1. Weather: A study in variables Pressure

2. Variable Review: Atmosphere - Structure  Consists of four major layers (top to bottom)  Thermosphere  Mesosphere  Stratosphere  Troposphere - where we live & weather happens  Mnemonic: Too Many Stupid Tests  As you move upward from the surface,  Pressure decreases in each layer  Temperature “zig zags” (  as you go up)  Consists of four major layers (top to bottom)  Thermosphere  Mesosphere  Stratosphere  Troposphere - where we live & weather happens  Mnemonic: Too Many Stupid Tests  As you move upward from the surface,  Pressure decreases in each layer  Temperature “zig zags” (  as you go up)

3. Heat transfer in atmosphere  Only 3 options:  Conduction  Convection  Radiation  Heat flow is ALWAYS from high energy to low energy  Heat energy measured with temperature  Only 3 options:  Conduction  Convection  Radiation  Heat flow is ALWAYS from high energy to low energy  Heat energy measured with temperature

4. Temperature affects air pressure Changing variables has effects!

5. Pressure Air pressure(book definition): the amount of force per unit area exerted by air.  Caused by gravity.  A measure of the force/weight of moving air molecules.  Measured with a barometer.  Milimeters of mercury (mmHg)  Milibars (mb)  One atmosphere at sea level = 14.7 psi Air pressure(book definition): the amount of force per unit area exerted by air.  Caused by gravity.  A measure of the force/weight of moving air molecules.  Measured with a barometer.  Milimeters of mercury (mmHg)  Milibars (mb)  One atmosphere at sea level = 14.7 psi

6. How does 14.7 psi feel? Two Volunteers? (must be prepared to summarize experience/observations) Two Volunteers? (must be prepared to summarize experience/observations)

7. Pressure  Gravity affects air pressure:  Keeps the atmosphere here! It causes air pressure! (Smaller planets/moons don’t have atmospheres due to LACK of gravity.)  Altitude affects air pressure:  Air pressure is affected by depth. The deeper we are in air, the more pressure there is.  Higher altitudes are like being in the “shallow end”.  Gravity affects air pressure:  Keeps the atmosphere here! It causes air pressure! (Smaller planets/moons don’t have atmospheres due to LACK of gravity.)  Altitude affects air pressure:  Air pressure is affected by depth. The deeper we are in air, the more pressure there is.  Higher altitudes are like being in the “shallow end”.

8. Pressure  The deeper we are in a fluid, the more pressure there is!  There are more molecules on top of you!  The deeper we are in a fluid, the more pressure there is!  There are more molecules on top of you!

9. Pressure: High/Low  High pressure =  there are more molecules bumping into a surface.  There are more molecules stacked on top of an area.  Low pressure =  There are less molecules bumping into a surface.  There are less molecules stacked on top of an area.  High pressure =  there are more molecules bumping into a surface.  There are more molecules stacked on top of an area.  Low pressure =  There are less molecules bumping into a surface.  There are less molecules stacked on top of an area.

10. How does temperature and water affect air pressure? Temperature Hypothesis: If temperature increases, then air pressure will _______________. Water Hypothesis: If water increases, then air pressure will ____________________. Temperature Hypothesis: If temperature increases, then air pressure will _______________. Water Hypothesis: If water increases, then air pressure will ____________________.

11. The effects of Water Vapor & Temperature  Temperature:  Higher temperature means less pressure.  Air is less dense and molecules are more spread out.  Lower temperature means more pressure.  Air is more dense and molecules are more compact.  Water vapor:  The more water vapor, the less pressure.  The less water vapor, the more pressure.  Water molecules weigh less(MW) than some gases.  Temperature:  Higher temperature means less pressure.  Air is less dense and molecules are more spread out.  Lower temperature means more pressure.  Air is more dense and molecules are more compact.  Water vapor:  The more water vapor, the less pressure.  The less water vapor, the more pressure.  Water molecules weigh less(MW) than some gases.

12. Pressure and Temperature  Hot fluids rise, cold fluids sink. We know that! (helps explain convection)  Warm temperatures mean molecules spread out.  Molecules are moving more. (fast dance tempo)  Lowers the density. Less dense means it rises.  Rising molecules means less of them bumping or stacking on the surface of the earth.  Warmer temperatures mean lower pressure.  Colder temperature = molecules huddling together(moving less) = high pressure. (slow dance tempo)  Hot fluids rise, cold fluids sink. We know that! (helps explain convection)  Warm temperatures mean molecules spread out.  Molecules are moving more. (fast dance tempo)  Lowers the density. Less dense means it rises.  Rising molecules means less of them bumping or stacking on the surface of the earth.  Warmer temperatures mean lower pressure.  Colder temperature = molecules huddling together(moving less) = high pressure. (slow dance tempo)

13. Wait a minute...  If warm air means less pressure, then why do we get colder rainy days with a low pressure system? And...  Why does a high pressure system seem to go with clear warm days?  We will discuss these answers as we add more variables!   If warm air means less pressure, then why do we get colder rainy days with a low pressure system? And...  Why does a high pressure system seem to go with clear warm days?  We will discuss these answers as we add more variables! 

14. Pressure and Wind  Nature abhors a vacuum!  Wind is a result of differences in air pressure.  Air will always move from areas of high pressure to areas of low pressure.(isobar map activity)  Isobars: lines connecting weather stations with equal pressure  Wind blows perpendicular to isobars.  The closer the isobars, the larger the pressure difference or pressure gradient.  The steeper the pressure gradient, the stronger/faster the winds in that area.  Nature abhors a vacuum!  Wind is a result of differences in air pressure.  Air will always move from areas of high pressure to areas of low pressure.(isobar map activity)  Isobars: lines connecting weather stations with equal pressure  Wind blows perpendicular to isobars.  The closer the isobars, the larger the pressure difference or pressure gradient.  The steeper the pressure gradient, the stronger/faster the winds in that area.

15. What causes differences in pressure?  Because the earth is heated unevenly, there will always be pressure differences.  So, as long as the sun will shine, the wind will blow.  Where on Earth, in general, is it the hottest?  Where on Earth, in general, is it the coldest?  Because the earth is heated unevenly, there will always be pressure differences.  So, as long as the sun will shine, the wind will blow.  Where on Earth, in general, is it the hottest?  Where on Earth, in general, is it the coldest?

16. Global Pressure Patterns Lowest Pressure Highest Pressure

17. Global Wind Patterns