Answers to Thermal Wind Exercises

Exercise 1: Use the thermal wind concept to explain how winds change with height in a cold core low pressure system such as a winter storm.

Pick a point just north of the cold core low pressure system. In the Northern Hemisphere, the surface geostrophic wind is from the east, that is, the surface geostrophic wind vector points west from the point. Assume this vector has a magnitude of 20 knots. With the lower thickness values coinciding with the low pressure center, the thermal wind vector also points toward the west. Assume the thermal wind has a magnitude of 50 knots. Thus the addition of the surface wind vector and the thermal wind vector results in an upper level geostrophic wind vector of 70 knots from the east, that is, pointing toward the west. Hence, the general conclusion is that with cold core low pressure centers winds increase with height.

Exercise 2: Use the thermal wind concept to explain how winds change with height in a warm core low pressure system such as a hurricane.

Pick a point just north of the warm core low pressure system. In the Northern Hemisphere, the surface geostrophic wind is from the east, that is, the surface geostrophic wind vector points west from the point. Assume this vector has a magnitude of 60 knots, similiar to that of a hurricane. With the higher thickness values coinciding with the low pressure or hurricane center, the thermal wind vector points toward the east opposite in direction from the surface wind vector. Assume the thermal wind has a magnitude of 50 knots. Thus the addition of the west-pointing surface wind vector and the east-pointing thermal wind vector results in an upper level geostrophic wind vector of 10 knots from the east, that is, pointing toward the west. Hence, the general conclusion is that with warm core low pressure centers winds decrease with height.