Solar wind proton precipitation to the surface of Mercury

Mapping Intimacies ◽

10.5194/epsc2020-31 ◽

2020 ◽

Author(s):

Shahab Fatemi ◽

Andrew R. Poppe ◽

Stas Barabash

Keyword(s):

Solar Wind ◽

Dynamic Pressure ◽

Solar Wind Plasma ◽

Solar Wind Dynamic Pressure ◽

Solar Wind Proton ◽

Entire Surface ◽

The North ◽

Proton Precipitation ◽

Neutral Sodium ◽

The Imf

We examine the effects of the interplanetary magnetic field (IMF) orientation and solar wind dynamic pressure on the solar wind proton precipitation to the surface of Mercury. We use the Amitis model, a three-dimensional GPU-based hybrid model of plasma (particle ions and fluid electrons), and explain a method we found necessary to accurately calculate plasma precipitation to the surface of Mercury through the highly dynamic Hermean magnetosphere. We use our model to explain ground-based telescope observations of Mercury's neutral sodium exosphere, and compare our simulation results with MESSENGER observations. For the typical solar wind dynamic pressure near the orbit of Mercury (i.e., ~7-8 nPa) our model shows a high solar wind proton flux precipitates through the magnetospheric cusps to the high latitudes on both hemispheres on the dayside with a higher precipitation rate to the southern hemisphere compared to the north, which is associated with the northward displacement of Mercury's intrinsic magnetic dipole. We show that this two peak pattern, which is also a common feature observed for neutral sodium exosphere, is controlled by the radial component (Bx) of the IMF and not the Bz component. Our model also suggests that the southward IMF and its associated magnetic reconnection do not play a major role in controlling plasma precipitation to the surface of Mercury through the magnetospheric cusps, in agreement with MESSENGER observations that show that, unlike the Earth, there is almost no dependence between the IMF angle and magnetic reconnection rate at Mercury. For the typical solar wind dynamic pressure, our model suggests that the solar wind proton precipitation through the cusps is longitudinally centered near noon with ~11o latitudinal extent in the north and ~21o latitudinal extent in the south, which is consistent with MESSENGER observations. We found an anti-correlation in the incidence area on the surface and the incidence particle rate between the northern and southern cusp precipitation such that the total area and the total rate through both of the cusps remain constant and independent of the IMF orientation. We also show that the solar wind proton incidence rate to the entire surface of Mercury is higher when the IMF has a northward component and nearly half of the incidence flux impacts the low latitudes on the nightside. During extreme solar events (e.g., Coronal Mass Ejections) a large area on the dayside surface of Mercury is exposed to the solar wind plasma, especially in the southern hemisphere. Our model suggests that over 70 nPa solar wind dynamic pressure is required for the entire surface of Mercury to be exposed to the solar wind plasma.

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On the response of ionospheric electrojets to solar wind discontinuities

Annales Geophysicae ◽

10.5194/angeo-27-3791-2009 ◽

2009 ◽

Vol 27 (10) ◽

pp. 3791-3803 ◽

Cited By ~ 1

Author(s):

M. Palmroth ◽

T. I. Pulkkinen ◽

J. Polvi ◽

A. Viljanen ◽

P. Janhunen

Keyword(s):

Solar Wind ◽

Dynamic Pressure ◽

Pressure Change ◽

Solar Wind Dynamic Pressure ◽

Simultaneous Increase ◽

Sudden Increase ◽

Step Size ◽

Ionospheric Response ◽

Superposed Epoch Analysis ◽

The Imf

Abstract. We investigate the ionospheric response to solar wind discontinuities as detected by the IE index computed from IMAGE ground magnetometers. The solar wind discontinuities include both sudden increases as well as decreases of the solar wind dynamic pressure, recorded by the SWEPAM instrument of the ACE spacecraft during the period 1998–2004. In our statistical study, we identify four categories of events: 1) sudden increases of the dynamic pressure with a simultaneous increase of the interplanetary magnetic field (IMF) magnitude; 2) sudden increases of the dynamic pressure accompanied with a simultaneous decrease of the IMF; 3) sudden decreases of the dynamic pressure accompanied with a sudden increase of the IMF; and 4) sudden decreases of the dynamic pressure with relatively steady IMF. We perform a superposed epoch analysis for the four event categories to distinguish the ionospheric response. We find that the IE index increases/decreases in response to the solar wind dynamic pressure increases/decreases regardless of the simultaneous change in the IMF or the amount of estimated input energy. We investigate the magnitude of the ionospheric response according to the IMF north-south direction, the dynamic pressure step size as well as the pressure level prior the dynamic pressure change. We find that the ionospheric result is augmented for larger pressure steps, while the prior IMF has a role only in some of the event categories. We also perform global MHD simulation runs to investigate the ionospheric dissipation rate during such solar wind discontinuities, and find that the simulation results are in good qualitative accordance with the observational statistical results.

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GPS phase scintillation at high latitudes during geomagnetic storms of 7–17 March 2012 – Part 1: The North American sector

Annales Geophysicae ◽

10.5194/angeo-33-637-2015 ◽

2015 ◽

Vol 33 (6) ◽

pp. 637-656 ◽

Cited By ~ 12

Author(s):

P. Prikryl ◽

R. Ghoddousi-Fard ◽

E. G. Thomas ◽

J. M. Ruohoniemi ◽

S. G. Shepherd ◽

...

Keyword(s):

Magnetic Field ◽

Solar Wind ◽

Geomagnetic Storms ◽

Dynamic Pressure ◽

Auroral Oval ◽

Solar Wind Dynamic Pressure ◽

Polar Cap ◽

The North ◽

Auroral Emission ◽

Ground Magnetic

Abstract. The interval of geomagnetic storms of 7–17 March 2012 was selected at the Climate and Weather of the Sun-Earth System (CAWSES) II Workshop for group study of space weather effects during the ascending phase of solar cycle 24 (Tsurutani et al., 2014). The high-latitude ionospheric response to a series of storms is studied using arrays of GPS receivers, HF radars, ionosondes, riometers, magnetometers, and auroral imagers focusing on GPS phase scintillation. Four geomagnetic storms showed varied responses to solar wind conditions characterized by the interplanetary magnetic field (IMF) and solar wind dynamic pressure. As a function of magnetic latitude and magnetic local time, regions of enhanced scintillation are identified in the context of coupling processes between the solar wind and the magnetosphere–ionosphere system. Large southward IMF and high solar wind dynamic pressure resulted in the strongest scintillation in the nightside auroral oval. Scintillation occurrence was correlated with ground magnetic field perturbations and riometer absorption enhancements, and collocated with mapped auroral emission. During periods of southward IMF, scintillation was also collocated with ionospheric convection in the expanded dawn and dusk cells, with the antisunward convection in the polar cap and with a tongue of ionization fractured into patches. In contrast, large northward IMF combined with a strong solar wind dynamic pressure pulse was followed by scintillation caused by transpolar arcs in the polar cap.

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Magnetopause energy and mass transfer: results from a global MHD simulation

Annales Geophysicae ◽

10.5194/angeo-24-3467-2006 ◽

2006 ◽

Vol 24 (12) ◽

pp. 3467-3480 ◽

Cited By ~ 24

Author(s):

M. Palmroth ◽

T. V. Laitinen ◽

T. I. Pulkkinen

Keyword(s):

Magnetic Field ◽

Mass Transfer ◽

Solar Wind ◽

Energy Transfer ◽

Dynamic Pressure ◽

Solar Wind Dynamic Pressure ◽

Closed Field ◽

Dayside Magnetopause ◽

Solar Wind Parameters ◽

The Imf

Abstract. We use the global MHD model GUMICS-4 to investigate the energy and mass transfer through the magnetopause and towards the closed magnetic field as a response to the interplanetary magnetic field (IMF) clock angle θ=arctan (BY/BZ), IMF magnitude, and solar wind dynamic pressure. We find that the mass and energy transfer at the magnetopause are different both in spatial characteristics and in response to changes in the solar wind parameters. The energy transfer follows best the sin2 (θ/2) dependence, although there is more energy transfer after large energy input, and the reconnection line follows the IMF rotation with a delay. There is no clear clock angle dependence in the net mass transfer through the magnetopause, but the mass transfer through the dayside magnetopause and towards the closed field occurs preferably for northward IMF. The energy transfer occurs through areas at the magnetopause that are perpendicular to the subsolar reconnection line. In contrast, the mass transfer occurs consistently along the reconnection line, both through the magnetopause and towards the closed field. Both the energy and mass transfer are enhanced in response to increased solar wind dynamic pressure, while increasing the IMF magnitude does not affect the transfer quantities as much.

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Ionospheric and geomagnetic responses to changes in IMF BZ: a superposed epoch study

Annales Geophysicae ◽

10.1007/s00585-997-0217-9 ◽

1997 ◽

Vol 15 (2) ◽

pp. 217-230 ◽

Cited By ~ 7

Author(s):

C. J. Davis ◽

M. N. Wild ◽

M. Lockwood ◽

Y. K. Tulunay

Keyword(s):

Magnetic Field ◽

Solar Wind ◽

Dynamic Pressure ◽

Wind Pressure ◽

Solar Wind Dynamic Pressure ◽

High Latitudes ◽

Winter Solstice ◽

Ionospheric Response ◽

Dst Index ◽

The Imf

Abstract. Superposed epoch studies have been carried out in order to determine the ionospheric response at mid-latitudes to southward turnings of the interplanetary magnetic field (IMF). This is compared with the geomagnetic response, as seen in the indices Kp, AE and Dst. The solar wind, IMF and geomagnetic data used were hourly averages from the years 1967–1989 and thus cover a full 22-year cycle in the solar magnetic field. These data were divided into subsets, determined by the magnitudes of the southward turnings and the concomitant increase in solar wind pressure. The superposed epoch studies were carried out using the time of the southward turning as time zero. The response of the mid-latitude ionosphere is studied by looking at the F-layer critical frequencies, foF2, from hourly soundings by the Slough ionosonde and their deviation from the monthly median values, δfoF2. For the southward turnings with a change in Bz of δBz > 11.5 nT accompanied by a solar wind dynamic pressure P exceeding 5 nPa, the F region critical frequency, foF2, shows a marked decrease, reaching a minimum value about 20 h after the southward turning. This recovers to pre-event values over the subsequent 24 h, on average. The Dst index shows the classic storm-time decrease to about –60 nT. Four days later, the index has still to fully recover and is at about –25 nT. Both the Kp and AE indices show rises before the southward turnings, when the IMF is strongly northward but the solar wind dynamic pressure is enhanced. The average AE index does register a clear isolated pulse (averaging 650 nT for 2 h, compared with a background peak level of near 450 nT at these times) showing enhanced energy deposition at high latitudes in substorms but, like Kp, remains somewhat enhanced for several days, even after the average IMF has returned to zero after 1 day. This AE background decays away over several days as the Dst index recovers, indicating that there is some contamination of the currents observed at the AE stations by the continuing enhanced equatorial ring current. For data averaged over all seasons, the critical frequencies are depressed at Slough by 1.3 MHz, which is close to the lower decile of the overall distribution of δfoF2 values. Taking 30-day periods around summer and winter solstice, the largest depression is 1.6 and 1.2 MHz, respectively. This seasonal dependence is confirmed by a similar study for a Southern Hemisphere station, Argentine Island, giving peak depressions of 1.8 MHz and 0.5 MHz for summer and winter. For the subset of turnings where δBz > 11.5 nT and P ≤ 5 nPa, the response of the geomagnetic indices is similar but smaller, while the change in δfoF2 has all but disappeared. This confirms that the energy deposited at high latitudes, which leads to the geomagnetic and ionospheric disturbances following a southward turning of the IMF, increases with the energy density (dynamic pressure) of the solar wind flow. The magnitude of all responses are shown to depend on δBz. At Slough, the peak depression always occurs when Slough rotates into the noon sector. The largest ionospheric response is for southward turnings seen between 15–21 UT.

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The responses of the earth’s magnetopause and bow shock to the IMF Bz and the solar wind dynamic pressure: a parametric study using the AMR-CESE-MHD model

Journal of Space Weather and Space Climate ◽

10.1051/swsc/2018030 ◽

2018 ◽

Vol 8 ◽

pp. A41 ◽

Cited By ~ 4

Author(s):

Juan Wang ◽

Zhifang Guo ◽

Yasong S. Ge ◽

Aimin Du ◽

Can Huang ◽

...

Keyword(s):

Solar Wind ◽

Mach Number ◽

Dynamic Pressure ◽

Bow Shock ◽

Solar Wind Dynamic Pressure ◽

The Earth ◽

Shock Location ◽

Mhd Model ◽

Upstream Solar Wind ◽

The Imf

We have used the AMR-CESE-MHD model to investigate the influences of the IMF Bz and the upstream solar wind dynamic pressure (Dp) on Earth’s magnetopause and bow shock. Our results present that the earthward displacement of the magnetopause increases with the intensity of the IMF Bz. The increase of the northward IMF Bz also brings the magnetopause closer to the Earth even though with a small distance. Our simulation results show that the subsolar bow shock during the southward IMF is much closer to the Earth than during the northward IMF. As the intensity of IMF Bz increases (also the total field strength), the subsolar bow shock moves sunward as the solar wind magnetosonic Mach number decreases. The sunward movement of the subsolar bow shock during southward IMF are much smaller than that during northward IMF, which indicates that the decrease of solar wind magnetosonic Mach number hardly changes the subsolar bow shock location during southward IMF. Our simulations also show that the effects of upstream solar wind dynamic pressure (Dp) changes on both the subsolar magnetopause and bow shock locations are much more significant than those due to the IMF changes, which is consistent with previous studies. However, in our simulations the earthward displacement of the subsolar magnetopause during high solar wind Dp is greater than that predicted by the empirical models.

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A modelling approach to infer the solar wind dynamic pressure from magnetic field observations inside Mercury’s magnetosphere

Astronomy and Astrophysics ◽

10.1051/0004-6361/201832764 ◽

2018 ◽

Vol 614 ◽

pp. A132 ◽

Cited By ~ 7

Author(s):

S. Fatemi ◽

N. Poirier ◽

M. Holmström ◽

J. Lindkvist ◽

M. Wieser ◽

...

Keyword(s):

Magnetic Field ◽

Solar Wind ◽

Interplanetary Magnetic Field ◽

Dynamic Pressure ◽

Solar Wind Plasma ◽

Solar Wind Dynamic Pressure ◽

Field Observations ◽

Simulation Results ◽

Upstream Solar Wind ◽

Good Agreement

Aims. The lack of an upstream solar wind plasma monitor when a spacecraft is inside the highly dynamic magnetosphere of Mercury limits interpretations of observed magnetospheric phenomena and their correlations with upstream solar wind variations. Methods. We used AMITIS, a three-dimensional GPU-based hybrid model of plasma (particle ions and fluid electrons) to infer the solar wind dynamic pressure and Alfvén Mach number upstream of Mercury by comparing our simulation results with MESSENGER magnetic field observations inside the magnetosphere of Mercury. We selected a few orbits of MESSENGER that have been analysed and compared with hybrid simulations before. Then we ran a number of simulations for each orbit (~30–50 runs) and examined the effects of the upstream solar wind plasma variations on the magnetic fields observed along the trajectory of MESSENGER to find the best agreement between our simulations and observations. Results. We show that, on average, the solar wind dynamic pressure for the selected orbits is slightly lower than the typical estimated dynamic pressure near the orbit of Mercury. However, we show that there is a good agreement between our hybrid simulation results and MESSENGER observations for our estimated solar wind parameters. We also compare the solar wind dynamic pressure inferred from our model with those predicted previously by the WSA-ENLIL model upstream of Mercury, and discuss the agreements and disagreements between the two model predictions. We show that the magnetosphere of Mercury is highly dynamic and controlled by the solar wind plasma and interplanetary magnetic field. In addition, in agreement with previous observations, our simulations show that there are quasi-trapped particles and a partial ring current-like structure in the nightside magnetosphere of Mercury, more evident during a northward interplanetary magnetic field (IMF). We also use our simulations to examine the correlation between the solar wind dynamic pressure and stand-off distance of the magnetopause and compare it with MESSENGER observations. We show that our model results are in good agreement with the response of the magnetopause to the solar wind dynamic pressure, even during extreme solar events. We also show that our model can be used as a virtual solar wind monitor near the orbit of Mercury and this has important implications for interpretation of observations by MESSENGER and the future ESA/JAXA mission to Mercury, BepiColombo.

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