Positive Interplanetary Magnetic Field Research Articles

Multiple Satellite Observations of the High‐Latitude Cusp Aurora During Northward IMF Conditions

AbstractCusp auroras poleward of the typical auroral oval are ascribed to high‐latitude lobe reconnection when the Interplanetary Magnetic Field (IMF) Bz is predominantly northward. In this study, we further investigate the ionospheric characteristics of a unique high‐latitude cusp region employing multiple satellite observations. A cusp aurora event with wide spatial spread was observed in the postnoon polar cap region. It was found to be associated with northward IMF Bz and positive By components. The cusp aurora was located from 68° to 86° in magnetic latitude and within 15–17 hr in magnetic local time. This broad coverage in the polar cap indicates direct precipitating particles from the magnetosheath. Particle energy is different between the equatorward and poleward edges of the cusp aurora. The precipitating ions at the equatorward side maintain magnetosheath particle characteristics as expected, while ions with higher energies occurred in the poleward side. Further, the poleward edge of the cusp aurora was nearly situated in the center of a convection shear and was associated with an upward field‐aligned current. These observations suggest a lobe cell circulation, hence we attribute the formation of the cusp aurora to the high‐latitude lobe reconnection. Simultaneous observations in the southern hemisphere indicate the absence of cusp aurora. The auroral presence only in the northern hemisphere is probably due to the combination of large dipole tilt angle and positive IMF Bz, which facilitates the lobe reconnection.

Fast and accurate evaluation of deep-space galactic cosmic ray fluxes with HelMod-4/CUDA

The accurate knowledge of cosmic ion fluxes is essential for fundamental physics, deep space missions, and exploration activities in the solar system. In the HelMod-4 model the Parker transport equation is solved using a Monte Carlo approach to evaluate the solar modulation effect on local interstellar spectra of Galactic Cosmic Rays (GCRs). This work presents the latest updates to the HelMod-4 model parameters, focusing on the descending phase of solar cycle 24. The updates are motivated by the latest high-precision measurements from the AMS-02 detector which revealed for the first time with high accuracy the features of GCR fluxes’ evolution during a period of positive interplanetary magnetic field polarity. Furthermore, we present HelMod-4/CUDA, a GPU-accelerated approach for solving the Parker equation in the heliosphere using a stochastic differential equation method. The code is an evolution of the HelMod-4 code, porting the algorithm to GPU architecture using the CUDA programming language. This approach achieves significant speedup compared to a CPU implementation. The HelMod-4/CUDA code has been validated by comparing its results with the most precise and updated experimental GCR spectra observed during high and low solar activity periods, both in the inner and outer heliosphere, at the Earth location, and outside the ecliptic plane. The comparison shows that HelMod-4 and HelMod-4/CUDA can be equivalently used to provide solar-modulated spectra with a similar degree of accuracy in reproducing observed data.

IMF By Effects on the Strength and Latitude of Polar Electrojets: CHAMP and Swarm Joint Observations

AbstractIn this study, the impact of the interplanetary magnetic field (IMF) By component on the peak strength and position of polar electrojets (PEJs) is analyzed, based on 16 years of joint observations from Challenging Minisatellite Payload (CHAMP; 2000–2010) and Swarm (2014–2020) satellites, while focusing on the local time and hemispherical differences. With a more positive IMF By, the duskside eastward PEJ enhances significantly at June solstice in the Northern Hemisphere. Around midnight, the impact of IMF By on the PEJ is more significant in the winter hemisphere; the westward PEJ is stronger in the Northern (Southern) Hemisphere for a more positive (negative) IMF By. In 03–08 MLT, the impact of IMF By is similar in both the winter and summer hemispheres: for IMF By > 0 and By < 0, the PEJ in the dawn sector is stronger in the December and June solstices, respectively. Around noon, a more duskward (dawnward) IMF By component leads to a higher eastward (westward) PEJ in the northern (southern) summer hemisphere. The northern westward (eastward) PEJ peaks at higher latitudes than the southern PEJ for a negative (positive) IMF By.

Investigation of Different ΣO/N2 Variations Observed by GOLD During a Minor Geomagnetic Storm From 2 to 4 August 2021

AbstractDuring a minor geomagnetic storm occurring from Aug 2 (day‐of‐year (DOY) 214) to Aug 4 (DOY 216), 2021, the National Aeronautics and Space Administration Global‐scale Observations of the Limb and Disk (GOLD) mission observed different column density ratio of O to N2 (ΣO/N2) variations in storm main and recovery phases. The percentage difference of ΣO/N2 between DOY 215 (disturbed day, main phase) and DOY 213 (quiet reference day) exhibits a depletion on the east side of the GOLD field‐of‐view (FOV). However, that of ΣO/N2 between DOY 216 (recovery phase) and 213 shows depletions on the west side of GOLD FOV. The National Center for Atmospheric Research Thermosphere Ionosphere Electrodynamics General Circulation Model qualitatively reproduced the observations. Analysis of the model output illustrates that the ΣO/N2 patterns in the two days are both formed due to the classical thermospheric composition theory and formed on DOY 214 and 215, respectively. Further investigation found that the ΣO/N2 depletion on DOY 214 and 215 both initially formed near 120–180°E, but the one on DOY 215 then quickly moved westward into the GOLD FOV, from local post‐midnight to pre‐midnight, near 19 UT. Then it moves equatorward and slowly westward. This results in the observed depletion structure on the west side of GOLD FOV. Model simulations show that the quick westward movement near 19 UT is due to the dominant positive Interplanetary Magnetic Field east‐west component (By) conditions.

Investigation of Interhemispheric Asymmetry of the Thermospheric Composition Observed by GOLD During the First Strong Geomagnetic Storm in Solar‐Cycle 25, 1: IMF By Effects

AbstractAn interhemispheric asymmetry of thermospheric Oxygen (O) to Nitrogen (N2) column density ratio (∑O/N2) variations was observed by the Global‐scale Observations of the Limb and Disk (GOLD) during the 3–5 November 2021 geomagnetic storm. ∑O/N2 depletion is more equatorward in the local morning than in the local afternoon in the northern hemisphere (NH), while more equatorward in the local afternoon than the local morning in the southern hemisphere (SH). The Thermosphere Ionosphere Electrodynamics General Circulation Model simulations reproduced the observed ∑O/N2 asymmetry. The impacts of interplanetary magnetic field (IMF) east‐west component (By) on the interhemispheric asymmetry of ∑O/N2 depletion was investigated. Comparisons of simulation results with and without real By show that the dominant positive IMF By results in the Joule heating maximum occurring in the local afternoon of NH and local morning in the SH during the storm initial phase, which generates the corresponding ∑O/N2 changes. Additionally, the IMF By during this storm are more crucial in the SH than in the NH. Without By, equatorward penetration of the ∑O/N2 depletion in GOLD Field of View are almost same in the SH. However, in the NH, there is still more equatorward depletion in the local morning than the local afternoon without By.

GPS Loss of Lock Events and Their Dependence on the Interplanetary Magnetic Field Orientation

AbstractThe study investigates the influence of interplanetary magnetic field (IMF) orientation on loss of lock (LoL) events in Global Positioning System signals. We analyzed LoLs recorded on two Swarm satellites between July 2014 and December 2021, examining how the signs of the IMF Bx, By, and Bz components affect the distribution of events at high latitudes. Our results reveal an asymmetric distribution of LoL events over 75° magnetic latitude. In the Northern hemisphere, more events occur in the post‐noon sector with negative IMF By, and in the pre‐noon sector with positive IMF By. Conversely, in the Southern hemisphere, pre‐noon events increase with negative IMF By, while post‐noon events increase with positive IMF By. At lower latitudes (50°–75°), IMF By does not significantly affect the event distribution, which mainly concentrates in the night sector for both hemispheres. Additionally, we found a connection between IMF By and Bx, primarily due to the IMF spiral structure. Finally, we discuss our findings in the context of the SuperDARN data‐driven model of ionospheric convection patterns, which shows that LoL events frequently cluster in the cusp region, as well as the area where the two convection cells separate.

Investigation of the Southern Hemisphere Mid‐High Latitude Thermospheric ∑O/N2 Responses to the Space‐X Storm

AbstractThe geomagnetic storm on February 3, 2022 caused the loss of 38 Starlink satellites of Space‐X. The Global‐scale Observations of the Limb and Disk (GOLD) observations and Multi‐Scale Atmosphere Geospace Environment (MAGE) model simulations are utilized to investigate the thermospheric composition responses to the Space‐X storm. The percentage difference of the GOLD observed thermospheric O and N2 column density ratio (∑O/N2) between the storm time (February 3, Day‐of‐Year [DOY] 34) and quiet time (DOY 32) shows a depletion region in the local noon sector mid‐high latitudes in the southern hemisphere, which corresponds to the east side of GOLD field‐of‐view (FOV). This is different from the classic theory of thermospheric composition disturbance during geomagnetic storms, under which the ∑O/N2 depletion is usually generated at local midnight and high latitudes, and thus, appear on the west side of GOLD FOV. MAGE simulations reproduce the observations qualitatively and indicate that the ∑O/N2 depletion is formed due to strong upwelling in the local morning caused by strong Joule heating. Interestingly, enhanced equatorward winds appear near local midnight, but also in the local morning sector, which transports ∑O/N2 depletion equatorward. The depletion corotates toward the local afternoon and is observed in the GOLD FOV. The equatorward winds in the local morning are due to the ion‐neutral coupling under the conditions of a dominant positive interplanetary magnetic field east‐west component (By) during the storm.

A statistical study of space hurricanes in the Northern Hemisphere

The space hurricane is a newly discovered large-scale three-dimensional magnetic vortex structure that spans the polar ionosphere and magnetosphere. At the height of the ionosphere, it has a strong circular horizontal plasma flow with a nearly zero-flow center and a coincident cyclone-shaped aurora caused by strong electron precipitation associated with intense upward magnetic field-aligned currents. By analyzing the long-term optical observation onboard the Defense Meteorological Satellite Program (DMSP) F16 satellite from 2005 to 2016, we found that space hurricanes in the Northern Hemisphere occur in summer and have a maximum occurrence rate in the afternoon sector around solar maximum. In particular, space hurricanes are more likely to occur in the dayside polar cap at magnetic latitudes greater than 80°, and their MLT (magnetic local time) dependence shows a positive relationship with the IMF (interplanetary magnetic field) clock angle. We also found that space hurricanes occur mainly under dominant positive IMF By and Bz and negative Bx conditions. It is suggested that the stable high-latitude lobe reconnection, which occurs under the conditions of a large Earth’s dipole tilt angle and high ionosphere conductivity in summer, should be the formation mechanism of space hurricanes. The result will give a better understanding of the solar wind–magnetosphere–ionosphere coupling process under northward IMF conditions.

Effect of IMF By on the Entry of Solar Wind Ions Into the Near‐Earth Tail Lobe: Global Hybrid Simulation and MMS Observation

AbstractGlobal simulations predict that the low‐latitude mantle may be an important pathway for the solar wind entry into the tail magnetosphere close to the current sheet when interplanetary magnetic field (IMF) By dominates over IMF Bz. To evaluate this entry mechanism in the near‐Earth tail (X ∼ −10–−20 RE), we investigate the predictions from 3D global hybrid simulations as well as in situ observations by magnetospheric multiscale (MMS) spacecraft. The simulations predict that the low‐latitude mantle plasma can appear in the near‐Earth tail lobe extending inward approximately 5 RE from the flank magnetopause. The low‐latitude mantle plasma appears in the dawnside northern lobe and duskside southern lobe during positive IMF By, while the opposite asymmetry is seen during negative IMF By. After a change in the IMF By direction arriving at the bow shock nose, it takes another ∼15–30 min for the asymmetry to completely reverse to the opposite sense in the near‐Earth tail. We present six MMS events in the tail lobe showing that the existence and absence of the low‐latitude mantle plasma is consistent with the predicted asymmetries. Statistical analysis of 5 years of MMS observations shows that the dependencies of the magnitudes of the lobe densities and tailward field‐aligned flow speeds on the IMF By directions are consistent with the predicted contributions from the low‐latitude mantle plasma in the expected lobe regions.

Observational Properties of 15MLT‐PCA in the Southern Hemisphere and the Switching Effects of IMF By on 15MLT‐PCA Occurrence

AbstractBased on Special Sensor Ultraviolet Spectrographic Imager on Defense Meteorological Satellite Program spacecraft (DMSP/SSUSI) observations in the Northern Hemisphere, a particular polar cap arc observed at ∼1,500 magnetic local time (MLT) sector was identified and was named 15MLT‐PCA. A 15MLT‐PCA model proposed for the Northern Hemisphere suggests that the 15MLT‐PCA is caused by a lobe reconnection related to the tilt angle and lobe field line twisting due to a long‐lasting positive interplanetary magnetic field (IMF) By condition. However, it is unclear if the 15MLT‐PCA can be observed in the Southern Hemisphere and how the IMF By influences its occurrence and location. Using the long‐term DMSP/SSUSI observations in the Southern Hemisphere, we confirmed that the 15MLT‐PCA could be observed in the Southern Hemisphere in summer under long‐lasting negative IMF By and predominantly positive IMF Bx. The ion energy dispersion and some other statistical properties are also investigated. Further, we showed that the IMF By has a switching effect on the occurrence of the 15MLT‐PCA using multiple cases. We found that the 15MLT‐PCA disappear as soon as the IMF By changed to an unfavorable condition, but it seems that the favorable conditions need to be maintained for ∼1 hr for the occurrence of 15MLT‐PCA. We also found that the IMF By magnitude is well correlated to the MLT location of the 15MLT‐PCA. We suggest that all the results support the 15MLT‐PCA model and imply that a magnetotail lobe reconnection should be common in the summer hemisphere because the well‐known Parker Spiral favors meeting the model's IMF requirements.

Классификация магнитосферных откликов на взаимодействие с диамагнитными структурами медленного солнечного ветраОСФЕРНЫХ ОТКЛИКОВ НА ВЗАИМОДЕЙСТВИЕ С ДИАМАГНИТНЫМИ СТРУКТУРАМИ МЕДЛЕННОГО СОЛНЕЧНОГО ВЕТРА

We propose a possible classification of the responses of the magnetosphere to the interaction with diamagnetic structures (DS), which form the basis of the slow solar wind. The main determinants of the classification are the value and orientation of the vertical component Bz of the interplanetary magnetic field (IMF) and the solar wind density N. We have identified three types of magnetospheric responses. Type 1 has two subtypes whose main difference is the presence or absence of auroras on the day side of the magnetosphere. Within an hour before DS arrival, Bz has a positive value (up to 12 nT) or fluctuates about 0 in the range from –1 to +1 nT. For both subtypes, the duration of substorm disturbances approximately coincides with the duration of DS, and their intensity does not exceed AE~500 nT. Type 2 is characterized by the fact that before the contact with DS positive IMF Bz (0–10 nT) is recorded for an hour, and at the interface of DS a rapid (≤2 min) change in the orientation of the IMF vertical component from north to south occurs. For type 3, Bz within an hour before the contact with DS is negative (from –10 to 0 nT).
 We address the problem of DS energy transfer to the magnetosphere.

CLASSIFICATION OF MAGNETOSPHERIC RESPONSES TO INTERACTION WITH DIAMAGNETIC STRUCTURES OF SLOW SOLAR WIND

We propose a possible classification of the responses of the magnetosphere to the interaction with diamagnetic structures (DS), which form the basis of the slow solar wind. The main determinants of the classification are the value and orientation of the vertical component Bz of the interplanetary magnetic field (IMF) and the solar wind density N. We have identified three types of magnetospheric responses. Type 1 has two subtypes whose main difference is the presence or absence of auroras on the day side of the magnetosphere. Within an hour before DS arrival, Bz has a positive value (up to 12 nT) or fluctuates about 0 in the range from –1 to +1 nT. For both subtypes, the duration of substorm disturbances approximately coincides with the duration of DS, and their intensity does not exceed AE~500 nT. Type 2 is characterized by the fact that before the contact with DS positive IMF Bz (0–10 nT) is recorded for an hour, and at the interface of DS a rapid (≤2 min) change in the orientation of the IMF vertical component from north to south occurs. For type 3, Bz within an hour before the contact with DS is negative (from –10 to 0 nT).
 We address the problem of DS energy transfer to the magnetosphere.

An Explicit IMF B Dependence on Solar Wind‐Magnetosphere Coupling

AbstractPresently, all empirical coupling functions quantifying the solar wind—magnetosphere energy—or magnetic flux conversion assume that the coupling is independent of the sign of the dawn‐dusk component (B ) of the Interplanetary Magnetic Field (IMF). In this paper we present observations strongly suggesting an explicit IMF B effect on the solar wind‐magnetosphere coupling. When the Earth's dipole is tilted in the direction corresponding to northern winter, positive IMF B is found to on average lead to a larger polar cap than when IMF B is negative during otherwise similar conditions. This explicit IMF B effect is found to reverse when the Earth's dipole is inclined in the opposite direction (northern summer) and is consistently observed from both hemispheres. We interpret the different responses of the polar cap size due to the sign of IMF B to likely be a result of differences in the dayside reconnection rate.

Can Enhanced Flux Loading by High‐Speed Jets Lead to a Substorm? Multipoint Detection of the Christmas Day Substorm Onset at 08:17 UT, 2015

AbstractThis paper describes highly interesting observations of the 25 December 2015 substorm onset at 08:17 UT during northward interplanetary magnetic field (IMF) while magnetosheath contained several intervals of negative Bz. A unique alignment of several spacecraft near the Earth‐Sun line together with magnetohydrodynamic simulations, ground‐based magnetometer, and auroral observations allow a comprehensive timing analysis of the events leading to substorm onset. Perplexingly, prior to substorm onset Geotail measured for 26 min positive IMF Bz just upstream of the bow shock, while simultaneously MMS spacecraft measured several intervals of strong negative Bz in the dayside magnetosheath. These strong pulses of negative Bz in the magnetosheath were associated with high dynamic pressure magnetosheath jets, likely created by foreshock transients during strongly radial IMF interval. Multipoint plasma and magnetic field measurements from ARTEMIS and THEMIS spacecraft were used to determine tail reconnection time at 8:14 and location at x=−33RE. Ground‐based observations of Pi2 pulsations and auroral brightening, with observations of a dipolarization front by THEMIS spacecraft, allowed determination of substorm onset to be at ≈08:17. All MMS spacecraft detected the same magnetosheath jet structure with Bz=−25 nT at ∼08:00 while IMF was northward. Based on DMSP observations and timing analysis we propose that these jets produced magnetopause reconnection leading to final, critical flux enhancement in the midtail region, which may have triggered reconnection 12–14 min later after jet observations.

Hemispheric Asymmetry of the Premidnight Aurora Associated With the Dawn‐Dusk Component of the Interplanetary Magnetic Field

AbstractIt has been known for decades that the nightside aurora in the Northern Hemisphere (NH) tends to be brighter when the interplanetary magnetic field (IMF) measured at Earth has a dawnward (negative y) component compared to a duskward (positive y) component. This asymmetric response to the polarity of IMF By has been explained by an interhemispheric current flowing out of the NH due to a nonuniform “penetration” of IMF By onto the magnetotail. If such a hypothesis is correct, it should predict a brighter aurora in the nightside Southern Hemisphere (SH) for positive IMF By than negative IMF By. Here we investigate this hypothesis using Thermosphere, Ionosphere, Mesosphere, Energetics and Dynamics/Global Ultraviolet Imager data. The present study not only reproduces the result previously found in NH but also shows an opposite change to its Northern Hemispheric counterpart in SH in response to the different IMF By polarity. When comparing north to south, for negative IMF By, the premidnight auroral energy flux is greater in NH than that in SH. The result becomes opposite for positive IMF By. This result is consistent with the hypothesis of the existence of an interhemispheric field‐aligned current.

Secular Variations of a Shift of the Heliospheric Current Sheet

The shift of the heliospheric current sheet (HCS) can be judged by the correlation between polarities of the interplanetary magnetic field (IMF) observed near the Earth. Here the IMF polarities which were reconstructed from the geomagnetic data of the mid-latitude stations beginning from 1844 are studied. The correlation of positive and negative IMF sectors is the evidence of a shift of the heliospheric current sheet towards the Northern Hemisphere in cycles 15–19 of solar activity, and towards the south, in cycles 10–14. We suggest that there is a regular secular cycle of the south–north asymmetry of the current sheet. Correspondingly, a similar cycle is also characteristic of the solar magnetic field.

Formation of the Dayside Magnetopause and Its Boundary Layers Under the Radial IMF

AbstractThe global structure of magnetopause boundary layers under the radial interplanetary magnetic field (IMF) conditions is studied by a comparison of experimental and simulation results. In magnetohydrodynamic simulations, the hemispherical asymmetry of the reconnection locations was found. The draped field adjacent to the magnetopause points northward in the Northern Hemisphere, but it is oriented southward in the Southern Hemisphere at the beginning of the simulation for negative IMF Bx. The magnetopause region affected by the positive IMF Bz component enlarges over time, and the density profile exhibit a north‐south asymmetry near the magnetopause. The experimental part of the study uses the Time History of Events and Macroscale Interactions during Substorm data. We analyze profiles of the plasma parameters and magnetic field as well as the ion pitch‐angle distributions. The nonsimultaneous appearance of parallel and antiparallel aligned flows suggests two spatially separated sources of these flows. We have identified (1) the inner part of the low‐latitude boundary layer (LLBL) on closed magnetic field lines; (2) the outer LLBL on open field lines; (3) the inner part of the magnetosheath boundary layer (MSBL) formed by dayside reconnection in the Southern Hemisphere; and (4) the outer MSBL resulting from lobe reconnection in the Northern Hemisphere.

Interhemispheric Asymmetry of the Sunward Plasma Flows for Strongly Dominant IMF BZ > 0

AbstractSuper Dual Auroral Radar Network (SuperDARN) convection maps obtained simultaneously in both hemispheres are averaged to infer polar cap ionospheric flow patterns under strongly dominant positive interplanetary magnetic field (IMF) Bz component. The data set consisted of winter observations in the Northern Hemisphere simultaneously with summer observations in the Southern Hemisphere. Long‐lasting high‐latitude dayside reverse convection cells are shown to have faster sunward flows at near‐magnetic noon hours in the summer/Southern Hemisphere. Sunward flows typically deviate from the midnight‐noon meridian toward 10–11 h of magnetic local time in the summer/Southern Hemisphere and are more aligned with the midnight‐noon meridian in the winter/Northern Hemisphere. Flow deviations in the winter/Northern Hemisphere can be both toward prenoon and postnoon hours, and there is no clear relationship between flow deviation and the IMF By component. No strong preference for the sunward flow occurrence depending on the IMF Bx polarity was found. In addition, the rate of the sunward flow speed increase in response to an increase in driving conditions was found to be comparable for the IMF Bx > 0 and Bx < 0.

Nightside Ionospheric Convection Asymmetries During the Early Substorm Expansion Phase: Relationship to Onset Local Time

AbstractWe present Super Dual Auroral Radar Network observations of ionospheric convection during substorms. Substorms were grouped according to their onset latitude, onset magnetic local time, and the prevailing sense of interplanetary magnetic field (IMF) BY. The radar observations were then sorted according to substorm group and average convection patterns produced. Here we discuss the patterns corresponding to substorms with onsets occurring in the 65∘–67∘ onset latitude range, at either early (20–22 h) or late (01–03 h) magnetic local times, during intervals of either dominant positive or negative IMF BY. We show that the morphology of the convection patterns differs from that predicted by existing empirical models, with the location of the nightside convection throat being largely consistent with the location of substorm onset. The expected IMF BY‐induced dawn‐dusk convection asymmetry can be enhanced on the nightside when the substorm onset occurs at a fortuitous location but can equally be removed or even reversed from this expected state. Thus, the nightside convection asymmetries are seemingly unrelated to the instantaneous sense of IMF BY.

IMF Control of Alfvénic Energy Transport and Deposition at High Latitudes

AbstractWe investigate the influence of the interplanetary magnetic field (IMF) clock angle ϕIMF on high‐latitude inertial Alfvén wave (IAW) activity in the magnetosphere‐ionosphere transition region using Fast Auroral SnapshoT (FAST) satellite observations. We find evidence that negative IMF Bz coincides with nightside IAW power generation and enhanced rates of IAW‐associated electron energy deposition, while positive IMF Bz coincides with enhanced dayside wave and electron energy deposition. Large ( nT) negative IMF By coincides with enhanced postnoon IAW power, while large positive IMF By coincides with enhanced but relatively weaker prenoon IAW power. For each ϕIMF orientation we compare IAW Poynting flux and IAW‐associated electron energy flux distributions with previously published distributions of Alfvénic Poynting flux over ∼2–22 mHz, as well as corresponding wave‐driven electron energy deposition derived from Lyon‐Fedder‐Mobarry global MHD simulations. We also compare IAW Poynting flux distributions with distributions of broad and diffuse electron number flux, categorized using an adaptation of the Newell et al. (2009) precipitation scheme for FAST. Under negative IMF Bz in the vicinity of the cusp (9.5–14.5 magnetic local time), regions of intense dayside IAW power correspond to enhanced diffuse electron number flux but relatively weaker broadband electron precipitation. Differences between cusp region IAW activity and broadband precipitation illustrate the need for additional information, such as fields or pitch angle measurements, to identify the physical mechanisms associated with electron precipitation in the vicinity of the cusp.