Science Tutorial TEK 8.10A: Solar Energy & Convection

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1 Name: Teacher: Pd. Date: Science Tutrial TEK 8.10A: Slar Energy & Cnvectin TEK 8.10A: Recgnize that the Sun prvides the energy that drives cnvectin within the atmsphere and ceans, prducing winds and cean currents. Energy frm the Sun travels thrugh space t Earth as radiant (electrmagnetic) energy. This frm f energy des nt need matter t be transferred frm ne place t anther. When radiant energy reaches Earth s atmsphere and the surface f Earth, it is either absrbed and cnverted t thermal energy, r reflected back t space. Abut 50% is absrbed and cnverted at the Earth s surface, and 15% is absrbed and cnverted by the Earth s atmsphere. The rest (35%) is reflected back t space and thus des nt heat the Earth. The mlecules in the matter absrbing the radiant energy begin t vibrate faster what we sense as heat. Nt all substances are heated by radiant energy. Mst f the gases in the atmsphere, such as nitrgen, xygen and argn (99.9% f the atmsphere) are transparent t radiant energy, and d nt heat up as the radiant energy passes thrugh them. Only the greenhuse gases such as water vapr, carbn dixide, methane, zne and CFCs gain thermal energy when struck with radiant energy. The Earth radiates its stred energy back t space as infrared radiatin, at almst the same rate as it absrbs radiant energy frm the Sun. In this way, the Earth s average temperature stays nearly cnstant. Hwever, during the last 100 years, the amunt f radiant energy that the Earth absrbs has risen slightly, because f the increased amunt f greenhuse gases in the atmsphere. This means that the Earth s average temperature is nw slwly rising. The lwest layer f the atmsphere, the trpsphere, is where all weather ccurs and almst all f Earth s life resides. Because mst f the radiant energy cming frm the Sun is absrbed at the Earth s surface, temperatures near the surface are usually the warmest. Air temperature in the trpsphere typically drps abut 6.5 C with every 1000 meters gain f elevatin. Thermal energy at the surface f the Earth can be transferred t air near the surface by the prcess f cnductin. In cnductin, the mlecules f the water r land at the surface vibrate and tuch the air mlecules next t them, causing the air mlecules t als vibrate. In this way, the air becmes as warm as the surface. When the air mlecules next t the Earth s surface becme warmer and vibrate mre quickly, they take up mre space (by buncing ff ne anther mre quickly) and thus becme less dense.

2 Accrding t the principle f buyancy, in a fluid (liquid r gas) medium, less dense materials flat upward and denser materials sink. This means that the air warmed at the surface f Earth rises, t be replaced by sinking cler air. This prcess f mving thermal energy is called cnvectin, the transfer f thermal energy by the flw f matter in a fluid. Cnvectin currents mve thermal energy thrugh the atmsphere bth n a lcal scale and glbally. Wind, a mass f mving air mlecules, is caused by cnvectin currents. Fr example, if yu have visited a beach n an cean r large lake during a sunny day, yu may have nticed that the breeze is almst always blwing ff the water and nt the land. This sea breeze is the result f lcal cnvectin currents. Sunlight heats the land mre quickly than the water, causing the air ver the land t rise. This rising air must be replaced by air blwing in ff the water. As the warm air rises, it cls ff and flws ut ver the water, t replace the air that flwed frm the water t the land. This circular flw f air is a cnvectin current. At night, the sea breeze is replaced by a land breeze, because the land cls ff very quickly nce the Sun sets, while the water stays at abut the same temperature and nw is warmer. Warm air rises ver the water, and is replaced by air flwing ff f the nw cler land. The diagrams belw shw the cnvectin currents f sea and land breezes. On a glbal scale, the wind blws in set patterns created by cnvectin. At the equatr, radiant energy hits the Earth mst directly, causing the warmest temperatures. Since warm air rises, there is a cntinuus upward flw f air at the equatr, with that air replaced by air at the surface n either side f the equatr. Once the warm air rises high in the atmsphere, it begins t cl, and flws bth nrth and suth in the upper atmsphere. At a latitude f abut 30 nrth and suth f the equatr, the nw cl air in the upper atmsphere sinks, and nce at the surface, flws back twards the equatr r twards the ple. The air at the grund generally flws bth twards the ple and the equatr, and warms since it is near the surface. At abut 60 N and S, the nw warm air rises again int the upper atmsphere, where it flws either twards the ple r equatr. At the ples, the nw cld air in the upper atmsphere sinks again, and flws back twards the equatr alng the grund. The result is a glbal wind pattern shwn n the next page.

3 Sinking Air at 90 N Westerlies Trade Winds Plar Easterlies Rising Air at 60 N Sinking Air at 30 N Rising Air at Equatr Rising Air at 60 N Sinking Air at 30 N Rising Air at Equatr Trade Winds In these glbal cnvectin currents, the wind that flws nrth r suth seems t turn t the right in the nrthern hemisphere, and t the left in the suthern hemisphere. This is because f the Crilis effect, the result f the Earth spinning under the winds, making it seem as if the winds were turning, when pltted in relatin t the grund. When the wind blws ver the cean fr lng perids f time in the same directin, fictin between the water and the air causes the water near the surface t flw in the same directin as the wind. Glbal surface wind currents (shwn in the straight red arrws belw) and surface cean currents flw in similar patterns. NOAA In the majr cean basins, the surface currents flw clckwise in the nrthern hemisphere and cunterclckwise in the suthern hemisphere. In the Atlantic Ocean, the very warm water f the Gulf Stream current flws frm the eastern United States twards nrthern Eurpe. As it flws nrtheastward, it cls and

4 gets mre salty, because f evapratin. When the nw cld and salty water reaches Greenland in the nrthern Atlantic Ocean, the water sinks because f its high density and flws suthward at the bttm f the Atlantic twards Antarctica. This cnvectin current is part f a wrldwide system f surface and deepwater currents. Practice Questins 1. All f the energy that causes weather n Earth cmes frm the, in the frm f energy. 2. Abut % f the radiant energy that reaches Earth is absrbed by the Earth s surface and abut % is absrbed by the atmsphere. When the radiant energy is absrbed, it is cnverted int energy. 3. Abut % f the radiant energy that reaches Earth is reflected back int space. Almst all f the radiant energy that is absrbed by Earth is eventually radiated back t space as radiatin, a frm f radiant energy. 4. The lwest level f the atmsphere, where all weather ccurs, is called the. 5. Thermal energy frm the surface f the Earth is transferred t the atmsphere by. 6. The prcess f, the transfer f thermal energy by the flw f matter in a fluid, causes wind because air rises and air sinks. 7. A ccurs at the cast f ceans and ther large water bdies during sunny days, because the heats up mre quickly than the, causing the wind t blw frm the t the. 8. A ccurs at the cast f ceans and ther large water bdies at night, because the cls dwn mre quickly than the, causing the wind t blw frm the t the. 9. On a glbal scale, warm air rises at the, cl air sinks at degrees nrth and suth latitude, warm air rises at degrees nrth and suth latitude, and cld air sinks at the nrth and suth.

5 10. Between the equatr and 30 N latitude, the wind generally blws frm a directin. 11. Between 30 N and 60 N latitude, the wind generally blws frm a directin. 12. Between 60 N and the Nrth Ple, the wind generally blws frm a directin. 13. Surface cean currents are pushed by glbal patterns. 14. Surface currents in the majr cean basins generally circulate in a directin in the nrthern hemisphere and in a directin in the suthern hemisphere. 15. Deep water cean currents are fed frm very, water which sinks because it is very dense.