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B. Ferdousi

Bio: B. Ferdousi is an academic researcher from University of New Hampshire. The author has contributed to research in topics: Ionosphere & Geomagnetic storm. The author has an hindex of 3, co-authored 6 publications receiving 86 citations. Previous affiliations of B. Ferdousi include University of California, Los Angeles & Boston University.

Papers
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Journal ArticleDOI
TL;DR: Two mechanisms for the generation of the pre-onset current sheet are discussed, namely magnetic flux addition to the tail lobes, or other high-latitude perturbations, and magnetic flux evacuation from the near-Earth tail associated with dayside reconnection.
Abstract: Modes and manifestations of the explosive activity in the Earth’s magnetotail, as well as its onset mechanisms and key pre-onset conditions are reviewed. Two mechanisms for the generation of the pre-onset current sheet are discussed, namely magnetic flux addition to the tail lobes, or other high-latitude perturbations, and magnetic flux evacuation from the near-Earth tail associated with dayside reconnection. Reconnection onset may require stretching and thinning of the sheet down to electron scales. It may also start in thicker sheets in regions with a tailward gradient of the equatorial magnetic field $B_{z}$ ; in this case it begins as an ideal-MHD instability followed by the generation of bursty bulk flows and dipolarization fronts. Indeed, remote sensing and global MHD modeling show the formation of tail regions with increased $B_{z}$ , prone to magnetic reconnection, ballooning/interchange and flapping instabilities. While interchange instability may also develop in such thicker sheets, it may grow more slowly compared to tearing and cause secondary reconnection locally in the dawn-dusk direction. Post-onset transients include bursty flows and dipolarization fronts, micro-instabilities of lower-hybrid-drift and whistler waves, as well as damped global flux tube oscillations in the near-Earth region. They convert the stretched tail magnetic field energy into bulk plasma acceleration and collisionless heating, excitation of a broad spectrum of plasma waves, and collisional dissipation in the ionosphere. Collisionless heating involves ion reflection from fronts, Fermi, betatron as well as other, non-adiabatic, mechanisms. Ionospheric manifestations of some of these magnetotail phenomena are discussed. Explosive plasma phenomena observed in the laboratory, the solar corona and solar wind are also discussed.

96 citations

Journal ArticleDOI
TL;DR: In this article, the authors focused on thermospheric wind driving and its impact on SAPS and R2 FAC during the 17 March 2013 geomagnetic storm using both observations and the physics-based Rice Convection Model-Coupled Thermosphere, Ionosphere, Plasmasphere, electrodynamics (RCM•CTIPe) model that self-consistently couples the magnetosphere•ionosphere•thermosphere system.
Abstract: Subauroral Polarization Streams (SAPS) are associated with closure of region 2 field‐aligned current (R2 FAC) through the low conductivity region. Although SAPS have often been studied from a magnetosphere‐ionosphere coupling perspective, recent observations suggest strong interaction also exists between SAPS and the thermosphere. Our study focuses on thermospheric wind driving and its impact on SAPS and R2 FAC during the 17 March 2013 geomagnetic storm using both observations and the physics‐based Rice Convection Model‐Coupled Thermosphere, Ionosphere, Plasmasphere, electrodynamics (RCM‐CTIPe) model that self‐consistently couples the magnetosphere‐ionosphere‐thermosphere system. Defense Meteorological Satellite Program (DMSP)‐18 and Gravity Field and Steady‐State Ocean Circulation Explorer (GOCE) satellite observations show that, as the storm progresses, sunward ion flows intensify and expand equatorward and are accompanied by strengthening of subauroral neutral winds with some delay. Our model successfully reproduces time evolution and overall structure of the sunward ion drift and neutral wind. A force term analysis is performed to investigate the momentum transfer to the neutrals from the ions. Contrary to previous studies showing that Coriolis force is the main driver of neutrals during storm time, we find that the ion drag is the largest force driving westward neutral wind in the SAPS region where the ion density is low in the trough region. Furthermore, simulations with and without the neutral wind dynamo effect are compared to quantify the effect of the neutral to plasma flow. The comparison shows that the self‐consistent active ionosphere thermosphere coupling increases the R2 FAC and the westward ion drift equatorward of the SAPS region by 20% and 40% by the flywheel effect, respectively.

19 citations

Journal ArticleDOI
TL;DR: In this paper, the authors used a magnetohydrodynamic global simulation model of the Earth magnetosphere and ionosphere, OpenGGCM-CTIM model, to investigate signal propagation paths and signal travel times.
Abstract: Distinguishing the processes that occur during the first 2 min of a substorm depends critically on the correct timing of different signals between the plasma sheet and the ionosphere. To investigate signal propagation paths and signal travel times, we use a magnetohydrodynamic global simulation model of the Earth magnetosphere and ionosphere, OpenGGCM-CTIM model. By creating single impulse or sinusoidal pulsations in various locations in the magnetotail, the waves are launched, and we investigate the paths taken by the waves and the time that different waves take to reach the ionosphere. We find that it takes approximately about 27, 36, 45, 60, and 72 s for waves to travel from the tail plasma sheet at x = −10,−15,−20,−25, and −30 RE , respectively, to the ionosphere, contrary to previous reports. We also find that waves originating in the plasma sheet generally travel faster through the lobes than through the plasma sheet.

17 citations

Journal ArticleDOI
TL;DR: An unsupervised classification method for magnetospheric regions, that could constitute the first-step of a multi-step method for the automatic identification of magnetosphere processes of interest, based on Self Organizing Maps.
Abstract: . In magnetospheric missions, burst-mode data sampling should be triggered in the presence of processes of scientific or operational interest. We present an unsupervised classification method for magnetospheric regions that could constitute the first step of a multistep method for the automatic identification of magnetospheric processes of interest. Our method is based on self-organizing maps (SOMs), and we test it preliminarily on data points from global magnetospheric simulations obtained with the OpenGGCM-CTIM-RCM code. The dimensionality of the data is reduced with principal component analysis before classification. The classification relies exclusively on local plasma properties at the selected data points, without information on their neighborhood or on their temporal evolution. We classify the SOM nodes into an automatically selected number of classes, and we obtain clusters that map to well-defined magnetospheric regions. We validate our classification results by plotting the classified data in the simulated space and by comparing with k-means classification. For the sake of result interpretability, we examine the SOM feature maps (magnetospheric variables are called features in the context of classification), and we use them to unlock information on the clusters. We repeat the classification experiments using different sets of features, we quantitatively compare different classification results, and we obtain insights on which magnetospheric variables make more effective features for unsupervised classification.

8 citations


Cited by
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TL;DR: In this article, electric field penetration events were identified using F-region vertical-drift measurements obtained in the October 6-13, 1984 period by Jicamarcan incoherent-backscatter radar and corresponding h-prime F measurements from ionosondes at Fortaleza, Cachoeira Paulista, and Dakar.
Abstract: Electric-field-penetration events have been identified using F-region vertical-drift measurements obtained in the October 6-13, 1984 period by the Jicamarcan incoherent-backscatter radar and corresponding h-prime F measurements from ionosondes at Fortaleza, Cachoeira Paulista, and Dakar. Predictions made using the Rice Convection Model for the pattern, strength, and duration of the low-latitude electric field occurring in response to an increasing high-latitude convection agree with observations. The observed 1-2 h duration of the low-latitude response to decreased convection can be explained by the fossil-wind theory of Richmond (1983).

330 citations

01 Aug 2009
TL;DR: In this article, the scaling of the growth rate of the fastest growing instability with respect to the Lundquist number is shown to follow from the classical dispersion relation for tearing modes.
Abstract: Thin current sheets in systems of large size that exceed a critical value of the Lundquist number are unstable to a super-Alfvenic tearing instability. The scaling of the growth rate of the fastest growing instability with respect to the Lundquist number is shown to follow from the classical dispersion relation for tearing modes. As a result of this instability, the system realizes a nonlinear reconnection rate that appears to be weakly dependent on the Lundquist number, and larger than the Sweet-Parker rate by an order of magnitude (for the range of Lundquist numbers considered). This regime of fast reconnection appears to be realizable in a dynamic and highly unstable thin current sheet, without requiring the current sheet to be turbulent.

209 citations

01 Dec 2013
TL;DR: In this article, a dipolarizing flux bundle (DFB) is a small magnetotail flux tube (typically 65% of the BBF flux transport) that is used to transport the flux in the tail of the magneto-graph.
Abstract: A dipolarizing flux bundle (DFB) is a small magnetotail flux tube (typically 65% of BBF flux transport, even though they last only ~30% as long as BBFs. The rate of DFB flux transport increases with proximity to Earth and to the premidnight sector, as well as with geomagnetic activity and distance from the neutral sheet. Under the latter two conditions, the total flux transport by a typical DFB also increases. Dipolarizing flux bundles appear more often during increased geomagnetic activity. Since BBFs have been previously shown to be the major flux transporters in the tail, we conclude that DFBs are the dominant drivers of this transport. The occurrence rate of DFBs as a function of location and geomagnetic activity informs us about processes that shape global convection and energy conversion.

118 citations

01 Nov 2004
TL;DR: In this article, the lower-hybrid drift instability is simulated in an ion-scale current sheet using a fully kinetic approach with values of the ion to electron mass ratio up to m(i)/m(e)=1836.
Abstract: The lower-hybrid drift instability is simulated in an ion-scale current sheet using a fully kinetic approach with values of the ion to electron mass ratio up to m(i)/m(e)=1836. Although the instability is localized on the edge of the layer, the nonlinear development increases the electron flow velocity in the central region resulting in a strong bifurcation of the current density and significant anisotropic heating of the electrons. This dramatically enhances the collisionless tearing mode and may lead to the rapid onset of magnetic reconnection for current sheets near the critical scale.

113 citations

01 Dec 2007
TL;DR: In this paper, a focused review of the role of entropy in plasma sheet transport is presented and new calculations of the implications of plasma sheet entropy conservation for the case where the plasma pressure is not isotropic.
Abstract: [1] This paper presents a focused review of the role of entropy in plasma sheet transport and also describes new calculations of the implications of plasma sheet entropy conservation for the case where the plasma pressure is not isotropic. For the isotropic case, the entropy varies in proportion to log[PV5/3], where P is plasma pressure and V is the volume of a tube containing one unit of magnetic flux. Theory indicates that entropy should be conserved in the ideal MHD approximation, and a generalized form of entropy conservation also holds when transport by gradient/curvature drift is included. These considerations lead to the conclusion that under the assumption of strong, elastic pitch angle scattering, PV5/3 should be approximately conserved over large regions of the plasma sheet, though gradient/curvature drift causes major violations in the innermost region. Statistical magnetic field and plasma models lead to the conclusion that PV5/3 increases significantly with distance downtail (pressure balance inconsistency). We investigate the possibility that the inconsistency could be removed or reduced by eliminating the assumption of strong, elastic pitch angle scattering but find that the inconsistency becomes worse if the first two adiabatic invariants are conserved as the particles drift. We consider two previously suggested mechanisms, bubbles and gradient/curvature drift, and conclude that the combination of the two is likely adequate for resolving the pressure balance inconsistency. Quantitatively accurate estimation of the efficiency of these mechanisms depends on finding a method of estimating PV5/3 (or equivalent) from spacecraft measurements. Two present approaches to that problem are discussed.

111 citations