GEO101IN Introduction to Weather and Climate February 27, 2005

1
GEO101IN Introduction to Weather and
ClimateFebruary 27, 2005

• Will it rain this afternoon?
• The North American monsoon
• Why the summer rains are hard to predict
• Guest Lecture Danny Lopez on the Rain Ceremony
• Worktime classworks 3,4 questions and answers
• Graphing data
• Heat, energy and work
• Storm systems
• Plans for class March 5th

2
Summer rainfall North American monsoon
Photo Aguado and Burt , Ch. 6

• Monsoon circulation winds change with the
  seasons
• Ingredients
• Summertime difference in land vs. ocean heating
• High humidity (dew point)
• Summertime daily surface heating

Photo http//meted.ucar.edu/ mesoprim/cape/print.
htm
3
Summertime difference in land vs. ocean heating

• Why does the land heat up more, and more rapidly,
  than the ocean?

4
Summertime difference in land vs. ocean heating

• Specific heat capacity Quantity of heat required
  to raise the temperature of a unit mass of a
  substance by 1 degree in temperature.
• Specific heat capacity of dry air 0.25
  calories/gramoC
• Specific heat capacity of granite rock 0.2
  calories/gramoC
• Specific heat capacity of pure water 1.0
  calories/gramoC
• Heat transfer equation The change in heat
  content of a substance is equal to its mass
  multiplied by its specific heat capacity,
  multiplied by the change in temperature it
  undergoes.

5
Summertime difference in land vs. ocean heating

• Summertime surface winds are driven by the
  difference in heating between ocean and land

6
High humidity must be available

• Dew point temperature at which air reaches
  saturation (rate of condensation of water
  droplets exceeds rate of evaporation)
• Where's the moisture coming from?

7
Summertime daily surface heatingcreates
conditions conducive to thunderstorms

• Strong heating of the atmosphere by the Sun from
  below
• Winds moving moist warm air up mountain slopes
• Rapid upward air motion fueled by latent
  heating...

8
Why else is moist air necessary?
Ascent of dry air
Ascent of moist air
Figures from Aguado and Burt (2004)

• Rapid upward air motion fueled by latent heating
• Heat released from condensation of liquid water
  keeps rising air warm, lowers density relative to
  dry air
• Moist air rises farther and cools faster than dry
  air
• Condensing water may fall as rain

9
Why is summer rainfall so unpredictable?
Rain likely...
Rain not likely...
Rain likely...
Cumulonimbus congestus, cumulus cloud photos from
Aguado and Burt (2004)

• Summer rainfall depends on all the factors being
  in place (Classwork Q. 4)
• Summertime heating, adequate moisture
• Southwesterly winds, rapid ascent of moist air
  fueled by latent heating
• Rapid cloud water droplet growth, inadequate
  re-evaporation near surface
• Complicating factors soil moisture, tropical
  storms, local conditions... Classwork Question 5

10
GEO101IN Introduction to Weather and
ClimateFebruary 27, 2005

• Will it rain this afternoon?
• The North American monsoon
• Why the summer rains are hard to predict
• Guest Lecture Danny Lopez on the Rain Ceremony
• Worktime classworks 3,4 questions and answers
• Graphing data
• Heat, energy and work
• Storm systems
• Plans for class March 5th

11
GEO101IN Introduction to Weather and
ClimateFebruary 27, 2005

• Will it rain this afternoon?
• The North American monsoon
• Why the summer rains are hard to predict
• Guest Lecture Danny Lopez on the Rain Ceremony
• Worktime classworks 3,4 questions and answers
• Graphing data
• Heat, energy and work
• Storm systems
• Plans for class March 5th

12
Next (March 5th)

• Review of major meteorological concepts
• Guest speaker on weather forecasting products
• Field trip to Tucson/University of Arizona
• Stay tuned for logistics
• Classwork forecasting exercise
• Readings AB 385-9, 401-2, 407-9
• Username geo101in
• Password tocc2005