How to create temperature gradient E-W rather than N-S?

[atpollard]

The specific feature I'm trying to replicate is the east being much colder than the west at the same latitude.

I don’t think that this is possible without approaching tidal lock. If the world rotates on a North-South axis in anything approaching 24 hours, the East and West will alternate day/night too rapidly to have a significant difference in temperature … the atmosphere will conduct heat and moderate the temperatures in horizontal bands.

A very slow rotation – like a 700 hour day – will allow the east or west hemisphere to experience a one week, all daylight summer, a one week slow sunset fall, a one week, all night winter and a one week slow sunrise spring.

With respect to the 90 degree inclination, the world rotates on a polar east-west axis (with north-south being defined by the celestial plane of the sun and planets). Assuming 24 hour rotation day and 365 day revolution year … The East polar hemisphere will experience 3 months of Tropical/Desert no sunset Summer, followed by 3 months of temperate sunrise-sunset fall, followed by 3 months of Arctic darkness Winter, followed by 3 months of temperate sunrise-sunset spring. During the Spring and Fall, the East and West Hemispheres will diverge towards opposite seasons as your map indicates (without the eternal day/night of tidal lock).

To heat only one side of a rotating sphere involves a minor heat source orbiting in a nearly geo-stationary orbit … a micro-sun orbiting over the east hemisphere. The micro-sun would need to advance slowly around the globe to move the ‘seasons’ east-west, otherwise one hemisphere gets perpetual summer and the other perpetual winter. I think that this starts to move from sci-fi into fantasy (not a criticism, just an observation) ... but Ptolemy would approve.