skip to main content

Title: Effect of IMF B y on the Entry of Solar Wind Ions Into the Near‐Earth Tail Lobe: Global Hybrid Simulation and MMS Observation

Global simulations predict that the low‐latitude mantle may be an important pathway for the solar wind entry into the tail magnetosphere close to the current sheet when interplanetary magnetic field (IMF)Bydominates over IMFBz. To evaluate this entry mechanism in the near‐Earth tail (X ∼ −10–−20RE), we investigate the predictions from 3D global hybrid simulations as well as in situ observations by magnetospheric multiscale (MMS) spacecraft. The simulations predict that the low‐latitude mantle plasma can appear in the near‐Earth tail lobe extending inward approximately 5REfrom the flank magnetopause. The low‐latitude mantle plasma appears in the dawnside northern lobe and duskside southern lobe during positive IMFBy, while the opposite asymmetry is seen during negative IMFBy. After a change in the IMFBydirection arriving at the bow shock nose, it takes another ∼15–30 min for the asymmetry to completely reverse to the opposite sense in the near‐Earth tail. We present six MMS events in the tail lobe showing that the existence and absence of the low‐latitude mantle plasma is consistent with the predicted asymmetries. Statistical analysis of 5 years of MMS observations shows that the dependencies of the magnitudes of the lobe densities and tailward field‐aligned flow speeds on the IMFBydirections are consistent with the predicted contributions from the low‐latitude mantle plasma in the expected lobe regions.

more » « less
Author(s) / Creator(s):
 ;  ;  ;  ;  ;  ;  
Publisher / Repository:
DOI PREFIX: 10.1029
Date Published:
Journal Name:
Journal of Geophysical Research: Space Physics
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. Abstract

    Lobe reconnection is usually thought to play an important role in geospace dynamics only when the Interplanetary Magnetic Field (IMF) is mainly northward. This is because the most common and unambiguous signature of lobe reconnection is the strong sunward convection in the polar cap ionosphere observed during these conditions. During more typical conditions, when the IMF is mainly oriented in a dawn‐dusk direction, plasma flows initiated by dayside and lobe reconnection both map to high‐latitude ionospheric locations in close proximity to each other on the dayside. This makes the distinction of the source of the observed dayside polar cap convection ambiguous, as the flow magnitude and direction are similar from the two topologically different source regions. We here overcome this challenge by normalizing the ionospheric convection observed by the Super Dual Aurora Radar Network (SuperDARN) to the polar cap boundary, inferred from simultaneous observations from the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE). This new method enable us to separate and quantify the relative contribution of both lobe reconnection and dayside/nightside (Dungey cycle) reconnection during periods of dominating IMFBy. Our main findings are twofold. First, the lobe reconnection rate can typically account for 20% of the Dungey cycle flux transport during local summer when IMFByis dominating and IMFBz ≥ 0. Second, the dayside convection relative to the open/closed boundary is vastly different in local summer versus local winter, as defined by the dipole tilt angle.

    more » « less
  2. Abstract

    The magnetospheric substorm is a key mode of flux and energy transport throughout the magnetosphere associated with distinct and repeatable magnetotail dynamical processes and plasma injections. The substorm growth phase is characterized by current sheet thinning and magnetic field reconfiguration around the equatorial plane. The global characteristics of current sheet thinning are important for understanding of magnetotail state right before the onset of magnetic reconnection and of the key substorm expansion phase. In this paper, we investigate this thinning at different radial distances using plasma sheet (PS) energetic (>50 keV) electrons that reach from the equator to low altitudes during their fast (∼1 s) travel along magnetic field lines. We perform a multi‐case study and a statistical analysis of 34 events with near‐equatorial observations of the current sheet thinning by equatorial missions and concurrent, latitudinal crossings of the ionospheric projection of the magnetotail by the low‐altitude Electron Losses and Fields Investigation (ELFIN) CubeSats at approximately the same local time sector. Energetic electron fluxes thus collected by ELFIN provide near‐instantaneous (<5 min duration) radial snapshots of magnetotail fluxes. Main findings of this study confirm the previously proposed concepts with low‐altitude energetic electron measurements: (a) Energy distributions of low‐altitude fluxes are quantitatively close to the near‐equatorial distributions, which justifies the investigation of the magnetotail current sheet reconfiguration using low‐altitude measurements. (b) The magnetic field reconfiguration during the current sheet thinning (which lasts ≥ an hour) results in a rapid shrinking of the low‐altitude projection of the entire PS (from near‐Earth, ∼10RE, to the lunar orbit ∼60RE) to 1–2° of magnetic latitude in the ionosphere. (c) The current sheet dipolarization, common during the substorm onset, is associated with a very quick (∼10 min) change of the tail magnetic field configuration to its dipolar state, as implied by a poleward expansion of the PSPS at low altitudes.

    more » « less
  3. Abstract

    In this paper, we present a case study of the radial interplanetary magnetic field (IMFBx)‐induced asymmetric solar wind‐magnetosphere‐ionosphere (SW‐M‐I) coupling between the northern and southern polar caps using ground‐based and satellite‐based data. Under prolonged conditions of strong earthward IMF on 5 March 2015, we find significant discrepancies between polar cap north (PCN) and polar cap south (PCS) magnetic indices with a negative bay‐like change in the PCN and a positive bay‐like change in the PCS. The difference between these indices (PCN‐PCS) reaches a minimum of −1.63 mV/m, which is approximately three times higher in absolute value than the values for most of the time on this day (within ±0.5 mV/m). The high‐latitude plasma convection also shows an asymmetric feature such that there exists an additional convection cell near the noon sector in the northern polar cap, but not in the southern polar cap. Meanwhile, negative bays in the north‐south component of ground magnetic field perturbations (less than 50 nT) observed in the nightside auroral region of the Northern Hemisphere are accompanied with the brightening and widening of the nightside auroral oval in the Southern Hemisphere, implying a weak, but clear energy transfer to the nightside ionosphere of both hemispheres. After the hemispheric asymmetries in the polar caps disappear, a substorm onset takes place. All these observations indicate that IMFBx‐induced single lobe reconnection that occurred in the Northern Hemisphere plays an important role in hemispheric asymmetry in the energy transfer from the solar wind to the polar cap through the magnetosphere.

    more » « less
  4. Abstract

    There is still an inadequate understanding of how the interplanetary magnetic field (IMF) east‐west component (By) affects thermospheric composition, and other ionospheric and thermospheric fields in a systematic way. Utilizing the state‐of‐art first‐principles Coupled Magnetosphere Ionosphere Thermosphere (CMIT) modeling and TIMED/Global Ultraviolet Imager (GUVI)‐observed ΣO/N2covering an entire solar cycle (year 2002–2016), as well as a neutral parcel trajectory tracing technique, we emphasize that not only the direction ofBy, but also its strength relative to the IMF north‐south component (Bz) that has important effects on high latitude convection, Joule heating, electron density, neutral winds, and neutral composition patterns in the upper thermosphere. The Northern Hemisphere convection pattern becomes more twisted for positiveBycases than negative cases: the dusk cell becomes more rounded compared with the dawn cell. Consequently, equatorward neutral winds are stronger during postmidnight hours in negativeBycases than in positiveBycases, creating a favorable condition for neutral composition disturbances (characterized by low ΣO/N2) to expand to lower latitudes. This may lead to a more elongated ΣO/N2depletion area along the morning‐premidnight direction for negativeByconditions compared with the positiveByconditions. Backward neutral parcel trajectories indicate that a lower ΣO/N2parcel in negativeBycases comes from lower altitudes, as compared with that for positiveBycases, leading to larger enhancements of N2in the former case.

    more » « less
  5. At the Earth’s low-latitude magnetopause, the Kelvin-Helmholtz (KH) waves, which are driven by the super-Alfvénic velocity shear across the magnetopause, have been frequently observed during periods of northward interplanetary-magnetic-field (IMF) and believed to contribute to efficiently transporting the solar wind plasmas into the magnetosphere. On the other hand, during southward IMF periods, the signatures of the KH waves are much less frequently observed and how the KH waves contribute to the solar wind transport has not been well explored. Recently, the Magnetospheric Multiscale (MMS) mission successfully detected signatures of the KH waves near the dusk-flank of the magnetopause during southward IMF. In this study, we analyzed a series of two- and three-dimensional fully kinetic simulations modeling this MMS event. The results show that a turbulent evolution of the lower-hybrid drift instability (LHDI) near the low-density (magnetospheric) side of the edge layer of the KH waves rapidly disturbs the structure of the layer and causes an effective transport of plasmas across the layer. The obtained transport rate is comparable to or even larger than that predicted for the northward IMF. These results indicate that the diffusive solar wind transport induced by the KH waves may be active at the flank-to-tail magnetopause during southward IMF. 
    more » « less