Defense Meteorological Satellite Program Observations Research Articles

Role of Subauroral Polarization Streams in Deep Injections of Energetic Electrons Into the Inner Magnetosphere

AbstractThe electric fields of subauroral polarization streams (SAPS) have been suggested to affect energetic charged particles' dynamics in the inner magnetosphere, though their role on radiation belt electrons has never been properly quantified. A moderate geomagnetic storm on 2015‐09‐07 caused the deep injection of 10–100s of keV electrons in Earth's inner magnetosphere to low L* (L* < 4). Using a 2‐D test particle tracer, we present the effects of electric fields given by the Volland‐Stern model, a SAPS (Goldstein et al., 2005, https://doi.org/10.1029/2005ja011135) model, and a modified SAPS model on the energetic electron deep injections. The modified SAPS model reflects the SAPS electric field observations by the Van Allen Probes and is supported by Defense Meteorological Satellite Program observations. Simulations suggest that the SAPS electric field pushes 10–20 MeV/G electrons Earthward to L* ∼ 2.7 in 2.5 hr, much deeper compared to the Volland‐Stern electric field.

Inter‐Hemispheric Energy Input Into the Ionosphere‐Thermosphere System During Magnetic Storms: What We Can and Cannot Learn From DMSP Observations

AbstractWe present a long‐term superposed epoch analysis and statistical study with 427 magnetic storms caused by coronal mass ejections and the subsequent magnetospheric energy input into the ionosphere‐thermosphere system. Electron and ion precipitating energy flux data along with plasma drift velocity and magnetic field data (used for Earth‐bound Poynting flux computations) are used in this study. By carefully exploring conjugated inter‐hemispheric energy inputs as a function of storm intensity and seasons, we find that near two‐decades of Defense Meteorological Satellite Program observations indicate that the northern hemisphere (NH) receives slightly more energy than the southern hemisphere (SH) (Poynting flux and integrated electron/ion precipitating energy flux), with the NH receiving more energy as the storm becomes more intense. However, for the Poynting flux case, we find that generally the SH receives more energy when the east‐west component of the interplanetary magnetic field (IMF) becomes highly positive (By ≥ +5 nT), whereas this pattern reverses for cases when IMF By is highly negative (By ≤ −5 nT). The inter‐hemispheric interpretation for electron and ion precipitation energy inputs is ambiguous due to a severe lack of conjugated observations around the midnight sector for both hemispheres.

Poynting Flux Input to the Auroral Ionosphere: The Impact of Subauroral Polarization Streams and Dawnside Auroral Polarization Streams

AbstractThe Poynting vector (Poynting flux) from Earth's magnetosphere downward toward its ionosphere carries the energy that powers the Joule heating in the ionosphere and thermosphere. The Joule heating controls fundamental ionospheric properties affecting the entire magnetosphere‐ionosphere‐thermosphere system, so it is necessary to understand when and where the Poynting flux is significant. Taking advantage of new data sets generated from DMSP (Defense Meteorological Satellite Program) observations, we investigate the Poynting flux distribution within and around the auroral zone, where most magnetosphere‐ionosphere (M‐I) dynamics and thus Joule heating occurs. We find that the Poynting flux, which is generally larger under more active conditions, is concentrated in the sunlit cusp and near the interface between Region 1 and 2 currents. The former concentration suggests voltage generators drive the cusp dynamics. The latter concentration shows asymmetries with respect to the interface between the Region 1 and 2 currents. We show that these reflect the controlling impact of subauroral polarization streams and dawnside auroral polarization streams on the Poynting flux.

Storm‐Time Subauroral Ionospheric Plasma Density Irregularities and the Substorm Current Wedge

AbstractWe report on the development of plasma density irregularities in the subauroral ionosphere over the North American sector during the 17 March 2015 Saint Patrick's Day geomagnetic storm. Data from network of ground‐based observation instruments including the National Oceanic and Atmospheric Administration Continuously Operating Reference Station global navigation satellite system receivers and Time History of Events and Macroscale Interactions during Substorms (THEMIS) all‐sky imagers, as well as in situ measurements from the Defense Meteorological Satellite Program (DMSP) and the Van Allen Radiation Belt Storm Probes (RBSP) spacecrafts, were examined to characterize the spatial and temporal development of subauroral irregularities. The auroral electrojet (AE) index was used as primary indicator of substorm occurrences, aided by some cross‐referencing with the SYM‐H index and SYM‐H time derivative. Special attention was given to substorms that happened at the beginning of this geomagnetic storm. Analysis of Global Positioning System (GPS) rate‐of‐total electron content index (ROTI) data along an east‐west cut line near the US‐Canada border indicates that subauroral ionospheric irregularities may start to form as early as a few minutes after a substantial increase in the AE index. Contemporaneous DMSP and RBSP observations confirmed the presence of subauroral polarization streams wave structures when the aforementioned enhancement in AE index and GPS ROTI occurred. An equatorward expansion of bright auroral arc and subsequent auroral breakups were also seen in the THEMIS all‐sky imager observation data. The relatively short time scales for irregularities to develop suggest possible roles played by the penetration of magnetotail plasma flow bursts into the plasmasphere and the substorm current wedge development in their formation in the subauroral ionosphere.

Transpolar Pc1 Wave Ducting: Swarm, DMSP, and Ground Observations

AbstractAlfvén mode Pc1 waves undergo mode conversion to the fast mode due to induced Hall current in the ionosphere. The fast mode Pc1 waves are trapped and propagate across the magnetic field through the ionospheric waveguide. This process is called Pc1 wave ducting (PWD). Ducting is expected to be in any direction, but most of the existing literature investigated only PWDs toward the equator. In this paper, we report the rare observations of PWD propagating from sub‐auroral latitudes and pervading the polar cap using Swarm satellites, ground magnetometers, and Defense Meteorological Satellite Program (DMSP) satellites. We first identify the injection region of Pc1 wave where localized broadband transverse waves, isolated aurora, and energetic proton precipitations are concurrently observed. Then, we compare ducting characteristics in the ionosphere between the two hemispheres. For the three events investigated here, PWDs in the Southern Hemisphere (SH) pervaded the polar cap while Pc1 waves in the Northern Hemisphere (NH) did not. This hemispheric asymmetry is attributed to the plasma density in the SH sufficient to form the Pc1 waveguide. However, a sharp plasma density gradient on the propagation path still interrupts the ducting even in higher plasma density () regions. The observation of two intersecting Swarm satellites indicates the PWD is not only elongated meridionally, but also can have a significant zonal extent beyond that of the injection region.

Storm time polar cap expansion: interplanetary magnetic field clock angle dependence

Abstract. It is well known that the polar cap, delineated by the open–closed field line boundary (OCB), responds to changes in the interplanetary magnetic field (IMF). In general, the boundary moves equatorward when the IMF turns southward and contracts poleward when the IMF turns northward. However, observations of the OCB are spotty and limited in local time, making more detailed studies of its IMF dependence difficult. Here, we simulate five solar storm periods with the coupled model consisting of the Open Geospace General Circulation Model (OpenGGCM) coupled with the Coupled Thermosphere Ionosphere Model (CTIM) and the Rice Convection Model (RCM), i.e., the OpenGGCM-CTIM-RCM, to estimate the location and dynamics of the OCB. For these events, polar cap boundary location observations are also obtained from Defense Meteorological Satellite Program (DMSP) precipitation spectrograms and compared with the model output. There is a large scatter in the DMSP observations and in the model output. Although the model does not predict the OCB with high fidelity for every observation, it does reproduce the general trend as a function of IMF clock angle. On average, the model overestimates the latitude of the open–closed field line boundary by 1.61∘. Additional analysis of the simulated polar cap boundary dynamics across all local times shows that the MLT of the largest polar cap expansion closely correlates with the IMF clock angle, that the strongest correlation occurs when the IMF is southward, that during strong southward IMF the polar cap shifts sunward, and that the polar cap rapidly contracts at all local times when the IMF turns northward.

The Occurrence of Embedded Region 1 and 2 Currents Depends on Geomagnetic Activity Level

AbstractEmbedded Region 1 and 2 field‐aligned currents (FACs), intense FAC layers of mesoscale latitudinal width near the interface between large‐scale Region 1 and Region 2 FACs, are related to dramatic phenomena in the ionosphere such as discrete arcs, inverted‐V precipitation, and dawnside auroral polarization streams. These relationships suggest that the embedded FACs are potentially important for understanding ionospheric heating and magnetosphere‐ionosphere (M‐I) coupling and instabilities. Previous case studies of embedded FACs have led to the speculation that they may result from enhanced M‐I convection during active times. To explore this idea further, we investigate statistically their occurrence rates under a variety of geomagnetic conditions with a large event list constructed from 17 years of Defense Meteorological Satellite Program observations. The identification procedure is fully automated and explicit. The statistical results indicate that embedded Region 1 and 2 FACs are common, and that they have a higher chance to occur when the level of geomagnetic activity is higher (given by various indices), supporting the idea that they result from enhanced M‐I convection.

Altitude Extension of the NCAR‐TIEGCM (TIEGCM‐X) and Evaluation

AbstractThe upper boundary height of the traditional community general circulation model of the ionosphere‐thermosphere system is too low to be applied to the topside ionosphere/thermosphere study. In this study, the National Center for Atmospheric Research Thermosphere‐Ionosphere‐Electrodynamics General Circulation Model (NCAR‐TIEGCM) was successfully extended upward by four scale heights from 400–600 km to 700–1,200 km depending on solar activity, named TIEGCM‐X. The topside ionosphere and thermosphere simulated by TIEGCM‐X agree well with the observations derived from a topside sounder and satellite drag data. In addition, the neutral density, temperature, and electron density simulated by TIEGCM‐X are morphologically consistent with the NCAR‐TIEGCM simulations before extension. The latitude‐altitude distribution of the equatorial ionization anomaly derived from TIEGCM‐X is more reasonable. During geomagnetic storm events, the thermospheric responses of TIEGCM‐X are similar to NCAR‐TIEGCM. However, the ionospheric storm effects in TIEGCM‐X are stronger than those in NCAR‐TIEGCM and are even opposites at some middle and low latitudes due to the presence of more closed magnetic field lines. Defense Meteorological Satellite Program observations prove that the ionospheric storm effect of TIEGCM‐X is more reasonable. The well‐validated TIEGCM‐X has significant potential applications in ionospheric/thermospheric studies, such as the responses to storms, low‐latitude dynamics, and data assimilation.

Continuous Enhancements of Electron Temperature in the Subauroral Ionosphere Over Eight Days During the 2015 St. Patrick’s Day Storm

AbstractWe have used measurements of the Defense Meteorological Satellite Program (DMSP) satellites to study variations of electron temperature in the subauroral ionosphere during the magnetic storm on 17–25 March 2015. This magnetic storm had a long recovery phase of 7 days, and the ionospheric behavior over the entire storm time was seldom investigated. In this study, we find that the electron temperature at subauroral latitudes was continuously enhanced for 8 days, from the storm onset to the end of the recovery phase. The maximum electron temperature during the storm times was 1000–4000 K higher than the maximum electron temperature during quiet times. This long‐lasting enhancement of subauroral electron temperature was attributed to energy transfer among the solar wind, magnetosphere, ring current, plasmasphere, and ionosphere driven by high‐speed solar wind streams and fluctuating interplanetary magnetic field during the entire 8‐day period of the storm. The electron temperature enhancements were quite symmetric in the post‐midnight sector but became strongly asymmetric near dawn between the southern and northern hemispheres. The asymmetric enhancements of electron temperature near dawn may be related to the magnetic declination and the daytime midlatitude trough in the southern hemisphere. Large daily variations of maximum electron temperature in the post‐midnight sector were observed and may be related to the offset between geomagnetic and geographic latitudes. These DMSP observations provide new insight on ionospheric response to intense magnetic storms.

Dynamics of the Tongue of Ionizations During the Geomagnetic Storm on September 7, 2015

AbstractThe dynamic evolution of the double tongue of ionization (TOI) into a single TOI at 400 km altitude during the geomagnetic storm on September 7, 2015 was studied using the Defense Meteorological Satellite Program observations and Thermosphere Ionosphere Electrodynamic General Circulation model simulations. The double TOIs occurred in the presence of increased southward Bz and weak positive By, while the single TOI occurred in the presence of northward turning of Bz and duskward turning of By. In both double and single TOI events, the plasma at middle latitudes in the afternoon (prenoon) sector was greatly enhanced due to the local upward (upward) and zonal (meridional) E × B drift. The transition process is due to both the northward and duskward turning of interplanetary magnetic field (IMF). The northward turning of IMF Bz weakens the storm enhanced density (SED) and the TOI in both afternoon and morning sectors, while the increasing duskward IMF By strengthens the morning TOI.

Effects of Solar Activity on Ionospheric Ion Upflow During Geomagnetic Quiet Periods: DMSP Observations

Abstract Based on the Defense Meteorological Satellite Program (DMSP) observations during Solar Cycle 23, this paper examines solar activity dependence of ionospheric bulk ion upflow events (IUEs) in the Southern Hemisphere (SH). Much previous similar work was conducted over the Northern Hemisphere (NH) with measurements from European Incoherent Scatter (EISCAT). To eliminate the influence of geomagnetic disturbance on IUEs, we pick out observations during geomagnetic quiet periods (with Kp ≤ 2+). Results show that, ion upward densities and fluxes are dramatically elevated at times of high solar activity (HSA) but ion upward drifts and occurrences are increased at times of low solar activity (LSA) in the SH, which is consistent with the situation in the NH. The ratios between HSA and LSA for these four parameters (IUEs’ density, flux, upward drift and occurrence) are ~2.71, ~1.98, ~0.76 and ~0.57, respectively. Furthermore, lower flux event takes place frequently at LSA as the background ion density is low but the upward drift is large, while higher flux event happens commonly at times of HSA accompanied by high ion density but low upward velocity. Quantitatively, an increase in unit of solar activity (characterized by P index) causes a 4.2×108 m−3 increase in ion density and a 1.2×1011 m−2·s−1 enhancement in upward flux, together with a 0.6 m·s−1 and 0.02 % decrease in ion upward velocity and uprate, respectively. The acceleration from the ambipolar electric field is thought to be a possible mechanism affecting the dependence of IUEs on solar variations. For HSA, the acceleration from the ambipolar electric field weakens, but a large number of background ions provide abundant seeds for acceleration and upflow, which maintains a high IUE flux. It is inferred that upflow events and upward drifts are inhibited by the enhanced ionospheric background density.

Formation of Double Tongues of Ionization During the 17 March 2013 Geomagnetic Storm

AbstractDuring geomagnetic disturbances, enhanced high‐latitude convection transports ionospheric F2‐region plasma from the dayside midlatitude region into the polar cap, leading to structures such as tongues of ionization (TOIs) and patches. In this study, we investigate the dynamic evolution of TOIs during the 17 March 2013 storm using a high‐resolution coupled thermosphere‐ionosphere‐electrodynamics model and Defense Meteorological Satellite Program (DMSP) satellite observations. Both model and observations show the occurrence of two TOIs simultaneously. One originates in the morning convection cell and the other one in the evening cell. DMSP observations also show similar signatures of two density peaks inside the polar cap. Further diagnostic analysis and control simulations show that the morning TOI is associated with auroral precipitation and is transported into the polar cap region by the convection electric field. This study reveals that the plasma transport in both the afternoon and morning sectors play critical roles in the dynamic evolution of polar ionospheric structures.

Long‐Term Trend of Topside Ionospheric Electron Density Derived From DMSP Data During 1995–2017

AbstractIn recent decades, significant efforts have been made to characterize and understand the global pattern of ionospheric long‐term trend. However, little attention has been paid to the topside ionosphere trend. In this study, the unique in situ data measured by series Defense Meteorological Satellite Program (DMSP) satellites were utilized to derive the long‐term trend of the topside ionosphere for the first time. We checked carefully data quality, gap, and consistency between different satellites for both electron density and ion temperature, and compared the techniques of artificial neuron network (ANN) and multiple linear regression methods for deriving the trend. The electron density (Ne) trend in the middle and low latitudes at ~860 km around 18 MLT was derived using the ANN method from 1995–2017. The trend from DMSP observations has a mean magnitude ranging from ~ − 2% to ~2% per decade, with clear seasonal, latitude and longitude variations. The derived trend was evaluated by directly comparing with the simulated trend at 500 km from the NCAR‐TIEGCM driven by realistic changes of CO2 level and geomagnetic field. The observed and simulated trends have similar geographic distribution patterns at 18 MLT. The good agreement between the observed trend around 860 km and the simulated trend near 500 km implies that the physical processes controlling the Ne trends above the peak height might be identical. Further control simulations show that the geomagnetic field secular variation is the dominant factor of the electron density trend at around 500 km, rather than the CO2 long‐term enhancement.

Abnormal Subauroral Ion Drifts (ASAID) and Pi2s During Cross‐Tail Current Disruptions Observed by Polar on the Magnetically Quiet Days of October 2003

AbstractIn this study we further investigate the development of abnormal subauroral ion drifts/polarization streams (ASAID/ASAPS) during the magnetically quiet days of 9–10 October 2003. Our main aim is to provide direct observational evidence verifying that the Defense Meteorological Satellite Program F15 detected quiet‐time ASAID/ASAPS features developed due to the formation of a magnetospheric cold plasma ripple‐hot ring current interface. By utilizing multisatellite and multi‐instrument Cluster_C2, Polar, and Defense Meteorological Satellite Program observations, we investigate plasma rippling and Pi2 pulsation events. In good agreement with the associated empirical scenario of plasma sheet rippling, we demonstrate with various C2 and Polar events the following observational results. (1) The rippling of the plasma sheet's inner edge was related to the process of cross‐tail current disruption and its earthward propagation. (2) The Pi2 pulsation of the cross‐tail EY field reversed the local convection flow when EY was dawnward directed and thus caused plasma ripples while (3) energy was provided by the earthward flows' braking/deceleration. (4) The ASAID/ASAPS feature's underlying EY is antisunward (or dawnward) and EZ is inward (or earthward). By tracking the cross‐tail current disruptions' tailward (by Cluster_C2) and earthward (by Polar) propagations, almost simultaneously, our results demonstrate also that the convection flows' local reversal by the dawnward EY is a common feature of both the tailward and the earthward flows. This study demonstrates also, with multiple plasmapause and EY detections made by Polar, the multiple and mixed occurrences of ASAID and SAID in the plasmasphere's rippled outer edge.

DMSP observations of high latitude Poynting flux during magnetic storms

Previous studies have demonstrated that energy can enter the high-latitude regions of the Ionosphere-Thermosphere (IT) system on open field lines. To assess the extent of high-latitude energy input, we have carried out a study of Poynting flux measured by the Defense Meteorological Satellite Program (DMSP) satellites during magnetic storms. We report sporadic intense Poynting fluxes measured by four DMSP satellites at polar latitudes during two moderate magnetic storms which occurred in August and September 2011. Comparisons with a widely used empirical model for energy input to the IT system show that the model does not adequately capture electromagnetic (EM) energy at very high latitudes during storms. We have extended this study to include more than 30 storm events and find that intense EM energy is frequently detected poleward of 75° magnetic latitude.

Effects of electrojet turbulence on a magnetosphere‐ionosphere simulation of a geomagnetic storm

AbstractIonospheric conductance plays an important role in regulating the response of the magnetosphere‐ionosphere system to solar wind driving. Typically, models of magnetosphere‐ionosphere coupling include changes to ionospheric conductance driven by extreme ultraviolet ionization and electron precipitation. This paper shows that effects driven by the Farley‐Buneman instability can also create significant enhancements in the ionospheric conductance, with substantial impacts on geospace. We have implemented a method of including electrojet turbulence (ET) effects into the ionospheric conductance model utilized within geospace simulations. Our particular implementation is tested with simulations of the Lyon‐Fedder‐Mobarry global magnetosphere model coupled with the Rice Convection Model of the inner magnetosphere. We examine the impact of including ET‐modified conductances in a case study of the geomagnetic storm of 17 March 2013. Simulations with ET show a 13% reduction in the cross polar cap potential at the beginning of the storm and up to 20% increases in the Pedersen and Hall conductance. These simulation results show better agreement with Defense Meteorological Satellite Program observations, including capturing features of subauroral polarization streams. The field‐aligned current (FAC) patterns show little differences during the peak of storm and agree well with Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) reconstructions. Typically, the simulated FAC densities are stronger and at slightly higher latitudes than shown by AMPERE. The inner magnetospheric pressures derived from Tsyganenko‐Sitnov empirical magnetic field model show that the inclusion of the ET effects increases the peak pressure and brings the results into better agreement with the empirical model.

Double‐peak subauroral ion drifts (DSAIDs)

AbstractThis paper reports double‐peak subauroral ion drifts (DSAIDs), which is unique subset of subauroral ion drifts (SAIDs). A statistical analysis has been carried out for the first time with a database of 454 DSAID events identified from Defense Meteorological Satellite Program observations from 1987 to 2012. Both case studies and statistical analyses show that the two velocity peaks of DSAIDs are associated with two ion temperature peaks and two region‐2 field‐aligned currents (R2‐FACs) peaks in the midlatitude ionospheric trough located in the low‐conductance subauroral region. DSAIDs are regional and vary significantly with magnetic local time. DSAIDs can evolve from/to SAIDs during their lifetimes, which are from several minutes to tens of minutes. Comparisons between the ionospheric parameters of DSAIDs and SAIDs indicate that double‐layer region‐2 field‐aligned currents (R2‐FACs) may be the main driver of DSAIDs. It is also found that DSAIDs happen during more disturbed conditions compared with SAIDs.

Occurrence of equatorial spread F during intense geomagnetic storms

AbstractEquatorial spread F (ESF) has been observed in response to the prompt penetration of magnetospheric electric field to equatorial latitudes during intense (minimum Dst ≤ −100 nT; Bz ≤ −10 nT for at least 3 h) magnetic storms using global ion density plots of Defense Meteorological Satellite Program (DMSP) over nearly one solar cycle (1996–2005). Geostationary amplitude scintillation observations from Calcutta at VHF and L band for 1996–2005 and GPS amplitude scintillation measurements during 2004–2005 from the Indian Satellite Based Augmentation System Geostationary and GPS Navigation Outlay (GPS Aided GEO Augmented Navigation) network of stations all over India have been used to corroborate the DMSP observations. Subsequent to the time of southward interplanetary magnetic field Bz crossing −10 nT for an intense storm, it has been observed that within 4 h, ESF is generated at a longitude where the local time is dusk.

Field‐aligned currents during the extreme solar minimum between the solar cycles 23 and 24

AbstractThe solar minimum between solar cycles 23 and 24 was unusually long and deep. The upward region‐1 (R1) field‐aligned current (FAC) response to this extreme solar minimum was investigated using Defense Meteorological Satellite Program observations. The solar cycle responses on the dayside are different than those on the nightside. The field‐aligned current density (J//) on the dayside, at 12–17 magnetic local time (MLT), peaks in the declining phase of the solar cycle, in 2003, when the solar wind speed also peaks, whereas J// on the nightside, at 18–23 MLT, appears insensitive to the solar cycle. In 1995–2010, J// at 15–17 MLT reaches the lowest value during the extreme solar minimum in 2009, when the solar wind speed also reaches the lowest value. At 12–17 MLT, R1 is located mostly on open field lines or at the boundary layer, where the current is driven mostly by the velocity shear at the magnetopause boundary. However, on the nightside, R1 is located mostly on the closed field lines where J// is not driven directly and immediately by the solar wind. The nightside current width (Λ) exhibits a solar cycle effect such that Λ is smaller at the solar minimum and smallest in 2009. However, the dayside Λ exhibits little solar cycle effect. As a result, the FAC intensity (latitudinally integrated J//) exhibits a solar cycle variation at all local times and the FAC intensity is lower during the extreme solar minimum than that of the previous solar minimum.

Comment on “Empirical relationship between electron precipitation and far‐ultraviolet auroral emissions from DMSP observations” by Sotirelis et al.

AbstractSotirelis et al. (2013), which reported on comparisons of Defense Meteorological Satellite Program (DMSP) F16 Special Sensor Ultraviolet Spectrographic Imager (SSUSI) Lyman‐Birge‐Hopfield short and long (LBHS and LBHL) far ultraviolet (FUV) radiances with Special Sensor J/5 (SSJ/5) in situ particle fluxes, overlooked comparable comparisons of observations made by the same two instruments reported in Knight et al. (2008, 2012). The results are compared, and it is found that the statistical ratio of SSUSI LBHL to SSJ/5 electron energy flux reported by Soterelis et al. is a factor of ~2 greater than would be expected based on Knight et al. (2008, 2012). This difference is mainly caused by a SSUSI calibration change.