Cumulifor m clouds develop as air slowly rises over Lake Powell in Utah. Figure 6.1 Dew forms on clear nightswhen objects on the surface cool to a temperature below the dew point. If these beads of water should freeze, they would become frozen dew. Figure 6.2 These are the delicate ice-crystal patterns that frost exhibits on a window during a cold winter morning.

Figure 6.3 Hygroscopic nuclei are “water-loving”, and water vapor rapidly condenses on their surfaces. Hydrophobic nuclei are “water-repelling” and resist condensation. Figure 6.4 The high relative humidity of the cold air above the lake is causing a layer of haze to form on a still winter morning. Figure 6.5 Radiation fog nestled in a valley. Figure 6.6 Advection fog rolling in past the Golden Gate Bridge in San Francisco. As fog moves inland, the air warms and the fog lifts above the surface. Eventually, the air becomes warm enough to totally evaporate the fog. Figure 6.7 Along an irregular coastline, advection fog is more likely to form at the headland where moist surface air converges and rises than at the beach where air diverges and sinks . Figure 6.8 Tiny drops, each one made from many fog droplets, drip from the needles of this tree and provide a valauble source of moisture during the otherwise dry summer along the coast of California. Figure 6.9 Even in a summer, warm air rising above thermal pools in Yellowstone National Park condenses into a type of ateam fog. Figure 6.10 The mixing of two unsatured air parcels can produce fog. Notice in the saturated mixed parcel that the actual mixing ratio (w) is too high. As the mixed parcel cools below its saturation point, water vapor would condense onto nuclei, producing liquid droplets. This would keep tha actual mixing ratio close to the saturation mixing ratio, and the relative humidity of the mixed parcel would remain close to 100 percent.

Figure 6.11 Average annual number of days with dense fog throughout the United States.

Figure 6.12 Helicopters hovering above na area of shallow fog (diagram a) can produce a clear area (photograph b) by mixing the drier air into the foggy air below. Figure 6.13 Cirrus clouds. Figure 6.14 Cirrocumulus clouds. Figure 6.15 Cirrostratus clouds with a faint halo. Figure 6.16 Altocumulus clouds. Figure 6.17 Altostratus clouds. The appearance of a dimly visible “watery sun” through a deck of gray clouds is usually a good indication that the clouds are altostratus. Figure 6.18 The nimbostratus is the sheetlike cloud from which light rain is falling. The ragged-appearing cloud beneath the nimbostratus is stratus fractus, or scud. Figure 6.19 Stratocumulus clouds. Notice that the rounded masses are larger than those of the altocumulus. Figure 6.20 A layer of low-lying stratus clouds. Figure 6.21 Cumulus clouds. Small cumulus clouds such as these re sometimes called fair weather cumulus, or cumulus humilis. Figure 6.22 Cumulus congestus. This line of cumulus congestus clouds is building along Maryland’s eastern shore. Figure 6.23 A cumulonimbus cloud. Strong upper-level winds blowing from right to left produce a well-defined anvil. Sunlight scattered by falling ice crystals produces the white (bright) area beneath the anvil. Notice the heavy rain shower falling from the base of the cloud. Figure 6.24 A generalized illustration of basic cloud types based on height above the surface and vertical development. Figure 6.25 Lenticular clouds forming one on top of the other on the eastern side of the Sierra Nevada.

Figure 6.26 The cloud forming over and downwind of Mt. Rainier is called a banner cloud. Figure 6.27 A pileus cloud forming above a developing cumulus cloud. Figure 6.28 Mammatus cloud forming beneath a thunderstorm. Figure 6.29 A contrail forming behind a jet aircraft. Figure 6.30 The clouds in this photograph are nacreous clouds. They form in the stratosphere and are most easily seen at high latitudes. Figure 6.31 The wavy clouds in this photograph are noctilucent clouds. They are usually observed at high latitudes, at altitudes between 75 and 90 km above the earth’s surface. Figure 6.32 Clouds in the horizon appear closer together than clouds overhead. Note that the amount of clear space between each cloud is the same. To the observer, however, there appears to be more space between clouds 1 and 2 than between clouds 3 and 4.

Figure 6.33 The geostationary satellite moves through space at the same rate that the earth rotates, so it remains above a fixed spot on the equator and monitors one area constantly. Figure 6.34 The laser-beam ceilometer sends pulses of infrared radiation up to the cloud. Part of this beam is reflected back to the ceilometer. The interval of time between pulse transmission and return is a measure of cloud height, as displayed on the indicator screen. Figure 6.35 Polar-orbiting satellites scan from north to south, and on each sucessive orbit the satellite scans na area farther to the west.

Figure 6.36 Generally, the lower the cloud, the warmer its top. Warm objects emit more infrared energy than do cold objects. Thus, na infrared satellite picture can distinguish warm, low (gray) clouds from cold, high (white) clouds. Figure 6.37a A visible image of the eastern Pacific taken on the same day at just about the same time as Fig. 6.37b. Figure 6.37b An infrared image of the eastern Pacific taken on the same day at just about the same time as Fig.6.34c. Figure 6.37c An enhanced infrared image of the eastern Pacific taken on the same day as the images shown in Fig.6.37(a) and (b). Figure 6.38 Infrared water vapor image. The daker areas represent dry air aloft; the brighter the gray, the more moist the air in the middle or upper troposphere. Bright white areas represent dense cirrus clouds or the tops of thunderstorms. The area in color represents the coldest cloud tops.