Long-term trends in the total columns of ozone and its precursor gases derived from satellite measurements during 2004–2015 over three different regions in South Asia: Indo-Gangetic Plain,Himalayas and Tibetan Plateau

ABSTRACT

Long-term (2004–2015) satellite data over three adjacent yet contrasting regions: Indo-Gangetic Plain, Himalayas and Tibetan Plateau (TP) were used to study the spatiotemporal distribution of total ozone column (TOC) and its precursor gases (such as nitrogen dioxide (NO₂), methane (CH₄) and carbon monoxide (CO)). The ozone precursor emission data and forest fire points were used to explore the findings. Trace gases showed increasing trend probably due to increasing emission from South Asia as supported by the Emission Database for Global Atmospheric Research emission data. Strong seasonal variation in trace gases was observed with the highest value during the pre-monsoon season, over three regions, possibly due to the biomass burning, pollution build-up and also long-range transport of pollution. TOC exhibited the similar seasonal variation as shown by the earlier ground-based studies over the region. The total column of precursor gases (except methane) exhibited strong seasonality with the highest column during the pre-monsoon season. Patterns in the variations of TOC and related precursors over the Himalayas were similar with that of the TP. Seasonal climatological trends also exhibited increasing pattern except for CO. This work provides an overview on the long-term TOC and its precursor gases which are necessary to understand the regional climate variability especially over the Himalayas and Tibetan Plateau region.     

Multisatellite observations and numerical simulation of an along‐coast cumulus cloud line induced by sea‐breeze circulation

A coastal cumulus cloud‐line formation along the east coast of the USA was observed on a National Oceanic and Atmospheric Administration (NOAA) Polar Orbiting Environmental Satellite (POES) Advanced Very High Resolution Radiometer (AVHRR) satellite image from 17 August 2001. The cloud line starts to form at about 16:00 UTC (local 12:00 noon) and follows the coastline from Florida to North Carolina. The length and width of the cloud line are about 850 km and 8.5 km, respectively. A 15‐min interval sequence of NOAA Geostationary Operational Environmental Satellite (GOES) images shows that the cloud line maintains the shape of the coastline and penetrates inland for more than 20 km over the next 6‐h timespan. Model simulation with actual atmospheric conditions as inputs shows that the cloud line is formed near the land–sea surface temperature (SST) gradient. The synoptic flow at all model levels is in the offshore direction prior to 16:00 UTC whereas low‐level winds (below 980 hPa) reverse direction to blow inland after 16:00 UTC. This reversal is due to the fact that local diurnal heating over the land takes place on shorter time‐scales than over the ocean. The vertical wind at these levels becomes stronger as the land–SST increases during the summer afternoon, and the leading edge of the head of the inland wind ascends from 920 hPa to about 850 hPa in the 3 h after 16:00 UTC. Model simulation and satellite observations show that the cloud line becomes very weak after 21:00 UTC when the diurnal heating decreases.     

Spatial dispersion of aerial plankton over east-central Florida: Aeolian transport and coastline concentrations

Based on previous radar observations that diurnal 'aerial plankton' (i.e., the ensemble of small, weakly flying insects that drift with the wind ) is usually absent over the ocean, we hypothesized that the insect targets employ flight tactics to resist being drifted overwater. We expected that if aerial insects actively resist overwater drift, then (1) radar-observed clear-air echoes should accumulate along the coastline when winds blow offshore, but they should be advected inland rapidly when winds blow onshore; and (2) accumulations of aerial plankton should be greatest along stretches of coastline most nearly perpendicular to the ambient wind flow. We tested these predictions by comparing the distribution of clear-air radar reflectivity at different sites and under different regimes of wind during the Convection and Precipitation/Electrification (CaPE) Experiment, which was conducted on the east coast of Florida in the summer of 1991. Elevated levels of clearair reflectivity were evident along the coast on mornings when winds were from the west, but not on mornings with easterly winds. On days with westerly winds, this coastal enhancement occurred only in the morning, prior to the onset of the sea breeze. Following sea breeze development, coastal concentrations of clear-air echoes were advected westward and they dispersed rapidly; levels of clear-air reflectivity became depressed overall throughout the study area in the afternoon compared to the morning. Clear-air reflectivity was higher along a north-facing coastline compared to a south-facing coastline when winds had a northward component, with a mirror-image reversal of this pattern on days with southward winds. In contrast, clear-air echoes were uniformly nearly absent from the airspace over the adjacent ocean at all times of the day on all days. These findings support the hypothesis that the organisms comprising the aerial plankton respond behaviourally to coastlines to avoid being blown out to sea. Persistent concentrations of aerial plankton along coastlines may have important consequences for insect population dynamics and local ecosystem structure in coastal regions.     

A modeling of the sea breeze and its impacts on ozone distribution in northern Taiwan

A high-resolution air pollution numerical model system (APOPS) is applied to simulate the sea/land breeze and its impacts on the ozone distribution in northern Taiwan. The system can successfully simulate local flow patterns such as sea/land breezes and mountain-valley wind. The predicted surface ozone concentrations also agree with observed surface ozone values (Wang, Z., et al., Tellus, 52B, 2000, 1189). The sea/land breezes in northern Taiwan play a significant role in the distribution of ozone and transport of ozone from the urban to the coastal and mountain areas. The sea breeze is a weak system, extending vertically to a height of less than 1 km with the wind speed less than 4 ms^-1. The land breeze can transport the photochemically produced ozone and its precursors over the sea. The accumulated ozone on the sea can return to the land in the daytime with the sea breeze. This kind of transport tends to contribute significantly to high-ozone episodes in clean coastal and mountain regions.     

Precipitation dynamics in Ecuador and northern Peru during the 1991/92 El Nino: A remote sensing perspective

The formation, dynamics and spatial distribution of heavy precipitation during the 1991/92 El Nino in Ecuador and northern Peru were examined by means of Meteosat-3 imagery, NOAA-AVHRR-based multichannel sea surface temperatures (MCSST) and additional meteorological observations. The Convective and Stratiform Technique (CST) was used for rain retrieval by means of Meteosat IR data and a cross-correlation approach was applied to Meteosat image sequences to derive cloud motion winds (CMW) which are essential for the analysis of circulation patterns leading to severe precipitation. From an analysis of 45 days with severe precipitation it is proven that three mechanisms were responsible for the formation of heavy rains. Each mechanism reveals a specific localized impact. (1) The most frequent mechanism (frequency of ～61%) represents an extended land-sea breeze system. During such weather conditions, predominantly locally confined precipitation patterns occured. Areas affected by the sea wind front during the day were the coastal plains up to the 1000 m contour line on the western Andean slope. Local maxima in the frequency of cloudiness leading to precipitation could be found at isolated peaks of a lower coastal cordillera. At night the highest frequency of precipitation was found over the warm water surface of the Gulf of Guayaquil, mainly due to its coastal shape which significantly favours convergence of the nocturnal land breeze. (2) Convection, initiated in the coastal plain and on the western Andean slopes during the afternoon, was significantly intensified by an entrainment of remainders of cirrus shields from the Amazon basin. These cloud fragments spilled over the Andes with well-developed trades in the mid/upper troposphere which blew in the opposite direction to the daily sea/up-slope breeze. The spill over points were characterized by areas of deep convection on the western Andean slopes and were frequently valley axes perpendicular to the mountain chain as well as the Andean depression in southern Ecuador. (3) During the main El Nino phase (March-April), heavy and persistent precipitation was extended over wide areas of the coastal plain showing neither a distinct diurnal cycle nor preferential areas. Deep convection was frequently organized in mesoscale convective complexes (MCC) and was spatially correlated with MCSST > 27 . The extensive instability of the troposphere during these weather conditions was marked by convective cloud streets and an intensification of the meridional Hadley circulation off the coast of southern Ecuador and Peru.     

Regional CO pollution over the Indian-subcontinent and various transport pathways as observed by MOPITT

We used day-side Measurement of Pollution in the Troposphere (MOPITT) carbon monoxide (CO) retrievals (2000–2007) to examine the regional CO emission and its transport pathways during the summer/winter monsoon, with a specific focus on the Indian-subcontinent. It is observed that MOPITT CO retrievals at 850 hPa level in general show large scale features of CO emission in India, as reflected in the bottom-up inventory. In particular, high CO mixing ratios over the eastern north-eastern part of India, along the Indo-Gangetic (IG) region, and low CO mixing ratios over central India are generally captured from the MOPITT data. A strong plume with enhanced CO mixing ratios at 350?hPa is observed during the summer monsoon, demonstrating large scale vertical transport of the boundary layer CO from the Indian region into the upper troposphere. During winter outflow CO from the Indian region is found to be transported over the Arabian Sea and Bay of Bengal and reaches up to Saudi Arabia and north-eastern Africa. It is observed that emissions from Southeast Asia and the eastern north-eastern Indian region have the greatest impact over the Bay of Bengal and the eastern Indian Ocean, while emissions from the rest of India dominate over the Arabian Sea and the western Indian Ocean.     

The positive temperature anomaly as detected by Landsat TM data in the eastern Marmara Sea (Turkey): possible link with the 1999 Izmit earthquake

A long (～15 km) and narrow (～4 km) offshore positive temperature anomaly (～1.7° C) is observed in the Landsat Thematic Mapper (TM) thermal infrared (TIR) image acquired the day following the large ?zmit earthquake (Mw 7.4) of 17 August 1999, in eastern Marmara Sea, Turkey. The earthquake was generated along the North Anatolian Fault, which ruptured for about 150 km, and the anomaly formed at the western termination of this rupture. Discussions of this anomaly may develop by processes different than the seismic activity and considerations on fault geometry and sea bathymetry characteristics suggest that the anomaly may result from aftershock activity near the western end of the earthquake fault. The formation of the anomaly requires the addition of a large quantity of hot waters to the sea. The ascent to the sea bottom of fault‐driven hot fluids (seismic pumping) and formation of thermal plumes may be the processes by which the sea surface temperature increased. Recent works and the present study suggest that TIR data analysis may be used as a tool in seismological studies.     

Monitoring coastal erosion at the Black Sea coasts in Turkey using satellite data: A case study at the Lake Terkos,north-west Istanbul

There is justifiable cause for concern over the adequacy of our water supplies. To control and protect aquatic ecosystems and drinking water supplies, continuous monitoring is essential. An example related to the careless attitudes towards the Lake Terkos, Istanbul, which create the danger of waterlessness for citizens was given in this study. The width of the natural land barrier between the Black Sea and the Lake Terkos has decreased over the years due to illegal sand excavation along the coastline of the sea very close to the northern part of the lake. As a result of this process the offshore bar formation along the coastline has been destroyed and even removed at different parts, which caused morphological changes of the coastline along some parts of the northern coasts of the sea. In this paper, the coastal erosion during a 14-year period was monitored by using multitemporal satellite sensor data and some suggestions for precautions were made.     

Evaluating the impact of coastal land uses on water‐clarity conditions from Landsat TM/ETM+ imagery: Candarli Bay,Aegean Sea

Landsat TM and ETM+ imagery was evaluated as a potential data source for monitoring the coastal degradation of Candarli Bay and its basin on the eastern coast of the Aegean Sea. The bay is under pressure from conflicting uses, and there is an information need for future management plans for the area surrounding the bay. Spatial and temporal distributions of land use/land cover patterns were derived by unsupervised classification with the ISODATA algorithm. The post‐classification comparison technique was applied to evaluate decadal changes in land area. The turbidity patterns of the bay were determined from sea surface reflectances, and at‐satellite temperatures for the sea area were calculated. The processed images show that the water clarity conditions were affected by the adjacent coastal land uses and by river discharges. In accordance with the change‐detection analysis of land‐use patterns, the forested areas were decreased by 21%, whereas the increase in urban areas was determined as 105% within a decade.     

Simulation of the sea breeze under opposing synoptic conditions

The numerical atmospheric mesoscale model ADREA, developed at NCSR Demokritos, has been applied over a two-dimensional, approximately east-west, vertical cross-section of the Attika basin, including Hymettos mountain top (1026m). The sea breeze cell produced at the eastern coast of a 12km wide plain, adjacent to the easterly mountain foot, was studied in case of westerly synoptic wind. It was found that the mountain influences remarkably the circulation formation and evolution. The flow and temperature patterns of the predicted sea breeze were compared with observations made at eastern Attika in 29 June 1991, in moderate, offshore geostrophic wind and showed a fairly good agreement.     

Global distribution of tropospheric ozone and its precursors: a view from space

Satellite-borne tropospheric ozone measurements obtained from the tropospheric ozone residual (TOR) method, CO from the MOPITT (at 850 hPa level) measurements and NO₂ from the SCIAMACHY measurements for the three-year period 2003–2005 have been utilized to examine the distribution of the pollutant sources and long-range transport on a global scale. Elevated tropospheric ozone columns have been observed over regions of high NO₂ and CO concentrations in the northern and southern hemispheres. High levels of the tropospheric ozone column have been observed below about 5°S in the vicinity of the biomass burning regions and extend from continents out over the Atlantic during October. The seasonal distribution of tropospheric O₃ and its precursors in the southern hemisphere shows the strong correlation with the seasonal variation of biomass burning in Africa and South America. Northern hemisphere summer shows the widespread ozone and CO pollution throughout the middle latitudes. The inter-hemispheric gradient of ozone and CO found to be decreased during October. Large-scale transport of the ozone and CO over the Atlantic and Pacific Oceans has been clearly identified. Strong inter-continental transport has been observed to occur from west to east along with the mid-latitude winds in the northern hemisphere.     

On the variation of the tropospheric ozone over Indian region in relation to the meteorological parameters

Using monthly mean satellite measurements of TOMS/SBUV tropospheric ozone residual (TOR) data and meteorological parameters (tropopause height (TPH), 200 hPa geopotential height (GPH) and outgoing longwave radiation (OLR)) during 1979–2001, seasonal variability of TOR data and their association with meteorological parameters are outlined over the Indian region. Prominent higher values of TOR (44–48 DU, which is higher than the globally averaged 31.5 DU) are observed over the northern parts of the country during the summer monsoon season (June–September). Similar to the TOR variation, meteorological parameters (tropopause height, 200 hPa geopotential height and outgoing longwave radiation) also show higher values during the summer monsoon season, suggesting an in phase relationship and strong association between them because of deep convection present during summer monsoon time. The monthly trends in TOR values are found to be positive over the region. TOR has significant positive correlations (5% level) with GPH, and negative correlations with OLR and TPH for the month of September. The oxidation chains initiated by CH₄ and CO show the enhanced photochemical production of ozone that would certainly become hazardous to the ecological system. Interestingly, greenhouse gases (GHG) emissions were found to have continuously increased over the Indian region during the period 1990–2000, indicating more anthropogenic production of ozone precursor gases causing higher level of tropospheric ozone during this period.     

Dynamic simulation and visualisation of coastal erosion

A key requirement for effective coastal zone management is good knowledge and prediction of land erosion rates due to encroachment of the sea. However, in addition to demarcation of the hazard through modelling and mapping, a policy of risk mitigation necessitates significant attention should also be addressed to communicating the transient behaviour of the predictions and associated uncertainty. With climate change and sea level rise implying that historical rates of change may not be a reliable guide for the future, enhanced visualisation of the evolving coastline has the potential to improve awareness of this changing risk. This visual content is developed by linking scientific modelling with the transformation of digital elevation models, and then using GIS to integrate other spatiotemporal content. The resulting high-resolution visualisations may meet demands from decision-makers for tools to communicate scientific results more effectively, due to their realism and apparent authenticity. Nevertheless they can also produces a tension with the underlying scientific content because of the necessary extrapolation of extra detail, and the lack of established procedures to communicate the resulting uncertainty in the visualisation. Coastal managers also have concerns about releasing the visualisations to the general public. These issues are explored through analysis of future cliff erosion in Norfolk on the eastern coast of Great Britain.     

A study of spatial and temporal dynamics of total ozone over Southwest China with multi-source remote-sensing data

This article describes a study of the spatial and temporal dynamics of total ozone over Southwest China using satellite-retrieved total ozone products from 1996 to 2008 and a ground-based Dobson spectrophotometer. The findings indicated that the value of total ozone (265.7 Dobson unit (DU)) over Southwest China is lower than the value (273.7 DU) over the adjacent region at the same latitude by about 8 DU, and is about 13.8 DU lower than the global average at the same latitude (279.5 DU), and that there is a distinctly low-value area due to the higher elevation. The relationship of total ozone and the elevation presents a negative correlation, the terrain being the main factor to affect this condition. In the long term, the variation of total ozone exhibits a slightly increasing trend from 1996 over this region. Total ozone presents an obvious seasonal change, with the largest value appearing in springtime and the smallest appearing in wintertime. The difference between the regional seasonal mean value of total ozone in springtime and wintertime is about 28 DU, although the difference between the maximum and minimum monthly total ozone throughout a year is up to 50 DU. There is a positive correlation between the variation of total ozone and relative humidity. Relative humidity may be an important factor impacting on the pattern of seasonal change of total ozone.     

A synoptic picture of the impact of the 26th December 2004 Indian Ocean tsunami on the coast of Sri Lanka

A numerical simulation of the 26th December 2004 Indian Ocean tsunami for the entire coast of Sri Lanka is presented. The simulation approach is based on a fully nonlinear Boussinesq tsunami propagation model and a robust coseismic source. The simulation is first confronted to available measured wave height. The agreement between observations and the predicted wave heights allowed a reasonable validation of the simulation. As a result a synoptic picture of the tsunami impact is provided over the entire coast of Sri Lanka. It is found that amplification due to shoaling applies mainly in the Eastern and Southern coast because, here, the wave is propagating across the sea floor slope, while propagating along the slope for the Western coast. Spots of high waves are due to wave focusing in some coastal areas while local submarine canyons in other areas inhibit the wave amplification.     

Shoreline changes in west-central Florida between 1987 and 2008 from Landsat observations

Shoreline changes caused by sediment erosion and accretion have important consequences for coastal ecosystems and coastal communities. Assessing such changes over long stretches of coastline, such as along the west-central Florida coast, represents a challenge to coastal zone managers. In this study, we used nine Landsat Thematic Mapper (TM) images from the west-central Florida coast (adjacent to Tampa Bay, FL) to study historical shoreline changes from 1987 to 2008. Specifically, we sought to evaluate the change of shorelines during the cold (1987–1998) and warm (1998–2008) phases of the Atlantic Multidecadal Oscillation (AMO). The cloud-free images selected for this study were collected during the periods when maximum tidal excursions were less than 9 cm from mean sea level, assuring minimal interference from tidal influence. The images revealed that the southern section of the Tampa Bay inlet showed a mean shoreline accretion rate of 1.30 m year^–1 and a cumulative mean shoreline change of 27.29 m over the past 21 years. The northern section of the Tampa Bay inlet showed a mean accretion rate of 0.34 m year^–1, with a cumulative mean shoreline change of 7.06 m during the past 21 years. Both sections experienced beach nourishment conducted by local communities which, while irregular, were effective in reducing beach erosion. The dynamics of opposing shores in the various inlets in the barrier islands of the study region varied substantially, with many showing accretion in the channel on one side but erosion on the other side.     

Coastline interpretation from multispectral remote sensing images using an association rule algorithm

On the basis of the Apriori algorithm, a class association rule algorithm is presented. A sea–land separation method was designed, and then a shoreline detection method proposed for interpreting multispectral remote sensing images. When separating the land from the sea, not only the spectral attributes but also the texture attributes and basic statistical values were considered in attribute space. To test the feasibility of the method, a Landsat Enhanced Thematic Mapper Plus (ETM+) image scene was used to interpret the coastline. First, the association rules of the sea–land separation of the study area were discovered from learning samples by using the class association rule algorithm. Second, the sea and the land of the image were separated with the mined rules. Third, the coastline was interpreted from the separation result. The accuracy of the interpretation result was computed with a proposed line matching accuracy evaluation algorithm. We show that the proposed method can interpret the coastline accurately and does not require any complex preprocessing.     

The use of optic and radar satellite data for coastal environments

The pressure of population and its demands for fuel, for heating or industrial usage, causes destruction of the natural environment. One of the clearest examples for the accelerated degradation of changes in the forest area and coastline is in the Kilyos–Karaburun coastline located in the northern part of Istanbul metropolitan city. The open‐pit mining activities in the region are threatening the balances of both sea and land ecosystems, and cause degradation of forest areas and changes along the coastline. In this paper, the changes are examined with multisensor satellite data such as Landsat Thematic Mapper (TM), SPOT Panchromatic (P), and RADARSAT images by using different image‐processing techniques. The degrees of changes in coastline length and coastal region area were calculated, and the effectiveness of the use of different image data sets was outlined for coastal environments.     

Assessment of the role of remote sensing techniques in monitoring shoreline changes: a case study of the Kerala coast

The narrow stretch of Kerala coast in the south-western part of India shows dynamic changes in shoreline assuming a critical nature, which called for identification of causative factors. An attempt is made here to evaluate the use of LANDSAT imagery and air photographs in assessing and monitoring shoreline changes, using the Kerala coast as a case study, under the end-to-end experiments of the National Natural Resources Management System (NNRMS).

Geological and terrain remote sensing based on lithological, structural and geomorphic analysis coupled with available data and field studies have revealed that the overall configuration of the coastline is controlled by both NNW-SSE and ENE-WSW trending lineaments, which are found to be neotectonically active. The differential movements along coastal segments have contributed to the compound nature of the coast. This aided by slope morphometry of the foreshore is found to cause variation in erosion/accretion in different stretches with varying intensity. The role of mud banks as a special causative factor is also stressed.

This end-to-end experiment on the application of remote-sensing techniques for monitoring spatial changes in coastline, in particular to the study area, has shown that vulnerable areas could be identified using the spatial resolution of the present LANDSAT system. However, with improved spatial resolution, as available in the airborne MSS imagery, sequential aerial photography could be a semi-operational tool in user applications in contrast to the low resolution of the present LANDSAT system.     

Numerical modeling of land and sea breeze circulation along a complex coastline

The wind distribution in the atmospheric boundary layer is affected by air motions on all scales. In low-latitude coastal areas, however, the wind flows generally are dominated by the diurnally varying land and sea breezes. These flow patterns have been known to exert great influence on local environments by spreading wind-driven brish fires, for example, or dispersing natural or man-made air pollutants. The purpose of this paper is to present a mathematical model that can simulate land and sea breezes in coastal areas.The model equations, based on the primitive equations for the planetary boundary layer with the hydrostatic approximation, are solved numerically with appropriate initial and boundary conditions obtained from interpolation of observational data. Turbulent diffusion of momentum and heat is parameterized through the use of similarity theory for the surface layer supplemented by empirical relationships. This model has been applied to the Tampa Bay area along the Gulf of Mexico. The computed wind field not only simulates the strong land-bound sea breeze at the surface during the day and a weak return flow during the night, but it also retrieves the essential features of land/sea breeze along a complex coastline.