Volume 49, Issue 19 e2022GL099858
Research Letter
Free Access

Dynamic Jovian Magnetosphere Responses to Enhanced Solar Wind Ram Pressure: Implications for Auroral Activities

Enhao Feng

Enhao Feng

Department of Physics, The University of Hong Kong, Hong Kong, Hong Kong

Department of Earth Sciences, The University of Hong Kong, Hong Kong, Hong Kong

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Binzheng Zhang

Corresponding Author

Binzheng Zhang

Department of Earth Sciences, The University of Hong Kong, Hong Kong, Hong Kong

Correspondence to:

B. Zhang,

[email protected]

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Zhonghua Yao

Zhonghua Yao

Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, China

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Peter A. Delamere

Peter A. Delamere

Department of Physics, University of Alaska Fairbanks, Fairbanks, AK, USA

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Zhiqi Zheng

Zhiqi Zheng

Department of Earth Sciences, The University of Hong Kong, Hong Kong, Hong Kong

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Oliver J. Brambles

Oliver J. Brambles

O. J. Brambles Consulting, Preston, UK

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Sheng-Yi Ye

Sheng-Yi Ye

Department of Earth and Space Sciences, Southern University of Science and Technology, Shenzhen, China

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Kareem A. Sorathia

Kareem A. Sorathia

Applied Physics Laboratory, Johns Hopkins University, Laurel, MD, USA

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First published: 21 September 2022
Citations: 2

Abstract

The main emission (ME) of the Jovian aurora is thought to be related to the current system associated with the breakdown of plasma corotation in the middle magnetosphere. According to the mainstream corotation breakdown model, the intensity of the Jovian ME is expected to decrease when the solar wind (SW) ram pressure increases, which is not fully consistent with auroral observations. In addition to the field-aligned current (FAC), Alfvénic power (AP) play an important role in regulating planetary auroral emissions. We use three-dimensional global simulations to investigate how these proxies of auroral emission respond to enhanced SW ram pressure. We found that during SW compression, both FAC and AP experience up-down-up trends, which is not revealed by any previous simulations, while could potentially explain many observations. The results suggest that different Jovian auroral activities including brightening or dimming can be observed during SW compression period.

Key Points

  • High resolution global magnetohydrodynamics model of Jovian magnetosphere that can reproduce the radial density profile of Jovian magnetosphere is conducted

  • Hemispheric field-aligned currents (FACs) and Alfvénic power (AP) exhibit non-linear responses during solar wind compression (SWC)

  • The responses of both FAC and AP to SWC shows agreement with many auroral observations

Plain Language Summary

Jupiter has the largest magnetosphere and the most intense auroral emissions in the solar system. However, the mechanisms of Jovian auroral emissions are not fully understood. The corotation breakdown model is expected to explain the main emission (ME) of the Jovian aurora. According to the mainstream corotation breakdown model, with enhanced solar wind (SW) ram pressure, the intensity of Jovian auroral ME is expected to decrease. However, observations have shown that aurora gets brighter to a certain extent. This inconsistency drives us to explore the auroral activities response to enhanced SW ram pressure through numerical simulations. Our results are consistent with many observations, and based on the simulation results we expect that the brightening or dimming of Jovian aurora may be predictable. The results can significantly improve our understanding on the Jovian magnetospheric response modes to enhanced SW ram pressure, and the Jovian auroral mechanisms.

1 Introduction

Jupiter has the largest magnetosphere and the most intense auroral emissions in the solar system. To the first order, the large-scale magnetospheric current system associated with the breakdown of plasma corotation in the middle Jovian magnetosphere is thought to drive the main emission (ME) of the Jovian aurora (e.g., Cowley & Bunce, 2001; Hill, 2001; Southwood & Kivelson, 2001). Considering the conservation of angular momentum, when the magnetosphere moves inward, for example, due to enhanced solar wind (SW) ram pressure events, the angular velocities of the plasma is expected to increase, leading to a reduced velocity shear and a decrease in the corotation-related currents (e.g., Cowley & Bunce, 2001; Cowley et al., 2007; Hill, 1979; Southwood & Kivelson, 2001). Thus, the intensity of the Jovian main auroral emission is expected to decrease when under enhanced SW ram pressure. However, this theoretical prediction of reduced magnetospheric current is inconsistent with existing Jovian auroral observations during enhanced SW ram pressure events. For example, enhancements of the auroral emissions in radio, infrared urn:x-wiley:00948276:media:grl64803:grl64803-math-0001, urn:x-wiley:00948276:media:grl64803:grl64803-math-0002 emission, and X-ray wavelengths are found during solar wind compression (SWC) periods (e.g., Baron et al., 1996; Connerney & Satoh, 2000; Dunn et al., 2016; Gurnett et al., 2002; Hess et al., 2014; Sinclair et al., 2019), but the interpretations for these wavelengths are not straightforward because of a lack of spatial resolution and temporal sampling. However, ultraviolet (UV) emissions, which can be separated into polar emissions, MEs, and equatorward emissions (Nichols et al., 2009), are relatively more direct and persuasive because Jupiter's UV auroras can be observed directly with high spatial and temporal resolution equipment such as Hubble Space Telescope (HST). Also, Jupiter's auroral UV emissions, especially in the polar and main ones, are found to be enhanced during SWC (e.g., Nichols et al., 20092017; Yao et al., 2022). In addition, Bonfond et al., 2020 summarized the divergence between corotation model and observation events in the aspect of dawn/dusk asymmetries, global auroral brightening with SWC, etc. The divergence between the axisymmetric theoretical model and the observations suggest that other mechanisms may play a role in regulating the response of Jovian auroral emissions during dynamic periods such as enhanced SW ram pressure.

To understand the observed behavior of the Jovian auroral response during SW ram pressure enhancement events, three-dimensional global magnetohydrodynamics (MHD) simulations have been used to study the dynamic evolution. The global MHD simulations by Chané et al. (2017) suggested that the dawn-dusk asymmetries are strengthened when the density of SW is high, resulting in an increased brightness of the main aurora. In the Chané et al. (2017) study, during an idealized SWC event, the simulated ME (upward currents) on the nightside gets brighter while on the dayside the ME darkens for about 1–2 hr, and then recovers. However, this weakening-recovery of the dayside ME immediately after the SWC has not been found in auroral observations yet. Another global simulation of an idealized SWC event by Sarkango et al. (2019) suggested that the compression of the magnetosphere causes the corotation-related currents to decrease on the dayside and increase on the nightside, resulting in reduced total currents. Although the Sarkango et al. (2019) study is consistent with the prediction based on the corotation breakdown model, the decreased ME (upward currents) right after the commencement of the SWC, and the sustained reduction period (∼50 hr) after the shock arrivals is inconsistent with auroral observations. Although the two numerical simulations gave opposite responses of the Jovian auroral emission to SWC events, which is possibly related to the differences in numerical schemes, grid resolution and boundary conditions, etc., both simulations show similar enhancement of day-night asymmetry during SWC. In addition, asymmetric local time distribution is shown in the local-time dependent auroral current model by Ray et al. (2014).

In these global simulation studies, the “ME” was approximated by the upward field-aligned currents (FACs), carried by precipitating electrons, which are known as invert-V events in the geospace (Fridman & Lemaire, 1980; Knight, 1973). Recently, Nichols and Cowley (2022) found that the magnetosphere-ionosphere coupling current system and the Jovian dawn side ME were highly correlated. In addition, in situ observations have shown that planetary auroral precipitation have more than one type of precipitating electrons (e.g., Mauk et al., 2017; Newell et al., 2009). Thus, FAC may not necessarily be the only leading factor representing the response of the Jovian aurora emissions to changing upstream driving. For example, in the terrestrial magnetosphere, upward FAC only overlaps with a small part of auroral oval on the duskside (e.g., Korth et al., 2014), contributing only about 30% of the total auroral power (Newell et al., 2009). Besides upward FACs, Keiling et al. (2003) have shown that the “Alfvénic oval” powered by magnetospheric Alfvénic Poynting flux contributes to the terrestrial auroral oval, contributing about 30% of total auroral power (Newell et al., 2009). The remaining component is the diffuse aurora (e.g., Li et al., 2021; Newell et al., 20092010), which is the least sensitive aurora to SW variation. Thus, we do not consider the diffuse aurora in this work. For the Jovian magnetosphere, both observations and theoretical studies have shown that Alfvén waves appear quite ubiquitous in the Jovian magnetosphere and have been associated to various auroral features (e.g., Damiano et al., 2019; Gershman et al., 2019; Lysak et al., 2021; Mauk et al., 2017; Pan et al., 2021; Saur et al., 2018). The processes of the Alfvén waves were not considered in both the axisymmetric corotation breakdown model of the ME and the existing global simulations of the Jovian magnetosphere.

In this study, we consider both upward FAC and downward Alfvénic Poynting flux as proxies of Jovian auroral emission in global magnetospheric simulations and investigate the responses to SWC events. These simulation results provide new insights into the observed changes in brightness and morphology of Jovian aurora during SWC events and facilitate understanding of the mechanisms driving the Jovian aurora. In the near future, it should even be possible to assess quantitatively the auroral contributions of FAC and Alfvénic power (AP). However, this last step is out of the scope of this paper since it will require in situ observational constrains that are not available yet. The paper is organized as follows: Section 2 describes the simulation setups; Section 3 describes the simulation results, and Section 4 discusses the driving mechanism and possible implications for auroral observations.

2 Simulation Information

We performed numerical simulations based on the global Jovian magnetosphere model developed by B. Zhang et al. (2018). The MHD equations are solved using the Grid Agnostic MHD for Extended Research Applications code (B. Z. Zhang et al., 2019), which is based on finite-volume techniques for solving the equations on a non-orthogonal, curvilinear grid adapted to Jovian magnetospheric problems. In the solar-magnetic (SM) coordinate system, a stretched spherical grid extends to 100 Jupiter Radii (RJ) in the sunward direction and −1,000 RJ in the anti-sunward direction, ±400 RJ in the directions perpendicular to the sun-Jupiter axis. The grid is spherical polar near the low-altitude (inner) boundary with axis of symmetry along the SM x-axis. The grid resolution is highly non-uniform with ∆r = 0.6 RJ in the radial direction near the simulated Jupiter's dayside magnetopause, and approximately ∆r = 0.23 RJ near the inner boundary, which is set to be a spherical shell at 2.5 RJ. In this work, we focus on the global responses of FAC and AP. Although meso-scale structures may introduce perturbations, they are not expected to change the global configuration. Therefore, the spatial resolution used in this work is sufficient to resolve the global response of the system.

In the simulations, a dipole placed at the origin is used to represent the Jovian intrinsic magnetic field. Since dipole tilt is not the main factor controlling the responses of FAC and AP, to simplify the analysis, the tilt angle is ignored in the numerical experiments. The rapid rotation of the Jupiter is implemented through imposing a corotation potential after the electrostatic magnetosphere-ionosphere coupling (Merkin & Lyon, 2010). To implement mass loading from Io, we use the following simple spatial function for representing the density distribution related to the Io plasma torus:
urn:x-wiley:00948276:media:grl64803:grl64803-math-0003(1)
where urn:x-wiley:00948276:media:grl64803:grl64803-math-0004 is the rate of Io plasma number density added to the system (in cm−3/s) and the parameter A is used to control the total Io mass loading rate. In the following simulations, we use A = 130 and B = 5, which gives a fixed Io mass loading rate of approximately 1,000 kg/s. Numerical experiments have shown that the value of parameter (B ≥3) has little effect on the simulation results, especially the radial density profile. The mass loading was switched on at 05:00 simulation time (ST) with a fixed rate throughout the entire simulation.

The speed of SW was set to be Vx = 300 km/s before the compression and Vx = 600 km/s after the compression, with Vy = Vz = 0. The density of SW was 0.4/cc before the compression, and 0.8/cc after the compression. The changes in the SW conditions correspond to a factor of eight increase in the SW ram pressure. The magnitude of the interplanetary magnetic field (IMF) is fixed as Bx = Bz = 0, By = −0.5 nT, corresponding to nominal IMF conditions near the orbit of Jupiter (e.g., Jackman & Arridge, 2011). The time history of SW/IMF input is shown in Figure 1.

Details are in the caption following the image

The time history of the ideal solar wind (SW)/interplanetary magnetic field (IMF) input used in the simulation to study solar wind compression (SWC).

The simulation is ran for approximately 300 hr to reach a quasi-balanced state, in which the radial density profile within the magnetodisc remains approximately the same in a local-time averaged sense. Then the onset time of SWC (defined by the time when the shock reaches the magnetopause) is ST = 365 hr, and the upstream conditions were fixed after the onset of SWC.

Figure 2 demonstrates the effectiveness of the global Jovian magnetosphere model in reproducing the observed plasma number density profile within the magnetodisc. A simulated average radial density profile of our model is shown together with in situ measurements and empirical distributions summarized by Bagenal and Delamere (2011). The radial density profile is very important to evaluate whether a MHD model is effective. For example, if the numerical diffusion is relatively high, the growth of Kelvin-Helmholtz instability will be suppressed and the gradient of radial profile will be reduced, resulting in an unrealistic magnetosphere compared with the observations. On the other hand, high numerical diffusion will smooth out the variations of the magnetic field, that is, Alfvén wave propagation. As a consequence, Alfvénic processes are under resolved. Using the same MHD solver, we have reproduced the Alfvénic oval (Keiling, 2021) in terrestrial magnetospheric simulations (e.g., B. Zhang et al., 20122014). Thus, we are confident that the global model is simulating the transport of large-scale Alfvén wave power properly. As shown in Figure 2, the simulated density profiles are in good agreement with observations especially in the middle magnetosphere between 8 and 50 RJ, suggesting that the numerical experiments are suitable for investigating the dynamic responses of the Jovian magnetosphere/disc under SWC events.

Details are in the caption following the image

Average radial density profile, compared with Figure 1 from Bagenal and Delamere (2011). The cyan shadow represents the density distribution while red line represents the mean density.

To calculate the Alfvénic Poynting flux in the simulations, we record the instantaneous electric field E and magnetic field B in the MHD domain at r = 2.5 RJ (every 140 s), and then compute the perturbation of electric field δE and magnetic field δB by subtracting a 2,400-s running average of each recorded field. This process is similar to a bandpass filter with a period range of 140–2,400 s, which is within the periods of observational ULF waves based on Juno measurements (Pan et al., 2021). Numerical experiments have shown that using a different bandpass filter (e.g., 140–1,800 s) impacts the magnitude slightly but not the pattern of the simulated Poynting flux, which is consistent with the simulated AP in the terrestrial magnetosphere (B. Zhang et al., 2014). Thus, the conclusion of our study based on the simulated AP is not determined by the choice of the bandpass filter. The Alfvénic Poynting flux along the average direction of the magnetic field is calculated as:
urn:x-wiley:00948276:media:grl64803:grl64803-math-0005(2)
where urn:x-wiley:00948276:media:grl64803:grl64803-math-0006 is the average magnetic field vector within the 24 min window and urn:x-wiley:00948276:media:grl64803:grl64803-math-0007 is the corresponding magnitude of the average magnetic field. urn:x-wiley:00948276:media:grl64803:grl64803-math-0008 is mapped to the ionosphere assuming urn:x-wiley:00948276:media:grl64803:grl64803-math-0009 is constant, which is used as an approximation of the Alfvénic aurora at the ionosphere (B. Zhang et al., 2015). The FAC urn:x-wiley:00948276:media:grl64803:grl64803-math-0010 is derived using the Ampere's law:
urn:x-wiley:00948276:media:grl64803:grl64803-math-0011(3)
where B is the instantaneous magnetic field from the MHD simulation recorded at the low-altitude boundary (2.5 RJ), and b is the unit vector of the corresponding dipole field. The upward part of urn:x-wiley:00948276:media:grl64803:grl64803-math-0012 is used as an approximation for the invert-V aurora in the following section.

3 Simulation Results

Figure 3a shows the simulated response of hemispherically integrated upward FAC and downward AP. The arrival time of the shock front due to SWC is also indicated in the figure, which is the time when the enhanced SW reached the subsolar magnetopause. Before the SWC, the Jovian magnetosphere has reached a quasi-balanced but dynamic state, with an average hemispheric upward FAC around 45 MA. Within approximately 4.6 hr after the SWC, the hemispheric FAC increased to a peak value around 65 MA. After that, the hemispheric FAC decreased within 14 hr, and the lowest level 32 MA occurred around 18 hr after the SWC. However, the reduced FAC state was not sustained. At about 25 hr after the SWC, the hemispheric FAC recovered to a level comparable to the state before compression and continued to increase with time, up to approximately 80 MA.

Details are in the caption following the image

Panel (a) shows the time history of upward field-aligned current (FAC; red line) and downward Alfvénic power (blue line) form simulation time (ST) = 330–507 hr. Green area denotes the quiet period and the white area denotes the solar wind compression (SWC) period. Four yellow dotted lines indicates the sampling ST. Panels (b–e) show the distributions of instantaneous FAC, and the integrated upward FAC at each time are marked in the lower left corner of each panel. Panels (f–i) show the downward Poynting flux average in 9 hr in the northern hemisphere, and the 9-hr average integrated downward Poynting flux at each time are marked in the lower left corner of each panel.

Figures 3b–3e show the instantaneous distributions of the simulated FAC in the northern hemisphere, representing the states −19, 5 18, and 99 hr from the commencement of the SWC (0 hr), respectively. After the SWC, the upward FAC (red in the figures) was significantly enhanced within 5 hr and expanded to lower latitudes at 12MLT (Figure 3c). At 18 hr after SWC, FAC decreased to a minimum level with a distribution above 80° on the dayside. While at 99 hr after the SWC, the intensity of FAC has risen to a higher level compared to the state before the SWC, with a significant equatorward expansion in the distribution.

The response of the hemispheric downward AP exhibit similar behavior as the total FAC. As shown in Figure 3a, before the SWC, the total AP was dynamic but varied around 4,000 GW. As the SWC arrived at the Jovian magnetopause, the AP increased up to 16,000 GW, and remained at a higher level (around 7,000 GW) for about 18 hr after the SWC. However, this high level of the AP was not sustained, and the AP decreased to a lowest level (2,000 GW) around ST = 400 hr. After ST = 410 hr, the AP increased slowly with cyclic enhancement in the total power. These explosive energy release processes occur in the global simulation regardless of the SWC, although their periodicity and intensity are different after the SWC. These transient events are possibly related to the reconfiguration of the outer Jovian magnetosphere, and their driving mechanism is out of the scope of this study, which will be investigated in a follow-up study.

Figures 3f–3i show the 9-hr average spatial distribution of the simulated downward Poynting flux before and after the SWC, representing the states of magnetosphere Alfvénic activity at −19, 5 18, and 99 hr from the commencement of the SWC (0 hr). Before the SWC, downward Alfvénic Poynting flux was at a low level, about 3,293 GW. However, after SWC, downward AP was rapidly enhanced, especially on dayside. Approximately 18 hr after the SWC, Alfvénic Poynting flux became weaker. However, about 99 hr after the SWC, the 9-hr average Alfvénic Poynting flux increased to more than 7,300 GW and mainly distributed in the noon region. In particular, the morphology of the result is related to SW conditions and mapping method. For simplicity, we map the physical variables via dipole magnetic field lines from inner magnetosphere to ionosphere. In fact, because of the fast rotation of Jupiter, mapping via the real stretched field lines will cause the distribution of northern Alfvénic Poynting flux turn anticlockwise. Thus, if we do the mapping via the real field lines, the most powerful region of the northern hemisphere should not be the noon, but turn to afternoon, which is consistent with the typical morphology of the ME.

As a supplement, the distributions of density, magnetic field, FAC, pressure and plasma β in the equatorial plane and the X-Z plane at three key snapshots (15 hr before SWC, 5 hr after SWC, and 55 hr after SWC) are shown in Supporting Information S1.

4 Discussion

The changes of FAC and AP in our simulations show similarity with observations in which Jupiter's auroral emission at each wavelength are found to be enhanced during SWC (e.g., Baron et al., 1996; Connerney & Satoh, 2000; Dunn et al., 2016; Gurnett et al., 2002; Hess et al., 2014; Sinclair et al., 2019), especially for the UV cases (Nichols et al., 20092017; Yao et al., 2022). For example, through the analysis of Jovian UV auroral images observed by HST, Nichols et al. (2017) have found that the auroral UV power were enhanced during SWC. If we consider the time interval from DOY 141 to 147 in Figure 2 of Nichols et al. (2017), there was a SW forward shock occurred at about DOY 141.5, and about half a day (DOY 142) after a SW forward shock, the estimated total UV power (including a part of the polar region and the whole circle of MEs) was at a very high level, up to 5,500 GW. Afterward, the total UV power decreased to less than 1,000 GW after about 1–2 days, and then began to show an upward trend (from DOY 144). The SWC was very weak and the magnetopause expanded again after about DOY 147, so we do not consider the subsequent changes here. This observed time series of auroral UV power response with up-down-up trend shows similar characteristics to both the simulated upward FAC and downward AP in our numerical experiment. In addition, Yao et al. (2022) studied the auroral images from HST and the detections from Juno, and found that main auroral brightening (MAB) events are correlated with magnetopause compression, and the brightening of these events are seen in all local time sectors. Yao et al. (2022) have also suggested that MAB events may occur within the time interval determined as compression, or after. In our simulation, both the upward FAC and downward AP were enhanced approximately 18 hr after the occurrence of SWC, which is consistent with the observations. In our simulation, there is a delay time about 5 hr for the FAC to peak, and it takes about 2–3 hr for the AP to accumulate, although the AP increase is more impulsive after SWC. Observations have also shown that there is a time delay between the onset time of SWC and the peak of aurora brightening (Kita et al., 2019). As shown in Table 1 in Kita et al. (2019), there is a delay time of 5.97–12.48 hr for three specific cases. However, the delay time in Kita et al. (2019) is very model dependent and shock condition dependent, so the specific delay time is not representative. In spite of this, we can learn that there is at least several hours delay for the observational Jovian aurora to peak after the SWC. We will discuss the factors that affect the time delay at the end of the discussion section. Overall, the simulation results show consistency with Jovian UV auroral responses to SWC.

Within a few hours after SWC, the simulated upward FAC increases significantly. This is because with the arrival of interplanetary shock, the dayside is compressed immediately, resulting in the increase of equatorial plasma velocity shear and the corresponding increase of the dayside FAC, especially the region from dawn to noon. After the upward FAC reaches a maximum value within several hours of magnetosphere compression, the middle magnetospheric plasma moves inward as a consequence of magnetospheric compression, resulting in reduced equatorial velocity shear because of conservation of angular momentum. As a result, the total upward FAC also decreases. This part of the response is similar with the prediction of the corotation breakdown model (e.g., Cowley & Bunce, 2001; Cowley et al., 2007; Hill, 1979; Southwood & Kivelson, 2001), although the corresponding physical processes may be slightly different. Cowley et al. (2007) proposed that a “reversed” current system related to super-corotation could be formed during rapid compression, and the resulting FAC would first increase for a short time interval before decreasing. This process looks superficially similar to the initial increase of FAC in our model. However, it should be emphasized that both the super-corotation and corotation breakdown processes are common in the simulation, regardless of SWC, resulting in a much more complicated Jovian current system than axial symmetric model predictions. Indeed, super-corotation, which is responsible for generating a part of the FAC, occurs in our simulation, mostly near magnetopause and a region from magnetotail to dawn side in the middle magnetosphere. On the other hand, corotation breakdown also occurs in the simulation, and it takes place closer to the inner side, and a region from dusk to magnetotail in the middle magnetosphere. Thus, super-corotation and corotation breakdown are different mechanisms, occurring in different regions in the MHD simulations. Both mechanisms may operate at the same time. According to the simulation, the super-corotation related current system is unlikely the “reversed” current system that generates during rapid compression. Finally, about 10 hr after the reduced period of upward FAC, the magnitude of the total upward FAC increases to a level higher than the original level before compression, which is possibly related to the enhanced magnetospheric convection due to the compression. Further quantitative analysis is required to determine the detailed physical processes/mechanisms related to the increase in the total FAC after the SWC.

The total downward AP increases not so long after the interplanetary shock arrives at the dayside magnetopause, which is different from the delayed response in the upward FAC. This difference is mainly due to the fact that large amount of AP is generated at the dayside magnetopause due to the drastic change in the shape of the magnetosphere, while the upward FAC is mostly related to the global reconfiguration of the magnetospheric current system in the middle-to-outer magnetosphere. However, we should note that the release/unloading of AP requires system-level loading of magnetic flux, so the time of peak auroral brightening does not necessarily correspond to the time of peak AP. About 50 hr after the SWC, the total downward AP shows an upward trend. This increase is related to the enhanced magnetotail activities. In the simulations, we found that these magnetic activities are related to the reconfiguration of the Jovian magnetosphere driven by fast planetary rotation. For example, when the interchange structures in the magnetodisc moves outward to the magnetotail and dawn side, the variations of magnetic field is modulated and the AP is enhanced. During SWC, we find more intense magnetotail activities through tail reconnections, which generates more Alfvénic wave power toward low altitudes. Future quantitative analysis is needed to quantify these processes in detail.

Although the numerical experiments show agreement with existing Jovian auroral observations during SWC events, other factors may also play important roles and require further investigations, for example, the mass of the disc, the upstream conditions and the hot plasma population(s). For example, the time delay between the FAC response and the SWC onset suggests that the Alfvénic transit time may play an important role in determining the response time scales. With a more massive magnetodisc, the transit time is expected to be longer, resulting in more delayed response in both the rising and falling stages in the FAC. The later increase of Alfvenic Poynting flux is also possibly related to the state of the magnetodisc. On the other hand, the influence of different upstream conditions (e.g., the amplification of SW speed and density, and the duration of SW compression or relaxation) needs to be further investigated. Also, realistic SW inputs will be used in future studies. It is also important to note that we have not yet implemented the hot plasma population in the global simulation, which results in a slightly smaller Jovian magnetosphere. The size of the magnetosphere is expected to influence the Alfvénic transit time and the transit time of the shock, and the latter will further influence the change rate of velocity shear. Finally, comparative studies with other rotating systems, such as Saturn, will be included in the future.

In summary, when looking at the changes of Jupiter's aurora related to SW activities, which is a very complex problem, both FAC and AP should be considered. The real situation depends on many factors such as compression conditions and the disc conditions. Under different upstream and disc conditions, observing the Jupiter's aurora in different time periods may have different auroral phenomena (e.g., brightening or dimming) response to SWC.

Acknowledgments

Binzheng Zhang was supported by the National Natural Science Foundation of China (Grant No. 41922060), the RGC General Research Fund (Grant No. 17300719 and 17308520). Zhonghua Yao was funded by the Key Research Program of the Institute of Geology and Geophysics, CAS, grant no. IGGCAS-201904. Peter Delamere was funded by NASA grants 80NSSC19K0822 and 80NSSC20K1279. Sheng-Yi Ye was supported by the Strategic Priority Research Program of the Chinese Academy of Sciences (grant No. XDB 41000000).

    Data Availability Statement

    The model outputs used to generate the figures for analysis presented in this paper are publicly available online (https://doi.org/10.17605/OSF.IO/BDZYF).