Ghee Fry
Exploration Physics International, Inc.
Wei Sun
Geophysical Institute, Univ. Alaska, Fairbanks
Model Description
Simulation of the Evolution of
the IMF During Four Event Periods
3D Shock
Propagation Movie
Kinematic Model
References
Recent papers
HAF Model Description
The Hakamada-Akasofu-Fry Version 2 (HAFv2) solar wind model is a "modified kinematic" model. "Kinematic"
in that the model kinetically projects the flow of the solar wind from inhomogeneous
sources near the sun out into interplanetary space. "Modified" in that the model
adjusts the flow for stream-stream interactions as faster streams overtake slower ones.
Whereas the MHD solutions integrate the equations of motion to obtain velocity, the
kinematic model begins with the equations integrated twice to yield the fluid-parcel
positions; velocity then comes from dx/dt.
Ambient Wind. The model has two components: ambient and
event-driven. The ambient, or background, solar wind is established by the model's initial
conditions on the inner boundary. The outflow of plasma is radial from a rotating,
inhomogeneous source surface at 2.5 solar radii from the center of the sun. The IMF lines
have their foot-points anchored to the source surface, and are dragged along with the
plasma flow. The rotation of the sun and the frozen-field condition results in a
garden-hose pattern (the so-called "Parker model") when the IMF lines are
displayed in the ecliptic plane. Alternating slower and faster streams are emitted from
the sun along fixed radials as the rotating source region sweeps past. If the speed
differential is great enough, co-rotating interaction regions and even shock interfaces
may form.
Event-Driven Wind. During events, the propagation of disturbances is taken care
of in the following way: Energy is input at the inner boundary. The event-driven component
is represented by time-dependent boundary conditions. Solar observations provide the start
time and evolution of the energy source, its location and size. Disturbance energy is
characterized by enhanced solar wind speeds on the source surface. The compression of
solar wind streams at the stream-stream interaction region may lead to the development of
shocks.
It is important to note that the HAF model inputs
are handled in a standardized and consistent way. The internal parameters have been
calibrated by comparisons with MHD simulations (e.g., Sun et al., 1985). The
event-period conditions are based upon empirical algorithms and parameters derived from
observational studies. |
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