Combining Remote and in situ Parker Solar Probe and STEREO Data to Understand Solar Wind Density Structures

The instrument suite on Parker Solar Probe offers an unprecedented viewpoint of the ambient solar wind and structure therein, shortly after its formation and release from the solar corona. We take advantage of the synergistic observations of the first Parker Solar Probe encounters and the STEREO COR2 deep field campaigns covering the same time periods to study mesoscale solar wind density structures. They often occur in a quasi-periodic train, especially near the heliospheric current sheet. Some may be a consequence of the development of dynamics en route; many are remnants of the formation and release of the solar wind, and provide important constraints on solar wind models. The opportunity to combine the different observing angles and fields of view of the white light WISPR observations and white light STEREO COR2 observations with in situ density and plasma measurements from SWEAP allows better understanding of the characteristics and properties of mesoscale density structures. The in situ data measure precise size scales, plasma boundaries, and relationships between density and other parameters. They help in the interpretation of the structures seen in white light images and in unraveling projection effects. The white light images enhance the in situ data by providing global heliospheric context, as well as the occurrence rate and 2-D size scales of structures as a function of latitude and distance from the Sun. Together, these observations provide crucial constraints on the formation of structures in the solar wind.