Dayside Cusp Research Articles

Science Highlights from the Kjell Henriksen Observatory on Svalbard

The Kjell Henriksen Observatory (KHO) is the world's largest optical observatory for auroral and airglow measurements, operated by the University Centre in Svalbard (UNIS). KHO is a unique site that lies underneath the dayside cusp, a funnel-shaped region where particles from the Sun can directly enter the Earth's upper atmosphere, including the ionosphere. Building on the pioneering observations of its predecessor --- the Auroral Station in Adventdalen, Svalbard --- KHO has played a pivotal role in advancing our understanding of phenomena in the polar atmosphere. The Auroral Station and KHO have amassed climatological measurements over Svalbard for an impressive 40-year period. KHO's diverse instrumentation, combined with other co-located optical and radar infrastructure and in-situ measurements from satellites and sounding rockets, has paved the way for impactful multi-instrument studies. Serving as an accessible testbed for instrument development, new types of instruments have recently been installed, both at KHO and on satellites. Beyond its scientific contributions, KHO has become an integral part of the Longyearbyen community, with students, visitors, and locals participating in tours and educational initiatives. This connection underscores KHO's multi-functional role, not only as a centre for excellent research but also as a vital hub for public outreach and engagement.

Comprehensive Pattern of the Ionospheric Troughs Localization in the Winter Southern Hemisphere

AbstractA comprehensive pattern of localization of ionization troughs has been constructed for all local time hours. It includes high‐latitude troughs (HLT), main (or sub‐auroral) troughs (MIT), mid‐latitude ring ionospheric troughs (RIT), low‐latitude troughs (LLT), and quasi‐troughs. The CHAMP satellite data recorded in the southern hemisphere for quiet geomagnetic conditions under high solar activity were used. The separation of HLT and MIT was based on the model of auroral diffuse precipitation (Vorobjev et al., 2013). This model describes zone I of diffuse precipitation at the equatorward edge of the auroral oval and zone II of diffuse precipitation at its poleward edge. To distinguish between MIT and RIT the dynamics of both troughs during geomagnetic disturbances was examined. Because the position of all ionospheric structures, including the auroral oval, depends on longitude, the analysis in each local time sector was conducted within the framework of the longitudinal effect. Each local time sector exhibits specificity. (a) The noon sunlit ionosphere is strongly influenced by the dayside cusp; MIT occurs only at shadow longitudes. (b) In the daytime, strong plasma peaks are observed at latitudes of diffuse precipitation in zone I. (c) In the afternoon/evening sector, the plasma peaks are often observed equatorward of the auroral oval. Both peaks are sometimes accompanied by a quasi‐trough. (d) In the evening, HLT sometimes appears slightly equatorward of auroral oval. (e) In the nighttime, at longitudes of America and the Atlantic, a wide electron density minimum is formed near the Polar circle, which masks the MIT minimum.

Interhemispheric Asymmetry in the Seasonal Ionospheric Outflow

AbstractA comprehensive statistical study is conducted on O+ and H+ outflows obtained from the TEAMS/FAST data during the 23rd solar cycle (1996–2007). The study investigates interhemispheric asymmetry in ionospheric outflows during local summer, winter, and equinox seasons. Data are classified into two distinct periods: the pre‐storm and geomagnetic storm phases. Numerous statistical asymmetries are identified. The findings indicate that the dayside cusp consistently demonstrates more outflow rates of O+ and H+ in the northern hemisphere than southern hemisphere during geomagnetic storms in all seasons as well as during the pre‐storm period in the summer season with the exception of H+ during summer storms. Conversely, the nightside O+ and H+ outflow rates are higher in the southern hemisphere during pre‐storm and storm periods in the summer season. Additionally, the dawnside and duskside outflow rates of O+ and H+ are predominantly stronger in the southern hemisphere.

Temporal Evolution of O+ Population in the Near‐Earth Plasma Sheet During Geomagnetic Storms as Observed by the Magnetospheric Multiscale Mission

AbstractDuring geomagnetic storms, the increase in energy input into the ionosphere in the form of Poynting flux and electron precipitation leads to an enhanced ionospheric outflow that results in an increase of the O+ content in the magnetosphere. Using different missions and instrumentation, two main ionospheric sources have been identified for the oxygen ions reaching the inner magnetosphere during geomagnetic storms: the dayside cusp, and the night side auroral region. Evidence of both pathways have been presented in the literature. However, the relative contribution of each of these pathways to the enhancement of O+ observed in near‐Earth plasma sheet, as well as the dynamics involved during the development of geomagnetic storms remains an open question. Here, we present the first statistical study to date to address this question, in the form of a superposed epoch analysis of O+ and H+ moments obtained by the Magnetospheric Multiscale (MMS) mission throughout the main phase of 90 geomagnetic storms with a minimum SYM‐H of at least −50 nT. The results show a clear increase in the oxygen density in the near‐Earth plasma sheet, with values further from Earth remaining low. Temperature values for both species show an increase with the progress of the storms. These results combined suggest that, during the main phase of geomagnetic storms, most of the oxygen ions observed in the near‐Earth plasma sheet are traveling directly from the nightside auroral region.

The 2022 Starlink Geomagnetic Storms: Global Thermospheric Response to a High‐Latitude Ionospheric Driver

AbstractIn this study, we present ionospheric observations of field‐aligned currents from AMPERE and the ESA Swarm A satellite, in conjunction with high‐resolution thermospheric density measurements from accelerometers on board Swarm C and GRACE‐FO, for the third and 4 February 2022 geomagnetic storms that led to the loss of 38 Starlink internet satellites. We study the global storm time response of the thermospheric density enhancements, including their decay and latitudinal distribution. We find that the thermospheric density enhances globally in response to high‐latitude energy input from the magnetosphere‐solar wind system and takes at least a full day to recover to pre‐storm density levels. We also find that the greatest density perturbations occur at polar latitudes consistent with the magnetosphere‐ionosphere dayside cusp, and that there appeared to be a saturation of the thermospheric density during the geomagnetic storm on the fourth. Our results highlight the critical importance of high‐latitude ionospheric observations when diagnosing potentially hazardous conditions for low‐Earth‐orbit satellites.

Structure of the High-Latitude Noon Ionosphere of the Southern Hemisphere

The structure of the winter noon ionosphere of the southern hemisphere was studied. This structure includes the dayside cusp, associated high-latitude ionospheric trough (HLT), main ionospheric trough (MIT), electron density (Ne) peak at latitudes about 70°, mid-latitude ring ionospheric trough (RIT), and low-latitude quasi-trough. Data from the CHAMP satellite in the southern hemisphere for quiet geomagnetic conditions under high solar activity were selected for analysis. The DMSP satellite data and a model of auroral diffuse precipitation were also used. This model represents two zones of auroral diffuse precipitation on the equatorward and poleward edges of the auroral oval. It is shown that the situation in the winter noon ionosphere of the southern hemisphere depends cardinally on longitude. At sunlit longitudes, only the HLT is observed, and MIT is formed in the shadow region. At intermediate longitudes, both troughs can be observed and, therefore, there is a problem of their separation. The positions of all structures of the ionosphere depend on the longitude; in particular, the positions of the daytime MIT are changed by 6°−7°. At latitudes of the dayside cusp, both the peak and the minimum of Ne can be observed. A high and narrow peak of Ne is regularly recorded in the CHAMP data at latitudes of the equatorward zone of diffuse precipitation (68°−72°). In the shadow region, this peak forms the MIT poleward wall, and at sunlit longitudes a quasi-trough equatorward of this peak is sometimes observed. The RIT is rarely formed during the day, only at the American and Atlantic longitudes.

Observations of Mercury's Plasma Sheet Horn: Characterization and Contribution to Proton Precipitation

AbstractThe Mercury Surface, Space ENvironment, GEochemistry and Ranging (MESSENGER) spacecraft was the first spacecraft to orbit the planet Mercury. Previous analysis of MESSENGER data has established that of all the planets in the solar system, Mercury's magnetosphere is the most like Earth's, dominated by the Dungey cycle in its dynamic response of the magnetosphere to solar wind forcing. In this work, we identify and describe for the first time Mercury's northern plasma sheet horn—a Dungey cycle feature key to plasma precipitation. We find three possible geometries for potential horn observation by MESSENGER and describe a case study of each. Two additional case studies are presented with geometries particularly favorable to estimating plasma precipitation within the horns. Estimates of proton precipitation flux are performed, which show precipitation levels on the order of 107 per cm2 per second, on the same order of magnitude as the estimated proton precipitation flux in the dayside cusp despite the higher average energy of the protons in the horn. Potential paths for future study of the horns are discussed.

Magnetosphere Distortions During the “Satellite Killer” Storm of February 3–4, 2022, as Derived From a Hybrid Empirical Model and Archived Data Mining

AbstractA pair of relatively mild geomagnetic storms of February 3–4, 2022, resulted in the loss of 38 Starlink satellites. In this work we reconstruct a sequence of magnetospheric configurations during that event, based on the largest ever archive of historical data, a new magnetic field model, and the nearest‐neighbor method of mining the solar wind, magnetosphere, and ground activity data. The model is constructed as a combination of main modular framework, explicitly representing magnetic effects of principal current systems, and a high‐resolution superstructure, based on expanding the field of equatorial currents into a sum of quasi‐orthogonal harmonics, whose purpose is to correct residual inaccuracies of the modular component. In addition, the variable penetration of the interplanetary magnetic field (IMF) into the magnetosphere is taken into account in the form of a potential field, parameterized by the observed IMF components. Despite relatively modest intensity of the event in terms of Sym‐H peak values, surprisingly strong transient distortions of the global magnetic field are found. Whereas under quiet pre‐storm conditions the midnight segment of synchronous orbit and the dayside cusps mapped, respectively, to ∼67° and ∼77° of corrected latitude, at the peak of the storm their footpoints shifted equatorward to as low as ∼63° and ∼67°–68°, with formation of entangled flux‐rope‐like structures and magnetic neutral lines at distances R ∼ 12–15 RE on the nightside. At nearly the same time, a deep magnetic depression and, possibly, an island of reversed field polarity forms even closer, in the post‐dusk sector of geosynchronous orbit.

Variations of Electron Fluxes in the Outer Radiation Belt: Influence of High-Latitude Traps in the Dayside Cusps

Bifurcation of the drift trajectory of an energetic particle, which occurs near the daytime magnetopause, transfers it from the equatorial region to high-latitude zones located in the vicinity of the dayside magnetospheric cusps. With strong rearrangements of the magnetospheric field occurring during a magnetic storm, the approach of the drift trajectory to the dayside magnetopause, leading to the loss of particles from the belt (“dropout”) upon crossing it, also gives rise to the simultaneous exit of the near-equatorial drift trajectory into the bifurcation zone. The processes of violation of adiabatic invariants occurring in this case should lead to the exchange of particles between high-latitude traps and the near-equatorial trapping zone. These effects should be taken into account in further modeling of variations in the outer radiation belt in the course of a magnetic storm, carried out in relation to individual storms.

Statistical Distribution of Decameter Scale (50 m) Ionospheric Irregularities at High Latitudes

AbstractWe present a study of decameter scale ionospheric irregularities using in‐situ electron density data from the NorSat‐1 satellite. During the current period of low solar activity, NorSat‐1 frequently observes significant plasma irregularities from several 10 s km down to several decameter. These are often observed near the dayside cusp and dawnside auroral zone. The decameter‐scale irregularities are positively correlated with intermediate‐scale (10 km) density gradients, for both negative and positive gradients encountered by the satellite. The statistical distribution of electron density over two winter months in the northern hemisphere along NorSat‐1 orbits, shows significant density increases in the cusp ionosphere (75°–80° Magnetic LATitude) and in regions near the dawnside auroral oval. Intermediate scale density gradients and small‐scale irregularities are clearly associated with these density enhancements. We postulate that these density enhancements and irregularities are due to auroral particle precipitation/plasma dynamics.

Impact of Storm-Enhanced Density (SED) on Ion Upflow Fluxes During Geomagnetic Storm

The impact of the dynamic evolution of the Storm-Enhanced Density (SED) on the upward ion fluxes during the March 06, 2016 geomagnetic storm is studied using comprehensive multi-scale datasets. This storm was powered by a Corotating Interaction Region (CIR), and the minimum Sym-H reached ∼−110 nT. During the ionospheric positive storm phase, the SED formed and the associated plume and polar cap patches occasionally drifted anti-sunward across the polar cap. When these high-density structures encountered positive vertical flows, large ion upward fluxes were produced, with the largest upward flux reaching 3 × 1014 m−2s−1. These upflows were either the type-1 ion upflow associated with fast flow channels, such as the subauroral polarization stream (SAPS) channel, or the type-2 ion upflow due to soft particle precipitations in the cusp region. The total SED-associated upflow flux in the dayside cusp can be comparable to the total upflow flux in the nightside auroral zone despite the much smaller cusp area compared with the auroral zone. During the ionospheric negative storm phase, the ionospheric densities within the SED and plume decreased significantly and thus led to largely reduced upward fluxes. This event analysis demonstrates the critical role of the ionospheric high-density structures in creating large ion upward fluxes. It also suggests that the dynamic processes in the coupled ionosphere-thermosphere system and the resulting state of the ionospheric storm are crucial for understanding the temporal and spatial variations of ion upflow fluxes and thus should be incorporated into coupled geospace models for improving our holistic understanding of the role of ionospheric plasma in the geospace system.

History of the Super Dual Auroral Radar Network (SuperDARN)-I: pre-SuperDARN developments in high frequency radar technology for ionospheric research and selected scientific results

Abstract. Part I of this history describes the motivations for developing radars in the high frequency (HF) band to study plasma density irregularities in the F region of the auroral zone and polar cap ionospheres. French and Swedish scientists were the first to use HF frequencies to study the Doppler velocities of HF radar backscatter from F-region plasma density irregularities over northern Sweden. These observations encouraged the author of this paper to pursue similar measurements over northeastern Alaska, and this eventually led to the construction of a large HF-phased-array radar at Goose Bay, Labrador, Canada. This radar utilized frequencies from 8–20 MHz and could be electronically steered over 16 beam directions, covering a 52∘ azimuth sector. Subsequently, similar radars were constructed at Schefferville, Quebec, and Halley Station, Antarctica. Observations with these radars showed that F-region backscatter often exhibited Doppler velocities that were significantly above and below the ion-acoustic velocity. This distinguished HF Doppler measurements from prior measurements of E-region irregularities that were obtained with radars operating at very high frequency (VHF) and ultra-high frequency (UHF). Results obtained with these early HF radars are also presented. They include comparisons of Doppler velocities observed with HF radars and incoherent scatter radars, comparisons of plasma convection patterns observed simultaneously in conjugate hemispheres, and the response of these patterns to changes in the interplanetary magnetic field, transient velocity enhancements in the dayside cusp, preferred frequencies for geomagnetic pulsations, and observations of medium-scale atmospheric gravity waves with HF radars.

Dayside Cusp Aurorae and Ionospheric Convection Under Radial Interplanetary Magnetic Fields

AbstractDayside cusp aurorae are created from particles precipitating into the cusp, and ionospheric convection is driven by solar wind electric fields. In this study, we coordinated the observations obtained from the all‐sky camera on Svalbard, the Super Dual Auroral Radar Network, SuperMAG magnetometer data, and far ultraviolet imagers on board the Defense Meteorological Satellite Program satellites for the event January 4, 2014 to examine the morphology of aurorae and the patterns of ionospheric convection for radial interplanetary magnetic field (IMF). During the event, a poleward‐moving auroral form and antisunward ionospheric convection were observed when the IMF turned into almost purely radial. Moreover, both types of antisunward and sunward convection were simultaneously observed near the footprint of the cusp at different times during the radial IMF period. The antisunward convection and sunward convection are typically an indicator of the dayside reconnection for the southward IMF and the lobe reconnection for the northward IMF, respectively. All those observations support the concept of low‐latitude dayside and high‐latitude lobe reconnection for the radial IMF. This study further shows that the coexistence of the two types of reconnection for radial IMF, resulting in an interplay of repetitive antisunward and sunward convection.

The Polar Cap (PC) Index: Invalid Index Series and a Different Approach

AbstractThe Polar Cap (PC) indices are derived from the magnetic variations generated by the transpolar convection of magnetospheric plasma and embedded magnetic fields driven by the interaction with the solar wind. The PC indices are potentially very useful for space weather monitoring and forecasts and for related research. However, this study suggests that the PC index series in the near‐real‐time and final versions endorsed by the International Association for Geomagnetism and Aeronomy (IAGA) are invalid and unreliable. Both versions include solar wind sector (SWS) effects in the calculation of the reference levels from which magnetic disturbances are measured. The SWS effects are caused by current systems in the dayside Cusp region related to the Y‐component, BY, of the interplanetary magnetic field (IMF). However, the IAGA‐endorsed handling of SWS effects may generate unfounded PC index changes of up to 4 mV/m at the nightside away from the Cusp. For the real‐time PCN and PCS indices, the cubic spline‐based reference level construction may cause additional unjustified index excursions of more than 3 mV/m with respect to the corresponding final index values. Noting that PC index values above 2 mV/m indicate geomagnetic storm conditions, such unjustified contributions invalidate the PC index series and prove the IAGA‐endorsed derivation methods erroneous. Alternative derivation methods are shown to provide more consistent index reference levels for both final and real‐time PC indices, to reduce their unfounded excursions, and to significantly increase their reliability.

Statistical Study of the Relationship Between Ion Upflow and Field‐Aligned Current in the Topside Ionosphere for Both Hemispheres During Geomagnetic Disturbed and Quiet Time

AbstractA statistical study of ion upflow and field‐aligned currents (FACs) has been performed in the topside ionosphere of both hemispheres for magnetic quiet and disturbed times by using DMSP satellite observations from 2010–2013. Distributions in MLT/MLat reveal that ion upflow occurrence shows a dawn‐dusk asymmetry distribution that matches well with the Region 1 FACs. In addition, there are highest occurrence regions near noon and within the midnight auroral disturbance area, corresponding to dayside cusp and nightside auroral disturbance regions, respectively. Both the ion upflow occurrence and FAC regions expand equatorward to a wider area during disturbed times.

Ionospheric Plasma Irregularities Based on In Situ Measurements From the Swarm Satellites

AbstractIn this study, we present global climatological distributions of ionospheric plasma irregularities based on measurements by the Swarm satellites. These first global statistics obtained by direct, in situ measurements of plasma variations with Swarm confirm the presence of three main regions of strong ionospheric irregularities: the magnetic equator extending from postsunset to early morning, in the auroral ovals (from dayside cusp to nightside), and inside the polar caps. At equatorial latitudes, ionospheric irregularities form two bands of enhanced plasma fluctuations centered around ±10° magnetic latitude. Due to different plasma processes, ionospheric irregularities at high and low latitudes show different distributions. Though the averaged intensity of plasma irregularities is weaker at equatorial latitudes than at high latitudes, the occurrence rate of significant plasma fluctuations (corresponding to extreme events) is much higher at the equator than that at high latitudes. Equatorial irregularities display clear seasonal and longitudinal variations; that is, they are most prominent over South America during the December solstice and are located over Africa during the June solstice. The magnitude of ionospheric irregularities at all latitudes is strongly controlled by the solar activity. Ionospheric irregularities become significantly weaker after 2016 during the current declining phase of solar activity. The interplanetary magnetic field Bz modulates the occurrence of ionospheric irregularities at both high and low latitudes.

Factors Controlling O+ and H+ Outflow in the Cusp During a Geomagnetic Storm: FAST/TEAMS Observations

AbstractFactors related to two sources of energy input to the ionosphere, the Poynting flux associated with both quasistatic fields (Sdc) and Alfvénic fluctuations (Sac), and the soft electron precipitation, are investigated to evaluate their correlations with the O+ and the H+ outflows in the dayside cusp region by using recalibrated FAST/Time‐of‐Flight Energy, Angle, and Mass Spectrograph (TEAMS) data during the 24–25 September 1998 geomagnetic storm studied by Strangeway et al. (2005, https://doi.org/10.1029/2004JA010829). The Poynting flux and the soft electron precipitation are well correlated with ion outflow flux in the dayside cusp region. Sdc shows the highest correlation with the O+ outflows, while it is the electron number flux that correlates best with the H+ outflows. The Alfvénic waves play an essential role in accelerating outflows. The averaged O+/H+ flux ratio is 3.0 and is positively correlated to the Poynting flux, suggesting that the O+ flux increases more strongly with the energy input.

Direct Observations of a Polar Cap Patch Formation Associated With Dayside Reconnection Driven Fast Flow

AbstractDayside solar‐produced concentrated F region plasma can be transported from the midlatitude region into the polar cap during geomagnetically disturbed period, creating plasma density irregularities like polar cap patches, which can cause scintillation and degrade performance of satellite communication and navigation at polar latitudes. In this paper, we observed and investigated a dynamic formation process of a polar cap patch during the 13 October 2016 intense geomagnetic storm. During the storm main phase, storm‐enhanced density (SED) was formed within an extended period of strong southward interplanetary magnetic field (IMF) Bz condition. Total electron content (TEC) map shows that a polar cap patch was segmented from the SED plume. The Sondrestrom Incoherent Scatter Radar (ISR) was right underneath the segmentation region and captured the dynamic process. It shows that the patch segmentation was related with a sudden northeastward flow enhancement reaching ~2 km/s near the dayside cusp inflow region. The flow surge was observed along with abrupt E region electron temperature increase, F region ion temperature increase, and density decrease. The upstream solar wind and IMF observations suggest that the flow enhancement was associated with dayside magnetic reconnection triggered by a sudden and short period of IMF By negative excursion. Quantitative estimation suggests that plasma density loss due to enhanced frictional heating was insufficient for the patch segmentation because the elevated F region density peaking at ~500 km made dissociative recombination inefficient. Instead, the patch was segmented from the SED by low‐density plasma transported by the fast flow channel from earlier local time.

The Relationship Between Cusp Region Ion Outflows and East‐West Magnetic Field Fluctuations at 4,000‐km Altitude

AbstractA number of interdependent conditions and processes contribute to ionospheric‐origin energetic ( 10 eV to several keV) ion outflows. Due to these interdependences and the associated observational challenges, energetic ion outflows remain a poorly understood facet of atmosphere‐ionosphere‐magnetosphere coupling. Here we demonstrate the relationship between east‐west magnetic field fluctuations ( ) and energetic outflows in the magnetosphere‐ionosphere transition region. We use dayside cusp region FAST satellite observations made near apogee ( 4,180‐km altitude) near fall equinox and solstices in both hemispheres to derive statistical relationships between ion upflow and spectral power as a function of spacecraft frame frequency bands between 0 and 4 Hz. Identification of ionospheric‐origin energetic ion upflows is automated, and the spectral power in each frequency band is obtained via integration of power spectral density. Derived relationships are of the form for upward ion flux at 130‐km altitude, with the mapped upward ion flux for a nominal spectral power nT . The highest correlation coefficients are obtained for spacecraft frame frequencies 0.1–0.5 Hz. Summer solstice and fall equinox observations yield power law indices 0.9–1.3 and correlation coefficients , while winter solstice observations yield 0.4–0.8 with . Mass spectrometer observations reveal that the oxygen/hydrogen ion composition ratio near summer solstice is much greater than the corresponding ratio near winter. These results reinforce the importance of ion composition in outflow models. If observed perturbations result from Doppler‐shifted wave structures with near‐zero frequencies, we show that spacecraft frame frequencies 0.1–0.5 Hz correspond to perpendicular spatial scales of several to tens of kilometers.

Multi‐Instrument Observations of Ion‐Neutral Coupling in the Dayside Cusp

AbstractUsing data from the Scanning Doppler Imager, the Super Dual Auroral Radar Network, the EISCAT Svalbard Radar, and an auroral all‐sky imager, we examine an instance of region neutral winds which have been influenced by the presence of poleward moving auroral forms near the dayside cusp region. We observe a reduction in the time taken for the ion drag force to reorientate the neutrals into the direction of the convective plasma (on the order of minutes), compared to before the auroral activity began. Additionally, because the ionosphere near the cusp is influenced much more readily by changes in the solar wind via dayside reconnection, we observe the neutrals responding to an interplanetary magnetic field change within minutes of it occurring. This has implications on the rate that energy is deposited into the ionosphere via Joule heating, which we show to become dampened by the neutral winds.