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Lecture 7 (10/21) Hurricanes and Tropical Meteorology Tropical Meteorology Anything between about 30N and 30S in latitude Or between Tropic of Cancer (23.5N) and Tropic of Capricorn(23.5S) Fuzzy definition Radiation budget > 0 in tropics Job of tropics = export heat poleward

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lecture 7 10 21

Lecture 7 (10/21)

Hurricanes and

Tropical Meteorology

tropical meteorology
Tropical Meteorology
  • Anything between about 30N and 30S in latitude
  • Or between Tropic of Cancer (23.5N) and Tropic of Capricorn(23.5S)
  • Fuzzy definition
  • Radiation budget > 0 in tropics
  • Job of tropics = export heat poleward
tropical meteorology3
Tropical Meteorology
  • Very difficult compared to mid-latitudes
  • Can’t just measure pressure and get an approximate wind field
  • Geostophic Balance - doesn’t happen in in tropics
  • Effects of Earth’s rotation not a big player (Coriolis force is small)
  • Try to measure convergence (winds coming together and divergence- winds pulling apart) to deduce areas of upward motion
other problems
Other Problems
  • Lack of data in tropics
  • Most of area is not covered with land so less observations
  • Countries with less advanced obs networks
  • Best sources for winds are: aircraft reports, wind profilers, reconnaissance flights, satellite-derived wind reports (cloud-tagging)
tropical cyclone classification
Tropical Cyclone Classification
  • TC’s form from a wave or disturbance
  • Trop disturbance = any area of “disturbed weather” ex: stalled out front
  • Trop wave = elongated area of low pressure (just a trough). Go from East to West (direction of winds at these latitudes).
  • Trop depression = closed low (trough pinches off)
  • Trop storm = 39-73mph, hurricane=74+
strength versus intensity
Strength Versus Intensity
  • Intensity = core region (center to 100 km)
  • An increase in intensity = stronger max winds or lower minimum surface pressure
  • Intensity can change quickly
  • Strength = outer part of core
  • Associated with area weighted average wind speed outside of core
eyewall cycle
Eyewall Cycle
  • Happens in intense hurricanes
  • Closed rainbands form a bit outside eyewall and move towards eye
  • Old eye deteriorates from subsidence (sinking air) induced by rainband
  • Closed rainband becomes new eyewall (most intense when eyewall is well defined)
  • Intensity changes during this but not strength
  • Whole cycle repeats itself
eyewalls rainbands
Eyewalls & Rainbands
  • Region of clouds/intense rain/strongest winds that seperates sinking air in eye from rest of storm
  • Typically not vertical (45 deg slope = common)
  • Rainbands = stronger areas of rain with higher clouds between them
  • Sometimes, tornadic supercells will form in rainbands as storm hits land (b/c of added friction)
inflow and outflow
Inflow and Outflow
  • Inflow in a TC happens near ocean’s surface (under clouds) in planetary boundary layer
  • Little known about hurricane inflow
  • Outflow = usually anticyclonic aloft (upper-level high)
  • Anticyclonic outflow helps push out the stable “exhaust” of a hurricane
fun facts
Fun Facts
  • Anticyclonic outflow (almost) never displaced toward equatorward side
  • TC’s need 80 degree Fahrenheit water
  • TC’s need deep, warm water too (winds stir it up)
  • recurvature = term for TC switching from Northeastward to Northwestward movement
  • Usually means the peak for the storm - starts to decay after that
  • Bill Gray at CSU = hurricane guru - uses climatology and old navy radiosonde data to come up with theory/predictions

FAQ’s from the National Hurricane Center

http://www.aoml.noaa.gov/hrd/tcfaq/tcfaqHED.html (G12 & D7 on FAQ’s)

Current Satellite Loops


Tropical model data output

http://www.essc.psu.edu/~rhart/tcgengifs/ (GFDL)

The coolest website ever (shows movie of enhanced satellite imagery of Michelle) (need high speed connection) http://rsd.gsfc.nasa.gov/pub/goes/QTmovies/0111.michelle.mov

for next time
For Next time:
  • Mid-semester gift. No reading assignment. We will be discussing Radar next week and the book does not have anything useful to read about it.
  • However, still be sure to do Homework 7 (Hurricanes and Tropical Meteorology)
  • We will still have the quiz next week