SH013-01
Evaluating Electrostatic Analyser measurements of 3D Solar Wind Velocity Distributions: The SIRTH Method
Evaluating Electrostatic Analyser measurements of 3D Solar Wind Velocity Distributions: The SIRTH Method
Tuesday, 8 December 2020: 07:00
Virtual
Abstract:
The solar wind is often characterised by few key parameters, such as density, velocity, and temperature. These parameters only describe the underlying 3D velocity distribution well for a Maxwellian distribution. Since the solar wind often deviates from a Maxwellian, it is desirable to characterise distributions in more detail.
We analyse data from Helios E1 instrument 1a, an electrostatic analyser that separates ions with respect to their E/q ratio. A typical problem with instrument 1a data is the overlap of protons and alphas in the proton velocity frame.
The magnetic field represents a prominent direction for the gyromotion of ions, but typically does not align with the instrumental frame of reference. We therefore rotate the experimental data accordingly before we translate the coordinate system into the proton maximum.
We further refine our coordinate system such that the magnetic field axis, alphas and protons lie in one coordinate plane. The assumption of gyrotropy is then sufficient to separate protons and alphas in most cases. Density and temperature changes along the magnetic field direction can now be derived without contamination by alphas and protons, respectively.
We call it Subgrid, Interpolation, Rotation, Translation and Histogramming (SIRTH) method, closely following the individual implementation steps. We present first results for proton plasma properties in 40s time resolution.
The concept of this method can also be applied to other electrostatic analysers like 3DP-PESA on Wind, SWEAP-SPAN on Parker Solar Probe and SWA-PAS on Solar Orbiter.
We analyse data from Helios E1 instrument 1a, an electrostatic analyser that separates ions with respect to their E/q ratio. A typical problem with instrument 1a data is the overlap of protons and alphas in the proton velocity frame.
The magnetic field represents a prominent direction for the gyromotion of ions, but typically does not align with the instrumental frame of reference. We therefore rotate the experimental data accordingly before we translate the coordinate system into the proton maximum.
We further refine our coordinate system such that the magnetic field axis, alphas and protons lie in one coordinate plane. The assumption of gyrotropy is then sufficient to separate protons and alphas in most cases. Density and temperature changes along the magnetic field direction can now be derived without contamination by alphas and protons, respectively.
We call it Subgrid, Interpolation, Rotation, Translation and Histogramming (SIRTH) method, closely following the individual implementation steps. We present first results for proton plasma properties in 40s time resolution.
The concept of this method can also be applied to other electrostatic analysers like 3DP-PESA on Wind, SWEAP-SPAN on Parker Solar Probe and SWA-PAS on Solar Orbiter.