INTRODUCTION TO PHYSICAL GEOGRAPHY
Why is dry skin a winter affliction?
Have you ever noticed how your skin will itch in the winter, especially when it's really cold outside? Dry skin and chapped lips are the result of dry air literally sucking the moisture out of your cells. But why does it happen in the winter? There is dry air in the summer, too. Yes, but not nearly so dry as it is in the winter.
I. Water vapor in the air
A. Solubility of water
1. Relative humidity
2. Effect of temperature on absolute and relative humidity
B. Using the graph to predict effects of temperature change on humidity
1. Understanding winter dry skin
C. Predicting the effects of air movement on humidity
1. Adiabatic heating and cooling
a. Lapse rates
2. Predicting rain shadows
a. Downwind from cold currents
b. Downwind from mountains
Objectives/Questions:
1. Use the graph on page 80 of Strahler and Strahler that shows the effect of temperature on absolute humidity in saturated air to determine a. the absolute humidity in saturated air at 10, 15, and 20° C. b. the relative humidity of saturated air at 15 ° C. c. the relative humidity of 20° C air that has 10 g of H2O/kg of air.
2. Use the graph of explain what happens to the humidity of the air in 1c if temperature were to increase. If temperature were to decrease.
3. Use the graph to explain why the air in your house is much dryer in the winter than it is in the summer.
4. Condensation releases energy. What affect does this have on the lapse rate for rising air?
5. San Francisco, CA typically enjoys west winds blowing of the a Pacific Ocean that is cooler than the land in the summer. Explain why this means there is little summer rain in San Francisco.
6. Winter storms moving toward Philadelphia from Ohio rarely bring much
snow to Philadelphia even though the air is cold. Use the topography of
the Pa to explain why this is true.