Air pressure and winds

1. Chapter 8 (part II) Air pressure and winds

2. Forces that Influence Winds • Pressure Gradient Force: difference in pressure over distance • Directed perpendicular to isobars from high to low. • Large change in pressure over s short distance is a strong pressure gradient and vice versa. • The force that causes the wind to blow.

7. Forces that Influence Winds • Coriolis Force • Apparent deflection due to rotation of the Earth (the rotation rate of Venus is so slow that the Coriolis force is extremely small on Venus) • Right in northern hemisphere and left in southern hemisphere • Stronger wind = greater deflection • No Coriolis effect at the equator greatest at poles. • Only influence direction, not speed • Only has significant impact over long distances

11. Forces that Influence Winds • Geostrophic Winds • Earth turning winds • Travel parallel to isobars • Spacing of isobars indicates speed; close = fast, spread out = slow • Topic: Math & Geostrophic Winds Vg = 1 x Δp fρ d

15. Forces that Influence Winds • Gradient Winds Aloft • Cyclonic: counterclockwise • Anticyclonic: clockwise • Gradient wind parallel to curved isobars • Cyclostrophic near Equator • Observation: Estimates Aloft • Clouds indicate direction of winds, place pressure in location consistent with cloud location.

20. Stepped Art Fig. 8-29, p. 214

21. Forces that Influence Winds • Winds on Upper-level Charts • Winds parallel to contour lines and flow west to east • Heights decrease from north to south • Surface Winds • Friction reduces the wind speed which in turn decrease the Coriolis effect. • Winds cross the isobars at about 30° into low pressure and out of high pressure • Buys-Ballots Law

25. Winds and Vertical Motion • Replacement of lateral spreading of air results in the rise of air over a low pressure and subsidence over high pressure • Hydrostatic equilibrium and equation • Topic: Hydrostatic equation Δp = -ρg Δz