R. J. Barnes

Multiradar observations of the polar tongue of ionization

[1] We present a global view of large-scale ionospheric disturbances during the main phase of a major geomagnetic storm. We find that the low-latitude, auroral, and polar latitude regions are coupled by processes that redistribute thermal plasma throughout the system. For the large geomagnetic storm on 20 November 2003, we examine data from the high-latitude incoherent scatter radars at Millstone Hill, Sondrestrom, and EISCAT Tromso, with SuperDARN HF radar observations of the high-latitude convection pattern and DMSP observations of in situ plasma parameters in the topside ionosphere. We combine these with north polar maps of stormtime plumes of enhanced total electron content (TEC) derived from a network of GPS receivers. The polar tongue of ionization (TOI) is seen to be a continuous stream of dense cold plasma entrained in the global convection pattern. The dayside source of the TOI is the plume of storm enhanced density (SED) transported from low latitudes in the postnoon sector by the subauroral disturbance electric field. Convection carries this material through the dayside cusp and across the polar cap to the nightside where the auroral F region is significantly enhanced by the SED material. The three incoherent scatter radars provided full altitude profiles of plasma density, temperatures, and vertical velocity as the TOI plume crossed their different positions, under the cusp, in the center of the polar cap, and at the midnight oval/polar cap boundary. Greatly elevated F peak density (>1.5E12 m 3 ) and low electron and ion temperatures (2500 K at the F peak altitude) characterize the SED/TOI plasma observed at all points along its high-latitude trajectory. For this event, SED/TOI F region TEC (150–1000 km) was 50 TECu both in the cusp and in the center of the polar cap. Large, upward directed fluxes of O+ (>1.E14 m 2 s 1 ) were observed in the topside ionosphere

Development of large‐scale Birkeland currents determined from the Active Magnetosphere and Planetary Electrodynamics Response Experiment

The Active Magnetosphere and Planetary Electrodynamics Response Experiment uses magnetic field data from the Iridium constellation to derive the global Birkeland current distribution every 10 min. We examine cases in which the interplanetary magnetic field (IMF) rotated from northward to southward resulting in onsets of the Birkeland currents. Dayside Region 1/2 currents, totaling ~25% of the final current, appear within 20 min of the IMF southward turning and remain steady. Onset of nightside currents occurs 40 to 70 min after the dayside currents appear. Thereafter, the currents intensify at dawn, dusk, and on the dayside, yielding a fully formed Region 1/2 system ~30 min after the nightside onset. The results imply that the dayside Birkeland currents are driven by magnetopause reconnection, and the remainder of the system forms as magnetospheric return flows start and progress sunward, ultimately closing the Dungey convection cycle.

Increased living donor volunteer rates with a formal recipient family education program

We have generally encouraged living donation among our kidney recipients. However, an examination of our clinical practice revealed inconsistencies in the depth and content of information transmitted to kidney recipient families regarding living donation. We therefore initiated a structured education program, including an educational video, to ensure that all recipient families would receive a similar exposure to a standard block of information. After the program had been functioning for over a year, we compared the living donor (LD) volunteer rates between the 3-year period before (BEFORE) and the 18 months after (AFTER) initiation of the formal education program. There were 1,363 patients registered on our kidney transplantation waiting list during the 54-month study period (757 white [56%] and 580 black [43%]). We found that 33.4% of the kidney transplant candidates in the period BEFORE the LD education program had at least one potential LD tissue typed, compared with 39.4% in the period AFTER starting the program (P = 0.03). The increase in the proportion of patients with potential donors was greatest among the black (P < 0.05) and elderly (P < 0.01) registrants, which were the groups with the lowest volunteer rates before the program began. Among the registrants with at least one potential donor, the percentage of registrants who ultimately received an LD transplant was highly correlated with the number of donors (R = 0.98). The rate of LD kidney transplantation was significantly higher (P = 0.02) for the patients referred in the period AFTER initiation of the LD education program compared with the period BEFORE the program. The 1- and 3-year graft survival rates for the 170 LD transplants performed in these patients were 96.9% and 93.2%, respectively. These were significantly better than the corresponding 83.9% and 71.4% rates for the 341 kidney transplants from cadaver donors in these registrants (P < 0.001). Black recipients of LD transplants had graft survival rates comparable to whites; the 3-year graft survival rate for LD transplants was 93.9% in whites and 90.6% in blacks (P = NS). We conclude that living kidney donor volunteer rates can be improved by a formal family education program, especially for subgroups of patients with low volunteer rates. A substantial benefit is derived by black patients, who generally experience low graft survival rates with cadaver-donor kidneys. A local formal LD education program is a useful adjunct to national organ donation campaigns.

Global storm time depletion of the outer electron belt

Abstract The outer radiation belt consists of relativistic (>0.5 MeV) electrons trapped on closed trajectories around Earth where the magnetic field is nearly dipolar. During increased geomagnetic activity, electron intensities in the belt can vary by orders of magnitude at different spatial and temporal scales. The main phase of geomagnetic storms often produces deep depletions of electron intensities over broad regions of the outer belt. Previous studies identified three possible processes that can contribute to the main‐phase depletions: adiabatic inflation of electron drift orbits caused by the ring current growth, electron loss into the atmosphere, and electron escape through the magnetopause boundary. In this paper we investigate the relative importance of the adiabatic effect and magnetopause loss to the rapid depletion of the outer belt observed at the Van Allen Probes spacecraft during the main phase of 17 March 2013 storm. The intensities of >1 MeV electrons were depleted by more than an order of magnitude over the entire radial extent of the belt in less than 6 h after the sudden storm commencement. For the analysis we used three‐dimensional test particle simulations of global evolution of the outer belt in the Tsyganenko‐Sitnov (TS07D) magnetic field model with an inductive electric field. Comparison of the simulation results with electron measurements from the Magnetic Electron Ion Spectrometer experiment shows that magnetopause loss accounts for most of the observed depletion at L>5, while at lower L shells the depletion is adiabatic. Both magnetopause loss and the adiabatic effect are controlled by the change in global configuration of the magnetic field due to storm time development of the ring current; a simulation of electron evolution without a ring current produces a much weaker depletion.

Technique: Large‐scale ionospheric conductance estimated from combined satellite and ground‐based electromagnetic data

[1] A technique for estimating the large-scale spatial distribution of the height-integrated electrical conductivity (conductance) of the Earth’s high-latitude ionosphere is presented. By combining satellite magnetic perturbation data with ground-based magnetometer and HF radar observations the Hall (SH) and Pedersen (SP) conductances are independently calculated. Magnetic perturbations observed at the Earth’s surface are combined with those recorded by satellites to calculate the horizontal ionospheric current (~ ?). Combined HF radar and satellite ion drift data give the ionospheric electric field ( ~?), which combined with ~ J ? allows SH and SP to be estimated from Ohm’s law. Conductance results from preliminary application of the technique to an event with a 1 hour integration time are presented. Significant uncertainties arise due to sparse ground magnetometer and electric field coverage. The resulting conductance distribution shows an enhancement in the auroral regions as expected from a statistical model conductance. However, the calculated conductance enhancement is located between the region 1 and region 2 Birkeland currents. This agrees with the statistical model data in the morning sector but disagrees in the evening sector. Comparison of the conductance results with conductance data inferred from in situ precipitating particle observations shows colocated enhancements. The calculated data also show a low (<1) Hall to Pedersen conductance ratio in regions near downward Birkeland current.

Comparison of predictive estimates of high‐latitude electrodynamics with observations of global‐scale Birkeland currents

Two of the geomagnetic storms for the Space Weather Prediction Center (SWPC) Geospace Environment Modeling (GEM) challenge [cf. Pulkkinen et al., 2013] occurred after data were first acquired by the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE). We compare Birkeland currents from AMPERE with predictions from four models for the 4-5 April 2010 and 5-6 August 2011 storms. The four models are: the Weimer [2005b] field-aligned current statistical model; the Lyon-Fedder-Mobarry magnetohydrodynamic (MHD) simulation; the Open Global Geospace Circulation Model MHD simulation; and the Space Weather Modeling Framework MHD simulation. The MHD simulations were run as described in Pulkkinen et al. [2013] and the results obtained from the Community Coordinated Modeling Center (CCMC). The total radial Birkeland current, ITotal, and the distribution of radial current density, Jr, for all models are compared with AMPERE results. While the total currents are well correlated, the quantitative agreement varies considerably. The Jr distributions reveal discrepancies between the models and observations related to the latitude distribution, morphologies, and lack of nightside current systems in the models. The results motivate enhancing the simulations first by increasing the simulation resolution, and then by examining the relative merits of implementing more sophisticated ionospheric conductance models, including ionospheric outflows or other omitted physical processes. Some aspects of the system, including substorm timing and location, may remain challenging to simulate, implying a continuing need for real-time specification.

The response of the high-latitude ionosphere to the coronal mass ejection event of April 6, 2000: A practical demonstration of space weather nowcasting with the Super Dual Auroral Radar Network HF radars

The ionosphere at high latitudes is the site of important effects in space weather. These include strong electrical currents that may disrupt power systems through induced currents and density irregularities that can degrade HF and satellite communication links. With the impetus provided by the National Space Weather Program, the radars of the Super Dual Auroral Radar Network have been applied to the real-time specification (“nowcasting”) of conditions in the high-latitude ionosphere. A map of the plasma convection in the northern high-latitude ionosphere is continually generated at the Johns Hopkins University Applied Physics Laboratory (JHU/APL) SuperDARN web site using data downloaded in real time from the radars via Internet connections. Other nowcast items include information on the conditions of HF propagation, the spatial extent of auroral effects, and the total cross polar cap potential variation. Time series of various parameters and an animated replay of the last 2 hours of convection patterns are also available for review. By comparing with simultaneous measurements from an upstream satellite, it is possible to infer the effective delay from the detection of changes in the solar wind at the satellite to the arrival of related effects in the high-latitude ionosphere. We discuss the space weather products available from the JHU/APL SuperDARN web site and their uses by simulating a nowcast of the ionosphere on April 6, 2000, during the arrival of a coronal mass ejection (CME)-related shock. The nowcast convection pattern in particular satisfies a critical need for timely, comprehensive information on ionospheric electric fields.

Electrodynamic context of magnetopause dynamics observed by magnetospheric multiscale

Magnetopause observations by Magnetospheric Multiscale (MMS) and Birkeland currents observed by the Active Magnetosphere and Planetary Electrodynamics Response Experiment are used to relate magnetopause encounters to ionospheric electrodynamics. MMS magnetopause crossings on 15 August and 19 September 2015 occurred earthward of expectations due to solar wind ram pressure alone and coincided with equatorward expansion of the Birkeland currents. Magnetopause erosion, consistent with expansion of the polar cap, contributed to the magnetopause crossings. The ionospheric projections of MMS during the events and at times of the magnetopause crossings indicate that MMS observations are related to the main path of flux transport in one case but not in a second. The analysis provides a way to routinely relate in situ observations to the context of in situ convection and flux transport.

Dawn and dusk sector comparisons of small‐scale irregularities, convection, and particle precipitation in the high‐latitude ionosphere

Received 7 June 2001; revised 31 October 2001; accepted 4 December 2001; published 19 September 2002. [1] Small-scale ionospheric irregularities and auroral precipitation are common features of the auroral ionosphere, but their spatial association has not been examined on global scales. In this paper, we compare electron and ion precipitation from individual passes of the Defense Meteorological Satellite Program (DMSP) spacecraft with concurrent observations of ionospheric irregularities and plasma convection from the Northern Hemisphere component of the Super Dual Auroral Radar Network (SuperDARN). Because of the nature of the DMSP orbits and the spatial resolution of the SuperDARN measurements these comparisons have been limited to the dusk and postdawn sectors and spatial dimensions greater than 100 km. We have found that the SuperDARN radars generally observe ionospheric irregularities over a greater latitudinal extent than the DMSP satellites observe particle precipitation. Specifically, ionospheric irregularities are observed both equatorward and poleward of the convection reversal boundary (CRB) in the dawn and dusk sectors, whereas particle precipitation is only observed equatorward of the CRB. Under conditions where the radars can detect the true equatorward boundary of the irregularities, they are observed to extend equatorward of the particle precipitation. Both irregularities and particle precipitation expand equatorward with increasing geomagnetic activity, and there is evidence that precipitation regions with higher energy flux are associated with regions of stronger sunward convection. These results suggest that SuperDARN can provide a coarse determination of the auroral-oval position that will complement measurements with optics and particle detectors. More importantly, they demonstrate the spatial relationships between precipitation, electric fields, and ionospheric irregularities that result from the electrical coupling between the magnetosphere and ionosphere and the dependence of ionospheric plasma instabilities on the ionospheric electric field and precipitation-induced electron-density gradients. INDEX TERMS: 2760 Magnetospheric Physics: Plasma convection; 2407 Ionosphere: Auroral ionosphere (2704); 2463 Ionosphere: Plasma convection; 2455 Ionosphere: Particle precipitation; 2439 Ionosphere: Ionospheric irregularities;

Deriving Global Convection Maps From SuperDARN Measurements

A new statistical modeling technique for determining the global ionospheric convection is described. The Principal Component Regression (PCR) based technique is based on SuperDARN observations and is an advanced version of the principal component regression technique that Waters et al. [2015] used for the SuperMAG data. While SuperMAG ground magnetic field perturbations are vector measurements, SuperDARN provides line-of-sight (LOS) measurements of the ionospheric convection flow. Each LOS flow has a known azimuth (or direction) which must be converted into the actual vector flow. However, the component perpendicular to the azimuth direction is unknown. Our method uses historical data from the SuperDARN data base and Principal Component Regression to determine a fill-in model convection distribution for any given Universal Time (UT). The fill-in data process is driven by a list of state descriptors (magnetic indices and the solar zenith angle). The final solution is then derived from a spherical cap harmonic fit to the SuperDARN measurements and the fill-in model. When compared with the standard SuperDARN fill-in model we find that our fill-in model provides improved solutions, and the final solutions are in better agreement with the SuperDARN measurements. Our solutions are far less dynamic than the standard SuperDARN solutions which we interpret as being due to a lack of Magnetosphere-Ionosphere inertia and communication delays in the standard SuperDARN technique while it is inherently included in our approach. Rather, we argue that the magnetosphere-ionosphere system has inertia that prevents the global convection from changing abruptly in response to an IMF change.