Expert: Philip A. Stahl - 3/22/2010

Question
Does the magnetosphere's protective effect diminish during reversals of the earth's magnetic field? If so might some mass extinctions have been caused by the solar wind stripping the atmosphere?

Answer
Hello,

Yes, the protective effect of the Earth's magnetosphere will diminish during a field reversal, in particular because such reversals include an interval wherein no magnetic field exists. This may last from 100 to 1000 years, perhaps more. In such a case, the magnetic field -which normally acts as a protective barrier to the flux of energized particles known as the solar wind- ceases to do that. This means that in the event of major solar flares, the particle flux might attain levels that can be lethal to some life forms.

It's conceivable then that some extinctions in the past may have been caused by this agency. Note- I am treating the magnetosphere as a separate entity from the atmosphere. Thus, it isn't at all clear that any "raw" (unmediated) solar wind or plasma would "strip the atmosphere" away - though we have experienced mammoth solar flares (such as in 1973) that did strip away up to 20% of the ozone layer, as recorded by Skylab.

The problem with the energetic particles is in exposing many life forms to much higher radiation levels. To give you an indicator of the magnitude, when a medium intensity (not even terribly large) solar wind normally "blows" along the magnetosphere boundary an effective MHD (magneto-hydrodynamic) generator is produced. All such "generators" are defined by virtue of the free electrons and protons in the solar wind cutting across the Earth's resident magnetic field.

With an induced voltage of this generator up to 150 kV (150,000 V) a total power of more than 1 million megawatts is produced. That is 1 million joules of energy per second.

Let us hope such a field reversal doesn't occur in our lifetimes!