大气科学之湿度.ppt

思考题 1、天气报告中的风速是（ ）的平均风速。 a. 15min. b. 10min. c. 5min. d. 2min. 2、天气报告中的风向是以（ ） 以正北为基准，顺时针方向旋转 b. 以正北为基准，逆时针方向旋转 c. 以正南为基准，顺时针方向旋转 d. 以正南为基准，逆时针方向旋转 3、影响风的因子有哪些？ 4、地球表面有哪些盛行的风带？ Coriolis Force For a southward moving rocket, the initial eastward speed is slow compared to the rotational speed of the earth near the equator. The earth has a larger eastward motion near the equator than the rocket has so the rocket will appear to have a westward component to its motion. The rocket will have turned to the right. Coriolis Force Affects direction, not speed of object Maximum at the poles Zero at the equator Proportional to wind speed Always acts to the right of the motion in Northern Hemisphere. Always acts to the left of the motion in the Southern Hemisphere. The strength of Coriolis force is influenced by latitude and the speed of the moving object Coriolis parameter f = 2?sin? Coriolis Force+PGF Apply this knowledge to wind forced by horizontal pressure gradient force and balanced by the Coriolis force: Net Force = PGFH + Co L H 980 mb 984 mb 988 mb Start with no velocity -- what are the forces on the parcel? Coriolis Force+PGF L H 980 mb 984 mb 988 mb PGF Since there is no initial speed, the Coriolis force is zero. But There is PGF. As soon as the parcel starts to move, the Coriolis force is no longer zero. The Coriolis force is small at first, but as the speed increases, the Coriolis force increases. Coriolis Force+PGF L H 980 mb 984 mb 988 mb PGF Co V The PGF still exceeds the Coriolis force. The parcel continues to increase in speed, and the Coriolis force continues to increase in magnitude, further turning the parcel’s direction to the right (Northern Hemisphere!). Geostrophic Wind L H 980 mb 984 mb 988 mb PGF Co V Eventually the Coriolis and PGF balance each other. Since there is no unbalanced force, there is no acceleration. The wind continues to move at constant speed in a straight line (remember, no Friction). This is called: