Journal
ASTROPHYSICAL JOURNAL SUPPLEMENT SERIES
Volume 246, Issue 2, Pages -Publisher
IOP Publishing Ltd
DOI: 10.3847/1538-4365/ab60a3
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Funding
- STFC Ernest Rutherford Fellowship [ST/N003748/2]
- Leverhulme Trust Visiting Professorship program
- STFC [ST/P000622/1]
- NASA [NNN06AA01C, NNX17AI18G, 80NSSC19K0829]
- NASA ECIP grant [80NSSC19K0912]
- STFC [ST/P000622/1, ST/N003748/2] Funding Source: UKRI
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The first two orbits of the Parker Solar Probe spacecraft have enabled the first in situ measurements of the solar wind down to a heliocentric distance of 0.17 au (or 36 R-circle dot). Here, we present an analysis of this data to study solar wind turbulence at 0.17 au and its evolution out to 1 au. While many features remain similar, key differences at 0.17 au include increased turbulence energy levels by more than an order of magnitude, a magnetic field spectral index of -3/2 matching that of the velocity and both Elsasser fields, a lower magnetic compressibility consistent with a smaller slow-mode kinetic energy fraction, and a much smaller outer scale that has had time for substantial nonlinear processing. There is also an overall increase in the dominance of outward-propagating Alfvenic fluctuations compared to inward-propagating ones, and the radial variation of the inward component is consistent with its generation by reflection from the large-scale gradient in Alfven speed. The energy flux in this turbulence at 0.17 au was found to be similar to 10% of that in the bulk solar wind kinetic energy, becoming similar to 40% when extrapolated to the Alfven point, and both the fraction and rate of increase of this flux toward the Sun are consistent with turbulence-driven models in which the solar wind is powered by this flux.
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