 Coriolis force is an apparent force that accounts for motion on a rotating sphere, such as Earth. We can break the explanation of the Coriolis force into two cases. Zonal flow, which is east-west, and merienal flow, which is north-south. The explanation for both cases relies on conservation of angular momentum. For zonal flow, imagine an air parcel moving to the east with a velocity u. Angular acceleration is just the angular velocity squared times the radius of rotation. If the parcel is moving at a velocity of u relative to Earth's surface, then it has some extra angular momentum, which is u divided by r. To find the total angular acceleration that the moving air parcel has, we need to square the angular momentum of the air parcel, which is omega plus u divided by r, and then multiply it by r. We then subtract the air's acceleration, which is just omega squared r. The difference to good approximation is 2 omega times u, which is just the Coriolis force, and in the case of eastward motion is pointed away from Earth's axis in the northern hemisphere. Thus, the Coriolis force turns the air parcel to the right for zonal flow. If the air parcel moves to the west, then by the same argument, the Coriolis force points towards Earth's rotation axis in the northern hemisphere, which again turns the air parcel to the right. The explanation for the meridional flow is simpler. An air parcel initially has the angular momentum of the Earth at its latitude. If it moves north at the same height, then it has more angular momentum than the Earth below it. And so it goes faster than the Earth and appears to move to the right. If it moves south at the same height, then it has less angular momentum than Earth and appears to slow down relative to Earth and thus appears to move to the right.