Abstract We study anisotropic magnetohydrodynamic (MHD) turbulence in the slow solar wind measured by Parker Solar Probe (PSP) and Solar Orbiter (SolO) during its first orbit from the perspective of variance anisotropy and correlation anisotropy. We use the Belcher & Davis approach (M1) and a new method (M2) that decomposes a fluctuating vector into parallel and perpendicular fluctuating vectors. M1 and M2 calculate the transverse and parallel turbulence components relative to the mean magnetic field direction. The parallel turbulence component is regarded as compressible turbulence, and the transverse turbulence component as incompressible turbulence, which can be either Alfvénic or 2D. The transverse turbulence energy is calculated from M1 and M2, and the transverse correlation length from M2. We obtain the 2D and slab turbulence energy and the corresponding correlation lengths from those transverse turbulence components that satisfy an angle between the mean solar wind flow speed and mean magnetic field θ UB of either (i) 65° < θ UB < 115° or (ii) 0° < θ UB < 25° (155° < θ UB < 180°), respectively. We find that the 2D turbulence component is not typically observed by PSP near perihelion, but the 2D component dominates turbulence in the inner heliosphere. We compare the detailed theoretical results of a nearly incompressible MHD turbulence transport model with the observed results of PSP and SolO measurements, finding good agreement between them.
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An Empirically Driven MHD Model to Predict the Solar Wind at Parker Solar Probe and Solar Orbiter during the Current Solar Minimum
Since the launch on 2018 August 12, the Parker Solar Probe (PSP) has completed its first five orbits around the Sun, having reached down to ~28 solar radii at perihelion 5 on 2020 June 7. More recently, the Solar Orbiter (SolO) made its first close approach to the Sun at 0.52 AU on 2020 June 15, nearly 4 months after the launch. Using a 3D heliospheric MHD model coupled with the Wang-Sheeley-Arge (WSA) coronal model using the Air Force Data Assimilative Photospheric flux Transport (ADAPT) magnetic maps as input, we simulate the time-varying inner heliosphere, including the trajectories of PSP and SolO, during the current solar minimum period between 2018 and 2020. Above the ADAPT-WSA model outer boundary at 21.5 solar radii, we solve the Reynolds averaged MHD equations with turbulence and pickup ions taken into account and compare the simulation results with the PSP solar wind and magnetic field data, with particular emphasis on the large-scale solar wind structure and magnetic connectivity during each solar encounter.
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- Award ID(s):
- 2028154
- NSF-PAR ID:
- 10275901
- Date Published:
- Journal Name:
- American Geophysical Union, Fall Meeting 2020, abstract #SH021-08
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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