Semi-empirical model for retrieval of soil moisture using RISAT-1 C-Band SAR data over a sub-tropical semi-arid area of Rewari district,Haryana (India)

We have estimated soil moisture (SM) by using circular horizontal polarization backscattering coefficient (\(\sigma ^{\mathrm{o}}_{\mathrm{RH}}\)), differences of circular vertical and horizontal \(\sigma ^{\mathrm{o}} \, (\sigma ^{\mathrm{o}}_{\mathrm{RV}} {-} \sigma ^{\mathrm{o}}_{\mathrm{RH}})\) from FRS-1 data of Radar Imaging Satellite (RISAT-1) and surface roughness in terms of RMS height (\({\hbox {RMS}}_{\mathrm{height}}\)). We examined the performance of FRS-1 in retrieving SM under wheat crop at tillering stage. Results revealed that it is possible to develop a good semi-empirical model (SEM) to estimate SM of the upper soil layer using RISAT-1 SAR data rather than using existing empirical model based on only single parameter, i.e., \(\sigma ^{\mathrm{o}}\). Near surface SM measurements were related to \(\sigma ^{\mathrm{o}}_{\mathrm{RH}}\), \(\sigma ^{\mathrm{o}}_{\mathrm{RV}} {-} \sigma ^{\mathrm{o}}_{\mathrm{RH}}\) derived using 5.35 GHz (C-band) image of RISAT-1 and \({\hbox {RMS}}_{\mathrm{height}}\). The roughness component derived in terms of \({\hbox {RMS}}_{\mathrm{height}}\) showed a good positive correlation with \(\sigma ^{\mathrm{o}}_{\mathrm{RV}} {-} \sigma ^{\mathrm{o}}_{\mathrm{RH}} \, (R^{2} = 0.65)\). By considering all the major influencing factors (\(\sigma ^{\mathrm{o}}_{\mathrm{RH}}\), \(\sigma ^{\mathrm{o}}_{\mathrm{RV}} {-} \sigma ^{\mathrm{o}}_{\mathrm{RH}}\), and \({\hbox {RMS}}_{\mathrm{height}}\)), an SEM was developed where SM (volumetric) predicted values depend on \(\sigma ^{\mathrm{o}}_{\mathrm{RH}}\), \(\sigma ^{\mathrm{o}}_{\mathrm{RV}} {-} \sigma ^{\mathrm{o}}_{\mathrm{RH}}\), and \({\hbox {RMS}}_{\mathrm{height}}\). This SEM showed \(R^{2}\) of 0.87 and adjusted \(R^{2}\) of 0.85, multiple R=0.94 and with standard error of 0.05 at 95% confidence level. Validation of the SM derived from semi-empirical model with observed measurement (\({\hbox {SM}}_{\mathrm{Observed}}\)) showed root mean square error (RMSE) = 0.06, relative-RMSE (R-RMSE) = 0.18, mean absolute error (MAE) = 0.04, normalized RMSE (NRMSE) = 0.17, Nash–Sutcliffe efficiency (NSE) = 0.91 (\({\approx } 1\)), index of agreement (d) = 1, coefficient of determination \((R^{2}) = 0.87\), mean bias error (MBE) = 0.04, standard error of estimate (SEE) = 0.10, volume error (VE) = 0.15, variance of the distribution of differences \(({\hbox {S}}_{\mathrm{d}}^{2}) = 0.004\). The developed SEM showed better performance in estimating SM than Topp empirical model which is based only on \(\sigma ^{\mathrm{o}}\). By using the developed SEM, top soil SM can be estimated with low mean absolute percent error (MAPE) = 1.39 and can be used for operational applications.     

Characteristics of surface ozone in Agra,a sub-urban site in Indo-Gangetic Plain

In the present study, measurements of surface ozone (\(\hbox {O}_{3}\)) and its precursors (NO and \(\hbox {NO}_{2}\)) were carried out at a sub-urban site of Agra (\(27{^{\circ }}10'\hbox {N}\), \(78{^{\circ }}05'\hbox {E}\)), India during May 2012–May 2013. During the study period, average concentrations of \(\hbox {O}_{3}\), NO, and \(\hbox {NO}_{2}\) were \(39.6 \pm 25.3\), \(0.8 \pm 0.8\) and \(9.1 \pm 6.6 \, \hbox {ppb}\), respectively. \(\hbox {O}_{3}\) showed distinct seasonal variation in peak value of diurnal variation: summer \({>}\) post-monsoon \({>}\) winter \({>}\) monsoon. However, \(\hbox {NO}_{2}\) showed highest levels in winter and lowest in monsoon. The average positive rate of change of \(\hbox {O}_{3}\) (08:00–11:00 hr) was highest in April (16.3 ppb/hr) and lowest in August (1.1 ppb/hr), while average negative rate of change of \(\hbox {O}_{3}\) (17:00–19:00 hr) was highest in December (–13.2 ppb/hr) and lowest in July (–1.1 ppb/hr). An attempt was made to identify the \(\hbox {VOC--NO}_{\mathrm{x}}\) sensitivity of the site using \(\hbox {O}_{3}/\hbox {HNO}_{3}\) ratio as photochemical indicator. Most of the days this ratio was above the threshold value (12–16), which suggests \(\hbox {NO}_{\mathrm{x}}\) sensitivity of the site. The episodic event of ozone was characterized through meteorological parameters and precursors concentration. Fine particles (\(\hbox {PM}_{2.5}\)) cause loss of ozone through heterogeneous reactions on their surface and reduction in solar radiation. In the study, statistical analyses were used to estimate the amount of ozone loss.     

Principle of Formation of the Earth’s Crust under Natural Stress Conditions

This article formulates the experimentally substantiated physical principle that the natural stress condition of the Earth’s crust is formed due to the superposition of stress fields, which is caused by the gravitational forces of the Earth and by tectonic and astrophysical forces that are produced by physical processes in space. The natural stress field is represented by the stress tensor regulatory components: \(\sigma _{z}^{{\text{N}}}\) = \( - \gamma H + {{\sigma }_{{zT}}} + {{\sigma }_{{z{\text{AF}}}}}\), \(\sigma _{x}^{{\text{N}}}\) = \( - \lambda \gamma H + {{\sigma }_{{xT}}} + {{\sigma }_{{x{\text{AF}}}}}\), \(\sigma _{y}^{{\text{N}}}\) = \( - \lambda \gamma H + {{\sigma }_{{yT}}} + {{\sigma }_{{y{\text{AF}}}}}\).     

Stress-dependent hydraulic properties of clayey-silt aquitards in eastern Australia

Clayey-silt aquitards account for 60 % of the ~100-m-thick alluvial sediment sequence in the Gunnedah area of eastern Australia. To better understand the stress-dependent hydraulic properties of these low-permeability units, oedometer test data presented for the first time in this study have been integrated with geotechnical centrifuge permeameter tests. Estimates of vertical pre-consolidation effective stress (\(\sigma_{\text{p}}^{'}\)), vertical in situ effective stress (\(\sigma_{\text{i}}^{'}\)), and over-consolidation ratio (OCR) were used to determine whether centrifugation stresses caused compression of core samples, and the degree to which vertical hydraulic conductivity (K _v) assessments were representative of the core samples tested. Results suggest that minimally disturbed drill core from semi-consolidated sediments (e.g., alluvial, colluvial, and eolian deposits) evaluated in this study should have target centrifugation stress less than \(\sigma_{\text{p}}^{'}, \) where OCR < 1 and \(\sigma_{\text{i}}^{'}\) where OCR > 1 to avoid significant changes in hydraulic properties during plastic straining. The results also imply that the stress-dependent response of aquitards is critical to understand the sensitivity of groundwater resources in areas with multiple stakeholders such as mining, coal seam gas, and agriculture developments. Groundwater in alluvial sediments that is essential for irrigation, water supply, and base flows to rivers must be sufficiently disconnected from groundwater in coal seams that are depressurized for extraction of energy resources.     

Competing effects of crystal chemistry and silicate melt composition on trace element behavior in magmatic systems: insights from crystal/silicate melt partitioning of the REE,HFSE, Sn,In, Ga,Ba, Pt and Rh

We present new partition coefficients for the REE, HFSE, Sn, In, Ga, Ba, Pt and Rh between clinopyroxene, olivine and basaltic melt as a function of crystal chemistry and melt composition at temperatures of 1190–1300 °C and 1-bar pressure. Two components, namely \(\mathrm {Al_2O_3}\) and \(\mathrm {Na_2O}\), were chosen to be investigated since they are known to affect the structure of silicate melts and especially clinopyroxene crystal chemistry. The amount of \(^{[4]}\mathrm{Al}\) in clinopyroxene will result in an increase of \(D_i^\mathrm{{cpx/melt}}\) even after applying a correction factor to account for the effect of melt polymerization. Moreover, the positive correlation between \(^{[4]}\mathrm{Al}\) and \(D_i^\mathrm{{cpx/melt}}\) is not restricted to the REE, but also applies for Sn, Ga, In, and Ba. The addition of up to 2.6 wt% \(\mathrm {Na_2O}\) to the silicate melt universally increases the \(D_i^\mathrm{{cpx/melt}}\) without any concomitant change in crystal chemistry or a significant effect in melt polymerization. This compositional effect is likely due to the ability of Na to break REE–Al complexes in the melt. Our results emphasize the importance of considering all variables that affect the behavior of trace elements in magmatic systems before applying the lattice strain model and derive meaningful results for the changes in the parameters of the crystallographic sites.     

Modeling competing hydraulic fracture propagation with the extended finite element method

We present an extended finite element framework to numerically study competing hydraulic fracture propagation. The framework is capable of modeling fully coupled hydraulic fracturing processes including fracture propagation, elastoplastic bulk deformation and fluid flow inside both fractures and the wellbore. In particular, the framework incorporates the classical orifice equation to capture fluid pressure loss across perforation clusters linking the wellbore with fractures. Dynamic fluid partitioning among fractures during propagation is solved together with other coupled factors, such as wellbore pressure loss (\(\Delta p_w\)), perforation pressure loss (\(\Delta p\)), interaction stress (\(\sigma _\mathrm{int}\)) and fracture propagation. By numerical examples, we study the effects of perforation pressure loss and wellbore pressure loss on competing fracture propagation under plane-strain conditions. Two dimensionless parameters \(\Gamma = \sigma _\mathrm{int}/\Delta p\) and \(\Lambda = \Delta p_w/\Delta p\) are used to describe the transition from uniform fracture propagation to preferential fracture propagation. The numerical examples demonstrate the dimensionless parameter \(\Gamma \) also works in the elastoplastic media.     

Comparison of earthquake source characteristics in the Kachchh Rift Basin and Saurashtra horst,Deccan Volcanic Province,western India

Seismic source parameters of small to moderate sized intraplate earthquakes that occurred during 2002–2009 in the tectonic blocks of Kachchh Rift Basin (KRB) and the Saurashtra Horst (SH), in the stable continental region of western peninsular India, are studied through spectral analysis of shear waves. The data of aftershock sequence of the 2001 Bhuj earthquake (\(M_{w}\) 7.7) in the KRB and the 2007 Talala earthquake (\(M_{w}\) 5.0) in the SH are used for this study. In the SH, the seismic moment (\(M_{o})\), corner frequency \((f_{c})\), stress drop (\(\varDelta \sigma \)) and source radius (r) vary from \(7.8\times 10^{11}\) to \(4.0\times \)10\(^{16}\) N-m, 1.0–8.9 Hz, 4.8–10.2 MPa and 195–1480 m, respectively. While in the KRB, these parameters vary from \(M_{o} \sim 1.24 \,\times \, 10^{11}\) to \(4.1 \times 10^{16}\) N-m, \(f_{c }\sim \) 1.6 to 13.1 Hz, \(\varDelta \sigma \sim 0.06\) to 16.62 MPa and \(r \sim 100\) to 840 m. The kappa (K) value in the KRB (0.025–0.03) is slightly larger than that in the SH region (0.02), probably due to thick sedimentary layers. The estimated stress drops of earthquakes in the KRB are relatively higher than those in SH, due to large crustal stress concentration associated with mafic/ultramafic rocks at the hypocentral depths. The results also suggest that the stress drop value of intraplate earthquakes is larger than the interplate earthquakes. In addition, it is observed that the strike-slip events in the SH have lower stress drops, compared to the thrust and strike-slip events.     

New paleomagnetic results on $$\sim $$2367 Ma Dharwar giant dyke swarm,Dharwar craton,southern India: implications for Paleoproterozoic continental reconstruction

Here we report new paleomagnetic results and precise paleopole position of the extensional study on \(\sim \)2367 Ma mafic giant radiating dyke swarm in the Dharwar craton, southern India. We have sampled 29 sites on 12 dykes from NE–SW Karimnagar–Hyderabad dykes and Dhone–Gooty sector dykes, eastern Dharwar craton to provide unambiguous paleomagnetism evidence on the spectacular radiating dyke swarm and thereby strengthening the presence of single magmatic event at \(\sim \)2367 Ma. A total of 158 samples were subjected to detailed alternating field and thermal demagnetization techniques and the results are presented here along with previously reported data on the same dyke swarm. The remanent magnetic directions are showing two components, viz., seven sites representing four dykes show component (A) with mean declination of \(94{{}^{\circ }}\) and mean inclination of \(-\,70{{}^{\circ }}\) (\(\hbox {k}=87\), \(\upalpha _{95}=10{{}^{\circ }}\)) and corresponding paleopole at \(16{{}^{\circ }}\hbox {N}\), \(41{{}^{\circ }}\hbox {E}\) (\(\hbox {dp}=15{{}^{\circ }}\) and \(\hbox {dm}=17{{}^{\circ }}\)) and 22 sites representing 8 dykes yielded a component (B) with mean declination of \(41{{}^{\circ }}\) and mean inclination of \(-\,21{{}^{\circ }}\) (\(\hbox {k}=41\), \(\upalpha _{95}=9{{}^{\circ }}\)) with a paleopole at \(41{{}^{\circ }}\hbox {N}\), \(200{{}^{\circ }}\hbox {E}\) (\(\hbox {dp}=5{{}^{\circ }}\) and \(\hbox {dm}=10{{}^{\circ }}\)). Component (A) results are similar to the previously reported directions from the \(\sim \)2367 Ma dyke swarm, which have been confirmed fairly reliably to be of primary origin. The component (B) directions appear to be strongly overprinted by the 2080 Ma event. The grand mean for the primary component (A) combined with earlier reported studies gives mean declination of \(97{{}^{\circ }}\) and mean inclination of \(-\,79{{}^{\circ }}\) (\(\hbox {k}=55\), \(\upalpha _{95}=3{{}^{\circ }}\)) with a paleopole at \(15{{}^{\circ }}\hbox {N}\), \(57{{}^{\circ }}\hbox {E}\) (\(\hbox {dp}=5{{}^{\circ }}\), \(\hbox {dm}=6{{}^{\circ }}\)). Paleogeographical position for the Dharwar craton at \(\sim \)2367 Ma suggests that there may be a chance to possible spatial link between Dharwar dykes of Dharwar craton (India), Widgemooltha and Erayinia dykes of Yilgarn craton (Australia), Sebanga Poort Dykes of Zimbabwe craton (Africa) and Karelian dykes of Kola-Karelia craton (Baltica Shield).     

Ionic conductivity in gem-quality single-crystal alkali feldspar from the Eifel: temperature,orientation and composition dependence

We measured the ion conductivity of single-crystal alkali feldspar originating from two different locations in the Eifel/Germany, named Volkesfeld and Rockeskyller sanidine and having potassium site fractions \(C_\mathrm{K}\) of 0.83 and 0.71, respectively. The dc conductivities resulting from electrochemical impedance spectroscopy over the temperature range of 300–900 \(^{\circ }\hbox {C}\) show a weak composition dependence but pronounced differences between the b-direction [\(\perp (010)\)] and \(c^{*}\)-direction [\(\perp (001)\)] of the monoclinic feldspar structure. Conductivity activation energies obtained from the observed linear Arrhenius plots are close to 1.2 eV in all cases, which is closely similar to the activation energies of the \(^{22}\mathrm{Na}\) tracer diffusivity in the same crystals. Taking into account literature data on K tracer diffusion and diffusion correlation effects, the present results point to a predominance of the interstitialcy mechanism over the vacancy mechanism in mass and charge transport on the alkali sublattice in potassium-rich alkali feldspar.     

Geochemical assessment of fluoride enrichment and nitrate contamination in groundwater in hard-rock aquifer by using graphical and statistical methods

This systematic study was carried out with objective to delineate the various sources responsible for \(\hbox {NO}_{3}^{-}\) contamination and \(\hbox {F}^{-}\) enrichment by utilizing statistical and graphical methods. Since Central Ground Water Board, India, indicated susceptibility of \(\hbox {NO}_{3}^{-}\) contamination and \(\hbox {F}^{-}\) enrichment, in most of the groundwater, \(\hbox {NO}_{3}^{-}\) and \(\hbox {F}^{-}\) concentration primarily observed \({>}45\) and \({>}1.5~\hbox {mg/L}\), respectively, i.e., higher than the permissible limit for drinking water. Water Quality Index (WQI) indicates \({\sim }22.81\%\) groundwater are good-water, \({\sim }71.14\%\) groundwater poor-water, \({\sim }5.37\%\) very poor-water and 0.67% unsuitable for drinking purpose. Piper diagram indicates \({\sim }59.73\%\) groundwater hydrogeochemical facies are Ca–Mg–\(\hbox {HCO}_{3 }\) water-types, \({\sim }28.19\%\) Ca–Mg–\(\hbox {SO}_{4}\)–Cl water-types, \({\sim }8.72\%\) Na–K–\(\hbox {SO}_{4}\)–Cl water-types and 3.36% Na–K–\(\hbox {HCO}_{3 }\) water-types. This classification indicates dissolution and mixing are mainly controlling groundwater chemistry. Salinity diagram indicate \({\sim }44.30\%\) groundwater under in low sodium and medium salinity hazard, \({\sim }49.66\%\) groundwater fall under low sodium and high salinity hazard, \({\sim }3.36\%\) groundwater fall under very-high salinity hazard. Sodium adsorption ratio indicates \({\sim }97\%\) groundwater are in excellent condition for irrigation. The spatial distribution of \(\hbox {NO}_{3}^{-}\) indicates significant contribution of fertilizer from agriculture lands. Fluoride enrichment occurs in groundwater through the dissolution of fluoride-rich minerals. By reducing the consumption of fertilizer and stress over groundwater, the water quality can be improved.     

Carbon dioxide,water vapour and energy fluxes over a semi-evergreen forest in Assam,Northeast India

The eddy covariance method is a powerful technique for quantification of \(\hbox {CO}_{2},\) \(\hbox {H}_{2}\)O and energy fluxes in natural ecosystems. Leaf area index (LAI) and its changes are significant drivers of \(\hbox {CO}_{2}\) and \(\hbox {H}_{2}\)O exchange in a forest ecosystem due to their role in photosynthesis. The present study reports the seasonal variation of \(\hbox {CO}_{2}\) and energy fluxes and their relationship with other meteorological parameters of a semi-evergreen primary forest of Kaziranga National Park, Assam, India during February 2016–January 2017. The diurnal pattern of half hourly average \(\hbox {CO}_{2 }\) fluxes over the forest was found to be mostly dominated by the incident photosynthetically active radiation. During the period of study, diurnal variations of \(\hbox {CO}_{2}\) flux showed a maximum value of \(-9.97\,\upmu \)mol \(\hbox {m}^{-2}\hbox {s}^{-1}\) in the month of June during summer which is also the beginning of the monsoon season. The monthly averaged diurnal \(\hbox {CO}_{2}\) flux and variation in LAI of the forest canopy closely followed each other. The annual net ecosystem exchange of the forest estimated from the \(\hbox {CO}_{2}\) flux data above the canopy is 84.21 g C \(\hbox {m}^{-2}\,\hbox {yr}^{-1}\). Further studies are in progress to confirm these findings. The estimated average annual evapotranspiration of the semi-evergreen forest is 2.8 ± 0.19 mm \(\hbox {day}^{-1}\). The study of partitioning of energy fluxes showed the dominance of latent heat fluxes over sensible heat fluxes. The energy balance closure was found to increase with an increase in instability and the highest closure of around 83% was noted under neutral conditions.     

Effect of solar flare on the equatorial electrojet in eastern Brazil region

The effect of solar flare, sudden commencement of magnetic storm and of the disturbances ring current on the equatorial electrojet in the Eastern Brazil region, where the ground magnetic declination is as large as \(20^{^{\circ }}\hbox {W}\) is studied based on geomagnetic data with one minute resolution from Bacabal during November–December 1990. It is shown that the mean diurnal vector of the horizontal field was aligned along \(2{^{\circ }}\hbox {E}\) of north at Huancayo and \(30{^{\circ }}\hbox {W}\) of north at Bacabal during the month of December 1990. Number of solar flares that occurred on 30 December 1990 indicated the direction of solar flare related \(\Delta H\) vector to be aligned along \(5{^{\circ }}\hbox {E}\) of north at Huancayo and \(28{^{\circ }}\hbox {W}\) of north at Bacabal. This is expected as the solar flare effects are due to the enhanced conductivity in the ionosphere. The SC at 2230 UT on 26 November 1990 produced a positive impulse in \(\Delta X\) and negative impulse in \(\Delta Y\) at Bacabal with \(\Delta H\) vector aligned along \(27{^{\circ }}\hbox {W}\) of north. At Huancayo the \(\Delta H\) vector associated with SC is aligned along \(8{^{\circ }}\hbox {E}\) of north, few degrees east to the alignment of the diurnal vector of H. The magnetic storm that followed the SC had a minimum Dst index of –150 nT. The corresponding storm time disturbance in \(\Delta X\) at Huancayo as well as at Bacabal were about –250 nT but \(\Delta Y\) at Bacabal was about +70 nT and very small at Huancayo, that give the alignment of the H vector due to ring current about \(16{^{\circ }}\hbox {W}\) of north at Bacabal and almost along N–S at Huancayo. Thus alignment of the \(\Delta H\) vector due to ring current at Bacabal is \(14{^{\circ }}\hbox {E}\) of the mean direction of \(\Delta H\) vector during December 1990. This is consistent with the direction of ring current dependent on the dipole declination at the ring current altitude which is about \(5{^{\circ }}\hbox {W}\) of north over Bacabal and the deviation of declination due to the ring current during disturbed period given by the angle (\(\psi \)-D).     

Application of environmental isotopes and hydrochemistry in the identification of source of seepage and likely connection with lake water in Lesser Himalaya,Uttarakhand, India

Oxygen (\({\updelta }^{18}\hbox {O}\)) and hydrogen (\({\updelta }^{2}\hbox {H}\) and \(^{3}\hbox {H}\)) isotopes of water, along with their hydrochemistry, were used to identify the source of a newly emerged seepage water in the downstream of Lake Nainital, located in the Lesser Himalayan region of Uttarakhand, India. A total of 57 samples of water from 19 different sites, in and around the seepage site, were collected. Samples were analysed for chemical tracers like \(\hbox {Ca}^{++}\), \(\hbox {Mg}^{++}\), \(\hbox {Na}^{+}\), \(\hbox {K}^{+}\), \({\hbox {SO}_{4}}^{--}\) and \(\hbox {Cl}^{-}\) using an Ion Chromatograph (Dionex IC-5000). A Dual Inlet Isotope Ratio Mass Spectrometer (DIIRMS) and an Ultra-Low Level Liquid Scintillation Counter (ULLSC), were used in measurements of stable isotopes (\({\updelta }^{2}\hbox {H}\) and \({\updelta }^{18}\hbox {O}\)) and a radioisotope (\(^{3}\hbox {H}\)), respectively. Results obtained in this study repudiate the possibility of any likely connection between seepage water and the lake water, and indicate that the source of seepage water is mainly due to locally recharged groundwater. The study suggests that environmental isotopes (\({\updelta }^{2}\hbox {H}\), \({\updelta }^{18}\hbox {O}\) and \(^{3}\hbox {H}\)) can effectively be used as ‘tracers’ in the detection of the source of seepage water in conjunction with other hydrochemical tracers, and can help in water resource management and planning.     

Near InfraRed Imaging Spectrograph (NIRIS) for ground-based mesospheric OH(6-2) and $$\hbox {O}_{2}$$(0-1) intensity and temperature measurements

This paper describes the development of a new Near InfraRed Imaging Spectrograph (NIRIS) which is capable of simultaneous measurements of OH(6-2) Meinel and \(\hbox {O}_{2}\)(0-1) atmospheric band nightglow emission intensities. In this spectrographic technique, rotational line ratios are obtained to derive temperatures corresponding to the emission altitudes of 87 and 94 km. NIRIS has been commissioned for continuous operation from optical aeronomy observatory, Gurushikhar, Mount Abu (\(24.6^{\circ }\hbox {N}\), \(72.8^{\circ }\hbox {E}\)) since January 2013. NIRIS uses a diffraction grating of 1200 lines \(\hbox {mm}^{-1}\) and 1024\(\times \)1024 pixels thermoelectrically cooled CCD camera and has a large field-of-view (FOV) of \(80^{\circ }\) along the slit orientation. The data analysis methodology adopted for the derivation of mesospheric temperatures is also described in detail. The observed NIRIS temperatures show good correspondence with satellite (SABER) derived temperatures and exhibit both tidal and gravity waves (GW) like features. From the time taken for phase propagation in the emission intensities between these two altitudes, vertical phase speed of gravity waves, \(c_{z}\), is calculated and along with the coherent GW time period ‘\(\tau \)’, the vertical wavelength, \(\lambda _{z}\), is obtained. Using large FOV observations from NIRIS, the meridional wavelengths, \(\lambda _{y}\), are also calculated. We have used one year of data to study the possible cause(s) for the occurrences of mesospheric temperature inversions (MTIs). From the statistics obtained for 234 nights, it appears that in situ chemical heating is mainly responsible for the observed MTIs than the vertical propagation of the waves. Thus, this paper describes a novel near infrared imaging spectrograph, its working principle, data analysis method for deriving OH and \(\hbox {O}_{2}\) emission intensities and the corresponding rotational temperatures at these altitudes, derivation of gravity wave parameters (\(\tau \), \(c_{z}\), \(\lambda _{z}\), and \(\lambda _{y})\), and results on the statistical study of MTIs that exist in the earth’s mesospheric altitudes.     

Fluvial geochemistry of Subarnarekha River basin,India

The fluvial geochemistry of the Subarnarekha River and its major tributaries has been studied on a seasonal basis in order to assess the geochemical processes that explain the water composition and estimate solute fluxes. The analytical results show the mildly acidic to alkaline nature of the Subarnarekha River water and the dominance of \(\hbox {Ca}^{2+}\) and \(\hbox {Na}^{+}\) in cationic and \(\hbox {HCO}_{3}^{-}\) and \({\hbox {Cl}}^{-}\) in anionic composition. Minimum ionic concentration during the monsoon and maximum concentration in the pre-monsoon seasons reflect concentrating effects due to decrease in the river discharge and increase in the base flow contribution during the pre-monsoon and dilution effects of atmospheric precipitation in the monsoon season. The solute acquisition processes are mainly controlled by weathering of rocks, with minor contribution from marine and anthropogenic sources. Higher contribution of alkaline earth \((\hbox {Ca}^{2+}{+}\,\hbox {Mg}^{2+})\) to the total cations \((\hbox {TZ}^{+})\) and high \((\hbox {Na}^{+}+\hbox {K}^{+})/\hbox {Cl}^{-}\), \((\hbox {Na}^{+}+\hbox {K}^{+})/\hbox {TZ}^{+}\), \(\hbox {HCO}_{3}^{-}/(\hbox {SO}_{4}^{2-}+\hbox {Cl}^{-})\) and low \((\hbox {Ca}^{2+}+\hbox {Mg}^{2+})/(\hbox {Na}^{+}+\hbox {K}^{+})\) equivalent ratios suggest that the Subarnarekha River water is under the combined influence of carbonate and silicate weathering. The river water is undersaturated with respect to dolomite and calcite during the post-monsoon and monsoon seasons and oversaturated in the pre-monsoon season. The pH–log \(\hbox {H}_{4}\hbox {SiO}_{4}\) stability diagram demonstrates that the water chemistry is in equilibrium with the kaolinite. The Subarnarekha River annually delivered \(1.477\times 10^{6}\) ton of dissolved loads to the Bay of Bengal, with an estimated chemical denudation rate of \(77\hbox { ton km}^{-2}\hbox { yr}^{-1}\). Sodium adsorption ratio, residual sodium carbonate and per cent sodium values placed the studied river water in the ‘excellent to good quality’ category and it can be safely used for irrigation.     

Indian summer monsoon forcing on the deglacial polar cold reversals

The deglacial transition from the last glacial maximum at \(\sim \)20 kiloyears before present (ka) to the Holocene (11.7 ka to Present) was interrupted by millennial-scale cold reversals, viz., Antarctic Cold Reversal (\(\sim \)14.5–12.8 ka) and Greenland Younger Dryas (\(\sim \)12.8–11.8 ka) which had different timings and extent of cooling in each hemisphere. The cause of this synchronously initiated, but different hemispheric cooling during these cold reversals (Antarctic Cold Reversal \(\sim \)3\(^{\circ }\hbox {C}\) and Younger Dryas \(\sim \)10\(^{\circ }\hbox {C}\)) is elusive because \(\hbox {CO}_{2}\), the fundamental forcing for deglaciation, and Atlantic meridional overturning circulation, the driver of antiphased bipolar climate response, both fail to explain this asymmetry. We use centennial-resolution records of the local surface water \(\delta ^{18}\hbox {O}\) of the Eastern Arabian Sea, which constitutes a proxy for the precipitation associated with the Indian Summer Monsoon, and other tropical precipitation records to deduce the role of tropical forcing in the polar cold reversals. We hypothesize a mechanism for tropical forcing, via the Indian Summer Monsoons, of the polar cold reversals by migration of the Inter-Tropical Convergence Zone and the associated cross-equatorial heat transport.     

Strain responses of frozen clay with thermal gradient under triaxial creep

Thermal gradient is one of the main features for the temperature distribution in artificial frozen shaft lining (FSL). The time-dependent strain responses and the corresponding heterogeneity characteristics of frozen soils with thermal gradient are of potential significance for stability assessment and prediction of FSL, especially of the FSL embedded in thick alluvium. A series of triaxial creep tests were carried out on frozen saturated clay under various thermal gradients and creep stresses. The experimental results indicated that the triaxial creep curves for frozen clay with thermal gradient exhibit viscous characteristics, and the creep rate \(\Delta \varepsilon_{\text{a}} /\Delta t\) decreases with the increase in creep time \(t\) and decrease in thermal gradient. The stress–strain curve under different \(t\) showed that the creep stress has a marked growth when axial strain \(\varepsilon_{\text{a}} \le 1\,\%\). However, when \(\varepsilon_{\text{a}} \ge 1\,\%\), the growth rate decreases gradually. The deviation between measured radial strain \(\varepsilon_{\text{r}}^{\text{m}}\) under the middle specimen section height SSH and the calculated radial strain \(\varepsilon_{\text{r}}^{\text{c}}\) from the volumetric strain increases following a unified equation with the increase in axial strain. The radial strain \(\varepsilon_{\text{r}}^{\text{f}}\) for frozen clay with thermal gradient after experiment increases with the increase in SSH, and the slope of \( \varepsilon_{\text{r}}^{\text{f}} - {\text{SSH}} \) curve is significantly dependent on the thermal gradient and creep stress. The variation of \(\varepsilon_{\text{r}}^{\text{m}} - \varepsilon_{\text{r}}^{\text{c }}\) during experiment and \(\varepsilon_{\text{r}}^{\text{f}}\) distribution after experiment are the macro-responses of internal micro-heterogeneities in frozen soils induced from thermal gradient, and are closely related to strain rate and its variation. These observations and findings provide an insight into the creep mechanism and the estimation method of creep deformation for frozen soils with thermal gradient.     

Mineral shock signatures in rocks from Dhala (Mohar) impact structure,Shivpuri district,Madhya Pradesh,India

A concrete study combining optical microscopy, Raman spectroscopy and X-ray diffractometry, was carried out on subsurface samples of basement granite and melt breccia from Mohar (Dhala) impact structure, Shivpuri district, Madhya Pradesh, India. Optical microscopy reveals aberrations in the optical properties of quartz and feldspar in the form of planar deformation feature-like structures, lowered birefringence and mosaics in quartz, toasting, planar fractures and ladder texture in alkali feldspar and near-isotropism in bytownite. It also brings to light incidence of parisite, a radioactive rare mineral in shocked granite. Raman spectral pattern, peak positions, peak widths and multiplicity of peak groups of all minerals, suggest subtle structural/crystallographic deviations. XRD data further reveals minute deviations of unit cell parameters of quartz, alkali feldspar and plagioclase, with respect to standard \({\upalpha }\)-quartz, high- and low albite and microcline. Reduced cell volumes in these minerals indicate compression due to pressure. The \(\hbox {c}_{0}/\hbox {a}_{0}\) values indicate an inter-tetrahedral angle roughly between \(120^{\mathrm{o}}\) and \(144^{\mathrm{o}}\), further pointing to a possible pressure maxima of around 12 GPa. The observed unit cell aberration of minerals may indicate an intermediate stage between crystalline and amorphous stages, thereby, signifying possible overprinting of decompression signatures over shock compression effects, from a shock recovery process.     

Thermodynamics and phonon dispersion of pyrope and grossular silicate garnets from ab initio simulations

The phonon dispersion and thermodynamic properties of pyrope (\(\hbox {Mg}_3\hbox {Al}_2\hbox {Si}_3\hbox {O}_{12}\)) and grossular (\(\hbox {Ca}_3\hbox {Al}_2\hbox {Si}_3\hbox {O}_{12}\) ) have been computed by using an ab initio quantum mechanical approach, an all-electron variational Gaussian-type basis set and the B3LYP hybrid functional, as implemented in the Crystal program. Dispersion effects in the phonon bands have been simulated by using supercells of increasing size, containing 80, 160, 320, 640, 1280 and 2160 atoms, corresponding to 1, 2, 4, 8, 16 and 27 \(\mathbf {k}\) points in the first Brillouin zone. Phonon band structures, density of states and corresponding inelastic neutron scattering spectra are reported. Full convergence of the various thermodynamic properties, in particular entropy (S) and specific heat at constant volume (\(C_\mathrm{{V}}\)), with the number of \(\mathbf {k}\) points is achieved with 27 \(\mathbf {k}\) points. The very regular behavior of the S(T) and \(C_\mathrm{{V}}(T)\) curves as a function of the number of \(\mathbf {k}\) points, determined by high numerical stability of the code, permits extrapolation to an infinite number of \(\mathbf {k}\) points. The limiting value differs from the 27-\(\mathbf {k}\) case by only 0.40 % at 100 K for S (the difference decreasing to 0.11 % at 1000 K) and by 0.29 % (0.05 % at 1000 K) for \(C_\mathrm{{V}}\). The agreement with the experimental data is rather satisfactory. We also address the problem of the relative entropy of pyrope and grossular, a still debated question. Our lattice dynamical calculations correctly describe the larger entropy of pyrope than grossular by taking into account merely vibrational contributions and without invoking “static disorder” of the Mg ions in dodecahedral sites. However, as the computed entropy difference is found to be larger than the experimental one by a factor of 2–3, present calculations cannot exclude possible thermally induced structural changes, which could lead to further conformational contributions to the entropy.