Tail Lobe Research Articles

Evaluation of harmonic scalpel assisted extracapsular dissection for benign parotid tumors

To investigate the clinical outcomes and prognosis of harmonic scalpel assisted extracapsular dissection for benign parotid tumors. A total of 132 patients with full medical archives who were diagnosed as benign parotid tumors from 3 medical centers were retrospectively analyzed. The included patients were divided into 3 groups according to tumor positions, namely, superficial pre-auricular, superficial tail, and deep lobe. The intra- and peri-operative variables, complications, functional outcomes and recurrence rates were analyzed with SPSS 16.0 software package. The surgical and drainage time were longer and the blood loss and drainage amount were significantly greater in deep lobe group (P<0.01). Facial nerve damage occurred more frequently in deep lobe group (P=0.022), while damages of great auricular nerve and parotid fascia, as well as capsule rupture were similar among 3 groups (P>0.05). More patients with decreased sensation or sialocele were observed in deep lobe group (P=0.004, 0.043, respectively), and no significant differences were found for wound infection and Frey's syndrome among 3 groups (P>0.05).Transient facial nerve paralysis occurred more frequently in deep lobe group (P<0.01), while permanent facial nerve paralysis was similar (P=0.052). No significant difference was observed for tumor recurrence (P=1.000). HS-ECD displays good outcomes and prognosis for benign tumor of parotid gland, with improved esthetic and functional results as well as fewer complications and recurrence rate postoperatively.

Magnetosphere response to the IMF turning from north to south

In this paper, the Space Weather Modeling Framework (SWMF) is used to simulate the real-time response of the magnetosphere to a solar wind event on June 5, 1998, in which the interplanetary magnetic field shifted its direction from north to south. Since most current models do not take into account convective effects of the inner magnetosphere, we first study the importance of Rice Convection Model (RCM) in the global model. We then focus on the following four aspects of the magnetosphere’s response: the magnetosphere’s density distribution, the structure of its magnetic field lines, the area of the polar cap boundary, and the corresponding ionospheric current change. We find that (1) when the IMF changes from north to south in this event, high magnetosheath density is observed to flow downstream along the magnetopause with the solar wind; low-latitude reconnection at dayside occurs under the southward IMF, while the magnetic field lines in the tail lobe caudal, caused by the nightside high latitude reconnection, extend into the interplanetary space. Open magnetic field lines exist simultaneously at both high and low latitudes at the magnetopause; (2) the area of the polar cap is obviously increased if the IMF turns from the north to the south; this observation is highly consistent with empirical observations; (3) the ionospheric field align current in the northern hemisphere is stronger than in the southern hemisphere and also increases as the IMF changes from north to south. SWMF with the Rice Convection effect provides reliable modeling of the magnetospheric and ionospheric response to this solar wind variation.

Transport of Mass and Energy in Mercury's Plasma Sheet

AbstractWe examined the transport of mass and energy in Mercury's plasma sheet (PS) using MESSENGER magnetic field and plasma measurements obtained during 759 PS crossings. Regression analysis of proton density and plasma pressure shows a strong linear relationship. We calculated the polytropic index γ for Mercury's PS to be ~0.687, indicating that the plasma in the tail PS behaves nonadiabatically as it is transported sunward. Using the average magnetic field intensity of Mercury's tail lobe as a proxy for magnetotail activity level, we demonstrated that γ is lower during active time periods. A minimum in γ was observed at R ~ 1.4 RM, which coincides with previously observed location of Mercury's substorm current wedge. We suggest that the nonadiabatic behavior of plasma as it is transported into Mercury's near‐tail region is primarily driven by particle precipitation and particle scattering due to large loss cone and particle acceleration effect, respectively.

Magnetotail Hall Physics in the Presence of Cold Ions

AbstractWe present the first in situ observation of cold ionospheric ions modifying the Hall physics of magnetotail reconnection. While in the tail lobe, Magnetospheric Multiscale mission observed cold (tens of eV) E × B drifting ions. As Magnetospheric Multiscale mission crossed the separatrix of a reconnection exhaust, both cold lobe ions and hot (keV) ions were observed. During the closest approach of the neutral sheet, the cold ions accounted for ∼30% of the total ion density. Approximately 65% of the initial cold ions remained cold enough to stay magnetized. The Hall electric field was mainly supported by the j × B term of the generalized Ohm's law, with significant contributions from the ∇·Pe and vc×B terms. The results show that cold ions can play an important role in modifying the Hall physics of magnetic reconnection even well inside the plasma sheet. This indicates that modeling magnetic reconnection may benefit from including multiscale Hall physics.

Improved recovery of human islets from young donor pancreases utilizing increased protease dose to collagenase for digesting peri-islet extracellular matrix.

Human islet isolation from young donor pancreases (YDP) utilizing the current purified standard dose of collagenase-protease enzyme mixtures often results in the release of a high percentage of mantled islets. Mantled islets are those surrounded by exocrine tissue and are difficult to purify by density gradient centrifugation, leading to poor islet recovery. Based on difference in extracellular matrix, and total collagen content between YDP and old donor pancreas (ODP, > 35 Y) led us to compare results from islet isolation using increased collagenase combination (ICC) or increased protease combination (IPC), to the standard enzyme combination (SEC) in a "trisected" pancreas model to overcome the donor-to-donor variability. These results showed a reduced percentage of mantled islets (17%±7.5%) and higher postpurification islet recovery (83.8%±5.6%) with IPC. Furthermore, these results were confirmed in 13 consecutive whole pancreas islet isolations utilizing IPC from VitaCyte, Roche, or SERVA collagenase-protease enzyme mixtures. Results obtained from in vitro and in vivo islet functional assessment indicated that islets isolated using IPC retained normal islet morphology, insulin secretion, and the ability to reverse diabetes after transplantation in diabetic nude mice. This is the first report utilizing trisected pancreas to assess the effectiveness of different enzyme combinations to improve islet recovery from young donor pancreases.

Diagnostics of Closed Magnetic Flux Depletion in the Near‐Earth Magnetotail During the Substorm Growth Phase

AbstractBased on magnetohydrodynamics simulations, it was recently suggested that magnetotail reconfiguration during the substorm growth phase results from combined action of two large‐scale processes: (1) open magnetic flux accumulation (OMFA) in the tail lobes and (2) closed magnetic flux depletion (CMFD) in the near‐Earth tail, caused by flux evacuation to the dayside magnetopause. Simultaneous action of uniform along the tail OMFA and strongly nonuniform CMFD leads to different rates of magnetic flux growth in different tail cross sections. According to Global magnetohydrodynamics simulations CMFD is about 35% of OMFA, the corresponding differences of magnetic flux increase in two‐tail cross sections at −7RE and −20RE being as large as 0.1–0.2 GWb. To study this effect on real data, we applied the recent method of magnetotail flux estimation (Shukhtina et al., ) to simultaneous Cluster and Geotail observations in the tail lobes. By finding such rare observations in the inner and middle magnetotail (at&lt;X &gt; −10 RE and − 21RE) we confirm a larger magnetic flux increase in the midtail, with the ratio between OMFA and CMFD comparable to that obtained in magnetohydrodynamics, although with a large scatter. These results confirm the scenario of two decoupled magnetotail regions with different convection regimes during the growth phase. Convection is depressed in the midtail plasma sheet, showing the pressure crisis in action inherent to tail‐like 2‐D magnetic configuration. At the same time convection is substantially enhanced in the inner magnetosphere, where the pressure crisis is solved due to azimuthal flux transport around the Earth, essentially a 3‐D effect.

The Twisted Configuration of the Martian Magnetotail: MAVEN Observations

AbstractMeasurements provided by the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft are analyzed to investigate the Martian magnetotail configuration as a function of interplanetary magnetic field (IMF) BY. We find that the magnetotail lobes exhibit a ~45° twist, either clockwise or counterclockwise from the ecliptic plane, up to a few Mars radii downstream. Moreover, the associated cross‐tail current sheet is rotated away from the expected location for a Venus‐like induced magnetotail based on nominal IMF draping. Data‐model comparisons using magnetohydrodynamic simulations are in good agreement with the observed tail twist. Model field line tracings indicate that a majority of the twisted tail lobes are composed of open field lines, surrounded by draped IMF. We infer that dayside magnetic reconnection between the crustal fields and draped IMF creates these open fields and may be responsible for the twisted tail configuration, similar to what is observed at Earth.

Photoemission and electrostatic potentials on the dayside lunar surface in the terrestrial magnetotail lobes.

Despite the need to accurately predict and assess the lunar electrostatic environment in all ambient conditions that the Moon encounters, photoemission and electrostatic potentials on the dayside lunar surface in the terrestrial magnetotail lobes remain poorly characterized. We study characteristics and variabilities of lunar photoelectron energy spectra by utilizing Acceleration, Reconnection, Turbulence, and Electrodynamics of the Moon's Interaction with the Sun (ARTEMIS) and Apollo measurements in combination with the Flare Irradiance Spectral Model (FISM). We confirm that the photoelectron spectral shapes are consistent between ARTEMIS and Apollo and that the photoelectron flux is linearly correlated with the FISM solar photon flux. We develop an observation-based model of lunar photoelectron energy distributions, thereby deriving the current balance surface potential. The model predicts that dayside lunar surface potentials in the tail lobes (typically tens of volts) could increase by a factor of 2 - 3 during strong solar flares.

27 August 2001 substorm: Preonset phenomena, two main onsets, field‐aligned current systems, and plasma flow channels in the ionosphere and in the magnetosphere

AbstractWe supplement the results of the 27 August 2001 substorm studied earlier in the series of papers. Described is the plasma flow in the nightside ionosphere from the near‐polar region from the polar cap to the auroral oval during the substorm preonset phase and two expansion onsets, EO1 and EO2, produced by reconnection in the closed tail (magnetic reconnection (MR1) and in the open tail lobes (MR2), respectively. We discuss the location of the MR2 region (is it near, middle, and/or distant tail?) and the EO2 trigger mechanism. The upward substorm current wedge field‐aligned current (FAC) and the downward FAC in the polar cap dusk sector that were both produced by different types of magnetosphere‐ionosphere feedback instability are found to provide the main contribution to the system of FACs during EO1 and EO2. Also, we obtain the estimates for the EO1 and EO2 power and energy. Addressed are the variations in the tail lobe magnetic flux and their (variations) association with EO2. In addition, we describe a 3‐D system of mesoscale cells, each of which involves a plasma vortex and a local FAC maximum. The cells of this system in the inner magnetosphere and in the tail lobes intensify one after other within 2 min interval. At last, we substantiate the assumption that the fast plasma flow recorded by the Cluster satellites 7 min prior to EO1 was a bursty bulk flow from the most distant tail.

Particle‐in‐cell modeling of spacecraft‐plasma interaction effects on double‐probe electric field measurements

AbstractThe double‐probe technique, commonly used for electric field measurements in magnetospheric plasmas, is susceptible to environmental perturbations caused by spacecraft‐plasma interactions. To better model the interactions, we have extended the existing particle‐in‐cell simulation technique so that it accepts very small spacecraft structures, such as thin wire booms, by incorporating an accurate potential field solution calculated based on the boundary element method. This immersed boundary element approach is effective for quantifying the impact of geometrically small but electrically large spacecraft elements on the formation of sheaths or wakes. The developed model is applied to the wake environment near a Cluster satellite for three distinctive plasma conditions: the solar wind, the tail lobe, and just outside the plasmapause. The simulations predict the magnitudes and waveforms of wake‐derived spurious electric fields, and these are in good agreement with in situ observations. The results also reveal the detailed structure of potential around the double probes. It shows that any probes hardly experience a negative wake potential in their orbit, and instead, they experience an unbalanced drop rate of a large potential hill that is created by the spacecraft and boom bodies. As a by‐product of the simulations, we also found a photoelectron short‐circuiting effect that is analogous to the well‐known short‐circuiting effect due to the booms of a double‐probe instrument. The effect is sustained by asymmetric photoelectron distributions that cancel out the external electric field.

Magnetotail magnetic flux monitoring based on simultaneous solar wind and magnetotail observations

AbstractThe magnetotail magnetic flux (MTF) is an important global variable to describe the magnetospheric state and dynamics. Existing methods of MTF estimation on the basis of the polar cap area, inferred from observations of global auroras and field‐aligned currents, do not allow benchmarking due to the absence of a gauge for comparison; besides, they rarely allow a systematic nearly real time MTF monitoring. We describe three modifications (F0, F1, and F2) of the method to calculate the MTF, based on simultaneous spacecraft observations in the magnetotail and in the solar wind, suitable for real‐time MTF monitoring. The MTF dependence on the solar wind parameters and the observed tail lobe magnetic field is derived from the pressure balance conditions. An essential part of this study is the calibration of our approximate method against global 3‐D MHD simulations and the empirical T14 magnetospheric field model. The calibration procedure provides all variables required to evaluate F0, F1, and F2 quantities and, at the same time, computes the reference MTF value through any tail cross section. It allowed us to extend the method to be used in the near tail, investigate its errors, and define the applicability domain. The method was applied to Cluster and THEMIS measurements and compared with methods of polar cap area calculation based on IMAGE and AMPERE observations. We also discuss possible applications and some recent results based on the proposed method.

Optimization of Saturn paraboloid magnetospheric field model parameters using Cassini equatorial magnetic field data

Abstract. The paraboloid model of Saturn's magnetosphere describes the magnetic field as being due to the sum of contributions from the internal field of the planet, the ring current, and the tail current, all contained by surface currents inside a magnetopause boundary which is taken to be a paraboloid of revolution about the planet-Sun line. The parameters of the model have previously been determined by comparison with data from a few passes through Saturn's magnetosphere in compressed and expanded states, depending on the prevailing dynamic pressure of the solar wind. Here we significantly expand such comparisons through examination of Cassini magnetic field data from 18 near-equatorial passes that span wide ranges of local time, focusing on modelling the co-latitudinal field component that defines the magnetic flux passing through the equatorial plane. For 12 of these passes, spanning pre-dawn, via noon, to post-midnight, the spacecraft crossed the magnetopause during the pass, thus allowing an estimate of the concurrent subsolar radial distance of the magnetopause R1 to be made, considered to be the primary parameter defining the scale size of the system. The best-fit model parameters from these passes are then employed to determine how the parameters vary with R1, using least-squares linear fits, thus providing predictive model parameters for any value of R1 within the range. We show that the fits obtained using the linear approximation parameters are of the same order as those for the individually selected parameters. We also show that the magnetic flux mapping to the tail lobes in these models is generally in good accord with observations of the location of the open-closed field line boundary in Saturn's ionosphere, and the related position of the auroral oval. We then investigate the field data on six passes through the nightside magnetosphere, for which the spacecraft did not cross the magnetopause, such that in this case we compare the observations with three linear approximation models representative of compressed, intermediate, and expanded states. Reasonable agreement is found in these cases for models representing intermediate or expanded states.

Magnetospheric dynamics during the storm of February 14, 2009

The structure of the magnetic field in the magnetospheric during the storm of February 14, 2009 is studied. The model parameters that characterize the magnetospheric magnetic field are calculated every hour on the basis of solar wind data and the evolution of the magnetic field during the storm is reproduced using the A2000 model of the Earth’s magnetosphere. It is shown that extremely quiet geomagnetic conditions in 2009 promoted the expansion of the magnetosphere and were favorable for the formation of magnetic-island-like structures (plasmoids) in the geomagnetic tail. It is ascertained that negative variations in the B z component could occur in the nightside magnetosphere in situations where the magnetic flux through the tail lobes exceeded certain thresholds, which depend on the parameters of the magnetospheric current systems. It is shown that the formation of magnetic islands decreases the magnetic flux through the tail lobes and prevents excessively strong development of the magnetic field in the tail.

Relation of the auroral substorm to the substorm current wedge

The auroral substorm is an organized sequence of events seen in the aurora near midnight. It is a manifestation of the magnetospheric substorm which is a disturbance of the magnetosphere brought about by the solar wind transfer of magnetic flux from the dayside to the tail lobes and its return through the plasma sheet to the dayside. The most dramatic feature of the auroral substorm is the sudden brightening and poleward expansion of the aurora. Intimately associated with this expansion is a westward electrical current flowing across the bulge of expanding aurora. This current is fed by a downward field-aligned current (FAC) at its eastern edge and an upward current at its western edge. This current system is called the substorm current wedge (SCW). The SCW forms within a minute of auroral expansion. FAC are created by pressure gradients and field line bending from shears in plasma flow. Both of these are the result of pileup and diversion of plasma flows in the near-earth plasma sheet. The origins of these flows are reconnection sites further back in the tail. The auroral expansion can be explained by a combination of a change in field line mapping caused by the substorm current wedge and a tailward growth of the outer edge of the pileup region. We illustrate this scenario with a complex substorm and discuss some of the problems associated with this interpretation.

Time‐dispersed ion signatures observed in the Martian magnetosphere by MAVEN

AbstractMars Atmosphere and Volatile EvolutioN mission's (MAVEN) high‐cadence measurements reveal the frequent occurrence of ion energy dispersion events inside the Martian magnetosphere. The systematics of observed dispersion signatures suggest time dispersion of a broad source spectrum over a flight distance of a few thousand kilometers and disfavor mechanisms involving spatial dispersion. Pickup of heavy planetary ions in strong variable electric fields provides one potential mechanism that could produce the observed time dispersion signatures. The periodicity of many observed dispersion signatures, with frequencies near the upstream proton cyclotron frequency, suggests a possible role for low‐frequency plasma waves in accelerating the observed ions from a source near the induced magnetospheric boundary to the observation location inside the magnetospheric tail lobes. The observed dispersion signatures may provide a new way to track the flow of energy from the upstream region through the magnetosphere and the role of waves in driving the escape of ions from the atmosphere.

Simulations of the Earth's magnetosphere embedded in sub‐Alfvénic solar wind on 24 and 25 May 2002

AbstractDuring 24 and 25 May 2002, the solar wind conditions at Earth's orbit were very unusual: the density was extremely low (below 0.1/cc) and, as a result, the flow was subfast and sub‐Alfvénic (the Alfvén Mach number was as low as 0.4 in the rest frame of the Earth). Consequently, the Earth's bow shock disappeared and two Alfvén wings formed on the flanks of the magnetosphere. These two long structures (estimated extension of 600 RE for this event) affect the incoming plasma as follows: the velocity is reduced and the magnetic field rotates. In the present study, global magnetohydrodynamical simulations of the magnetosphere are performed for such upstream solar wind conditions. The simulations show how the magnetosphere configuration dramatically changes when the sub‐Alfvénic solar wind reaches the magnetosphere: the dayside magnetopause expands up to 20 RE, and on the nightside the position of the last closed magnetic field line diminishes to 20 RE. As a result the closed magnetic field line region becomes very symmetric. The open field line configuration also changes such that field lines emanating from the Northern Hemisphere all point in the direction of the dawn Alfvén wing (around 8:00 LT), while the field lines from the Southern Hemisphere all point in direction of the other wing (around 22:00 LT). During the formation of the Alfvén wings, the tail lobes completely disappeared and the auroral activity greatly diminished, i.e., the magnetosphere becomes geomagnetically quiet.

MHD simulations using average solar wind conditions for substorms observed under northward IMF conditions

AbstractSubstorms are known to sometimes occur even under northward interplanetary magnetic field (IMF) conditions. In this paper, we perform three‐dimensional global magnetohydrodynamic simulations to examine dayside reconnection, tail, and ionospheric signatures for two cases of substorm observations under prolonged northward and dawnward IMF conditions: (1) a strongly northward/dawnward IMF case with BIMF = (0, −20, 20) nT; (2) a weakly northward/dawnward IMF case with BIMF = (0, −2, 2) nT. Throughout the simulations, we used the constant solar wind conditions to reflect the prolonged solar wind conditions around the substorm times. We found that, in both cases, the tail reconnection occurred after the usual high‐latitude reconnection on the dayside, providing a possible energy source for later triggered substorm observations under northward IMF conditions. The presence of an equal amount of IMF By allows the high‐latitude reconnected magnetic field lines to transport to the tail lobe, eventually leading to the tail reconnection. The simulation results also revealed the following major differences between the two cases: First, the reconnection onset (both on dayside and in the tail) occurs earlier in the strongly northward IMF case than in the weakly northward IMF case. Second, the polar cap size, which is finite in both cases despite the northward IMF conditions and thus supports the lobe energy buildup needed for the substorm occurrences, is larger in the strongly northward IMF case. Accordingly, the polar cap potential is far larger in the strongly northward IMF case (hundreds of kilovolt) than in the weakly northward IMF case (tens of kilovolt). Third, in the strongly northward IMF case, the strong earthward tail plasma flow appears to be caused by the enhanced convection (so enhanced duskward Ey) due to the tail reconnection. In contrast, in the weakly northward IMF case, the earthward tail plasma flow increases gradually in association with a modestly increased duskward electric field. In addition, the inner plasma pressure and the cross tail current near the reconnection site increase significantly in the strongly northward IMF case but less significantly in the weakly northward IMF case after the onset of the tail reconnection. In conclusion, the simulation results support observations of the substorms under northward IMF conditions in the presence of an equal amount of IMF By by demonstrating the energy input via dayside reconnection and the subsequent occurrence of the tail reconnection.

Further evidence for the role of magnetotail current shape in substorm initiation

Substorm initiation still remains an unsolved problem, even though there is a consensus among most researchers that its main stages include dayside reconnection and substorm expansion. Dayside reconnection results in magnetotail flux buildup to a certain critical level, after which [or after the interplanetary magnetic field (IMF) Bz turns northward] the substorm expansion begins. One problem with the above scenario is that the critical amount of magnetic flux differs from one substorm to another, and not every northward turning of the IMF Bz triggers a substorm. We suggest that an important factor in substorm dynamics may be the variable shape and alignment of the magnetospheric tail current sheet, which bends and warps in response to diurnal/seasonal changes of the Earth’s dipole tilt angle and also in response to more rapid changes of the solar wind flow direction. Both of these factors may be important, if one assumes that the deformed current sheet becomes unstable at lower values of the tail lobe magnetic flux/pressure than the planar sheet. To investigate this idea, we examined large multi-year sets of THEMIS, Cluster, and Geotail data and established a relationship between the tail lobe Bx and the dipole tilt angle. Further examinations of substorm events during 2005–2010 supported the hypothesis that their probability and intensity indeed depended on the concurrent values of the tilt angle.

The formation of a transient current system near the inner edge of the magnetospheric tail current

The structure of the magnetic field near the inner edge of the magnetospheric tail during the preliminary phase of the magnetic storm on Feb. 14, 2009 was studied based on the data of THEMIS satellites. The magnetic field of the currents that were flowing in the magnetospheric tail was obtained by subtracting the effect of the geomagnetic dipole and the magnetic field of magnetospheric currents other than the tail currents (mainly magnetopause currents) from the magnetic field measured on board the satellites. The paraboloid model of the magnetosphere (A2000) was used for calculating the magnetic field of magnetospheric currents. The comparison of calculations and measurements at five satellites in geomagnetically quiet periods allows one to obtain typical radial profiles of magnetic-field components along the magnetospheric tail. It was demonstrated that the nonstandard structure of the magnetic field near the inner edge of the tail-current sheet before the onset of the magnetic storm on February 14, 2009 is connected with the formation of the transient current system in the magnetosphere. A circular current in the equatorial plane was formed before the onset of the storm in the course of adiabatic compression of the magnetosphere by the solar wind to maintain the magnetic flux through the tail lobes. The spatial position and intensity of the current were determined.

Thin current sheet formation in response to the loading and the depletion of magnetic flux during the substorm growth phase

AbstractThe physics of geomagnetic substorms has been under debate for a long time. Although the growth phase has received less attention than the spectacular expansion phase, the state of the magnetotail at the end of the growth phase, i.e., a thin current sheet (CS) formation is of central importance because it provides the magnetotail conditions for the expansion phase onset. This study investigates CSs evolution during the substorm growth phase. The growth phase physics considered here includes the removal of closed magnetic flux in the near‐Earth tail and the addition of magnetic flux into the tail lobes. It is found that two separate CSs evolve at distinct locations in the near‐Earth and the midtail region in response to the depletion and the loading of magnetic flux. The relative current densities in the dual‐current‐sheet configuration depends strongly on whether the depleted or the added magnetic flux dominates. The presented results suggest that substorm expansion onset may be associated only with reconnection onset in the near‐Earth CS, while midtail reconnection causes bursty bulk flows or bubbles.