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: