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This report presents a method for constructing a simplified numerical description of the electric current distributions in the ionosphere and gap region based on dipole-aligned loop elementary currents (DALECs). A theoretical basis for DALECs is presented, along with a prototypical algorithm for constructing an elementary numerical DALEC. The algorithm is verified and validated by combining DALECs with an efficient Biot-Savart solver in order to estimate magnetic disturbance on the Earth's surface. We examine (1) simple scenarios with known solutions and (2) hemispherical magnetic disturbance fields obtained from a state-of-the-art global geospace circulation model. [ABSTRACT FROM AUTHOR]

The geospace plume, referring to the combined processes of the plasmaspheric and the ionospheric storm‐enhanced density (SED)/total electron content (TEC) plumes, is one of the unique features of geomagnetic storms. The apparent spatial overlap and joint temporal evolution between the plasmaspheric plume and the equatorial mapping of the SED/TEC plume indicate strong magnetospheric‐ionospheric coupling. However, a systematic modeling study of the factors contributing to geospace plume development has not yet been performed due to the lack of a sufficiently comprehensive model including all the relevant physical processes. In this paper, we present a numerical simulation of the geospace plume in the 31 March 2001 storm using the Multiscale Atmosphere‐Geospace Environment model. The simulation reproduces the observed linkage of the two plumes, which, we interpret as a result of both being driven by the electric field that maps between the magnetosphere and the ionosphere. The model predicts two velocity channels of sunward plasma drift at different latitudes in the dusk sector during the storm main phase, which are identified as the sub‐auroral polarization stream (subauroral polarization streams (SAPS)) and the convection return flow, respectively. The SAPS is responsible for the erosion of the plasmasphere plume and contributes to the ionospheric TEC depletion in the midlatitude trough region. We further find the spatial distributions of the magnetospheric ring current ions and electrons, determined by a delicate balance of the energy‐dependent gradient/curvature drifts and the E× Bdrifts, are crucial to sustain the SAPS electric field that shapes the geospace plume throughout the storm main phase. The first whole geospace simulation to demonstrate coherent storm‐time evolution of plasmaspheric and total electron content (TEC) plumesThe model demonstrates plasmasphere erosion and TEC depletion by the subauroral polarization streams (SAPS)SAPS is sustained by magnetospheric ion and electron distributions formed by a delicate balance of energy‐dependent and E× Bdrifts The first whole geospace simulation to demonstrate coherent storm‐time evolution of plasmaspheric and total electron content (TEC) plumes The model demonstrates plasmasphere erosion and TEC depletion by the subauroral polarization streams (SAPS) SAPS is sustained by magnetospheric ion and electron distributions formed by a delicate balance of energy‐dependent and E× Bdrifts

The 17 March 2015 St. Patrick's Day Storm is the largest geomagnetic storm to date of Solar Cycle 24, with a Dstof −223 nT. The magnetopause moved inside geosynchronous orbit under high solar wind dynamic pressure and strong southward interplanetary magnetic field Bzcausing loss; however, a subsequent drop in pressure allowed for rapid rebuilding of the radiation belts. The 17 March 2013 storm also shows similar effects on outer zone electrons: first, a rapid dropout due to inward motion of the magnetopause followed by rapid increase in flux above the prestorm level early in the recovery phase and a slow increase over the next 12 days. These phases can be seen in temporal evolution of the electron phase space density measured by the Energetic Particle, Composition, and Thermal Plasma Suite (ECT) instruments on Van Allen Probes. Using the Lyon‐Fedder‐Mobarry global MHD model driven by upstream solar wind measurements, we simulated both St. Patrick's Day 2013 and 2015 events, analyzing Lyon‐Fedder‐Mobarry electric and magnetic fields to calculate radial diffusion coefficients. These coefficients have been implemented in a radial diffusion code, using the measured electron phase space density following the local heating as the initial radial profile and outer boundary condition for subsequent temporal evolution over the next 12 days, beginning 18 March. Agreement with electron phase space density at 1000 MeV/G measured by the MagEIS component of the ECT instrument suite on Van Allen Probes was much improved using radial diffusion coefficients from the MHD simulations relative to coefficients parameterized by a global geomagnetic activity index. Radial diffusion coefficient calculated from LFM MHD model agrees with the diffusion coefficient calculated from RBSP measurementsRadial diffusion coefficient calculated from LFM MHD model is much lower than Bratigam and Albert and Ozeke'sAgreement between radial diffusion model and RBSP measurement was much improved using radial diffusion coefficients from the MHD simulations

The 17–18 March 2015 storm is the largest geomagnetic storm in the Van Allen Probes era to date. The Lyon-Fedder-Mobarry global MHD model has been run for this event using ARTEMIS data as solar wind input. The ULF wave power spectral density of the azimuthal electric field and compressional magnetic field is analyzed in the 0.5–8.3 mHz range. The lowest three azimuthal modes account for 70% of the total power during quiet times. However, during high activity, they are not exclusively dominant. The calculation of the radial diffusion coefficient is presented. We conclude that the electric field radial diffusion coefficient is dominant over the magnetic field coefficient by one to two orders of magnitude. This result contrasts with the dominant magnetic field diffusion coefficient used in most 3-D diffusion models. LFM global MHD model is run and ULF wave power spectrum is analyzed for March 2015 stormThe lowest three azimuthal modes account for 70% of the total ULF power during quiet times but not exclusively dominant during active timesThe electric field radial diffusion coefficient is dominant over the magnetic field coefficient by one to two orders of magnitude

We have recently implemented a new module that includes both the anomalous electron heating and the electron‐neutral cooling rate correction associated with the Farley‐Buneman Instability (FBI) in the thermosphere‐ionosphere electrodynamics global circulation model (TIEGCM). This implementation provides, for the first time, a modeling capability to describe macroscopic effects of the FBI on the ionosphere and thermosphere in the context of a first‐principle, self‐consistent model. The added heating sources primarily operate between 100 and 130 km altitude, and their magnitudes often exceed auroral precipitation heating in the TIEGCM. The induced changes in Eregion electron temperature in the auroral oval and polar cap by the FBI are remarkable with a maximum Teapproaching 2200 K. This is about 4 times larger than the TIEGCM run without FBI heating. This investigation demonstrates how researchers can add the important effects of the FBI to magnetosphere‐ionosphere‐thermosphere models and simulators. A new module associated with the Farley‐Buneman Instability has been implemented in the TIEGCMMaximum E region Te enhancement is close to 2200 KElectron temperature enhancement is proportional to the strengths of electric fields

It is well known that the use of tightly focused continuous wave lasers can be an effective treatment of common telangiactasia. In general, the technique requires the skills of a highly dexterous surgeon using the aid of optical magnification. Due to the nature of this approach, it has proven to be largely impractical. To overcome this, we have developed an automated system that alleviates the strain on the user associated with the manual tracing method. The device makes use of high contrast illumination, simple monochromatic imaging, and machine vision to determine the location of blood vessels in the area of interest. The vessel coordinates are then used as input to a two-dimensional laser scanner via a near real-time feedback loop to target, track, and treat. Such mechanization should result in increased overall treatment success, and decreased patient morbidity. Additionally, this approach enables the use of laser systems that are considerably smaller than those currently used, and consequently the potential for significant cost savings. Here we present an overview of a proof-of-principle system, and results using examples involving in vivoimaging of human skin. © 2004 Society of Photo-Optical Instrumentation Engineers.

The role of diffuse electron precipitation in the formation of subauroral polarization streams (SAPS) is investigated with the Multiscale Atmosphere‐Geospace Environment (MAGE) model. Diffuse precipitation is derived from the distribution of drifting electrons. SAPS manifest themselves as a separate mesoscale flow channel in the duskside ionosphere, which gradually merges with the primary auroral convection toward dayside as the equatorward auroral boundary approaches the poleward Region‐2 field‐aligned currents (FACs) boundary. SAPS expand to lower latitudes and toward the nightside during the main phase of a geomagnetic storm, associated with magnetotail earthward plasma flows building up the ring current and intensifying Region‐2 FACs and electron precipitation. SAPS shrink poleward and sunward as the interplanetary magnetic field turns northward. When diffuse precipitation is turned off in a controlled MAGE simulation, ring current and duskside Region‐2 FACs become weaker, but subauroral zonal ion drifts are still comparable to auroral convection. However, subauroral and auroral convection manifest as a single broad flow channel without showing any mesoscale structure. SAPS overlap with the downward Region‐2 FACs equatorward of diffuse precipitation, where poleward electric fields are strong due to a low conductance in the subauroral ionosphere. The Region‐2 FACs extend to latitudes lower than the diffuse precipitation because the ring current protons penetrate closer to the Earth than the electrons do. This study reproduces the key physics of SAPS formation and their evolution in the coupled magnetosphere‐ionosphere during a geomagnetic storm. Diffuse electron precipitation is demonstrated to play a critical role in determining SAPS location and structure. Subauroral polarization streams (SAPS) are a mesoscale (∼100–500 km) plasma flow channel frequently observed in the duskside subauroral ionosphere. This study investigates how diffuse electron precipitation affects the location and structure of SAPS, using the newly developed, state‐of‐the‐art geospace model of Multiscale Atmosphere‐Geospace Environment (MAGE). The MAGE model has the capability to directly simulate diffuse precipitation using particle drift physics. MAGE numerical experiments show that SAPS exhibit as a separate flow channel when diffuse precipitation is included in the simulation, but subauroral and auroral convections become one broad channel when diffuse precipitation is turned off. SAPS are produced in the gap region between the low latitude boundaries of electron aurora and downward field‐aligned current (FAC) on the duskside, where the ionospheric conductance is low due to lack of ionization while downward region‐2 FAC closes through this low conductance region. Strong poleward electric fields are generated to drive large westward ion drifts in the SAPS channel. Tracing back to the magnetosphere, the gap between the inner boundaries is formed because the ring current protons, whose distribution primarily determines the downward FAC, penetrate deeper than the electrons. Thus diffuse aurora, with plasma sheet as the source population, occurs poleward of the lower boundary of the downward Region‐2 current. This study demonstrates the importance of including diffuse precipitation in coupled geospace models to understand the dynamics of SAPS. A fully coupled geospace model captures the key physical mechanism and distinct spatial structure of subauroral polarization streamsThe separation of the flow channel from the main auroral convection is determined by diffuse electron precipitation boundaryThe evolution of the SAPS in the ionosphere and magnetosphere is reproduced by the simulation in accordance with observations A fully coupled geospace model captures the key physical mechanism and distinct spatial structure of subauroral polarization streams The separation of the flow channel from the main auroral convection is determined by diffuse electron precipitation boundary The evolution of the SAPS in the ionosphere and magnetosphere is reproduced by the simulation in accordance with observations

The pursuit of realistic simulation of the physics of plasma transport, ring current formation and storm‐triggered Earth magnetic and electric field is an ongoing challenge in magnetospheric physics. To this end, we have implemented a coupling of the Lyon‐Fedder‐Mobarry (LFM) global magnetohydrodynamic model with the Rice convection model‐equilibrium (RCM‐E) of the inner‐magnetosphere and plasma sheet. This one‐way coupling scheme allows continuous update of the RCM‐E boundary conditions from the plasma moments calculated by the LFM while preserving entropy conservation. This results in a model that has the high‐resolution self‐consistent description of the inner magnetosphere and includes the effects of time‐dependent outer‐magnetospheric electromagnetic fields and plasma configurations. In addition, driving the RCM‐E in this way resolves the issue of having a plasma‐β‐constrained region in the coupled model of LFM‐RCM and expands the RCM‐E simulation region farther out into plasma sheet where the storm‐time plasma transportation takes place. In the ionosphere, the RCM‐E replaces the ionospheric electric field model of LFM with the one used by the RCM. The electric potential produced, along with the realistic ionospheric precipitation patterns shows strong consistency with the transportation patterns in the plasma sheet featured with well‐resolved bubbles and bursty bulk flows. Results from the simulations of an idealized event will be presented and discussed. Understanding the important phenomena in the inner magnetosphere such as plasma transport, ring current formation, storm‐triggered Earth electromagnetic field changes and related ionospheric signatures is of great importance to space weather research. We implement a new coupling scheme of two models: the Lyon‐Fedder‐Mobarry (LFM) global magnetohydrodynamic model that simulates the global evolution of the magnetosphere and the Rice convection model‐equilibrium (RCM‐E) which self‐consistently describes the dynamics in the inner magnetosphere. Compared with the coupled model of LFM‐RCM, this new coupling scheme expands the RCM simulation region significantly farther out into plasma sheet, so the trajectory and evolution of the plasma flows can be tracked. In addition, the built‐in potential solver of RCM‐E allows us to more accurately connect the plasma distribution to the ionospheric potential by the Birkeland currents. The resulting electric potential better resolves the ionospheric features that correspond to the flow patterns in the plasma sheet than that in LFM‐RCM. The simulated precipitation patterns on the polar cap resemble the aurora observations during the injection events. Self‐consistent inner‐magnetosphere model is driven by inputs from the Lyon‐Fedder‐Mobarry global magnetohydrodynamic modelThe expanded inner magnetospheric modeling region captures high‐resolution bursty bulk flows in the plasma sheetRealistic bursty bulk flows induced aurora patterns are simulated Self‐consistent inner‐magnetosphere model is driven by inputs from the Lyon‐Fedder‐Mobarry global magnetohydrodynamic model The expanded inner magnetospheric modeling region captures high‐resolution bursty bulk flows in the plasma sheet Realistic bursty bulk flows induced aurora patterns are simulated

The role of solar wind density in the cross polar cap potential (CPCP) response under northward interplanetary magnetic field is investigated with observation‐based global simulations. A rare event was reported by Clauer et al. (2016) during which the ionospheric electric field EISPdoes not saturate under extreme interplanetary electric field (IEF) of ∼15 mV/m. While commonly utilized coupling functions based on IEF fail to provide an unambiguous explanation for the linear response, the Lyon‐Fedder‐Mobarry‐Magnetosphere‐Ionosphere Coupler/Solver model is used to explore the mechanisms in this study. The model first reproduces the observed linear features of the EISP. The simulated CPCP also responds linearly to IEF variations. A controlled simulation is designed with solar wind density artificially reduced to 10% of the observed value while all other parameters such as the IEF are kept the same. The controlled simulation shows saturation of the EISPas well as the CPCP. Further analysis shows the difference in the magnetosheath plasma β, implying the distinct dominant forces between the two simulations. The Lopez magnetosheath force balance theory is used to explain the CPCP responses under different solar wind densities. This comparison study highlights the role of solar wind density in determining the magnetosphere‐ionosphere response to extreme interplanetary drivings. The cross polar cap potential is the electrical potential imposed on the Earth by solar wind driver. It measures the electrodynamic coupling between the Earth and the solar wind. Typically, this potential is thought to depend mostly on the electric field in the solar wind and would saturate when the solar wind electric field exceeds certain threshold. Recently, a rare case was found when the potential did not saturate under very large solar wind electric field. We use global magnetosphere‐ionosphere model to investigate this event and found the solar wind density plays a critical role in affecting the potential response under the extreme driving conditions. A rare event of linear CPCP response to very large interplanetary electric field is investigatedGlobal magnetosphere‐ionosphere simulations show that the high solar wind density contributes to the linear CPCP response in the presence of strong IEFThe magnetosheath force balance theory is applicable under extreme driving conditions

Prompt enhancement of relativistic electron flux at L= 3–5 has been reported from Van Allen Probes Relativistic Electron Proton Telescope (REPT) measurements associated with the 17 March 2015 interplanetary shock compression of the dayside magnetosphere. Acceleration by ∼1 MeV is inferred on less than a drift timescale as seen in prior shock compression events, which launch a magnetosonic azimuthal electric field impulse tailward. This impulse propagates from the dayside around the flanks accelerating electrons in drift resonance at the dusk flank. Such longitudinally localized acceleration events produce a drift echo signature which was seen at >1 MeV energy on both Van Allen Probe spacecraft, with sustained observations by Probe B outbound at L= 5 at 2100 MLT at the time of impulse arrival, measured by the Electric Fields and Waves instrument. MHD test particle simulations are presented which reproduce drift echo features observed in the REPT measurements at Probe B, including the energy and pitch angle dependence of drift echoes observed. While the flux enhancement was short lived for this event due to subsequent inward motion of the magnetopause, stronger events with larger electric field impulses, as observed in March 1991 and the Halloween 2003 storm, produce enhancements which can be quantified by the inward radial transport and energization determined by the induction electric field resulting from dayside compression. Prompt MeV electron enhancement at L= 3‐5 is seen in Van Allen Probes measurements from 17 March 2015 IP shock magnetopause compressionMHD test particle simulations reproduce drift echoes observed by the REPT instrumentAzimuthal electric field impulse responsible for acceleration and radial transport is consistent with EFW measurements

The reaction of the magnetosphere‐ionosphere system to dynamic auroral potential drops is investigated using the Lyon‐Fedder‐Mobarry global model including, for the first time in a global simulation, the dissipative load of field‐aligned potential drops in the low‐altitude boundary condition. This extra load reduces the field‐aligned current (j||) supplied by nightside reconnection dynamos. The system adapts by forcing the nightside X line closer to Earth, with a corresponding reduction in current lensing (j||/B= constant) at the ionosphere and additional contraction of the plasma sheet during substorm recovery and steady magnetospheric convection. For steady and moderate solar wind driving and with constant ionospheric conductance, the cross polar cap potential and hemispheric field‐aligned current are lower by approximately the ratio of the peak field‐aligned potential drop to the cross polar cap potential (10–15%) when potential drops are included. Hemispheric ionospheric Joule dissipation is less by 8%, while the area‐integrated, average work done on the fluid by the reconnecting magnetotail field increases by 50% within |y| < 8 RE. Effects on the nightside plasma sheet include (1) an average X line 4 REcloser to Earth; (2) a 12% higher mean reconnection rate; and (3) dawn‐dusk asymmetry in reconnection with a 17% higher rate in the premidnight sector. Auroral potential drops reduce hemispheric field‐aligned current and cross polar cap potential in global simulationsCause nightside reconnection to migrate earthward and reduce the area of the plasma sheetIncrease the nightside reconnection rate, with a larger rate in the premidnight sector relative to the postmidnight

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Ionospheric responses to the initial phases of three geomagnetic storms: 2–5 April 2004, 7–9 November 2004, and 13–16 December 2006, were compared using both ground‐based GPS total electron content (TEC) data and coupled magnetosphere ionosphere thermosphere (CMIT) model simulations. The onset times for these storms all occurred at local daytime in the North American sector. This similarity of onset times and other factors resulted in some common features in their ionospheric response. These common features include (1) enhanced TEC (positive response) at low and middle latitudes in the daytime, (2) depleted TEC (negative response) around the geomagnetic equator in the daytime, (3) a north‐south asymmetry in the positive response as the northern hemispheric response appeared to be more pronounced, and (4) negative response at high latitudes as the storms progressed. The CMIT model captured most of these features. Analysis of model results showed that storm‐time enhancements in the daytime eastward electric field were the primary cause of the observed positive storm effects at low and middle latitudes as well as the negative response around the geomagnetic equator in the daytime. These eastward electric field enhancements were caused by the penetration of high latitude electric fields to low latitudes during southward interplanetary magnetic field (IMF) periods, when IMF Bzoscillated between southward and northward direction in the initial, shock phase of the storms. Consequently, the ionosphere was lifted up at low and middle latitudes to heights where recombination was weak allowing the plasma to exist for a long period resulting in higher densities. In addition, the CMIT model showed that high‐latitude negative storm responses were related to the enhancements of molecular nitrogen seen in TIMED/Global Ultraviolet Imager observations, whereas the negative storm effects around the geomagnetic equator were not associated with thermospheric composition changes; they were the result of plasma transport processes.