Alfven Waves in the Solar Corona and Solar Wind: An Updated Energy Budget

The Sun's upper atmosphere is heated to temperatures greater than 1 million K, and solar plasma flows out into the heliosphere at supersonic speeds. There are many different proposed explanations for how the solar corona is heated and how the solar wind is accelerated, and we still do not have observations that allow us to distinguish conclusively between those rival theories. However, we are continuing to collect data on magnetohydrodynamic (MHD) waves and turbulence, which appear to exist nearly everywhere above the solar surface, and which are relevant to constrain a broad class of models that rely on damping these fluctuations to produce heat. This presentation will review recent improvements in our observational database of Alfvenic (i.e., transverse and incompressible) MHD fluctuations. First, new constraints on wave amplitudes in polar coronal holes, at heliocentric distances between 1.5 and 4 solar radii, will be presented from a new analysis of Ultraviolet Coronagraph Spectrometer (UVCS) Lyman alpha data. Second, in-situ measurements from the first two perihelia of Parker Solar Probe (PSP) — at heliocentric distances between 35 and 215 solar radii — will also be analyzed. Incorporating multiple sources of data provides a better global picture of how waves from the Sun propagate, dissipate, and heat the plasma. If I am feeling lucky, I may also make predictions about the properties of the MHD fluctuations to be seen during future perihelia of PSP (i.e., from 35 down to 9 solar radii).