Michael was a long-term visiting scientist in 19, and an NCAR Affiliate Scientist from 2003 until his appointment as HAO Director.
Michael's scientific research activity is principally in helioseismology, asteroseismology, solar physics, and inverse problems.
Helioseismology was able to rule out the possibility that the solar neutrino problem was due to incorrect models of the interior of the Sun.
Features revealed by helioseismology include that the outer convective zone and the inner radiative zone rotate at different speeds, which is thought to generate the main magnetic field of the Sun by a dynamo effect, and that the convective zone has "jet streams" of plasma (more precisely, torsional oscillations) thousands of kilometers below the surface.
The data from time-series of solar spectra show all the oscillations overlapping.
Thousands of modes have been detected (with the true number perhaps being in the millions).
This sunspot absorption causes a seismic deficit that can be imaged at the antipode of the sunspot.
To facilitate spaceweather forecasting, seismic images of the central portion of the solar far side have been produced nearly continuously since late 2000 by analysing data from the SOHO spacecraft, and since 2001 the entire far side has been imaged with this data.
The "5-minute oscillation" is the series of p-mode lines on the right between about 2 and 7 m Hz.
(l=20, m=16 and n=14.) Note that the increase in the speed of sound as waves approach the center of the sun causes a corresponding increase in the acoustic wavelength.