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Conceptual Model of:

Conceptual Model of:. Orographic Cloudiness: Lee cloudiness Lee waves High lee cloudiness. Cloud Structure in Satellite Image. Lee Waves. Narrow cloud bands in the lee of the mountain ranges: width between approx. 4 - 30 Km Perpendicular to the wind direction

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Conceptual Model of:

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  1. Conceptual Model of: Orographic Cloudiness:Lee cloudiness Lee waves High lee cloudiness

  2. Cloud Structure in Satellite Image

  3. Lee Waves • Narrow cloud bands in the lee of the mountain ranges: width between approx. 4 - 30 Km • Perpendicular to the wind direction • Easily visible in VIS: white; only dark grey in IR and only visible if broad enough

  4. High Lee Cloud • Ci shields in the lee of the mountain range • Bright in IR only translucent grey in VIS • Is blown downstream with the upper level wind: • Large extensions can occur (up to 1000s kms) • Can be detached from mountain chain • Life duration is several hours.

  5. Superposition of both lee cloud types

  6. lee

  7. high lee

  8. lee lee high lee

  9. Meteorological - Physical Background

  10. Conditions for the development of lee cloud • Air flowing perpendicular onto a mountain range is forced to rise • If the air is stable: • begins to oscillate in the lee • dependant on different conditions: • stability, wind speed, dimension of the mountains. • Internal gravity waves: • lower layers: short wave length: parallel cloud lines • higher layers: longer wave length: high lee cloudiness

  11. Some parameters describing the process • Brunt - Vaisala Frequency • N**2 = g/T (dT/dz + g/cp) • thresholds for stability (N2>0 - stable) • Scorer Parameter • l(z) = N(z)/U(z) • Stability combined with characteristic of wind field (U: wind perpendicular to mountains on windward side) • Waves are formed at small values • Critical mountain width • L > 2π U/N: lee waves can be formed

  12. Key Parameters

  13. Relevant numerical parameters and their typical distribution • Wind direction must have a component perpendicular to the mountain range • Wind speed increases with height • Stable layer

  14. Relevant numerical parameters and their typical distribution • High lee cloudiness occurs preferably on the anticyclonic jet side cyclonic anti- cyclonic

  15. cyclonic anticyclonic Carpathian

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