physical geography lecture 08 - precipitation, air masses, and storms 110216
TRANSCRIPT
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Physical Geography
Chapters 5 & 6:Precipitation, Air Masses,
Storms, and other fun stuff
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Formation of Precipitation:The Bergeron Process
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The Collision-coalescence process
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Some Different Forms of Precipitation
• Rain– Drizzle vs. showers
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Some Different Forms of Precipitation
• Snow• Sleet• Glaze (ice storm)
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Hail
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The Formation of Hail
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The Formation of Hail
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Global Precipitation
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Global Precipitation:The ITCZ Connection
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Precipitation in the U.S.
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What Is An Air Mass?A large parcel of air with
characteristics distinguishing it from surrounding air1000 mi (1600 km) across,
several miles deepConditions of temp., humidity,
stability consistent horizontally at any altitude
Moves as a coherent whole, not easily torn apart by local turbulence
Source region: Where an air mass originates
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Source Regions Extensive, physically uniform surface area High or low latitude
Not found in the midlatitudes (too much atmospheric activity) High pressure zones are common source regions
(because air sinks, stays close to the ground, where it picks up surface characteristics)
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Air Mass Movement & Modification
Once an air mass moves, it influences the regions it enters
It is also influenced by those regions, especially in its lower section, closest to the ground
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Buffalo, NY (Dec., 2001)--Nearly seven feet of lake effect snow fell in 5 days
Areas commonly affectedaround the Great Lakes
Lake-effect snow:cP air crossing warmer water
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Air Mass ClassificationLatitude
A = arctic/antarcticP = polarT = tropicalE = equatorial
Surface Conditionsm = maritimec = continental
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Major Air Mass Source Regions
(c)AmPcPmTcT(m)E
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Air Masses of North America
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So what happens when these air masses meet???
They start frontin’.
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Frontal lifting
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Movement of a Warm Front
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Warm Front: Development
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Movement of a Cold Front
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Cold Front: Development
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Comparison: Note the shapeof the frontal boundary
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Stationary Front
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Occluded Front
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Fronts on a Weather Map
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Putting it together:Note line A – A’
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A cross section along line A – A’ (from the map on the previous slide)
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Real-World Application:An Atlantic Storm
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Life-cycle of a Midlatitude Cyclone
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A Hypothetical Weather Map(note the alternating Highs and Lows…)
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How do theUpper-level Winds Move?
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Major Midlatitude Disturbances
Midlatitudes are the most dynamic weather regionWhere polar and tropical air masses meet and mix
Midlatitude cyclones(a.k.a. depressions, lows, wave cyclones)Large low pressure systems (1000+ miles across)
moving from west to east in the region of the Westerlies (35º to 70º N and S latitude)
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Characteristic weather changes with the passage of a cold front: Sharp temp. drop as the front approaches As the front approaches, wind direction is southerly After the front passes, wind shifts to more northerly
(opposite for the Southern Hemisphere) Air pressure drops as the front approaches, rises
after it passes Clear skies, followed by clouds and precip. along
the edge of the front, then colder with clear skies again as the front passes
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Mapping it out:
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Midlatitude Anticyclones
High pressure systems moving west to eastNo frontsSubsidenceClear, dry weatherCold in winterMay stagnate, stalling other weather
systems behind them
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Now on to the fun stuff!
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Lightning
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Lightning
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Thunder
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Tornadoes
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Tornado formation
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4949
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Tropical Disturbances
Tropical Depression - winds up to 38 mphTropical Storm - winds 39 - 73 mphHurricane - winds 74+ mph
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Hurricanes
Four different names for the same event:
HurricaneTyphoonCyclones, tropical cyclonesBaguios
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Hurricane Origins Form in tropical and subtropical zones approx. 8 to 15 N or S
latitude Rarely form within 3 N or S of equator (no Coriolis force), rarely
cross it Tend to form in or just poleward of the ITCZ Tend to form in late summer and fall (warmest sea sfc. temps.) Storm’s low pressure cell feeds off warm sea sfc. temps. (up to
81F!) Gains energy from release of latent heat of condensation during
intense precipitation Always form over oceans Do not / rarely form in the south Atlantic or southeast Pacific
because the water is too cold and air pressure too high Storm intensity lessens as it gains latitude (into cooler waters) or
moves over land
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Hurricanes
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Hurricane Tracking
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Pressure Signature of a Hurricane
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Hurricane Structure
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Hurricane Katrina making landfall
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Storm Surge
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Storm surge damage in Galveston, TX from Hurricane Ike (Category 2)