Forecast Question:
Will a severe thunderstorm develop today? Or not?
Having a solid understanding of atmospheric thermodynamics helps forecasters answer this question every day…
Thermodynamics M. D. Eastin

Atmospheric Vertical Structure &
Thunderstorms
 Vertical Structure
 Thunderstorms
 Single Cell
 Multicell
 Supercell
 Importance of Thermodynamics
Thermodynamics M. D. Eastin

Atmospheric Vertical Structure
Standard Atmosphere:
• The vertical variability of pressure and density is much larger than the horizontal and temporal variations of these quantities
• Earth’s atmosphere extends
>150 km above sea level
• Half the mass of the atmosphere lies within the lowest ~6.0 km above mean sea level (MSL)
• 99% of the mass lies within the lowest 30 km above MSL
Thermodynamics M. D. Eastin

Atmospheric Vertical Structure
Standard Atmosphere:
• Vertical distribution of temperature can be divided into four distinct layers
• The troposphere accounts for
>80% of the mass, nearly all of the water vapor, clouds and precipitation in the Earth’s atmosphere
Thermodynamics M. D. Eastin

Atmospheric Vertical Structure
Standard Atmosphere:
• Relatively little mixing occurs between the ozone rich stratospheric air and the moist, ozone-poor tropospheric air
• The troposphere and stratosphere together account for 99.9% of the atmospheric mass
Thermodynamics M. D. Eastin

Atmospheric Vertical Structure
Standard Atmosphere:
• Mesosphere is the region where aurora borealis are sometimes observed
Thermodynamics M. D. Eastin

Atmospheric Vertical Structure
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)
Thermodynamics M. D. Eastin

Atmospheric Vertical Structure
Standard Atmosphere:
• The changes in temperature with height are very important for driving vertical motions in the atmosphere
• Below the tropopause, pressure and density decrease with height more rapidly in cold layers than in warm layers
• We will soon learn why soon
• These differences between cold and warm layers are critical for the development of thunderstorms
Thermodynamics M. D. Eastin

Thunderstorms
Why do forecasters worry about thunderstorms?
• Flash Floods
• Large Hail
• Strong winds
• Lightning
• Tornadoes
• Change people’s daily plans
• Damage homes and towns
• Influence local economies
Thermodynamics M. D. Eastin

Thunderstorms
What are the important ingredients for thunderstorm development?
Thermodynamics M. D. Eastin

Thunderstorms
Why do thunderstorms differ in size, shape, and longevity?
Thermodynamics M. D. Eastin

Thunderstorms
Three Primary Types:
1.
Single Cell (or “air mass”)
2.
Multi-cell (e.g., squall lines)
3.
Supercells
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)
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
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 moisture and heat
• Often produce large hail and flash floods
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
Thermodynamics M. D. Eastin

Thunderstorms
Supercell Thunderstorms:
Thermodynamics M. D. Eastin

Thunderstorms
Supercell Thunderstorms:
Thermodynamics M. D. Eastin

Thermodynamics M. D. Eastin

Importance of Thermodynamics
• All thunderstorms are driven 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…
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)
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.
Thermodynamics M. D. Eastin