Page 200 - Geosystems An Introduction to Physical Geography 4th Canadian Edition

164 part I The energy–atmosphere System
Daytime valley-breeze conditions
◀Figure 6.17 Conditions for daytime valley breezes and nighttime mountain breezes.
within the gyre and some of which makes landfall. Debris from the 2011 Japan tsunami added more mate­ rial into the North Pacific; computer models based on winds and currents estimate the extent of the debris, some of which has already washed up on North American coastlines (Figure 6.19). (Go to marinedebris.noaa .gov/tsunamidebris for more on the tsu­ nami debris.)
Equatorial Currents Trade winds drive the ocean surface waters west­ ward in a concentrated channel along the equator (Figure 6.18). These equatorial currents remain near the equator because of the weakness of the Coriolis force, which diminishes to zero at that latitude. As these sur­ face currents approach the western margins of the oceans, the water ac­ tually piles up against the eastern shores of the continents. The aver­ age height of this pileup is 15 cm. This phenomenon is the western intensification.
The piled­up ocean water then goes where it can, spilling northward and southward in strong currents, flowing in tight channels along the eastern shorelines. In the Northern Hemisphere, the Gulf Stream and the Kuroshio (a current east of Japan) move forcefully northward as a result of western intensification. Their speed and depth increase with the constriction of the area they occupy. The warm, deep, clear water of the ribbon­like Gulf Stream (Figure 5.8) usually is 50–80 km wide and 1.5–2.0 km deep, moving at 3–10 km·h−1. In 24 hours, ocean water can move 70–240 km in the Gulf Stream.
upwelling and Downwelling Flows Where surface water is swept away from a coast, either by surface di­ vergence (induced by the Coriolis force) or by offshore winds, an upwelling current occurs. This cool water generally is rich in nutrients and rises from great depths to replace the vacating water. Such cold upwelling cur­ rents exist off the Pacific coasts of North and South America and the subtropical and midlatitude west coast of Africa. These areas are some of Earth’s prime fishing regions.
Higher temperature (lower pressure)
Lower temperature (higher pressure)
Warmer air Nighttime mountain-breeze conditions
Lower temperature (higher pressure)
Higher temperature (lower pressure)
Cooler air
wind off the coast of Japan, dumping nearly 30000 rubber ducks, turtles, and frogs into the North Pacific. Westerly winds and the North Pacific Current swept this floating cargo at up to 29 km a day across the ocean to the coast of Alaska, Canada, Oregon, and California. Other toys drifted through the Bering Sea and into the Arctic Ocean (see dashed red line in Figure 6.19).
In August 2006, Tropical Storm Ioke formed about 1285 km south of Hawai‘i. The storm’s track moved west­ ward across the Pacific Ocean as it became the strongest super typhoon in recorded history—a category 5, as we discuss in Chapter 8. Turning northward before reach­ ing Japan, the storm moved into higher latitudes around the Pacific gyre. Typhoon Ioke remnants eventually crossed the Aleutian Islands, reaching 55° N as an extra­ tropical depression. The storm roughly followed the path around the Pacific Gyre and along the track of the rubber duckies.
Marine debris circulating in the Pacific Gyre is the subject of ongoing scientific study. Although plastics, especially small­sized plastic fragments, are predomi­ nant, this debris also consists of metals, fishing gear, and abandoned vessels, some of which remains in circulation