Browsing by Author "Sazykin, Stanislav"

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    On the contribution of plasma sheet bubbles to the storm time ring current
    (Wiley, 2015) Yang, Jian; Toffoletto, Frank R.; Wolf, Richard A.; Sazykin, Stanislav
    Particle injections occur frequently inside 10 Re during geomagnetic storms. They are commonly associated with bursty bulk flows or plasma sheet bubbles transported from the tail to the inner magnetosphere. Although observations and theoretical arguments have suggested that they may have an important role in storm time dynamics, this assertion has not been addressed quantitatively. In this paper, we investigate which process is dominant for the storm time ring current buildup: large-scale enhanced convection or localized bubble injections. We use the Rice Convection Model-Equilibrium (RCM-E) to model a series of idealized storm main phases. The boundary conditions at 14–15 Re on the nightside are adjusted to randomly inject bubbles to a degree roughly consistent with observed statistical properties. A test particle tracing technique is then used to identify the source of the ring current plasma. We find that the contribution of plasma sheet bubbles to the ring current energy increases from ~20% for weak storms to ~50% for moderate storms and levels off at ~61% for intense storms, while the contribution of trapped particles decreases from ~60% for weak storms to ~30% for moderate and ~21% for intense storms. The contribution of nonbubble plasma sheet flux tubes remains ~20% on average regardless of the storm intensity. Consistent with previous RCM and RCM-E simulations, our results show that the mechanisms for plasma sheet bubbles enhancing the ring current energy are (1) the deep penetration of bubbles and (2) the bulk plasma pushed ahead of bubbles. Both the bubbles and the plasma pushed ahead typically contain larger distribution functions than those in the inner magnetosphere at quiet times. An integrated effect of those individual bubble injections is the gradual enhancement of the storm time ring current. We also make two predictions testable against observations. First, fluctuations over a time scale of 5–20 min in the plasma distributions and electric field can be seen in the central ring current region for the storm main phase. We find that the plasma pressure and the electric field EY there vary over about 10%–30% and 50%–300% of the background values, respectively. Second, the maximum plasma pressure and magnetic field depression in the central ring current region during the main phase are well correlated with the Dst index.
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    Polarization jet events and excitation of weak SAR arcs
    (2002) Sazykin, Stanislav; Fejer, B.G.; Galperin, Y.I.; Zinin, L.V.; Grigoriev, S.A.; Mendillo, M; Rice Space Institute; American Geophysical Union
    Polarization Jet (PJ), also known as Sub-Auroral Ion Drift (SAID), events are supersonic westward plasma drifts on the equatorward edge of the diffuse aurora in the evening and nighttime sector. Their optical F-region signatures are weak 630.0 nm red arcs colocated with regions of fast convection. These weak arcs resemble Stable Auroral Red (SAR) arcs observed during the recovery phase of magnetic storms, but have lower intensities, shorter lifetimes, and occur without a significant heat flux from the magnetosphere. Previous model studies underestimated the brightness of weak SAR arcs. We present calculations showing that ion-neutral collisional heating and ion composition changes during PJ events may be an additional source of 630.0 nm emission, and propose experimental tests that could verify our modeling results.
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    RCM-E simulation of bimodal transport in the plasma sheet
    (American Geophysical Union, 2014) Yang, Jian; Wolf, Richard A.; Toffoletto, Frank R.; Sazykin, Stanislav; Wang, Chih-Ping
    Plasma sheet transport is bimodal, consisting of both large-scale adiabatic convection and intermittent bursty flows in both earthward and tailward directions. We present two comparison simulations with the Rice Convection Model-Equilibrium (RCM-E) to investigate how those high-speed flows affect the average configuration of the magnetosphere and its coupling to the ionosphere. One simulation represents pure large-scale slow-flow convection with time-independent boundary conditions; in addition to the background convection, the other simulation randomly imposes bubbles and blobs through the tailward boundary to a degree consistent with observed statistical properties of flows. Our results show that the bursty flows can significantly alter the magnetic and entropy profiles in the plasma sheet as well as the field-aligned current distributions in the ionosphere, bringing them into much better agreement with average observations.
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    RCM-E simulation of substorm growth phase arc associated with large-scale adiabatic convection
    (Wiley, 2013) Yang, Jian; Wolf, Richard A.; Toffoletto, Frank R.; Sazykin, Stanislav
    [1] Substorm auroral breakup often occurs on a longitudinally elongated arc at the end of a growth phase. We present an idealized high-resolution simulation with the Rice Convection Model-Equilibrium (RCM-E) to investigate how large-scale adiabatic convection under equilibrium conditions can give rise to an auroral arc. We find that a thin arc that maps to the magnetic transition region at r ~ 8 RE emerges in the late growth phase. The simulation implies that the arc in the premidnight sector is associated with a sheet of additional region 1 sense field-aligned current (FAC) just poleward of the main region 2 FAC, while the arc in the postmidnight sector is associated with the poleward portion of the main upward region 2 FAC. Explanations for the location and the thickness of the arc are proposed, based on the simulation.
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    Space Weather Event Modeling of Plasma Injection Into the Inner Magnetosphere with the Rice Convection Model
    (2011) Song, Yang; Sazykin, Stanislav
    The inner magnetosphere modeling is an important component of the magnetosphere simulation frameworks with significant implications for space weather and a. principle methodology to understand the magnetospheric response to changes in the solar wind. The thesis shows our efforts in constructing and validating the contemporary Rice Convection Model (RCM) code and its interface as a next-generation code to predict electric fields, field-aligned currents, and energetic particle fluxes in the inner magnetosphere and subauroral ionosphere during geomagnetic disturbed times. The RCM was used to simulate the geomagnetic storms with fixed boundary conditions of time-dependent Tsyganenko-Mukai boundary conditions. This work shows the results of two extremely- strong storm events with significant interchange motion. The ring current injection predicted by the RCM is shown to be overestimated, consistent with the previous results of overestimating particle fluxes by the RCM. This effect is magnified here since the southward component of interplanetary magnetic field is very strong reaching about 50 nT. Time-dependent Borovsky's boundary condition is implemented and used to alleviate the huge pressure and get better tendency of ring current energy calculated by the Dessler-Parker-Sckopke relation. This work also describes a new module of generalized Knight's relation to compute the parallel potential drops from the calculated field-aligned currents through Vasyliunas equation. It gives different ionospheric conductance and plasma drift signatures particularly around the midnight. The inclusion of parallel electric fields will replace the treatments of energy flux in the substorm simulations since that the Hardy normalization cannot perform the desired function during the substorm expansion phase and the energy flux floor gives arbitrary enhanced the precipitating energy flux and ionospheric conductances at high latitude especially for the westward clectrojet around the midnight. Since the original Knight's relation gives too large field-aligned potential drop, the modified Knight's relation is applied and implemented successfully into the RCM. Therefore, the RCM is capable of real time event simulation including strong geomagnetic storms and magnetospheric substorms, although full validation of model predictions with typical observations remains to be done.