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1. An Empirically Driven MHD Model to Predict the Solar Wind at Parker Solar Probe and Solar Orbiter during the Current Solar Minimum

   Kim, T. K. ; Pogorelov, N. ; Arge, C. N. ; Jones-Mecholsky, S. I. ( December 2020 , American Geophysical Union, Fall Meeting 2020, abstract #SH021-08)

   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.
2. Solar Toroidal Field Evolution Spanning Four Sunspot Cycles Seen by the Wilcox Solar Observatory, the Solar and Heliospheric Observatory/Michelson Doppler Imager, and the Solar Dynamics Observatory/Helioseismic and Magnetic Imager

   https://doi.org/10.3847/2041-8213/ac52ae  

   Liu, Allison L. ; Scherrer, Philip H. ( February 2022 , The Astrophysical Journal Letters)

   Abstract Forty-four years of Wilcox Solar Observatory, 14 years of Michelson Doppler Imager on the Solar and Heliospheric Observatory, and 11 years of Helioseismic and Magnetic Imager on the Solar Dynamics Observatory magnetic field data have been studied to determine the east–west inclination—the toroidal component—of the magnetic field. Maps of the zonal averaged inclination show that each toroidal field cycle begins at around the same time at high latitudes in the northern and southern hemispheres, and ends at the equator. Observation of these maps also shows that each instance of a dominant toroidal field direction starts at high latitudes near sunspot maximum and is still visible near the equator well past the minimum of its cycle, indicating that the toroidal field cycle spans approximately two sunspot cycles. The length of the extended activity cycle is measured to be approximately 16.8 yr.
3. Evolution of Solar Wind Turbulence from 0.1 to 1 au during the First Parker Solar Probe–Solar Orbiter Radial Alignment

   https://doi.org/10.3847/2041-8213/abf7d1  

   Telloni, Daniele ; Sorriso-Valvo, Luca ; Woodham, Lloyd D. ; Panasenco, Olga ; Velli, Marco ; Carbone, Francesco ; Zank, Gary P. ; Bruno, Roberto ; Perrone, Denise ; Nakanotani, Masaru ; et al ( May 2021 , The Astrophysical Journal Letters)
4. A Solar Coronal Hole and Fast Solar Wind Turbulence Model and First-orbit Parker Solar Probe (PSP) Observations

   https://doi.org/10.3847/1538-4357/abb132  

   Adhikari, L. ; Zank, G. P. ; Zhao, L.-L. ( October 2020 , The Astrophysical Journal)
5. Identifying the Coronal Source Regions of Solar Wind Streams from Total Solar Eclipse Observations and in situ Measurements Extending over a Solar Cycle

   Habbal, S. R. ; Druckmuller, M. ( April 2021 , The astrophysical journal)

   This Letter capitalizes on a unique set of total solar eclipse observations, acquired between 2006 and 2020, in white light, \ion[Fe xi] 789.2 nm (\Tfexi\ = $1.2 \pm 0.1$ MK) and \ion[Fe xiv] 530.3 nm (\Tfexiv\ = $ 1.8 \pm 0.1$ MK) emission. They are complemented by \insitu\ Fe charge state and proton speed measurements from ACE/SWEPAM-SWICS, to identify the source regions of different solar wind streams. The eclipse observations reveal the ubiquitous presence of open structures throughout the corona, invariably associated with \ion[Fe xi] emission from $\rm Fe^{10+}$, thus revealing a constant electron temperature, \Tc\ = \Tfexi\, in the expanding corona. The \insitu\ Fe charge states are found to cluster around $\rm Fe^{10+}$, independently of the 300 to 700 km $\rm s^{-1}$ stream speeds, referred to as the continual solar wind. $\rm Fe^{10+}$ thus yields the fiducial link between the continual solar wind and its \Tfexi\ sources at the Sun. While the spatial distribution of \ion[Fe xiv] emission, from $\rm Fe^{13+}$, associated with streamers, changes throughout the solar cycle, the sporadic appearance of charge states $> \rm Fe^{11+}$, \insitu, exhibits no cycle dependence regardless of speed. These latter streams are conjectured to be released from hot coronal plasmas atmore »temperatures $\ge \rm $ \Tfexiv\ within the bulge of streamers and from active regions, driven by the dynamic behavior of prominences magnetically linked to them. The discovery of continual streams of slow, intermediate and fast solar wind, characterized by the same \Tfexi\ in the expanding corona, places new constraints on the physical processes shaping the solar wind.« less