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We provide high-resolution maps of quasi-static Poynting flux (PF) in each hemisphere based on nine-satellite years of Defense Meteorological Satellite Program (DMSP) data. Conjugate comparisons fr...

The magnetic storm of 22-23 June 2015 was one of the largest in the current solar cycle. We present in situ observations from the Magnetospheric Multiscale Mission (MMS) and the Van Allen Probes (VAP) in the magnetotail, field-aligned currents from AMPERE (Active Magnetosphere and Planetary Electrodynamics Response), and ionospheric flow data from Defense Meteorological Satellite Program (DMSP). Our real-time space weather alert system sent out a "red alert," correctly predicting Kp indices greater than 8. We show strong outflow of ionospheric oxygen, dipolarizations in the MMS magnetometer data, and dropouts in the particle fluxes seen by the MMS Fast Plasma Instrument suite. At ionospheric altitudes, the AMPERE data show highly variable currents exceeding 20 MA. We present numerical simulations with the Block Adaptive Tree-Solarwind - Roe - Upwind Scheme (BATS-R-US) global magnetohydrodynamic model linked with the Rice Convection Model. The model predicted the magnitude of the dipolarizations, and varying polar cap convection patterns, which were confirmed by DMSP measurements.

Using Poker Flat Incoherent Scatter Radar data from the International Polar Year, we observed unexpected short-lived enhancements of a few 100 K in the F region ion temperature, or “Ti spikes”, in conjunction with sharp F region plasma density drops near the dusk plasmapause. The geomagnetic conditions were moderately to weakly disturbed and the dusk spikes were often the largest Ti values recorded within the day. Taking various other observations into consideration, we conclude that the radar observed ion frictional heating events driven by large ion-neutral relative drifts caused by temporary intensifications in the convection pattern. The heating rate was enhanced through an increase in the size of the convection pattern, causing the neutrals just poleward of the dusk plasmapause to be moving antisunward while ions were moving sunward.

[1] For the first time, equatorial plasma depletions (EPDs) have been imaged in the longitude-altitude plane using radiotomography. High-resolution (~10 km) reconstructions of electron density were derived from total electron content (TEC) measurements provided by a receiver array in Peru. TEC data were obtained from VHF/UHF signals transmitted by the Coherent Electromagnetic Radio Tomography (CERTO) beacon on the C/NOFS satellite. EPDs generated premidnight were observed near dawn. On one night, the bubble densities were highly reduced, 100–1000 km wide, and embedded within a layerlike ionosphere. Three nights later, the EPDs exhibited similar features but were embedded in a locally uplifted ionosphere. The C/NOFS in situ instruments detected a dawn depletion where the reconstruction showed lifted EPDs, implying that the postmidnight electric fields raised sections of ionosphere to altitudes where embedded/reactivated fossil EPDs were detected as dawn depletions. Satellites flying under domelike distortions of the ionosphere may observe these distortions as broad plasma decreases (BPDs).

[1] When the interplanetary magnetic field (IMF) is dawnward or duskward, magnetic merging between the IMF and the geomagnetic field occurs near the cusp on the dayside flanks of the magnetosphere. During these intervals, flow channels in the ionosphere with velocities in excess of 2 km/s have been observed, which can deposit large amounts of energy into the high-latitude thermosphere. In this study, we analyze an interval on 5 April 2010 where there was a strong dawnward impulse in the IMF, followed by a gradual decay in IMF magnitude at constant clock angle. Data from the Sondrestrom incoherent scatter radar and the Defense Meteorological Satellite Program spacecraft were used to investigate ionospheric convection during this interval, and data from the Active Magnetospheric and Planetary Electrodynamics Response Experiment (AMPERE) were used to investigate the associated Field-Aligned Current (FAC) system. Additionally, data from AMPERE were used to investigate the time response of the dawnside FAC pair. We find there is a delay of approximately 1.25 h between the arrival of the dawnward IMF impulse at the magnetopause and strength of the dawnward FAC pair, which is comparable to substorm growth and expansion time scales under southward IMF. Additionally, we find at the time of the peak FAC, there is evidence of a reconfiguring four-sheet FAC system in the morning local time sector of the ionosphere. Additionally, we find an inverse correlation between the dawn FAC strength and both the solar wind Alfvenic Mach number and the SYM-H index. No statistically significant correlation between the FAC strength and the solar wind dynamic pressure was found.

A three-day period from January 27 through January 29, 1992 is analyzed using one minute resolution solar wind data from the IMP-8 satellite and the ionospheric convection pattern data derived from the four operational DMSP satellites. During this period there were several clear reversals of the sign of the z component of the interplanetary magnetic field (IMF) which is known to have a direct effect on the convection patterns observed in the polar ionosphere. Polar convection patterns observed by the frequent passes of four DMSP satellites are examined following each sign change to determine the time lag between the change in the IMF at the magnetopause and the establishment of a new global convection signature in the ionosphere. After removing the transit time for the IMF to travel from the position of the IMP-8 satellite to the magnetopause, a further time lag of about 17 to 25 minutes is observed for the five cases where the IMF turned from northward to southward. A longer lag of between 28 and 44 minutes is observed for the two cases where the IMF turned from southward to northward. These lags are interpreted as the inertial response time of the ionosphere in reacting tomore » the change in the IMF. 16 refs., 4 figs.« less

[1] With the launch of the Defense Meteorological Satellite Program F-15 spacecraft in late 1999, data for calculating Earth-directed, magnetospheric Poynting flux became available for the 09–21 solar local time sectors. We have assembled a data base for this key element of the upper atmosphere energy budget, for the interval 2000–2005. Here we briefly introduce the data set and show a subset that reveals a pattern of extreme Poynting flux deposition associated with a large east-west interplanetary magnetic field component. At such times the dayside high-latitude Poynting flux may exceed 170 mW/m2—an order of magnitude above typical values. The likely source of these events is merging at the magnetopause flank and lobe. A significant fraction of these events occur with high speed solar wind. This pattern of extreme Poynting flux deposition has, to date, eluded detection. Energy deposition at these high rates is a likely source of previously reported, but poorly understood, near-cusp neutral density enhancements.

[1] During a period of predominantly north-westward flow for IMF BZ negative and IMF BY positive, a sequence of three distinct negative excursions of IMF BY resulted in a train of three eastward directed flow channels, interleaved by westward flow enhancements propagating into the polar cap. The high resolution of the EISCAT Svalbard radar data enables us to track formation and movement of the flow channels, which are interpreted as a sequence of intermittent reconnection alternating between different reconnection sites. Our observations are consistent with the view that a new region of reconnected flux manifests as development of a distinct flow channel near the polar cap boundary, and that successive events stay separated while pushing each other into the polar cap. Each flow channel will remain separated from neighboring channels mapping to different reconnection sites as long as the magnetic tension force with its associated field aligned current systems is maintained.

[1] During June 2008 broad plasma density decreases (BPDs) were detected repeatedly by the Planar Langmuir Probe (PLP) on board the Communication/Navigation Outage Forecasting System (C/NOFS) satellite. These density minima, not to be confused with Equatorial Plasma Bubbles (EPBs), occurred within 15° of the equator, consisted of reductions in plasma density up to an order of magnitude and extended across several degrees in azimuth along the orbit. Analysis revealed that the BPDs occurred nearly daily from May through July 2008 on C/NOFS, and that the widest BPDs were observed in the vicinity of the South Atlantic Anomaly (SAA). Similar BPDs simultaneous with the C/NOFS measurements were observed by instruments on the CHAllenging Minisatellite Payload (CHAMP) and Defense Meteorological Satellite Program (DMSP) satellites. An examination of plasma densities observed by the DMSP satellites over several years revealed that these phenomena were a frequent occurrence during (1) the period around June solstices; during (2) solar minimum years; (3) in the vicinity of the SAA. Neutral densities were examined during periods when BPDs were detected, and at times there are simultaneous neutral depletions. One possible explanation is a decrease in temperature of both ions and neutrals in the equatorial region at these times, consistent with downwelling in the ionosphere and thermosphere. Measurements of plasma temperatures on DMSP support this hypothesis.

[1] Typically the solar radio emission at 10.7 cm is used to scale the critical euv radiation that is absorbed by the Earth's neutral atmosphere. In the latter half of 2008 this radio emission from the Sun was at the lowest levels seen in the last 50 years and the persistence of these low levels has never been recorded before. Here we show that these uniquely low levels of solar radiation produce similarly unique behavior in the Earth's ionosphere and the upper atmosphere. Most remarkably, the altitude extent of the ionosphere is significantly smaller than our present reference models would predict for these levels of solar activity. The transition height resides near 450 km at night and rises to only 850 km during the daytime. At night, this unusually contracted ionospheric shell around the equator has a temperature of only 600 K and prior to sunrise the ion number densities at the transition height fall below 104 cm−3.

[1] We report an event of unusually elongated, bright airglow plume, which is considered as an optical manifestation of tongue of ionization (TOI) in the central polar cap. This optical structure was detected with an all-sky airglow imager at Resolute Bay (74.73°N, 265.07°E) during a large magnetic storm on December 15, 2006. The absolute optical intensity of the plume was ≈1 kR, which is much brighter than that of non-stormtime polar cap patches. Two-dimensional imaging capability of the all-sky imager demonstrates that some meso-scale structures (≈250–600 km) were embedded within the plume. Simultaneous ion density and drift measurements with the DMSP spacecraft strongly suggest that the plume was extending from the dayside as a narrow stream of dense plasma and thus is an optical manifestation of polar cap TOI. The DMSP data also implies that the possible source of the plume is a narrow stream of storm enhanced density (SED) transported from lower latitudes. The DMSP auroral particle observation demonstrates that the polar cap extremely expanded equatorward during this interval. This extreme expansion allowed the anti-sunward convection to capture plasmas within the SED and deliver them deep into the polar cap as a luminous airglow plume. This observation claims that the plasma transport from the dayside lower latitudes plays an important role in controlling the plasma environment in the polar cap ionosphere during magnetic storms.

[1] In this letter we present the first two-dimensional observations of sub-auroral ion drift (SAID) variability within the sub-auroral polarization stream (SAPS) using a new mid-latitude SuperDARN radar located at Wallops Island, VA. The radar data are complemented with observations from the DMSP F15, TIMED, and NOAA-18 spacecraft to confirm that a backscatter feature observed at the equatorward edge of the auroral oval is a manifestation of SAPS/SAID. During a several hour long period on August 6, 2005, the velocity data indicate that significant changes in the SAPS flow occurred on time scales of a few minutes. The Wallops HF radar observations demonstrate that the SAPS phenomenon is a source of small-scale irregularities extending over many hours of MLT and that the electric fields associated with SAID in particular are highly variable.

[1] We report IMAGE EUV observations of a striking undulatory motion of the plasmapause that occurred on 17 April 2002, in which a large ripple propagated westward across the duskside plasmapause. From the plasmapause motion we infer a peak E-field of ≈3 mV/m associated with the undulation, and estimate the undulation's equatorial azimuthal speed to be 0.9 rad/hr ≈ 4 RE/hr, corresponding to ≈1 km/s in the ionosphere (using an R3/2 dependence to map from the equator). Because DMSP ion drift data at 850 km altitude show the presence of a subauroral polarization stream (SAPS) flow channel ≈1 km/s at the same location and time as the undulation, we assert that SAPS was responsible for removal of plasma during the undulation. The SAPS apparently formed in response to a 19:00 UT substorm onset.

[1] The long-standing hypothesis that plasmaspheric dynamics are described by superposition of corotation and solar-wind-driven sunward convection is tested via direct comparison between plasmasphere observations and simulation output. The observations consist of global plasmasphere images produced by the IMAGE extreme ultraviolet (EUV) imager during plasmasphere erosion on 2 June 2001. The simulation is a plasmapause evolution model driven by a time-varying Volland-Stern (VS) electric potential distribution. On the dawnside and much of the nightside the model matches the EUV plasmapause position to within 0.2–0.5 earth radii (RE). Near dusk the model plasmapause is about 0.7–1.2 RE farther out than the EUV plasmapause, suggesting that an improved model should include the duskside flow enhancement known as the sub-auroral polarization stream (SAPS). We demonstrate that including a simplified ad-hoc SAPS potential can correct the model on the duskside.

[1] Theoretical arguments and MHD simulations have suggested that the potential drop across the polar-cap ionosphere approaches a constant value when the IMF is very large and southward. This idea has been difficult to test because the conditions producing this effect are extremely rare. During the 31 March 2001 storm the IMF was directed southward for over 6 hours with a magnitude of ∼36 nT to ∼20 nT while the DMSP-F13 satellite crossed the polar region, obtaining a good measure of the true polar cap potential drop. The observed potentials are compared with predictions from a theoretical model of the saturation process [Hill et al., 1976; Siscoe et al., 2002]. Clear evidence of a non-linear response consistent with the model predictions for height-integrated Pedersen conductivities in the range of 5–10 S are shown.

[1] Results from kinetic simulations of hot ion transport in the inner magnetosphere are used to show that the ring current energy content must have a nonlinear (asymptotic) coupling relationship to extreme solar wind conditions due to saturation of the near-Earth convection electric field Ey, conv (defined as a function of cross polar cap potential ΔΦPC). This study examines the Bastille Day magnetic storm (July 14–17, 2000), where the z-component of the interplanetary magnetic field reached −58 nT and the solar wind speed exceeded 1100 km s−1. A large discrepancy in the modeled ΔΦPC confirms a nonlinear response of the high-latitude potential during this event. It is found that this nonlinearity of Ey, conv is necessary to obtain reasonable agreement between the simulation results and the observed geoeffectiveness (Dst) of the storm.