Highlights from An EU project funded in Framework Programme V
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) Partnership
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 Objectives
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 New Nomenclature
Observations of STT at mountain peak stations: What is the influence on ozone?
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.
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
Seasonal variation of 7Be, a „stratospheric“ tracer (LRU, AUTH) Little seasonal variation, summer maximum: Reflects minimum in washout and higher tropopause in summer
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
1-year Climatology of Ozone in the Troposphere Obtained by Combining MOZAIC Measurements with Back Trajectories (TUM) Upper troposphereMiddle troposphere Lower troposphere
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)
Ozone lidar measurements at Garmisch-Partenkirchen (IFU) FLEXPART stratospheric ozone tracer (TUM) ECMWF O3 ECHAM full chemistry simulation(IMAU)
7Be and 10Be both decrease (washout), but their ratio increases Deep STT event, as seen at Jungfraujoch (LRU, VERA and AUTH)
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
Model intercomparison exercise(KNMI) Large differences are found among the models for the concentrations of the stratospheric tracer at 700 hPa
Stratosphere Lowermost Stratosphere Troposphere Boundary layer A New Concept ofStratosphere-Troposphere Exchange
A deep TST event, delivering possibly polluted boundary-layer air to the lowermost stratosphere(ETHZ)
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
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
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
Fraction of total tropospheric mass FLEXPART concentration of STT air in the troposphere, in dependence of the „age“(TUM) 0-1 days 1-4 days 4-10 days 10-20 days 20-90 days >90 days
Stratospheric air that arrives at the surface Net STE Within 1 day Within 4 days 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
Maxima at the END of the Pacific stormtrack and at the START of the Atlantic stormtrack Almost no deep intrusions over large parts of Asia 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
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.
Photolysis of Tropospheric O3 Photolysis of Stratospheric O3 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
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
STT variability based on re-analysis data: Influence of the North Atlantic Oscillation on STT NAO+ minus NAO-(TUM)During NAO+ STTis shifted towards higher latitudes and altitudes in the middle latitudes NAO+ (winter) NAO- Location of STT events + measure of storm track(in green) (ETHZ)
Climate variability based on re-analysis data: Influence of El Nino/Southern Oscillation on STE (TUM) 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
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!
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
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