  The solar disk is a bright source of multi-GeV gamma rays, due to the
interactions of hadronic cosmic rays with the solar atmosphere. However, the
underlying production mechanism is not understood, except that its efficiency
must be greatly enhanced by magnetic fields that redirect some cosmic rays from
ingoing to outgoing before they interact. To elucidate the nature of this
emission, we perform a new analysis of solar atmospheric gamma rays with 9
years of Fermi-LAT data, which spans nearly the full 11-year solar cycle. We
detect significant gamma-ray emission from the solar disk from 1 GeV up to
$\gtrsim200$ GeV. The overall gamma-ray spectrum is much harder ($\sim
E_{\gamma}^{-2.2}$) than the cosmic-ray spectrum ($\sim E_{\rm CR}^{-2.7}$). We
find a clear anticorrelation between the solar cycle phase and the gamma-ray
flux between 1-10 GeV. Surprisingly, we observe a spectral dip between
$\sim$30-50 GeV in an otherwise power-law spectrum. This was not predicted, is
not understood, and may provide crucial clues to the gamma-ray emission
mechanism. The flux above 100 GeV, which is brightest during the solar minimum,
poses exciting opportunities for HAWC, LHAASO, IceCube, and KM3NeT.
