FIGURE 7. 33 A microwave pulse is sent out from the radar transmitter. The pulse strikes raindrops and a fraction of its energy is reflected back to the radar unit, where it is detected and displayed, as shown in Fig. 7.34.

Lightning!

FIGURE 14.30 The generalized charge distribution in a mature thunderstorm.

FIGURE 14.28 The lightning stroke can travel in a number of directions. It can occur within a cloud, from one cloud to another cloud, from a cloud to the air, or from a cloud to the ground. Notice that the cloud-to-ground lightning can travel out away from the cloud, then turn downward, striking the ground many miles from the thunderstorm. When lightning behaves in this manner, it is often described as a “bolt from the blue.”

Figure 14.26 The development of a lightning stroke. (a) When the negative charge near the bottom of the cloud becomes large enough to overcome the air’s resistance, a flow of electrons—the stepped leader—rushes toward the earth.

Figure 14.26 The development of a lightning stroke. (b) As the electrons approach the ground, a region of positive charge moves up into the air through any conducting object, such as trees, buildings, and even humans.

Figure 14.26 The development of a lightning stroke. (c) When the downward flow of electrons meets the upward surge of positive charge, a strong electric current—a bright return stroke—carries positive charge upward into the cloud.

ACTIVE FIGURE 14. 31 The development of a lightning stroke ACTIVE FIGURE 14.31 The development of a lightning stroke. (a) When the negative charge near the bottom of the cloud becomes large enough to overcome the air’s resistance, a flow of electrons — the stepped leader — rushes toward the earth. (b) As the electrons approach the ground, a region of positive charge moves up into the air through any conducting object, such as trees, buildings, and even humans. (c) When the downward flow of electrons meets the upward surge of positive charge, a strong electric current — a bright return stroke — carries positive charge upward into the cloud. Visit the Meteorology Resource Center to view this and other active figures at academic.cengage.com/login

Figure 2 Various electrical phenomena observed in the upper atmosphere.

Cloud to Ground

Ground to Cloud

Cloud to Cloud

Forked Lightning

Sheet Lightning Scott A. Mandia

“Heat Lightning”

Ribbon Lightning

Bead Lightning Three frames from a motion-picture film of bead lightning, showing the appearance of luminous beadlike segments in the lightning flash. (E. Philip Krider, Institute of Atmospheric Physics, University of Arizona)

Ball Lightning

Red Sprites and Blue Jets

St. Elmo’s Fire This photo shows natural coronal discharge, or St. Elmo's fire, off the top of an antenna mast. It was taken in the early evening of August 21, from the Langmuir Laboratory for Atmospheric Research in New Mexico (USA). The electric field at the time of this discharge was about +11 kV/m, under a dying thunderstorm

St. Elmo’s Fire

GLOBAL LIGHTNING FLASH DENSITY

U.S. LIGHTNING FLASH DENSITY