Indian Landmass Research Articles

Era-interim Forced Simulation of the Indian Summer Monsoon

In the present study, mean rainfall for the months of June-July-August-September (JJAS) during summer monsoon is simulated over India and its adjoining regions for a period between 1982 and 2006. The study was carried out using Regional Climate Model (RegCM) version 4.6 at a resolution of 25 km. The simulated mean JJAS monsoon rainfall was validated against the observational IMD data. Comparison of JJAS seasonal mean summer rainfall for the first decade 1982–1991, with the later decade 1997–2006 indicate that the intensity of rainfall increases over Indian land-mass during the later decade under the forced conditions of Era-Interim. The observed JJAS mean rainfall indicates two maximum rainfall areas i.e. the Western Ghats and the Himalayan region. A significant bias is observed in the central and Jammu and Kashmir (J&K) region. The JJAS mean seasonal surface air temperature distribution at 0.25 × 0.25-degree grids resolution shows a decreasing trend of temperature over the Indian landmass.

Sustainable Development of the Marine Leisure Industry Along the Indian Coastline

Marine leisure organisation has the intrinsic capability to land up one of the tremendous supporters of the GDP of India each time created in a maintainable way with appropriate control faster rather than later. The perfect seashores of India which can be long and massive, a few being hard and motorable throughout low tide may be domestic to distinct water sports activities activities with worldwide measures. The Cruise organization comprehensive of beach the front transportation and circulate travels may be a noteworthy wellspring of amusement for household and remote visitors. Beacon the tour enterprise with its associated tools is likewise being created through the legislature. The submerged social legacy locales at Dwarka, Mahabalipuram, Rameshwaram and Poompuhar can be created as vacationer visit territories through submarines like that created in Mauritius. The marine the tour business enterprise may be coordinated with the voyage thru the rich social legacy of Indian land mass. The legislature in accordance with the Tourism association and practical development desires have strategized extraordinary hobby intends to present a noteworthy elevate to the marine relaxation employer. With the brand new authorities the interest plans must be actualized to in reality assist the business enterprise that might enlarge to be a noteworthy supporter of the GDP of the country.

Distribution and dispersal of surface sediments on the continental margins of India

Abstract The vast area, varying climate regimes, diverse source terrain lithology of the mainland India generate complex weathering and erosional patterns and leads to diverse sediment distribution and dispersal on the surrounding continental margins of India. Thus, to delineate the sources, distribution and sediment dispersal pathways around India, 254 sediment cores from the eastern and western continental margins of India were investigated for physical properties using non-destructive, whole core logging technique combined with grain-size analyses. The distribution of magnetic susceptibility, gamma ray density and grain-size traces the sources in the Indian landmass which contribute sediments to the margins and demarcates their extent of influence. The results from the magnetic susceptibility distribution indicate that the dominant influx of modern high susceptibility sediment into the margins of India originates from the weathering of Deccan Basalts and its subsequent transportation by Narmada and Tapti Rivers in the west coast and Krishna and Godavari Rivers in the east coast. Though the Himalayan sources are the second largest supplier of magnetic minerals to the shelf, their contribution, when compared to the Deccan sediments is not significant. The lack of present-day sedimentation in the outer shelf regions of margins of India is evident from the gamma ray density distribution and is confirmed by the discrete sample grain-size analysis. Gamma ray density variations in the margins follow the same pattern as the grain size variations and demarcate the boundary between inner shelf modern clayey sediments and the outer shelf relict carbonate sands. Regional distribution maps of physical properties and grain-size for both the margins of India are presented and geographical limits of each provenance are defined, thus providing a comprehensive picture of sediment distribution and dispersal patterns in the area and highlights the use of magnetic susceptibility as a powerful tool in deciphering the source to sink pathways of sediments.

Source attribution of carbon monoxide and ozone over the Indian subcontinent using MOZART-4 chemistry transport model

Daily simulations of tropospheric carbon monoxide (CO) and ozone (O3) have been made using MOZART-4 (Model for OZone And Related chemical Tracers version 4) during 2007–08. The model simulated CO and O3 are evaluated against MOZAIC (Measurement of Ozone and Water Vapor by Airbus In-Service Aircraft) airborne observations over Hyderabad and IASI (Infrared Atmospheric Sounding Interferometer) retrievals over five most populous cities of India i.e. Mumbai, Delhi, Bangalore, Hyderabad, and Ahmedabad. The MOZAIC tropospheric column showed winter maxima and summer minima for CO whereas spring maxima and summer minima for O3. These seasonal features are reproduced well by model over Hyderabad. Model lower and middle tropospheric CO (O3) columns are positively biased by about 14 (8) ppbv as compared to MOZAIC observations. Model underestimated (overestimated) IASI CO columns during pre-monsoon (post-monsoon) while it overestimated IASI O3 columns throughout the year. Model simulated column of CO and O3 are positively biased by 4–13% and 23–33% respectively as compared to the IASI retrievals over five most populous cities. Tagged and sensitivity simulations of MOZART-4 have been used to quantify the contribution of different sources to the tropospheric CO and O3 distribution over the Indian landmass region. At surface, anthropogenic contribution varies from 55% to 81% during different seasons with an annual average contribution of 67%. This contribution decreases with increasing altitude up to 35% at 300 hPa. The contribution of photochemically produced CO is found to be 9–33% at surface. Unlike ANT-CO, the photochemically produced CO increases with altitude as it reaches up to 48% at 300 hPa. Surface BB-CO contributes upto 30% over parts of North East India during pre-monsoon season. Contribution of NAT-CO is found to be negligible (Approximately 6%) near surface as well as at the higher altitudes. Sensitivity simulations are used to decompose the total ozone (TO) into contributions from enhancement of ozone from Indian anthropogenic emissions, referred as Indian pollution ozone (IPO) and from the total background ozone (TBO). Annual total ozone is found to be 30 to 70 ppbv at surface and 77 to 85 ppbv at 300 hPa over the Indian landmass region. IPO and TBO contribute annually 58% and 42% at surface while 45% and 55% at 300 hPa respectively. The IPO contributes strongly at surface, with maximum (68%) impact during pre-monsoon season.

New Insights into the Convective System Characteristics Over the Indian Summer Monsoon Region Using Space-Based Passive and Active Remote Sensing Techniques†

The characteristics of convective systems over the Indian summer monsoon (ISM) region derived by using a unique combination of four satellites METEOSAT, TRMM, COSMIC and CloudSat comprising of both active and passive remote sensing sensors are discussed for the first time. Six years of observations during ISM brought out the preferential geographical regions and time for formation of shallow, deep, and very deep convective systems. It has been observed that shallow, deep, and very deep convective clouds are abundant over ISM region and their distributions show a relatively high frequency of occurrence over the Head Bay of Bengal as compared to other regions. The mean vertical structure of clouds are also been studied using CloudSat observations over several latitudinal belts. The time of maximum occurrence of convective type cloud systems are also quantified using the present observations. The analysis suggests that the deep and very deep convective cloud systems peak during late afternoon hours over many parts of the Indian landmass with few exceptions such as over foothills of the Himalayas, where it peaks during the early morning hours. The three-dimensional structures of convective systems are also discussed. The significance of the present results lie in providing new insights into the characteristics of convective systems by investigating CAPE, clouds, and precipitation, which in turn play a vital role in understanding the internal dynamics of ISM.

Assessment of Rainfall Thresholds for Rain-Induced Landslide Activity in North Sikkim Road Corridor in Sikkim Himalaya, India

Land sliding is a perennial problem in the Eastern Himalayas. Out of 0.42 million km2 of Indian landmass prone to landslide, 42% fall in the North East Himalaya, specially Darjeeling and Sikkim Himalaya. Most of these landslides are triggered by excessive monsoon rainfall between June and October in almost every year. Various attempts in the global scenario have been made to establish rainfall thresholds in terms of intensity – duration of antecedent rainfall models on global, regional and local scale for triggering of the landslide. This paper describes local aspect of rainfall threshold for landslides based on daily rainfall data in and around north Sikkim road corridor region. Among 210 Landslides occurring from 2010 to 2016 were studied to analyze rainfall thresholds. Out of the 210 landslides, however, only 155 Landslides associated with rainfall data which were analyzed to yield a threshold relationship between rainfall intensity-duration and landslide initiation. The threshold relationship determined fits to lower boundary of the Landslide triggering rainfall events is I = 4.045 D - 0.25 (I=rainfall intensity (mm/h) and D=duration in (h)), revealed that for rainfall event of short time (24 h) duration with a rainfall intensity of 1.82 mm/h, the risk of landslides on this road corridor of the terrain is expected to be high. It is also observed that an intensity of 58 mm and 139 mm for 10-day and 20-day antecedent rainfall are required for the initiation of landslides in the study area. This threshold would help in improvement on traffic guidance and provide safety to the travelling tourists in this road corridor during the monsoon.

Evaluation of the Weather Research and Forecasting Model Forecasts for Indian Summer Monsoon Rainfall of 2014 Using Ground Based Observations

The present study focuses on evaluating the ability of short-range rainfall forecasts from the Weather Research and Forecasting (WRF) model against observed gridded rainfall data from the India Meteorological Department (IMD) available over the Indian landmass during Indian summer monsoon (ISM) viz. June to September for the year 2014. The spatial distribution of the WRF predicted rainfall matches well with the IMD observed rainfall and indicates systematic rainfall biases over the Indian landmass. In general, precipitation is underestimated in dry, low elevation areas and overestimated in wet, high elevation areas by the WRF model. Based on rainfall verification scores, it was found that low and moderate rainfall was forecasted reasonably well by the WRF model compared to heavy rainfall. Moreover, extremal dependency score (EDS) has been used to verify heavy rainfall forecasts, as the traditional threat scores saturates towards high rainfall thresholds. Further, the separate analysis was carried out over five different homogeneous rainfall zones of India. Results show that the WRF model was able to predict rainfall reasonably well with higher correlation coefficient, lower bias and root mean square deviation in most of the zones. Moreover, the WRF rainfall forecasts at high spatial resolution (5 km) were also examined over Karnataka, India using dense rain gauge network.

The current status of orogenesis in the Central Indian Tectonic Zone: A view from its Southern Margin

The Central Indian Tectonic Zone, because of its critical position in the tectonic framework of East Gondwanaland, holds insights into our understanding of the assembly and dispersal of Columbia and Rodinia supercontinents through the growth of the Greater Indian Landmass. The tectonic zone, which is now a collage of different supracrustal and granulite‐gneiss belts, bears testimony to a multistage orogenic evolution from Late Palaeoproterozoic to Early Neoproterozoic time. In this contribution, the current status of orogenic evolution in the Central Indian Tectonic Zone has been reviewed using petrological and geochronological constraints from the Sausar Mobile Belt, its southernmost constituent. It reveals a three‐stage evolution leading to the growth of the Greater Indian Landmass: (a) c. 1.6–1.5‐Ga accretionary orogenesis produced the first nucleus of Greater India through the assembly of arc, back arc, and continental margins; (b) a phase of Middle Proterzoic extension led to the disintegration of the Proto‐Greater India; and (c) classical Himalayan‐style continental collision between 1.06 and 0.93 Ga finally stitched the North and South India blocks to produce the final configuration of the Greater Indian Landmass. It is argued that the Late Palaeoproterozoic to Early Mesoproterozoic orogenesis in India and former Gondwanaland and Laurentian fragments is a globally significant amalgamation event separate from the Columbia Supercontinent assembly.

Disentangling the influencing factors driving the cooling trend in boreal summer over Indo-Gangetic river basin, India: role of Atlantic multidecadal oscillation (AMO)

Using the Community Earth System Model (CESM)-Large Ensemble (LE) surface air temperature (SAT) data, we investigate the multidecadal changes in SAT variability over Central Indian landmass, particularly the Indo-Gangetic (IG) river basin. This region comes under the active influence of the Indian summer monsoon, and during the summer monsoon months (JJA), we observe an amplified cooling (< − 3 °C) trend (1961–2000) in SAT. This SAT trend is considered as a superposition of external forcings and natural climatic variability. The forced response is computed by averaging the trend in 35 ensemble members, which displays a moderate cooling trend due to aerosol-, ozone-, and volcano-only forcings. But the internal variability introduces a wide range of uncertainties in SAT, with majority of the members display a strong cooling trend in the Central Indian region. During the entire period, natural climatic variability dominates over the forced response, which strongly overrides the greenhouse gas (GHG) warming. Here, we separate out the influence of global climate variability on regional climate variability and identify the specific internal variability which is responsible for the multidecadal cooling trend in the analyzed region. Furthermore, we investigate the specific physical mechanism driving the cooling trend and analyze the role of Atlantic multidecadal oscillation (AMO) in its negative phase. The covariability is − 0.74, i.e., AMO accounts for ~ 55% of total variance in the multidecadal variability. In the negative phase of AMO, strong signals of Rossby waves emanating from North Atlantic Ocean propagate across the Eurasian continent, and in the latter half of the twentieth century, the effect of this cold sea surface temperature (SST) anomaly is felt in the Central Indian landmass (particularly over IG river basin) through teleconnection. This study will increase the predictability of multidecadal variability in SAT during summer monsoon season over the Central Indian region with AMO as a strong driving component.

Aerosols impact on the convective and non-convective rain distribution over the Indian region: Results from WRF-Chem simulation

The Weather Research and Forecasting (WRF) model coupled with chemistry (WRF-Chem) is used to simulate rainfall pattern over the Indian landmass during a normal monsoon year (June–September 2010). Sensitivity analysis is performed using three different microphysical (MP) schemes (Thompson, Morrison, and Lin) to simulate the rainfall pattern and distribution over India. A significant difference in the rainfall amount, as well as distribution, is observed among the MP schemes, despite using the same model configuration and the meteorological and chemical initial and boundary condition. Lin MP scheme performed better than other schemes in simulating the rainfall over the Indian domain. Heavy rainfall along the foothills of the Himalayas, the mountainous coastal region of western India, and the northeastern part of India and sparse rainfall over northwest India are captured realistically in the model, which agrees well with the observed rainfall pattern over India. The spatial distribution of aerosol optical depths retrieved from the MODIS satellites is broadly well simulated by the model.The model simulated convective and non-convective rainfall characteristics over the Indian landmass are found to be consistent with the monsoon precipitation climatology. It is shown that the change in both convective and non-convective rainfall due to aerosols and chemistry is non-negligible over India during monsoon season. The total rainfall is found to increase significantly over the entire Western Ghats and some part of northeast India, while it is diminished over the northwest, north and east India when aerosol chemistry effects are considered in the model simulation. Additional analysis is performed to simulate the perturbations in convective and non-convective rainfall due to aerosols (e.g., dust, sea salt, black carbon etc.). Results show that the effect of aerosols on convective and non-convective rainfall distribution over India is non-linear. Depending on the meteorological conditions, topography, and the type of aerosol, the aerosol impact and feedback on monsoon rainfall can be positive, negative, or neutral.

Magnetotelluric investigation of lithospheric electrical structure beneath the Dharwar Craton in south India: Evidence for mantle suture and plume-continental interaction

Broad-band and long period magnetotelluric measurements made at 63 locations along ∼500 km long Chikmagalur-Kavali profile, that cut across the Dharwar craton (DC) and Eastern Ghat Mobile Belt (EGMB) in south India, is modelled to examine the lithosphere architecture of the cratonic domain and define tectonic boundaries. The 2-D resistivity model shows moderately conductive features that intersperse a highly resistive background of crystalline rocks and spatially connect to the exposed schist belts or granitic intrusions in the DC. These features are therefore interpreted as images of fossil pathways of the volcanic emplacements associated with the greenstone belt and granite suite formation exposed in the region. A near vertical conductive feature in the upper mantle under the Chitradurga Shear Zone represents the Archean suture between the western and eastern blocks of DC. Although thick (∼200 km) cratonic (highly resistive) lithosphere is preserved, significant part of the cratonic lithosphere below the western DC is modified due to plume-continental lithosphere interactions during the Cretaceous–Tertiary period. A west-verging moderately conductive feature imaged beneath EGMB lithosphere is interpreted as the remnant of the Proterozoic collision process between the Indian land mass and East Antarctica. Thin (∼120 km) lithosphere is seen below the EGMB, which form the exterior margin of the India shield subsequent to its separation from East Antarctica through rifting and opening of the Indian Ocean in the Cretaceous.

Isotopic investigation of the moisture transport processes over the Bay of Bengal

To study the atmospheric moisture transport processes from the source to a receiver region, isotopic analysis of rainwater from Port Blair (as source region), the Andaman Islands, Bay of Bengal has been carried out. In addition to the island site, rainwater collected at three sites on the Indian mainland (as receiver region) namely Nagpur, Kolkata, and Tezpur has also been isotopically analyzed. We present a daily variation of long-term (2012–2015) record of rain isotope from Port Blair to understand the moisture dynamics on a sub-seasonal timescale. It was observed that the Port Blair rainwater oxygen isotope ratios (δ18O) maintain a temporally dependent correlation with the average rainfall over the Core Monsoon Zone (CMZ) of India, though the seasonal rainfall over these two regions appears to be mutually independent. Rain isotopes are controlled more by the moisture dynamics rather than the individual rainfall events. Consequently, the correlation between rainfall over the CMZ and δ18O of Port Blair rain provides conclusive evidence of the transport of the Bay of Bengal (BoB) moisture to the central and the northeast Indian regions during the summer monsoon season. The spatial dependency of Port Blair rain-isotopes with the CMZ rain shows interannual variability and also indicates different pathways of the BoB moisture to the Indian mainland within a given season. The pathways of the source moisture to the receiver are identified by the trajectory analysis with Port Blair being the source area. We observed analogous variation in δ18O of island rain and that of the mainland rain, and δ18O at these two regions is modulated by the monsoon intra-seasonal oscillation (MISO). The correlation between the two isotopic records appears to arise from the propagation of the rain/cloud band from the Bay to the Indian landmass and the associated moisture transport linked to the MISO.

Contrasting monthly trends of Indian summer monsoon rainfall and related parameters

Recent studies have reported contrasting inferences in the variability and trends of Indian summer monsoon rainfall (ISMR). These studies have analysed the ISMR variability from a seasonal perspective. The present study observed the monthly ISMR trends from June to September for the period 1980–2015.The results show a significant contrasting trend of rainfall over India (in the heavy, moderate as well as low rainfall regions) in each month of the summer season. A significant decline of rainfall is occurring in June over the monsoon onset regions of the southwest coast of India. The rainfall trend over India exhibits a pattern similar to active type (above normal rainfall over central India and below normal in the foothills of Himalayas and southeast India) in July and September, conversely, a pattern similar to break type occurs in August. The monthly variability of summer rainfall is due to the changing pattern of low pressure over the Indian landmass and the associated modulation of zonal and meridional moisture flow as well as low-level vertical motion. The study also observes widespread spatial variability in the monthly trends of ISMR and concludes that the seasonal trend analysis does not reveal the actual pattern in the monthly trends of ISMR.

SEASONAL AND SPATIAL VARIABILITY OF OZONE INFERRED FROM GLOBAL CHEMISTRY TRANSPORT MODEL SIMULATIONS OVER INDIA

Abstract. In the present study, 3-D chemical transport model, MOZART-4 (Model for Ozone and Related chemical Tracers-Version-4) has been used to study the seasonal and spatial distribution of surface ozone (O3) over India. To illustrate the capabilities of model, the simulations are compared with the ground-based observations. The model reproduces the principal features present in ground-based observations. However, model is unable to simulate very low concentration of O3 during monsoon months. The model simulations are used to quantify the contribution of background ozone and Indian anthropogenic emissions to the variability of surface O3. The spatial distribution of total O3 (TO) shows maximum over Indo-Gangetic plains (IGP) and Eastern India while minimum over southern Indian region. The seasonal cycle of TO vary from 34.2 ± 7.6 to 51.9 ± 4.9 ppbv over the Indian landmass region due to changes in its topography and ozone lifetime. Annual mean total background O3 (TBO) over India shows highest during spring (29.3 ± 5.0 ppbv) and lowest during monsoon (19.6 ± 3.4 ppbv). Both Natural background O3 (NBO) and pollution background O3 (PBO) shows a minimum in summer which are essentially following the seasonal changes of total ozone. Significant variation of India pollution O3 (IPO) is found over India and the spatial variation of IPO follows the spatial variation of TO as well as spatial variation of emission of ozone precursors.

The geological evolution of the Gangpur Schist Belt, eastern India: Constraints on the formation of the Greater Indian Landmass in the Proterozoic

AbstractThe Central Indian Tectonic Zone (CITZ) is a Proterozoic suture along which the Northern and Southern Indian Blocks are inferred to have amalgamated forming the Greater Indian Landmass. In this study, we use the metamorphic and geochronological evolution of the Gangpur Schist Belt (GSB) and neighbouring crustal units to constrain crustal accretion processes associated with the amalgamation of the Northern and Southern Indian Blocks. The GSB sandwiched between the Bonai Granite pluton of the Singhbhum craton and granite gneisses of the Chhotanagpur Gneiss Complex (CGC) links the CITZ and the North Singhbhum Mobile Belt. New zircon age data constrain the emplacement of the Bonai Granite at 3,370 ± 10 Ma, while the magmatic protoliths of the Chhotanagpur gneisses were emplaced at c. 1.65 Ga. The sediments in the southern part of the Gangpur basin were derived from the Singhbhum craton, whereas those in the northern part were derived dominantly from the CGC. Sedimentation is estimated to have taken place between c. 1.65 and c. 1.45 Ga. The Upper Bonai/Darjing Group rocks of the basin underwent major metamorphic episodes at c. 1.56 and c. 1.45 Ga, while the Gangpur Group of rocks were metamorphosed at c. 1.45 and c. 0.97 Ga. Based on thermobarometric studies and zircon–monazite geochronology, we infer that the geological history of the GSB is similar to that of the North Singhbhum Mobile Belt with the Upper Bonai/Darjing and the Gangpur Groups being the westward extensions of the southern and northern domains of the North Singhbhum Mobile Belt respectively. We propose a three‐stage model of crustal accretion across the Singhbhum craton—GSB/North Singhbhum Mobile Belt—CGC contact. The magmatic protoliths of the Chhotanagpur Gneisses were emplaced at c. 1.65 Ga in an arc setting. The earliest accretion event at c. 1.56 Ga involved northward subduction and amalgamation of the Upper Bonai Group with the Singhbhum craton followed by accretion of the Gangpur Group with the Singhbhum craton–Upper Bonai Group composite at c. 1.45 Ga. Finally, continent–continent collision at c. 0.96 Ga led to the accretion of the CGC with the Singhbhum craton–Upper Bonai Group–Gangpur Group crustal units, synchronous with emplacement of pegmatitic granites. The geological events recorded in the GSB and other units of the CITZ only partially overlap with those in the Trans North China Orogen and the Capricorn Orogen of Western Australia, indicating that these suture zones are not correlatable.

On the connection between remote dust aerosol and Indian summer monsoon

Understanding of interaction between remote dust aerosol and Indian summer monsoon (ISM) remains dubious in literature because of wide disagreement among previous studies. This problem is revisited using version-2 of Modern-Era Retrospective Analysis for Research and Applications (MERRA-2) datasets. ISM variability at intraseasonal timescale is not constrained by the changes in dust aerosols over the most parts of West Asia and North Africa. A new hypothesis is proposed to explain covariability of dust over the Arabian Sea and ISM circulation. Large-scale forcing modulates monsoon intraseasonal oscillations (ISOs) and creates active-like condition over the Indian landmass extending up to the Arabian Sea and the Arabian Peninsula. Organized convection induces anomalous southwesterly and northwesterly circulation as a response to enhanced latent heating. Enhanced northwesterly winds strengthen transport of dust over the Arabian Sea. Augmented dust forcing and associated warming over the Arabian Sea is unlikely to create a positive feedback because of its limited spatial extent. Findings of the present study provide a new insight into remote dust-ISM connection problem and the hypothesis proposed differs considerably from the previously proposed hypotheses.

Investigation of a regional ozone reduction event over eastern India by integrating in situ and satellite measurements with WRF-Chem simulations

This study examines various physical and chemical processes contributing towards an anomalous low surface ozone (O3) event at a tropical urban site Bhubaneswar (20.29° N, 85.83° E) located in eastern India. Surface O3 generally peaks during winter (~ 40 ppbv) at Bhubaneswar. However, during 5–11 December 2010, surface O3 decreased rapidly from 48°ppbv on December 4 to 14°ppbv on December 6. Average surface O3 concentration before and after the event was 50.4 ± 5.8 ppbv and 47.8 ± 2.4 ppbv, respectively, with two-day running mean ranging from 15.5 to 30.5 ppbv during the event. This event is analyzed using in situ surface O3, meteorological parameters, backward air trajectories, and simulations using the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem). Our analysis shows that this low O3 event was driven by advection of cleaner low O3 marine masses to Bhubaneswar associated with a rare low-pressure event over Bhubaneswar (occurred only once in winter during 2005–2014). Analysis of modeled spatial distribution of surface O3 showed that this event was not confined to Bhubaneswar only and significantly reduced surface O3 over a large area comprising most of the Indian land mass, the Bay of Bengal (BOB), and Burma as well. The study elucidates the importance of transport processes in controlling trace gas levels and highlights the advantage of Bhubaneswar as a strategic location to study atmospheric chemistry in contrasting air masses, i.e., polluted air masses from the Indo-Gangetic Plain (IGP) versus pristine air masses from the BOB.

Retrieval of Aerosol Optical Depth From INSAT‐3D Imager Over Asian Landmass and Adjoining Ocean: Retrieval Uncertainty and Validation

AbstractAn algorithm for aerosol optical depth (τ) retrieval from imager data onboard geostationary Indian National Satellite (INSAT‐3D) is described. The basic principles of the algorithm are adopted from Geostationary Observational Environmental Satellite Aerosol and Smoke Algorithm, where darkest observations over a time period and constant background aerosol optical depth (τb) value are used to derive surface reflectance. However, in INSAT‐3D algorithm spatially and temporally dynamic τb derived from Moderate Resolution Imaging Spectroradiometer (MODIS)‐aqua is used. The theoretical simulations suggest retrieval uncertainty of around ±30–45% depending on the certainty of aerosol optical properties and other parameters used in radiative transfer calculations. Retrieval uncertainty is less over dark regions and lower scattering angles. INSAT‐3D τ at 0.55 μm is derived operationally for the first time over Asia and adjoining ocean at 30‐min temporal resolution. The retrieval algorithm is validated against in situ Sun‐sky radiometer measurements at 26 Aerosol Robotic Network sites and Sun‐photometer measurements during Sagar‐Sampada cruise in the northern Arabian Sea. The validation study encompassing 3,803 and 844 data points over land and ocean stations show correlations ranging from 0.70 to 0.91 and 0.79 to 0.91, respectively. The uncertainty of retrievals is within 45% over land and within 30% over ocean. The diurnal variability of INSAT‐3D and Aerosol Robotic Network τ in India and southeast Asia is also presented. The comparison of INSAT‐3D and MODIS‐aqua monthly average τ shows correlation ranging from 0.74 to 0.89 and 0.65 to 0.97 over Indian landmass and adjoining ocean, respectively. The validation suggests that INSAT‐3D can be used for aerosol monitoring and can be merged with MODIS‐aqua/terra aerosol product to generate combined aerosol product at high temporal resolution.

RegCM4 model sensitivity to horizontal resolution and domain size in simulating the Indian summer monsoon

The sensitivity to model resolution and domain size of the regional climate model RegCM4 is examined in simulating a deficit (1987), excess (1988), and normal (1989) Indian summer monsoon (ISM) rainfall. The initial and boundary conditions are prescribed by the European Centre for Medium-Range Weather Forecasts (ECMWF) Interim reanalysis at 1.5° × 1.5° (EIN15). The model simulated precipitation is compared with India Meteorological Department (IMD) gridded precipitation data (0.25° × 0.25°) and other parameters are compared with EIN15. In the present study, eight different horizontal resolutions such as 60, 55, 50, 45, 40, 36, 27 and 18 km are used whereas four different domain sizes (D01, D02, D03, and D04; largest to smallest) centered at the Indian landmass are considered to investigate the model performance.Results illustrate that the RegCM4 has the capability to depict the important semi-permanent features of the ISM, however, skills vary with the resolutions and domain sizes. Experiments with different resolutions reveal that the lower (850 hPa) and upper (200 hPa) tropospheric circulations are stronger over the Arabian Sea and Bay of Bengal in the 36 and 40 km grid-spacing simulations and closer to EIN15, however, it is weaker in the high-resolution simulations at 27 and 18 km grid-spacing. The biases in vertically integrated moisture transport (VIMT) are positive in the model simulations with resolutions from 36 to 60 km, but, it is negative with 27 and 18 km grid resolution. The simulated precipitation intensity increases as one moves from coarse to higher resolution till grid spacing 36 km. The model efficiency reduces to simulate higher precipitation intensity over the maximum precipitation zones of India during summer monsoon season when grid spacing 27 km and 18 km are used. The overall performance is better with the use of 36–40 km grid spacing than other resolutions in simulating ISM and associated rainfall. The sensitivity of domain sizes is examined by confining the model resolution at 40 km. The model simulated meteorological parameters, as well as derived parameters (such as pattern and intensity of precipitation, geopotential height, relative humidity, air temperature, wind, and CAPE), are represented better in D02 than other domains. The present study proposes a Comprehensive Rating Matrices (CRM) to evaluate the model performance considering all experiments (horizontal resolution and domain size) and different homogeneous regions, including errors obtained using different statistical methods. The CRM and statistical based skill score (SS) suggest that the performance of RegCM4 is the best at 40 km horizontal resolution followed by 36 km and 45 km grid-spacing and the D02 domain is suitable for ISM simulation.

Eastern Ghats Belt, Grenvillian-Age Tectonics and the Evolution of the Greater Indian Landmass: A Critical Perspective

The configuration of the Greater Indian Landmass was achieved during the late Proterozoic era (Grenvillian-age) through tectonic cycles involving cratonic blocks of India and East Antarctica in the broad framework of the assembly of the supercontinent Rodinia. Geological evidences are recorded from orogenic belts separating southern, northern and western cratonic blocks of India and its transcontinental neighbor East Antarctica. Eastern Ghats Belt of India played a pivotal role in the continental amalgamation process and it evolved in tandem with the Central Indian Tectonic Zone and the Aravalli Delhi Mobile Belt. We have collated geological and geochronological evidences from the cratonic blocks and the bounding orogenic belts to trace back the Grenvillian-age tectonics surrounding India and its eventual manifestation as the configuration of the Greater Indian Landmass. The status of the Greater Indian Landmass as a part of Rodinia is debated and unresolved issues are highlighted.