Final answer:
The initial rotation in a supercell thunderstorm is primarily caused by wind shear, where differing wind speeds and directions create a horizontal rotating column of air that can be tilted into a vertical rotation by an updraft, potentially forming a tornado. The Coriolis force affects large-scale rotations like hurricanes but is not the direct cause of supercell rotation.
Step-by-step explanation:
The initial rotation in a supercell thunderstorm is attributed to the wind shear in the atmosphere. This phenomenon occurs when there's a difference in wind speeds and directions over a short distance within the atmosphere. Specifically, in a supercell, the changing wind speed and direction with height (often caused by the jet stream's strong cold winds aloft interacting with weaker warm winds from the Gulf of Mexico) result in a horizontal rotating column of air. This horizontal rotation is then tilted into a vertical rotation due to updraft within the thunderstorm, potentially leading to the formation of a tornado.
The Coriolis force also influences the rotation of large-scale weather systems like hurricanes and tropical cyclones, causing them to spin in different directions depending on the hemisphere. However, it's important to note that the Coriolis effect is not typically the direct cause of rotation in supercell thunderstorms, which are much smaller scale phenomena than hurricanes or global wind patterns.