B. M. Pathan

Indian Institute of Geomagnetism, Mumbai, Mahārāshtra, India

Are you B. M. Pathan?

Claim your profile

Publications (65)71.12 Total impact

  • Earth Planets and Space 08/2014; · 2.92 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Systematic ground-based magnetometer measurements from Thumba (8.47°N, 76.6°E) and Tirunelveli (8.73°N, 77.8°E), India, revealed a movement of the magnetic dip equator towards the south. The magnetic dip angle measured over Thumba increased by about 2° during 1985–2010. In view of the movement of the dip equator over Thumba, the dependence of the generation of streaming plasma waves on the dip angle is examined. An order of magnitude calculation using the results obtained from the thin-shell model of the electrojet is performed. The calculation suggests that the streaming waves over Thumba during magnetically quiet periods at noontime exist when the dip angle is <1.5° and that these waves are generally absent whenever the dip angle is ≥1.5°. Evidence based on in situ rocket and ground-based radar measurements is provided by comparing earlier and recent observations.
    Journal of Atmospheric and Solar-Terrestrial Physics 10/2013; · 1.42 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Onset of a geomagnetic substorm often intensifies the westward auroral electrojet, as well as produces asymmetric magnetic field at low/mid latitudes. Auroral electrojet and low latitude asymmetric indices are known to correlate well during substorms. These indices have been widely used to monitor the duration and strength of substorm activities. However, several processes, other than substorms, introduce local time asymmetry in magnetic field at low latitudes, which can substantially influence the ASY indices. Large number of substorms are observed in association with changes in the interplanetary magnetic field (IMF). It is known that sharp IMF Bz orientation changes result in penetration of interplanetary electric field (IEF) to lower latitudes, which affects the geomagnetic fields to different degree in different local times. In the present study, we demonstrate that sharp IMF Bz fluctuations during the expansion phases of substorms introduce additional asymmetry at low latitudes. The effect is clearly seen in ASYH, whereas ASYD remains almost unaltered.
    Journal of Atmospheric and Solar-Terrestrial Physics 03/2013; · 1.42 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: 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 degree S, 11.75 degree E; corrected geomagnetic 63.11 degree S, 53.59 degree E) in February 2010. This is the first paper using the imaging Riometer data from Maitri. Present paper introduces the detail 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 non-storm time substorm. The level of CNA strongly depends upon the strengthening of convectional electric field and the duration of south-ward turning of interplanetary magnetic field before the substorm onset.
    Journal of Earth System Science 01/2013; · 0.70 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: [1] Systematic investigations of optical dayglow emissions at OI 557.7, OI 630.0, and OI 777.4 nm have been carried out simultaneously over a large field of view (~140°). These emission intensities are obtained during January–March in the years 2011 and 2012 from Hyderabad (17.5°N, 78.5°E), India, using a high spectral resolution multiwavelength imaging echelle spectrograph. Spectral analyses of planetary wave type periodicities in all the dayglow emission intensities are performed, and their association with lower atmospheric and direct solar forcings is presented. This analysis revealed that periods near the atmospheric free normal modes of 5, 10, 16, and 25 days (which are produced mainly in the troposphere) are found to register their presence in the upper atmospheric emission intensities. In an earlier study during high solar activity period (2001), sunspot numbers (SSNs) and the daily averaged OI 630.0 nm dayglow intensities were seen to be covarying. In contrast, the variability in the dayglow emission intensities during relatively low solar activity epoch (2011) shows no or weaker correlation with that of the SSN but a greater similarity with that of the equatorial electrojet strength. Periodicities of both lower atmospheric normal modes and those related to sunspots are found during moderate solar activity (2012). Based on this analysis, it appears that the upper atmospheric dayglow emissions respond mainly to lower atmospheric forcing during low solar activity, solar forcing in high solar activity, and both during moderate solar activity level.
    Journal of Geophysical Research 01/2013; 118(7):4618–4627. · 3.17 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The present investigation brings out, in contrast to the earlier works, the changes in the equatorial electrojet (EEJ) current in response to a few moderate (M-class) and low (C and B class) intensity solar flares during 2005–2010. Special care is taken to pick these flare events in the absence of prompt electric field perturbations associated with geomagnetic storms and substorms that also affect the electrojet current. Interestingly, only the normalized (with respect to the pre-flare level) deviations of daytime EEJ (and not the deviations alone) change linearly with the increases in the EUV and X-ray fluxes. These linear relationships break down during local morning hours when the E-region electric field approaches zero before reversal of polarity. This elicits that the response of EEJ strength corresponding to less-intense flares can be appropriately gauged only when the local time variation of the quiet time E-region zonal electric field is taken into account. The flare events enhanced the EEJ strength irrespective of normal or counter electrojet (CEJ) conditions that shows that solar flares change the E-region ionization density and not the electric field. In addition, the enhancements in the X-ray and EUV fluxes, for these flares occurring during this solar minimum period, are found to be significantly correlated as opposed to the solar maximum period, indicating the differences in the solar processes in different solar epochs.
    Journal of Atmospheric and Solar-Terrestrial Physics 01/2013; s 105–106:170–180. · 1.42 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The quiet-time (K p ≤ 3) daily variations of the geomagnetic field at the Indian Antarctic station, Maitri (Geographic Coord.: 70.75 • S, 11.73 • E; Geomagnetic Coord.: 66.84 • S, 56.29 • E) during two consecutive years of a solar minimum are considered in order to investigate the characteristics of the solar quiet (S q) current system. The present work reports the signatures of the south limb of the S q current loop of the southern hemisphere over a sub-auroral station. It is observed that the seasonal variation of the S q current strength over Maitri is strongest during the summer months and weakest during the winter months. In spite of the total darkness during the winter months, an S q pattern is identified at Maitri. The range of the horizontal field variation in the daily S q pattern during summer is one order higher than that during winter. An interesting feature regarding the phase of the local time variation in the seasonal pattern is found here. A sharp shift in the time of the peak S q current to later local times (>1 hour per month) is observed during January–February and July–August, which may correspond to the transition from the complete presence, or absence, of sunlight to partial sunlight. The differences in the incoming solar UV radiation during such transitions can cause a sudden change in the local ionospheric conductivity pattern, and can also trigger some unusual thermo-tidal activity, that might be responsible for modifying the global S q pattern.
    Earth Planets and Space 11/2012; 64:1023-1031. · 2.92 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Schumann resonances (SR) are lightening generated global electromagnetic modes in extremely low frequency (ELF) range operating in the Earth-ionosphere cavity. The 1st harmonic is at nearly 7.8 Hz and subsequent harmonics are separated by approximately 6 Hz. In this paper an attempt has been made to study the characteristics of SR using ground magnetic data from searchcoil magnetometers operating at a low latitude station Shillong (geographic co-ordinate lat 25.92 N, long 91.88 E) and a sub-auroral Indian Antarctic station Maitri (geographic co-ordinate lat 70.75 S, long 11.75 E). The universal time (UT) diurnal patterns of amplitudes of different harmonics show the dominance of thunderstorm activities in three major sectors viz. south-east Asia, Africa and South America, whereas the frequency variation pattern suggests the tidal influence. The seasonal variation of SR amplitude shows increase during local summer at Shillong as well as Maitri. Amplitudes as well as frequency exhibit distinct seasonal characteristics at both the stations, there by exhibiting the local influence on global SR modes. noindent
    07/2012;
  • 07/2012;
  • [Show abstract] [Hide abstract]
    ABSTRACT: Substorms at the auroral latitudes trigger a peculiar dynamics where a sharp depression in the AL index is observed along with an abrupt absorption in the cosmic noise due to ionospheric disturbances caused by high electron precipitation. However, such abrupt absorption may not always be seen during a substorm. Maitri (70°45' S, 11°45'E, geographic; 66°S, 53°21E, geomagnetic) is considered to be located at sub-auroral latitude and behaves as an auroral station during disturbed period. India has recently installed an Imaging Riometer at this sub auroral location. Using the data of cosmic noise intensity from Imaging riometer and the simultaneous magnetic field variation from digital flux gate magnetometer (DFM), a statistical study was performed in corroboration with the prevailing interplanetary conditions. Pi2 geomagnetic pulsations often accompanied by pulsations in particle precipitation flux have been thoroughly analyzed. Diurnal and seasonal patterns of such events were also statistically examined.
    07/2012;
  • 07/2012;
  • [Show abstract] [Hide abstract]
    ABSTRACT: In the present study, we investigate the geomagnetic field response to positive and negative solar dynamic pressure pulses. The positive (negative) pressure pulse compresses (enlarges) the Earth's magnetosphere, resulting in the enhancement (reduction) in the horizontal component of the Earth's magnetic field. It has been observed that the signature of the geomagnetic field response to the solar wind pressure pulse varies with latitude, as well as with magnetic local time. Our analysis shows that between 40° and 70° geomagnetic latitude, preliminary reverse impulse (PRI) occurs in the dawn- noon sector. Thus, asymmetry in PRI occurrence is evident between dawn-noon and dusk-midnight sector. The amplitude of main impulse is found to be larger in dusk-midnight sector than dawn-noon sector.
    07/2012;
  • [Show abstract] [Hide abstract]
    ABSTRACT: A case of the drastic effects of an eastward prompt penetration and a westward overshielding electric field successively affecting the daytime equatorial ionosphere during the space weather event that occurred on 24 November 2001 is presented. Under the influence of the strong eastward prompt penetration electric field starting from 11:25 Indian standard time (IST), the equatorial electrojet (EEJ) strength reached the maximum value of 225 nT at 12:42 IST, almost 7 times greater than the monthly quiet time mean at the same time. This peak EEJ value exceeds the maximum observed values during the month of November for the entire solar cycle by more than 100 nT, irrespective of quiet or disturbed conditions. Further, owing to an ensuing overshielding event that occurred during the main phase of the storm rather than the end of the main phase, this unusually large EEJ showed an equally strong polarity reversal along with a weakening of the sporadic E layer over the equator. The EEJ strength was reduced from +225 to -120 nT at ˜13:45 IST, resulting in a strong counter electrojet condition. The latitudinal variation of the F region electron density data from the CHAMP satellite reveal an ill-developed equatorial ionization anomaly at 17:00 IST (11:24 UT) over the Indian sector due to this significant weakening of the zonal electric field. These observations showcase the significant degree to which the low-latitude ionosphere can be affected by the interplanetary electric field.
    Journal of Geophysical Research 03/2012; 117(A3):3331-. · 3.17 Impact Factor
  • Source
    A K Singh, A K Sinha, R Rajaram, B M Pathan
    [Show abstract] [Hide abstract]
    ABSTRACT: The westward flowing toroidal ring current at about 2–7 R E in the Earth's equatorial plane consists of sym-metric and asymmetric parts. Zonal mean of H disturbances from longitudinally distributed low latitude stations repre-sents the symmetric contribution, whereas departure from the zonal mean gives local time dependent asymmetric com-ponent at each of the stations. Through a standard analysis of closely spaced low latitude geomagnetic data we demon-strate 24 h periodicity in the asymmetric component of the storm-time ring current, which is related to the changing lo-cal time due to rotation of the Earth. Detailed examination of shorter period oscillations, when observed globally, often show westward propagating modes. Eastward propagating mode was also observed in one case. Based on satellite and radar observations covering a narrow longitude region, west-ward and eastward propagating modes had been reported in earlier studies. In this study, we report that similar propagat-ing modes which are available on global scale, can be iden-tified using ground-based magnetometer data. These glob-ally propagating modes, observed from ground-based stud-ies, find obvious practical application in diagnostics of the magnetosphere, especially the ring current region. Simulta-neous use of satellite and ground-based data should establish the morphology of such modes.
    Annales Geophysicae 01/2012; 30:131-141. · 1.52 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Magnetic data from a newly commissioned Indian Antarctic station Bharati (corrected geomagnetic (CGM) coordinates 74.7°S, 97.2°E) and closely-spaced IMAGE chain observatories (∼100° magnetic meridian in Northern hemisphere) has been analyzed to study the climatology of substorms which were localized poleward of the standard auroral oval. We considered four austral summers (year 2007–2010) when data from Bharati was available. Several very high latitude substorms were observed in this duration when the solar activity remained unexpectedly low for a long time. Various features of very high latitude substorms, e.g., local time dependence, interplanetary state, hemispherical asymmetry and their nightside low latitude signatures are examined. Events studied here, suggested the following properties of substorms occurring at very high latitudes: (1) maximum occurrence was observed near magnetic midnight (21:00–02:00 MLT). (2) In contradiction to earlier reports, many substorms were observed even during negative IMF Bz condition. In addition, majority of substorms occurred during low or moderate solar wind streams. (3) Magnetic signatures were often pronounced in the winter hemisphere. (4) Even if widely used standard AE indices fail to monitor very high latitude substorms, their low latitude signatures are often evident.
    Advances in Space Research 01/2012; 50:1512-1523. · 1.18 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Low latitude asymmetric (ASY) indices, in addition to auroral indices, have been widely used to monitor the phenomena of magnetic substorm. However, low latitude ASY indices get strongly affected by various current systems in the magnetosphere and the ionosphere and may not have any direct relation with substorm activity. Intense and long-lasting solar flares are known to produce significant magnetic field disturbances on the dayside of the Earth, which could be an additional source of low latitude asymmetry. We examine the effect of solar flares on non-substorm and substorm times ASY indices using solar flare and indices data during the solar cycles 22 and 23 (year 1986 - 2008). It is observed that long-lasting intense solar flares during non-substorm time generate asymmetry similar to substorm events in ASY indices. In addition, substorm time ASY indices are also substantially affected by intense solar flares. We suggest that the occurrence of solar flares must be taken into account, especially in case studies where some conclusions are made based on the enhancements in ASY indices.
    Journal of Atmospheric and Solar-Terrestrial Physics 01/2012; 77:119-124. · 1.42 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Using multi-instrumental and multistation data, we present low-latitude ionospheric-thermospheric behavior during the geomagnetic storm of 15 May 2005. The diurnal pattern of total electron content (TEC) at a chain of equatorial to low-latitude stations shows strong positive ionospheric storm on 15 May. Latitudinal variation of TEC shows development of strong equatorial ionization anomaly (EIA) on the same day. Evidence, in terms of equatorial electrojet (EEJ) and magnetogram signatures, is presented for the prompt penetration of interplanetary electric field (IEF) as the cause of the positive ionospheric storm. Consequent to the storm time circulation resulting from the extra energy deposition via Joule heating over high latitudes, compositional changes occur in the global thermosphere. TEC enhancements on 16 May are attributed to enhancement of atomic oxygen at equatorial and low latitudes and the negative ionospheric storm on 17 May observed beyond certain low latitudes is explained in terms of enhancement of molecular species because of the storm time neutral composition changes. Strong ESF plume structures on range time intensity (RTI) map and L-band scintillation and TEC depletions in GPS measurements are observed in the longitude sectors where the local time of sudden storm commencement (SSC) falls after the post sunset hours. The ionospheric zonal electric fields are altered by the combined effects of eastward disturbance dynamo electric fields and direct prompt penetration of eastward electric fields associated with the northward turning of interplanetary magnetic field (IMF) Bz leading to subsequent development of ESF after midnight.
    Journal of Geophysical Research 01/2011; · 3.17 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The global component of fairweather electricity is subject to special attention to watch the solar-terrestrial effects and secular changes in climate. It is generally considered that the diurnal variation of atmospheric electricity parameters, if they are not following the Carnegie pattern, are not representative of the global thunderstorm activity. Some of the results obtained from Maitri (70°45′54″S, 11°44′03″), are discussed here in context with global thunderstorm activity and space weather influences. The diurnal pattern of the Potential Gradient and current density strongly deviate from the Carnegie curve. We have showed that this deviation is not due to the local electrical influence but due to the global thunderstorm activity. During fairweather condition the parameters are representing the global thunderstorm activity and to some extent they respond to the upper atmospheric electro dynamic phenomenon. The mean value of the potential gradient (77.7 V/m) and current density (2.13 pA/m2) well below the expected global mean but close to the value reported from the same location and season in the past years. The mean conductivity, 3.34 × 10−14 mhom−1, is slightly at higher side and they exhibit a different diurnal trend comparing to the past measurements at this location. KeywordsConductivity–Conduction current–Potential Gradient–Global Lightning Flash numbers–Geomagnetic substorm
    Journal of the Geological Society of India 01/2011; 78(3):199-210. · 0.57 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Depletion in plasma density at the dip equator in response to a solar eclipseSolar eclipse triggered a counter electrojet like condition near dip equatorZonal electric field is being surmised to reverse as a function of height
    Journal of Geophysical Research 01/2011; 116. · 3.17 Impact Factor
  • Source
    Current science 01/2011; 101:1073-1078. · 0.91 Impact Factor