The PV-perspective Part I Based partly on: Weather analysis and forecasting: Applying Satellite...
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Transcript of The PV-perspective Part I Based partly on: Weather analysis and forecasting: Applying Satellite...
The PV-perspective Part I
Based partly on:
Weather analysis and forecasting: Applying Satellite Water Vapor Imagery and Potential Vorticity Analysis
By Patrick Santurette and Christo Georgiev
Elsevier Academic Press
Storyline:
Why is PV weather relevant?
How can you read a PV chart
Link between WV imagery and PV
Certain “extreme” weather phenomena and their PV signature
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PV = (ζ θ + f )(−g∂θ
∂p)
vertical stabilityof the atmosphere
Ertel Potential Vorticity
vertical component of rel. vorticity potential temperature f planetary vorticity p pressureg gravitational constant
A measure of the rotation of an air mass
1
PV = *
€
PV = (ζ θ + f )(−g∂θ
∂p)
A measure of the rotation of an air mass
+ PV anomalies are associated with a cyclonic wind field
Ertel potential vorticity
f planetary vorticity vertical component of rel. vorticity potential temperature p pressureg gravitational constant
19
PV anomalies and the wind field
PV and wind - 12 Nov 1996 12UTC
2
0
PVU
6
Figures courtesy Linda Schlemmer
PVU
Alps Alps
€
PV = (ζ θ + f )(−g∂θ
∂p)
vertical stabilityof the atmosphere
+ PV anomalies indicate areas ofreduced vertical Stability underneath
Ertel potential vorticity
f planetary vorticity vertical component of rel. vorticity potential temperature p pressureg gravitational constant
22
Stability / CAPE (convective available potential energy)
100 200 500 1000 J/kg
© NERC Satellite Receiving Station Dundee
figures courtesy Linda Schlemmer
PV stre
amer
23
Alps
Alps
Cross-section
Vertical cross-section
shading: PVcontours: potential temperature
hPa
100
200
300
400
500
600
700
-40 -30 -20 -10 0 10 lon
Static stability
> 0 stable
< 0 unstable
colder
less stable
stable
€
∂∂z
€
∂∂z
CF
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
Funatsu and Waugh 2008
Santurette and Georgiev2005
2D
Jet
EW
3D
0 0.25 1 2 4 6 8 10 PVU
stratosphericair (high PV)
tropospheric air(low PV)
Pole
Alps
tropopause
MotivationA first look at instantaneous PV2
wind > 25m/s
Winter Summer
X X
-height of isentropes varies with season-latitude of intersection of dyn. TP with isentropes varies with season-daily plots might differ substantially from these zonal and seasonal mean plots
320K good in winter, 335K good in summer for mid-latitudes
310K
Nov. 1996
320K
Nov. 1996
330K
Nov. 1996
! Some features are cut-off on one level and connected on an other
340K
Nov. 1996
350K
Nov. 1996
Winter Summer-theta on PV2 mapse.g. from the University of Reading
! Problems in the tropics, not always uniquely defined -> tropopause folds
Theta on PV2
K
Tropopause height
30000 45000 60000 75000 90000 10500 12000 135000 [m2/s2]
[103 m]5 5.1 5.2 5.3 5.4 5.5 5.6 5.7 5.8 5.9 6
Geopotential height [m]
Comparison to geopotential height3
0 0.25 1 2 4 6 8 10
Potential vorticity [PVU]
[PVU]wind vectors vel > 25 m/s
Cross-section
Vertical cross-section
shading: PVcontours: potential temperature
hPa
100
200
300
400
500
600
700
-40 -30 -20 -10 0 10 lon
Static stability
> 0 stable
< 0 unstable
colder
less stable
stable
€
∂∂z
€
∂∂z
CF
0 0.25 1 2 4 6 8 10
Potential vorticity
wind vectors vel > 25 m/s
Thetae on 850 hPa
LL L L
2 10 18 26 34 42 50 58 66 [K]
SLP < 1005hPa, 5hPa contours
Link to surface fields4
cold and dry air
There is a clear relation between PV and water vapour imagery:
•A low tropopause can be identified in the WV imagery as a dark zone.
•As a first approximation, the tropopause can be regarded as a layer with high relative humidity, whereas the stratosphere is very dry, with low values of relative humidity.
•The measured radiation temperature will increase if the tropopause lowers. This is because the radiation, which is measured by the satellite, comes as a first approximation from the top of the moist troposphere.
•High radiation temperatures will result in dark areas in the WV imagery.
http://www.zamg.ac.at/docu/Manual/SatManu/main.htm
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
tropopause
stratosphere (dry)
stratosphere (dry)
troposphere (moist)
troposphere (moist)
tropopause
WV signal
WV signal
cross-section through atrough
cross-section through the jet
http://www.zamg.ac.at/docu/Manual/SatManu/main.htm
Geopotential
Tropopauseheight
Concept
TP heightblue
Upper-level PV signature of several (extreme) weatherevents
Schlans November 2002 Gondo October 2000
Heavy precipitation along the Alpine south-side
Example case: Schlans November 2002
IR
850hPa vel + rain
320K PV
16.11.2002
figures courtesyEvelyn Zenklusen
PV on 320KSLP
strong convective activityalong eastern flank
formation of low pressure systems
L
Floods in Algeria November 2001
cyclonic windfield which can reach the surface
wind on 850hPa
precipitation
IR meteosat
Kona lows
occurrence:from October until March in the subtropical central- and north Pacific
weather impact: strong rain fall, hail showers, land slides, flooding, storm winds, high surf, waterspouts and severe thunderstorms
Hawaii as a kona low reaches maui (John Fischer, 2002)
Slide courtesy Michael Graf
„kona low“ November 1996
figures courtesy Michael Graf
PV on 330K, SLP
PV on 330K, SLP GOES-9 IR
HI
HI
„kona low“ November 1996
PV on 330K, SLP GOES-9 IR
L
L
L
L
blocks identified as persistent upper-level low PV anomalies (Schwierz et al. 2004)
Blocking from a PV persepctive
TP
Z
block
January 2007 Atlantic Blocking
PVU
PV anomalies and polar lows
290 K 290 K 290 K
05 Feb 2001 18 UTC25 Dec 1995 06 UTC 18 Jan 1998 00 UTC
PV
on
290K
isen
trop
ic s
urfa
ce
Links - PV loops on the web:
University of Washington:http://www.atmos.washington.edu/~hakim/tropo/trop_theta.html
University of Reading:http://www.met.rdg.ac.uk/Data/CurrentWeather/index.html
DLR (analysis)http://www.pa.op.dlr.de/arctic/
At ETH see course website
Satellite pictures and PV manual:http://www.zamg.ac.at/docu/Manual/SatManu/main.htm