Hemispheric Power Research Articles

Auroral precipitating energy during long magnetic storms

AbstractThe power energy input carried by precipitating electrons into the auroral zone is an important parameter for understanding the solar wind‐magnetosphere energy transfer processes and magnetic storms triggering. Some magnetic storms present a peculiar long recovery phase, lasting for many days or even weeks, which can be associated with the intense and long‐duration auroral activity named HILDCAA (High Intensity Long Duration Continuous AE Activity). The auroral energy input during HILDCAAs has been pointed out as an essential key issue, although there have been very few quantitative studies on this topic. In the present work, we have estimated the auroral electron precipitating energy during the events of long (LRP) and short (SRP) storm recovery phase. The energy has been calculated from the images produced by the Ultraviolet Imager (UVI) on board the Polar satellite. In order to obtain accurate energy values, we developed a dayglow estimate method to remove solar contamination from the UVI images, before calculating the energy. We compared the UVI estimate to the Hemispheric Power (HP), to the empirical power obtained from the AE index, and to the solar wind input power. Our results showed that the UVI electron precipitating power for the LRP events presented a quasiperiodic fluctuation, which has been confirmed by the other estimates. We found that the LRP events are a consequence of a directly driven system, where there is no long‐term energy storage in the magnetosphere, and the auroral electrojets during these events are directly affected by the electron precipitating power.

Universal time variation of high‐latitude thermospheric disturbance wind in response to a substorm

AbstractThe temporal and spatial variation in thermospheric winds are studied at 400 km altitude in response to substorms that start at different universal time (UT), using a global ionosphere and thermosphere model. The substorm‐induced disturbance winds at high latitudes are mainly in the poleward, westward, and upward directions in the dusk sector and in the equatorward, westward, and upward directions in the nighttime. The daytime perturbation is due to ion drag, driven by variations in interplanetary magnetic field Bz, whereas the nighttime perturbation is due to both the Bz and hemispheric power input. The nightside disturbed winds respond somewhat later than the dayside owing to low background ion density. Ion drag is the dominant driving force in the daytime for both meridional and zonal disturbed winds, whereas Joule heating is the dominant factor for the vertical winds. The nighttime meridional and zonal winds are driven by a combination of ion drag, Joule heating, and heating of the auroral belt, whereas the vertical winds are mainly caused by auroral belt heating. The viscous force acts to resist the ion drag, whereas the Coriolis force is negligible. The disturbed winds exhibit large variations with UT during equinox and local winter conditions. With more solar illumination, stronger disturbed winds can be generated. Weak or even opposite variations with UT in the disturbed winds are found in local summer, which is due to a smaller UT variation of the daytime ion density and a larger contribution from auroral heating than from ion drag.

The effect of ring current electron scattering rates on magnetosphere‐ionosphere coupling

AbstractThis simulation study investigated the electrodynamic impact of varying descriptions of the diffuse aurora on the magnetosphere‐ionosphere (M‐I) system. Pitch angle diffusion caused by waves in the inner magnetosphere is the primary source term for the diffuse aurora, especially during storm time. The magnetic local time (MLT) and storm‐dependent electrodynamic impacts of the diffuse aurora were analyzed using a comparison between a new self‐consistent version of the Hot Electron Ion Drift Integrator with varying electron scattering rates and real geomagnetic storm events. The results were compared with Dst and hemispheric power indices, as well as auroral electron flux and cross‐track plasma velocity observations. It was found that changing the maximum lifetime of electrons in the ring current by 2–6 h can alter electric fields in the nightside ionosphere by up to 26%. The lifetime also strongly influenced the location of the aurora, but the model generally produced aurora equatorward of observations.

Universal time variations of the auroral hemispheric power and their interhemispheric asymmetry from TIMED/GUVI observations

AbstractThis paper quantitatively analyzes the auroral hemispheric power (HP) and its interhemispheric asymmetry as a function of universal time (UT) for geomagnetically quiet conditions (Kp 1–3) from Thermosphere Ionosphere Mesosphere Energetics and Dynamics/Global Ultraviolet Imager (TIMED/GUVI) imaging observations. The HP variation with UT can be approximately characterized as two cases: One is for similar HP variations in the equinoxes in the Northern Hemisphere and for the June solstices of both hemispheres, and the other is for similar HP patterns in the equinoxes in the Southern Hemisphere and for the December solstices of both hemispheres. In the equinoxes, the HP variations are interhemispherically asymmetric due to different occurrence time of the HP peak. In the solstices, the HP is generally interhemispherically symmetric in its diurnal variations, but there is interhemispheric asymmetry in the magnitudes of the maximum HP. For geomagnetically quiet conditions (Kp = 2), in the equinoxes relative interhemispheric differences are typically between 0 and 20%, with respect to the averaged HP from the two hemispheres, while during the solstices, the maximum relative interhemispheric asymmetry can be as large as 30% in December, but it is only ~15% in June. These two cases are mainly associated with variations of auroral precipitation power in the night side sector (21:00–03:00 magnetic local time/MLT), which are primarily controlled by solar illumination conditions in both hemispheres and are also attributed to the difference in the geographical area of the auroral oval in the two hemispheres. Furthermore, the general interhemispheric symmetry of the HP variations in solstices suggests that auroral acceleration is not only controlled locally by solar illumination conditions, which has been well known previously, but also might be affected by processes in the precipitation source region.

Functional neuroimaging of post-mortem tissue: lithium-pilocarpine seized rats express reduced brain mass and proportional reductions of left ventral cerebral theta spectral power.

Structural imaging tools can be used to identify neuropathology in post-mortem tissue whereas functional imaging tools including quantitative electroencephalography (QEEG) are thought to be restricted for use in living subjects. We are not aware of any study which has used electrophysiological methods decades after death to infer pathology. We therefore attempted to discriminate between chemically preserved brains which had incurred electrical seizures and those that did not using functional imaging. Our data indicate that modified QEEG technology involving needle electrodes embedded within chemically fixed neural tissue can be used to discriminate pathology. Forty (n = 40) rat brains preserved in ethanol-formalin-acetic acid (EFA) were probed by needle electrodes inserted into the dorsal and ventral components of the left and right cerebral hemispheres. Raw microvolt potentials were converted to spectral power densities within classical electroencephalographic frequency bands (1.5 Hz to 40 Hz). Brain mass differences were shown to scale with left hemispheric ventral theta-band spectral power densities in lithium-pilocarpine seized rats. This relationship was not observed in non-seized rats. A conspicuous absence of pathological indicators within dorsal regions as inferred by microvolt fluctuations was expected given the known localization of post-ictal damage in lithium-pilocarpine seized rats. Together, the data demonstrate that post-mortem neuroimaging is both possible and potentially useful as a means to identify neuropathology without structural imaging techniques or dissection.

Focal attenuation of specific electroencephalographic power over the right parahippocampal region during transcerebral copper screening in living subjects and hemispheric asymmetric voltages in fixed brain tissue

Covering the heads of human volunteers with a toque lined with copper mesh compared to no mesh resulted in significant diminishments in quantitative electroencephalographic power within theta and beta-gamma bands over the right caudal hemisphere. The effect was most evident in women compared to men. The significant attenuation of power was verified by LORETA (low resolution electromagnetic tomography) within the parahippocampal region of the right hemisphere. Direct measurements of frequency-dependent voltages of coronal section preserved in ethanol-formalin-acetic acid from our human brain collection revealed consistently elevated power (0.2μV2Hz−1) in right hemispheric structures compared to left. The discrepancy was most pronounced in the grey (cortical) matter of the right parahippocampal region. Probing the superficial convexities of the cerebrum in an unsectioned human brain demonstrated rostrocaudal differences in hemispheric spectral power density asymmetries, particularly over caudal and parahippocampal regions, which were altered as a function of the chemical and spatial contexts imposed upon the tissue. These results indicate that the heterogeneous response of the human cerebrum to covering of the head by a thin conductor could reflect an intrinsic structure and unique electrical property of the (entorhinal) cortices of the right caudal hemisphere that persists in fixed tissue.

Resting State EEG Hemispheric Power Asymmetry in Children with Dyslexia.

Dyslexia is a neurodevelopmental disorder estimated to affect between 4 and 7% of the population. It is often referred to as a learning disability and is characterized by deficits in the linguistic system. To better understand the neural underpinnings of dyslexia, we examined the electroencephalography (EEG) power spectra between pre-adolescents with dyslexia and neurotypical control children during eyes closed state. We reported the differences in spontaneous oscillatory activity of each major EEG band (delta, theta, alpha, and beta) adopting a global as well as in a region-by-region and hemispheric approach to elucidate whether there are changes in asymmetry in children with dyslexia compared to controls. We also examined the relationship between EEG power spectra and clinical variables. The findings of our study confirm the presence of an atypical linguistic network, evident in children with dyslexia. This abnormal network hallmarked by a dominance of theta activity suggests that these abnormalities are present prior to these children learning to read, thus implicating delayed maturation and abnormal hypoarousal mechanisms.

Functional and structural balances of homologous sensorimotor regions in multiple sclerosis fatigue

Objective Fatigue in Multiple Sclerosis (MS) is a highly disabling symptom affecting social relationships and daily cognitive and physical activities of patients, being complained by up to 90% of MS sufferers. Among the central mechanisms behind it, an involvement of sensorimotor networks is evident from structural and functional studies. We aimed at assessing whether functional/structural balances of homologous sensorimotor regions – known to be crucial for sensorimotor networks effectiveness – decrease with MS fatigue increase. Methods Functional connectivity measures at rest and during a simple motor task (weak handgrip of either the right or left hand) were derived from primary sensorimotor areas EEG recordings in twenty-seven mildly disabled MS patients. Structural MRI-derived inter-hemispheric asymmetries included the cortical thickness of Rolandic regions and the volume of thalami. Results Fatigue symptoms increased together with the functional inter-hemispheric imbalance of sensorimotor homologous areas activities at rest and during movement, in absence of any appreciable parenchymal asymmetries. Conclusion People with MS suffering of chronic fatigue have higher left (dominant) than right hemispheric primary sensorimotor activity power in the resting state, without structural asymmetries. Key message This finding supports the development of compensative interventions that may revert these neuronal activity imbalances to relieve fatigue in MS.

Simulating electron and ion temperature in a global ionosphere thermosphere model: Validation and modeling an idealized substorm

Electron and ion temperatures control many chemical and physical processes in the ionosphere–thermosphere system. Recently, improved electron and ion energy equations were implemented in the Global Ionosphere Thermosphere Model (GITM). The source energy of the electron temperature (Te) includes thermal conduction, heating due to photoionization, elastic collisions with ions, elastic and inelastic collisions with neutrals, auroral precipitation, and heat flux from inner magnetosphere. The source terms in the ion temperature (Ti) equation include thermal conduction, and elastic collisions with electrons and neutrals. The new implementation of Te improved the ionospheric density at middle and high latitudes with respect to IRI. The improved GITM also reproduced the diurnal variation in Te and Ti observed by incoherent scatter radars at low and middle latitudes. The model was used to investigate an idealized substorm statistically described by Clausen et al. (2014). It was found that the responses of the E-region Ne and Te were highly correlated with the variation in auroral hemispheric power. The change of the F-region Te was correlated with the E-region Te and Ne, which was consistent with observations. The response of the F-region Ne to the particle precipitation was delayed by about 30min, and lasted significantly longer than the enhanced precipitation. The variations of Ti in both the E- and F-regions were dominated by IMF-driven ion drifts through frictional energy coupling with the neutrals. It was also found that the increase of the mid-latitude heat flux by one order of magnitude enhanced Te, electron density and TEC by up to 120%, 80% and 80% respectively between dusk and midnight.

Estimation of energy budget of ionosphere-thermosphere system during two CIR-HSS events: observations and modeling

We analyze the energy budget of the ionosphere-thermosphere (IT) system during two High-Speed Streams (HSSs) on 22–31 January, 2007 (in the descending phase of solar cycle 23) and 25 April–2 May, 2011 (in the ascending phase of solar cycle 24) to understand typical features, similarities, and differences in magnetosphere-ionosphere-thermosphere (IT) coupling during HSS geomagnetic activity. We focus on the solar wind energy input into the magnetosphere (by using coupling functions) and energy partitioning within the IT system during these intervals. The Joule heating is estimated empirically. Hemispheric power is estimated based on satellite measurements. We utilize observations from TIMED/SABER (Thermosphere-Ionosphere-Mesosphere Energetics and Dynamics/Sounding of the Atmosphere using Broadband Emission Radiometry) to estimate nitric oxide (NO) and carbon dioxide (CO2 ) cooling emission fluxes. We perform a detailed modeling study of these two similar HSS events with the Global Ionosphere-Thermosphere Model (GITM) and different external driving inputs to understand the IT response and to address how well the model reproduces the energy transport. GITM is run in a mode with forecastable inputs. It is shown that the model captures the main features of the energy coupling, but underestimates NO cooling and auroral heating in high latitudes. Lower thermospheric forcing at 100 km altitude is important for correct energy balance of the IT system. We discuss challenges for a physics-based general forecasting approach in modeling the energy budget of moderate IT storms caused by HSSs.

Dependence of the high-latitude plasma irregularities on the auroral activity indices: a case study of 17 March 2015 geomagnetic storm

The magnetosphere substorm plays a crucial role in the solar wind energy dissipation into the ionosphere. We report on the intensity of the high-latitude ionospheric irregularities during one of the largest storms of the current solar cycle—the St. Patrick’s Day storm of 17 March 2015. The database of more than 2500 ground-based Global Positioning System (GPS) receivers was used to estimate the irregularities occurrence and dynamics over the auroral region of the Northern Hemisphere. We analyze the dependence of the GPS-detected ionospheric irregularities on the auroral activity. The development and intensity of the high-latitude irregularities during this geomagnetic storm reveal a high correlation with the auroral hemispheric power and auroral electrojet indices (0.84 and 0.79, respectively). Besides the ionospheric irregularities caused by particle precipitation inside the polar cap region, evidences of other irregularities related to the storm enhanced density (SED), formed at mid-latitudes and its further transportation in the form of tongue of ionization (TOI) towards and across the polar cap, are presented. We highlight the importance accounting contribution of ionospheric irregularities not directly related with particle precipitation in overall irregularities distribution and intensity.

A simulation study of the thermosphere mass density response to substorms using GITM

AbstractThe temporal and spatial variations of the thermospheric mass density during a series of idealized substorms were investigated using the Global Ionosphere Thermosphere Model (GITM). The maximum mass density perturbation of an idealized substorm with a peak variation of hemispheric power (HP) of 50 GW and interplanetary magnetic field (IMF) Bz of −2 nT was ~14% about 50 min after the substorm onset in the nightside sector of the auroral zone. The mass density response to different types of energy input has a strong local time dependence, with the mass density perturbation due to only an IMF Bz variation peaking in the dusk sector and the density perturbation due to only HP variation peaks in the nightside sector. Simulations with IMF Bz changes only and HP changes only showed that the system behaves slightly nonlinearly when both IMF and HP variations are included (a maximum of 6% of the nonlinearity) and that the nonlinearity grows with energy input. The neutral gas heating rate due to Joule heating was of same magnitude as the heating rate due to precipitation, but the majority of the temperature enhancement due to the heating due to precipitation occurs at lower altitude as compared to the auroral heating. About 110 min after onset, a negative mass density perturbation (~−5%) occurred in the night sector, which was consistent with the mass density measurement of the CHAMP satellite.

Dynamics of the high‐latitude ionospheric irregularities during the 17 March 2015 St. Patrick's Day storm: Ground‐based GPS measurements

AbstractWe report first results on the study of the high‐latitude ionospheric irregularities observed in worldwide GPS data during the St. Patrick's Day geomagnetic storm (17 March 2015). Multisite GPS observations from more than 2500 ground‐based GPS stations were used to analyze the dynamics of the ionospheric irregularities in the Northern and Southern Hemispheres. The most intense ionospheric irregularities lasted for more than 24 h starting at 07 UT of 17 March. This period correlates well with an increase of the auroral Hemispheric Power index. We find hemispheric asymmetries in the intensity and spatial structure of the ionospheric irregularities. Over North America, the ionospheric irregularities zone expanded equatorward below ~45°N geographic latitude. Additionally, the strong midlatitude and high‐latitude GPS phase irregularities in the auroral oval were found to be related to the formation of storm enhanced density and deepening of the main ionospheric trough through upper atmosphere ionization by energetic particle precipitation. Significant increases in the intensity of the irregularities within the polar cap region of both hemispheres were associated with the formation and evolution of the storm enhanced density/tongue of ionization structures and polar patches.

Simulation of long-term variations of the F2-layercritical frequency f0F2 at the northern tropical crest of ionization at Phu Thuy, Hanoi, Vietnam using the thermosphere-ionosphere-electrodynamicsgeneral circulation model (TIE-GCM)

In this work, the long-term variations of the simulated f0F2 by the NCAR thermosphere ionosphere-electrodynamics general circulation model (TIE-GCM) at the northern tropical crest of ionization at Phu Thuy-Vietnam (geographic latitudes 21.030N and longitude: 105.950E) during the period from 1962 to 2002 are examined to evaluate the ability of this model to reproduce the major features of the f0F2 as observed. The TIE-GCM simulates the influences of migrating and non-migrating diurnal and semidiurnal tides at the lower thermosphere, and changes of geomagnetic activity on the long-term variation of the f0F2. It reproduces well the diurnal and seasonal variations. We analyze the diurnal and seasonal variations of the observed f0F2 at Phu Thuy in approximately the same solar activity condition as in 1964, 1996 for the March and September equinoxes and June and December solstices. The local time and seasonal structures of these simulated results correspond well to those that are observed in 1964. On the contrary, the TIE-GCM model does not reproduce the amplitude observed at Thuy Phu in 1996. The TIE-GCM model with the chosen inputs does not yet allow us to explain well the long-term variations observed at Phu Thuy. We also try the different numerical simulations to understand how the long-term variation of the f0F2 is formed, how it relates to the current global system and its relationship with the thermosphere wind. The simulations show that the calculated NmF2 values are lower than the observed values. We find that the modeled contributions of the migrating and non-migrating diurnal and semidiurnal tides may cause them to play a major role in reducing the amplitude of the NmF2. The contributions of the integrated hemispheric power of auroral electrons and the cross polar cap potential seem to play an important role in increasing the amplitude of the NmF2. Keywords: F2 layer; Long-term trends; Ionosphere equatorial ionization anomaly; Ionosphere (ionospheric conductivities, ionospheric currents and electric field), thermospheric tides, Electrodynamics of the ionosphere (ionospheric dynamo).

Electron precipitation models in global magnetosphere simulations

AbstractGeneral methods for improving the specification of electron precipitation in global simulations are described and implemented in the Lyon‐Fedder‐Mobarry (LFM) global simulation model, and the quality of its predictions for precipitation is assessed. LFM's existing diffuse and monoenergetic electron precipitation models are improved, and new models are developed for lower energy, broadband, and direct‐entry cusp precipitation. The LFM simulation results for combined diffuse plus monoenergetic electron precipitation exhibit a quadratic increase in the hemispheric precipitation power as the intensity of solar wind driving increases, in contrast with the prediction from the OVATION Prime (OP) 2010 empirical precipitation model which increases linearly with driving intensity. Broadband precipitation power increases approximately linearly with driving intensity in both models. Comparisons of LFM and OP predictions with estimates of precipitating power derived from inversions of Polar satellite UVI images during a double substorm event (28–29 March 1998) show that the LFM peak precipitating power is >4× larger when using the improved precipitation model and most closely tracks the larger of three different inversion estimates. The OP prediction most closely tracks the double peaks in the intermediate inversion estimate, but it overestimates the precipitating power between the two substorms by a factor >2 relative to all other estimates. LFMs polar pattern of precipitating energy flux tracks that of OP for broadband precipitation exhibits good correlation with duskside region 1 currents for monoenergetic energy flux that OP misses and fails to produce sufficient diffuse precipitation power in the prenoon quadrant that is present in OP. The prenoon deficiency is most likely due to the absence of drift kinetic physics in the LFM simulation.

Abstract T P121: Combinations of Fast and Slow Eye Movement Strategies Improve Clinical Outcomes and EEG Activity in Stroke Patients, a Randomized Controlled Trial

Introduction: The majority of our patients with middle cerebral artery (MCA) infarcts have impaired latency of visual saccades, saccadic dysmetria and saccadic intrusions of pursuits. We wanted to see if the utilization of eye movement rehabilitation in cases of middle cerebral artery infarction would result in changes of brain function and patient clinical outcomes. Hypothesis: We assessed the hypothesis that visual training of fast and slow eye movements to novel targets will result in changes in EEG activity, decrease physical and cognitive impairment and increase clinical outcomes in stroke patients. Methods: A sample size of 60 subjects (80% power, alpha of 0.05 at 95% CI) with acute MCA ischemic stroke within the first 48 hours of clinical evolution were randomized to an active treatment (n=30) group that performed eye movement strategies and a matched control group (n= 30) that did not. All subjects underwent CT and MRI and received standard therapies and NIH Stroke Scales and QEEG. Results: A significant reduction of the NIHSS scale was found after a week of practicing our eye movement strategies, indicating a clinical improvement. There was a significant reduction of the DAR index after eye movement exercises. QEEG brain mapping demonstrated a significant reduction of the spectral power in the Delta and an increment in the Alpha bands also demonstrated with the reduction of the DAR index. The brain symmetry index significantly increased after eye movement exercises indicating an augmentation of balance of the absolute mean value of the hemispheric power difference in the frequency range from 1 to 30 Hz. There was a significant reduction of the PRI index after eye movement exercises, indicating an increment of the fast (alpha +beta), compared with the slow (delta + theta) activities. A significant correlation was found between NIHSS (before) and DAR (after). Conclusions: The stroke patients undergoing eyes exercises had a significant neurological recovery with decreased impairment and improvement of electrical brain activity both reflected in the modifications of the NIHSS scale, and the DAR and BSI QEEG indices and strong correlations of DAR post-exercise with NIHSS scores before eye movement training strategies.

Martí y el Caribe

El artículo pone de manifiesto la relevancia del pensamiento de José Martí para comprender los procesos socio-culturales e históricos del Caribe en el contexto finisecular de la Revolución de Independencia Cubana (1895-1898). Retamar evalúa además la sagaz crítica que Martí ejerce ante los crecientes intereses de Estados Unidos por regir los destinos del Caribe. En el corazón del Caribe, comienza y termina la vida de Martí, y en su sinergia vital con las islas se le revelan los grandes desafíos culturales de su existencia: la esclavitud social y política del ser humano, la opresión colonial de la metrópoli española y su reemplazo por un poder neocolonial, Estados Unidos, un nuevo poder hemisférico que él es el primero en identificar en toda su magnitud.

GABA-mediated changes in inter-hemispheric beta frequency activity in early-stage Parkinson’s disease

In Parkinson’s disease (PD), elevated beta (15–35Hz) power in subcortical motor networks is widely believed to promote aspects of PD symptomatology, moreover, a reduction in beta power and coherence accompanies symptomatic improvement following effective treatment with l-DOPA. Previous studies have reported symptomatic improvements that correlate with changes in cortical network activity following GABAA receptor modulation. In this study we have used whole-head magnetoencephalography to characterize neuronal network activity, at rest and during visually cued finger abductions, in unilaterally symptomatic PD and age-matched control participants. Recordings were then repeated following administration of sub-sedative doses of the hypnotic drug zolpidem (0.05mg/kg), which binds to the benzodiazepine site of the GABAA receptor. A beamforming based ‘virtual electrode’ approach was used to reconstruct oscillatory power in the primary motor cortex (M1), contralateral and ipsilateral to symptom presentation in PD patients or dominant hand in control participants. In PD patients, contralateral M1 showed significantly greater beta power than ipsilateral M1. Following zolpidem administration contralateral beta power was significantly reduced while ipsilateral beta power was significantly increased resulting in a hemispheric power ratio that approached parity. Furthermore, there was highly significant correlation between hemispheric beta power ratio and Unified Parkinson’s Disease Rating Scale (UPDRS). The changes in contralateral and ipsilateral beta power were reflected in pre-movement beta desynchronization and the late post-movement beta rebound. However, the absolute level of movement-related beta desynchronization was not altered. These results show that low-dose zolpidem not only reduces contralateral beta but also increases ipsilateral beta, while rebalancing the dynamic range of M1 network oscillations between the two hemispheres. These changes appear to underlie the symptomatic improvements afforded by low-dose zolpidem.

Solar wind‐magnetosphere energy coupling function fitting: Results from a global MHD simulation

AbstractQuantitatively estimating the energy input from the solar wind into the magnetosphere on a global scale is still an observational challenge. We perform three‐dimensional magnetohydrodynamic (MHD) simulations to derive the energy coupling function. Based on 240 numerical test runs, the energy coupling function is given by. We study the correlations between the energy coupling function and a wide variety of magnetospheric activity, such as the indices ofDst,Kp,ap,AE,AU,AL, the polar cap index, and the hemispheric auroral power. The results indicate that this energy coupling function gives better correlations than theεfunction. This result is also applied to a storm event under northward interplanetary magnetic field conditions. About 13% of the solar wind kinetic energy is transferred into the magnetosphere and about 35% of the input energy is dissipated in the ionosphere, consistent with previous studies.

OVATION Prime‐2013: Extension of auroral precipitation model to higher disturbance levels

AbstractOVATION Prime (OP) is an auroral precipitation model parameterized by solar wind driving. Distinguishing features of the model include an optimized solar wind‐magnetosphere coupling function (dΦMP/dt) which predicts auroral power significantly better than Kp or other traditional parameters, the separation of aurora into categories (diffuse aurora, monoenergetic, broadband, and ion), the inclusion of seasonal variations, and separate parameter fits for each magnetic latitude (MLAT) × magnetic local time (MLT) bin, thus permitting each type of aurora and each location to have differing responses to season and solar wind input—as indeed they do. We here introduce OVATION Prime‐2013, an upgrade to the 2010 version currently widely available. The most notable advantage of OP‐2013 is that it uses UV images from the GUVI instrument on the satellite TIMED for high disturbance levels (dΦMP/dt > 1.2 MWb/s which roughly corresponds to Kp = 5+ or 6−). The range of validity is approximately 0 < dΦMP/dt ≤ 3.0 MWb/s (Kp about 8+). Other upgrades include a reduced susceptibility to salt‐and‐pepper noise, and smoother interpolation across the postmidnight data gap. The model is tested against an independent data set of hemispheric auroral power from Polar UVI. Over the common range of validity of OP‐2010 and OP‐2013, the two models predict auroral power essentially identically, primarily because hemispheric power calculations were done in a way to minimize the impact of OP‐2010s noise. To quantitatively demonstrate the improvement at high disturbance levels would require multiple very large substorms, which are rare, and insufficiently present in the limited data set of Polar UVI hemispheric power values. Nonetheless, although OP‐2010 breaks down in a variety of ways above Kp = 5+ or 6−, OP‐2013 continues to show the auroral oval advancing equatorward, at least to 55° MLAT or a bit less, and OP‐2013 does not develop spurious large noise patches. We will also discuss the advantages and disadvantages of other precipitation models more generally, as no one model fits best all possible uses.