Refresher lecture objectives:

1
ATMS 305 Atmospheric Thermodynamics and Statics

• Refresher lecture objectives
• Review the vertical structure of the atmosphere
  (WH 1.3.4)
• Review thunderstorm classification and structure
  (WH 8.3.2)
• Review Newtons Second Law (WH 7.3.2) and
  introduce Polly Parcel

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ATMS 305 Review

• Our driving concern (as TV or Operational)
  weather forecasters
• Does a severe thunderstorm form on this day?
• Or not?

http//www.mesonet.org/sites/photos.php?siteRETR
dirne
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ATMS 305 Refresher

• Standard Atmosphere
• Vertical variability of pressure and density is
  much larger than horizontal and temporal
  variability of these quantities
• Half the mass of the atmosphere lies 5.5 km
  above sea level
• 99 of the mass of the atmosphere lies within the
  lowest 30 km above sea level

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ATMS 305 Refresher

• Standard Atmosphere
• Vertical distribution of temperature can be
  divided into four distinct layers
• Troposphere accounts for 80 of the mass and
  virtually all of the water vapor, clouds, and
  precipitation in the earths atmosphere

5
ATMS 305 Refresher

• Standard Atmosphere
• Relatively little mixing between dry, ozone-rich
  stratospheric air and relatively moist,
  ozone-poor tropospheric air
• The troposphere and stratosphere together account
  for about 99.9 of the atmospheric mass.

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ATMS 305 Refresher

• Standard Atmosphere
• Mesosphere region in which auroras are
  sometimes observed

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ATMS 305 Refresher

• Standard Atmosphere
• Thermosphere vertical temperature profile
  depends upon the amount of solar activity.

8
ATMS 305 Refresher

• Earths Atmosphere
• The ratio of pressure to density is larger in
  warm layers than in cold.
• Below the turbopause, pressure and density
  decrease with height more rapidly in cold layers
  than in warm layers.

We will soon be seeing why in coming lectures
These differences between warm and cold air are
VERY important in driving the circulations in our
atmosphere.
9
ATMS 305 Review
What, me worry?

• Why do we as forecasters need to worry about
  thunderstorms?

• flash floods
• large hail
• high winds
• lightning
• tornadoes

http//hypocrisytoday.com/alfred.htm
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ATMS 305 Refresher

• Important ingredients for thunderstorm
  development?

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ATMS 305 Refresher
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ATMS 305 Refresher
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ATMS 305 Refresher

• Important ingredients for thunderstorm
  development?

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ATMS 305 Refresher

• Thunderstorm types
• Air-mass (single cell)
• Multi-cell
• Squall line
• Right-moving
• Supercell

http//www.stormhunter.net/stormphotos/miscellaneo
us_pictures/mis-1/image3.htm
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ATMS 305 Refresher

• Air-mass (single cell)
• cumulus stage
• mature stage
• dissipating stage
• Fail-safe self-destruct mechanism

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ATMS 305 Refresher

• Multi-cell
• Squall line
• squall nickname related to gust front

http//www.cimms.ou.edu/doswell/microbursts/Figur
e_02.JPG, NOAA Photograph, taken by Irv Watson
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ATMS 305 Refresher

• Multi-cell
• Idealized, symmetric
• Overtakes environmental air at low-levels
• Cold downdraft air acts as wedge to force moist
  air upward
• Air rises spontaneously beyond a certain level
• Massive amounts of moisture are condensed out

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ATMS 305 Refresher

• Multi-cell
• Idealized (cont.)
• Modify large-scale environment by transporting
  vast quantities of warm, moist air from near the
  earths surface and replacing it with cool air
• Updrafts/downdrafts play complementary roles in
  idealized multi-cell storm maintenance

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ATMS 305 Refresher

• Multi-cell split
• Forms two supercell storms
• BL vortex tube is lifted by updraft (a)
• Pressure perturbations caused by counter-rotating
  vortices induce downdraft and split (b)
• Most NH supercell storms have CCW rotating
  updrafts not due to Coriolis force

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ATMS 305 Refresher

• Supercell
• Cyclonically rotating updraft
• Deep convection is favored under conditions of
  warm advection
• Warm advection veering winds
• Veering winds favor cyclonically rotating
  updrafts

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ATMS 305 Refresher

• Supercell
• schematic
• Strong asymmetry at low levels right-moving
  storms
• Bounded weak echo region (BWER), or vault,
  corresponds to the updraft
• Heaviest rain and hail occur in downdraft NW of
  axis of rotation

composite based on radar imagery
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ATMS 305 Refresher

• Supercell
• Low-level schematic
• Mesocyclone (M) resembles a miniature
  extratropical cyclone
• Most low-level inflow takes place east of M
• Vertical shear is enhanced by a factor of 3 or
  more in section AA due to the presence of the
  gust front

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ATMS 305 Refresher

• Supercell
• Self-amplifying process
• Vertical shear of the environmental air flowing
  into the storm strengthens the rotation of the
  updraft and the associated mesocyclone
• Existence of the mesocyclone amplifies the
  updraft and strengthens the gust front

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ATMS 305 Refresher

• Supercell
• Hook-shaped radar echo
• Updraft located in echo-free region (vault), 10
  m s-1
• Largest hail falls to the ground in a narrow band
  around the periphery of the vault

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ATMS 305 Refresher

• Supercell (cont.)
• Vertical shear of environmental flow is critical
• Maintains sloping updraft, essential for
  maintenance of storm
• Counterclockwise rotation of ascending air in
  more intense storms (mesocyclone)

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ATMS 305 Refresher

• Supercell (cont.)
• Trajectory A exits from storm through anvil.
  Small precipitation particle, updraft forces its
  exit
• Trajectories B C start as similar raindrops,
  end as different rain types (due to differences
  in accumulated mass).

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Thunderstorm A Diagram
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ATMS 305 Refresher

• Introducing
• Polly Parcel and

Newtons second law for motion in the vertical
following Polly Parcel.
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ATMS 305 Refresher

• Our T-storm refresher showed us the importance of
  updrafts (w gt 0) and of downdrafts (w lt 0).
• ATMS 305 will help us to forecast updrafts and
  downdrafts ? forecast Thunderstorms!!