Interplanetary magnetic field properties and variability near Mercury's orbit

James, M. K.; Imber, Suzanne M.; Bunce, E. J.; Yeoman, T. K.; Lockwood, Mike; Owens, M. J.; Slavin, J. A.

doi:10.1002/2017ja024435

Cited by 45 publications

(63 citation statements)

References 86 publications

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“…This is more apparent in Figure a, which shows that the largest number of FTEs are seen at a magnetic local time of 10 h, with 288 FTEs observed between 9 and 11 h MLT compared to 238 between 13 and 15 h MLT. This asymmetry may be due to the unusual conditions observed in the IMF during the period examined (James et al, ; Lockwood et al, ), whereby in the majority of passes IMF B X is positive, leading to a similar bias toward − B Y due to the Parker spiral (Parker, ). This in turn leads to increased probability of near‐antiparallel fields in the prenoon sector of the portion of the magnetosphere sampled by MESSENGER.…”

Section: Discussionmentioning

confidence: 97%

The Influence of IMF Clock Angle on Dayside Flux Transfer Events at Mercury

Leyser

Imber

Milan

et al. 2017

Geophysical Research Letters

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Analysis of MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) data has shown for the first time that the orientation of the interplanetary magnetic field (IMF) in the magnetosheath of Mercury plays a crucial role in the formation of flux transfer events (FTEs) at the dayside magnetopause. During the first 4 Hermean years of MESSENGER's orbit around Mercury, we have identified 805 FTEs using magnetometer data. Under conditions of near-southward IMF, at least one FTE was detected on nearly 70% of passes through the magnetopause but the observation rate during northward IMF was less than 20%. FTEs were also observed preferentially in the prenoon sector. FTEs have been observed at Earth at all locations on the magnetopause under a wide range of solar wind conditions by single spacecraft such as

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Section: Discussionmentioning

confidence: 97%

The Influence of IMF Clock Angle on Dayside Flux Transfer Events at Mercury

Leyser

Imber

Milan

et al. 2017

Geophysical Research Letters

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“…With eccentricity ϵ ≈0.2, Mercury's distance from the Sun varies from ∼0.31 AU at perihelion to ∼0.46 AU at aphelion, where 1 AU (astronomical unit) is the distance of the Earth from the Sun. As a consequence, solar wind plasma and IMF conditions change considerably during one revolution of Mercury around the Sun (Sarantos et al, ; Korth et al, ; James et al, ). In this study, we have chosen our solar wind plasma and IMF configurations within the range of the observed values near Mercury.…”

Section: Modelmentioning

confidence: 99%

“…In this study, we have chosen our solar wind plasma and IMF configurations within the range of the observed values near Mercury. For runs T1 to T6, we set the solar wind parameters close to the median of the most probable values observed at Mercury's perihelion and aphelion, explained by Sarantos et al (), Korth et al (), and James et al (). For these runs, we set the IMF magnitude | B | = 18 nT, solar wind density n sw = 30 cm −3 , solar wind speed | v sw | = 370 km/s, and solar wind ion and electron temperatures T =12 eV.…”

Section: Modelmentioning

confidence: 99%

“…Although some of these studies were conducted prior to the MESSENGER observation of the northward offset in Mercury's magnetic dipole, some models, even without including a dipole offset, predicted a noticeable north‐south asymmetry in the solar wind precipitation to the dayside surface of Mercury (e.g., Benna et al, ; Burger et al, ; Kallio & Janhunen, ; Sarantos et al, ). Several of these models suggested that this asymmetry arises when the radial component of the IMF ( B x ) is dominant (e.g., Massetti et al, ; Sarantos et al, ; Varela et al, ), which is a typical feature of the Parker spiral near Mercury's orbit (James et al, ; Korth et al, ; Sarantos et al, ). After the discovery of Mercury's dipole offset, it was suggested that the north‐south asymmetry in the solar wind plasma precipitation to high latitudes could be an effect of the magnetic dipole offset (e.g., Winslow et al, ).…”

Section: Introductionmentioning

confidence: 99%

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Hybrid Simulations of Solar Wind Proton Precipitation to the Surface of Mercury

2020

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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 using a hybrid-kinetic model. We use our model to explain observations of Mercury's neutral sodium exosphere and compare our results with MESSENGER observations. For the typical solar wind dynamic pressure at Mercury our model shows a high proton flux precipitates through the magnetospheric cusps to the high latitudes on both hemispheres on the dayside, centered near the noon meridian with ∼11 • latitudinal extent in the north and ∼21 • latitudinal extent in the south, which is consistent with MESSENGER observations. We show that this two-peak pattern is controlled by the radial component (B x ) of the IMF and not the B z . Our model 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 cusps. We found that the total precipitation 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), 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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“…Therefore, to understand the structure of Mercury's magnetosphere and its response to the solar wind plasma and IMF variations, we need to understand the interaction between the solar wind and Mercury's magnetosphere and distinguish between the contributions from external and internal magnetic sources (e.g. Raines et al 2015;Johnson & Hauck 2016;James et al 2017).…”

Section: <3mentioning

confidence: 99%

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

Fatemi

Poirier

Holmström

et al. 2018

A&A

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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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Interplanetary magnetic field properties and variability near Mercury's orbit

Cited by 45 publications

References 86 publications

The Influence of IMF Clock Angle on Dayside Flux Transfer Events at Mercury

The Influence of IMF Clock Angle on Dayside Flux Transfer Events at Mercury

Hybrid Simulations of Solar Wind Proton Precipitation to the Surface of Mercury

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

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