Highlights from

1
Highlights from

• An EU project funded in
• Framework Programme V

2
Partnership

• Techn. Univ. Munich, Germany (TUM)
• Karlsruhe Res. Center, Germany (IFU)
• Max-Planck-Institute for Meteorology, Hamburg,
  Germany (MPI)
• University of Agricultural Sciences, Vienna,
  Austria (BOKU)
• U.K. Meteorological Office, U.K. (UKMO)
• Utrecht University, Netherlands (IMAU)
• Meteorological Institute, Netherlands (KNMI)
• Consiglio Nazionale dell Ricerche, Bologna, Italy
  (CNR)
• Aristotelian University of Thessaloniki, Greece
  (AUTH)
• National Technical University of Athens, Greece
  (NTUA)
• University of Berne, Switzerland (LRU)
• Vienna Environmental Research Accelerator,
  Vienna, Austria (VERA)
• ETH Zurich, Switzerland (ETHZ)

3
Objectives

• develop a 3-D Lagrangian perspective of STE, with
  a focus on deep exchange events
• investigate the mixing of stratospheric and
  tropospheric air
• do measurements to estimate the impact of STE on
  tropospheric chemistry
• intercompare and validate methods and models used
  to calculate STE
• examine variability and trends of STE during the
  past few decades and under scenarios of climate
  change
• study the relative impact of STE on the oxidation
  capacity of the troposphere

4
New Nomenclature

• Use STE as a general term, referring to
  stratosphere-troposphere exchange in both
  directions
• Use STT specifically for one-way
  stratosphere-to-troposphere transport
• Use TST specifically for one-way
  troposphere-to-stratosphere transport

5
Observations of STT at mountain peak stations
What is the influence on ozone?
6
Seasonal variation of ozone contribution of
stratospherically influenced air to the observed
ozone mixing ratio at the Zugspitze peak (IFU)
Obtained from monthly statistics (1990-2000)
based on data filtering using 7Be and relative
humidity. Total stratospheric contribution may
be larger, due to unidentified aged
stratospheric air.
7
Identification of stratospheric intrusions atMt.
Cimone based on different observation criteria
(7Be, humidity, etc.) (CNR)

• Daily average ozone increase on days with an
• intrusion is 5-7 relative to the monthly average

8
Seasonal variation of 7Be, a stratospheric
tracer (LRU, AUTH)
Little seasonal variation, summer
maximum Reflects minimum in washout and higher
tropopause in summer
9
10Be / 7Be climatology (LRU, VERA, AUTH) First
time ever 10Be monitoring in Europe Worldwide
available atmospheric 10Be data multiplied
7Be, 10Be have same sources and sinks, but
different radioactive decay times. Thus, their
ratio is not affected by washout (Raisbeck et
al., 1981) Making certain assumptions, Dibb et
al. (1994) derived surface ozone from the
stratosphere using the 10Be / 7Be ratio. Monte
Carlo simulation quantification is very
sensitive to assumptions applied.
Jungfraujoch
Zugspitze
10
Upper troposphereMiddle troposphere
Lower troposphere
1-year Climatology of Ozone in the Troposphere
Obtained by Combining MOZAIC Measurements with
Back Trajectories (TUM)
11
Model validation and intercomparison
12
A deep STT event
Water vapor satellite image plus isentropic PV
(20/6/01) (courtesy of Owen Cooper, NOAA)
FLEXPART stratospheric ozone tracer column
between 5.5 and 11 km altitude (TUM)
13
Ozone lidar measurements at Garmisch-Partenkirchen
(IFU)
FLEXPART stratospheric ozone tracer (TUM)
ECMWF O3
ECHAM full chemistry simulation (IMAU)
14
Deep STT event, as seen at Jungfraujoch (LRU,
VERA and AUTH)
15
Comparison of ozone lidar observation with an
ozone sounding at Thessaloniki (AUTHNTUA)
16
Lidar observation of a deep stratospheric
intrusion event over Garmisch-Partenkirchen (IFU)
17
Model intercomparison exercise (KNMI)
Lagrangian models without turbulence
underestimate the extension of the
intrusion Eulerian climate (-chemistry)
models suffer from numerical diffusion and coarse
resolution and overestimate the extent of the
intrusion
Trajectory models Lagrangian models with
turbulence and convection Eulerian
models Eulerian models
7 models were requested to simulate the same
stratospheric intrusion event Stratospheric
tracer with a lifetime of 2 days in the
troposphere
18
Model intercomparison exercise (KNMI)

• Large differences are found among the models for
  the
• concentrations of the stratospheric tracer at 700
  hPa

19
A new concept and new STE properties
20
A New Concept ofStratosphere-Troposphere Exchange
21
A deep TST event, delivering possibly polluted
boundary-layer air to the lowermost stratosphere
(ETHZ)
22
Lagrangian Tools to Study Deep STE(ETHZ and
TUM)
LAGRANTO (ETHZ) Trajectory model Focus on
timescales of a few days FLEXPART (TUM)
Lagrangian particle dispersion model Extend
the timescales Parameterizations of
turbulence and convection
23
Comparison of FLEXPART extratropical net STE with
Appenzeller et al. (1996) budget study using
downward control (TUM)
Broken line Appenzeller et al. Solid line
FLEXPART Lagrangian method
Northern Hemisphere Southern Hemisphere
Stronger seasonal cycle, but annual mean net mass
flux in good agreement
24
How long has air spent in the troposphere when it
(re-)enters the stratosphere? (TUM)
Fresh return fluxes are highly sensitive to
parameterizations (equivalent to the cancellation
of terms in the Wei formula), BUT THEY ARE
NOT VERY RELEVANT!
More than 90 of the flux into the stratosphere
is less than 6 hours old
all ¼ ½ 1 2 3 4 6 8 10 20
40 90 365 days
25
FLEXPART concentration of STT air in the
troposphere, in dependence of the age (TUM)
0-1 days
1-4 days
4-10 days
20-90 days
gt90 days
10-20 days
26
The seasonality of deep STE using FLEXPART (TUM)
Take seasonal variation of ozone at the
tropopause and assume 1-month lifetime in
troposphere
Within 40 days
STT
27
Winter Climatology (1979-1993) of Deep STT Events
Using LAGRANTO (ETHZ)
Frequency () of destinations of STT particles
that arrive below 700 hPa within 4 days
28
Winter Climatology (1979-1993) of Deep TST Events
Using LAGRANTO (ETHZ)
Frequency of sources below 700 hPa of TST
particles within 4 days
Maxima at the start of the stormtracks downwind
of North America and Japan. Emissions from these
regions may reach the lowermost stratosphere
within short timescales.
29
Simulated chemical effects of STT
30
Influence of STT on the oxidizing capacity of the
troposphere, according to ECHAM (IMAU)
Seasonal cycle of the calculated tropospheric OH
budgets for the NH
31
Influence of mixing of stratospheric
andtropospheric air on OH concentrations (BOKU)
OH radicals are enhanced by up to a factor 25
relative to the no-mixing case There is a slight
speed-up of ozone destruction, due to mixing
32
STE interannual variability and possible future
changes
33
NAO minus NAO- (TUM)During
NAO STTis shifted towards higher latitudes and
altitudes in the middle latitudes
STT variability based on re-analysis
data Influence of the North Atlantic Oscillation
on STT

NAO (winter) NAO- Location of
STT events measure of storm track (in
green) (ETHZ)
34
Difference in stratospheric tracerconcentration
for El Nino minus La Ninain the eastern
PacificDuring El Nino STE in the tropical
eastern Pacific is shifted towards higher
altitudes
Climate variability based on re-analysis
data Influence of El Nino/Southern Oscillation
on STE (TUM)
35
MAECHAM simulation of 10Be, 7Be transport (MPI)
Annual mean residual meridional mass flux
10Be / 7Be
Annual mean residual circulation amplifies from
1860 to 2000 to 2100, leading to enhanced STE
Cyclonic activity intensifies in SH, but
decreases in NH! Asymmetry in 10Be/7Be changes!
36
A glance into a future ozone scenario (A1FI) with
STOCHEM (UKMO)
Difference (ppbv) between stratospheric ozone at
the surface for the years 2091-94 and 1991-1994
37
A glance into a future scenario with STOCHEM
(UKMO)
Total surface ozone at Mace Head decreases (due
to enhanced water vapor in the future climate) if
precursor emissions remain unchanged, but the
contribution of ozone from the stratosphere
increases