Environmental Problems, Their Causes, and Sustainability 1

figure. Scientists hypothesize that the rising vortex ofair starts spinning because the air near the ground inthe funnel is moving slower than the air above. Thisrolls or spins the air ahead of the advancing front in avertically rising air mass or vortex.Large and dangerous storms called tropical cyclonesare spawned by the formation of low-pressurecells of air over warm tropical seas. Figure 6-4 showsthe formation and structure of a tropical cyclone. Tracethe flows in this figure. Hurricanes are tropical cyclonesthat form in the Atlantic Ocean; those forming in thePacific Ocean usually are called typhoons. Tropical cyclonestake a long time to form and gain strength. As aresult, meteorologists can track their paths and windspeeds and warn people in areas likely to be hit bythese violent storms.Hurricanes and typhoons can kill and injure peopleand damage property and agricultural production.But sometimes the long-term ecological and economicbenefits of a tropical cyclone can exceed its short-termharmful effects.For example, in parts of Texas along the Gulf ofMexico, coastal bays and marshes normally are closedoff from freshwater and saltwater inflows. In August1999, Hurricane Brett struck this coastal area. Accordingto marine biologists, it flushed out excess nutrientsfrom land runoff and dead sea grasses and rotting vegetationfrom the coastal bays and marshes. It alsocarved 12 channels through the barrier islands alongthe coast, allowing huge quantities of fresh seawater toflood the bays and marshes. This flushing out of thebays and marshes reduced brown tides consisting ofexplosive growths of algae feeding on excess nutrients.It also increased growth of sea grasses, which serve asnurseries for shrimp, crabs, and fish and food for millionsof ducks wintering in Texas bays. Production ofcommercially important species of shellfish and fishalso increased.4Rising winds exitfrom the storm athigh altitudes.The calm centraleye usually is about24 kilometers(15 miles) wide.Gales circle the eye at speedsof up to 320 kilometers(200 miles) per hour321Moist surface windsspiral in toward thecenter of the storm.Figure 6-4 Formation of a tropical cyclone. Those forming in the Atlantic Ocean usually are called hurricanes;those forming in the Pacific Ocean usually are called typhoons.104 CHAPTER 6 Climate and Terrestrial Biodiversity