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UGAMP GROUP
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Cambridge, Chemistry News
Personnel changes
There have been a relatively large number of personnel changes within the group since the last newsletter.
First we welcome Prof. Gerard Jennings as a visiting scientist from Ireland. He will be spending some time working with the tropospheric chemistry group. His email address during his stay is: sgj@atm.ch.cam.ac.uk.
Other new faces include Maurette Cahill (Ph.D. student) who is funded under the NERC HPC special topic II grant to do some tropospheric chemistry modelling on the Cray T3D, looking at ACSOE data. Juliane Mossinger also joins the group. We also welcome Simon Hall and Dr. Anne Griffiths who will be working with David Lary on data assimilation. Lastly, we welcome Dr. Helen Rodgers as a post-doc, poached (!) from our UGAMP colleagues at Oxford where she did her Ph.D. She will be working with the SLIMCAT model.
Over the past 6 months or so, we've had to say farewell to quite a few familiar faces. Kathy Preston (from Rod Jones' group) left to do a post- doc with NIWA in New Zealand in July 1996. About the same time, Joachim Sessler finished his Ph.D. and left academic life to start work with a consultancy firm in his native Germany. Sarah Goodchild left in October to start a new job with the UK Met. Office. Jim Sussler (from Rod Jones' group) left to take up a post-doc position back in his native USA. Dr. Nik Nikiforakis became an employee of the Dept. of Applied Mathematics but still hangs around the group! Dr. Oliver Wild finished his Ph.D. and started a post-doc, working for Michael Prather in the Earth System Science Dept. at the University of California. Dr. Jamie Kettleborough also started a post-doc position in the USA with Jim Holton at Washington University. Iarla Kilbane-Dawe finished his thesis and started work at the European Ozone Research Coordinating Unit across the road. Finally, Zoe Stockwell is about to leave at the end of January 1997 to start a new job with the Dutch Met. service to do some research into cloud chemistry. All have hopefully enjoyed their time in the group and will be missed. We wish them all well in their future careers.
Congratulations are also due to Dr. David Lary on his award of the Royal Society fellowship.
Details of all Centre for Atmospheric Science
personnel, including those who've left can be
found on the web page:
http://www.atm.ch.cam.ac.uk/cas/cas_members.html
Some recent publications
(also see publications for Imperial College)
Chipperfield M.P., M.L. Santee, L. Froidevaux, G.L. Manney, W.G. Read, J.W. Waters, A.E. Roche, J.M. Russell, Analysis of UARS data in the southern polar vortex in September 1992 using a chemical transport model, J. Geophys. Res., in press, 1996.
Chipperfield M.P., A.M. Lee and J.A. Pyle, Model calculations of ozone depletion in the Arctic polar vortex for 1991/92 to 1994/95, Geophys. Res. Lett., 23, 559-562, 1996.
Chipperfield M.P., E.R. Lutman, J.A. Kettleborough and J.A. Pyle, Model studies of chlorine deactivation and formation of ClONO2 collar in the Arctic polar vortex, J. Geophys. Res., Halkidiki Ozone Conference Special Issue, in press, 1996.
Ghosh S., J.A. Pyle and P. Good, The temperature dependence of the ClO concentration near the stratopause, J. Geophys. Res., accepted for publication, 1996.
Lary D.J., Gas phase atmospheric bromine photochemistry, J. Geophys. Res., 101, D1, 1505- 1516, 1996.
Lary D.J., M.P. Chipperfield, R. Toumi and T.M. Lenton, Heterogeneous atmospheric bromine photochemistry, J. Geophys. Res., 101, D1, 1489- 1504, 1996.
Lee A.M., G.D. Carver, M.P. Chipperfield and J.A. Pyle, Three-dimensional chemical forecasting: A methodology, J. Geophys. Res., ASHOE special issue, in press, 1996.
Sessler J., P. Good, A.R. MacKenzie and J.A. Pyle, What role do type I PSC and aerosol parametrizations play in modelled lower stratospheric chlorine activation and ozone loss? J. Geophys. Res., in press, 1996.
Glenn Carver
(Cambridge, Chemistry)
Progress with Data Assimilation
Steady progress is being made with the data assimilation of atmospheric constituents. Two new people have come to work on the project: Simon Hall and Anne Griffith. Simon Hall has just finished his PhD in Astrophysics at Cambridge and is working on the programming and visualisation aspects of the project. Anne Griffith has just finished her PhD in Applied Maths (Data Assimilation) at Reading, and will be working on developing the mathematical aspects. A warm welcome to both of them!
The main focus of the work is to produce the first ever self consistent data set of atmospheric chemical constituents. This data set will then be used as the observational basis to perform a thorough and detailed analysis of the chemistry. Particular attention will be paid to the relative roles of the various catalytic cycles, and the interaction between chemistry and dynamics, in polar and mid-latitude ozone loss.
In regions where poor agreement is found between observations and model potential causes will be thoroughly investigated as valuable pointers to improving our understanding. The discrepancies may be due to factors such as an incomplete description of the chemistry or incorrect rate constants.
We plan to pay particular attention to the treatment of model and analysis errors. This may include the implementation of a Kalman filter.
David Lary
(Cambridge, Chemistry)
A systematic study of atmospheric chemical mechanisms
Together with Dudley Shallcross, Kathy Law and Slimane Bekki, work is underway to implement a very detailed chemical scheme including oxygen, hydrogen, nitrogen, chlorine, bromine, sulphur and hydrocarbon species. Various mathematical techniques will be used to perform a systematic study of nonlinear chemical interactions present and to obtain an optimum specie and reaction set for use in large scale chemical-transport models. The particular focus of this work will be the role of hydrocarbons in the lower stratosphere, the tropospheric oxidation of hydrocarbons by halogens, the role of various nitrates as NOx reservoirs, the potential effect on all of this of heterogeneous reactions on carbon aerosols, as well as a range of other issues.
I would like to thank the Royal Society for awarding me a Royal Society University Research Fellowship at Cambridge, and the NERC and EU for granting research support.
David Lary
(Cambridge, Chemistry)
Cambridge, DAMTP News
Personnel changes
DAMTP says goodbye to John Scinocca, Jamie Kettleborough, Richard Scott and soon Gavin Esler. However, Mike Greenslade, Stephen Griffiths and Ali Mohebalhojeh have joined us since the last newsletter.
The DAMTP World-Wide Web home page is at:
http://www.atmos-dynamics.damtp.cam.ac.uk/
and has details of all DAMTP personnel.
Recent publications
Please see the web page:
http://www.atmos-dynamics.damtp.cam.ac.uk/papers.html
for details of publications.
Sparling, L. C., J. A. Kettleborough, et al.: Diabatic Cross-isentropic Dispersion, J. Geophys. Res., (submitted).
Warner, C. D., and M. E. McIntyre: Gravity wave spectral models and the shapes of gravity wave spectra at low vertical wavenumbers. Proc. NATO Adv. Res. Workshop ASI Series, Vol 1, ed. K. Hamilton, Gravity Wave Processes and Their Parameterization in Global Climate Models, Springer Verlag, Berlin (in press).
Balluch, M., and P. H. Haynes: Quantification of Lower Stratospheric Mixing Processes Using Aircraft Data, J. Geophys. Res., (submitted).
McIntyre, M. E., and I. Roulstone: Hamiltonian Balanced Models: Constraints, slow manifolds and velocity splitting, J. Fluid Mech., (accepted).
Haynes, P. H.: The Latitudinal Structure of the Quasi-Biennial Oscillation, Q. J. Roy. Met. Soc., (submitted).
Warner, C. D., and M. E. McIntyre: On the propagation and dissipation of gravity-wave spectra through a realistic middle atmosphere, J. Atmos. Sci., 53, 3213--3235.
McIntyre, M. E.: Lucidity, Hypercredulity and Civilised Existence, or, What Has Music got to do with Quantum Mechanics?, Interdisciplinary Science Reviews, (accepted)
Tan, D. G. H., P. H. Haynes, A. R. Mackenzie, and J. A. Pyle, 1996: The effects of fluid- dynamical stirring and mixing on the deactivation of stratospheric chlorine, J. Geophys. Res., (submitted).
Scott, R.: Seasonal and Interannual Variations of the Stratospheric Circulation, (Ph.D. Thesis)
Scinocca, J., and P. H. Haynes, 1997: Dynamical forcing of stratospheric waves by the tropospheric circulation, J. Atmos. Sci., (submitted).
Haynes, P. H., and J. Anglade: Vertical-Scale Cascade in Tracer Fields, J. Atmos. Sci., (submitted).
Computing news
From April 1 N. Pinhey will no longer be UGAMP-funded, though his job will remain much the same. N. Pinhey's current work involves porting the parallelised SGCM to the Hitachi SR2201 at Cambridge, following which he will change the communication libraries used from PVM to MPI and then change the decomposition scheme from 1D to 3D to permit low (horizontal) resolution experiments to be run efficiently on 64 processors or less.
Research
CD Warner and ME McIntyre: Work on gravity-wave spectral propagation.
There are two current strands to this work. First, we have completed the first 100 day run with a new gravity wave parametrization derived from the power spectral model of Warner and McIntyre (see references above). This EUGCM run will shortly be analysed in detail and the results will be used to inform a decision on gravity wave parametrization scheme choices for the forthcoming AMIP2 programme. Implementations of the new parametrization for ECMWF IFS and UKMO UM models are the logical next step.
Second, two proposals have been written to apply for NERC and EC funds to continue the development of the power spectral model into an 'intermediate model' (intermediate in the sense of too big to be a parametrization but too small to model the fine detail of gravity wave breaking). The EC proposal, will (if funded) also allow us to expand the gravity-wave work to take advantage of our continental colleaguesŐ wave observing capabilities.
JA Kettleborough with LC Sparling and others (see reference above)
This work gives new constraints on lower-stratospheric chemical transport, confirming that cross-isentropic diffusion is not enough to support the version of the "flowing processor hypothesis" that envisages flow out the bottom of the polar vortex followed by equatorward advection and upward diffusion into the midlatitude stratosphere.
ME McIntyre with J Thuburn (see reference above)
This work clarifies some fundamental issues about lower-stratospheric transport, chemical correlations, and their treatment by numerical advection schemes.
ME McIntyre with I Roulstone and J Theiss (see reference above)
This work on fundamentals of Hamiltonian balanced dynamics continues to develop. J Theiss is working with ME McIntyre and I Roulstone of the Met Office to develop and clarify the theory further.
Edinburgh News
Personnel changes
Peter Stott, Gordon Watson and Phil Mote all departed the UGAMP fold during the summer. Peter is now at the Hadley Centre, Gordon is with Edinburgh University Computing Services and Phil has returned to the U.S. Phil, Peter and Bob Harwood are continuing to collaborate on revisions to a paper on stratospheric flow during two recent winters simulated by the USMM which they have submitted to the J. Atmos. Sci.
Studies with the COSMIC model
The COSMIC (COupled Stratosphere-Mesosphere Interactive Chemistry) model comprises the USMM coupled to the TOMCAT off-line chemical transport model. The two models are run in tandem with TOMCAT using winds and temperatures from the USMM, and the radiation scheme of the USMM using ozone from TOMCAT. Ian MacKenzie has been using this model to investigate the importance of chemical-radiative feedback in the polar regions during winter and spring when ozone in the lower stratosphere is being rapidly destroyed by chemistry. Initial experiments have focused on the 1992 Antarctic winter, comparing results from two runs of the COSMIC model beginning on August 14, identical except that one run included heterogeneous chemical reactions on PSCs, and the other did not. The USMM components of the runs were initialised and forced at the lower boundary with UKMO data. The southern hemisphere ozone field was initialised from MLS observations, and the other chemical species initialised from a 2-D model, with the concentration of the chlorine compounds scaled to give a total inorganic chlorine loading of 3.4 ppbv.
(contd. at top of next column)
(contd. from previous column)
Preliminary analysis indicates that the inclusion of heterogeneous reactions leads to a cooler lower stratosphere and a warmer upper stratosphere at high latitudes, which is what is expected from purely radiative effects associated with the lesser ozone amount in the lower stratosphere. Further diagnoses will look at the differences in radiative and dynamical heating rates and the consequent impact on the advection of passive tracers in the USMM as the runs are extended through the time of the final warming and vortex break up. It is planned to repeat the USMM parts of these COSMIC runs using the same lower boundary forcing and time-evolving ozone field but starting from slightly different initial conditions to ascertain if an ensemble of runs is required to isolate the feedback effects from other non-linear responses. Also, the TOMCAT runs may be repeated with a fixed chemical scheme but forced by winds and temperatures from previous COSMIC runs with and without heterogeneous chemistry. This should help to reveal the impact on the total ozone depletion of dynamical changes caused by radiative feedback.
Imperial College News
Personnel changes
We are pleased to welcome Alice Larkin, from University of Leeds, who has joined us as a postgraduate student.
Research activities
Radiation schemes
Further development of the extended Morcrette radiation scheme:
- LW - Water vapour - All the Pade coefficients for water vapour lines have been refitted using newly calculated line-by-line (GENLN2 version 4.0) reference transmissivities weighted by the Planck function or its derivative.
- CO2 and Ozone - All transmission tables have been recomputed using double precision and GENLN2.
- SW - The spectral range has been extended down to 0.12 microns (from 0.25 microns) so that solar heating up to 95km can be calcu- lated. A new parameterization of the Schu- mann-Runge bands and continuum of molecular oxygen has been developed from a higher resolution shortwave scheme. The new parameterization can calculate fluxes as well as heating rates and is accurate and fast. The Herzberg continuum is also included using the Shine (1989) parametrization.
The new scheme has been made considerably faster and more memory efficient than the original Morcrette scheme and because of its range of applicability it removes the requirement to match the results of different middle and lower atmosphere schemes in the EUGCM.
The scheme works very accurately as a stand- alone radiation code and has recently been implemented in the EUGCM. The first long runs and tests should be finished soon; initial results suggest an improvement in the model's lower stratospheric temperature structure.
Modelling radiation exchange within and between cloud structures:
In order to study the 3D radiative transfer in cloud a radiation finite element method (RFEM - developed at the Centre for Analytical Research in the Environment at IC) will be used to simulate a boundary layer capped by a layer of inhomogeneous stratocumulus cloud. Preliminary tests include the comparison of the results of a simple 1-D situation of RFEM with those from a standard discrete ordinates method. For this Mie scattering code has been used to specify the scattering parameters, at several wavelengths in the visible and near infrared, required by the codes.
Use of Hadley Centre radiation code:
We are investigating possible approaches to extending the range of applicability of the Edwards and Slingo radiation code into the middle atmosphere.
Wenyi Zhong &
Conrad Winchester
(Imperial)
Antarctic polar response to a prescribed ozone depletion
The UGCM has been used to study the effect of changes in polar ozone on the radiation balance, temperature structure and evolution of the polar vortex in winter high latitudes. Previous work has shown that the prescribed ozone depletion has caused a reduction in the net radiative heating within the vortex, a temperature reduction in the lower and middle stratosphere and a delay in the final warming of some 30 days. Comparing these results with 5 years of the AMIP Y1 integrations and TOVS 1979/1987 data show that the delay in the final warming and vortex breakdown is statistically significant and similar in magnitude to that observed.
Equatorial stratospheric winds
The effect of the equatorial stratospheric winds on the extratropical stratosphere is being investigated using a two-dimensional model with parametrized planetary wave winds. Current work is concentrating on inverting the potential vorticity using the gradient wind approximation. The diagnosed winds are then used in the next iteration step. Preliminary results suggest that the phase and direction of the equatorial winds are both important in predicting the state of the Arctic winter polar vortex.
Simon Ibbotson
(Imperial)
Solar variability and climate change
Experiments with the UGCM have been carried out to investigate the impact of solar variability on the troposphere and lower stratosphere. Previous work had suggested that changes to lower stratospheric ozone may play a key role and the new results confirm this. The ozone increase, at higher levels of solar activity, causes heating of the low latitude lower stratosphere, local deceleration of the polewards branches of the Hadley cells, broadening of the Hadley cells and polewards shifts of the mid-latitude jet-streams and storm tracks. All the 'solar maximum' experiments show this qualitative behaviour but the degree to which this happens depends sensitively on the latitudinal structure of the low latitude increases in ozone. It has not yet proved possible to unequivocally extract these from satellite data so the actual response of the atmosphere (as modelled by the UGCM) is still uncertain.
Recent publications
Haigh J D, 1996, The impact of solar variability on climate. Science, 272, 981-984.
Toumi R, J D Haigh and K S Law, 1996, A tropospheric ozone - lightning climate feedback. Geophys.Res.Lett., 23, 1037-1040.
Zhong W, J D Haigh, R Toumi and S Bekki, 1996, Infrared heating rates in the stratosphere due to volcanic sulphur dioxide. Quart.J.R.Meteorol.Soc., 122, 1459-1466.
Bekki S, J A Pyle, W Zhong, R Toumi, J D Haigh and D M Pyle, 1996, Role of microphysical and chemical processes in prolonging the climate forcing of the Toba eruption. Geophys.Res.Lett., 23, 2669-2672.
Zhong W, R Toumi and J D Haigh, 1996, Seasonal variation of radiative forcing of climate from stratospheric ozone depletion calculated from observed temperature trends. Geophys.Res.Lett., 23, 3183-3186.
Oxford News
Middle Atmosphere
Warwick Norton has been continuing to study mesospheric phenomena in the EUGCM, in collaboration with John Thuburn; a new DPhil student. Maisa Rojas-Corradi, from Chile, is also working with him on this. Recent studies with the model have looked at the structure and evolution of the '2-day wave' and the diurnal tide, and the evolution and control by gravity-wave drag of the cold summer mesopause. Further details are given in an article in this issue (see UGCM Modelling).
Suzanne Rosier has now obtained her DPhil, and has moved to Reading, to work with Keith Shine.
Helen Rogers recent work
has focused on
experiments with SLIMCAT (a high-resolution
chemical-transport model) and a contour
advection model, to simulate the transport of
sulphuric acid (associated with Pinatubo aerosol)
in the lower stratosphere. The effects of particle
sedimentation were included in SLIMCAT. The
simulations show small-scale features not readily
observable with current observational techniques.
Comparisons with ISAMS measurements have
been made, for both Northern and Southern
hemispheres. Helen has now completed her DPhil
and has moved to the
Chemistry Department at
Cambridge.
Alan Iwi has been studying an interesting example of isentropic transport into the tropics of the middle stratosphere, in MLS H2O, MLS O3 and ISAMS N2O data, and has modelled this using contour advection and domain-filling trajectories, driven by horizontal winds from the UKMO assimilation and diabatic vertical winds. He has also found statistically significant pole- equator temperature anticorrelations in the middle and upper stratosphere, by analysing ISAMS and UKMO assimilated temperatures; he is investigating whether these are associated with periods of enhanced global meridional circulation. Euain Drysdale continues to use the UKMO SMM to model equatorial waves in the lower stratosphere. He has recently focused on getting the model to run at a higher vertical resolution (1km). This is needed in order to model various classes of vertically propagating waves which are thought to be significant in the driving of the QBO. The model is now performing well at the higher resolution, and experiments are being performed in which different classes of waves are forced in the model, and its response to these waves observed.
A new DPhil student, Sophia Oliver, joined us in November, and is working with David Andrews on modelling atmospheric tides.
David Andrews is on sabbatical from January-September 1997, and will be concentrating on writing a basic undergraduate textbook on Atmospheric Physics.
Rutherford Appleton Laboratory News.
TOASTE-C
Work continues on the use of contour advection to study mixing of stratospheric and tropospheric air. Methods have been developed for using global contours to allow the measurement of local stretching rates within a single synoptic system. The contours are first used to identify the rate at which stretching and folding are taking place along the edge of the jet, and then selected sections of contour re-advected using fixed parcels (i.e. no re-noding takes place) in order to get local stretching rate measures. Results indicate that local regions of stretching may not correspond to local collapse perpendicular to a contour (i.e. material can flow into a region along the isentropic surface). This can result in increasing contour lengths even where a trough is broadening. On the other hand in regions of large deformation, the along contour stretching rate can be as large as the rate of structural collapse perpendicular to the contour. These effects are not uniform with potential temperature:- stretching and collapse rates at 305K and 315K can be smaller by factors of 2 than those at 310K. On the observational side, and extensive campaign took place in June of 1996, involving the use of airborne lidar, and ground based lidar, sondes and radar to observe a cut-off low propagating over Europe. Efforts are being made to get the UM going locally on a new alpha-station 255/233 in order to model this campaign.
QBO
Work continues on studying the effect of the QBO on tracer distribution. We have submitted two papers to JGR concerning the QBO's interaction with the SAO and planetary waves, and the effect this has on the double peak. The first paper concentrates on the observed variability seen in HALOE methane, while the second details the results of a 2-d modelling study to investigate the underlying mechanisms which contribute to the observed variation. These papers expand on material presented at previous UGAMP meetings. This work is now being extended to 3-d using the UKMO SMM.
We are also using the SMM to look at the relative importance of internal stratospheric variability in determining the winter circulation, and in particular in the evolution of sudden warmings. We have successfully bid for a NERC grant to fund this work until summer 1999.