Meteorological analysis of SCAVEX flights
Peter van Velthoven
Overview of flights 5-4-1: Stratosphere+low level clouds 11-4-1: Clouds northeast of trough (turning wind profile) 18-4-1: Stratosphere+cloud layer+perhaps outflow of uplift 25-4-1: Thin “föhn layer”, subsidence, lee waves 2-5-1: EW, uninteresting?, some North African air 3-5-1: Possibly föhn outflow, lee waves, air from West Atlantic
and North African lowermost troposphere. 4-5-1: Occasionally clouds? , some North African air 11-4-2: Large scale uplift in cloud system over North Italy 22-4-2: Profiles in frontal cloud band and trough (stratosphere) 23-4-2: High cloud band 24-4-2: EW flight below trough and through frontal clouds north
of Alps (with southward winds).
5 April 2001: stratosphere + low level clouds
5 April 2001
North-south X-section at 11 E of cloud cover
5 April 2001: NOAA 14h23
11 April 2001: clouds northeast of trough
11 April 2001 10h11-12h39
X-section versus time of cloud cover
11 April 2001
NS X-section of cloud coverat 10 E
projection!
18 April 2001: stratosphere+deep cloud layer
18 April 2001: stratosphere+cloud layer
Outflow north Italy?
25 April 2001: predicted föhn counteracted by subsidence
25 April 2001: predicted föhn was counteracted by subsidence
•High clouds above aircraft
•Thin ascending layer on southern slopes
•Lee waves
Vertical wind dp/dt (t)
•Possible föhn counteracted by subsidence
•East-west flight in large anticylone
•Profile just up to tropopause
•Some uplifted air from north Africa
2 May 2001
3 May 2001: possible föhn, lee waves
lee waves
föhn uplift
not enough high clouds
Some air from West Atlantic and North African lowermost troposphere
North Italy
4 May 2001: NS flight to ItalyRelatively cloud free? Over north Italy ascent but no deep clouds, except occa-sionally? Air from the North Africa BL.
North Italy profile
4 May 2001Occasionally clouds ... RH signature
4 May 2001: Air from the North African BL
Pressure
300 hPa
Trajectories 8h32-9h
11 April 2002
Large scale uplift in a cloud system over north Italy.
Some air from North Africa at low levels over north Italy.
North Italy
11 April 2002: Large scale uplift in a cloud system over north Italy.
“Föhn index”
22 April 2002
Profiles in frontal cloud band and trough (stratosphere)
IR -12 h
23 April 2002
Wind from northeast, high cloud band
IR 12h30
North Italy
24 April 2002
Below trough and frontal clouds
IR 14h
Föhn index predictions
18-4-2001 (northward flight, no profile in Italy, outflow?) (25-4-2001+subsidence) (2-5-2002+subsidence, east-west flight) 3-5-2001 (evidence for föhn clouds and precipitation) 11-4-2002 (interesting case)Southward föhn-like : (5-4-2001, small winds in Alps, only northward flight) 11-4-2001 (rather flow around Alps in LT, northward
wind component at 300 hPa, southward component at 850 hPa .... hence complex case)
24-4-2002 (east-west flight north of Alps)
Northward föhn-like: