Study Guide (lecture # 19)

Book pages: 177-204, 210-217

Review:

• eddy life cycle (Chap. 7.3.2)
• explanation of: jet entrance, then jet exit regions (Chap. 6.5)

Today's topics:

• Review: momentum & energy flow; jet stream variations, satellite loop interpretation

Jargon:

+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

Review:

I. Course Started with simple, "imaginary" circulations:

• interpretation based on general physical concepts
• progressively greater complexity revealed

• adds quantitative information to our description
• looked at basic cycle first
  (symbols >, <, /\, and \/ are intended to be arrow heads showing direction of energy flow)
  
  solar input --- > PE --- conversion --- > KE -- > friction
  . . . . . . . . . . . . .. |
  . . . . . . . . . . . .. .\/ longwave radiation .

  
  solar input --- > APE --- conversion --- > KE -- > friction
  . . . . . . . . . . . . . . /\
  . . . . . . . . . . . . . .. | .longwave radiation .

• standard 4-box energy diagram
  • though APE is 1000 times smaller than PE, APE is important
  • splits APE and KE into zonal mean and eddy parts
  • provides formulas for energy conversions
  • lumps together sources and sinks of radiant energy, of westerly momentum
• momentum flow:
  • 8 steps: from tropical source at surface to midlatitude sink
  • See web site: Summary of Momentum Cycle
• total energy flow:
  • momentum and KE strongly related
  • heat and APE strongly related
  • 8 analogous steps in APE flow: from tropical solar source to higher latitude sink
  • See web site: Summary of Energy Flow

• Needed to examine nonzonal observations
  • important events grouped into 5 (partly overlapping) geographic categories:
    1. near the east coasts of continents (land/sea contrast)
    2. near subtropical west coasts (land/sea contrast) (includes deserts)
    3. tropical land masses (land/sea contrast)
    4. major mountainous areas
    5. along midlatitude frontal cyclone tracks (differs from 1. in S. Hemisphere)
• Kuo-Eliassen equation:
  • looked at how eddies (and diabatic processes) result in Hadley and Ferrel cells
  • eddy heat and momentum fluxes contrary to thermal wind balance
  • ageostrophic circulation set up to maintain thermal wind balance
• Eddy life cycles:
  • mean flow variations create preferred regions for eddy development, decay, etc.
  • geographic distribution in observations results
• Jet stream variations:
  • need Kuo-Eliassen and life cycles information to understand the jet maxima
  • also linked to tropical convection (forms tropical anticyclone)
  • Why is the jet exit region also where the eddies have the greatest momentum convergence? (Answer: because the eddies create opposing advection of planetary angular momentum, too.)
  • summary diagram(s) fig 6.21, (Also: Namias & Clapp figure if time permits)

1. Amazon deforestation
   • The water mass comprising the Hadley cell precipitation is locally recycled as well as imported
   • In Amazon basin more than half the rainfall is from locally evaporated moisture. (problem set #8, 1998)
   • Removing the trees alters the surface energy budget.
   • Assuming that a "grass covered" surface dries out unlike a "rainforest covered" surface, then:
     • albedo increases: less solar energy absorbed
     • evaporation decreases: less precipitation, possibly higher surface temperatures since less latent heat flux in surface energy budget
     • warning:
       • some models show these changes, but not all.
       • effects are interactive. For example: less precipitation probably means fewer clouds, so the albedo changes are not "simple"

2. 1997-98 el nino: the atmosphere makes a sensitivity experiment! Note these connections seen earlier in the course:
   • ICZ convection enhanced where warmest water is (mentioned before; see Chapter 6.5 if you want further information). That leads to:
   • A divergent circulation creates a streamfunction anomaly pattern creating an upper level anticyclone (application of Rossby wave source concept) in the subtropics. That leads to:
   • Jet stream and thus the storm track elongated eastward, further across the Pacific than usual. (ergo: above normal precipitation here in California).

3. interpretation of a satellite loop for the tropical Pacific: January 1979
   • ICZ convection not a continuous band
   • high-cloud bands streaming out of convection
     • “Hadley” circulation
     • these merge with subtropical jet (sharp polar-side boundary)
   • tilted trough
     • enhances low latitude convergence & convective instability
     • aids polward momentum transport
   • Schematic upper flow deduced:
     double slashes show wind directions (from NW or from SW)
     <-- is intended to be easterly motion.
     But => is intended to mean: "implies"

NH Hadley . . . upper trough . . .. . . . . . /^| . . streaky - jet cirrus, sharp N edge of cloud band
. . . . low level NW \_/ winds . . . . . ./^| . NH Hadley cell
. . . . . . . . .\_/ . . . . . . . . . . . . . /^| . { convect. cloud }
. . . . . . . { low level convergence => convection } . . . . . . . . <-- low level easterlies
EQ . . . . . . . .{ conv. cloud } . . . . . . . . . . . . . . . . . . . . . . . . . <-- . . . . . . . . EQ
. . . . . . . . . . . . .{ cloud band } . . /^|
. . . . . . . . . . . . . . . . . . { SPCZ band } . /^|
SH Hadley cell . . . . . . . . . . . .{ cloud band }