This proposal lies within the broad area of "sun", and addresses the science area "3. Solar atmosphere." as the solar plasma flows out from the corona and transitions into the solar wind, IT…

The National Aeronautics and Space Administration (NASA) awarded a $640,439.00 grant to the University of Delaware to study the transition region of the solar wind as it flows out from the corona and into the heliosphere. The research aims to characterize the large-scale heliospheric conditions in this region, which is critical for understanding the origin of various physical processes in the solar wind. The study will combine remote sensing observations from the STEREO mission with global magnetohydrodynamic (MHD) simulations that incorporate turbulence modeling and kinetic effects. The results will help provide crucial contextual predictions for in-situ measurements by the upcoming Parker Solar Probe mission. This grant supports goals from the National Academies' Decadal Survey related to predicting variations in the space environment and discovering fundamental heliospheric processes. The University of Delaware is a private, non-profit, land-grant university that conducts a wide range of research across scientific and technical domains under federal contracts and grants.

This proposal lies within the broad area of "sun", and addresses the science area "3. Solar atmosphere." as the solar plasma flows out from the corona and transitions into the solar wind, IT transforms from a magnetically structured, subsonic, and sub-alfvenic regime into a supersonic and super-alfvenic flow dominated by hydrodynamics. Recent observational work [1] indicates that this transition may also coincide with the onset of large scale turbulence in the solar wind. Useful markers of this transition are the alfven critical surface and the first beta = 1 surface (the plasma beta is the ratio of gas to magnetic pressure, and is an important parameter that organizes the properties of heliospheric plasmas [2, 3]). In particular, when the flow speed u exceeds the alfven speed v_a , the magnetic field rigidity can no longer enforce plasma CO-rotation. And when the beta increases to unity, the plasma pressure may displace the magnetic field and more isotropic motions are possible. The region in which these two crucial conditions, u>v_a and beta ~ 1, are attained becomes in effect the region in which the corona gives up control of the plasma and the solar wind as an independent entity is born. A knowledge of the large scale heliospheric conditions in this region is of particular importance for characterizing the origin of various physical processes that occur in the solar wind. IT is also the region in which the surrounding medium exerts a torque on the solar atmosphere, and the region in which in-situ generation of turbulent correlations begins. We propose to study and characterize this transition region of the solar wind by combining two approaches - we make use of novel processed images obtained from remote sensing observational data (stereo) - and combine this with well tested global MHD simulations of the solar wind that incorporate turbulence modeling and kinetic effects. Recent observational work has provided glimpses of the length scales at which turbulence may influence the solar wind plasma as IT flows outward, defining in effect an expanding causal region of influence; once quantified, this region of influence will help organize our proposed studies. The turbulence parameters computed from the simulations also enable estimations of the characteristic scales at which in-situ turbulence may influence the dynamics of the solar wind. The parker solar probe (PSP) will soon explore this region, spanning the outer corona and the inner heliosphere, for the first time; our synergistic approach will provide crucial contextual predictions for in-situ PSP measurements. Methodology: we will use well tested MHD simulations of the solar wind that include turbulence modeling [4] to study the structure and dynamics of the young solar wind and localize the sonic, alfven, and beta = 1 surfaces, and measure the angular momentum of the wind, in a 3D model heliosphere. The effects of solar variability will be incorporated by performing simulations with varying solar source dipole tilts and turbulence levels, and by using magnetogram data from different epochs as boundary conditions. The model results will be compared with spacecraft observations processed using novel remote imaging techniques. The results will be used to predict plasma regimes along the PSP trajectory, accounting for the expected solar activity variations during different epochs of the orbit. This study addresses goals of the decadal survey under goal 1. "predict the variations of the space environment" and under goal 4. "discover and characterize fundamental processes that occur within the heliosphere".