  Macroscopic dark matter (macros) is a broad class of alternative candidates
to particle dark matter. These candidates would transfer energy to matter
primarily through elastic scattering. A sufficiently large macro passing
through the atmosphere would produce a straight channel of ionized plasma. If
the cross-section of the macro is $\sigma_x \gtrapprox 6 \times 10^{-9} cm^2$,
then under atmospheric conditions conducive to lightning (eg. a thunderstorm)
the plasma channel would be sufficient to seed a lightning strike with a single
leader. This is entirely unlike ordinary bolt lightning in which a long
sequence of hundreds or thousands of few-meter-long leaders are strung
together. This macro-induced lightning would be extremely straight, and thus
highly distinctive. Neither wind shear nor magnetohydrodynamic instabilities
would markedly spoil its straightness. The only photographically documented
case of a straight lightning bolt is probably not straight enough to have been
macro-induced.
  We estimate the region of macro parameter space that could be probed by a
search for straight lightning from the number of thunderstorms happening on
Earth at any time. We also estimate the parameter space that can be probed by
carefully monitoring Jupiter, e.g. using the Hubble Space Telescope.
  All code and data is available at
https://github.com/cwru-pat/macro_lightning.
