THE RESTLESS SKY: Storm Systems and El Niño

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Chapter Outline

  • 5.1

    Thunderstorms

  • 5.2

    Thunderstorm Hazards: Lightning and Tornadoes

  • 5.3

    Nature’s Deadliest Storms: Hurricanes

  • 5.4

    Midlatitude Cyclones

  • 5.5

    El Niño’s Wide Reach

  • 5.6

    Geographic Perspectives: Are Atlantic Hurricanes a Growing Threat?
Tornadoes are violently rotating columns of air that extend downward from the base of a severe thunderstorm. No two tornadoes are exactly alike. This long and ropy tornado was photographed in the Texas panhandle near Amarillo. A cloud of debris has formed where the tornado touches the ground.
(© A. T. Willett/Alamy)

LIVING PHYSICAL GEOGRAPHY

  • Why do some thunderstorms rotate?

  • How wide is a bolt of lightning?

  • Do tornadoes ever strike the same place twice?

  • What does the word hurricane mean?

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THE BIG PICTURE

Atmospheric systems range in size and strength from afternoon thunderstorms to large and intense hurricanes. Atlantic hurricanes may become stronger in the coming decades.

LEARNING GOALS

After reading this chapter, you will be able to:

  • 5.1

    Distinguish among three types of thunderstorms and describe the weather associated with each.

  • 5.2

    Discuss how lightning and tornadoes form and the hazards that each presents.

  • 5.3

    Explain how hurricanes develop, where they occur, and what makes them dangerous.

  • 5.4

    Review the major characteristics and stages of development of a midlatitude cyclone.

  • 5.5

    Discuss how El Niño forms and describe its global effects.

  • 5.6

    Assess the current and potential vulnerability of the United States to major hurricanes.

THE HUMAN SPHERE:

The EF5 Tornado

THE LARGEST and most locally intense storm on the planet is the EF5 tornado (as rated on the enhanced Fujita scale; see Section 5.2). An EF5 tornado has wind speeds of more than 322 km/h (200 mph). There have been approximately 60 EF5 tornadoes in the United States over the last six decades, an average of one per year. In some years, there are none, and in other years, several develop during a single tornado outbreak over the course of a few days. Canada, the country with the second highest tornado activity after the United States, has seen only one EF5 tornado in its recorded history.

Winds in an EF5 tornado can destroy most human-built structures and cause a significant human death toll. One of the more recent EF5 tornadoes was the tornado that struck Moore, Oklahoma, on May 20, 2013, killing 23 people and injuring almost 400 others. It had a diameter of 2.1 km (1.3 mi), and its peak wind speeds were about 340 km/h (210 mph). Figure 5.1 shows some of the damage done by this tornado.

Figure 5.1

Tornado damage. This aerial photo shows the damage done by the EF5 tornado that struck Moore, Oklahoma, on May 20, 2013. A tornado warning system alerted people to find safety before the tornado struck and kept the death toll to 23.
(Jocelyn Augustino/FEMA)

This chapter highlights storm systems in the atmosphere. We start with thunderstorms and the phenomena they produce, such as lightning and tornadoes. We then move to the smaller-scale phenomena of hurricanes and midlatitude cyclones. Finally, we examine El Niño, an atmospheric system that is not a storm but has a global influence on Earth’s storm systems. In the Geographic Perspectives, we will look at the influence of climate change on Atlantic hurricanes.

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