Table of Contents * Previous Chapter
The implementation of the ECMWF IFS model has been an important development in CGAM during the last few months. As reported by Roger Brugge, the model is now running satisfactorily and its performance is currently being assessed. The IFS is also being incorporated into the coupled atmosphere-ocean model currently under development at CGAM and U. of Oxford.
Two UGAMP studentships have been allocated this year. Stuart Brentnall will be studying tropical ocean/atmosphere interactions under the supervision of Kelvin Richards at U. of Southampton. Sarah Verbikas will be studying westerly wind bursts over the tropical Pacific Ocean jointly with Julia Slingo and Sean Lawrence (U. of Leicester). Sarah will be based at Reading. Hopefully, both students will contribute to the coupled ocean-atmosphere modelling which will be an important part of UGAMP's future work.
Julia Slingo
Emma Lutman finished her Ph.D. earlier this year and left us to do a post-doc at Bristol University, Geography Department where she will be working on tropospheric chemical trajectory modelling. We all wish her well.
New to the group in October will be Catherine Thompson who will be taking up the position of Scientific Support for 2 years. She will be getting the SLIMCAT model going on the Cray T3D at Edinburgh for some high resolution stratospheric chemistry modelling in collaboration with Kate Searle and Glenn Carver.
We were moderately successful in our submission of proposals to Framework IV, getting about half of those we submitted. Those funded include; TOASTE, APE.
Glenn Carver
Shuzhan Ren has recently left for Toronto.
Eduard Neven has joined us (email ecn20@amtp.cam.ac.uk)
Ben Edgington will soon be leaving us bound for Reading and remaining in the UGAMP 'family'.
Chris Warner and Michael McIntyre's work on propagation of gravity wave spectra has now been submitted as a paper to JAS:
`On the propagation and dissipation of gravity-wave spectra through a realistic middle atmosphere'
Preprints available from Chris.
While writing this paper, we came to the conclusion that correctly choosing the slope of the vertical wavenumber spectrum for smallest vertical wavenumbers is essential to obtain the observed wave-energy altitude dependence
Energy goes as exp(-z/2.3H),
where z is the altitude and H is the density scale height.
We believe this may be a chance for a clean and important `first' as the spectral behaviour at small vertical wavenumber cannot, as far as we are aware, be determined from observations, and yet it is precisely these small vertical wavenumber wave packets that determine the wave-induced force at the highest (mesospheric) altitudes.
Chris Warner
Peter Stott and Gordon Watson have been running the USMM on a Cray C90 at Cineca in Italy. The larger memory available on this machine has enabled them to investigate the behaviour of the model at high resolution, in particular during a stratospheric warming. The first phase of this work has been completed by Gordon in June, and in the second phase, Peter will go to Cineca in September. Unfortunately therefore, Peter will not be able to attend the UGAMP meeting in Cambridge but Gordon will report on our progress so far.
Peter Stott has additional funding for one year to finance a pilot project to couple the USMM with a photochemical scheme. The semi-lagrangian scheme from the IFS will be incorporated in the USMM which will enable the USMM to be run with fully interactive chemistry whilst avoiding the problems of spectral advection of tracers. The model will be used to simulate the stratosphere during recent well observed winters and to test the sensitivity of stratospheric dynamics and photochemistry to changes in the concentration of greenhouse gases.
Anne Pardaens
Warwick Norton, with John Thuburn, has been doing some extended runs with the EUGCM to assess the seasonal evolution and variability in the model. The integrations use a modified version of the PSSJ gravity wave drag scheme. The orographic gravity wave drag is only imposed below 100 hPa (stress going linearly with height to zero). At 100 hPa a spatially uniform source of upward momentum for the gravity wave drag scheme is specified. The breaking criterion of the PSSJ scheme has been modified to make the gravity waves break less violently. Four integrations have been, or are in the progress of being, run. The first is for 5 years of the model at T21. This version of the model has also been run for 500 days at T42. A version of the model has been run for 3 years with an even more gentle breaking criterion of the gravity wave drag scheme. An integration has just started using Rayleigh friction.
Results show that the model captures many features of the observed climatology of the middle atmosphere reasonably well. However there are some clear problems, particularly in early winter in both hemispheres, and in late winter in the southern hemisphere. There are sensitivities of the results to the gravity wave drag used, including the breaking criteria. Surprisingly, higher horizontal resolution appears to make little difference.
Suzanne Rosier has been carrying out simulations of early winter 1991/92, using the UKMO Stratosphere-Mesosphere Model. This is the period that she had previously studied intensively using ISAMS data. The model simulations have revealed that the location and alignment of the polar westerly vortex are particularly important in the development of the observed near-major sudden warming in mid January. In addition, it appears that inertial instability of tropical regions might also influence the higher latitude evolution by moderating the usual cross-equatorial summer-to-winter circulation in the upper stratosphere.
Helen Rogers has been running the SLIMCAT model (courtesy of Martyn Chipperfield) with a view to interpreting ISAMS sulphuric acid data. The sulphuric acid is associated with Pinatubo aerosol, and is thought to be a more conservative tracer than aerosol itself. Validation runs in the absence of diabatic heating showed very good agreement between SLIMCAT and independent runs using an isentropic contour advection scheme. Initial runs with SLIMCAT, using ISAMS sulphuric acid data and including diabatic heating, have highlighted mechanisms responsible for the transport of air from the tropics to midlatitudes in the lower stratosphere.
Euain Drysdale has been using the UKMO Stratosphere-Mesosphere model to investigate waves in the equatorial stratosphere, with the intention of investigating whether a QBO can be produced in the model. To date, a Kelvin wave has been introduced to the model and the resultant acceleration in the mean flow investigated. A start has been made to the modelling of the Rossby-gravity wave thought to be responsible for the easterly phase of the QBO.
Alan Iwi has been investigating whether stratospheric tracer information (e.g. N2O from ISAMS) can be used in a comparatively simple assimilation scheme. The idea is to use UKMO assimilated stratospheric winds (which do not use tracer information) as a first guess, to produce improved wind values, especially in low latitudes. He has also been studying interesting features in the ISAMS low-latitude stratospheric N2O fields and is starting to carry out contour advection simulations of such features.
Tim Hateley continues to perform vital computer system management and programming services for the group. Among other things he has recently been writing a program to convert data in UTF to NetCDF. Eventually a version of the `write_netcdf' routines will be used by UMAP to produce NetCDF data files directly from the UGAMP model. Reasons for doing this are: to produce portable, self-describing datasets, to create 4-D datasets more easily than by using UTF Vx.x., datasets are directly readable by IDL and many other graphics packages, alot of other Meteorology/Oceanography organisations use Netcdf, Netcdf files will be readable (sometime) by MADPO, to get away from the use of UTF.
David Andrews has been writing up some tidal-modelling studies (intended for tidal information in the ISAMS data) with a former student, Andrew Wood. Since Andrew has now (alas) moved out of the field, David has had to adapt and run Andrew's model himself - his first experience of Fortran programming since punched cards (or was it paper tape?) went out of fashion...
David Andrews
Good News! We submitted a proposal to the EC for the continued funding of TOASTE - Transport of Ozone and Stratosphere Troposphere Exchange - which was successful. We have funding for 3 years divided between six groups: RAL (coordinators), Univ. Aberystwyth (Geraint Vaughan), Univ. Cambridge (Peter Haynes / Kathy Law), CNRS Paris (Gerard Ancellet), Univ. Cologne (Adolf Ebel / Hendrik Elbern), Univ Munich (Volkmar Wirth).
Lesley Gray (l.j.gray@rl.ac.uk)
Table of Contents * Previous Chapter