Equatorial Geophysical Research Laboratory

Tirunelveli, India

Equatorial Geophysical Research Laboratory

Tirunelveli, India
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Balan N.,National Institute for Space Research | Balan N.,Nagoya University | Tulasiram S.,Indian Institute of Geomagnetism | Kamide Y.,Nagoya University | And 5 more authors.
Earth, Planets and Space | Year: 2017

A computer program is developed to automatically identify the geomagnetic storms in Dst index by applying four selection criteria that minimize non-storm-like fluctuations. The program is used to identify the storms in Kyoto Dst and USGS Dst in 50 years (1958-2007). The identified storms (DstMin ≤ -50 nT) are used to investigate their seasonal variations. It is found that the overall seasonal variations of the storm parameters such as occurrence, average intensity (average DstMin) and average strength (average 〈DstMP〉) in both versions of Dst exhibit clear semiannual variations with equinoctial maxima and solstice minima; and the maxima and minima in intensity and strength (~±17% each) are less than those in occurrence (~±28%). Wavelet spectra of the storms reveal the existence of distinct semiannual component in four solar cycles (SCs 20-23) and weak longer and shorter-period components in some SCs. The semiannual variation observed also in the mean energy input during the main phase (MP) of the storms estimated from Dst is interpreted in terms of the (1) equinoctial mechanism based on the varying angle between the Earth-Sun line and Earth's dipole axis and (2) Russell-Mcpherron effect based on the varying angle between the GSM Z-axis and GSE Y-axis; and the yearly range of the dipole tilt angle μ (23.2°) involved in the equinoctial mechanism is found larger than the title angle θ (16.3°) involved in the RM effect.[Figure not available: see fulltext.] © 2017 The Author(s).


Sathishkumar S.,Equatorial Geophysical Research Laboratory | Sridharan S.,National Atmospheric Research Laboratory | Muhammed Kutty P.V.,Equatorial Geophysical Research Laboratory | Gurubaran S.,Indian Institute of Geomagnetism
Journal of Atmospheric and Solar-Terrestrial Physics | Year: 2017

The medium frequency radar deployed at Tirunelveli (8.7°N, 77.8°E), which is located near the southmost tip of peninsular India, have been providing continuous data from the year 1993 to the year 2012 that helped to study the long term tendencies in the lunar tidal variabilities over this geographic location. In the present paper we present the results of seasonal, interannual and long-term variabilities of lunar semi-diurnal tides in the upper mesosphere over Tirunelveli. The present study also includes comparison with model values. The study shows that the tidal amplitudes are larger in the meridional components of the mesospheric winds than the zonal winds. The seasonal variations of the tides are similar in both the components. The tides show maximum amplitudes of about ∼5 m/s in February/March, secondary maximum amplitudes of about ∼3 m/s in September and minimum amplitudes during summer months (May-August). The observed seasonal variation of the lunar tides do not compare well with Vial and Forbes (1994) model values, though it is consistent with earlier observations. The lunar tidal phase in meridional winds leads that in zonal winds from January to June and from September to November, while the latter leads the former during July/August. The lunar tides show large interannual variability. There are unusual amplitude enhancements in the lunar tide in meridional winds during the winters of 2006 and 2009, when major sudden stratospheric warmings (SSW) occurred at high latitude northern hemisphere, whereas zonal lunar tide does not show any clear association with the SSW. Vertical wavelengths of lunar tides in zonal and meridional wind are in the range of 20-90 km. The vertical wavelengths of lunar tides in both zonal and meridional component are smaller in June and larger in November and December. The monthly mean zonal and meridional winds are subjected to regression analysis to study the tidal response to long-period oscillations, namely, quasi-biennial oscillation (QBO), solar cycle variation and El-nino southern oscillation (ENSO). It is found the lunar tide in both zonal and meridional winds show significant QBO response, whereas zonal tide only shows significant negative response to solar cycle and positive response to ENSO. Besides, zonal tide only shows significant long-term increasing trend. © 2017 Elsevier Ltd.


Kumar K.N.,Indian Institute of Science | Taori A.,National Atmospheric Research Laboratory | Sathishkumar S.,Equatorial Geophysical Research Laboratory | Kamalakar V.,Sri Venkateswara University | And 5 more authors.
Journal of Geophysical Research: Space Physics | Year: 2012

In this paper we study the planetary-scale wave features using concurrent observations of mesospheric wind and temperature, ionospheric h'F, and tropospheric wind from Tirunelveli, Gadanki, and Kolhapur, all located in the Indian low latitudes, made during February 2009. Our investigations reveal that 3 to 5 day periodicity, characterized as ultrafast Kelvin (UFK) waves, was persistent throughout the atmosphere during this period. These waves show clear signatures of upward wave propagation from troposphere to the upper mesosphere, linking the ionosphere through a clear correlation between mesospheric winds and h'F variations. We also note that the amplitude of this wave decreased as we moved away from the equator. These results are the first of their kind from Indian sector, portraying the vertical as well as latitudinal characteristics of the 3 to 5 day UFK waves simultaneously from the troposphere to the ionosphere. © 2012. American Geophysical Union. All Rights Reserved.


Rao S.V.B.,Sri Venkateswara University | Eswaraiah S.,Sri Venkateswara University | Eswaraiah S.,Chungnam National University | Venkat Ratnam M.,National Atmospheric Research Laboratory | And 5 more authors.
Journal of Geophysical Research D: Atmospheres | Year: 2014

An advanced meteor radar, viz, Sri Venkateswara University (SVU) meteor radar (SVU MR) operating at 35.25 MHz, was installed at Sri Venkateswara University (SVU), Tirupati (13.63°N, 79.4°E), India, in August 2013 for continuous observations of horizontal winds in the mesosphere and lower thermosphere (MLT). This manuscript describes the purpose of the meteor radar, system configuration, measurement techniques, its data products, and operating parameters, as well as a comparison of measured mean winds in the MLT with contemporary radars over the Indian region. It is installed close to the Gadanki (13.5°N, 79.2°E) mesosphere-stratosphere-troposphere (MST) radar to fill the region between 85 and 100 km where this radar does not measure winds. The present radar provides additional information due to its high meteor detection rate, which results in accurate wind information from 70 to 110 km. As a first step, we made a comparison of SVU MR-derived horizontal winds in the MLT region with those measured by similar and different (MST and MF radars) techniques over the Indian region, as well as model (horizontal wind model 2007) data sets. The comparison showed an exquisite agreement between the overlapping altitudes (82-98 km) of different radars. Zonal winds compared very well, as did the meridional winds. The observed discrepancies and limitations in the wind measurement are discussed in the light of different measuring techniques and the effects of small-scale processes like gravity waves. This new radar is expected to play an important role in our understanding of the vertical and lateral coupling of different regions of the atmosphere that will be possible when measurements from nearby locations are combined. ©2014. American Geophysical Union. All Rights Reserved.


Behera J.K.,Indian Institute of Geomagnetism | Sinha A.K.,Indian Institute of Geomagnetism | Singh A.K.,National Institute of Oceanography of India | Rawat R.,Indian Institute of Geomagnetism | And 6 more authors.
Journal of Earth System Science | Year: 2014

Cosmic noise absorption (CNA) measurred by imaging riometer, is an excellent tool to passively study the high latitude D-region ionospheric conditions and dynamics. An imaging riometer has been installed at Indian Antarctic station Maitri (geographic 70.75°S, 11.75°E; corrected geomagnetic 63.11°S, 53.59°E) in February 2010. This is the first paper using the imaging riometer data from Maitri. The present paper introduces the details of this facility, including its instrumentation, related CNA theory and its applications. Sidereal shift of around 2 hours in the diurnal pattern validates the data obtained from the newly installed instrument. Moreover, the strength of cosmic noise signal on quiet days also varies with months. This is apparently due to solar ionization of D-region ionosphere causing enhanced electron density where collision frequency is already high. The main objective of installing the imaging riometer at Maitri is to study magneotspheric-ionospheric coupling during substorm processes. In the current study, we present two typical examples of disturbed time CNA associated with storm-time and non-storm time substorm. Results reveal that CNA is more pronounced during storm-time substorm as compared to nonstorm-time substorm. The level of CNA strongly depends upon the strengthening of convectional electric field and the duration of southward turning of interplanetary magnetic field before the substorm onset. © Indian Academy of Sciences.


Vineeth C.,Vikram Sarabhai Space Center | Pant T.K.,Vikram Sarabhai Space Center | Sumod S.G.,Vikram Sarabhai Space Center | Kumar K.K.,Vikram Sarabhai Space Center | And 2 more authors.
Journal of Geophysical Research: Space Physics | Year: 2011

Optically measured daylight mean mesopause temperatures over a dip equatorial station, Trivandrum (8.5° 77° dip lat. 0.5°), have been analyzed in conjunction with simultaneously measured equatorial electrojet (EEJ)-produced magnetic field at the surface. The signature of planetary wave-tidal interactions in the mesosphere-lower thermosphere (MLT) region has been observed for the first time in the day-to-day variability in the EEJ, i.e., the time of its peaking and the duration, as inferred from the EEJ-produced magnetic field on the ground. The present study shows that the planetary wave of quasi 16 day periodicity plays an important role in causing these variabilities, especially during the winter months. The quasi 16 day wave is found to be modulating the mesopause temperature (MT), duration, and time of the maximum EEJ intensity (DEEJ and TEEJ). During positive excursions of the planetary wave, TEEJ showed a shift toward evening, while the MT showed an increase and DEEJ showed a broadening. Similarly, all these parameters exhibited an opposite trend during negative excursions. The planetary wave-tidal interactions and subsequent modification of the tidal components have been shown to be responsible for the observed variations. This study presents a new perspective addressing the day-to-day variability of the EEJ. Copyright 2011 by the American Geophysical Union.


Vineeth C.,Vikram Sarabhai Space Center | Pant T.K.,Vikram Sarabhai Space Center | Gurubaran S.,Equatorial Geophysical Research Laboratory | Hossain M.M.,Vikram Sarabhai Space Center | Sridharan R.,Vikram Sarabhai Space Center
Earth, Planets and Space | Year: 2010

This paper deals with the variability of optically measured daytime OH temperatures during two different solar activity epochs, over Trivandrum (8.5°N, 76.5°E), a tropical station in India. The data used for the present study span the period of February-March, during the solar maximum year of 2001 and solar minimum year of 2005. The mean daytime temperature (180±5 K) during the 2001 study period was found to be lower than the mean temperature (195±9 K) of the 2005 study period by ∼15 K. However, apart from this noticeable shift in mean temperature level, the variabilities in the temperature of both years were strikingly similar. Moreover, the wave periodicities present during these periods were also quite similar. Possible reasons for these observations were investigated in the context of the various forcings that control the energetics of the equatorial mesopause region. The observations presented in this study are unique and reveal a number of newer aspects of the energetics of the tropical mesopause. Copyright © The Society of Geomagnetism and Earth, Planetary and Space Sciences (SGEPSS).

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