Alfvén Profile in the Lower Corona: Implications for Shock Formation

Observations of type II radio bursts and energetic electron events indicate that shocks can form at 1-3 solar radii and are responsible for the GeV nucleon−1 energies observed in ground level solar energetic particle (SEP) events. Here we provide the first study of the lower corona produced from 10 state-of-the-art models. In particular, we look to the Alfvén speed profiles as the criterion for shock formation, independent of exciting agent (e.g., flares and CMEs). Global magnetohydrodynamic models produce Alfvén speed profiles that are in conflict with observations: (1) multiple SEP events are observed with a single exciting agent, but most profiles are missing the "hump" required to form multiple shocks; and (2) few slow CMEs cause large SEP events, but most profiles drop very quickly, allowing all slow CMEs to drive strong shocks to form between 1 and 3 R☉. Simplified Alfvén wave-driven wind models have steeper profiles, but are still in disagreement with multiple shock formation. Only studies that include Alfvén waves with physically based damping are in agreement with observations. This implies the results of these one-dimensional local studies must be included in global models before we can study shock formation in the lower corona.