What are the units for flux levels in Solar Radiation Storms?
“ster” stands for ster-radian, which is a unit of “solid angle.” The reason that this is done used is because the instrument samples particles only over a limited angular volume. One takes the particle counts and divides by the solid angle subtended by the instrument to normalize the measurement per solid angle unit. To convert to the equivalent flux that one would expect in all directions, multiply by 4 x pi. Note that this is valid, however, only if the particle trajectories are uniformly distributed over all possible directions.
