1

http://visibleearth.nasa.gov/view_rec.php?id=190

First GOES 11 image

Fig. 6-CO, p.140Air-born dust from the Sahara Desert, Feb. 2001

dust from China over Japan.

3/5/2001

3/6/2001Fig. 6-1, p.142

FIGURE 6.1 A model of the atmosphere where air density remains constant with height. The air pressure at the surface is related to the number of molecules above. When air of the same temperature is stuffed into the column, the surface air pressure rises. When air is removed from the column, the surface pressure falls.

Fig. 6-2, p.143

It takes a shorter column of cold, dense air to exert the same sfc P as a taller column of warm, less dense air.

Warm air aloft = high P; cold air aloft = low P

FIGURE 6.2 It takes a shorter column of cold air to exert the same pressure as a taller column of warm air. Because of this fact, aloft, cold air is associated with low pressure and warm air with high pressure. The pressure differences aloft create a force that causes the air to move from a region of higher pressure toward a region of lower pressure. The removal of air from column 2 causes its surface pressure to drop, whereas the addition of air into column 1 causes its surface pressure torise. (The difference in height between the two columns is greatly exaggerated.)

2

Fig. 6-2c, p.143

The Pressure gradient force is due to the pressure difference and causes air to move from higher P to lower P (wind)

p.144

Air pressure = force of air molecules over a given area

Air above a region of surface high pressure is more dense than air above a region of surface low pressure (at the same temperature

P=T x Density x k, so…

P~ T x P

Fig. 6-3, p.145

FIGURE 6.3 Atmospheric pressure in inches of mercury and in millibars.

Fig. 6-4, p.146

FIGURE 6.4 The mercury barometer. The height of the mercury column is a measure of atmospheric pressure.

Fig. 6-5, p.146 Fig. 6-6, p.147

Recording barograph

3

Fig. 6-7, p.147

FIGURE 6.7 The top diagram (a) shows four cities (A, B, C, and D) at varying elevations above sea level, all with different station pressures. The middle diagram (b) represents sea-level pressures of the four cities plotted on a sea-level chart. The bottom diagram (c) shows isobars drawn on the chart (dark lines) at intervals of 4 millibars.

Fig. 6-8, p.148

FIGURE 6.8 (a) Surface map (left) and upper air map (right) for same day.

Fig. 6-8a, p.148

FIGURE 6.8 (a) Surface map showing areas of high and low P

Wind blows across the isobarsFig. 6-8b, p.148

(b) Upper-level (500-mb) map for the same day on right.Solid lines = contour lines in meters above sea level.Dashed red lines = isotherms in °C. Note wind blows parallel to the contour lines on upper air map!

p.149

Isobaric map

Because of the changes in air density, a surface of constant pressure rises in warm, less-dense air and lowers in cold, more-dense air. Fig. 6-9, p.150

FIGURE 6.9 The higher water level creates higher fluid pressure at the bottom of tank A and a net force directed toward the lower fluid pressure at the bottom of tank B. This net force causes water to move from higher pressure toward lower pressure.

4

Fig. 6-10, p.151

P gradient = 4 mb/100 km Net force = P gradient force = PGF

FIGURE 6.10 The pressure gradient between point 1 and point 2 is 4 mb per 100 km. The net force directed from higher toward lower pressure is the pressure gradient force. Fig. 6-11, p.151

FIG. 6.11 The closer the spacing of isobars, the greater the pressure gradient. The greater the pres. gradient, the stronger the pres. gradient force (PGF). The stronger the PGF, the greater the wind speed. The red arrows represent the relative magnitude of the force, which is always directed from higher toward lower pressure.

Fig. 6-12, p.152

FIGURE 6.12 Surface weather map for 6 A.M. (CST), Tuesday, November 10, 1998. Dark gray lines are isobars with units in millibars w/ 4 mb interval. A deep low with a central P of 972 mb (28.70 in.) is moving over NW Iowa. The dist. along the green line X-X’ is 500 km. The diff. in P between X and X’ is 32 mb, producing a P gradient of 32 mb/500 km. The tightly packed isobars along the green line are associated with strong northwesterly winds of 40 knots, with gusts even higher. Wind directions are given by lines that parallel the wind. Wind speeds are indicated by barbs and flags. (A wind indicated by the symbol would be a wind from the northwest at 10 knots. See blue insert.) The solid blue line is a cold front, the solid red line a warm front, and the solid purple (red ?) line an occluded front. The heavy dashed line is a trough. Fig. 6-13, p.152

FIGURE 6.13 On non rotating platform A, the thrown ball moves in a straight line. On platform B, which rotates counterclockwise, the ball continues to move in a straight line. However, platform B is rotating while the ball is in flight; thus, to anyone on platform B, the ball appears to deflect to the right of its intended path.

Fig. 6-14a, p.153

FIGURE 6.14 Except at the equator, a free-moving object will appear from the Earth to deviate from its path as the Earth rotates beneath it. The deviation (Coriolis “force”) is greatest at the poles and decreases to zero at the equator.

Coriolis effect

Fig. 6-15, p.154

FIGURE 6.15 Above the level of friction (~1000 m elev), air initially at rest will accelerate until it flows parallel to theisobars at a steady speed with the pressure gradient force (PGF) balanced by the Coriolis force (CF).

geostrophicwind

5

Fig. 6-16a, p.155

FIGURE 6.16 The isobars and contours on an upper-level chart are like the banks along a flowing stream. When they are widely spaced, the flow is weak; when they are narrowly spaced, the flow is stronger. The increase in winds on the chart results in a stronger Coriolis force (CF), which balances a larger pressure gradient force (PGF). Fig. 6-16b, p.155

Fig. 6-17a, p.155

FIGURE 6.17 Winds and related forces around areas of low and high pressure above the friction level in the Northern Hemisphere. Notice that the pressure gradient force (PGF) is in red, while the Coriolis force (CF) is in blue. Fig. 6-17b, p.155

FIGURE 6.17 Winds and related forces around areas of low and high pressure above the friction level in the Northern Hemisphere. Notice that the pressure gradient force (PGF) is in red, while the Coriolis force (CF) is in blue.

Fig. 6-18, p.156

FIGURE 6.18 An upper-level 500-mb map showing wind direction, as indicated by lines that parallel the wind. Wind speeds are indicated by barbs and flags. (See the blue insert.) Solid gray lines are contours in meters above sea level. Dashed red lines are isotherms in °C. p.157

Upper level chart that extends over the Northern and Southern hemispheres. Solid gray lines on the chart are isobars.

6

p.158

This drawing of a simplified upper level chart is based on cloud observations. Upper level clouds moving from the southwest (a) indicate isobars and winds aloft (b). When extended horizontally, the upper-level chart appears as in (c), where lower pressure is to the northwest and higher pressure is to the southeast. Fig. 6-19, p.159

FIGURE 6.19 (a) The effect of surface friction is to slow down the wind so that, near the ground, the wind crosses the isobars and blows toward lower pressure (friction lowers the wind speed which lowers Coriolis force). (b) This phenomenon at the surface produces an outflow of air around a high. Aloft, the winds blow parallel to the lines, usually in a wavy west-to-east pattern.

Fig. 6-20, p.159

FIGURE 6.20 (a) Surf. weather map showing isobars and winds on a day in Dec. in S. America. (b) The boxed area shows the idealized flow around surf.-pressure systems in the Southern Hemisphere. Fig. 6-21, p.160

FIGURE 6.21 Winds and air motions associated with surface highs and lows in the Northern Hemisphere.

Fig. 6-22, p.161

FIGURE 6.22 An onshore wind blows from water to land, whereas an offshore wind blows from land to water.

Fig. 6-23, p.161FIGURE 6.23 Wind direction can be expressed in degrees abouta circle or as compass points.

7

Fig. 6-24, p.161FIGURE 6.24 In the high country, trees standing unprotected from the wind are often sculpted into “flag” trees. Fig. 6-25, p.162

FIGURE 6.25 This wind rose represents the percent of time the wind blew from different directions at a given site during the month of January for the past ten years. The prevailing wind is NW and the wind direction of least frequency is NE.

Fig. 6-26, p.162

FIGURE 6.26 A wind vane and a cup anemometer. These instruments are part of the ASOS system. (For a complete picture of the system, see Fig. 3.17, p. 74). Fig. 6-27, p.162

FIGURE 6.27 The aero vane (skyvane).

p.162

FIGURE 5 A portion of a wind farm near the summit of Altamont Pass, California. With over 7000 wind turbines, this is the world’s largest wind energy development project.