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Isentropic Analysis

N–S Cross section along 78°W. Isentropic Analysis. Potential temp, θ (K). Pressure (hPa). 30 April 2012 Heather M. Archambault. South. North. Why use potential temperature θ as a vertical coordinate?. Why use potential temperature θ as a vertical coordinate?.

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Isentropic Analysis

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  1. N–S Cross section along 78°W Isentropic Analysis Potential temp, θ(K) Pressure (hPa) 30 April 2012 Heather M. Archambault South North

  2. Why use potential temperature θas a vertical coordinate?

  3. Why use potential temperature θas a vertical coordinate? • Can visualize 3D atmospheric flow

  4. Why use potential temperature θas a vertical coordinate? • Can visualize 3D atmospheric flow • Can track moisture moisture moves along θ surfaces, not along p or Z surfaces

  5. Why use potential temperature θas a vertical coordinate? • Can visualize 3D atmospheric flow • Can track moisture moisture moves along θ surfaces, not along p or Z surfaces • Useful for “potential vorticity thinking”

  6. Why use potential temperature θas a vertical coordinate? • Can visualize 3D atmospheric flow • Can track moisture moisture moves along θ surfaces, not along p or Z surfaces • Useful for “potential vorticity thinking” • Can use vertical profile of θ to diagnose static stability, frontal zones

  7. Potential temperature definition The temperature that a fluid parcel would acquire if adiabatically brought to a standard reference pressure

  8. Why are θ surfaces called “isentropes”? • Relationship between entropy (s) andθ • If entropy is constant, so is θ (a constant entropy surface is isentropic surface)

  9. Need to understand vertical variation ofθ to use it as a vertical coordinate

  10. Need to understand vertical variation ofθ to use it as a vertical coordinate • Atmosphere is stable: θ increases with height

  11. Need to understand vertical variation ofθ to use it as a vertical coordinate • Atmosphere is stable: θ increases with height • Atmosphere is neutral: θ is constant with height

  12. Need to understand vertical variation ofθ to use it as a vertical coordinate • Atmosphere is stable: θ increases with height • Atmosphere is neutral: θ is constant with height • Atmosphere is unstable: θdecreases with height

  13. Static Stability • Assessed by vertical spacing of θ • The lower the static stability, the greater the spacing of θ in the vertical (and vice versa)

  14. Identifying warm and cold air • Unlike for p surfaces, θ slopes down toward warm air and up toward cold air

  15. Identifying warm and cold air • Unlike for p surfaces, θ slopes down toward warm air and up toward cold air Z θ1 θ2 Warm surface

  16. Identifying warm and cold air • Unlike for p surfaces, θ slopes down toward warm air and up toward cold air Z Z θ1 θ1 θ2 θ2 Warm Cold surface surface

  17. Frontal zones • Regions of sloped, highly compact θ N–S Cross section along 78°W Potential temp, θ(K) Pressure (hPa) South North

  18. Frontal zones • Regions of sloped, highly compact θ

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