Apposite of atmospheric electric parameters with the energy coupling function (ε) during geomagnetic storms at high latitude     

C.P. Anil Kumar  C. Panneerselvam  K.U. Nair  H. Johnson Jeyakumar  C. Selvaraj  S. Gurubaran  C. Venugopal 《Atmospheric Research》2009,91(2-4):201-205

In this paper we are concerned with the variation of the atmospheric electric field and the air–earth current due to the excessive power generated by the solar wind-magnetosphere dynamo during geomagnetic storms, recorded at Maitri in Antarctica during 2004. A major part of the power generated by the solar wind-magnetosphere dynamo is used in the formation of the ring current and the rest is utilized for Joule heating and auroral particle precipitation. The method adopted by Frank-Kamenetsky et al. [Frank-Kamenetsky A.V., Troshichev O.A., Burns G.B., Papitashvili V.O., 2001. Variations of atmospheric electric field in the near-pole region related to the interplanetary magnetic field. J. Geophys. Res. 106, A1, 179–190.] was utilized to delineate the variations due to the signatures of tropical thunderstorm activity from the geoelectric data; while statistical methods used in our earlier studies were used to delimit variation due to the constant buffeting of the solar wind. We find that the solar wind-magnetosphere energy coupling function (ε) to be well correlated with the atmospheric electric parameters during the onset of geomagnetic disturbances. However the correlation breaks down during minor storms and sub-storm events.  相似文献   

Vertical structure of sea-breeze circulation over Thumba (8.5°N,?76.9°E,?India) in the winter months and a case study during W-ICARB field experiment     

T. J. Anurose  D. Bala Subrahamanyam  C. B. S. Dutt  N. V. P. Kiran Kumar  Sherine Rachel John  Sandhya K. Nair  M. Santosh  Mannil Mohan  P. K. Kunhikrishnan  S. Sijikumar  S. S. Prijith 《Meteorology and Atmospheric Physics》2012,115(3-4):113-121

This research article aims at characterization of the sea-breeze circulation over Thumba (8.5°N,?76.9°E,?India) in the winter season from December 2008 to February 2009, when this mesoscale circulation over the study domain was prominent. The characteristics of sea-breeze circulation cell comprising sea-breeze and compensatory return flow are investigated for clear-sky and cloudy days. The study indicated delayed onset of sea-breeze on the cloudy days as compared to the clear-sky days and the vertical thickness of sea-breeze circulation cell was found to be larger for the clear-sky days. Vertical thickness of the return flow for both clear-sky and cloudy days was larger than that of the sea-breeze flow. Simultaneous observations of upper-air meteorological parameters obtained through balloon-borne GPS sonde ascents carried out from Thumba and its adjoining coastal ocean on 29 January 2009 as part of the Winter phase of Integrated Campaign for Aerosols, gases and Radiation Budget (W-ICARB) are utilized for a case study towards investigation of diurnal evolution of the sea-breeze circulation cell. Results obtained from this study indicated systematic evolution of sea-breeze circulation over Thumba, however, it was not very clear over ocean which is attributed to cloudy conditions that prevailed on the day of measurement.  相似文献   

Laboratory technique for quantitative thermal emissivity measurements of geological samples     

George Mathew  Archana Nair  T. K. Gundu Rao  Kanchan Pande 《Journal of Earth System Science》2009,118(4):391-404

Thermal infrared spectroscopy is a powerful technique for the compositional analysis of geological materials. The spectral feature in the mid-IR region is diagnostic of the mineralogy and spectral signatures of mixtures of minerals that add linearly, and therefore, can be used as an important tool to determine the mineralogy of rocks in the laboratory and remotely for planetary exploration. The greatest challenge in the emission measurement lies in the measurement of the weak thermal photons emitted from geological materials in a laboratory setup, and accurately records the temperature of the rock sample. The present work pertains to the details of a new Thermal Emission Spectrometer (TES) laboratory that has been developed under the ISRO Planetary Science and Exploration (PLANEX) programme, for emission related mineralogical investigations of planetary surfaces. The focus of the paper is on the acquisition and calibration technique for obtaining emissivity, and the deconvolution procedure to obtain the modal abundances of the thermal emission spectra in the range of 6–25 μm using Fourier Transform Infrared (FTIR) spectroscopy. The basic technique is adopted from the work of Ruff et al (1997). This laboratory at the Department of Earth Sciences, IIT-Bombay is currently developing pure end mineral library of mineral particulates (<65 μm), and adding new end members to the existing ASU spectral library. The paper argues the need for considering Lunar Orbiter Thermal Emission Spectrometer (LOTES) for future Indian Moon mission programme (Chandrayan-II) to determine evidences of varied lithologies on the lunar surface.  相似文献   

Temperature dependent variation of pulsar periods     

M. C. Padmaraj  S. C. K. Nair 《Journal of Astrophysics and Astronomy》1985,6(3):165-169

Changes in the radii of neutron stars due to variations in core temperature are studied qualitatively in a simple model. The resulting irregular changes in pulsar periods are compared with observed values. For the millisecond pulsar PSR 1937 + 214 the random changes in period due to temperature variation is estimated to be of the order of 10^-14s yr^-1 which is two orders of magnitude smaller than the steady variation due to loss of energy by radiation.  相似文献   

Proper depiction of monsoon depression through IRS-P4 MSMR     

P. N. Mahajan  R. M. Khaladkar  S. G. Narkhedkar  Sathy Nair  P. C. Joshi  P. K. Pal 《Journal of Earth System Science》2004,113(2):223-233

In this paper, daily variations of satellite-derived geophysical parameters such as integrated water vapour (IWV), cloud liquid water content (CLW), sea surface temperature (SST) and sea surface wind speed (SSW) have been studied for a case of monsoon depression that formed over the Bay of Bengal during 19th-24th August 2000. For this purpose, IRS P4 MSMR satellite data have been utilized over the domain equator — 25‡N and 40‡-100‡E. An integrated approach of satellite data obtained from IRS-P4, METEOSAT-5 and INSAT was made for getting a signal for the development of monsoon depression over the Indian region. Variations in deep convective activity obtained through visible, infrared and OLR data at 06 UTC was thoroughly analyzed for the complete life cycle of monsoon depression. Geophysical parameters obtained through IRS-P4 satellite data were compared with vorticity, convergence and divergence at 850 and 200 hPa levels generated through cloud motion vectors (CMVs) and water vapour wind vectors (WVWVs) obtained from METEOSAT-5 satellite. This comparison was made for finding proper consistency of geophysical parameters with dynamical aspects of major convective activity of the depression. From the results of this study it is revealed that there was strengthening of sea surface winds to the south of low-pressure area prior to the formation of depression. This indicated the possibility of increase in cyclonic vorticity in the lower troposphere. Hence, wind field at 850 hPa with satellite input of CMVs in objective analysis of wind field using optimum interpolation (OI) scheme was computed. Maximum cyclonic vorticity field at 850 hPa was obtained in the region of depression just one day before its formation. Similarly, with the same procedure maximum anticyclonic vorticity was observed at 200 hPa with WVWVs input. Consistent convergence and divergence at 850 and 200 hPa was noticed with respect to these vorticities. In association with these developments, we could get lowest values of OLR (120 W/m² ) associated with major convective activity that was consistent with the maximum values of integrated water vapour (6-8gm/cm²) and cloud liquid water content (50-60 mg/cm² ) persisting particularly in the southwest sector of the monsoon depression.  相似文献   

IMPLICIT NONLINEAR NORMAL MODE INITIALIZATION: A MULTIGRID APPROACH          下载免费PDF全文

D. R. C. Nair  B. Chakravarty  P. Niyogi 《Acta Meteorologica Sinica》1993,7(1):19-30

The implicit nonlinear normal mode initialization (INMI) is applied to a tropical limited area shallow water model in spherical coordinates.The boundary condition for the INMI scheme is based on the boundary formulation of the model.The INMI scheme is found to be very efficient in suppressing spurious gravity wave oscillation and providing a well balanced initial data set for the model.The INMI scheme involves solving a number of elliptic type equations with varying complexity.and hence an efficient numerical technique is required for solving such equations.In order to make INMI computationally more attractive,we are employing the multigrid method for solving all the elliptic type equations in the INMI scheme.The numerical procedures for the development of such multigrid solvers are briefly described.  相似文献   

Hydrogeochemistry and water quality assessment of shallow aquifers in the western flanks of Southern Western Ghats,SW India     

Hema Chandrasekharan Nair  Damodaran Padmalal  Ammini Joseph  Vinod Padmakumari Gopinthan 《Arabian Journal of Geosciences》2018,11(4):73

The present study deals with the hydrogeochemistry and water quality of shallow aquifers in two important river basins—the Ithikkara and Kallada river basins—draining the south western flanks of Western Ghats in Kerala, South West India. Well water samples were collected from 20 dug wells with a depth range of 1 m below ground level (mbgl) to 18.2 mbgl during pre-monsoon, monsoon, and post-monsoon seasons of the year 2011–2012. These samples were analyzed for various physico-chemical parameters following standard methods and were evaluated for their interrelations and drinking water suitability. The pH of the water samples shows wide variation from highly acidic to highly alkaline water. About 80% of pre-monsoon samples recorded Fe²⁺ concentration above the permissible limit of drinking water standard. Water Quality Index (WQI) shows that majority of the well water samples fall in the category of excellent–good for drinking purpose. The results of the irrigation suitability assessment using the procedures like Percent Sodium, Sodium Absorption Ratio, Residual Sodium Carbonate, Kelly Index, Permeability Index, and Magnesium Hazard reveal that the well waters of the study area are fit for irrigation purpose. Na⁺/Cl^? ratio reflects the release of sodium to water due to silicate weathering. The samples have a Ca²⁺/Mg²⁺ ratio equal or greater than 2 indicating the effect of silicate minerals in contributing Ca²⁺ and Mg²⁺ ions to the well water. The saturation indices reveal that groundwater is supersaturated with SiO₂. Among the causative factors that determine the hydrochemical quality of well water samples, silicate weathering plays a pivotal role with significant input of ions from anthropogenic sources.  相似文献   

Diurnal variations of the low-level jet over peninsular India during the onset of Asian summer monsoon     

Sandhya K. Nair  Thara V. Prabha  N. Purushothaman  S. Sijikumar  S. Muralidharan  N. V. P. Kirankumar  D. B. Subrahamanyam  T. J. Anurose  S. S. Prijith  K. V. S. Namboodiri 《Theoretical and Applied Climatology》2015,120(1-2):287-298

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Seismic stratigraphy and the sedimentation history in the Laxmi Basin of the eastern Arabian Sea: Constraints from IODP Expedition 355     

Nisha Nair  Dhananjai K. Pandey  Anju Pandey  R. Prerna 《地学前缘(英文版)》2021,12(3):101111

Detailed interpretation of seismic stratigraphic sequences in the Laxmi Basin of the eastern Arabian Sea are presented in this study using closely spaced high resolution multi-channel seismic (MCS) data. Our stratigraphic interpretation is further corroborated using recent drilling results in the Laxmi Basin, derived from the long sediment cores collected during International Ocean Discovery Program (IODP) Expedition 355. Integrated core-log interpretation discussed in the present study, offer important insights about the lithostratigraphic variations in this region. Analyses of multi-channel seismic reflection data reveal five depositional sequences (ranging from Paleocene to Recent) that led to the development of this marginal basin since the Cenozoic period. Regional igneous basement is successfully imaged, which was also validated by deep sea coring during the IODP Expedition 355. In the present study, we primarily focus on the post-rift sedimentation in the Laxmi Basin and its possible mechanisms. Our detailed interpretation in the prevailing tectonic framework of the basin suggests that near-shelf oldest volcaniclastic sedimentation immediately overlying the acoustic basement is linked to the onset of India–Madagascar and India–Seychelles rifting activities during the Late Cretaceous period. Eventually, during the Early-Mid to Late Miocene, the basin received maximum sedimentation dominantly through an extensive mass transport mechanism implying possible large-scale deformation on the Indian shelf. Subsequent sediment input to the basin appears to have been fed variably via the Indus Fan as well as coastal discharge from the Indian mainland. The total sediment thickness in the Laxmi Basin ranges from 1.1 to 3.5 km. New stratigraphic information and sediment isopach maps presented here provide vital information about syn- and post-rift sedimentation pattern in the region and their long term tectonic implications.  相似文献   

Coastal Morphology and Long-term Shoreline Changes along the Southwest Coast of India     

L. Sheela Nair  R. Prasad  M. K. Rafeeque  T. N. Prakash 《Journal of the Geological Society of India》2018,92(5):588-595

The part of southwest coast of India extending from Poovar in the south to Kasaragod in the north is considered as one of the highly dynamic coastal areas of Indian peninsula. Over the years due to rapid urbanization as well as other natural and anthropogenic activities, the coast is under severe pressure which in turn has reduced the percentage status of healthy / stable coast. Unscientific shoreline protection methods adopted without conducting appropriate studies to assess the suitability of the said method to a particular coastal stretch has often led to negative impacts. As a result, many areas that were once stable have turned eroding and in certain cases, the observed extent of erosion is severe warranting immediate protection measures. In this context, a study was carried out to assess the long-term shoreline changes along the southwest coast and to decipher the causative factors responsible for these changes. Accordingly, a 46 year period from 1968 to 2014 was studied using multi-dated shoreline images and Survey of India (SOI) topographic charts. The DSAS software (USGS) is used to compute the rate of shoreline changes along different sectors of the coast and accordingly the entire coastal stretch is classified into 7 classes depicting the present status (stable / dynamically stable / unstable) of the coast. The analysis revealed that almost 60 % of the coastline is eroding with about 29 % showing an accreting trend.  相似文献