TY - JOUR

T1 - Annual variations in the Martian bow shock location as observed by the Mars Express mission

AU - Hall, Benjamin Edward Stanley

AU - Lester, Mark

AU - Sánchez-Cano, Beatriz

AU - Nichols, Jonathan

AU - Andrews, David

AU - Edberg, Niklas

AU - Opgenoorth, Hermann

AU - Fraenz, Markus

AU - Holmstrom, Mats

AU - Ramstad, Robin

AU - Witasse, Olivier

AU - Cartacci, Marco

AU - Cicchetti, A

AU - Noschese, R

AU - Orosei, R

PY - 2016/11

Y1 - 2016/11

N2 - The Martian bow shock distance has previously been shown to be anticorrelated with solar wind dynamic pressure but correlated with solar extreme ultraviolet (EUV) irradiance. Since both of these solar parameters reduce with the square of the distance from the Sun, and Mars' orbit about the Sun increases by ∼0.3 AU from perihelion to aphelion, it is not clear how the bow shock location will respond to variations in these solar parameters, if at all, throughout its orbit. In order to characterize such a response, we use more than 5 Martian years of Mars Express Analyser of Space Plasma and EneRgetic Atoms (ASPERA-3) Electron Spectrometer measurements to automatically identify 11,861 bow shock crossings. We have discovered that the bow shock distance as a function of solar longitude has a minimum of 2.39RM around aphelion and proceeds to a maximum of 2.65RM around perihelion, presenting an overall variation of ∼11% throughout the Martian orbit. We have verified previous findings that the bow shock in southern hemisphere is on average located farther away from Mars than in the northern hemisphere. However, this hemispherical asymmetry is small (total distance variation of ∼2.4%), and the same annual variations occur irrespective of the hemisphere. We have identified that the bow shock location is more sensitive to variations in the solar EUV irradiance than to solar wind dynamic pressure variations. We have proposed possible interaction mechanisms between the solar EUV flux and Martian plasma environment that could explain this annual variation in bow shock location.

AB - The Martian bow shock distance has previously been shown to be anticorrelated with solar wind dynamic pressure but correlated with solar extreme ultraviolet (EUV) irradiance. Since both of these solar parameters reduce with the square of the distance from the Sun, and Mars' orbit about the Sun increases by ∼0.3 AU from perihelion to aphelion, it is not clear how the bow shock location will respond to variations in these solar parameters, if at all, throughout its orbit. In order to characterize such a response, we use more than 5 Martian years of Mars Express Analyser of Space Plasma and EneRgetic Atoms (ASPERA-3) Electron Spectrometer measurements to automatically identify 11,861 bow shock crossings. We have discovered that the bow shock distance as a function of solar longitude has a minimum of 2.39RM around aphelion and proceeds to a maximum of 2.65RM around perihelion, presenting an overall variation of ∼11% throughout the Martian orbit. We have verified previous findings that the bow shock in southern hemisphere is on average located farther away from Mars than in the northern hemisphere. However, this hemispherical asymmetry is small (total distance variation of ∼2.4%), and the same annual variations occur irrespective of the hemisphere. We have identified that the bow shock location is more sensitive to variations in the solar EUV irradiance than to solar wind dynamic pressure variations. We have proposed possible interaction mechanisms between the solar EUV flux and Martian plasma environment that could explain this annual variation in bow shock location.

KW - Mars

KW - Bow Shock

KW - Ionosphere

KW - solar wind planetary interactions

KW - Seasonal variation

KW - Annual variation

KW - Mars Express

U2 - 10.1002/2016JA023316

DO - 10.1002/2016JA023316

M3 - Journal article

VL - 121

SP - 11,474–11,494

JO - Journal of Geophysical Research: Space Physics

JF - Journal of Geophysical Research: Space Physics

SN - 2169-9380

IS - 11

ER -