On the giant planets the thermal energy that drives convection comes both from the Sun and from the hot interiors of the planets themselves (Math Tools 10.2). Recall from Chapter 9 that convection results from vertical temperature differences. As heating drives air up and down, the Coriolis effect shapes that convection into atmospheric vortices, examples of which are familiar on Earth as high-pressure systems, hurricanes, and thunderstorms. On the giant planets, convective vortices are visible as isolated circular or oval cloud structures. The Great Red Spot on Jupiter and the Great Dark Spot on Neptune are classic examples. Observations of small clouds distributed within the Great Red Spot show that it is an enormous atmospheric whirlpool, or eddy, swirling around in a counterclockwise direction with a period of about 1 week. On a rapidly rotating planet, winds generated by Coriolis effects can be very strong.