A source or a sink? How the altitude of particle precipitation influence high-latitude electrodynamics

In this paper we establish the Pc 5 magnetic pulsation signatures of the cusp and boundary regions for the high‐latitude dayside cusp region. These signatures were determined by comparing spectrograms of the magnetic pulsations with optical observations of particle precipitation regions observed at the cusp. The ULF pulsations have a diurnal variation, and a cusp discriminant is proposed using a particular narrow‐band feature in the pulsation spectrograms. The statistical distribution of this pattern over a 253‐day period resembles the statistical cusp description using particle precipitation data from the Defense Meteorological Satellite Program (DMSP). The distribution of the ground‐based cusp discriminant is found to peak 1 hour earlier than the DMSP cusp distribution. This offset is due to the interplanetary magnetic field (IMF) being predominantly negative By for the period when the data were collected. We find the diurnal variations so repeatable that only three main categories of pulsation spectra explain 86 percent of all data observed. We find that these categories have statistically different IMF distributions. The identification of the signatures in the magnetic spectrograms of the boundary regions and central cusp allows the spectrogram to be used as a “time line” that shows when the station passed under different regions of the dayside oval.

A geomagnetic storm occurred on 27 February 2014 and the shock related to it arrived at Earth’s magnetosphere at ∼17:00 UT. Dayside cusp region scintillation over Antarctica have been studied along with the Global Positioning System (GPS) observed total electron content (TEC), and Defense Meteorological Satellite Program (DMSP) Precipitating Particles (SSJ), Bulk Plasma Parameters (SSIES) and Magnetic Fields (SSM) data. For the first time, similar variation trend in amplitude and phase scintillation has been found near the polar latitude. Amplitude scintillation index (mbox{S}_{4}) and phase scintillation index (sigma _{varphi }) show the similar enhancement trend at different numerical scale. During the southward interplanetary magnetic field (IMF) Bz condition there is a significant enhancement in the particle precipitation occurred through the dayside cusp region. During southward IMF Bz and dawnward By (mbox{By} < 0), high convection velocity guide solar wind plasma into the polar cap which enhances the phase scintillation, but, no amplitude scintillation enhancement at the similar numerical scale. The Halley and Dome C East radar data show that at the small to medium ionospheric irregularity speed, S4, and sigma _{varphi } variations are alike. If proper variation scale is chosen, mbox{S}_{4} also appears an appropriate scintillation index for the polar ionosphere. The possible mechanism for mbox{S}_{4} occurrence similar to the sigma _{varphi } at a dissimilar level has been discussed.Key points: Dayside cusp region amplitude and phase scintillation indices give similar information but at different numerical scale during the geomagnetic storm onset.Amplitude scintillation index is also an appropriate scintillation index for high latitude if proper numerical scales are chosen.SED or TOI does not necessarily produce ionospheric scintillation.Southward IMF Bz and westward IMF By allows the scintillation producing ionospheric irregularities to pass in deep inside the South Pole.

We compare observations of equatorial plasma bubbles (EPBs) by polar‐orbiting satellites of the Defense Meteorological Satellite Program (DMSP) with plasma density measurements from the Republic of China Satellite (ROCSAT‐1) in a low‐inclination orbit. DMSP data were acquired in the evening sector at low magnetic latitudes between 1989 and 2002. ROCSAT‐1 plasma densities were measured in March and April of 2000 and 2002. Observations of individual EPBs detected by both ROCSAT‐1 and DMSP were well correlated when satellite orbital paths crossed the same longitude within approximately ±15 min. We compiled a statistical database of ROCSAT‐1 EPB occurrence rates sorted by magnetic local time (MLT), magnetic latitude, and geographic longitude. The rate of ROCSAT‐1 EPB encounters at topside altitudes rose rapidly after 1930 MLT and peaked between 2000 and 2200 MLT, close to the orbital planes of DMSP F12, F14, and F15. EPB encounter rates have Gaussian distributions centered on the magnetic equator with half widths of ∼8°. Longitudinal distributions observed by ROCSAT‐1 and DMSP are qualitatively similar, with both showing significantly fewer occurrences than expected near the west coast of South America. A chain of GPS receivers extending from Colombia to Chile measured a west‐to‐east gradient in S4 indices that independently confirms the existence of a steep longitudinal gradient in EPB occurrence rates. We suggest that precipitation of energetic particles from the inner radiation belt causes the dearth of EPBs. Enhancements in the postsunset ionospheric conductance near the South Atlantic Anomaly cause a decrease in growth rate for the generalized Rayleigh‐Taylor instability. Results indicate substantial agreement between ROCSAT‐1 and DMSP observations and provide new insights on EPB phenomenology.

Abstract. Recent work has shown that solar wind dynamic pressure changes can have a dramatic effect on the particle precipitation in the high-latitude ionosphere. It has also been noted that the preexisting interplanetary magnetic field (IMF) orientation can significantly affect the resulting changes in the size, location, and intensity of the auroral oval. Here we focus on the effect of pressure pulses on the size of the auroral oval. We use particle precipitation data from up to four Defense Meteorological Satellite Program (DMSP) spacecraft and simultaneous POLAR Ultra-Violet Imager (UVI) images to examine three events of solar wind pressure fronts impacting the magnetosphere under two IMF orientations, IMF strongly southward and IMF Bz nearly zero before the pressure jump. We show that the amount of change in the oval and polar cap sizes and the local time extent of the change depends strongly on IMF conditions prior to the pressure enhancement. Under steady southward IMF, a remarkable poleward widening of the oval at all magnetic local times and shrinking of the polar cap are observed after the increase in solar wind pressure. When the IMF Bz is nearly zero before the pressure pulse, a poleward widening of the oval is observed mostly on the nightside while the dayside remains unchanged. We interpret these differences in terms of enhanced magnetospheric reconnection and convection induced by the pressure change. When the IMF is southward for a long time before the pressure jump, open magnetic flux is accumulated in the tail and strong convection exists in the magnetosphere. The compression results in a great enhancement of reconnection across the tail which, coupled with an increase of magnetospheric convection, leads to a dramatic poleward expansion of the oval at all MLTs (dayside and nightside). For near-zero IMF Bz before the pulse the open flux in the tail, available for closing through reconnection, is smaller. This, in combination with the weaker magnetospheric convection, leads to a more limited poleward expansion of the oval, mostly on the nightside. Key words. Magnetospheric physics (solar windmagnetosphere interactions; magnetospheric configuration and dynamics; auroral phenomena)

: The transfer of electromagnetic energy to heat, i.e., Joule heating, in the ionospheric gas is often the most dominant energy source for the polar regions. The Defense Meteorological Satellite Program (DMSP) has demonstrated that the Joule heating rate in the high-latitude ionosphere can be estimated with measurements of the perturbation magnetic field and precipitating particle population. These estimates of the Joule heating rate are subject to a number of assumptions and empirical formalisms that require validation. The NSF incoherent scatter radar located at Sondrestrom, Greenland, can measure the plasma parameters of interest and is at a latitude well suited for coincident measurements with DMSP. Recent radar improvements in altitude resolution and signal statistics in the E region has permitted the Joule heating rate to be more accurately determined than ever before. Also, the manner in which the Joule heating rate is now being calculated parallels that of DMSP allowing a more direct means of testing assumptions and comparing results. Here, we summarize the progress made over the program year and detail the observational program for conjunctions with the F12 and F13 DMSP satellites and the radar.

Energetic particle precipitation is the major source of electron production that controls the ionospheric Pedersen and Hall conductances at high latitudes. Many studies use empirical formulas to estimate conductances. The particle precipitation spectra measured by the Defense Meteorological Satellite Program (DMSP) Special Sensor J are often used as the input to the empirical formulas. In this study, we evaluate the empirical formulas of ionospheric conductances during four different types of auroral precipitation conditions based on 63 conjugate events observed by DMSP and EISCAT. The conductances calculated from the DMSP data with the empirical formulas are compared with those based on EISCAT measurements with the standard equations. The best correlation between these two is found when the empirical Robinson formulas (Robinson et al., 1987, https://doi.org/10.1029/ja092ia03p02565) are used in the presence of diffuse electron precipitation without ions. In the presence of ion precipitation, the correlation coefficients are smaller, but the correlation improves when the Galand formulas (Galand &amp; Richmond, 2001, https://doi.org/10.1029/1999ja002001) are used to estimate the contribution of ion precipitation to the conductances. We also found that pure ion precipitation can cause the increase of conductances up to 2–7 S for Pedersen and 2.5–10 S for Hall conductances, which is positively correlated with the auroral electrojet index. Overall, the empirical formulas applied to the DMSP particle spectra underestimate the ionospheric conductances.

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.

Vertical stacks of two-dimensional (2D) materials separated by a van der Waals gap and held together by van der Waals forces are immensely promising for a plethora of nanotechnological applications. Charge control in these stacks may be modeled with use of either a simple electrostatics approach or a detailed atomistic one. In this paper, we compare these approaches for a gated 2D transition-metal dichalcogenide bilayer and show that recently reported electrostatics-based models of this system give large errors in band energy compared with atomistic (density-functional-theory) simulations. These errors are due to the tails of the ionic potentials that reduce the electrical-equivalent van der Waals gap between the 2D layers, and can be corrected by use of the reduced gap in the electrostatic model. For a physical van der Waals gap (defined as the chalcogen-to-chalcogen distance) of 3 angstrom in a 2D bilayer, the electrical-equivalent gap is less than 1 angstrom. For the example of band-to-band-tunneling-based ultra-low-power transistors, this is seen to lead to errors of several hundred millivolts or more in the threshold voltage estimated from electrostatics.

Abstract. A statistical study has been performed by using two years of DMSP (Defense Meteorological Satellite Program) plasma observations to investigate the seasonal effect of SAPS (subauroral polarization stream) on the ion upflow in the duskside ionosphere of the Northern Hemisphere. There are obvious upflows occurring in the topside ionosphere around the SAPS region, exceeding 200 m s−1 at winter solstice, indicating an important relationship between SAPS and the local plasma upward motion. Both SAPS and ion upward velocities show similar seasonal variations, largest in winter and smallest in summer, irrespective of geomagnetic activity. A good correlation is found and a linear relationship is derived between SAPS and the ion upflow velocities. During December solstice the average upflow flux can reach about 2 × 108 cm−2 s−1 for more disturbed periods, which is comparable to the typical upflow flux in the dayside cusp region. The depression of the ion temperatures around the peak SAPS region can be understood in terms of the adiabatic cooling. The hot ion cools down when expanding into the low ion concentration region. The electron temperature elevates around the SAPS region because of the reduced Coulomb cooling in the low ion density region. Both the changes of ion and electron temperatures are larger in winter than in summer, however, for Kp &lt; 4 the electron temperatures are almost seasonably independent. The present work highlights the important role of the SAPS-related frictional heating at mid-latitudes on the local formation of the strong upward flow, which might provide a direct ionospheric ion source for the ring current and plasmasphere in the duskside sector.

Abstract. The two-cell aurora is characterized by azimuthally elongated regions of enhanced auroral brightness over extended local times in the dawn and dusk sectors. Its association with the convection, particle precipitation, and field-aligned currents under various phases of substorms has not been fully understood. With Polar Ultraviolet Imager auroral images in conjunction with Defense Meteorological Satellite Program (DMSP) F12 spacecraft on the dusk-side branch of the two-cell aurora, we are able to investigate an association of the auroral emissions with the electric fields, field-aligned currents, and energy flux of electrons. Results show that the substorm expansion onset does not significantly change the orientation of the dusk-side branch of the two-cell aurora. Also, the orientation of the magnetic deflection vector produced by the region 1 field-aligned current changed from 73±1° to the DMSP trajectory during the substorm growth phase, to 44±6° to the DMSP trajectory during the substorm expansion phase. With a comparison between the orientation of the dusk-side branch of the two-cell aurora and the orientation of the magnetic deflection vector, it is found that the angular difference between the two orientations is 28±5° during the substorm growth phase, and 13±6° during the substorm expansion phase.

Recent experimental evidence has shown that Defense Meteorological Satellite Program (DMSP) polar orbiting spacecraft at 840 km can develop electric potentials as severe as −1430 V while at high magnetic latitudes. To explore this charging region, an analysis of DMSP F6, F7, F8, and F9 satellite precipitating particle and ambient plasma measurements taken during periods of high, medium, and low solar flux is performed. One hundred eighty‐four charging events ranging from −46 to −1430 V are identified, and an extreme solar cycle dependence is found as charging is most frequent and severe during solar minimum. Satellite measurements and time‐dependent ionospheric model (TDIM) output are used to determine the cause of the solar cycle dependence and to characterize the environments which generate and inhibit these potentials. The electron precipitation associated with various DMSP charging levels is analyzed; it is suggested that precipitating electrons as low as 2 to 3 keV may contribute to charging though higher‐energy electrons make greater contributions. Secondary electron production due to incident electrons below 1 keV is shown to inhibit charging. The energetic electron fluxes shown to generate charging do not vary significantly over the solar cycle. Instead, DMSP ambient plasma data and TDIM generated results identify a variation in plasma density over 1 or more orders of magnitude as the cause of the solar cycle dependence, and an ambient plasma density of less than 104 cm−3 is found necessary for significant negative charging (≥100 V) to occur.

The assimilative mapping of ionospheric electrodynamics (AMIE) technique has been used to estimate global distributions of high‐latitude ionospheric convection and field‐aligned current by combining data obtained nearly simultaneously both from ground and from space. Therefore, unlike the statistical patterns, the “snapshot” distributions derived by AMIE allow us to examine in more detail the distinctions between field‐aligned current systems associated with separate magnetospheric processes, especially in the dayside cusp region. By comparing the field‐aligned current and ionospheric convection patterns with the corresponding spectrograms of precipitating particles, the following signatures have been identified: (1) For the three cases studied, which all had an IMF with negative y and z components, the cusp precipitation was encountered by the DMSP satellites in the postnoon sector in the northern hemisphere and in the prenoon sector in the southern hemisphere. The equatorward part of the cusp in both hemispheres is in the sunward flow region and marks the beginning of the flow rotation from sunward to antisunward. (2) The pair of field‐aligned currents near local noon, i.e., the cusp/mantle currents, are coincident with the cusp or mantle particle precipitation. In distinction, the field‐aligned currents on the dawnside and duskside, i.e., the normal region 1 currents, are usually associated with the plasma sheet particle precipitation. Thus the cusp/mantle currents are generated on open field lines and the region 1 currents mainly on closed field lines. (3) Topologically, the cusp/mantle currents appear as an expansion of the region 1 currents from the dawnside and duskside and they overlap near local noon. When By is negative, in the northern hemisphere the downward field‐aligned current is located poleward of the upward current; whereas in the southern hemisphere the upward current is located poleward of the downward current. (4) Under the assumption of quasi‐steady state reconnection, the location of the separatrix in the ionosphere is estimated and the reconnection velocity is calculated to be between 400 and 550 m/s. The dayside separatrix lies equatorward of the dayside convection throat in the two cases examined.

Abstract. The interpretation of structure in cusp ion dispersions is important for helping to understand the temporal and spatial structure of magnetopause reconnection. "Stepped" and "sawtooth" signatures have been shown to be caused by temporal variations in the reconnection rate under the same physical conditions for different satellite trajectories. The present paper shows that even for a single satellite path, a change in the amplitude of any reconnection pulses can alter the observed signature and even turn sawtooth into stepped forms and vice versa. On 20 August 1998, the Defense Meteorological Satellite Program (DMSP) craft F-14 crossed the cusp just to the south of Longyearbyen, returning on the following orbit. The two passes by the DMSP F-14 satellites have very similar trajectories and the open-closed field line boundary (OCB) crossings, as estimated from the SSJ/4 precipitating particle data and Polar UVI images, imply a similarly-shaped polar cap, yet the cusp ion dispersion signatures differ substantially. The cusp crossing at 08:54 UT displays a stepped ion dispersion previously considered to be typical of a meridional pass, whereas the crossing at 10:38 UT is a sawtooth form ion dispersion, previously considered typical of a satellite travelling longitudinally with respect to the OCB. It is shown that this change in dispersed ion signature is likely to be due to a change in the amplitude of the pulses in the reconnection rate, causing the stepped signature. Modelling of the low-energy ion cutoff under different conditions has reproduced the forms of signature observed.Key words. Ionosphere (particle precipitation) Magnetospheric physics (energetic particles, precipitating, magnetopause, cusp and boundary layers)

Poynting flux, which describes electromagnetic energy flux, is an important energy source for the high‐latitude upper atmosphere. After the launch of Defense Meteorological Satellite Program (DMSP) F15 spacecraft with a boom‐mounted magnetometer on board, there was a new opportunity to calculate Earth‐directed Poynting flux at satellite altitudes (~850 km) in the upper atmosphere. A persistent enhancement of thermospheric density in the dayside polar cap boundary regions has been reported in the CHAMP satellite observations. To understand the significance of different physical mechanisms including Poynting flux and particle precipitation, and the correlation between them, a statistical study of Poytning flux and particle energy flux in the dayside cusp and low‐latitude boundary layer (LLBL) regions has been conducted based on DMSP F15 measurements. DMSP satellite observations showed a dominate downward Poynting flux for most cases in the cusp region. Our analysis of DMSP F15 data for five years (2000–2004) reveals that approximately 53% of 660 cusp crossings at 800–850 km showed strong downward Poynting flux (S &gt; 10 mW/m2), 32% of the crossings had noticeable downward Poynting flux (S &gt; 3 mW/m2), and 7% of the crossings did not show clear Poynting flux (S &lt; 1 mW/m2). Only 13 out of 660 cusp crossings (~2%) showed noticeable upward Poynting flux. In the LLBL region, 35% of 11,641 LLBL crossings showed significant downward Poynting flux, 34% of the crossings had noticeable downward Poynting flux, and only 13% of the crossings did not show clear Poynting flux. On average, Poynting flux in LLBL is smaller than that in the cusp. The results show a slightly negative correlation between Poynting flux and particle precipitation energy flux in the dayside polar cap boundary regions. Statistically, Poynting flux in the cusp is enhanced during interplanetary magnetic field By positive conditions.

In this case study, we focus on how hemispheric differences in the electric potential distribution in the auroral zones are related to hemispheric differences in the energetic particle precipitation that indicate the presence of field‐aligned potential drops. Utilizing data during the spring and fall equinox in 2013 and 2014 from the Defense Meteorological Satellite Program (DMSP) F16 and F17 satellites, we systematically examine simultaneous measurements of plasma drift velocity and particle precipitation in magnetically conjugate regions across the auroral zone in both hemispheres. This allows us to establish the degree to which the interhemispheric differences in ionospheric electric potential may be accounted for by field‐aligned potential drops. Thirty‐seven eligible cases examined show accelerated electron energy spectra at conjugate locations in the northern and/or southern hemispheres. Of these 37 cases, 23 show conjugate differences in electric potential that agree qualitatively with the observed electron acceleration and average energy of precipitating electrons in each hemisphere. This result suggests that the hemispheric differences in ionospheric electric potential in the auroral zone may be most frequently accounted for by field‐aligned potential drops along the magnetic flux tubes connecting conjugate points to the equatorial plane. The spatial and temporal variability of the potential distribution, electron precipitation, and magnetic field configuration could account for deviations from the normally observed situation in the remaining cases. More magnetically conjugate observations at various altitudes in both hemispheres are needed to investigate this hemispheric coupling in more detail.