Chapter 6. Atmospheric and Oceanic. Circulations. Circulations

Transcription

1 Chapter 6 Atmospheric and Oceanic Circulations Robert W. Christopherson Charlie Thomsen Winds: Transfer energy and mass (1) Balance energy equatorial energy surplus and polar energy deficit (2) Generate Earth weather pattern (3) Generate ocean currents (4) Dilute air pollutants (5) Supply vegetation with CO2 in the air. Wind is a vector varible Temperature is a scalar variable. Atmospheric and Oceanic Circulations Wind Essentials Driving Forces within the Atmosphere Atmospheric Patterns of Motion Oceanic Currents

2 Wind Essentials Air Pressure and Its Measurement Mercury barometer Aneroid barometer Wind: Description and Measurement Wind Anemometer Wind vane Global Winds Barometers History: Torricelli, Galileo s pupil, working on mine-draining problem. Partially emptied chamber Figure 6.2 Air Pressure Readings Figure 6.3

3 Wind Vane and Anemometer Figure 6.4 Driving Forces within the Atmosphere Pressure Gradient Force Coriolis Force Friction Force Gravity Pressure Gradient Force Without pressure gradient force, the air will not move, then there will be no Coriolis force, no friction force. Figure 6.7

4 Coriolis Force It deflects and anything that flies or flows across Earth surface: wind, airplane, ocean currents etc. Coriolis Force only changes the direction of movement, not the speed. It is always perpendicular to the direction of movement, to the right hand side on Northern Hemisphere. Figure 6.9 Pressure + Coriolis + Friction Pressure Gradient Force only Pressure Gradient+Coriolis+Friction Forces Pressure Gradient +Coriolis Forces Figure 6.8 Atmospheric Patterns of Motion Primary High-Pressure and Low-Pressure Areas Upper Atmospheric Circulation Local Winds Monsoonal Winds

5 General Atmospheric Circulation Figure 6.12 General Atmospheric Circulation Figure 6.12 Primary High-Pressure and Low-Pressure Areas Equatorial low-pressure trough Polar high-pressure cells Subtropical high-pressure cells Subpolar low-pressure cells

6 Equatorial Low-Pressure Trough Intertropical convergence zone (ITCZ) Clouds and rain Trade winds: The trade winds were named during the era of sail ships that carried trade across the seas. Global Barometric Pressure Icelandic Low Aleutian Low Hawaiian High Azores High Figure 6.10 Global Barometric Pressure Pacific high Bermuda high Figure 6.10

7 Wind Portrait of the Pacific Ocean Wind pattern derived from a radar scatterometer aboard Seasat on a day in September. Note: compare wind pattern and the visible earth below: Figure 6.6 June July ITCZ Figure 6.11 Constant Isobaric Surface Two ways to visualize pressure field: (1) Isobar on Earth surface (isoline of constant air pressure) (2) Constant Isobaric Surface: surface height of constant pressure described by the isoline of constant height (similar to topo maps) Figure 6.15

8 Upper Atmospheric Circulation Rossby waves Jet stream: a fast flowing narrow air currents in the upper atmosphere (tropopause: the transition between troposphere and stratosphere) Rossby Waves Figure 6.16 Jet Streams Figure 6.17

9 Local Winds Land-sea breezes Mountain-valley breezes Katabatic winds Land-Sea Breezes Figure 6.18 Mountain-Valley Breezes Katabatic Wind: A regional scale gravity driven wind, usually needs a high plateau to cool the air, and become dense and flow downslope. Figure 6.19

10 Monsoonal Winds Regional wind systems seasonally changes direction and intensity associated with changes temperature and precipitation. Figure 6.20 Oceanic Currents Function: Mixing sea water Surface warm water with deep cold water CO2 absorption Climate Biogeochemical processes: phytoplankton growth Driving force: the frictional drag of winds Thus we have an Atmosphere-Sea are coupled system. Once the current starts to move, the Coriolis force will kick in. Then there is friction between upper and lower water, the shear stress. Major Ocean Surface Currents Surface ocean currents are driven by air circulation around subtropical high pressure cells. Figure 6.21

11 Equatorial Currents/Western Intesificaitn Corresponding to trade winds on both sides of the Equator, these winds drives the surface current westward along the equator, called equatorial currents. The equatorial currents push water piles up against the eastern shores of the continent. This is called western intensification. The piled up water will go either up north or down south. The Gulf Stream is one caused by western intensification. Upwelling/Downwelling Currents Upwelling Currents: When surface water is swept away from a coast, an upwelling current occurs. This cool water generally is nutrient rich, e.g. Pacific Coast of North and South America Downwelling Currents: Accumulation of surface water (e.g. western end of equatorial current) can gravitates downward to generate a downwelling current. Figure 6.22 Deep-Ocean Thermohaline Circulation Thermahaline Circulation is caused by differences in density as a result of temperature and salinity gradients. Cold and saltier water is heavier, thus tends to sink, forming downwelling currents. Figure 6.22

12 End of Chapter 6 Geosystems 7e An Introduction to Physical Geography Robert W. Christopherson Charlie Thomsen