  Linear wave solutions to the Charney-Hasegawa-Mima partial differential
equation with periodic boundary conditions have two physical interpretations:
Rossby (atmospheric) waves, and drift (plasma) waves in a tokamak. These waves
display resonance in triads. In the case of infinite Rossby deformation radius,
the set of resonant triads may be described as the set of integer solutions to
a particular homogeneous Diophantine equation, or as the set of rational points
on a projective surface. We give a rational parametrization of the smooth
points on this surface, answering the question: What are all resonant triads?
We also give a fiberwise description, yielding a procedure to answer the
question: For fixed $r \in \mathbb{Q}$, what are all wavevectors $(x,y)$ that
resonate with a wavevector $(a,b)$ with $a/b = r$?
