ATM S 542 Synoptic Meteorology Overview

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ATM S 542 Synoptic Meteorology Overview
Gregory J. Hakim University of Washington,
Seattle, USA
www.atmos.washington.edu/hakim

• Vertical structure of the atmosphere.
• Atmospheric phenomena by horizontal scale.
• Potential vorticity.
• Tropopause.

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Overview

• Asymptotic methods
• expand dependent variables in a power series.
• small parameters needed.
• co-operative dialog between math physics is
  helpful.
• Role of asymptotics in atmosphere/ocean dynamics.
• simplified equations for solution
  understanding.
• Goals
• survey atmosphere/ocean structure phenomena.
• bias toward extratropics atmosphere.
• motivate asymptotic methods for these problems.

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Jets, stirring, organized structures waves,
vortices, convection.
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Atmospheric Structure

• Atmosphere very thin gas layer.
• depth ltltlt radius earth.
• Troposphere weather layer
• 10 km deep.
• 80 mass of atmosphere.
• all H2O vapor.
• Tropopause jet streams.
• wave guide.
• unstable cyclones.

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Atmospheric Energy Spectrum
Energy increases with horizontal length scale.
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Atmospheric Phenomena by Scale
Long, slow
Short, fast
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Jet streams planetary waves
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Jet Streams
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Jets Geostrophic Balance
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Jet stream vorticity
Waves particles
Waves Information flows through the medium by
radiation.
Particles (vortices) Information flows through
the medium by material transport.
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Cyclones Anticyclones
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Cyclone Structure

• Center has lowest pressure.
• geostrophic winds.
• Warm air moves poleward.
• and upward.
• warm front.
• Cold air moves equatorward.
• and downward.
• cold front.
• Clouds precipitation.
• comma shape.

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North American Cyclone
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Pacific Extratropical Cyclone

• Intense vortex
• Cold air shallow cellular convection
• Warm air stratiform cloud
• Sharp frontal boundaries

L
Zoom in on cold front
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Scale collapse at cold front rope
cloud---narrow line convection.
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CycloneAnticyclone Track Density
Hoskins Hodges (2002)
Primary tracks coincide with time-mean jet stream
locations.
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Jet-Level 2.56 d Variance
Maximum variance in storm tracks.
Hoskins Hodges (2002)
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Baroclinic Waves Packets
Cyclones anticyclones often compose waves
within larger wave packets.
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Baroclinic Waves
Wavelength 4000 km Phase speed 15 m/s. Period
3 d. Due to baroclinic instability. Organize
into packets.
Lim Wallace (1991)
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Wave Packet Phase Group Speed
phase speed
group speed
Chang Yu (1999)
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Wave Packet Tracks
Jet-stream wave guides. Storm-track recycling.
Hakim (2003)
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Mesoscale Phenomena Smaller Scales
Fronts frontal waves. Gravity
waves. Convection. Shear instabilities.
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Frontal Waves
Wakimoto Bosart (2000)
Paldor et al. (1994)
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Tropopause Shear Line Instability
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Tropopause Shear Line Instability
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Tropopause Shear Line Instability
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Tropopause Shear Line Instability
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Moist Convection
Strong vertical mixing
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KelvinHelmholtz Instability
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Gravity Waves
Wavelength 10 km
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Gravity Waves
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How do we better understand cyclones
anticyclones?
Need to filter other disturbances from the
equations
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Ertel Potential Vorticity
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Vertical Profile of PV

• Tropopause
• Well-defined as PV jump.
• Dynamics focus here.

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Tropopause Topography (pressure)

• High pressure over poles.
• Low pressure over tropics.
• Strong gradient in mid-latitudes.
• Stronger gradient in winter.

source Hoinka (1998)
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Height-Latitude Tropopause Profile
Hoinka (1998)