http://localhost:8080/xmlui/handle/123456789/4 Tue, 14 Apr 2026 22:07:12 GMT 2026-04-14T22:07:12Z http://dspace.aries.res.in:80/xmlui/bitstream/id/248/theses.jpg http://localhost:8080/xmlui/handle/123456789/4 http://localhost:8080/xmlui/handle/123456789/1663 Studies of Non-Methane Hydrocarbons (NMHCs) in Ambient Air over the Central Himalayan and Associated Regions Rajwar, Mahendar Chand Air pollution is a major environmental challenge, with a substantial release of pollutants into Earth's atmosphere due to rapid urban and industrial growth over recent decades. Non-Methane Hydrocarbons (NMHCs) stand out among these pollutants, playing a crucial role in the formation of surface ozone (O3) and secondary organic aerosols (SOAs). In addition, a diverse range of NMHCs serves as effective atmospheric tracers with lifetimes varying from a few hours to several tens of days. NMHCs exhibit high reactivity, easily oxidized by hydroxyl (OH) radicals and ozone. Their chemical reactivity increases from light to higher hydrocarbons and from saturated alkanes to unsaturated alkenes. A large range of atmospheric lifetimes in NMHCs helps in assessing the atmospheric transport and photochemical aging. Despite observations of NMHCs over the Indian region being scarce and almost non-existent in the central Himalayas. Under these conditions, the present thesis work has attempted to characterize the NMHCs species over the central Himalayan and associated regions and to develop a better understanding of their role in O3 and SOAs formation process. Therefore, a study was conducted based on the first online observations of light NMHCs (C2-C5) at a mountain site (Nainital, 1958 m AMSL) in the central Himalayas and offline observations at an IGP foothill site (Haldwani 554 m AMSL). The diurnal variations showed higher daytime values at the mountain site and higher nighttime values at the IGP foothill site. Average levels of NMHCs were significantly higher at the IGP foothill site, with alkanes, alkenes and alkynes showing notable differences. Biomass burning and LPG evaporation played major roles, with ethane (40%) predominant in the central Himalayas and propane (27%) dominant at the IGP foothill site. Seasonal variations, correlation studies and comparisons with emission inventories highlighted the impact of combustion processes. The study also assessed the dominant role of propylene, ethylene and n-butane in OH reactivity, ozone formation potential (OFP) and aerosol formation potential (SOAFP) at both sites, emphasizing the need for their emission control strategies. Further, in addition to observations of light NMHCs, the health risks, OFP and SOAFP of aromatic hydrocarbons (C6-C8) were also assessed. First-time observations of BTEX (benzene, toluene, ethylbenzene and (m, p & o) xylene) in the central Himalayas (Nainital) revealed that the mountain site exhibited daytime higher values (up to ~6 ppbv), while the IGP foothill site showed elevated nighttime values (up to ~19 ppbv). Most of BTEX showed higher values in spring/autumn and winter in the mountain site and the IGP foothill site, respectively. BTEX levels were significantly higher at the IGP foothill site. Xylene was the most abundant (60-65%) aromatic at both sites, suggesting the influence of emissions from the IGP foothill on the mountain site. This contrasts with the composition used in emission inventories for this region. Analysis of interspecies ratios of toluene to benzene and ternary plots indicated the dominance of industrial sources, with some contributions from vehicular exhaust and biomass burning. The estimated OH reactivity, OFP and SOAFP potential were 4-6 times higher at the IGP foothill site than at the Himalayan site. Xylene played a significant role in these processes at both sites. Furthermore, benzene played a dominant role in the hazard ratio (HR) and the lifetime cancer risk (LCR) at both sites. The LCR at both sites crossed the probable risk limit. Apart from NMHCs, surface ozone behavior in Himalayan foothills was also studied. Doon Valley (Dehradun: 700 m) in the Himalayan foothills acts as one of the links between the Himalayas and the IGP. Surface ozone in the valley exhibited urban behavior with daytime peaks. Ozone showed higher values in spring (49.2±24.8 ppbv in May), driven by biomass burning. About 9-50% enhancement in ozone was found in the high-fire activity period (April-May). Ozone exceeds the 8-hours national air quality standard (50 ppbv) throughout the year, except in July-September. Moreover, a photochemical box model estimated ~41 ppbv and ~8 ppbv of ozone production and loss, respectively. The role of the HO2+NO reaction (85.6%) in ozone production and the O3+HO2reaction (56.2%) in ozone loss were seen. Exposure metrics analysis (M7 and AOT40) estimated an annual loss of 27-37 kilotons of wheat and 14 32 kilotons of rice production due to elevated ozone levels. Furthermore, the HR for BTEX and LCR values for benzene and ethylbenzene exceeded the standard limits (USEPA and WHO), indicating significant health risks to the population. In addition, the CAMS model and satellite based studies demonstrated the NOx-sensitive behavior of ozone production in this Himalayan region, where aromatics exhibited the maximum OFP among different NMHCs. This thesis work emphasizes the role of diverse emission sources and NMHCs distributions at the mountain and the IGP foothill sites, suggesting further comprehensive studies and long-term observations in different Indian regions. The observations presented in the work are deemed crucial for evaluating the impact of emissions in the Asian summer monsoon region, as also seen in the recent campaign (ACCLIP) conducted by NCAR and NASA in the Asian summer monsoon region. The thesis is submitted to Deen Dayal Upadhyaya Gorakhpur University, Gorakhpur, under the supervision of Dr. Manish Naja & Prof. Rakesh Kumar Tiwari. Wed, 01 May 2024 00:00:00 GMT http://localhost:8080/xmlui/handle/123456789/1663 2024-05-01T00:00:00Z http://localhost:8080/xmlui/handle/123456789/1662 Lower Atmospheric Studies Using ARIES StratosphericTropospheric (ST) Radar in Conjunction with In-situ and Auxiliary Observations Rajput, Akanksha The lower atmospheric processes impose a number of challenges, such as fundamental understanding of small-scale processes and extreme weather events in the area of atmospheric physics. Atmospheric turbulence is one of the important microscale processes due to its characteristics of efficient mixing of air having different properties within a time scale of less than 1 sec to typically 1 hour and corresponding length scales from 1 mm to 1 km. Consequently, it influences the dynamics and thermodynamics of precipitating systems, transport of water vapor and dust, heat transfer, as well as impacts telecommunications, remote sensing, and aviation, etc. To understand such processes, the study of variation in the vertical structure of turbulence characteristics and their scale sizes over different regions of the globe is a need of the hour. Further, over the mountainous terrain, the intensive interaction of atmospheric circulation on different spatial and temporal scales results in a combination of multiple transport processes such as turbulent motions, thermally driven circulations, terrain-forced winds, and moist convection. Therefore, mountainous regions serve as a natural laboratory to explore the role of orography in the various aspects of turbulence characteristics, diurnal variation of the atmospheric boundary layer, and different precipitating systems. Weather balloon experiments using radiosonde are one of the oldest in-situ measurement techniques to retrieve the vertical profiles of the turbulent characteristics in the lower atmosphere. Also, wind profiler radars operating at various frequencies have been extensively utilized throughout the globe for continuous monitoring of microscale and mesoscale weather phenomena and estimating their corresponding physical mechanisms and processes. The central objective of the present thesis is focused on the study of lower atmospheric dynamics and associated meteorological processes, considering the importance of the Himalayan mountainous site in terms of meteorological and climatic conditions. The dynamical features and variability of the turbulence characteristics and scale-size calculations at different temporal scales are carried out using radiosonde observations in the lower atmosphere up to 20 km. Turbulence characteristics are specifically focused on the variation of energy dissipation rate (ε), eddy diffusivity (K), refractive index structure parameter (Cn2), inner scale (lo), and outer scale (LB) over a mountainous site, Manora Peak Nainital. Results showed the lowest dissipation rate (− 4.5 m2 s-3) during the post-monsoon season while constant dissipation rate (~− 4 m2 s-3) below 5 km in winter. A constant variation of log K (~ − 0.01 m2 s-1) is observed above 8 km during all the seasons except during the monsoon, where larger buoyancy scales (>100 m) are found in the altitude range of 8–14 km. This study also reveals that orographic-induced local circulations can significantly control the large turbulence intensity even up to the deeper layer of 2 km from the surface during a weak wind regime as compared to a strong wind regime where large turbulence intensity is confined within 0.5 km. An attempt is also made in this thesis to investigate the lower troposphere dynamics within 2.5 km altitude by estimating the diurnal variation of turbulence characteristics along with the atmospheric boundary layer height (BLH) during two contrasting seasons, winter and spring, using 1290 MHz radar wind profiler measurements. Analysis showed deep convective (CBL ~ 750 m) and stable boundary layer (SBL ~ 500 m) with average values of log Cn2 and log ɛ ≈ -12 m-2/3 and -2 m2 s-3, respectively, in spring. During winter, BLH varies from shallow SBL of about 270 m to the maximum 630 m daytime CBL with mean values of about 405 ± 125 m. One major cause of deep SBL in spring is found under the weak stratification and weak flow regime case, where shear-induced turbulences are responsible for robust vertical mixing. Further, from the variation of BLH with aerosol loading and background atmospheric conditions (stability and wind shear), different pollution transport mechanisms are suggested over the region during the seasons. Additionally, the preliminary analysis of the data from only the wind profiler ARIES ST radar (ASTRad) operating at 206.5 MHz frequency and installed over the central Himalayan site is performed by validating the estimated wind profiles with concurrent radiosonde profiles. Additionally, dynamical and microphysical aspects of two cases of precipitation events during monsoon (Case-I) and western disturbances (Case-II) are investigated over the Manora Peak Nainital using ASTRad data and the Weather Research and Forecasting (WRF) model simulations. The vertical structure of precipitation systems is analyzed in this study using three Doppler moments (equivalent Reflectivity dBZe, Doppler velocity, and Spectral width) estimated from the ASTRad observations. The investigation of the dynamical structure of these events suggested the role of orography in the formation of a precipitation system for Case-II. Microphysical analysis using WRF simulations revealed Case-I as a mixed-phase and Case-II as a cold-phase microphysical process resulting in liquid precipitation during the summer monsoon while both solid and liquid precipitation during the western disturbance. Overall, all objectives of this thesis work are based on lower atmospheric dynamical processes over the central Himalayas, which have been investigated here using the wind profiler radar, radiosonde, WRF simulations, and other auxiliary datasets over the central Himalayas. The thesis is submitted to Deen Dayal Upadhyaya Gorakhpur University, Gorakhpur, under the supervision of Dr. Narendra Singh & Prof. Ravi Shankar Singh. Fri, 01 Dec 2023 00:00:00 GMT http://localhost:8080/xmlui/handle/123456789/1662 2023-12-01T00:00:00Z http://localhost:8080/xmlui/handle/123456789/1661 Observation and Modelling Studies on Meteorology Over Central Himalaya Singh, Jaydeep The sensitive ecosystem of the Himalayas, particularly the central Himalayan (CH) region, is experiencing enhanced stress from anthropogenic forcing that requires adequate atmospheric observations and an improved representation of the Himalayas in the models. However, the accuracy of atmospheric models remains limited in this region due to highly complex mountainous topography. The convective-permitting scale simulations by the limited area models, e.g., the Weather Research and Forecasting (WRF) model, are broadly used for a wide range of applications, including climate projections, weather predictions, and air quality forecasts. Such state-of-the-art models fill the gap in data scarcity over high mountain areas like the Himalayas. Their evaluation with observations and fine-tuning increases the certitude of the generated regional scale information. This thesis work first delineates the effects of spatial resolution on the modeled meteorology and dynamics over the CH by utilizing the Weather Research and Forecasting (WRF) model and extensively evaluated against the ground-based, remote-sensing, and re-analysis products. This analysis highlights that the WRF model set up at finer spatial resolution can significantly reduce the biases in simulated meteorology, and such an improved representation of CH can be adopted through domain feedback into regional-scale simulations. Model simulation implementing a high-resolution (3s) topography input (SRTM) improved the model performance immensely. Apart from the model resolution and unresolved topographic features, model physics, which is generally known as parameterization schemes, plays an important role in stimulating accurate simulation. After the successful evaluation of the model at various grid resolutions, the impact of the model physics schemes related to the sub-grid scale turbulence (six boundary layer schemes) and microphysical processes (seven microphysics schemes) are also evaluated over the central Himalaya region. The evaluation of the boundary layer schemes within the Weather Research and Forecasting (WRF) model is nearly non-existent over complex terrains of the Himalayan region. To achieve this, six different planetary boundary layer (PBL) schemes Yonsei University (YSU), Mellor-Yamada-Nakanishi-Niino level 3 (MYNN3), Shin-Hong Scale-aware (SHSS), Mellor-Yamada-Janjić (MYJ), Asymmetric Convective Model version 2 (ACM2), Quasi Normal Scale Elimination (QNSE) in the WRF model are evaluated against observational datasets. The evaluation is carried out for spring during clear-sky conditions using surface-based, balloon-borne, and radar wind profiler (RWP) observations. YSU and SHSS schemes are found to be the best schemes in reproducing the meteorology over the region. Model performance varies significantly with the employed PBL schemes in simulating the localized boundary layer height (LBL), and all PBL schemes can capture the daytime maxima of LBL heights with some overestimation, while YSU and SHSS schemes are closer to the observations followed by MYJ. The competing effect between the synoptic and local circulation was found to be a vital controlling factor in the boundary layer evolution over the mountain peak and affected the model performance. Further, cloud microphysics schemes are used to simulate the spatio-temporal distribution of the precipitation, especially at the convection-permitting scales, and are generally one of the major sources of uncertainty in the model. To test it, seven different microphysics schemes (Lin, Eta, WSM6, WSM5, WDM, Thompson, and Morrison) are evaluated during a heavy precipitation event (HPE) over the CH. The model successfully reproduced structural and dynamical characteristics associated with the extreme event, including water vapor transport and meteorological fields. Most of the microphysics schemes are found to simulate the temperature and specific humidity reasonably, except the Eta schemes. The precipitation pattern is found to be very sensitive to both the grid resolution and microphysics schemes. Further, model results suggested that the interaction between the moisture convergence system and orography caused the HPE. Additionally, the impact of the enhanced aerosol loading on the surface layer characteristics has been investigated using micrometeorological measurements during a severe dust storm that resulted in a five-fold enhancement in the fine particulate matter (PM2.5) over the central Himalaya. Interestingly, dust storms also had significant impacts on turbulent kinetic energy (2.9–9.6 m2 s−2), vertical momentum flux (0.9–3.3 Nm−2), and sensible heat flux (34.8 to −33.9 Wm−2), suggesting turbulent mixing of aerosols and cooling near the surface over the Himalayas. This analysis highlights that large-scale dust storms can profoundly impact air quality and surface layer characteristics by perturbing micrometeorology over the CH. Overall, this thesis work is based on meteorological studies, which have been carried out using the WRF model and observational datasets over the central Himalayas. The thesis is submitted to Deen Dayal Upadhyaya Gorakhpur University, Gorakhpur, under the supervision of Dr. Narendra Singh & Prof. Ravi Shankar Singh. Fri, 01 Sep 2023 00:00:00 GMT http://localhost:8080/xmlui/handle/123456789/1661 2023-09-01T00:00:00Z http://localhost:8080/xmlui/handle/123456789/1623 Multi-wavelength Studies of Gamma Ray Bursts (GRBs) and Associated Counterparts Dimple Gamma-ray bursts (GRBs) are brief but exceptionally bright flashes of γ-rays. They emit as much energy in a few seconds as thousands of Suns will produce in its entire lifetime. Even though they were discovered more than half a century ago, there are still unanswered questions about the nature of their central engines and progenitor systems. GRBs have traditionally been divided into short-duration and long-duration classes based on the T90 durations (the duration in which 90% of the fluence is collected) less than or greater than two, respectively. However, the T90 duration relies on multiple factors such as the sensitivity of the detector, variations in background levels, and the specific energy bands in which the burst is observed. Moreover, the proposed mechanisms involving massive star collapse for long GRBs and compact object mergers for short GRBs could not explain the recent observations. An unambiguous classification scheme correlated to progenitor models is still lacking. The overarching goal of this thesis is to solve the outstanding problem of GRB classification and uncover their progenitor diversity. A systematic multi-wavelength analysis of GRB properties from γ-rays to radio wavelengths is combined with advanced machine learning techniques to tackle this problem. This approach aims to identify correlations between observables that can reliably distinguish between intrinsic GRB subclasses. It also seeks to uncover potential subgroups within the traditionally defined duration categories. Through detailed case studies of ambiguous GRBs and multi-parameter analysis of GRB samples, the research presented in this thesis provides new insights into GRB progenitors. Unsupervised machine learning applied to light curves reveals distinct clusters that may correspond to different progenitor populations. The combination of comprehensive data analysis and sophisticated machine learning tools here represents a significant step forward in solving the long-standing classification problem and advancing our understanding of the progenitor system of GRBs. Looking ahead, future work will expand this research through inclusion of afterglow properties and larger GRB datasets from different instruments. The prospect of applying these techniques to upcoming wide-field surveys heralds new opportunities to definitively link GRB subclasses to progenitor systems. Moreover, the multimessenger observations of the bursts involving gravitational waves will further shed light on their progenitor systems. The thesis is submitted to Deen Dayal Upadhyaya Gorakhpur University, Gorakhpur, under the supervision of Dr. Kuntal Misra & Prof. Lallan Yadav. Fri, 01 Sep 2023 00:00:00 GMT http://localhost:8080/xmlui/handle/123456789/1623 2023-09-01T00:00:00Z