S P A R C Stratospheric Processes And their Role in Climate A project of the World Climate Research Programme Home Initiatives Organisation Publications Meetings Acronyms and Abbreviations Useful Links

Reports on the EGS-AGU-EUG Joint Assembly

Nice, France, 06-11 April 2003

AS1 Session: Open session on the lower, middle, and upper atmosphere

Convener: M. Juckes (M.N.Juckes@rl.ac.uk)

The session contained 21 oral and 28 posters presentations.

There were six presentations on GCMs, looking at the effects of ozone trends on climate variability (C. Cagnazzo); the response to volcanic forcing (M. Caian and J. Haigh); the impact of increasing stratospheric water vapour (I. MacKenzie and R. Harwood); stochastic gravity wave (GW) parameterisation (C. Piani); the beneficial impact of including interannual SST variability on the variability in the northern polar stratosphere (P. Braesicke and J. Pyle); and the increase in frequency of stratospheric warmings in a 4 times CO₂ experiment (J. Kettleborough).
There were three presentations on various aspects of stratospheric sudden warmings. K. Kodera described the Antarctic warming in September 2002, and the associated tropical response: cooling and reduced ascent in the stratosphere, enhanced ascent and a southwards shift of the Hadley cell in the troposphere; V. Sivakumar described Rayleigh lidar observations of the low latitude signal during NH events, and K. Mimura analysed dynamical feedback mechanisms.

Six presentations dealt with recent satellite measurements. W. Chu et al. described the first year of the SAGE III results (http://www-sage3.larc.nasa.gov/data/); Comparisons between HALOE temperatures and rocketsonde data showed agreement up to an altitude of 80 km (F. Schmidlin), SAGE II and SAGE III agree to within 7 % in the stratosphere (P. Wang), whereas SAGE II and GOMOS compare well on ozone and NO₂ (G. Taha). SAGE III limb scattering measurements may also provide ozone retrievals later in the year (D. Rault). In addition a wide range of data is available from infrared sounders on EOS Aqua (J Qin, http://daac.gsfc.nasa.gov/data/dataset/AIRS/).

Six presentations dealt with advances based on laboratory measurements: a low cost handheld LED instrument measuring column water vapour for use in schools (S. Limaye); possible absorption of atomic oxygen and iron by noctilucent clouds (B. Murray and J. Plane); retrieving aerosol from 1064 nm lidar (M. Adam) measurements of peroxy radicals using catalytic amplification (Z. Fleming); a ground-based SAGE III calibration instrument (B. Wenny); and laser-induced fluorescence for measurement of NO₂ and RO₂s (J. Matsumoto).

Twenty-one presentations analysed various processes: trends in the mesospheric temperature and mesopause "length of summer" (D. Offerman); a climatology of equatorial waves in the lower stratosphere (J. Tindall); Kelvin waves in total ozone (R. Timmermans); the forcing of the mesospheric tides by tropospheric solar forcing (mainly), convective heating and planetary waves (N. Grieger); the net equatorwards meridional mass flux in the winter, mid-latitude lowermost stratosphere (M. Juckes); noctilucent clouds and GW structures (P. Dalin et al.); spatially coherent modes in the NCEP reanalysis (P. Ribera); classification of air masses using total ozone and 450 K isentropic gradients of PV (M. Andrade); lightning discharge statistics from New Mexico and from the Iberian Peninsula (M. Vazquez-Prada); a clear power law structure in atmospheric dynamical fields analysed with respect to zonal wavenumber (A. Will); the use of different forms of potential vorticity to identify the polar vortex (R. Mueller and G. Guenther); dynamically induced decadal changes in planetary scale total ozone anomalies (D. Peters); ionosonde spread-F data (Daley and Wahi); geomagnetic storms and mesospheric ice particle concentration (V. Burabash); and vertical GW momentum flux from CRISTA temperature profiles (M. Ern).

Ozonesondes data were the subject of 5 presentations looking at: the passage of the ITCZ over Paramaribo, Surinam (J. Fortuin and H. Kelder); the ozone QBO during the SHADOZ experiment (J. Logan); ozone lamination, tropopause height, and the passage of the subtropical jet over Ankara (C. Kahya and D. Demirhan); and long-term ozone changes over Poland (Z. Litynska).

There were four talks using simplified or analytic models, showing: substantial long wave momentum fluxes in a highly idealised linear model of GW generated by tropospheric convective events (J. Holton and M. Alexander ); that a minus 3 power law is a consequence of a localised spectral power distribution in the Lagrangian framework (C. Hines); that there is a coupled inertial-barotropic instability mode which may explain the 2-day wave at the summer mesopause (H. Schroeder and G. Schmitz); and describing analytical solutions for GW in the terrestial and solar atmospheres (O. Savina).

Chemical transport models showed that: improved representation of extended UV photolysis affects upper stratospheric and mesospheric ozone (T. Reddman); the stratospheric circulation in ERA-15 is more realistic than ERA-40 (R. Ruhnke); and CRISTA ozone, nitric acid and CFC-11 agrees well with ROSE model results (V. Kuell).

AS8.01 Session: Aerosols and cirrus clouds near the tropopause

Convenors: B. Kärcher (bernd.kaercher@dlr.de), Th. Peter, C. Timmreck

This session consisted of two sub-sessions focusing on aerosols and cirrus clouds followed by a poster session with more than 25 presentations. Initially, talks were given on a satellite perspective of particles in the UTLS region, including presentations about the physical processes involved in the formation of new aerosol particles and ice crystals, descriptions of in situ and lidar observations, and modeling studies. In addition, the cirrus sub-session ended with a talk on current and future in situ measurement capabilities.

H. Clark described thin cirrus observations in the TTL made with the CLAES instrument. Cirrus was found to be most prevalent over land and warm oceanic areas, whereas some variability seen in cirrus data was correlated with intraseasonal variations of water vapour. E. Jensen gave an overview of physical processes and mechanisms that control the formation and maintenance of thin, laminar cirrus near the tropical tropopause. These clouds can be formed in situ by cooling and subsequent freezing of suitable aerosol particles, or they can be residuals from anvils in the outflow of deep convective clouds. Model results stressed the importance of laminar cirrus for dehydration of air entering the stratosphere. L. Moyer showed in situ water vapour and relative humidity data taken within the TTL during summer in the presence of significant convective activity. Surprisingly, high supersaturations over ice were found within cloud, thus raising the question about the mechanism responsible for the maintenance of supersaturation in the presence of cirrus cloud particles in cirrus anvils. These results were contrasted with data taken in clear, unsaturated air. S. Ismail showed a collection of thin cirrus and water vapour data taken during the airborne Lidar Atmospheric Sensing Experiment used in conjunction with temperature and moisture data to characterize spatial cloud structure, cloud top height, optical depth, aerosol scattering, extinction-to-backscatter ratio, and relationships between cirrus clouds and water vapour fields. F. Immler discussed data taken with the Mobile Aerosol Raman Lidar at midlatitudes and in the tropics during the INCA project. The differences found in depolarization and colour index of midlatitude cirrus suggest differences in microphysical properties of the ice crystals. The fraction of subvisible clouds detected was significantly higher in the tropics. In general, tropical cirrus differed from midlatitude cirrus in terms of horizontal extent and lifetime. U. Lohmann reported about first simulations of cirrus clouds with the ECHAM model coupled to a novel freezing parameterization. The potential of volcanic aerosol emissions to alter cirrus occurrence and properties were discussed. Under the working assumption that both background and volcanic aerosol particles freeze homogeneously, no systematic trend was found on cloud microphysical or optical cirrus properties in the case of the Mt. Pinatubo eruption. S. Dean highlighted investigations of orographic cirrus in the UKMO Unified Model and compared model output to climatological cloud amounts available from ISCCP. Without special care, the global model lacks cirrus cloud in the lee of orography as seen on the satellite data, in particular at midlatitudes. The importance of including a prognostic ice variable in the model was stressed, and thoughts about a parameterization of orographic cirrus were discussed. S. Borrmann reviewed in situ measurements of thin and subvisible cirrus clouds. The few existing interstitial aerosol and ice crystal size distributions were discussed along with developments concerning the role of cirrus in heterogeneous chemistry. A. Heymsfield investigated the microphysics of a cirrus layer at the tropical tropopause with observations taken during the CRYSTAL-FACE experiment. As convective cells were absent, the cloud likely formed in situ. Size distribution measurements revealed the growth of crystals downward from the cloud top to base, whereas saturation over ice decreased from top to base, showing strong supersaturation in the formation zone near saturation conditions lower down. J. Whiteway presented results from the EMERALD-2 campaign conducted from Darwin to study cirrus outflow from intense tropical convection. In situ and remote sensing data taken from two aircrafts showed variations in the dynamical setting, ice crystal properties, water vapour, and ozone within and around convective outflow.

R. Grainger reported on the status of new retrieval algorithms (PARTS project) which determine aerosol effective radius, surface area, and particle volume from SAGE II spectral measurements, and aerosol optical depth from the ATSR/2 instrument. Initial maps showing the evolution of the aerosol in the UTLS region have also been presented. An aerosol history will be constructed with the help of the new retrievals and additional surface-based and in situ measurements. M. Hermann reported on aerosol particle measurements taken from commercial aircraft (CARIBIC project). Sulfur was found to be most abundant in northern midlatitude samples, exhibiting a strong latitudinal concentration gradient and a maximum during summer. Deep convection and photochemical activity was responsible for new particle formation in tropical regions. The measurements indicate that the main processes regulating the formation of small aerosol particles must act on spatial scales of ~10 km. I. Ford discussed a burst of aerosol particle formation in the upper tropospheric outflow of a huge midlatitude storm cloud observed during the SUCCESS experiment. The outflow regions of mesoscale convective systems were estimated to contribute significantly to the global aerosol budget. The observations are consistent with an analytical model for the nucleation burst, assuming that the particles are formed from binary homogeneous nucleation of sulfuric acid and water vapour. D. Stevenson investigated the behaviour of volcanic aerosol particles near the tropopause with the help of a global CCM. The model study focused on the processes following the Laki eruption in 1783/1784, which added 122 Tg of sulfur dioxide just above the tropopause over Iceland. It was concluded from the simulated aerosol production, transport and removal processes associated with this eruption that long-lived aerosol perturbations require sulfur dioxide to be injected to mid-stratospheric levels of 20-25 km altitude and producing new particles there; alternatively, the eruption must continue over an extended time period.

AS8.025 Session: Processes controlling the Chemical Composition of the UTLS.

Conveners: B. Bregman (bregman@knmi.nl), K. Law, and H. Rogers.

The session (30 posters and 16 oral presentations) covered kinetic laboratory work, analysis of air-borne tracer data, and chemical modelling.

N. Butskovskaya investigated the reaction OH + CH₃CHO at 298 K and found the predominant channel: CH₃CO + H₂O. T. Bartels-Rauch studied the interaction of acetone on ice and found a negligible effect. L. Koch showed that the reaction of CH₃S + CO is not important for the formation of OCS. M. Blitz reported reduced acetone photolysis rates due to temperature dependent absorption cross sections and lower quantum yields. Chlorine activation on cirrus ice particles was investigated by M. Fernandez they found a significant suppression of the reaction HCl + ClNO₃ when the gas phase HNO₃ concentrations are larger than HCl. D. Johnson showed that radical propagation from the decomposition of butoxyl radicals decreases with decreasing temperature. T. Shepherd presented a model study on the HNO₃ uptake on aerosols and ice particles. N. Hill and A. Horn investigated interactions of organic species with ice and showed that acetone and methanol together with HNO₃ led to some ice surface modifications. Tropical ozone and NO₂ profiles were studied by F. Borchi, who showed that the relative contribution from transport and chemistry significantly depends on altitude. N. Huret investigated the influence of proton precipitation as a source for NO_x (=NO+NO₂) in the tropical LS. Space-borne total column and vertical profiles from NO₂ and NO₃ were used by J. Shillito to study night-time chemistry. A 3D-CTM was used by M. Kanakidou to investigate the importance of convection on oxygenated hydrocarbons in the UT and the impact on the HO_x (=HO₂+OH) budget. B. Morel showed the relative importance of large and small-scale planetary waves on meridional mixing at the edge of the tropical stratosphere. V. Sivakumar studied the subtropical tropopause structure; J. Baray and T. Portafaix focused on the relation between the southern subtropical barrier and ECWMF PV. M. Sprenger et al. used ECWMF analysis to estimate the global tropopause fold frequencies. Airborne in situ CO measurements were used by P. Hoor to investigate cross-tropopause transport, whilst A. Zahn used the CARIBIC O₃-CO relationship. M. Krebsbach by using the SPURT aircraft data, examined dehydration in the extra-tropical lowermost stratosphere. S. Assonov explored isotopic observations of CO₂ during CARIBIC to characterize the lowermost stratosphere. O₃ and N₂O ERS-2 data were used by B. Legras and J. Lefèvre to study turbulent diffusion at the edge of and within the Arctic polar vortex. G. Günther used the CLaMS model and SPURT trace gas data to estimate cross-tropopause fluxes and to characterise the air mass origin in the tropopause region. D. Brunner investigated turbulent decay times of tropospheric filaments in the lowermost stratosphere from aircraft data. M. Hegglin investigated the impact of convective transport and small-scale turbulence on NO_y by using the SPURT observations.

J. Crowley presented new temperature dependent rates of the reaction of acetaldehyde with OH and its importance for the HO_x budget in the UT. F. Pope discussed new formaldehyde photolysis data. T. Gierczak presented results from the photolysis and thermal decomposition of pernitric acid, which seemed slower than the latest recommendations; FIR photolysis study is ongoing. Smaller quantum yields than previously measured were found by D. Heard for the photolysis of acetone (> 310 nm and low temperatures), resulting in a 2 times longer chemical lifetime and a factor of two less HO_x production in the upper troposphere. E. Meijer presented results from the 3D CTM TM3 of the HO_x production by NMHC in the UT. H. Fischer gave a report on the SPURT campaigns, and addressed the depth and the seasonal cycle of the midlatitude tropopause mixing layer; there was evidence that the mixing layer follows the local tropopause. MOZAIC observations were presented by J.-P. Cammas , focusing on the CO – O₃ relation in the UTLS. G. Vaughan discussed dynamical mechanisms responsible for transport and mixing of air masses between troposphere and stratosphere. Breaking Rossby waves can generate inertia gravity waves, which then lead to layering and mixing of air masses. Other mechanisms were shear-induced turbulence and convection in post-cold frontal air masses. J. Whiteway showed very high-resolution turbulence measurements from the Egrett aircraft on flights over the Welsh mountains. L. Pan discussed a method for characterizing the extra-tropical tropopause using the thermal definition in order to look for thermal breaks in the tropopause, using aircraft data from SONEX, STRAT and POLARIS. H. Scheeren studied acetone and VOC data from STREAM campaigns; high concentrations of acetone and VOCs were found in the LS in summer (up to 2.5 ppbv acetone), but much lower in winter, with the VOC load being between 0.5 - 2.5 ppbC. H. Feldman presented water vapour from the assimilation model ROSE, which is nested with the high resolution EURAD model; the results suggest low biases of water vapour at 215 hPa compared to ECMWF data. J.-P. Pommereau presented tropical observations from long-duration balloon as part of the HIBISCUS project. Very large variability was found in the NO_x distribution near the tropical tropopause, whilst the variability in ozone was very small. D. Fahey stated that HCl would be a very useful tracer of STE on the basis of the correlation of HCl with O₃. F. Borchi compared tropical NO_x fields calculated by the 3D CTM REPROBUS with observations from the HIBISCUS project. M. Hitchmann discussed a connection between the Asian summer monsoon and the Australian High to explain the ‘croissant-shape’ area with high ozone columns found in the southern midlatitudes; different potential transport pathways were discussed. Finally R. Salawitch described the Tropical Chemistry-Climate Coupling experiment (TC4); a campaign is planned for 2004-2005 over Darwin or Guam.

AS.9 Session: Chemical Data Assimilation

Conveners: H. Eskes (eskes@knmi.nl), B. Khattatov, W. Lahoz.

There were 6 oral presentations:

D. Lary showed how data assimilation and related data analysis techniques can be used to improve our knowledge of atmospheric chemistry. Kalman filter analyses of ATMOS and UARS observations were presented. The representativeness error, information content, skill score and data heterogeneity were also discussed. Based on the assimilation, information on ranking the species can be derived: species with a high information content (like first of all ozone) strongly determine the chemistry and accurate measurements of these species have a high priority.

H. Elbern discussed the assimilation of chemical observations and focused on the terms "observability", "representativity" and "controllability". Many critical species are not observed by the present satellites and ground networks, (e.g. N₂O₅, ClO and HCl in the stratosphere, and hydrocarbons in the troposphere). The current stratospheric observations provide strong constraints, but the troposphere is still largely undersampled. He also stressed the importance of "controllability": an a-posteriori validation of the covariances in the assimilation with the chi-square test.

K. Wargan discussed the impact of using flow-dependent error correlations in data assimilation with the DAO Ozone DAS. The flow dependence is computed by evaluating the covariances at the end of 24h back trajectories. Benefits are found especially in unobserved regions (e.g. polar night).

S. Migliorini gave a detailed discussion on the observation operator and covariances for the assimilation of MIPAS profiles. This work closely follows the retrieval formalism of Rodgers, and special focus was given to the use of averaging kernels and complications related to vertical interpolations.

V. Yudin provided an overview of the tropospheric tracer assimilation work done at NCAR using the MOZART-2 model. The first results were shown for the Version 3 CO retrievals from the MOPITT instrument. New ideas are proposed for an improved representation of the model error.

Q. Errera described the 4D-Var chemical analysis of MIPAS observations, based on the BASCOE stratospheric modelling and assimilation system. This is one of the first systems to analyse ENVISAT-MIPAS observations of H₂O, O₃, HNO₃, CH₄, NO₂ and N₂O on a quasi-operational basis (since September 2002). The comparisons with UARS-HALOE measurements show good agreement for ozone and NO_x. The water vapour and methane concentrations were found to be smaller than HALOE.

The 15 posters of the session discussed assimilation techniques, covariance modelling and analyses of satellite observations of the atmospheric composition based on measurements from GOMOS, MIPAS, SCIAMACHY, ODIN, GOME, and MOPITT.

AS 20 Session : Polar Stratospheric Clouds

Convenors: K. Carslaw (carslaw@env.leeds.ac.uk), T. Deshler and J. Remedios

The aim of this session was to synthesise the current state of knowledge of PSCs and to present results from the latest campaigns. The oral session started with three presentations on solid PSC formation. T. Koop reported on our current understanding of solid particle nucleation in the polar stratosphere, on experiments attempted to quantify homogeneous and heterogeneous nucleation by freezing of HNO₃/H₂SO₄/H₂O solutions, as well as on more recent ideas on solid particle formation by sedimentation out of ‘mother clouds’. K. Drdla presented model calculations of the effect of variable concentrations of heterogeneous nuclei and compared them with observations. O. Möhler showed results from the AIDA chamber investigating the effect of heterogeneous nuclei on solid nitric acid particle formation. They have observed solid formation, but have yet to determine the molar composition of the particles. Overall, from these three presentations it can be concluded that solid PSCs could form heterogeneously, although the identity of possible nuclei in the stratosphere remains to be identified. R. Spang showed early observations of PSCs from MIPAS on ENVISAT, demonstrating the capability of the instrument to detect the temporal evolution of PSC cloud top height. M. Fromm showed an extensive record of POAM PSC observations, including the 2002/3 SOLVE II-VINTERSOL campaign. The PSC occurrence frequency changed through the winter, possibly in response to denitrification. G. Mann presented 3-D simulations of denitrification using the Leeds DLAPSE model and described the factors that appear to control the severity of denitrification. The 2002/3 winter was fairly strongly denitrified, though not as much as in 1999/2000. H. Schlager showed observations of denitrification from the NO_y instrument on board the Geophysica during the EUPLEX campaign, with a distinctive signature of de- and re-nitrification that agrees reasonably well with the DLAPSE model. Finally, in his solicited talk K. Mauersberger presented a very personal view of the discovery and significance of NAT particles. His work spans the full range of discoveries related to NAT, from the first laboratory determination of NAT thermodynamic properties to the first detection of NAT in the stratosphere by using balloon-borne instruments.

AS26 Session: Water vapour and its isotopic composition in the UT and stratosphere

Main Organizer: K. Boering (boering@cchem.berkeley.edu)

The goal was to discuss the latest developments in the measurement, modelling, and interpretation of water and its isotopic compositions (i.e., the deuterium, tritium, and oxygen-18 content).

A. Gettelman opened the session by introducing the topic of water vapour and its isotopic fractionation in the tropical tropopause layer (TTL); he compared new results from both trajectory-based and 3D global CTMs. K. Rosenlof presented observations from HALOE in the 100-70 hPa tropical region, as well as NOAA CMDL frost-point balloon observations in the LS, which show a significant decrease in water vapour over the past two years. She discussed the possible links both to decreases in tropical tropopause temperatures, as well as to increases in stratospheric CH₄ due to a widening of the tropical upwelling region. M. Dameris discussed the use of cloud-screened microwave limb-sounder data of relative humidity to produce the global distribution of ice-supersaturated regions at 147 and 215 hPa. M. Geller investigated the 3D-structure of temperatures in the tropical tropopause region and defined a "dehydration index" based on the volume of the atmospheric region with temperatures colder than a reference temperature. Linking the dehydration indices with tropical upwelling can explain the observation of the beating of 3 frequencies from the annual cycle in temperature and the temperature variations associated with the QBO and ENSO.

G. Toon (in absentia with assistance from R. Salawitch) presented ATMOS observations of HDO and H₂O using recently measured spectral lines that enable extension into the TTL. The isotopic composition remains quite-constant in the TTL, despite a decrease in water vapour mixing ratios by a factor of 5 with altitude within the TTL. The null isotopic gradient requires that a major role must be played by convective processes. J.A. Smith discussed the incorporation of isotope microphysics into both a parcel model and a large eddy simulation in order to quantify the source of deuterium for the TTL; D. Murtagh presented new measurements of HDO and H₂¹⁸O from the Odin satellite.

C. Webster presented in situ measurements of HDO, H₂¹⁶O, H₂¹⁸O, and H₂¹⁷O in the UTLS from the ALIAS instrument aboard the WB-57. High isotopic variability was observed, from near-Rayleigh distillation to highly enriched. A. Dessler showed model results for water vapour in the TTL including HDO and predicting that lofted ice is important in simulating the recently observed null gradient in isotopic composition. A. Zahn extended modelling of water vapour isotopic compositions into the middle and upper troposphere, where the oxidation of CH₄ (as well as isotope exchange reactions for the oxygen isotopes) become an important influence beyond the isotopic compositions determined by fractionation in the TTL.

The posters included: (a) water vapour observations by P. Mote (on subseasonal variability in the tropical tropopause region); G. Vaughan (on comparison of water vapour in the UT from radiosondes and two hygrometers); M. Coffey (on the long-term change in stratospheric water vapour from a reanalysis of column measurements from IR spectra); S. Nyeki (on column water vapour using a PFR radiometer at a high-Alpine site); and E. Chiou (on the upcoming SAGE II and SAGE III water vapour datasets); (b) observations of water vapour isotopes by N. Lautie (by Odin/SMR measurements); K. Jucks (on far-IR remote sensing from balloons); K. Boering (on the annual mean D/H ratio of water vapour entering the stratosphere inferred from high precision CH₄ and H₂ isotope measurements from the ER-2); and F. Rohrer (on the longest-lived mode of stratospheric tracer distributions from the relaxation of tritiated water vapour after the thermonuclear test explosions in the 1960s); (c) development of new instrumentation for measuring water isotopes by T. Hanisco (by aircraft-based instrumentation for in situ measurements in the UTLS using a new water photolysis system with the pre-existing OH instrument); P. Franz (on continuous-flow isotope ratio mass spectrometry to measure very small stratospheric water samples); J.-L. Bertaux (on "SOIR" – solar occultation in the infra-red); and M. Andres-Hernandez (on water vapour in the 920-950 nm range using cavity ringdown spectroscopy); and (d) modelling of water vapour and/or its isotopes in the UT and stratosphere by H. Wernli (on troposphere-to-stratosphere transport and implications for water vapour in the extratropical lowermost stratosphere based on a Langrangian climatology for the ECMWF 15-year reanalysis period); M. Bonazzola (on transport and dehydration in the tropical tropopause from 3-month back trajectories); H. Hatsushika (on a stratospheric "sprinkler" over the maritime continent from a trajectory analysis of 3D-AGCM-simulated 3D-wind and temperature); J. Lyons (on the mass-independent fractionation in stratospheric water using a midlatitude box model); E. Moyer (on 3D-NCAR MATCH CTM of seasonal variation in isotopic compositions); and G. Schmidt (3D-GISS GCM modeling of H₂¹⁸O, HDO, and HTO).