An Efficient, Time-Dependent High Speed Stream Model and Application to Solar Wind Forecasts

Predicting space weather effects of the solar wind requires knowing the location and properties of any embedded high speed streams (HSSs) or stream interactions regions that form as the fast solar wind catches up to slow preceding wind. Additionally, this information is critical for understanding how a coronal mass ejection (CME) interacts with the solar wind during its propagation. We present the Mostly Empirical Operation Wind with a High Speed Stream (MEOW-HiSS) model, which runs nearly instantaneously. This model is derived from MHD simulations of an idealized HSS emanating from a circular coronal hole (CH). We split the MHD HSS radial profiles into small regions well-described by simple functions (e.g. flat, linear, exponential, sinusoidal) that can be constrained using the MHD values. We then determine how the region boundaries and the constraining values change with CH area and the distance of the HSS front. MEOW-HiSS requires the CH area and front distance and produces the corresponding radial profile with an error less than 10\% for most parameters. MEOW-HiSS produces profiles at subsequent times with almost no loss in accuracy. We also compare MEOW-HiSS results to four HSS observed in situ at 1 au. We present a method for determining MEOW-HiSS inputs from EUV images and use these values to hindcast the observed cases. We find average accuracies of 2.8 cm^-3 in the number density, 56.7 km/s in the radial velocity, 2.2 nT in the absolute radial magnetic field, 1.6 nT in the absolute longitudinal magnetic field, and 7x10^4 K in the temperature.