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. 2020 Oct 28;47(20):e2020GL090115.
doi: 10.1029/2020GL090115. Epub 2020 Oct 19.

Plasma Double Layers at the Boundary Between Venus and the Solar Wind

Affiliations

Plasma Double Layers at the Boundary Between Venus and the Solar Wind

D M Malaspina et al. Geophys Res Lett. .

Abstract

The solar wind is slowed, deflected, and heated as it encounters Venus's induced magnetosphere. The importance of kinetic plasma processes to these interactions has not been examined in detail, due to a lack of constraining observations. In this study, kinetic-scale electric field structures are identified in the Venusian magnetosheath, including plasma double layers. The double layers may be driven by currents or mixing of inhomogeneous plasmas near the edge of the magnetosheath. Estimated double-layer spatial scales are consistent with those reported at Earth. Estimated potential drops are similar to electron temperature gradients across the bow shock. Many double layers are found in few high cadence data captures, suggesting that their amplitudes are high relative to other magnetosheath plasma waves. These are the first direct observations of plasma double layers beyond near-Earth space, supporting the idea that kinetic plasma processes are active in many space plasma environments.

Keywords: Venus; bow shock; double layer; kinetic physics; magnetosheath; solar wind interaction.

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Figures

Figure 1
Figure 1
(a) |B| and B, in VSO coordinates, (b) proton density from SPC, (c) proton flow velocity in VSO from SPC, (d) electron energy flux from SPANe, (e) proton energy flux from SPANi, (f) power spectra of V1 − V2 differential voltages for 400 Hz to 75 kHz, (g) same as (f), but for 20 Hz to 9.4 kHz, and (h) PSP trajectory (black dashed line) with notional bow shock (red line) and bow shock crossing times (blue boxes). A black arrow shows the outward normal to the heat shield. The green bar shows the heat shield plane. (i) Same as (h), with black crosses indicating burst data capture times.
Figure 2
Figure 2
(a) Three components of B, in VSO coordinates, (b) ion energy flux from SPANi, (c) proton flow velocity in VSO from SPC, (d) electron energy flux from SPANe, and (e and f) electron core density and temperature from fits to SPANe data. (g–l) Same quantities, for outbound bow shock crossing. Vertical solid lines indicate start and stop times of FIELDS burst data, and vertical lines indicate plasma double‐layer observations.
Figure 3
Figure 3
(a) Time series differential voltage waveforms in the heat shield plane, in spacecraft body coordinates. The blue trace indicates spacecraft x (close to the ecliptic plane), the red trace spacecraft y (close to normal to the ecliptic). Vertical lines indicate intervals with plasma double layers. (b) Windowed Fourier transform of the data in (a).
Figure 4
Figure 4
Each pair of panels shows time domain differential voltage data along two directions in the plane of the heat shield: maximum variance (top) and perpendicular (bottom). (a) shows a double layer (gray shading) with attendant electrostatic waves. (b)–(d) show data from subintervals of (a) at times indicated by vertical red lines. (e–h), (i–l), and (m–p) have the same format as (a)–(d) but for thee other double layers. (q) Vectors, for each of the four double layers, projected into the xy VSO plane, for the magnetic field (blue), effective double‐layer velocity assuming veff||B (solid purple) and assuming veff||B (dashed purple). The heat shield plane is shown in green, and its normal vector in black. A cartoon spacecraft bus is shown in gray. (r) Geometry of an oblique double‐layer crossing, in a plane containing B (blue) and veff (green).

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