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Thermodynamics M. D. Eastin
Atmospheric Vertical Structure &
Thunderstorms
Forecast Question:
Will a severe thunderstorm develop
today? Or not?
Having a solid understanding of
atmospheric thermodynamics
helps forecasters answer this
question every day…
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Thermodynamics M. D. Eastin
Atmospheric Vertical Structure &
Thunderstorms
Outline:
Vertical Structure
Thunderstorms
Single Cell
Multicell
Supercell
Importance of Thermodynamics
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Thermodynamics M. D. Eastin
Standard Atmosphere:
• The vertical variability in pressure
and density are much larger than
the horizontal and temporal
variability in these quantities
• Earth’s atmosphere extends
>150 km above sea level (ASL)
• 50% of the atmospheric mass
lies within the lowest ~6 km
above mean sea level (MSL)
• 99% of the mass lies within the
lowest 30 km above MSL
Atmospheric Vertical Structure
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Thermodynamics M. D. Eastin
Standard Atmosphere:
• Vertical distribution of temperature
can be divided into 4 distinct layers
• Troposphere
• Stratosphere
• Mesosphere
• Thermosphere
• The troposphere accounts for
~80% of the mass and nearly
all water vapor, clouds,
and precipitation
Atmospheric Vertical Structure
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Thermodynamics M. D. Eastin
Standard Atmosphere:
• Very little mixing occurs between
the dry, ozone-rich stratosphere
and the moist, ozone-poor
troposphere
• Together, the troposphere and
stratosphere account for 99%
of all atmospheric mass
Atmospheric Vertical Structure
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Thermodynamics M. D. Eastin
Standard Atmosphere:
• Mesosphere is the region where
aurora borealis (Northern Lights)
are sometimes observed
Atmospheric Vertical Structure
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Thermodynamics M. D. Eastin
Standard Atmosphere:
• Temperatures in the thermosphere
are highly dependent on solar
activity (e.g. sunspots and flares)
and can reach very high values
• The International Space Station
maintains a stable orbit within this
atmospheric layer (at ~350 km)
Atmospheric Vertical Structure
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Thermodynamics M. D. Eastin
Standard Atmosphere:
• Changes in temperature with
height are very important for
atmospheric vertical motions
• Below the tropopause, pressure
and density decrease with height
more rapidly in cold layers than in
warm layers
• We will soon learn why
• These differences between cold
and warm layers are critical for
the development of thunderstorms
Atmospheric Vertical Structure
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Thermodynamics M. D. Eastin
Why do forecasters worry about thunderstorms?
• Flash Floods
• Large Hail
• Strong winds
• Lightning
• Tornadoes
Thunderstorms
• Change people’s daily plans
• Damage homes and towns
• Influence local economies
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Thermodynamics M. D. Eastin
What are the important ingredients for thunderstorm development?
Thunderstorms
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Thermodynamics M. D. Eastin
Why do thunderstorms differ in size, shape, and longevity?
Thunderstorms
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Thermodynamics M. D. Eastin
Three Primary Types:
1. Single Cell (or “air mass”)
2. Multicell (e.g., “squall lines”)
3. Supercells
Thunderstorms
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Thermodynamics M. D. Eastin
Thunderstorms
Single Cell Thunderstorms:
• Cumulus Stage (cloud dominated by updrafts)
• Mature Stage (both updrafts and downdrafts present)
• Dissipating stage (cloud dominated by downdrafts)
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Thermodynamics M. D. Eastin
Thunderstorms
Multi-Cell Thunderstorms:
• Composed of multiple single cells
• Updrafts and downdrafts work in concert to regularly develop new single
cell storms on a preferred flank of the storm
• Warm updrafts rise rapidly
• Cold downdrafts act as a wedge forcing warm moist air upward
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Thermodynamics M. D. Eastin
Thunderstorms
Multi-Cell Thunderstorms:
• Warm air can rise spontaneously above certain levels
• Enormous quantities of moisture are condensed out of the air
• Modify the large-scale environment by transporting heat and moisture
• Often produce large hail and flash floods
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Thermodynamics M. D. Eastin
Thunderstorms
Supercell Thunderstorms:
• Strongest and most dangerous
• Large Hail
• Lightning
• Strong Tornadoes
• Single rotating updraft
• Two prominent downdrafts
• Occur when very warm air
resides beneath very cold air
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Thermodynamics M. D. Eastin
Thunderstorms
Supercell Thunderstorms:
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Thermodynamics M. D. Eastin
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Thermodynamics M. D. Eastin
Importance of Thermodynamics
• All thunderstorms are “powered” by strong updrafts and downdrafts
• The magnitude and location of all vertical motions are the result of
vertical temperature differences
• All thunderstorms “condense out” large quantities of water vapor,
producing clouds and precipitation
• All thunderstorms impact society (and they do so on a daily basis…)
• Successful forecasts of thunderstorms requires a solid understanding
of atmospheric thermodynamics…
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Thermodynamics M. D. Eastin
Atmospheric Vertical Structure &
Thunderstorms
Summary:
• Vertical Structure (variations in density, pressure, and temperature)
• Thunderstorms (produce severe weather and impact daily life)
• Single-cells
• Multi-cells
• Supercells
• Importance of Thermodynamics (critical to forecasts)
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Thermodynamics M. D. Eastin
References
Bluestein, H. B, 1993: Synoptic-Dynamic Meteorology in Midlatitudes. Volume II: Observations and Theory of Weather
Systems. Oxford University Press, New York, 594 pp.
Byers, H. R., and R. R. Braham, Jr., 1949: The Thunderstorm. Supt. Of Documents, U.S. Government Printing Office,
Washington, D.C., 287 pp.
Houze, R. A. Jr., 1993: Cloud Dynamics, Academic Press, New York, 573 pp.
Lemon, L. R. , and C. A. Doswell, 1979: Severe thunderstorm evolution and mesocyclone structure as related to
tornadogenesis., Mon. Wea. Rev., 107, 1184–1197.
Markowski, P. M., and Y. Richardson, 2010: Mesoscale Meteorology in Midlatitudes, Wiley Publishing, 397 pp.
Petty, G. W., 2008: A First Course in Atmospheric Thermodynamics, Sundog Publishing, 336 pp.
Tsonis, A. A., 2007: An Introduction to Atmospheric Thermodynamics, Cambridge Press, 197 pp.
Wallace, J. M., and P. V. Hobbs, 1977: Atmospheric Science: An Introductory Survey, Academic Press, New York, 467 pp.
Weisman, M. L. , and J. B. Klemp, 1986: Characteristics of Isolated Convective Storms. Mesoscale Meteorology and
Forecasting, Ed: Peter S. Ray, American Meteorological Society, Boston, 331-358.