An event‐based approach to validating solar wind speed predictions: High‐speed enhancements in the Wang‐Sheeley‐Arge model

Abstract

[1] One of the primary goals of the Center for Integrated Space Weather Modeling (CISM) effort is to assess and improve prediction of the solar wind conditions in nearEarth space, arising from both quasi-steady and transient structures. We compare 8 years of L1 in situ observations to predictions of the solar wind speed made by the WangSheeley-Arge (WSA) empirical model. The mean-square error (MSE) between the observed and model predictions is used to reach a number of useful conclusions: there is no systematic lag in the WSA predictions, the MSE is found to be highest at solar minimum and lowest during the rise to solar maximum, and the optimal lead time for 1 AU solar wind speed predictions is found to be 3 days. However, MSE is shown to frequently be an inadequate ''figure of merit'' for assessing solar wind speed predictions. A complementary, event-based analysis technique is developed in which high-speed enhancements (HSEs) are systematically selected and associated from observed and model time series. WSA model is validated using comparisons of the number of hit, missed, and false HSEs, along with the timing and speed magnitude errors between the forecasted and observed events. Morphological differences between the different HSE populations are investigated to aid interpretation of the results and improvements to the model. Finally, by defining discrete events in the time series, model predictions from above and below the ecliptic plane can be used to estimate an uncertainty in the predicted HSE arrival times.

Space Weather Quarterly Volume 5, Issue 3, 2008

“…Figures 1b and 1c show that the modeled background solar wind plasma and field parameters (before the arrival of the disturbance, on the far left side of the plot) are the same as in Figure 1a. However, a high-speed enhancement (HSE, which is the leading edge of a high-speed stream, HSS [Owens et al, 2005]), is clearly seen to arrive in the simulation before noon of 13 May. Behind the HSE, both the simulated solar wind speed and density are raised, making the solar wind speed significantly higher than the observed speed, while the density is now in closer agreement with the observed density.…”

THREE-DIMENSIONAL SOLARWINDMODELING FROM THE SUN TO EARTH BY A SIP-CESE MHD MODEL WITH A SIX-COMPONENT GRID

“…Figures 12(c) and (d) also display the distribution of the radial velocity v r at 5 R S from the MHD model and the WSA model, the latter of which is calculated by v r = 265 + 1.5 (1+f s ) 2/7 (5.8 − 1.6e [1−(θ b /7.5) 3 ] ) 3.5 with the help of θ b and the expansion factor f s (Owens et al 2005). By examining this figure, we observe that the expansion factor of the MHD model is higher than that of the PFSS model.…”

“…Some empirical functions with various free parameters, similar to the above formula, have been employed to derive the solar wind speed near the Sun (Arge et al 2004;Owens et al 2005). Here, the constant values of Q 1 , Q 0 , and M 0 are 1.5 × 10 −9 J m −3 s −1 , 1.18 × 10 −7 J m −3 s −1 and 7.9 × 10 −14 Nm −3 , respectively.…”

A probabilistic approach to the drag-based model

“…Brueckner et al, 1998). Another approach is represented by numerical MHD-based models of the heliospheric propagation of ICME, generally requiring a detailed knowledge of the state of the heliosphere and large computational facilities (as is the case for the WSA-ENLIL model Odstrcil and Pizzo, 1999;Odstrcil et al, 2004;Owens et al, 2005;Parsons et al, 2011). The numerical models are fairly accurate (Vr snak et al, 2014), and highly sensitive to the quality of the input parameters (Falkenberg et al, 2010b), as one may expect.…”