Browsing by Author "Nizar, S."

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Satellite-based top-down Lagrangian approach to quantify aerosol emissions over California
(John Wiley and Sons Ltd vgorayska@wiley.com Southern Gate Chichester, West Sussex PO19 8SQ, 2020) Nizar, S.; Dodamani, B.M.
Accurate forecasting of air quality demands better estimates of aerosol emissions. The accuracy of conventional bottom-up approaches to estimate aerosol emissions depends on the degree to which various influencing parameters are estimated. The availability of satellite observations not only enhances the capability of determining various influencing parameters, but also provides alternate ways of assessing aerosol sources. The present study employs a Lagrangian approach to the Advection Diffusion Equation (ADE) to estimate the transported aerosols and hence the Aerosol Source Strength (ASS) using satellite-measured Aerosol Optical Depth (AOD) and reanalysis wind data. This top-down approach is based on the advection and diffusion of atmospheric aerosols considering wind circulation and atmospheric conditions rather than using indicative parameters. ASS was computed every 3 hr at a 0.25°×0.25° grid across California during July 2018. For the computation, AOD retrievals were obtained from the Geostationary Operational Environmental Satellite (GOES)-16 with observations every 15 min. The data were resampled to the grid every 3 hr, and backward trajectories were run at every gridpoint to ascertain the initial aerosol concentration for the ADE. The final aerosol concentrations obtained from the ADE model were then compared with the observed AOD to obtain the ASS during that time period. The results are indicative of higher ASS around wildfire locations. The ASS values also show good correlation (R2=0.886) with Fire Radiative Power (FRP) obtained from Terra MODIS fire product. The method was further applied to investigate the spatial correlation of ASS with power plant density, which reveals a steady increase in ASS with power plant density (R2=0.82). © 2020 Royal Meteorological Society
Spatio-temporal distribution of rainfall and aerosols over urban areas of Karnataka
(2018) Nizar, S.; Dodamani, B.M.
Rapid increase of population and urban sprawl have an immense impact on local climatic conditions. Urban heat island, increased surface roughness and enhanced aerosol are some of the prominent factors affecting precipitation in such highly populated urban areas. Among these, the complex interaction of aerosol particles with solar radiation have acknowledged their importance in radiation budget and hence climate dynamics. Being cloud condensation nuclei they also influence cloud lifetime and microphysics in turn influencing precipitation. Present investigation emphases on understanding rainfall and aerosol trends and its spatial occurrence pattern with respect to urbanization. An approach where population as an indicator for urbanization is used in this study rather than a profound investigation on the individual factors of urban induced precipitation anomalies. Mann Kendall trend test is carried out at grid level on a 0.25 degree gridded rainfall data and the trends are then related with the distribution of population in the study area. Areas of significant rainfall trends are identified and are analyzed for spatial patterns around urban areas. These identified urban zones are then further analyzed for aerosol variability. Being a monsoon region, a seasonal variation of aerosols are performed. The results shows that during the monsoon season there is a significant increase in rainfall along the Western Ghats, whereas certain grids along the western coast located at the downwind of populated areas such a Mangalore shows a significant decreasing trend. The overall spatial pattern of rainfall trend during pre-monsoon season is indicative of the influence of urban areas on rainfall. This observation during the pre-monsoon season is quantified which shows that 61% of the trends are included within urban influence zones which are only 36% of the size of Karnataka. Further various cloud characteristics and its association with aerosol loading in these urban areas were investigated. The results are indicative of higher aerosol events suppressing rainfall in these urban areas. � 2018 SPIE.
Spatio-temporal distribution of rainfall and aerosols over urban areas of Karnataka
(SPIE spie@spie.org, 2018) Nizar, S.; Dodamani, B.M.
Rapid increase of population and urban sprawl have an immense impact on local climatic conditions. Urban heat island, increased surface roughness and enhanced aerosol are some of the prominent factors affecting precipitation in such highly populated urban areas. Among these, the complex interaction of aerosol particles with solar radiation have acknowledged their importance in radiation budget and hence climate dynamics. Being cloud condensation nuclei they also influence cloud lifetime and microphysics in turn influencing precipitation. Present investigation emphases on understanding rainfall and aerosol trends and its spatial occurrence pattern with respect to urbanization. An approach where population as an indicator for urbanization is used in this study rather than a profound investigation on the individual factors of urban induced precipitation anomalies. Mann Kendall trend test is carried out at grid level on a 0.25 degree gridded rainfall data and the trends are then related with the distribution of population in the study area. Areas of significant rainfall trends are identified and are analyzed for spatial patterns around urban areas. These identified urban zones are then further analyzed for aerosol variability. Being a monsoon region, a seasonal variation of aerosols are performed. The results shows that during the monsoon season there is a significant increase in rainfall along the Western Ghats, whereas certain grids along the western coast located at the downwind of populated areas such a Mangalore shows a significant decreasing trend. The overall spatial pattern of rainfall trend during pre-monsoon season is indicative of the influence of urban areas on rainfall. This observation during the pre-monsoon season is quantified which shows that 61% of the trends are included within urban influence zones which are only 36% of the size of Karnataka. Further various cloud characteristics and its association with aerosol loading in these urban areas were investigated. The results are indicative of higher aerosol events suppressing rainfall in these urban areas. Â© 2018 SPIE.
Spatiotemporal distribution of aerosols over the Indian subcontinent and its dependence on prevailing meteorological conditions
(Springer Netherlands rbk@louisiana.edu, 2019) Nizar, S.; Dodamani, B.M.
The prevailing meteorological conditions that influence the advection and diffusion of the atmosphere govern the distribution of atmospheric particles from its sources. The present study explores the spatiotemporal distribution of atmospheric aerosols over the Indian subcontinent (5°–40° N, 65°–100° E) and its dependence on the prevailing meteorological conditions. Eleven years (2002–2012) of Aerosol Optical Depth (AOD) obtained from the Moderate Resolution Imaging Spectroradiometer (MODIS) along with meteorological parameters extracted from reanalysis data are analysed at monthly timescales. Wind speed, wind divergence and planetary boundary layer height (PBLH) are studied as parameters for advection and diffusion of atmospheric aerosols. The result shows higher aerosol loading during the monsoon season with increased spatial variability. Wind speed and divergence correlate with AOD values both over land (R = 0.75) and ocean (R = 0.82) with increased aerosol loading at higher wind speeds, which are converging in nature. Owing to the varied climatology of the Indian subcontinent, land and ocean areas were classified into subregions. Analysis was carried out over these subregions to infer the influence of meteorological conditions on aerosol loading. Results are indicative of a distinct characteristic in the prevailing meteorological conditions that influence the distribution of certain aerosol types. Further, the PBLH was analysed as an indicator of atmospheric diffusion to infer its importance in aerosol distribution. The results indicate that PBLH explains almost 30 to 90% of the total variance in AOD over the subregions which is particularly evident during the winter and pre-monsoon seasons. © 2019, Springer Nature B.V.
Trends in Agro-Meteorological Parameters as Groundwater Exploitation Indicators
(2018) Pathak, A.A.; Nizar, S.; Dodamani, B.M.
Rainfall being a major component of the hydrologic cycle, influences the agricultural practices in an area. Thus, trends in rainfall as well as rainy days are of major concern to farmers. Present study focusses on understanding the rainfall trends and its spatial distribution along with the trends in vegetation. An approach where Normalized Difference Vegetation Index (NDVI) procured from MODIS NDVI as an indicator for vegetation was used in this study. Mann Kendall trend test was performed on a 0.25-degree gridded data and the trends were then compared with the distribution of groundwater stress map of the study area. The study tries to examine the coupled use of NDVI and rainfall trends to decrypt the groundwater exploitation in the region. Further Ghataprabha river basin being susceptible to drought by hosting most of the significantly decreasing trend was investigated further. The propagation of severe drought return periods within the basin resembles the agro-meteorological trends. Even within the limitations of the present study, the methodology with further modifications promises to portray strong indication of groundwater exploitation. � Published under licence by IOP Publishing Ltd.
Trends in Agro-Meteorological Parameters as Groundwater Exploitation Indicators
(Institute of Physics Publishing helen.craven@iop.org, 2018) Pathak, A.A.; Nizar, S.; Dodamani, B.M.
Rainfall being a major component of the hydrologic cycle, influences the agricultural practices in an area. Thus, trends in rainfall as well as rainy days are of major concern to farmers. Present study focusses on understanding the rainfall trends and its spatial distribution along with the trends in vegetation. An approach where Normalized Difference Vegetation Index (NDVI) procured from MODIS NDVI as an indicator for vegetation was used in this study. Mann Kendall trend test was performed on a 0.25-degree gridded data and the trends were then compared with the distribution of groundwater stress map of the study area. The study tries to examine the coupled use of NDVI and rainfall trends to decrypt the groundwater exploitation in the region. Further Ghataprabha river basin being susceptible to drought by hosting most of the significantly decreasing trend was investigated further. The propagation of severe drought return periods within the basin resembles the agro-meteorological trends. Even within the limitations of the present study, the methodology with further modifications promises to portray strong indication of groundwater exploitation. Â© Published under licence by IOP Publishing Ltd.