On the aerosol weekly cycle spatiotemporal variability over Europe

In this work, we focus on the spatial and temporal variability of the aerosol weekly cycle over Europe as these were recorded from TERRA MODIS and AQUA MODIS satellite instruments. Aerosol optical properties retrieved from MODIS TERRA (February 2000–February 2009) and AQUA (July 2002–December 2008) were used to produce an aerosol weekly cycle index. First, the general aerosol optical depth (AOD<sub>550 nm</sub>) weekly patterns were defined at a 1° × 1° resolution using the satellite-based index and six regions of interest were selected. To remove episodic dust transport events, two different aerosol flags, employing fine mode ratio (FMR<sub>550 nm</sub>) and AOD<sub>550 nm</sub> data, were applied diagnostically, showing that the observed weekly cycles over Europe are due to continental aerosols. A second spatial averaging method was then used for the investigation of the weekly variability and the statistical significance of the weekly cycle over each of the previously selected regions. Three major weekly cycle plumes are observed over Europe. A strong positive (higher values during midweek) weekly cycle plume appears over Central Europe, while a strong negative (higher values during weekend) weekly plume appears over the Iberian Peninsula and the North-eastern Europe. The temporal examination of the weekly cycles shows that in some areas there are seasonal differences in the sign of the weekly cycle. The aerosol weekly variability over different regions in Europe was examined in conjunction with the dominating synoptic wind patterns from the NCEP/NCAR reanalysis, showing that the seasonal weekly cycle plumes over regions situated in the eastern Europe and the Mediterranean Sea could be partly attributed to the westerly transport of continental aerosols

Characterisation of dust sources in Central Asia using remote sensing

Central Asian deserts are a significant source of dust in the middle latitudes, where economic activity and the health of millions of people are affected by dust storms. Detailed knowledge of sources of dust, controls on their activity, seasonality and atmospheric pathways are of crucial importance but to date, these data are limited. This thesis presents a detailed database ofsources ofdust emissions in Central Asia, from western China to the Caspian Sea, obtained by a multi-scale analysis of the Moderate Resolution Imaging Spectroradiometer (MODIS) satellite data. The multi-scale approach consists of the following steps: 1) MODIS Deep Blue Aerosol Optical Depth (DB AOD) at 10 km resolution, acquired between 2003 and 2014, is used to investigate the spatiotemporal distribution ofdust hotspots. 2) A dust enhancement algorithm was employed to obtain two composite images (Dust Enhancement Product, DEP) per day at 1 km resolution from MODIS Terra/Aqua acquisitions between 2003 and 2012, from which dust point sources (DPS) were detected by visual analysis of dust plumes and recorded in a database together with meteorological variables at each DPS location derived from the ERA-Interim reanalysis dataset. In all, more than 13500 DPS were identified. Using this multi-scale approach we provided a high resolution inventory of dust sources at sub-basin scale for Central Asia. Our analysis revealed several active source regions, the most active of which are the eastern part ofthe Taklmakan desert. An important finding was an increase in dust activity in the newly-formed desert ofthe Aralkum. Several ofthe identified dust source regions were not previously identified (e.g. sources in northern Afghanistan) or were not widely discussed in literature before (e.g. the Pre-Aral region in western Kazakhstan). Investigation of land surface characteristics and meteorological conditions at each source region revealed mechanisms for the formation of dust sources, including rapid desiccation of water bodies (e.g. Aral Sea), deflation of dust from fluvial sources (e.g. the Upper Amudarya region) and post-fire wind erosion (e.g. Pre-Aral and Lake Balkhash basins). Different seasonal patterns of dust emissions were observed as well as inter-annual trends. Comparison of DB AOD and DPS revealed a noticeable spatial bias in the AOD-based methods for detection of dust sources which is attributed to the fact that the highest atmospheric dust loadings are not always observed over the dust point sources

Spatiotemporal patterns of Saharan dust outbreaks in the Mediterranean Basin

Saharan dust outbreaks transport appreciable amounts of mineral particles into the atmosphere of the Mediterranean Basin. Atmospheric particulates have significant impacts on numerous atmospheric, climatic and biogeochemical processes. The recognition of background drivers, spatial and temporal variations of the amount of Saharan dust particles in the Mediterranean can lead to a better understanding of possible past and future environmental effects of atmospheric dust in the region. For this study the daily NASA Total Ozone Mapping Spectrometer's and Ozone Monitoring Instrument’s aerosol data (1979– 2012) were employed to estimate atmospheric dust amount. Daily geopotential height, wind vector and meridional flow data of the distinguished dust events were obtained from the NCEP/NCAR Reanalysis to compile mean synoptic composite maps. In order to identify the typical dust transportation routes and possible source areas, the backward trajectories were plotted using the NOAA HYSPLIT model. The main period of the dust transportation is from March to end of August, when the thermal convective activity forces the injection of particles to higher atmospheric levels. However, seasonality patterns of the different Mediterranean sub-basins show quite large differences. In western sub-basins, the maxima of Saharan dust outbreaks is in summer, related southwest flow between a southward emanating trough and the northward migrating subtropical high-pressure centre. In the eastern basin, dust storms occur typically in spring, generated by the warm sector winds on foreside of eastward moving Mediterranean and Sharav cyclones. The seasonal distribution of dust events in the central sub-basins shows a bimodal characteristic with a spring and summer peak

Merging regional and global aerosol optical depth records from major available satellite products

Satellite instruments provide a vantage point for studying aerosol loading consistently over different regions of the world. However, the typical lifetime of a single satellite platform is on the order of 5-15 years; thus, for climate studies, the use of multiple satellite sensors should be considered. Discrepancies exist between aerosol optical depth (AOD) products due to differences in their information content, spatial and temporal sampling, calibration, cloud masking, and algorithmic assumptions. Users of satellite-based AOD time-series are confronted with the challenge of choosing an appropriate dataset for the intended application. In this study, 16 monthly AOD products obtained from different satellite sensors and with different algorithms were inter-compared and evaluated against Aerosol Robotic Network (AERONET) monthly AOD. Global and regional analyses indicate that products tend to agree qualitatively on the annual, seasonal and monthly timescales but may be offset in magnitude. Several approaches were then investigated to merge the AOD records from different satellites and create an optimised AOD dataset. With few exceptions, all merging approaches lead to similar results, indicating the robustness and stability of the merged AOD products. We introduce a gridded monthly AOD merged product for the period 1995-2017. We show that the quality of the merged product is as least as good as that of individual products. Optimal agreement of the AOD merged product with AERONET further demonstrates the advantage of merging multiple products. This merged dataset provides a long-term perspective on AOD changes over different regions of the world, and users are encouraged to use this dataset

Global assessment of sand and dust storms

The specific objectives of the assessment are to: 1) Synthesise and highlight the environmental and socio-economic causes and impacts of SDS, as well as available technical measures for their mitigation, at the local, regional and global levels; 2) Show how the mitigation of SDS can yield multiple sustainable development benefits; 3) Synthesize information on current policy responses for mitigating SDS and 4) Present options for an improved strategy for mitigating SDS at the local, regional and global levels, building on existing institutions and agreements

SURFACE AND AEROSOL EFFECTS ON THE SOUTH ASIAN MONSOON HYDROCLIMATE

This work targets important couplings in the South Asian monsoon system at interannual or longer time-scales and associated processes and mechanisms: aerosol-hydroclimate, atmosphere-ocean, and land-atmosphere. Anomalous springtime absorbing aerosols loading over the Indo-Gangetic Plain (IGP) leads to large-scale variations of the monsoon: cloudiness reduction associated with increased aerosols is suggested to play an important role in triggering surface heating over India, which strengthens the monsoon. Indeed, a closer analysis with high resolution data depicts a complex interplay between aerosols, dynamics and precipitation. Interestingly, observations do not provide any evidence for the Elevated Heat Pump hypothesis, a mechanism proposed for the aerosol-monsoon link. Current coupled climate models, which have been extensively used to study aerosol-monsoon interactions, are shown to have large, systematic, and coherent biases in precipitation, evaporation, sea-surface temperature (SST) over the Indian Ocean during the monsoon. Models are also found to deficiently portray local and non-local air-sea interactions. For example, they tend to emphasize local oceanic forcing on precipitation or to poorly simulate the relationship between SST and evaporation. The Indian monsoon rainfall-SST link is also spuriously misrepresented, suggesting caution when interpreting model-based findings. Both regional and remote forcings modulate the annual cycle of the heat-low over the desert areas (including the Thar Desert) between Pakistan and northwestern India, source of most of the dust loading over India. Land-surface heating has a limited role in the development of the low. Regional orography and monsoon summertime deep-convection over the Bay of Bengal, with its upstream descent to the west and related northerlies, contribute to the strengthening of the low, indicating a monsoon modulation on desert processes, including dust emission. The Thar Desert is expanding westward and the potential impact of land-cover change (without consideration of the additional aerosol loading) on summer monsoon hydroclimate and circulation is found to be significant. Locally, the atmospheric water cycle weakens, air temperature cools and subsidence prevails. An anomalous northwesterly flow over the IGP weakens the monsoon circulation over eastern India, causing precipitation to decrease. Orographic enhanced precipitation occurs over the Eastern Himalayas and southern China

Numerical Prediction of Dust

Covers the whole breadth of mineral dust research, from a scientific perspective Presents interdisciplinary work including results from field campaigns, satellite observations, laboratory studies, computer modelling and theoretical studies Explores the role of dust as a player and recorder of environmental change This volume presents state-of-the-art research about mineral dust, including results from field campaigns, satellite observations, laboratory studies, computer modelling and theoretical studies. Dust research is a new, dynamic and fast-growing area of science and due to its multiple roles in the Earth system, dust has become a fascinating topic for many scientific disciplines. Aspects of dust research covered in this book reach from timescales of minutes (as with dust devils, cloud processes, and radiation) to millennia (as with loess formation and oceanic sediments), making dust both a player and recorder of environmental change. The book is structured in four main parts that explore characteristics of dust, the global dust cycle, impacts of dust on the Earth system, and dust as a climate indicator. The chapters in these parts provide a comprehensive, detailed overview of this highly interdisciplinary subject. The contributions presented here cover dust from source to sink and describe all the processes dust particles undergo while travelling through the atmosphere. Chapters explore how dust is lifted and transported, how it affects radiation, clouds, regional circulations, precipitation and chemical processes in the atmosphere, and how it deteriorates air quality. The book explores how dust is removed from the atmosphere by gravitational settling, turbulence or precipitation, how iron contained in dust fertilizes terrestrial and marine ecosystems, and about the role that dust plays in human health. We learn how dust is observed, simulated using computer models and forecast. The book also details the role of dust deposits for climate reconstructions. Scientific observations and results are presented, along with numerous illustrations. This work has an interdisciplinary appeal and will engage scholars in geology, geography, chemistry, meteorology and physics, amongst others with an interest in the Earth system and environmental change

Estimating PM2.5 in the Beijing-Tianjin-Hebei Region Using MODIS AOD Products from 2014 to 2015

Fine particulate matter with a diameter less than 2.5 μm (PM2.5) has harmful impacts on regional climate, economic development and public health. The high PM2.5 concentrations in China’s urban areas are mainly caused by combustion of coal and gasoline, industrial pollution and unknown/uncertain sources. The Beijing-Tianjin-Hebei (BTH) region with a land area of 218,000 km2, which contains 13 cities, is the biggest urbanized region in northern China. The huge population (110 million, 8% of the China’s population), local heavy industries and vehicle emissions have resulted in severe air pollution. To monitor ground-level PM2.5 concentration, the Chinese government spent significant expense in building more than 1500 in-situ stations (79 stations in the BTH region). However, most of these stations are situated in urban areas. Besides, each station can only represent a limited area around that station, which leaves the vast rural land out of monitoring. In this situation, geographic information system and remote sensing can be used as complementary tools. Traditional models have used 10 km MODIS Aerosol Optical Depth (AOD) product and proved the statistical relationship between AOD and PM2.5. In 2014, the 3 km MODIS AOD product was released which made PM2.5 estimation with a higher resolution became possible. This study presents an estimation on PM2.5 distribution in the BTH region from September 2014 to August 2015 by combining the MODIS satellite data, ground measurements of PM2.5, and meteorological documents. Firstly, the 3 km and 10 km MODIS AOD products were validated with AErosol RObotic NETwork (AERONET AOD. Then the MLR and GWR models were employed respectively to estimate PM2.5 concentrations using ground measurements and two MODIS AOD products, meteorological datasets and land use information. Seasonal and regional analyses were also followed to make a comparative study on strengths and weaknesses between the 3 km and 10 km AOD products. Finally, the number of non-accidental deaths attributed to the long-term exposure of PM2.5 in the BTH region was estimated spatially. The results demonstrated that the 10 km AOD product provided results with a higher accuracy and greater coverage, although the 3 km AOD product could provide more information about the spatial variations of PM2.5 estimation. Additionally, compared with the global regression, the geographically weighed regression model was able to improve the estimation results. Finally, it was estimated that more than 30,000 people died in the BTH region during the study period attributed to the excessive PM2.5 concentrations

New insights into dust aerosol entrainment mechanisms from satellite/ground-based data, climate modeling, and wind-tunnel experiments

Atmospheric dust aerosols have implications for Earth’s radiation budget, biogeochemical cycles, hydrological cycles, human health, and visibility. Currently, there is a considerable mismatch between climate model simulations and observations in representing the dust cycle in terms of emission, transport, and deposition. This mismatch is related partly to our inadequate understanding of the complex dust emission processes and partly to the way these processes are represented in climate models. In this work, we examine these problems from various perspectives with an interdisciplinary approach by integrating wind-tunnel experiments, geomorphological mapping, satellite observations, land surface modeling, atmospheric reanalysis, and fully coupled earth system modeling. The primary science contributions of this work are summarized here. First, we developed a detailed regional land cover map of the dust belt, the Middle East and North Africa. The developed map can be integrated in any regional dust models for better representing the spatial variation in dust source erodibility. We also developed a new observation-based soil erodibility map in global scale based on the correlation between reanalysis surface winds and satellite-observed aerosol optical depth data (AOD). Second, we integrated the developed observation-based erodibility map into the Community Earth System Model (CESM) and evaluated CESM’s performance in simulating mineral dust emission over the dust belt. Results show that the new erodibility map improves dust simulations in terms of AOD/dust optical depth (DOD) and the CESM captures large scale dust storms reasonably well when the winds are nudged towards ERA-Interim reanalysis data. Third, we conducted wind tunnel experiments and explored some of the lesser understood physical mechanisms of dust emission in sandblasting and direct aerodynamic entrainment. Results indicate that surface roughness can control dust emission in direct aerodynamic entrainment and that dust emission by direct aerodynamic entrainment can be significant under certain conditions compared to sandblasting. Lastly, we develop a principal component analysis based technique to extract locally mobilized dust component from the AOD data, which otherwise represent a mixture of several aerosol types and advected dust/aerosols.Geological Science