1. No category

What is a Sudden Stratospheric Warming?
rapid increase
of T at h~32 km
from Evelyn De Wachter (PhD thesis, IAP-Bern):
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reversal to westward wind
-> major SSW on 19 Feb. 2008
DIE$
Qualitative Explanation of Sudden Stratospheric Warming:
①  planetary wave (from troposphere at mid-latitudes) propagates into stratosphere
at high latitudes and „collapses“ at about 40-50 km
②  sudden deposition of westward wave momentum reverses the zonal mean
eastward wind (wave – mean flow interaction)
③  rapid increases of poleward wind, pressure, and temperature are forcing the
polar vortex (-> shifting or splitting of polar vortex)
upwelling of
isentrope
-> adiabatic
cooling in the
mesosphere
Flury et al.,
JGR, 2009:
SSW at
Bern
downwelling of
isentrope
-> adiabatic
heating
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upwelling and cooling
DID$
How is the response of ozone to the SSW?
Stratospheric ozone profiles are measured at University of Bern
since 1994 (http://www.iapmw.unibe.ch/research/projects/GROMOS)
Reasons:
- detection of long-term trends of the ozone layer
- cross-validation of satellite experiments
- ozone as tracer of middle atmosphere dynamics
- atmospheric research
NO + O3 "NO2 + O2
NO2 + O "NO + O2
############
O3 + O " 2O2
strong ozone depletion caused by the major stratospheric warming (19 Feb. 2008):
Chemical box model provides explanation for observations at!Bern. Catalytic ozone
destruction (due to the NO cycle) is accelerated if the temperature increases during
the SSW (Flury et al., 2009) => it was a combined effect of dynamics and chemistry
DIH$
Open questions in research on sudden stratospheric warmings
!  Meridional and vertical exchange and mixing of air masses by SSWs.
Is the Brewer-Dobson circulation decelerated or accelerated by SSWs?
!  Why is there upwelling in the upper troposphere and lower stratosphere?
!  Role of gravity waves during SSW
!  Large ionospheric disturbances occur in the equatorial ionosphere
during SSWs. Is it due to interaction between tides and planetary waves?
!  Why have there been no SSWs in the 90s?
!  Are there resonance periods of polar vortex oscillations ?
Average winter and summer
spectrum (1994-2010) of ozone
fluctuations above Bern
derived by bandpass filter-periodogram
using ozone profiles of GROMOS
radiometer:
•  ozone fluctuations at Bern possibly
•  reflect perturbations of the vortex
•  20 days could be a resonance period
•  winter spectrum has stronger peaks
than the summer spectrum
DII$
reservoirs of Cl
chemical reaction
takes place on the
surface of the
ice particle
ClONO2
HCl
n=1,2,3,...
ice particle: NAT
(nitric acid trihydrate)
T < -77 oC
3 H2O
(is reached in the
dark, cold winter stratosphere
+ cooling in updrafts)
n (HNO3 . 3 H2O)
Activation of Cl
+ Cl2
(n+1) (HNO3 . 3 H2O)
by mountain waves)
sunlight produces atomic Cl
Polar lower stratosphere:
(ozone hole)
ClO + ClO + M
Cl2O2 + hv
ClO2 + M
then:
2 x (Cl + O3)
Catalytic cycles:
2 Cl
and Cl2 + h!"
ice particle is now a bit larger
and Cl2 is now in the dangerous
gas phase!
Upper/middle stratosphere:
net:
Cl + O3 ==> ClO + O2
ClO + O ==> Cl + O2
-----------------net result: O3 + O ===> 2O2
Cl
PSC:
polar stratospheric
cloud (usually induced
O3 O3
O3
2 O3
->
->
->
->
Cl2O2 + M
Cl + ClO2
Cl + O2 + M
2 x (ClO + O2)
->
3 O2
O O
O
O
+ O3
ClO + O2
Harmful UV flux at
surface increases
with depletion of
ozone:
ClO +
Cl
O
+ O2
Catalytic destruction of O3 and
O by only one chlorine atom
Cl
Cl is now ready for the next cycle
PV (white lines) make sense!
http://mls.jpl.nasa.gov
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DIM$
Atmospheric waves from troposphere
Change of the polar vortex in the
stratosphere
Tides +
Seasons
CFCs
PSC
Variability of time series of O3 and H2O
observed by radiometers at Bern
Change of composition and circulation
of mesosphere and stratosphere
Solar activity and geomagnetic storms
Climate
Change
Volcano
+ ...
QBO (2.4 years)
SAO (0.5 years)
(11 years, 27 days)
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!  Observations can sometimes reveal relationships (e.g., wave-mean
flow interaction, polar ozone chemistry)
!  Description of the restless atmosphere rapidly increases with
advances in computer technology and remote sensing. However
understanding remains difficult!
!  IAP-Bern has a lot of instruments and data waiting for experimental
investigations, analysis and simulations
!  Future of high-resolution Earth system models is described in a
recent issue of a meteorological journal:
http://journals.ametsoc.org/toc/bams/91/10
Literature recommendation:
Newman, P. A., Oman, L. D., Douglass, A. R., Fleming, E. L., Frith, S. M., Hurwitz, M. M., Kawa, S. R., Jackman, C. H.,
Krotkov, N. A., Nash, E. R., Nielsen, J. E., Pawson, S., Stolarski, R. S., and Velders, G. J. M.:
What would have happened to the ozone layer if chlorofluorocarbons (CFCs) had not been regulated?
Atmos. Chem. Phys., 9, 2113-2128, doi:10.5194/acp-9-2113-2009, 2009 (open access)
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NASA