Modeling of Joint Parker Solar Probe–Metis/Solar Orbiter Observations

We present the first theoretical modeling of joint Parker Solar Probe (PSP)–Metis/Solar Orbiter (SolO) quadrature observations. The combined observations describe the evolution of a slow solar wind plasma parcel from the extended solar corona (3.5–6.3 R⊙) to the very inner heliosphere (23.2 R⊙). The Metis/SolO instrument remotely measures the solar wind speed finding a range from 96 to 201 km s−1, and PSP measures the solar wind plasma in situ, observing a radial speed of 219.34 km s−1. We find theoretically and observationally that the solar wind speed accelerates rapidly within 3.3–4 R⊙ and then increases more gradually with distance. Similarly, we find that the theoretical solar wind density is consistent with the remotely and in-situ observed solar wind density. The normalized cross helicity and normalized residual energy observed by PSP are 0.96 and −0.07, respectively, indicating that the slow solar wind is very Alfvénic. The theoretical NI/slab results are very similar to PSP measurements, which is a consequence of the highly magnetic field-aligned radial flow ensuring that PSP can measure slab fluctuations and not 2D ones. Finally, we calculate the theoretical 2D and slab turbulence pressure, finding that the theoretical slab pressure is very similar to that observed by PSP.