Matt Whiting wrote:
T o d d P a t t i s t wrote:

Pilots tend to think of Coriolis force as being in one
direction north of the equator, the opposite direction south
of the equator and zero at the equator (if they think of it
at all). However, it isn't zero at the equator, it's just
pointed straight up.

Is it pointed straight up or only affects objects moving straight up?

At the equator the Coriolis force would be straight up for an airplane
in level flight that's headed east and would be straight down if the
airplane is in level flight headed west. If the airplane is going up
or down then there would be a component of the Coriolis force towards
the west or east, respectively.

The direction of the Coriolis force will always be perpendicular to
both the velocity of the object (airplane in this case) and the axis of
the earth's rotation. In the case of level flight at the equator those
two vectors are in a plane that's tangent to the earth's surface at the
airplane's location and therefore the C. force is perpendicular and
must be directly up or down.

My engineering mechanics and physics classes were more than two decades
ago so I'm a little rusty, but I believe that coriolis
acceleration/force doesn't act straight up at the equator, but acts
perpendicular to the motion of an object moving up or down as opposed to
along the earth's surface. For example, assume a rod extending upward
at the equator, but normal to the earth's surface. Now put a metal
doughnut on the rod and then lift it upward several hundred feet.

In that case the velocity vector is upward, the axis of earth's
rotation is toward the north, and therefore the force will be
perpendicular to both and toward the west. The rod must act to oppose
that force if the donut is to travel straight up, so it exerts a force
toward the east.

doughhut will be accelerated by a force from the rod that acts in a
direction normal to the rod as the doughnut has to move faster as it
gains altitude, right?

Yes.