分类： 天文学 >> 天文学 提交时间： 2023-02-19
Trevor A. Bowen
Benjmin D. G. Chandran
Jonathan Squire
Stuart D. Bale
Die Duan
Kristopher G. Klein
Davin Larson
Alfred Mallet
Michael D. McManus
Romain Meyrand
Jaye L. Verniero
Lloyd D. Woodham
摘要： The dissipation of magnetized turbulence is an important paradigm for describing heating and energy transfer in astrophysical environments such as the solar corona and wind; however, the specific collisionless processes behind dissipation and heating remain relatively unconstrained by measurements. Remote sensing observations have suggested the presence of strong temperature anisotropy in the solar corona consistent with cyclotron resonant heating. In the solar wind, in situ magnetic field measurements reveal the presence of cyclotron waves, while measured ion velocity distribution functions have hinted at the active presence of cyclotron resonance. Here, we present Parker Solar Probe observations that connect the presence of ion-cyclotron waves directly to signatures of resonant damping in observed proton-velocity distributions. We show that the observed cyclotron wave population coincides with both flattening in the phase space distribution predicted by resonant quasilinear diffusion and steepening in the turbulent spectra at the ion-cyclotron resonant scale. In measured velocity distribution functions where cyclotron resonant flattening is weaker, the distributions are nearly uniformly subject to ion-cyclotron wave damping rather than emission, indicating that the distributions can damp the observed wave population. These results are consistent with active cyclotron heating in the solar wind.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Jia Huang
J. C. Kasper
L. A. Fisk
Davin E. Larson
Michael D. McManus
C. H. K. Chen
Mihailo M. Martinović
K. G. Klein
Luke Thomas
Mingzhe Liu
Bennett A. Maruca
Lingling Zhao
Yu Chen
Qiang Hu
Lan K. Jian
J. L. Verniero
Marco Velli
Roberto Livi
P. Whittlesey
Ali Rahmati
摘要： Switchbacks are rapid magnetic field reversals that last from seconds to hours. Current Parker Solar Probe (PSP) observations pose many open questions in regards to the nature of switchbacks. For example, are they stable as they propagate through the inner heliosphere, and how are they formed? In this work, we aim to investigate the structure and origin of switchbacks. In order to study the stability of switchbacks, we suppose the small scale current sheets therein may work to braid and stabilize the switchbacks. Thus, we use the partial variance of increments method to identify the small scale current sheets, and then compare their distributions in switchbacks. With more than one thousand switchbacks identified with PSP observations in seven encounters, we find many more current sheets inside than outside switchbacks, indicating that these micro-structures should work to stabilize the S-shape structures of switchbacks. Additionally, with the helium measurements, we study the variations of helium abundance ratios and alpha-proton differential speeds to trace switchbacks to their origins. We find both helium-rich and helium-poor populations in switchbacks, implying the switchbacks could originate from both closed and open magnetic field regions in the Sun. Moreover, we observe that the alpha-proton differential speeds also show complex variations as compared to the local Alfv\'en speed. The joint distributions of both parameters show that low helium abundance together with low differential speed is the dominant state in switchbacks. The presence of small scale current sheets in switchbacks along with the helium features are in line with the hypothesis that switchbacks could originate from the Sun via interchange reconnection process. However, other formation mechanisms are not excluded.
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