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Analysing the 2009 Stratospheric Warming using EP-Flux

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Mirjam Hirt

on 15 January 2015

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Transcript of Analysing the 2009 Stratospheric Warming using EP-Flux

Tropospheric planetary waves (wavenumber 1,2)
Dissipation of wave amplitude
-> EP-Flux Convergence
vertical propagation
Ayarzagüena, B., U. Langematz, and E. Serrano (2011), Tropospheric forcing of the stratosphere: A comparative study of the two different major stratospheric warmings in 2009 and 2010, J. Geophys. Res., 116,
Baldwin, Mark P., and Timothy J. Dunkerton. "Stratospheric harbingers of anomalous weather regimes." Science 294.5542 (2001): 581-584.
Holton, James R., and Gregory J. Hakim. An introduction to dynamic meteorology. Academic press, 2013.
James, Ian N. Introduction to circulating atmospheres. Cambridge University Press, 1995.
Labitzke, K., and M. Kunze (2009), On the remarkable Arctic winter in 2008/2009, J. Geophys. Res., 114, D00I02
Labitzke, Karin. Die Stratosphäre: Phänomene, Geschichte, Relevanz. Springer, 1999.
Langematz, U., Ayarzagüena, B.; Lecture and Handout about EP-FLux, Wetter und Klimadioagnose, 2014
Domeisen, D.I.V., 2012: Stratosphere - troposphere interaction during stratospheric sudden warming events, Ph.D. thesis, Massachusetts Institute of Technology. Department of Earth, Atmospheric, and Planetary Sciences
Steven Hardiman, Peter Haynes: Stratosphere-Troposphere interactions - Downward propagation of dynamical signals in the middle atmosphere, Presentation, University of Cambridge, UK
Charlton, A. J., 2003: The dynamical impact of the Stratosphere on the Troposphere, Ph. D. thesis, The University of Reading, Department of Meteorology
Adam Scaife, Stratosphere-Troposphere Coupling and Climate Prediction, Presentation, 2010
www.diplomet.info/Geopotential.html

Conditions of stratosphere during Winter 08/09


MATLAB Script provided by Blanca Ayarzügena

Monthly Mean EP-Flux and Divergence

Daily EP-Flux and Divergence

Data preparation with Climate Data Operators (CDOs)

Visulizations with Grid Analysis and Display System (GrADS)
Eric Förster, Mirjam Hirt, Ulrich Küster, Igor Kröner
Analysing a Stratospheric Warming using EP-Flux
Theory on wave propagation (Eliassen-Palm-Flux)
Sudden Stratospheric Warmings
ERA-Interim
Data used for the analysis
Major Stratospheric Warming during
Winter 2008/2009

Motivation
Why is it important to look on the stratospheric variability?
External forcings:
QBO (Holton-Tan effect)
11-year solar cycle
ENSO

Internal forcing:

tropospheric wave propagation


Influencing factors for SSW development
Description of Sudden Stratospheric Warmings
Literature
Summary and Conclusions
Labitzke (1965)
For some major and minor warmings -> relationship with circulation over western Europe
10 days after stratospheric warming: blocking pattern was set up at end of North Atlantic's storm track

Quiroz (1986)
Relationship between 500 hPa blocking and 10 hPa warming

Baldwin et al. (2003a), Charlton et al. (2003)
Including stratosphere information in statistical forecasts: increasing skill of troposphere forecasts by around 5 % for daily and around 20 % for monthly mean


Strong warming (up to 50K) in a few days
Weakening or break down of the polar vortex

Major stratospheric warming:
Easterly winds in 60°N, 10hPa
Reversed temperature gradient
Approximately once every two years

Geopotential Height at 10hPa

Ayarzagüena et al. (2011)
2009
2010
Transformed Eulerian Mean (TEM) Equation
The EP-Flux and Stratospheric Warmings
Divergence of EP-Flux (>0): acceleration
Convergence of EP-Flux (<0): deceleration

SSW:
The Charney-Drazin Criterion
Vertical wave propagation only possible, if :

0< U < Uc
,
Uc = Uc(1/k)


-> vertical wave propagation is only possible in "weak" west winds (<Uc)

-> waves with small wavenumber k can propagate in stronger west winds than waves with higher wavenumbers
About ERA-Interim
Global Reanalysis dataset from 1979-2013
Spatial resolution: 80km
Vertical resolution: 60 layers (up to 0.01hPa)

For our analysis
Daily values from 1979-2013
Used parameters:
Wind components (horizontal (u,v), vertical (w))
Temperature
Geopotential
http://old.ecmwf.int/publications/library/ecpublications/_pdf/era/era_report_series/RS_1_v2.pdf

E
CMWF
R
e-
A
nalysis
CDOs

MATLAB
Introduction
Rossby waves are able to propagate into the stratosphere
Stratospheric circulation is disturbed by planetary Rossby waves
-> transport momentum upward
-> interact with stratospheric flow
-> could lead to strong disruptions of the vortex
and Sudden Stratospheric Warmings

large stratospheric circulation anomalies can reach Earth’s surface
James, 1994


November - April monthly mean climatology

Winter 2008-2009 extract with daily values
Climatology
Stratosphere Troposphere
Interactions

Connection between troposphere and stratosphere can provide extra skill on extended range and seasonal timescales

-> representation of the stratosphere in forecast models is
extremely important




Understanding stratospheric variability could lead to better predictability of tropospheric weather and climate!
Basics
Troposphere is heated from below (long wave radiation from surface)
Tropospheric weather patterns change on timescales of few days

Stratosphere dominantly heated by absorbtion of short wave radiation by ozone
Circulation regimes in the stratosphere persist several weeks or more

Tropospheric circulation:
Planetary Rossby waves caused by asymmetric heating
and topography at Earth’s surface

Stratospheric circulation:
Interplay between
-> radiative processes (solar heating, chemical tracers)
-> dynamical processes (wave propagation, wave breaking)

Polar vortex:
Circumpolar flow with velocities from 50 m/s in the Northern Hemisphere winter to 90 m/s in the Southern Hemisphere winter

streamlines in the Northern Hemisphere on 31. December 2014 in 500 hPa
from http://earth.nullschool.net
streamlines in the Northern Hemisphere on 18. December 2014 in 10 hPa
from http://earth.nullschool.net
variations in strength of polar vortex are well characterized by “annular modes”
annular modes: hemispheric scale patterns characterized by synchronous fluctuations in pressure
e. g. the Arctic Oscillation “AO” is a annular mode over the near surface, NAO is annular mode over the North Atlantic

Annular Modes
tropospheric circulation after weak and strong vortex regimes
Storm tracks are displaced farther south during weak vortex regimes in Atlantic and Pacific
Storms are more likely during weak vortex regimes

Furthermore:

Large circulation anomalies in the lower stratosphere are related to shifts in the AO/NAO (Baldwin et al. 2003)

SSW can cause cold air outbreaks like in winter 2005/06 and 2008/09 (Adam Scaife, 2003)



Methodology
Climatological monthly mean
EP Flux vector
EP Flux vector divergence
Other relevant variables

Climatological evolution of a stratospheric winter

Evolution of the Major Stratospheric Warming in winter 2008/2009
Labitzke, K., and M. Kunze (2009), On the remarkable Arctic winter in 2008/2009, J. Geophys. Res., 114, D00I02
Split
Displacement
MSW in this Winter?
www.geo.fu-berlin.de/met/
Deceleration of the zonal mean wind
No wave propagation in east winds
-> polar vortex can be restored
TEM-Equation
more wave propagation in weaker westerly winds
easterly winds develop
Our tasks
In which months can the strongest connection between troposphere and stratosphere be found?
using EP Flux and other relevant variables. Same for quasi-geostrophic representation of EP Flux and interpret the differences.
Calculation of EP Flux
Prepared Data and Climatology
Temperature zonal mean 1979-2013
Zonal wind zonal mean 1979-2013
Weak vortex:
-> storms are more likely
-> storm tracks are farther south
-> influence on AO and NAO


Can be observed in the context of Sudden Stratospheric Warmings (SSW)

(SSW was found here at the IfM by Richard Scherhag on 27 January 1952 under the name "Berliner Phenomenon")


So what characterizes a SSW?
EP-Flux-Arrows: Direction and Strength of wave propagation

Divergence-Isolines: Influence of waves on zonal mean zonal wind

NCEP/NCAR Reanalysis
Stereographic representation of mean geopotential height and temperature in 10 hPa as well as geopotential height anomalies for winter 08/09
Conditions of troposphere during January 2009
EP Flux and Divergence monthly mean 1979-2013
Geopotential height
The Geopotential is defined as:
Gravitational acceleration dependent on the latitude and geometric height
Geopotential height:
Problem:
Gravitational acceleration globally not equal (lower above equator)

Energy required to lift air parcel globally not equal!
Solution:
Height defined by potential energy necessary to lift air parcel


Geopotential

Normalization to standard gravity at sea level :
Air density eliminated from meteorological equations
Height can be described as height of an isobar in gpm

SSW are mainly caused by planetary waves from the troposphere, which transfer their momentum and heat on the zonal stratospheric circulation
Stratospheric Warming
Understanding stratospheric variability could lead to better predictability of tropospheric weather and climate!
streamlines in the Northern Hemisphere on 24. July 2014 in 10 hPa
from http://earth.nullschool.net
from http://acd.ucar.edu/textbook/ch1/fig5.jpg
Composites of time-height development of northern annular mode for 18 weak and 30 strong vortex events from Baldwin et al. (2003)
Average latitudes of cyclones in the Atlantic and Pacific for 1080 days during weak vortex (red) and 1800 days during strong vortex regimes (blue) from Baldwin et al. (2003)
from http://upload.wikimedia.org/wikipedia/en/2/2e/Arctic_Oscillation-01.jpg
On northern hemisphere a MSW appears approximately every two years
Eliassen-Palm flux is complex, but
delivers useful information about
wave propagation
Zonally averaged (A=A+A') primitive equations
Residual circulation:



Eliassen-Palm Flux F



Quasi-geostrophic formulation:
Supervisor: Janice Scheffler
Full transcript