1 / 33

Session 2, Unit 3 Atmospheric Thermodynamics

Session 2, Unit 3 Atmospheric Thermodynamics. Ideal Gas Law. Various forms. Hydrostatic Equation. Air density change with atmospheric pressure. First Law of Thermodynamics. For a body of unit mass dq=Differential increment of heat added to the body

jadzia
Download Presentation

Session 2, Unit 3 Atmospheric Thermodynamics

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Session 2, Unit 3Atmospheric Thermodynamics

  2. Ideal Gas Law • Various forms

  3. Hydrostatic Equation • Air density change with atmospheric pressure

  4. First Law of Thermodynamics • For a body of unit mass • dq=Differential increment of heat added to the body • dw=Differential element of work done by the body • du=Differential increase in internal energy of the body

  5. Heat Capacity • At constant volume • At constant pressure

  6. Heat Capacity • Relationships

  7. Concept of an Air Parcel • An air parcel of infinitesimal dimensions that is assumed to be • Thermally insulated – adiabatic • Same pressure as the environmental air at the same level – in hydrostatic equilibrium • Moving slowly – kinetic energy is a negligible fraction of its total energy

  8. Adiabatic Process • Reversible adiabatic process of air

  9. Lapse Rate • Combine hydrostatic equation and ideal gas law • For adiabatic process

  10. Lapse Rate • Therefore dT/dz is Dry Adiabatic Lapse Rate (DALR)

  11. Dry Adiabatic Lapse Rate • Dry adiabatic lapse rate (DALR) • Or on a unit mass basis • Or the expression in the textbook:

  12. Lapse Rate • Effect of moisture Because Wet adiabatic lapse rate < DALR(temperature decreases slower as air parcel rises) • Condensation

  13. Lapse Rate • Superadiabatic lapse rate (e.g., 12oC/km) • Subadiabatic lapse rate (e.g., 8oC/km) • Atmospheric lapse rate • Factors that change atmospheric temperature profile • Standard atmosphere(lapse rate ~ 6.49 oC/km or 3.56 oF/1000 ft)

  14. Potential Temperature • Current state: T, P • Adiabatically change to: To, Po • Set Po = 1000 mb, To is potential temperature  • If an air parcel is subject to only adiabatic transformation,  remains constant • Potential temperature gradient

  15. Session 2, Unit 4Turbulence and MixingAir Pollution Climatology

  16. Atmospheric Turbulence • Turbulent flows – irregular, random, and cannot be accurately predicted • Eddies (or swirls) – Macroscopic random fluctuations from the “average” flow • Thermal eddies • Convection • Mechanical eddies • Shear forces produced when air moves across a rough surface

  17. Lapse Rate and Stability • Neutral • Stable • Unstable

  18. Richardson Number and Stability • Stability parameter • Richardson number • Stable • Neutral • Unstable

  19. Stability Classification Schemes • Pasquill-Gifford Stability Classification • Determined based on • Surface wind • Insolation • Six classes: A through F • Turner’s Stability Classification • Determined based on • Wind speed • Net radiation index • Seven classes • Feasible to computerize

  20. Inversions • Definition • Types • Radiation inversion • Evaporation inversion • Advection inversion • Frontal inversion • Subsidence inversion • Fumigation

  21. Planetary Boundary Layer • Turbulent layer created by a drag on atmosphere by the earth’s surface • Also referred to as mixing height • Inversion may determine mixing height

  22. Planetary Boundary Layer • Neutral conditions • Mixing height • Increased wind speed and surface roughness cause higher h.

  23. Planetary Boundary Layer • Unstable conditions • Mixing height

  24. Planetary Boundary Layer • Stable conditions • Mixing height

  25. Surface Layer • Fluxes of momentum, heat, and moisture remain constant • About lower 10% of mixing layer

  26. Surface Layer • Monin-Obukhov length • Monin-Obukhov length and stability classes

  27. Surface Layer Wind Structure • Neutral air

  28. Surface Layer Wind Structure • Unstable and stable air

  29. Friction Velocity • Measurements of wind speed at multiple levels can be used to determine both u* and z0

  30. Power Law for Wind Profile • Wind profile power law • Value of p

  31. Estimation of Monin-Obukhov Length • For unstable air • For stable air • Bulk Richardson Number

  32. Air Pollution Climatology • Meteorology vs. climatology • Meteorological measurements and surveys • Pollution potential-low level inversion frequency in US

  33. Air Pollution Climatology • Mean maximum mixing height determined by • Morning temperature sounding • Maximum daytime temperature • DALR • Stability wind rose

More Related