conceptual model of:
DESCRIPTION
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 - PowerPoint PPT PresentationTRANSCRIPT
Conceptual Model of:Orographic Cloudiness:
Lee cloudinessLee 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
• Easily visible in VIS: white; only dark grey in IR and only visible if broad enough
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.
Superposition of both lee cloud types
lee
highlee
lee highlee
lee
Meteorological - Physical Background
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
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
Key Parameters
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
Relevant numerical parameters and their typical distribution
• High lee cloudiness occurs preferably on the anticyclonic jet side
cyclonic
anti-cyclonic
Carpathian
anticycloniccyclonic