The Coriolis force is an apparent force. From an earth observer, it is an apparent curving of a wind flow. The earth spins counterclockwise when viewed from the North Pole and clockwise when viewed from the South Pole. Therefore, the Coriolis deflection is the opposite in the Northern Hemisphere as compared to the Southern Hemisphere. If you stand on the North Pole, your body will make a complete counterclockwise rotation in 24 hours. However, if you are on the equator, your body will not rotate but will rather face forward as you move with the earth. The Coriolis force is a maximum at the pole (perfect spin) and a minimum at the equator (no earth generated spin). The earth's linear velocity (distance per unit time) is a maximum at the equator and a minimum at the pole. An air parcel in the Northern Hemisphere moving from the equator toward the pole will carry its higher angular velocity as it moves north. This will cause the air parcel to deflect to the right of its path of motion. If an air parcel moves north to south in the Northern Hemisphere, it will carry its lower angular velocity with it. Since it is moving into a region of higher angular velocity, the earth will spin underneath the air parcel, causing again, an apparent deflection to the right. The word deflection is used because it is relative to an earth observer. Someone watching the air parcel from space would not see the parcel deflect but would rather see the parcel moving straight and the earth rotating out from under the air parcel. Even if air moves on a constant latitude (east to west or west to east) it will deflect to the right in the Northern Hemisphere. A wind moving to the east will have its own velocity added to the earth's velocity. This will cause the parcel to deflect to a region of higher velocity, which is right of the path of motion. A wind moving east to west will subtract from the earth's velocity and cause the parcel to deflect to a lower velocity, which will deflect the parcel to the right and away from the equator. |