research Testbed was recently developed, allowing for a range of data assimilation and forecasting experiments to be run with deterministic NAAPS and ENAAPS. The main findings are that the EAKF, with its flow‐dependent error covariances, makes better use of sparse observations such as AERONET AOT. Assimilating individual AERONET observations in the two‐dimensional variational system can increase the analysis errors when observations are located in high AOT gradient regions. By including AERONET with MODIS AOT assimilation, the magnitudes of peak aerosol events (AOT &gt; 1) were better captured with improved temporal variability, especially in India and Asia where aerosol prediction is a challenge. Assimilating AERONET AOT with MODIS had little impact on the 24 h forecast skill compared to MODIS assimilation only, but differences were found downwind of AERONET sites. The 24 h forecast skill was approximately the same for forecasts initialized with analyses from AERONET AOT assimilation alone compared to MODIS assimilation, particularly in regions where the AERONET network is dense; including the United States and Europe, indicating that AERONET could serve as a backup observation network for over‐land synoptic‐scale aerosol events.

Statistical Comparison of Cloud and Aerosol Vertical Properties between Two Eastern China Regions Based on CloudSat/CALIPSO Data

The relationship between cloud and aerosol properties was investigated over two 4° × 4° adjacent regions in the south (R1) and in the north (R2) in eastern China. The CloudSat/CALIPSO data were used to extract the cloud and aerosol profiles properties. The mean value of cloud occurrence probability (COP) was the highest in the mixed cloud layer (−40°C~0°C) and the lowest in the warm cloud layer (&gt;0°C). The atmospheric humidity was more statistically relevant to COP in the warm cloud layer than aerosol condition. The differences in COP between the two regions in the mixed cloud layer and ice cloud layer (&lt;−40°C) had good correlations with those in the aerosol extinction coefficient. A radar reflectivity factor greater than −10 dBZ occurred mainly in warm cloud layers and mixed cloud layers. A high-COP zone appeared in the above-0°C layer with cloud thicknesses of 2-3 km in both regions and in all the four seasons, but the distribution of the zonal layer in R2 was more continuous than that in R1, which was consistent with the higher aerosol optical thickness in R2 than in R1 in the above-0°C layer, indicating a positive correlation between aerosol and cloud probability.

Regional and local variations in atmospheric aerosols using ground-based sun photometry during Distributed Regional Aerosol Gridded Observation Networks (DRAGON) in 2012

Abstract. Aerosol mass concentrations are affected by local emissions as well as long-range transboundary (LRT) aerosols. This work investigates regional and local variations of aerosols based on Distributed Regional Aerosol Gridded Observation Networks (DRAGON). We constructed DRAGON-Japan and DRAGON-Osaka in spring of 2012. The former network covers almost all of Japan in order to obtain aerosol information in regional scale over Japanese islands. It was determined from the DRAGON-Japan campaign that the values of aerosol optical thickness (AOT) decrease from west to east during an aerosol episode. In fact, the highest AOT was recorded at Fukue Island at the western end of the network, and the value was much higher than that of urban areas. The latter network (DRAGON-Osaka) was set as a dense instrument network in the megalopolis of Osaka, with a population of 12 million, to better understand local aerosol dynamics in urban areas. AOT was further measured with a mobile sun photometer attached to a car. This transect information showed that aerosol concentrations rapidly changed in time and space together when most of the Osaka area was covered with moderate LRT aerosols. The combined use of the dense instrument network (DRAGON-Osaka) and high-frequency measurements provides the motion of aerosol advection, which coincides with the wind vector around the layer between 700 and 850 hPa as provided by the reanalysis data of the National Centers for Environmental Prediction (NCEP).

Satellite-measured atmospheric aerosol content in Korea: anthropogenic signals from decadal records

Spatiotemporal characteristics and anthropogenic signals of aerosol optical thickness (AOT) distributions over Korea are investigated in this study using AOT time-series data from the Moderate Resolution Imaging Spectroradiometer (MODIS). AOT observations, a quantitative measure of the atmospheric quality, had significant geographical variations during the study period (2000–2010). Comparing metro cities or counties with similar populations, western regions showed higher AOT values than eastern regions. Particular matter with a diameter < 10 µm (PM10), including aeolian dust or yellow dust, is the primary component of atmospheric aerosols, and their transport into the region has shown a strong seasonal pattern with its peak from March to April and lows from July to September. These seasonal dust patterns, however, did not correspond well to temporal AOT records, which typically reached the maximum level in June nationwide. Rather, widespread regional fire events and humidity showed significant correlations with AOT time-series. This correlation rapidly increased as the range of fire occurrence was extended to the west as far as 115°E. The relative humidity also had a significant correlation with AOT during the month of June. In addition to urban emission of anthropogenic aerosols, regional biomass burning and secondary growth of hygroscopic aerosols are considered important contributors to the degradation of the atmospheric environment during the non-Asian Dust season over the Korean Peninsula.

Entrainment Heat Flux Computed with Lidar and Wavelet Technique in Buenos Aires During Last Chaitén Volcano Eruption

At Lidar Division of CEILAP (CITEDEF-CONICET) a multiwavelength Raman-Rayleigh lidar optimized to measure the atmospheric boundary layer is being operated. This instrument is used for monitoring important aerosol intrusion events in Buenos Aires, such as the arrival of volcanic ashes from the Chaiten volcano eruption on May 2008. That was the first monitoring of volcanic ash with lidar in Argentina. In this event several volcanic ash plumes with high aerosol optical thickness were detected in the free atmosphere, affecting the visibility, surface radiation and therefore, the ABL evolution. In this work, the impact of ashes in entrainment flux ratio is studied. This parameter is obtained from the atmospheric boundary layer height and entrainment zone thickness using algorithms based on covariance wavelet transform.

Analysis of atmospheric vertical profiles in the presence of desert dust aerosols

The present work aims at studying a very recent episode of desert dust transport that affected Iberia in mid May 2015. The dust aerosols were detected over Évora, where a varied set of instrumentation for aerosol measurements is installed, including: a CIMEL sunphotometer integrated in AERONET, a Raman Lidar and a TEOM monitor, as well as ceilometer and a microwave radiometer (profiler). The aerosol occurrence, detected using the columnar, vertically-resolved and in situ measurements, was characterized by a fairly high aerosol optical thickness that reached a value of 1.0 at 440 nm and showed mass concentration peaks at the surface of the order of 100 μg/m3. Subsequently, the tropospheric vertical profiles of humidity and temperature obtained with the passive microwave (MW) radiometer are analysed in order to distinguish possible modifications that can be connected with the transport of desert dust. Modelling results are also examined and the total, SW and LW radiative forcings are investigated, taking into account the different vertical profiles obtained during the desert dust occurrence. It is found that the differences in the atmospheric profiles mostly affect the LW radiative forcing, with an underestimation of about 30% when the actual vertical profile is not considered.

Characteristics of aerosols over Beijing and Kanpur derived from the AERONET dataset

Beijing and Kanpur are two cities identified as high aerosol optical thickness (AOT) and complex composition of aerosols in Asian monsoon regions. Detail knowledge of key aerosol types in these two countries would be helpful for clarifying the mechanisms of aerosol radiative forcing and improving the accuracy of satellite remote sensing in these two countries. This study examines the characteristics of aerosol types over Beijing and Kanpur derived from a 12-year dataset from Aerosol Robotic Network (AERONET) stations and compares them via cluster analysis of optical and microphysical properties. Aerosols in Beijing are more complex than in Kanpur. Four fine-size dominated aerosol types (including two types of moderately absorbing aerosols, one highly absorbing aerosol type and one non-absorbing aerosol type) and one coarse-size dominated aerosol type are identified over Beijing. In Kanpur, two fine-sized dominated aerosol types (one high absorbing aerosol type and one non-absorbing aerosol type) and one coarse-sized dominated aerosol type are obtained. Compared to Beijing, the average SSAs of non-absorbing and high-absorbing aerosols are lower for the four wavelengths (440 nm, 676 nm, 869 nm, 1020 nm) in Kanpur. High absorbing aerosols usually occur in the months December to February (DJF) for both sites. The proportion in Kanpur (14%) is about twice that in Beijing (7%). Non-absorbing aerosols are usually observed in the months June to August (JJA) for both sites. Their proportion in Kanpur (31%) is ∼3 times larger than that in Beijing (11%). Coarse aerosols are frequently observed in the months March to May (MAM) for both sites. Their proportion in Kanpur (54%) is two times larger than in Beijing (21%).

Characteristics of Landsat 8 OLI-derived NDVI by comparison with multiple satellite sensors and in-situ observations

Vegetation indices are important remotely sensed metrics for ecosystem monitoring and land surface process assessment, among which Normalized Difference Vegetation Index (NDVI) has been most widely used. The newly launched Landsat 8 Operational Land Imager (OLI) sensor, together with its predecessor Landsat 7 Enhanced Thematic Mapper Plus (ETM+), provides continuous earth observations with an 8-day interval. The design improvements of the new sensor, including narrower near-infrared waveband, higher signal-to-noise ratio (SNR), and greater radiometric sensitivity highlight the need for investigating the land surface observation properties, especially its consistency with data from its predecessors and other satellite sensors. This study aims to evaluate the characteristics of Landsat 8 OLI-derived NDVI against Landsat 7 ETM+ by cross-comparison and by comparing with Moderate Resolution Imaging Spectroradiometer (MODIS) and Geostationary Ocean Color Imager (GOCI)-derived NDVIs as well as in-situ NDVI measurements. Simulations of Top of Atmosphere (TOA) reflectance and surface reflectance of broadleaf trees and water were conducted for Landsat 8 OLI, Landsat 7 ETM+, and MODIS in order to evaluate the impact of band pass difference on NDVI calculation. Four consecutive pairs of Landsat 8 OLI and Landsat 7 ETM+ data over China and Korea were examined, and NDVIs derived from TOA reflectance and surface reflectance by three atmospheric correction methods were evaluated. Both simulations and comparisons showed that NDVIs derived from atmospherically-corrected surface reflectance had good consistency, while the simulation showed that the agreement varied with atmospheric characteristics. The four pairs of Landsat 8 OLI and Landsat 7 ETM+ NDVI had a mean bias error within ±0.05, and R2 from 0.84 to 0.98. Vegetated land cover types were found to have better NDVI agreement than non-vegetated land cover types. Especially, Landsat 8 OLI consistently generated lower NDVI values in water area than Landsat 7 ETM+, which resulted from higher aerosol optical thickness in atmosphere. Landsat 8 OLI-derived NDVI showed better agreement with MODIS and GOCI NDVI than Landsat 7 ETM+, mainly on vegetated surfaces. Both Landsat 8 OLI and Landsat 7 ETM+ surface reflectance-derived NDVI agreed well with in-situ light emitting diode (LED) NDVI measurements at a homogeneous deciduous forest site. Landsat 8 OLI was also found to produce higher spatial variability of NDVIs than Landsat 7 ETM+ at vegetated and urban areas, but lower variability on water area. The overall good agreement between Landsat 8 OLI NDVI and Landsat 7 ETM+, MODIS and GOCI NDVIs as well as in-situ measurements ensures that it is reliable to integrate the new sensor observations with those from the multiple satellite sensors, given that the same atmospheric correction methods are applied. Furthermore, the greater NDVI contrast between vegetated areas and water areas, and the higher spatial variability of Landsat 8 OLI NDVI indicated that the new sensor has better capability in land surface process monitoring, such as land cover mapping, spatiotemporal dynamics of vegetation growth, and drought assessment.

Spatio-temporal variability of Suomi-NPP VIIRS-derived aerosol optical thickness over China in 2013

The Visible Infrared Imaging Radiometer Suite (VIIRS) aerosol optical thickness (AOT) at 550 nm Intermediate Product (IP) data was evaluated by comparing it with measurements from Aerosol Robotic Network (AERONET) and Moderate Resolution Imaging Spectroradiometer (MODIS) retrievals. The spatial and temporal variations in the regional AOT over China during 2013 (from 24 January to 31 December) were then firstly investigated using VIIRS aerosol IP data. Evaluation of VIIRS IP AOT with MODIS retrievals and AERONET measurements indicated that the performance of the VIIRS aerosol IP product is comparable to that of their counterparts from the heritage MODIS sensor. However, the VIIRS IP can produce more retrievals than MODIS due to its higher spatial resolution, therefore more suitable for regional AOT study. It was found that the VIIRS IP mean AOT over China differs from that of MODIS by −0.032 for the collocated retrievals, with a correlation of 0.928. Compared with AERONET measurements, VIIRS IP AOT shows a negative bias of −0.058 with the standard deviation of the difference of 0.192 over China. Among the 10 typical sites under study, the maximum annual average AOT550 values (with±standard deviation) were found in Chengdu (1.07±0.32), whereas the lowest annual mean AOT550 values were found in FB1 (0.242±0.25). The economically developed regions had high AOT values during all seasons. Based on the distribution of AOT, China can be divided into an economically developed eastern region with high AOT values and less-developed western regions, consistent with the boundary between China’s second and third terrain regions.

Development towards a global operational aerosol consensus: basic climatological characteristics of the International Cooperative for Aerosol Prediction Multi-Model Ensemble (ICAP-MME)

Abstract. Here we present the first steps in developing a global multi-model aerosol forecasting ensemble intended for eventual operational and basic research use. Drawing from members of the International Cooperative for Aerosol Prediction (ICAP) latest generation of quasi-operational aerosol models, 5-day aerosol optical thickness (AOT) forecasts are analyzed for December 2011 through November 2012 from four institutions: European Centre for Medium-Range Weather Forecasts (ECMWF), Japan Meteorological Agency (JMA), NASA Goddard Space Flight Center (GSFC), and Naval Research Lab/Fleet Numerical Meteorology and Oceanography Center (NRL/FNMOC). For dust, we also include the National Oceanic and Atmospheric Administration-National Geospatial Advisory Committee (NOAA NGAC) product in our analysis. The Barcelona Supercomputing Centre and UK Met Office dust products have also recently become members of ICAP, but have insufficient data to be included in this analysis period. A simple consensus ensemble of member and mean AOT fields for modal species (e.g., fine and coarse mode, and a separate dust ensemble) is used to create the ICAP Multi-Model Ensemble (ICAP-MME). The ICAP-MME is run daily at 00:00 UTC for 6-hourly forecasts out to 120 h. Basing metrics on comparisons to 21 regionally representative Aerosol Robotic Network (AERONET) sites, all models generally captured the basic aerosol features of the globe. However, there is an overall AOT low bias among models, particularly for high AOT events. Biomass burning regions have the most diversity in seasonal average AOT. The Southern Ocean, though low in AOT, nevertheless also has high diversity. With regard to root mean square error (RMSE), as expected the ICAP-MME placed first over all models worldwide, and was typically first or second in ranking against all models at individual sites. These results are encouraging; furthermore, as more global operational aerosol models come online, we expect their inclusion in a robust operational multi-model ensemble will provide valuable aerosol forecasting guidance.

Spatial and temporal variation of Visible Infrared Imaging Radiometer Suite (VIIRS)-derived aerosol optical thickness over Shandong, China

Spatial and temporal variations in regional aerosol optical thickness (AOT) at 550 nm over Shandong Province, China, based on one year’s Visible Infrared Imaging Radiometer Suite (VIIRS) data were investigated. The regional forest background (FB) annual mean AOT was 0.467 with a standard deviation of 0.339, which was much higher than the North America background continental AOT level of 0.10. Higher AOT values for the study region were mainly found in the spring and summer, especially from May to August, while the lowest mean values were seen in November and December. Urban areas all have obviously higher mean AOT values than those of the rural areas resulting from intense anthropogenic sources. Given that FB AOT represents the natural background level, we estimated that anthropogenic emissions and secondary aerosol generation contribute approximately 0.352 to aerosol loading in this region. Additionally, strong regional imbalance of AOT was found to be distributed over the study area. The maximum annual average AOT values occurred in inland cities, while coastal cities usually had lower AOT values.