[Lewis Thomson (OP)]

Donald has been thinking about this question recently.

"Earth's molten core produces a field that affects magnetic compasses on the surface and solar winds far above the atmosphere. How does it affect charged particles in a thunderstorm cloud? That is, how does the Earth's magnetic field affect lightning generation and discharge thru it's effect on charged particles? Obviously, it does not affect the lightning path, as it does not match field lines."

Leave your insights in the comments below...

[Origin]

The charged particles in a thunderstorm cloud are macroscopic, like ice crystals and water droplets.  The high winds in the cumulonimbus clouds would have many orders of magnitude greater effect than the magnetic field of the earth.  So I would say the Earth's magnetic field effect on lightening would be vanishingly small.

[evan_au]

The impact on the charged droplets might be small.
But the 10,000  to 30,000 Amps in a lightning strike would feel a force from the Earth's magnetic field.

The important question is whether the force from the magnetic field approaches the magnitude of the electrostatic force between the cloud and the ground?

[Bored chemist]

the 10,000  to 30,000 Amps in a lightning strike would feel a force from the Earth's magnetic field.

Briefly.
The displacement won't be very big.

[alancalverd]

Assume the magnetic field is horizontal (most thunderstorms occur at low latitudes) at 5 x 10^-5 tesla and apply Fleming's Lefthand Rule to the column of ionised air (about 1 cm diameter) to see how fast it will be displaced (eastwards, as conventional current flows upwards in most earth strikes and the field runs north-south).

The arithmetic is left as an exercise to the reader.