Low-latitude Boundary Layer Research Articles

Energy Conversion Associated With Anomalous Magnetic Topology Sublayers in the Inner Low‐Latitude Boundary Layer

AbstractThe low‐latitude boundary layer (LLBL) is a crucial region for the transfer of mass, momentum, and energy between the solar wind and the planetary magnetosphere. However, the processes of energy conversion within this layer are not well understood. In this study, the anomalous magnetic topology sublayers (AMTSs) within Earth's inner LLBL are investigated during the local reconnection inactive period, using data from the Magnetospheric Multiscale (MMS) mission. We present the first in situ observations showing that these AMTSs lead to significant energy conversion within the inner LLBL. The electron populations in AMTSs are dominated by either the magnetospheric or magnetosheath populations, creating a substantial electron temperature gradient between these sublayers. This temperature gradient, in turn, generates non‐ideal electric fields through the pressure gradient term. Our findings improve the understanding of dynamics in the planetary LLBL, highlighting the importance of AMTSs in the energy conversion process.

Mercury’s plasma environment after BepiColombo’s third flyby

Understanding Mercury’s magnetosphere is crucial for advancing our comprehension of how the solar wind interacts with the planetary magnetospheres. Despite previous missions, several gaps remain in our knowledge of Mercury’s plasma environment. Here, we present findings from BepiColombo’s third flyby, offering a synoptic view of the large scale structure and composition of Mercury’s magnetosphere. The Mass Spectrum Analyzer (MSA), Mass Ion Analyzer (MIA), and Mass Electron Analyzer (MEA) on the magnetospheric orbiter reveal insights, including the identification of trapped energetic hydrogen (H+) with energies around 20 keV e−1 evidencing a ring current, and a cold ion plasma with energies below 50 eV e−1. Additionally, we observe a Low-Latitude Boundary Layer (LLBL), which is a region of turbulent plasma at the edge of the magnetosphere, characterized by bursty ion enhancements, indicating an ongoing injection process in the duskside magnetosphere flank. These observations during cruise phase provide a tantalizing glimpse of future discoveries expected from the Mercury Plasma Particle Experiment (MPPE) instruments after orbit insertion, promising broader impacts on our understanding of planetary magnetospheres.

Classification and Distribution of the Dayside Ion Upflows Associated with Auroral Particle Precipitation

Two important phenomena of the solar wind–magnetosphere–ionosphere coupling are auroral particle precipitation and the formation of ions flowing upward from the ionosphere. They have opposite transport directions of energy and substance. Based on the observations of particle precipitation and ion drift from the DMSP F13 satellite in January and July 2005, the ionospheric ion upflows in dayside auroral oval (0600–1800 MLT) can be divided into five types according to the velocity of ion upflows and the spectrum characteristics of auroral particle precipitation, and the distribution for different types of ion upflows is studied. The results show that the ion upflows mainly occur in the geomagnetic latitude (MLAT) range of 70–80°.The main magnetospheric source region of ion upflows (type A and D) caused by the accelerated electron (mainly the soft electron) corresponds to Low Latitude Boundary Layer (LLBL) and Cusp, and ion upflows of type B and C (related to the process of ambipolar diffusion caused by electron acceleration) mainly occur in LLBL and Boundary Plasma Sheet (BPS), while ion upflows of type E without electron acceleration mainly occur in the central plasma sheet (CPS).The dawn–dusk asymmetry is obvious in the winter season, with the ion upflows mainly occurring on the dawn/dusk side ionosphere. However, the ion upflows in summer mainly occur at the magnetic noon, with a symmetric distribution centered at the magnetic noon. The occurrence of ion upflow in winter is significantly higher than that in summer, and it is significantly enhanced during the period of moderate geomagnetic activity. The upward region expands to the lower latitude when the geomagnetic activity is enhanced. The effect of interplanetary magnetic field (IMF) components has also been studied in this paper. When IMF Bx is negative, the upflow occurrence increases in the region of 1500–1800 MLT and 0600–0900 MLT, with the MLAT range below 70°. The direction of IMF By may lead to the high-incidence area reverse at the prenoon or postnoon region. The occurrence of ion upflows with the MLAT range below 75° increases significantly when IMF is southward. Type A ion upflow has the highest velocity of ion upflows, followed by type E, and type D has the lowest. The average velocity of ion upflows in winter is significantly higher than that in summer.

Cluster Observation of Ion Outflow in Middle Altitude LLBL/Cusp from Different Origins

The ionosphere is the ionized part of the upper atmosphere that is caused mainly by photoionization by solar extreme ultraviolet (EUV) emission and the atmospheric photochemistry process. The ionospheric ions escape from the ionosphere and populate the Earth’s magnetosphere. In this case study, ion outflows from two different origins were obtained by spacecraft Cluster C1 in the magnetospheric cusp region. One of the outflows was from the reflection of the dispersed solar wind particles. The other was the ionospheric outflow passing through the low latitude boundary layer of the cusp (LLBL/cusp), which was energized by downward Poynting flux. Similar to the reflected solar wind particles, outflowing ionospheric cold ions could also extend to the high-latitude region with magnetic field line convection, which mixed it up with solar wind particles. Based on the Cluster observation in the cusp region, two different origins of the outflowing particles were determined, and their unique mechanisms of formation were discussed. Results suggest that the strong electric field associated with solar wind particle precipitation may additionally accelerate the cold ionospheric ion flow in the LLBL/cusp.

Inner southern magnetosphere observation of Mercury via SERENA ion sensors in BepiColombo mission

Mercury’s southern inner magnetosphere is an unexplored region as it was not observed by earlier space missions. In October 2021, BepiColombo mission has passed through this region during its first Mercury flyby. Here, we describe the observations of SERENA ion sensors nearby and inside Mercury’s magnetosphere. An intermittent high-energy signal, possibly due to an interplanetary magnetic flux rope, has been observed downstream Mercury, together with low energy solar wind. Low energy ions, possibly due to satellite outgassing, were detected outside the magnetosphere. The dayside magnetopause and bow-shock crossing were much closer to the planet than expected, signature of a highly eroded magnetosphere. Different ion populations have been observed inside the magnetosphere, like low latitude boundary layer at magnetopause inbound and partial ring current at dawn close to the planet. These observations are important for understanding the weak magnetosphere behavior so close to the Sun, revealing details never reached before.

A Statistical Study of Magnetopause Boundary Layer Energetic Electron Enhancements Using MMS

We took a survey of boundary layer (or low-latitude boundary layer) crossings by the Magnetospheric Multiscale (MMS) mission. Out of 250 total crossings, about half showed enhancements of high-energy (>30 keV) electrons in the FEEPS sensor and a little less than half of those energetic electron events had whistler-mode waves present. Energetic electron enhancements were more likely to be present at magnetic local times closer to noon and at distances of less than about 20 Earth radii, but there was seemingly no correlation with magnetic latitude. For almost all of these events, the pitch angles of the FEEPS electrons were peaked at 90° or isotropic, not field-aligned. Most of the events for which we had data to make a determination showed either direct or indirect evidence of reconnection. Overall, energetic electron enhancements are a fairly common occurrence and there appears to be some connection between whistler waves, energetic electron enhancements, and reconnection, whether it is a direct link or some other process affecting all of them.

Kelvin-Helmholtz Vortices as an Interplay of Magnetosphere-Ionosphere Coupling

The solar wind-magnetosphere interaction drives diverse physical processes on the flanks of Earth’s magnetopause, and in turn these processes couple to the ionosphere. We investigate simultaneous multipoint in-situ spacecraft and ground-based measurements to determine the role of Kelvin-Helmholtz waves at the Earth’s magnetopause and the low-latitude boundary layer in the magnetosphere-ionosphere coupling process. Nonlinear Kelvin-Helmholtz waves develop into flow vortices that twist and/or shear flux tube magnetic fields, thereby generating localized field-aligned currents. Kelvin-Helmholtz vortices on the dusk (dawn) flanks of the magnetosphere generate clockwise (counter-clockwise) rotations and upward (downward) field-aligned currents inside the flux tubes, consistent with the region-1 field-aligned current. We present in-situ MMS and Cluster spacecraft observations of Kelvin-Helmholtz vortices at the magnetopause that map to the poleward edge of the auroral regions. The FAST spacecraft and the ground-based magnetometers from which spherical elementary currents (acting as a proxy for vertical currents) can be calculated observe corresponding field-aligned current signatures. This study demonstrates the role played by the Kelvin-Helmholtz waves in linking magnetopause boundary fluctuations to ionospheric phenomena.

Oxygen Ion Escape at Venus Associated With Three‐Dimensional Kelvin‐Helmholtz Instability

AbstractHow oxygens escape from Venus has long been a fundamental but controversial topic in the planetary research. Among various key mechanisms, the Kelvin‐Helmholtz instability (KHI) has been suggested to play an important role in the oxygen ion escape from Venus. Limited by either scarce in‐situ observations or simplified theoretical estimations, the mystery of oxygen ion escape process associated with KHI is still unsettled. Here we present the first three‐dimensional configuration of KHI at Venus with a global multifluid magnetohydrodynamics model, showing a significantly fine structure and evolution of the KHI. KHI mainly occurred at the low latitude boundary layer if defining the interplanetary magnetic field‐perpendicular plane as the equatorial plane, resulting in escaping oxygen ions through mixing with the solar wind at the Venusian boundary layer, with an escape rate around 4 × 1024 s−1. The results provide new insights into the basic physical process of atmospheric loss at other unmagnetized planet.

Coupling Between Alfvén Wave and Kelvin–Helmholtz Waves in the Low Latitude Boundary Layer

The Kelvin–Helmholtz (KH) instability of magnetohydrodynamic surface waves at the low latitude boundary layer is examined using both an eigenfrequency analysis and a time-dependent wave simulation. The analysis includes the effects of sheared flow and Alfvén velocity gradient. When the magnetosheath flows are perpendicular to the ambient magnetic field direction, unstable KH waves that propagate obliquely to the sheared flow direction occur at the sheared flow surface when the Alfvén Mach number is higher than an instability threshold. Including a shear transition layer between the magnetosphere and magnetosheath leads to secondary KH waves (driven by the sheared flow) that are coupled to the resonant surface Alfvén wave. There are remarkable differences between the primary and the secondary KH waves, including wave frequency, the growth rate, and the ratio between the transverse and compressional components. The secondary KH wave energy is concentrated near the shear Alfvén wave frequency at the magnetosheath with a lower frequency than the primary KH waves. Although the growth rate of the secondary KH waves is lower than the primary KH waves, the threshold condition is lower, so it is expected that these types of waves will dominate at a lower Mach number. Because the transverse component of the secondary KH waves is stronger than that of the primary KH waves, more efficient wave energy transfer from the boundary layer to the inner magnetosphere is also predicted.

MMS Observations of Double Mid-Latitude Reconnection Ion Beams in the Early Non-Linear Phase of the Kelvin-Helmholtz Instability

The MMS satellites encountered a Kelvin-Helmholtz instability (KHI) period in the early non-linear phase at the post-noon flank magnetopause on 8 Sep 2015. The adjacent magnetosheath was characterized by a pre-dominantly northward Bz > 0 magnetic field with weakly positive in-plane components in a GSM coordinate system. Ion velocity distribution functions indicate at least 17 KH vortex intervals with two typically D-shaped ion beam distributions, commonly associated with reconnection exhausts, that stream in both directions along a mostly northward magnetic field at 350–775 km/s with a median 525 km/s ion beam speed. The counter-streaming ion beams are superposed on a core population of slowly drifting magnetosheath ions with a field-aligned 50–200 km/s speed. Each interval lasted no more than 5.25 s with a median duration of 1.95 s corresponding to in-plane spatial scales 3 < ΔS < 22 di assuming a constant 1 di = 61 km ion inertial scale and a tailward VKH∼258 km/s KH vortex propagation speed along the MMS trajectory. The counter-streaming ions are predominantly observed in the warm KH vortex region between the cold magnetosheath proper and the hot isotropic ion temperature of a low-latitude boundary layer as the MMS constellation traverses a KH vortex. The in-plane spatial scales and the locations of the observed counter-streaming ion beams generally agree with the predictions of twice-reconnected magnetic fields at two mid-latitude reconnection (MLR) regions in a two-fluid three-dimensional numerical simulation previously reported for this KH event. MMS typically recorded a higher phase space density of the fast parallel ion beam that we associate with a tailward reconnection exhaust from the southern MLR (SMLR) and a lower phase space density of the fast anti-parallel ion beam that we associate with a tailward reconnection exhaust from the northern MLR (NMLR) of similar speed. This is either consistent with MMS being closer to the SMLR region than the NMLR region, or that the KHI conditions may have favored reconnection in the SMLR region for the observed in-plane magnetosheath magnetic field as predicted by a two-fluid three-dimensional numerical simulation.

Ion Pressure in the Precipitation Region of Dayside Low Latitude Boundary Layer

Ion Pressure in the Precipitation Region of Dayside Low Latitude Boundary Layer

Ion Pressure in Different Regions of the Dayside Auroral Precipitation

The ion pressure in the regions of ionospheric projections of the plasma mantle, polar cusp, low-latitude boundary layer, and the region of structured precipitation of the auroral oval during magnetic calm is studied based on data from the DMSP F6 and F7 low-altitude spacecraft. It is shown that the level of ion pressure in all of these regions does not depend on either the polarity or the value of the Bz component of the IMF. The ion pressure in the mantle varies from 0.02 to 0.06 nPa and does not depend on the magnitude of the solar wind dynamic pressure. The average pressure level is $$\left\langle {Pm} \right\rangle $$ = 0.03 ± 0.01 nPa. In the cusp area at IMF Bz > 0, the ion pressure (Pc) does not depend on the solar wind dynamic pressure (Psw), while the pressure at IMF Bz < 0 increases significantly with the increasing in Psw. The average pressure level is $$\left\langle {Pc} \right\rangle $$ = 1.0 ± 0.3 nPa, which is almost two orders of magnitude higher than that in the mantle. The ion pressure also increases with the solar wind dynamic pressure in both the LLBL and the auroral oval precipitation (AOP). The average pressure in the LLBL is $$\left\langle {{{P}_{L}}} \right\rangle $$ = 0.27 ± 0.07 nPa, while in the AOP region its average value is two times lower. The MLT pressure pattern in LLBL shows a pronounced increase in the noon sector (~11–14 MLT), the value of which increases with increasing in the solar wind dynamic pressure. In the AOP region the pressure is distributed over MLT fairly evenly, which results in a significant pressure difference (ΔP = PL – PA) in the noon sector between the low-latitude boundary layer and the auroral oval.

The Quasipersistent Feature of Highly Structured Field‐Aligned Currents in the Duskside Auroral Oval: Conjugate Observation Via Swarm Satellites and a Ground All‐Sky Imager

AbstractDuring northward interplanetary magnetic field (IMF), irregular magnetic perturbations were observed in the duskside aurora oval via Swarm satellites instead of large‐scale Region 1/2 magnetic perturbations. By taking advantage of Swarm constellation measurements, and their conjugate observations with an all‐sky imager on the ground, the features of the irregular magnetic perturbations were examined. Detailed analysis of the data from Swarm A and Swarm C for two events demonstrated that the irregular magnetic perturbations are a result of highly structured quasistatic field‐aligned currents (FACs), not dynamic Alfvén waves. The typical latitudinal size of the upward FACs is 20–30 km. In each region of the upward FACs, 630‐nm aurora emissions are relatively strong, indicating that the energy flux of precipitating electrons having energies of a few hundred electron volts is high in each of the upward FAC regions. The enhanced mesoscale auroras continued to exist for at least approximately 30 min. These indicate that the mesoscale FAC structures also have quasipersistent features. The precipitating particle data from the Defense Meteorological Satellite Program satellite, which passed through the field of view of the all‐sky imager, indicate that the source of the precipitating particles is the duskside low‐latitude boundary layer (LLBL). We suggest that the highly structured quasipersistent FACs flow along the magnetic field lines connected to the duskside LLBL where cold dense ions exist. The highly structured FACs in the duskside aurora oval are the phenomena that are pertinent to the magnetosphere for a northward IMF condition, not a simple remnant of the typical Region 1.

Plasma transport into the duskside magnetopause caused by Kelvin–Helmholtz vortices in response to the northward turning of the interplanetary magnetic field observed by THEMIS

Abstract. A train of likely Kelvin–Helmholtz (K–H) vortices with plasma transport across the magnetopause has been observed by the Time History of Events and Macroscale Interactions during Substorms (THEMIS) at the duskside of the magnetopause. This unique event occurs when the interplanetary magnetic field (IMF) abruptly turns northward, which is the immediate change to facilitate the K–H instability. Two THEMIS spacecraft, TH-A and TH-E, separated by 3 RE, periodically encountered the duskside magnetopause and the low-latitude boundary layer (LLBL) with a period of 2 min and tailward propagation of 212 km s−1. Despite surface waves also explaining some of the observations, the rotations in the bulk velocity observation, a distorted magnetopause with plasma parameter fluctuations and the magnetic field perturbations, as well as a high-velocity low-density feature indicate the possible formation of rolled-up K–H vortices at the duskside of the magnetopause. The coexistence of magnetosheath ions with magnetospheric ions and enhanced energy flux of hot electrons is identified in the K–H vortices. These transport regions appear more periodic at the upstream spacecraft and more dispersive at the downstream location, indicating significant transport can occur and evolve during the tailward propagation of the K–H waves. There is still much work to do to fully understand the Kelvin–Helmholtz mechanism. The observations of the direct response to the northward turning of the IMF, the possible evidence of plasma transport within the vortices, involving both ion and electron fluxes, can provide additional clues as to the K–H mechanism.

Conjunction Observations of Energetic Oxygen Ions O+ Accumulated in the Sequential Flux Ropes in the High‐Altitude Cusp

AbstractConjunction observations of the magnetic field and plasma by Cluster and TC‐1 at the dayside magnetosphere are presented to investigate the sequential flux ropes transferred from the low latitude boundary layer to the high‐altitude cusp on 10 March 2004.Three sequential flux ropes originating from the dayside low latitude magnetopause are first detected by TC‐1. After ~5.3 min, three sequential flux ropes accumulated with energetic oxygen ions are also detected by Cluster in the high‐altitude cusp. The recurrence period of these flux ropes is ~3 min. The number density of energetic oxygen ions in the cusp flux rope is ~0.25 cm−3 detected from CIS/CODF instrument on Cluster. It is found that oxygen ions with energy lager than 10 keV have a narrow pitch angle (less than 90°) distribution in the southern high‐altitude cusp. While oxygen ions with energy less than 10 keV are distributed in a wide pitch angle from 0 to 180°. Counter‐streaming energetic oxygen ions are found in these flux ropes in the high‐altitude cusp.This result suggests that the oxygen ions with energy less than 10 keV in the high‐altitude cusp have two source regions. One is from the dayside magnetopause, and the other is from the low‐altitude cusp. Our investigations first provide evidence that flux ropes at dayside low‐latitude magnetopause can carry energetic oxygen ions into the high‐altitude cusp region.

Magnetosphere‐Ionosphere Convection Under the Due Northward IMF

AbstractConvection under the due northward interplanetary magnetic field (IMF) is reproduced by the global simulation. The resulting magnetosphere is closed except in the XZ plane and separated from the solar wind by the separatrix generated from cusp nulls. Inside the separatrix, there exist three plasma regimes of the cusp high‐pressure region, the low‐latitude boundary layer (LLBL) and the plasma sheet. In the ionosphere, the northward Bz (NBZ) current and the reverse cell occur in higher latitudes than 80°, and the fun‐shaped arc‐like field‐aligned current and the main oval occur in lower latitudes than 80°. Magnetic field lines in the antisunward flow region of the reverse cell are connected to the LLBL that is accelerated to supersonic flow by the cusp pressure. Circulation on the reverse cell in the ionosphere is as a whole constructed to the interchange cycle in the magnetosphere. Convection is looked upon as the process to discharge stress generated by the dayside cusp reconnection. Magnetic stress generated by the reconnection is first converted to thermal energy in the cusp. This thermal energy is drained through three possible routes: release of plasma downtail through the LLBL, dissipation as electromagnetic energy through formation of the dynamo, and evacuation down to the ionosphere through the plasma sheet.

Prolonged Kelvin–Helmholtz Waves at Dawn and Dusk Flank Magnetopause: Simultaneous Observations by MMS and THEMIS

Abstract The Kelvin–Helmholtz (K-H) waves predominantly excited at the Earth’s low-latitude magnetopause were suggested to be dawn–dusk asymmetric. We report a prolonged simultaneous observations of the K-H waves on the dawn and dusk magnetopause by Magnetospheric Multiscale (MMS) and THEMIS-A (THA) spacecraft, respectively. The quasi-periodic K-H waves on both flanks have unambiguous low-density and high-speed patterns. The wave periods vary gradually on both flanks, with similar average periods (303 ± 107 s for MMS and 266 ± 102 s for THA). The lag time between the variations of the wave periods is close to the wave propagation time from THA to MMS, which suggests that the K-H waves generate and propagate quasi-symmetrically on both flanks. Larger local magnetic shear angles are observed on the trailing edges by MMS than by THA, which is probably due to the strong magnetic field distortion during the tailward propagation. The increased magnetic shear may excite magnetic reconnection, thus contributing to the formation of the low-latitude boundary layer.

Plasma Pressure under Magnetopause on the Dusk Flank in the Equatorial Plane for Large Negative ХGSM

The crossings of the magnetopause and low-latitude boundary layer by the THEMIS-B satellite in the spring of 2008 on the dusk flank under large negative XGSM (from –17RE to –19RE) are studied. The parameters of plasma and magnetic field are analyzed from the data of ESA and MGF instruments. The changes in the total pressure, magnetic field pressure, and plasma pressure component during the transition from the magnetosheath to the plasma sheet (PS) are analyzed. The values of plasma pressures under the magnetopause at the edge of the PS for the considered events are determined. The applicability of the obtained results to the determination of the position of the boundary between the tail current and the ring current is discussed.

Age of martian air: Time scales for martian atmospheric transport

The mean time since air in the Martian atmosphere was in the low-latitude boundary layer is examined using simulations of an idealized “mean age” tracer with the MarsWRF general circulation model. The spatial distribution and seasonality of the mean age in low- and mid-latitudes broadly follow contours of the mean meridional circulation, with the mean age increasing from 0 at the surface to a maximum of 60–100 sols in the upper atmosphere. Substantially older mean ages (exceeding 300 sols) are found in polar regions, with oldest ages in the lower atmosphere (10–100 Pa), above a near-surface layer with very young ages (around 20 sols). The annual maximum ages occur around the equinoxes, and the age in the polar lower atmosphere decreases during the autumn to winter transition. This autumn-winter decrease in age occurs because of mixing of polar and mid-latitude air when the polar vortex exhibits an annulus of high potential vorticity (PV) with a local minimum near the pole. There is no autumn-winter decrease and old ages persist throughout autumn and winter in simulations with CO2 phase changes disabled, and thus no latent heating, where there is a monopolar vortex (i.e., a monotonic increase in PV from equator to pole) forms. The altitudinal and seasonal variations in the mean age indicates similar variations in the transport of dust into polar regions and the mixing of polar air (with, e.g., low water vapor and high ozone concentrations during winter) into mid-latitudes.

Poynting Flux in the Dayside Polar Cap Boundary Regions From DMSP F15 Satellite Measurements

AbstractPoynting 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.