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Indian Institute of Geomagnetism (IIG)
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Recent Submissions
Harnessing electron spin hyperpolarization in chromophore? radical spin probes for subcellular resolution in Electron Paramagnetic Resonance Imaging: concept and feasibility
(2022) Rane, Vinayak
Obtaining a subcellular resolution for biological samples doped with stable radicals at room temperature (RT) is a long-sought goal in electron paramagnetic resonance imaging (EPRI). The spatial resolution in current EPRI methods is constrained either because of low electron spin polarization at RT or the experimental limitations associated with the field gradients and the radical linewidth. Inspired by the recent demonstration of a large electron spin hyperpolarization in chromophore-nitroxyl spin probe molecules, the present work proposes a novel optically hyperpolarized EPR imaging (OH-EPRI) method, which combines the optical method of two-photon confocal microscopy for hyperpolarization generation and the rapid scan (RS) EPR method for signal detection. An important aspect of OH-EPRI is that it is not limited by the abovementioned restrictions of conventional EPRI since the large hyperpolarization in the spin probes overcomes the poor thermal spin polarization at RT, and the use of two-photon optical excitation of the chromophore naturally generates the required spatial resolution, without the need for any magnetic field gradient. Simulations based on time-dependent Bloch equations, which took into account both the RS field modulation and the hyperpolarization generation by optical means, were performed to examine the feasibility of OH-EPRI. The simulation results revealed that a spatial resolution of up to 2 fL can be achieved in OHEPRI at RT under in vitro conditions. Notably, the majority of the requirements for an OH-EPRI experiment can be fulfilled by the currently available technologies, thereby paving the way for its easy implementation. Thus, the proposed method could potentially bridge the sensitivity gap between the optical and magnetic imaging techniques.
Unique observations of a geomagnetic SI+- SI- pair: solar sources and associated solar wind fluctuations
(2010) Rastogi, R. G.; Janardhan, P.; Ahmed, K.; Das, A. C.; Bisoi, Susanta K.
This paper describes the occurrence of a pair of oppositely directed sudden impulses (SI) in the geomagnetic field (X) at ground stations, called SI+ - SI- pairs, that occurred between 1835 UT and 2300 UT on 23 April 1998. The SI+ - SI- pair was closely correlated with corresponding variations in the solar wind density, while solar wind velocity and the southward component of the interplanetary magnetic field (Bz) did not show any correspondence. Further, this event had no source on the visible solar disk. However, a rear-side partial halo coronal mass ejection (CME) and an M1.4 class solar flare behind the west limb took place on 20 April 1998, the date corresponding to the traceback location of the solar wind flows. This event presents empirical evidence, which to our knowledge is the most convincing evidence for the association of specific solar events to the observations of an SI+ - SI- pair. In addition, it shows that it is possible for a rear-side solar flare to propagate a shock toward the Earth.
Unusual optical observations of OI greenline during a geospace event on 1 February 2008
(2011) Narayanan, V. Lakshmi; Gurubaran, S.; Emperumal, K.; Patil, P. T.
We herein report the first observations of an unusual phenomenon recorded by an all-sky airglow imager from the low†latitude site Panhala (16.8°N, 74.1°E, geographic; 8.2°N geomagnetic), on the night of 1 February 2008, during the main phase of a moderate geomagnetic storm. The observations of OI 557.7 nm emission reveal discrete, transient, filamentary structures referred to as "streaks". No such features were seen in the OI 630.0 nm emission and the mesospheric sodium and hydroxyl emissions. Here we speculate on possible mechanisms for generation of such structures, though we cannot conclude firmly that any one of them was responsible for the observed features. This is a puzzling observation made from very low geomagnetic latitude during the main phase of a moderate recurrent geomagnetic storm in the declining phase of solar cycle. In spite of the limitations in identifying the mechanism or mechanisms responsible for this striking observation, it is felt that understanding of processes driving such unusual and rare events will substantiate our knowledge on the mysterious coupling processes occurring in the equatorial upper atmosphere.
Observations of near-conjugate high latitude substorms and their low latitude implications
(2011) Singh, Anand K.; Jayashree, B.; Sinha, Ashwini K.; Rawat, Rahul; Pathan, B. M.; Dhar, Ajay
Geomagnetic substorms are triggered on the nightside of the earth's magnetosphere and the most dramatic effect is observed at the auroral latitudes (60°-70° magnetic). Magnetic field disturbances observed at a set of longitudinally distributed auroral stations are used to derive auroral electrojet (AE) indices being widely used to monitor substorm activities. We present observations of magnetic substorms having more prominent effect poleward of the standard auroral oval. Magnetic data from the third Indian Antarctic station, Bharati (BHA; corrected geomagnetic (CGM) coordinates: 74.7°S, 96.6°E) in conjunction with IMAGE chain data (near conjugate station Hornsund (HOR; CGM coordinates: 74.3N, 108.5°E) have been subjected to detailed examination to study such substorms. The substorms presented in this study were mainly localized to high latitudes and hence the standard AE indices failed to monitor such substorm activities. Nevertheless, typical low-latitude features of substorm, for example, positive bay and Pi2 burst on the nightside were distinctly evident.
Observations of peculiar sporadic sodium structures and their relation with wind variations
(2009) Sridharan, S.; Prasanth, P. Vishnu; Kumar, Y. Bhavani; Ramkumar, Geetha; Sathishkumar, S.; Raghunath, K.
Resonance lidar observations of sodium density in the upper mesosphere region over Gadanki (13.5°N, 79.2°E) rarely show complex structures with rapid enhancements of sodium density, completely different from normal sporadic sodium structures. The hourly averaged meteor radar zonal winds over Trivandrum (8.5°N, 76.5°E) show an eastward shear with altitude during the nights, when these events are formed. As suggested by Kane et al. [2001. Joint observations of sodium enhancements and field-aligned ionospheric irregularities. Geophysical Research Letters 28, 1375–1378], our observations show that the complex structures may be formed due to Kelvin–Helmholtz instability, which can occur in the region of strong wind shear.
Confirmation of secondary cosmic ray flux enhancement during the total lunar eclipse of 10 December 2011
(2013) Raghav, Anil; Bhaskar, Ankush; Yadav, Virendra; Bijewar, Nitinkumar; Pai, Chintamani; Koli, Ashish; Navale, Nilam; Singh, Gurinderpal; Dubey, Nitin; Pawar, Sushant; Parab, Pradnya; Narvankar, Gandhali; Rawoot, Vaibhav; Rawat, Vikas; Borse, Satish; Garad, Nagnath; Rozario, Carl; Kaushal, Nitin; Tiwari, Shailendrakumar; Press, M.R.
Temporal variation of secondary cosmic rays (SCR) flux was measured during the total lunar eclipse on 10 December 2011 and the subsequent full moon on 8 January 2012 from Mumbai (Geomagnetic latitude: 10.6°N), India. The measurements were done by using NaI (Tl) scintillation detector with energy threshold of 200 keV. The SCR flux shows approximately 8.1% enhancement during the lunar eclipse as compared to the average of pre- and post-eclipse periods. Weather parameters (temperature and relative humidity) were continuously monitored, and their correlations with temporal variation in SCR flux have been examined. The influences of geomagnetic field, interplanetary parameters, and tidal effect on SCR flux have been considered. Qualitative analysis of SCR flux variation indicates that local weather, interplanetary, and geomagnetic factors affecting SCR flux fail to explain the observed enhancement during the eclipse. Lunar tidal effect on magnetosphere and crust still remains a possible mechanism which needs to be investigated in detail. The enhancement during lunar eclipse and widely reported decrease during solar eclipses may unravel hitherto unnoticed factors modulating SCR flux.
Sunspot variablity and an attempt to predict solar cycle 23 by adaptive filtering
(1998) Rangarajan, G. K.
The series of annual mean relative sunspot numbers (R z) for 1749-1996 is subjected to the recently developed methodology of Singular Spectrum Analysis (SSA). This technique also enables data-adaptive filtering of the individual spectral components. Low order autoregressive modelling of the components are combined to provide a basis for predicting the solar cycle 23. The R z series is largely dominated by a doublet with periods 11.13 and 10.35 yr. close to the nominal solar cycle periodicity, a longer period variation (~110 yr.) which is the envelope of the amplitude maxima and two clusters of periodicities centred around 8 yr. and 5.5 yr. The solar magnetic cycle has no detectable component. The predicted maximum for cycle 23 will have a magnitude of ~130 and the epoch of maximum is expected between late 2000 A.D. and early 2001 A.D.
Surface signatures of meridional currents in the equatorial electrojet
(1997) Patil, A. R.; Rajaram, R.
Characteristics of probability distribution functions of low- and high-latitude current systems during Solar Cycle 24
(2019) Kakad, Bharati; Kakad, Amar
Recent solar cycles (SCs) 21-24 have experienced a gradual decrease in their activity with considerable weakening during current SC 24. This is a unique opportunity to examine the long-term response of Earth’s low-latitude ring-current and high latitude auroral elec trojet current systems during such systematically decreasing solar activity. With the advancement in technology, continuous recordings of ground/space magnetic field are available for the last few decades that allow us to explore the behaviour of probability distribution func tions (PDFs) linked with the ring-current and auroral electrojet current systems for past five SCs (20-24). Also, PDFs linked with solar wind parameters that drive these current systems like magnetic field and velocity at Earth's bow shock are examined. We noticed the significant narrowing of PDF of ring-current and auroral electrojet during SC 24. The number of one-hour intervals with Dst < 150 nT are less than 600 for SCs 20-23, which constitutes less than 0.7% of respective PDF, and number of one-hour intervals with Dst < 250 nT are less than 100 for SCs 20-23, which corresponds to less than 0.1% of respective PDF. But for SC 24 the Dst < 150 nT encountered only for 58 h, which corresponds to 0.06% of PDF and there are no intervals when Dst was < 250 nT. For auroral electrojet, the number of one-hour intervals with AE > 750 nT and AE > 1500 nT are less than 3060 and 70, respectively for SCs 20-23, which corresponds to <4% and <0.06% of respective PDFs. But for SC 24 the AE > 750 nT encountered only for 1398 h, which corresponds to 1.7% of PDF and there are only 9 intervals when AE increased above 1500 nT, which is 0.01% of PDF. It implies that the probability of intense ring-current and auroral electrojet current during SC 24 was unusually low. Such narrow ing is seen in PDFs of the interplanetary magnetic field and solar wind velocity as well. This fair quiet space weather experienced during SC 24 is attributed to the weakening of solar activity, which has subsequently influenced the strength of the interplanetary magnetic field and solar wind velocity at Earth's bow shock.
The interplanetary causes of magnetic storms, HILDCAAs and viscous interaction
(1999) Tsurutani, B. T.; Gonzalez, W. D.; Kamide, Y.; Ho, Christian M.; Lakhina, G. S.; Arballo, J. K.; Thorne, R. M.; Pickett, J. S.; Howard, R. A.
A review of the interplanetary causes of geomagnetic activity is presented. Intense southward interplanetary magnetic fields in the sheath region ahead of fast interplanetary manifestations of solar CMEs (ICMEs), and the intrinsically high BZ fields of magnetic clouds within ICMEs, are the two most predominant causes of major storms with DST ≤−100 nT. This is true during solar maximum when ICMEs dominate the interplanetary medium and also during the declining phase of the solar cycle when corotating streams and proto-corotating interaction regions (PCIRs) are the dominant large scale structures. PCIRs are high magnetic field regions caused by the interaction of coronal hole high-speed streams with the upstream slow speed streams. PCIRs cause only moderate to weak magnetic storms (rarely storms with DST 〈-−100 nT) because of the highly variable Bz structure within them. It is thought that the Bz fluctuations within the PCIR are compressed high-speed stream Alfvén waves. The Bz fluctuations associated with nonlinear Alfvén waves within the high-speed streams cause continuous auroral activity called HILDCAAs. These HILDCAA events lead to annual AE averages that are sometimes higher during the solar cycle descending phase (such as in 1974) than during solar maximum (1979 or 1981). We quantify an upper limit of the efficiency of viscous interaction energy input into the magnetosphere: 1 to 3 × 10−3 of the solar wind ram energy. This is in contrast to an efficiency of 5 to 10 × 10−2 for magnetic reconnection during substorms and magnetic storms. Finally, a specific mechanism of viscous interaction is explored: low latitude boundary layer (LLBL) resonant wave-particle interactions. The waves are sufficiently intense to cross-field diffuse magnetosheath plasma onto closed field lines to create the LLBL. Pitch angle scattering will lead to auroral energy deposition of ∼ 1 erg cm−2 s−, sufficient for the creation of the dayside aurora.
Seasonal variablities of low-latitude mesospheric winds
(1998) Rajaram, R.; Gurubaran, S.
Observations of mesospheric winds over a period of four years with the partial reflection radar at Tirunelveli (8.7°N, 77.8°E), India, are presented in this study. The emphasis is on describing seasonal variabilities in mean zonal and meridional winds in the altitude region 70-98 km. The meridional winds exhibit overall transequatorial flow associated with differential heating in the Northern and Southern Hemispheres. At lower altitudes (70-80 km) the mean zonal winds reveal easterly flow during summer and westerly flow during winter, as expected from a circulation driven by solar forcing. In the higher altitude regime (80-98 km) and at all altitudes during equinox periods, the mean zonal flow is subjected to the semi-annual oscillation (SAO). The interannual variability detected in the occurrence of SAO over Tirunelveli has also been observed in the data sets obtained from the recent UARS satellite mission. Harmonic analysis results over a period of two years indicate the presence of long-period oscillations in the mean zonal wind at specific harmonic periods near 240, 150 and 120 days. Results presented in this study are discussed in the context of current understanding of equatorial wave propagation.
Signature of midnight temperature maximum (MTM) using OI 630 nm airglow
(2006) Mukherjee, G. K.; Parihar, Navin; Niranjan, K.; Manju, G.
An anomalous behaviour of F-region neutral temperature at night, sometimes exceeding the maximum afternoon values has been recorded at equatorial latitudes. This feature is referred to as Midnight Temperature Maximum (MTM)1. The winds generated due to pressure bulge phenomena at the equator propagate polewards (northward) and its vertical component while propagating moves the F-region plasma downwards to a region of enhanced loss and airglow production. The optical signature of MTM phenomena (brightness wave) has been recorded at Kolhapur (16.8 °N, 74.2 °E, dip lat. 10.6 ºN) in India using OI 630 nm night airglow during December 2002 to April 2003 showing peaks in intensity around 0200–0400 hrs LT. The structures were prominent for about two to three hours. The digital ionosonde data of Trivandrum (8.5 ºN, 77.0 ºE, dip ~ 0.6 °S), Sriharikota (13.7 °N, 80.2 °E; dip ~ 10.5 °N) and Visakhapatnam (17.67 ºN, 83.32 ºE; dip ~ 20 °N) stations show the descent of the F-layer at all the low latitude stations during MTM disturbance. The meridional winds estimated from h'F data of Trivandrum and Sriharikota showed generation of poleward winds and time delay of about one-and-a-half hours was observed between the observed time of the descent of the layer (h'F) at Sriharikota and the time of observations of the signature of MTM phenomena at Kolhapur.
Variabilities of mesospheric tides and equatorial electrojet strength during major stratospheric warming events
(2009) Sridharan, S.; Sathishkumar, S.; Gurubaran, S.
The present study demonstrates the relationship between the high latitude northern hemispheric major sudden stratospheric warming (SSW) events and the reversal in the afternoon equatorial electrojet (EEJ), often called the counter-electrojet (CEJ), during the winter months of 1998–1999, 2001–2002, 2003–2004 and 2005–2006. As the EEJ current system is driven by tidal winds, an investigation of tidal variabilities in the MF radar observed zonal winds during the winters of 1998–1999 and 2005–2006 at 88 km over Tirunelveli, a site close to the magnetic equator, shows that there is an enhancement of semi-diurnal tidal amplitude during the days of a major SSW event and a suppression of the same immediately after the event. The significance of the present results lies in demonstrating the latitudinal coupling between the high latitude SSW phenomenon and the equatorial ionospheric current system with clear evidence for major SSW events influencing the day-to-day variability of the CEJ.
No electrostatic supersolitons in two-component plasmas
(2014) Verheest, Frank; Lakhina, G. S.; Hellberg, Manfred A.
The concept of acoustic supersolitons was introduced for a very specific plasma with five constituents, and discussed only for a single set of plasma parameters. Supersolitons are characterized by having subsidiary extrema on the sides of a typical bipolar electric field signature, or by association with a root beyond double layers in the fully nonlinear Sagdeev pseudopotential description. It was subsequently found that supersolitons could exist in several plasma models having three constituent species, rather than four or five. In the present paper, it is proved that standard two-component plasma models cannot generate supersolitons, by recalling and extending results already in the literature, and by establishing the necessary properties of a more recent model.
Ponderomotive processes as proxies for breaking of ion acoustic solitary waves
(2016) Kakad, Amar; Kakad, Bharati
Wave breaking is a ubiquitous nonlinear phenomenon in plasma that is followed by sudden drop of wave amplitude after a wave steepening. We perform fluid simulation of the ion acoustic solitary waves (IASWs) to investigate the start time of the wave steepening and breaking process. This simulation demonstrates that a long wavelength perturbation in the electron and ion equilibrium densities evolves into two long wavelength IASWs. These IASWs steepens and breaks into short wavelength solitary structures, which become stable ion acoustic solitons at later time. From the detailed analysis of simulation output, we accomplish the criteria for steepening and breaking of the IASWs based on the (a) acceleration of IASWs (b) balance between maximum potential energy and the maximum electron kinetic energy. Furthermore, we examined the ponderomotive potential and the ponderomotive frequency of the electrons and ions during the process of the generation, steepening and breaking of these IASWs. It is observed that the maximum ponderomotive potential of both electrons and ions enhances during the steepening and attains the maximum close to the breaking of the IASWs. The simulation shows that the electron (ion) average ponderomotive frequency is considerably higher than the electron plasma frequency in the initial phase of generation of IASWs, which rapidly oscillates and approaches to frequencies much smaller than electron (ion) plasma frequency. These ponderomotive frequencies remain unchanged until the start of steepening of the IASWs; however, both frequencies are found to increase during the steepening and breaking of these IASWs. Based on this information, we propose that the ponderomotive potential and ponderomotive frequencies of electrons and ions can be used as proxies to determine the steepening and breaking time of the IASWs. We find that the onset time of the wave breaking varies inversely with the thermal velocity of the electrons and the amplitude of the initial density perturbation (IDP), while it is directly proportional to the width of the IDP. It is also noted that the number of solitons formed in the system and their characteristics depends on the electron temperature, width, and amplitude of the IDP.
Extremely intense ELF magnetosonic waves: A survey of polar observations
(2014) Tsurutani, B. T.; Falkowski, Barbara J.; Pickett, J. S.; Verkhoglyadova, Olga P.; Santolik, Ondrej; Lakhina, G. S.
A Polar magnetosonic wave (MSW) study was conducted using 1 year of 1996-1997 data (during solar minimum). Waves at and inside the plasmasphere were detected at all local times with a slight preference for occurrence in the midnight-postmidnight sector. Wave occurrence (and intensities) peaked within ±5° of the magnetic equator, with half maxima at ~±10°. However, MSWs were also detected as far from the equator as +20° and 60° MLAT but with lower intensities. An extreme MSW intensity event of amplitude Bw=~±1 nT and Ew=~± 25 mV/m was detected. This event occurred near local midnight, at the plasmapause, at the magnetic equator, during an intense substorm event, e.g., a perfect occurrence. These results support the idea of generation by protons injected from the plasma sheet into the midnight sector magnetosphere by substorm electric fields. MSWs were also detected near noon (1259 MLT) during relative geomagnetic quiet (low AE). A possible generation mechanism is a recovering/expanding plasmasphere engulfing preexisting energetic ions, in turn leading to ion instability. The wave magnetic field components are aligned along the ambient magnetic field direction, with the wave electric components orthogonal, indicating linear wave polarization. The MSW amplitudes decreased at locations further from the magnetic equator, while transverse whistler mode wave amplitudes (hiss) increased. We argue that intense MSWs are always present somewhere in the magnetosphere during strong substorm/convection events. We thus suggest that modelers use dynamic particle tracing codes and the maximum (rather than average) wave amplitudes to simulate wave-particle interactions.
Development of fast image analysis technique for All-Sky images
(2014) Sharma, A. K.; Nade, D.P.; Nikte, S. S.; Ghodpage, R. N.; Patil, P. T.; Rokade, M. V.; Vhatkar, R. S.; Gurubaran, S.
This article describes the possibility of using the fast image analysis technique for qualitative and quantitative analysis of equatorial plasma bubble obtained using All-Sky imager (ASI) data. Automated image processing (generally) is useful for identification of equatorial plasma bubbles (EPBs) and its parameters. We have developed a fast (and efficient) analysis technique essential to study the data of images. The present work reports the results of a statistical study of the zonal plasma bubble velocities using nightglow OI 630.0 nm emission data, acquired by ASI (FOV 140°) at the low-latitude station Kolhapur (16.42°N, 74.2°E and 10.6°N dip lat.). Based on the observations of 15 nights made in January 2012, we have determined the velocity of EPB using our new method. The daily mean values of the EPB velocity match well with those of the earlier studies made at Kolhapur. We have found that, generally, the mean zonal drift velocities of the plasma bubbles tend to decrease with local time (after midnight). The most significant finding from this work is that the calculated velocities of plasma bubble using fast and scanning methods are nearly equal.
A comparison study of zonal drift velocities measurements as seen by MF spaced antenna and HF Doppler radar in the Indian dip equatorial mesospheric and lower thermospheric (80–100 km) region
(2010) Ramkumar, T. K.; Gurubaran, S.; Rajaram, R.; Tiwari, D.; Viswanathan, K. S.
The simultaneous measurements of zonal drift velocities, observed in the heights of 84-98 km in the Indian geomagnetic dip equatorial region by an medium frequency (MF, 1.98 MHz) spaced antenna and a high-frequency (HF, 18 MHz) Doppler radars, are compared on selected few days in the solar maximum years of 1998, 1999, and 2000. The agreement between the two radar measurements is found to be good below about 88 km, where the neutral turbulence induced ionospheric irregularities are more predominant. Above 90 km, however, the agreement becomes poor and at the highest height of 98 km it becomes the least. At this height, more often the HF Doppler radar shows a westward drift of about 200 m/s whereas the MF spaced antenna radar values lie within ±10 m/s and sometimes attain maximum values of ±50 m/s. Detailed discussions are made on the possible sources of underestimation of the drift velocities measured by the MF radar and the nature of scattering irregularities that are produced because of large neutral turbulences and plasma instabilities. It is suggested that these neutral and plasma turbulences (particularly type II plasma irregularities) contribute in a different manner to different radar frequencies and techniques and hence very different drift velocities in the heights of 90-100 km particularly in the geomagnetic dip equatorial region. Discussions are also made on the real atmospheric and ionospheric physical process prevailing in the 90–100 km region and (2) the technical aspects of the radars that limits them to measure only particular types of motion in this region.
Ion temperature and delta B effects on ULF fluctuations at the magnetopause
(1996) Pillay, R.; Bharuthram, R.; Lakhina, G. S.
In this paper, we present an extension of the work by Lakhina, Shukla and Stenflo (Geophys. Res. Lett. 20, 2419 1993) on the generation of ultralow frequency (ULF) fluctuations at the earth's magnetopause. A high beta model for the generation of these short wavelength fluctuations is described. In this model, drifts due to density and magnetic field gradients, present at the magnetopause, act as free energy sources for the excitation of the ULF waves. The model also considers both warm electrons and ions and is based on the SS equations (Shukla and Stenflo. J. Exp. Theor. Phys. 57, 692 1993) for low-frequency EM waves in non-uniform high beta magnetoplasmas. Using fluid theory the associated dispersion relation is first established, then numerically solved for unstable modes in different regions of parameter space.
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