“Zebra Stripes in Outer Space”:
Long-standing mystery of radiation belt signature explained
For some months, I had the privilege to work with Juan Roederer on a new theory to explain the existence of “zebra stripes” in the Earth’s Van Allen radiation belt particles, these zebra-like patterns in energy spectrograms that indicate highly organized compressions and expansions of the radiation belt particles as they circle the Earth. The result of our cogitation is the object of an article published in the Journal of Geophysical Research – Space Physics.
In 3 tweets, we argue that:
- “Zebra stripes” are signature of an azimuthal dependence in trapped particle distributions below L ~ 3.
- High-altitude ionospheric winds affect the azimuthal distribution of radiation belt intensity.
- The number of stripes indicates how many hours the population spent drifting under quiet conditions.
The mechanism that we propose to explain such feature can be likened to what happens in multi-lane highway traffic during rush hour, when an initial group of evenly spaced cars is segregated into high/low density bunches according to their acceleration power and the varying speed limits along their route. In the case of the Van Allen belt particles, it is the upper atmosphere that acts as the “traffic regulator”: ionospheric zonal winds in equatorial regions, which during quiet solar activity conditions blow eastward around midnight and westward around noon, induce electric fields which speed up or slow down the drift of the particles around the planet.
The effect of a variation in speed on the density of cars (aka the particles!) is illustrated in the following video: