Parker Spiral Magnetic Field Guide
The field shape
The Parker spiral describes how the solar magnetic field bends outward through the moving solar wind. The Sun rotates while plasma flows away. That motion stretches field lines into a spiral. This calculator turns the idea into useful numbers. It estimates radial field strength, azimuthal field strength, total magnitude, spiral angle, travel time, and longitude sweep.
Why the model matters
Spacecraft often measure magnetic fields far from the Sun. A Parker spiral estimate gives a first reference. It helps compare measured data with a simple steady wind model. The result can support studies of energetic particles, solar wind streams, and magnetic connectivity. It is not a full magnetohydrodynamic simulation. It is a clear baseline for fast checks.
Inputs and units
Use radial distance in astronomical units. Use a reference radius near the source surface. Enter the reference magnetic field in nanotesla. Enter solar wind speed in kilometers per second. The rotation period controls the angular rate. Latitude reduces the azimuthal term through the cosine factor. Polarity lets the radial field point outward or inward.
Reading the outputs
The radial component drops with the square of distance. The azimuthal component grows relative to it when wind is slow, distance is large, or rotation is fast. The spiral angle shows how much the field leans away from a radial line. A larger angle means a tighter spiral. Travel time estimates how long plasma needs to reach the selected radius. Magnetic pressure converts field magnitude into pressure units. Alfvén speed uses the optional proton density input.
Model limits
The calculator assumes constant solar wind speed. It also assumes steady rotation and no stream interaction regions. Real fields can differ during storms, sector crossings, and coronal mass ejections. Use the output as a structured estimate. Then compare it with observations, mission data, or detailed simulations. Small input changes can shift the azimuthal component. Therefore, test several wind speeds and latitudes. This gives better physical context for heliospheric magnetic field work. A careful workflow records each assumption. Keep the reference field, source radius, and wind speed beside every result. This makes later review easier. It also helps students see which variable controls each magnetic component most strongly during comparison work.