Page 199 - Geosystems An Introduction to Physical Geography 4th Canadian Edition

Chapter 6 atmospheric and Oceanic Circulations 163
Daytime sea-breeze conditions
Heated air rises over relatively warmer land
Thermal low
Higher temperature (lower pressure)
ONSHORE BREEZE
Cooler air is drawn inland by developing thermal low
Lower temperature (higher pressure)
Warm air cools and descends
Nighttime land-breeze conditions
Air cools and descends
are known for their ability to melt snow rapidly by subli­ mation, as discussed in Chapter 7.
Regionally, wind represents a significant and in­ creasingly important source of renewable energy. Focus Study 6.1 briefly explores the wind­power resource.
◀Figure 6.16 Temperature and pressure patterns for daytime sea breezes and nighttime land breezes.
Oceanic Currents
The atmospheric and oceanic sys­ tems are intimately connected in that the driving force for ocean currents is the frictional drag of the winds. Also important in shaping ocean cur­ rents is the interplay of the Coriolis force, density differences caused by temperature and salinity, the config­ uration of the continents and ocean floor, and the astronomical forces that cause tides.
Surface Currents
Figure 6.18 portrays the general pat­ terns of major ocean currents. Be­ cause ocean currents flow over long distances, the Coriolis force deflects them. However, their pattern of de­ flection is not as tightly circular as that of the atmosphere. Compare this ocean­current map with the map showing Earth’s pressure sys­ tems (see Figure 6.10), and you can see that ocean currents are driven by the atmospheric circulation around subtropical high­pressure cells in both hemispheres. The oceanic circulation systems are known as gyres and generally appear to be off­ set toward the western side of each
ocean basin. Remember, in the Northern Hemisphere, winds and ocean currents move clockwise about high­ pressure cells; in the Southern Hemisphere, circulation is counterclockwise, as shown on the map. You saw in Geosystems Now how these currents guided an oil­drilling platform to Tristan da Cunha, where it ran aground.
Examples of Gyre Circulation In 1992, a child at Dana Point, California (33.5° N), a small seaside community south of Los Angeles, placed a letter in a glass juice bot­ tle and tossed it into the waves, where it entered the vast clockwise­circulating gyre around the Pacific High (Figure 6.19). Three years passed as ocean currents carried the message in a bottle to the white sands of Mogmog, a small island in Micronesia (7° N). Imagine the journey of that note from California—travelling through storms and calms, clear moonlit nights and typhoons.
In January 1994, a powerful storm ravaged a con­ tainer ship from Hong Kong loaded with toys and other goods. One of the containers on board split apart in the
OFFSHORE BREEZE
Cooler air is drawn offshore
Heated air rises over relatively warmer water
Higher temperature (lower pressure)
Lower temperature (higher pressure)
CRITICALthinking 6.3
Construct Your own Wind-Power Assessment Report
go to www.canwea.ca/, www.awea.org/ and www.ewea .org/, the websites of the Canadian Wind energy associa- tion, the american Wind energy association, and the eu- ropean Wind energy association, respectively. Sample the materials presented and make your own assessment of the potential for wind-generated electricity, the reasons for de- lays in development and implementation, and the economic pros and cons. Propose a brief action plan for the future of this resource. •