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 = *

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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