Rising and Sinking Air Lets take a Parcel

Rising and Sinking Air

Let’s take a Parcel of Air, like this…. In this parcel…. .

…Air Molecules Are Always Moving • Temperature: average speed of the molecules in our parcel • Density: how tightly packed the molecules are in our parcel

Temperature and Density • Warm temperatures make molecules move faster, so they spread out and the air in our parcel becomes less dense • Cool temperatures make the molecules slow down, so they get closer together and the air becomes more dense • So………………

• …. . Warm air is less dense than cooler air because the air molecules move faster and are further apart • So far, so good? ?

Now I Might Confuse You!

• If we take our parcel of air…. air

Rising Air • …and we place it at the surface of the Earth, it warms up…. up

• …eventually, it becomes less dense than the surrounding air and begins to rise, rise just like a….

If you take a hot air balloon ride, does atmospheric pressure increase or decrease as you go up?

• Just like the balloon…. • As the parcel rises, it enters a region where the surrounding air pressure is lower… lower • Less air pressure on the parcel allows the molecules inside to spread out even more…. • …so the parcel will expand as it rises

• …but the molecules exert energy to expand the parcel, so they lose heat in the process, and…. and • …Our parcel begins to cool…the more it expands, the more it cools Air that rises always expands and cools!

But Wait, There’s More!!! • Eventually the temperature of the air within that parcel drops all the way to the dew point temperature

• Once it reaches dew point, the water vapor in our parcel condenses into water droplets, and a cloud forms…. . forms • …Do water molecules absorb or release heat to evaporate? . . . • Do they absorb or release heat to condense back into water droplets? • During condensation, the heat stored in that vapor is released…. . released

• …the heat released causes the parcel of air to rise further because it is again warmer than the surrounding air…. air • …. as it rises, it cools even more, causing further condensation… condensation • …and pretty soon, you may get one of these------>>>>>

…. which produce this!

• The opposite is true for a parcel which sinks…. • It starts out cool and dense, but as it sinks it encounters higher pressure

• So, the parcel shrinks, which allows the molecules less space to move around…. • …. less space makes them crash into each other more and speed up…. • …. so the temperature of our parcel warms Air that sinks always warms by compression!

Temperature Change w/Altitude Rising Expansion Cooling Sinking Compression Warming Video