NATIONAL SCIENCE EDUCATION STANDARDS CORRELATIONS Science as Inquiry Ability to do scientific inquiry (5-8, 9-12) Understanding of scientific inquiry (5-8, 9-12) Science in Personal and Social Perspectives Natural hazards (5-8) Natural and human-induced hazards (9-12)

Alex, Charley, Frances, Ivan, and Jeanne - names that will haunt you if you lived or vacationed in Florida during the 2004 hurricane season. These hurricanes all battered Florida one right after the other. Ivan even looped around to hit the U.S. a second time. With the intense 2004 hurricane season, many questions come to mind. Are hurricanes getting more intense? Lasting longer? More frequent? The answers may be blowing in the wind, but we'll look at hurricane data from the National Hurricane Center to try and elicit answers to these questions. But first, let's look at how hurricanes form.

Hurricanes require certain conditions in order to form. First, the ocean water down to a depth of about 200 feet must be 80°F or warmer. For this reason, hurricane season in the north Atlantic runs mostly from June 1 through November 30. Secondly, there must be sufficient force from the earth's rotation (known as the Coriolis Force) to create the hurricane's spin. This will only occur at a latitude of 5° or higher. Once these conditions have been met, the atmospheric conditions must be right. The air needs to be cooler the higher in the atmosphere you go, and the wind speed and direction must be the same from sea level to a height of about 9 kilometers. If all these conditions are met, a hurricane may form.

Assuming the conditions are right, how does a hurricane actually develop? Warm ocean water heats the air above it adding moisture through evaporation. This warm moist air rises leaving a low-pressure area at the bottom of the air column. Trade winds rush into this low-pressure area, and become part of the column of rising warm air. This column of air twists because of the earth's rotation. In the northern hemisphere, the rotation is toward the right creating a counterclockwise circulation pattern. As the speed of the spiraling air column picks up, the winds and clouds are pushed to the outer edge of the column (due to centrifugal force) creating a tube with a fairly still center - this is the eye of the storm. The strongest winds are found as part of the eyewall. At the top of the hurricane, around 40,000 feet, the air begins to circulate in the opposite direction. This acts as a release for the storm and helps prevent it from petering out. Also at this height, some of the colder high air slowly sinks back down via the eye. As it sinks, it is compressed causing it to warm, perpetuating the cycle.

The energy in a hurricane comes from the heat and water vapor from the ocean water. As the air rises, it cools and the water vapor condenses forming clouds and precipitation. These processes release the stored energy and fuel the hurricane. In one day, the energy released by the hurricane is equivalent to the amount of electricity used by the U.S. in 6 months.

Select areas of the earth are more likely to produce hurricanes. In general, hurricanes move in a westerly direction. In the north Atlantic, many hurricanes form off the coast of Africa and head toward the Caribbean and United States. In the Pacific Ocean, hurricanes form in the eastern portion of the ocean and head toward Asia rather than threatening the U.S. This is why the U.S. attention is focused mainly on Atlantic storms and not Pacific storms. The National Hurricane Center has identified monthly hurricane zones. These show where hurricanes are most likely to develop and the tracks they are likely to take throughout the hurricane season.

DATA ACTIVITY

Using archived hurricane data from the National Hurricane Center we'll look at the last 10 hurricane seasons (including the 2004 season) to determine if hurricanes are becoming more intense and/or more frequent.

Download the Bridge Hurricane Data Sheets. Have your students form team groups and assign each group a year. The hurricane data sheets summarize the named Atlantic storms from 1995 through 2004 with:

• Maximum wind speed in knots/hour (1 knot/hour = 1.15 miles/hour)
• Highest hurricane category attained by the storm (according to the Saffir-Simpson scale)
• Storm duration in days
• Total estimated damage costs given in US dollars (includes damage estimates outside of the US)

Have each group of students count the number of named storms, number of hurricanes, and number of category 3, 4, and 5 storms for their year. Then have them calculate the average maximum wind speed and average storm duration. Record these data in the summary table at the end of the Data Sheets. To get a graphic image of the trends over the past decade, create bar or line graphs for each data category in the summary table (e.g., number of major storms, hurricanes, categories, wind speed, duration, damages). Note: for each graph, Years should be on the X axis and the variable should be on the Y axis.