Open Geospace General Circulation Model Research Articles

Employing the Coupled EUHFORIA‐OpenGGCM Model to Predict CME Geoeffectiveness

AbstractEUropean Heliospheric FORecasting Information Asset (EUHFORIA) is a physics‐based data‐driven solar wind and coronal mass ejections (CMEs) propagation model designed for space weather forecasting and event analysis investigations. Although EUHFORIA can predict the solar wind plasma and magnetic field properties at Earth, it is not equipped to quantify the geo‐effectiveness of the solar transients in terms of geomagnetic indices like the disturbance storm time (Dst) index and the auroral indices, that quantify the impact of the magnetized plasma encounters on Earth's magnetosphere. Therefore, we couple EUHFORIA with the Open Geospace General Circulation Model (OpenGGCM), a magnetohydrodynamic model of the response of Earth's magnetosphere, ionosphere, and thermosphere to transient solar wind characteristics. In this coupling, OpenGGCM is driven by the solar wind and interplanetary magnetic field obtained from EUHFORIA simulations to produce the magnetospheric and ionospheric response to the CMEs. This coupling is validated with two observed geo‐effective CME events driven with the spheromak flux‐rope CME model. We compare these simulation results with the indices obtained from OpenGGCM simulations driven by the measured solar wind data from spacecraft. We further employ the dynamic time warping (DTW) technique to assess the model performance in predicting Dst. The main highlight of this study is to use EUHFORIA simulated time series to predict the Dst and auroral indices 1–2 days in advance, as compared to using the observed solar wind data at L1, which only provides predictions 1–2 hr before the actual impact.

Enhanced response of thermospheric cooling emission to negative pressure pulse

Nitric oxide (NO) emission via 5.3 µm wavelength plays dominant role in regulating the thermospheric temperature due to thermostat nature. The response of NO 5.3 mm emission to the negative pressure impulse during November 06–09, 2010 is studied by using Sounding of Atmosphere by Broadband Emission Radiometry (SABER) observations onboard the Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) satellite and model simulations. The TIMED/SABER satellite observations demonstrate a significant enhancement in the high latitude region. The Open Geospace General Circulation Model (OpenGGCM), Weimer model simulations and Active Magnetosphere and Planetary Electrodynamics Response Experiment measurements exhibit intensification and equatorward expansion of the field-aligned-currents (FACs) post-negative pressure impulse period due to the expansion of the dayside magnetosphere. The enhanced FACs drive precipitation of low energy particle flux and Joule heating rate affecting whole magnetosphere–ionosphere–thermosphere system. Our study based on electric fields and conductivity derived from the EISCAT Tromsø\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\\o }$$\\end{document} radar and TIEGCM simulation suggests that the enhanced Joule heating rate and the particle precipitations prompt the increase in NO cooling emission.

The predictive power of magnetospheric models for estimating ground magnetic field variation in the United Kingdom

Space weather events can have damaging effects on ground-based infrastructure. Geomagnetically induced currents (GIC) caused by rapid magnetic field fluctuations during geomagnetic storms can negatively affect power networks, railways as well as navigation systems. To reduce such negative impacts, good forecasting capability is essential. In this study we assess the performance of contemporary magnetohydrodynamic (MHD) models in predicting the external-only ground magnetic field perturbations at three United Kingdom observatories during two severe space weather events: September 2017 and March 2015. Simulated magnetic data were acquired via Community Coordinated Modeling Center (CCMC), using the following models: Space Weather Modeling Framework (SWMF), Open Geospace General Circulation Model (Open GGCM) and Lyon–Fedder–Mobarry (LFM) combined with the Rice Convection Model (RCM). All simulations use spacecraft measurements at L1 as their solar wind input in calculating ground perturbations. Qualitative and quantitative comparison between measured and modelled values suggest that the performance of MHD models vary with latitude, the magnetic component and the characteristics of the storm analysed. Most models tend to exaggerate the magnitude of disturbances at lower latitudes but better capture the fluctuations at the highest latitude. For the two storms investigated, the addition of RCM tends to result in overestimation of the amplitude of ground perturbations. The observed data-model discrepancies most likely arise due to the many approximations required in MHD modelling, such as simplified solar wind input or shift in location of the electrojets in the simulated magnetospheric and ionospheric currents. It was found that no model performs consistently better than any other, implying that each simulation forecasts different aspects of ground perturbations with varying level of accuracy. Ultimately, the decision of which model is most suitable depends on specific needs of the potential end user.

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.

Changes in the Magnetic Field Topology and the Dayside/Nightside Reconnection Rates in Response to a Solar Wind Dynamic Pressure Front: A Case Study

AbstractOne of the most significant observations associated with a sharp enhancement in solar wind dynamic pressure, , is the poleward expansion of the auroral oval and the closing of the polar cap. The polar cap shrinking over a wide range of magnetic local times (MLTs), in connection with an observed increase in ionospheric convection and the transpolar potential, led to the conclusion that the nightside reconnection rate is significantly enhanced after a pressure front impact. However, this enhanced tail reconnection has never been directly measured. We demonstrate the effect of a solar wind dynamic pressure front on the polar cap closure, and for the first time, measure the enhanced reconnection rate in the magnetotail, for a case occurring during southward background Interplanetary Magnetic Field (IMF) conditions. We use Polar Ultra‐Violet Imager (UVI) measurements to detect the location of the open‐closed field line boundary, and combine them with Assimilative Mapping of Ionospheric Electrodynamics (AMIE) potentials to calculate the ionospheric electric field along the polar cap boundary, and thus evaluate the variation of the dayside/nightside reconnection rates. We find a strong response of the polar cap boundary at all available MLTs, exhibiting a significant reduction of the open flux content. We also observe an immediate response of the dayside reconnection rate, plus a phased response, delayed by ∼15–20 min, of the nightside reconnection rate. Finally, we provide comparison of the observations with the results of the Open Geospace General Circulation Model (OpenGGCM), elucidating significant agreements and disagreements.

Plasma sheet injections into the inner magnetosphere: Two‐way coupled OpenGGCM‐RCM model results

AbstractPlasma sheet injections associated with low flux tube entropy bubbles have been found to be the primary means of mass transport from the plasma sheet to the inner magnetosphere. This phenomenon has been primarily studied with satellite data and stand‐alone ring current models with artificial boundary conditions. This study introduces a new two‐way coupling between a kinetic ring current model (Rice Convection Model, or RCM) and a global magnetosphere MHD model (Open Geospace General Circulation Model, or OpenGGCM). Multiple geomagnetic storms and one period of quiet are modeled to track and characterize inward flow behavior. Simulations show that (1) there is a clear association of plasma sheet injections with bubbles, (2) the majority of inward plasma transport in the magnetotail beyond 6.6 RE is due to bubbles, regardless of storm activity, and (3) the average peak velocity of injections is higher for increasing downtail distances, stronger storms (when compared with storms having similar drivers), and storms driven by corotating interaction regions (when compared with coronal mass ejection‐driven storms of similar strength).

The formation of superdense plasma sheet in association with the IMF turning from northward to southward

AbstractWe have studied two events in which relatively superdense plasma appeared near geosynchronous orbit after the interplanetary magnetic field (IMF) changed from a long period of northward condition to southward condition. We used the magnetosphere MHD model Open Geospace General Circulation Model to simulate these two events and compared the simulation results with observations. The observations and the simulation results show that an extended period of northward IMF caused a cold dense plasma sheet (CDPS) to form in the near tail, and a subsequent southward IMF caused a highly stretched near‐tail dipole field, which enhanced the earthward convection and eventually set off reconnection. Some of the cold dense plasma was thus consequently transported to geosynchronous orbit and formed a superdense plasma sheet (SDPS). CDPS is the main source of SDPS in its early stage after the IMF southward turning.

Using OpenGGCM to Compute and Separate Magnetosphere Magnetic Perturbations Measured on Board Low Earth Orbiting Satellites

We use Open Geospace General Circulation Model (OpenGGCM) simulations to predict magnetic field perturbations at Low Earth Orbiting (LEO) satellites such as Swarm, at high latitudes. The simulations allow us to separate three different major contributions to the observed perturbations, i.e., the perturbations caused by currents in the outer magnetosphere, field-aligned currents (FACs), and the currents flowing in the ionosphere. We find that at an altitude of 500 km the strongest contribution comes from FACs, followed by the perturbations caused by the ionospheric currents, while the magnetospheric currents make only a minor contribution. The high latitude perturbations do not average out over extended quiet time periods. There are significant variations in the patterns; however, on a large scale, the basic shape of the pattern remains stable. Thus, without explicitly removing the perturbations from the data, any spherical harmonics fit is expected to incur a bias. Although the predicted OpenGGCM perturbations do not compare particularly well with Swarm data, the simulations reproduce the overall pattern. However, they may still be useful to reduce the bias of the ensemble and produce better global spherical harmonic fits, by producing an ensemble whose external field contributions average out. Since this paper only scratches the surface of the role that models of the external field can play in producing unbiased internal field models, much progress is still possible, for example by improving the external model, investigating larger ensembles, and by considering data from geomagnetically disturbed times.

Testing the estimated hypothetical response of a major CME impact on Earth and its implications to space weather

AbstractThe high‐speed coronal mass ejection (CME), ejected on 23 July 2012, observed by STEREO‐A on the same day as the leading edge of the CME arrived at 1AU was unique both in respect to the observed plasma and magnetic structure and the large solar energetic particle flux that dynamically regulated the shock front. Because of its great intensity, it has been hailed as “Carrington 2” by some, warning that, had that CME been heading toward the Earth, it might have caused a major space weather event. We used the Rice Artificial Neural Network algorithms with the solar wind and interplanetary magnetic field parameters measured in situ by STEREO‐A as inputs to infer what the “geoeffectiveness” of that storm might have been. We have also used an MHD model in Open Geospace General Circulation Model to understand the global magnetospheric process in time sequence. We presently show our neural network models of Kp and Dst on our real‐time prediction site: http://mms.rice.edu/realtime/forecast.html. Running this event through our models showed that, in fact, this would have been an exceptional event. Our results show a prediction resulting in a Kp value of 8+, a Dst of nearly −250 nT, but when assumptions about maximum dipole angle tilt and density are made, predictions resulting in Kp of 11− and Dst dipping close to −700 nT are found. Finally, when solar energetic proton flux is included, the Kp and Dst predictions drop to 8− and ≈−625 nT, respectively.

Impact angle control of interplanetary shock geoeffectiveness

AbstractWe use Open Geospace General Circulation Model global MHD simulations to study the nightside magnetospheric, magnetotail, and ionospheric responses to interplanetary (IP) fast forward shocks. Three cases are presented in this study: two inclined oblique shocks, hereafter IOS‐1 and IOS‐2, where the latter has a Mach number twice stronger than the former. Both shocks have impact angles of 30° in relation to the Sun‐Earth line. Lastly, we choose a frontal perpendicular shock, FPS, whose shock normal is along the Sun‐Earth line, with the same Mach number as IOS‐1. We find that, in the IOS‐1 case, due to the north‐south asymmetry, the magnetotail is deflected southward, leading to a mild compression. The geomagnetic activity observed in the nightside ionosphere is then weak. On the other hand, in the head‐on case, the FPS compresses the magnetotail from both sides symmetrically. This compression triggers a substorm allowing a larger amount of stored energy in the magnetotail to be released to the nightside ionosphere, resulting in stronger geomagnetic activity. By comparing IOS‐2 and FPS, we find that, despite the IOS‐2 having a larger Mach number, the FPS leads to a larger geomagnetic response in the nightside ionosphere. As a result, we conclude that IP shocks with similar upstream conditions, such as magnetic field, speed, density, and Mach number, can have different geoeffectiveness, depending on their shock normal orientation.

The relation between transpolar potential and reconnection rates during sudden enhancement of solar wind dynamic pressure: OpenGGCM‐CTIM results

AbstractThis study investigates how solar wind energy is deposited into the magnetosphere‐ionosphere system during sudden enhancements of solar wind dynamic pressure (Psw), using the coupled Open Geospace General Circulation Model–Coupled Ionosphere Thermosphere Model (OpenGGCM‐CTIM) 3‐D global magnetosphere‐ionosphere‐thermosphere model. We simulate three unique events of solar wind pressure enhancements that occurred during negative, near‐zero, and positive interplanetary magnetic field (IMF) Bz. Then, we examine the behavior of the dayside and nightside reconnection rates and quantify their respective contributions to cross polar cap potential (CPCP), a proxy of ionospheric plasma convection strength. The modeled CPCP increases after a Psw enhancement in all three cases, which agrees well with observations from the Defense Meteorological Satellite Program spacecraft and predictions from the assimilative mapping of ionospheric electrodynamics technique. In the OpenGGCM‐CTIM model, dayside reconnection increases within 9–13 min of the pressure impact, while nightside reconnection intensifies about 13–25 min after the pressure increase. As the strong Psw compresses the dayside magnetosheath and, subsequently, the magnetotail, their magnetic fields intensify and activate stronger antiparallel reconnection on the dayside magnetopause first and near the central plasma sheet second. For southward IMF, dayside reconnection contributes to the CPCP enhancement 2–4 times more than nightside reconnection. For northward IMF, the dayside contribution weakens, and nightside reconnection contributes more to the CPCP enhancement. We find that high‐latitude magnetopause reconnection during northward IMF produces sunward ionospheric plasma convection, which decreases the typical dawn‐to‐dusk ionosphere electric field. This results in a weaker dayside reconnection contribution to the CPCP during northward IMF.

The relation between dayside local Poynting flux enhancement and cusp reconnection

[1] The Defense Meteorological Satellite Program (DMSP) F15 satellite frequently observes an unusually high level of local Poynting flux when the interplanetary magnetic field (IMF) is northward but also has a large By component. We use the Open Geospace General Circulation Model (OpenGGCM) coupled magnetosphere-ionosphere-thermosphere code to study several events where, under such conditions, unusually large earthward Poynting flux has been observed. We find that the Joule heating rate in the model agrees well with the observed Poynting flux. Analysis of the model results shows that the strong Poynting flux hot spots are physically linked with magnetic reconnection at the high-latitude cusps. The solar wind mechanical force and the J × B force act on the newly opened field lines created by cusp reconnection to produce a Pedersen current, which consequently generates an intense Joule heating region, and a pair of adjacent and opposite field-aligned currents (FACs) connecting to the magnetopause currents forming a closed circuit. The intense Joule heating region is also the region with strong downward Poynting flux. The distribution, scale, and magnitude of this Joule heating region and corresponding FACs in the polar regions are mainly controlled by IMF clock angle, IMF magnitude, and solar wind dynamic pressure. A northward IMF condition with a large By component will result in an extended region with intense Joule heating and FAC, thus making a spacecraft transiting the dayside region more likely to observe a strong downward Poynting flux.

Consequences of violation of frozen-in-flux: Evidence from OpenGGCM simulations

[1] It is widely believed that during a substorm, plasma instabilities occur before the onset of magnetic reconnection, signaling the end of the growth phase. Despite many years of effort, however, the details of how the instability and the onset of reconnection develop from closed field line configuration with finite normal magnetic field are not well understood. In this paper, we study an idealized simulation of a substorm that occurred on 23 March 2007, based on the Open Geospace General Circulation Model (OpenGGCM). Our analysis emphasizes the time development of the distribution of the entropy parameter and its convective time derivative, which should be zero in ideal MHD. In the late growth phase, the simulation exhibits, over a range of local times, a systematic violation of conservation of entropy that corresponds to what is called “antidiffusion.” Out of this background, a more localized disturbance develops in a region of high magnetic stretching, resulting in formation of a strong reduction of entropy (bubble) earthward of a local enhancement (blob). The process is accelerated when the current density exceeds a threshold for triggering an explicit resistivity in the code. The bubble moves earthward and the blob tailward, which leads to a reduction of the normal magnetic field and a thinning of the current sheet between them, making the magnetospheric configuration more conducive to tearing and other instabilities (we do not address specifically which instability has occurred). This positive feedback gives rise to increased violation of the perfect conductivity relation and eventually reconnection.

One‐way coupled OpenGGCM/RCM simulation of the 23 March 2007 substorm event

We present results of a simulation of a substorm on 23 March 2007 using the one‐way coupled Open Geospace General Circulation Model–Rice Convection Model (OpenGGCM/RCM). In the standalone RCM, inputs are typically taken from empirical models or inferred from satellite data; however, in this simulation, the OpenGGCM magnetic field and plasma information are used to supply inputs and boundary conditions for the RCM. The OpenGGCM ionospheric potential is used to drive a RCM run. That simulation is used to investigate the short time scale dynamics that occurred around substorm onset and assumes the OpenGGCM has a realistic representation of the inner magnetospheric magnetic field during this event. In these runs, a channel of low total entropy plasma opened up on the RCM tailward boundary around substorm onset, and plasma bubbles were injected into the inner magnetosphere. These bubbles were produced by nonadiabatic processes in the OpenGGCM such as magnetic reconnection. We compare the RCM energetic particle flux with measurements from two Los Alamos National Laboratory (LANL) satellites. A dispersionless electron injection is reproduced at the LANL‐89 location and a dispersed flux increase at the LANL‐97A location. The results indicate the low‐PV5/3 plasma accompanying magnetic field dipolarization produced earthward plasma motion as the result of these low‐entropy flux tubes interchanging their way into the inner magnetosphere; this process may play an important role in substorm particle injection. A comparison simulation in which the electric field is solved by the RCM is also presented, suggesting the need to use RCM's electric field for more accurate inner magnetosphere modeling.

Open Geospace General Circulation Model simulation of a substorm: Axial tail instability and ballooning mode preceding substorm onset

Recent global simulations of substorms show that before the onset of near‐Earth reconnection the pressure equilibrium in the tail breaks down. This instability has no cross‐tail variation and is thus not a ballooning mode, and it is also distinct from the tearing mode. Here, we analyze an Open Geospace General Circulation Model simulation run of the 23 March 2007 substorm and find the same instability. Because this mode has no significant cross‐tail variation associated with it we call it the KY0 mode. Besides the KY0 mode we also find the classical ballooning mode in the simulation. It has a wavelength of ∼0.5 RE and is marginally, but sufficiently, resolved as shown by a higher‐resolution control run. These results suggest a new scenario for the substorm expansion phase onset. During the growth phase magnetic flux is added to the lobes and the plasma sheet thins but remains in equilibrium. When force balance is no longer possible the KY0 instability grows and accelerates plasma tailward. The divergence of the resulting tailward flow reduces the normal magnetic field and thereby makes the current sheet tearing unstable. The tearing mode grows right out of the KY0 mode. The classical ballooning mode grows at the same time and is superimposed on the KY0 mode, but its role in initiating reconnection is still unclear. The growth time of the KY0 mode, ∼2 min, is both consistent with the notion of an explosive growth phase and with recent ground‐based observation of the initial growth of auroral arcs before auroral breakup.

OpenGGCM Simulations for the THEMIS Mission

The THEMIS mission provides unprecedented multi-point observations of the magnetosphere in conjunction with an equally unprecedented dense network of ground measurements. However, coverage of the magnetosphere is still sparse. In order to tie together the THEMIS observations and to understand the data better, we will use the Open Geospace General Circulation Model (OpenGGCM), a global model of the magnetosphere-ionosphere system. OpenGGCM solves the magnetohydrodynamic (MHD) equations in the outer magnetosphere and couples via field aligned current (FAC), electric potential, and electron precipitation to a ionosphere potential solver and the Coupled Thermosphere Ionosphere Model (CTIM). The OpenGGCM thus provides a global comprehensive view of the magnetosphere-ionosphere system. An OpenGGCM simulation of one of the first substorms observed by THEMIS on 23 March 2007 shows that the OpenGGCM reproduces the observed substorm signatures very well, thus laying the groundwork for future use of the OpenGGCM to aid in understanding THEMIS data and ultimately contributing to a comprehensive model of the substorm process.

Solar wind plasma entry into the magnetosphere under northward IMF conditions

This study examines how solar wind plasma enters the magnetosphere under northward interplanetary magnetic field (IMF) conditions, using the Open Geospace General Circulation Model (OpenGGCM) for various solar wind, IMF, and geomagnetic dipole conditions. We trace flow paths of individual fluid elements from the solar wind and study the variation of the topology of the magnetic field line along those flow paths. We find that there is an entry window through which the solar wind plasma can enter the magnetosphere as a result of double high‐latitude reconnection under northward IMF conditions. We investigate how the entry window depends on solar wind, IMF, and geomagnetic dipole parameters, and we estimate the solar wind plasma entry rate for various conditions. We find that the effective entry rate under northward IMF conditions is of the order of 1026 to 1027 particles per second. We also estimate the conditions for which solar wind plasma entry is most efficient. The newly created flux tubes with closed‐field topology are subsequently convected to the nightside and consequently cause magnetosheath plasma to be captured and enter the magnetosphere. Some captured dayside plasma takes about 90 min to convect along the magnetopause to a near tail flank region of the central plasma sheet, thus forming a cold dense plasma sheet. Double high‐latitude reconnection can also release the captured plasma. Thus a balance of inflow and outflow of the captured plasma is eventually established under prolonged northward IMF conditions. We find that high‐latitude reconnection is common under northward IMF conditions in our simulations. It occurs for IMF with any clock angle within [−90°, 90°], measured in front of the bow shock, and for any geomagnetic dipole tilt angle within [−30°, 30°]. An IMF field line with a zero x component usually first reconnects with a geomagnetic field line at the northern high‐latitude boundary when the geomagnetic dipole tilts positive toward the Sun, and vice versa for negative dipole tilt. Our simulations also show that ionosphere conductance affects the convection of the newly closed field lines. Consequently, ionosphere conductance can change the solar wind plasma effective entry rate and can cause asymmetric effective entry rate with respect to positive and negative IMF clock angles.