UGAMP
GROUP NEWS
Reading News
CGAM News
Last Summer saw four departures from CGAM. Ben Edgington moved jobs, but not house, and is now with Hitachi in Maidenhead; Colin Jones left to join the Swedish Met Service in Norrkoping; Dingmin Li joined the UK Met. Office to work on data assimilation, and Sarah Verbickas completed her thesis on westerly wind bursts. We wish them all well.
Since then we have been trying to recoup this deficit. In the Autumn, Veronica Asenek and Hamish Struthers began work on the new data assimilation project. Veronica is from Cameroon but has spent several years at the University of Surrey, while Hamish arrived directly from New Zealand.
The New Year brought the welcome arrival of two more new faces. Ross Bannister will be initially diagnosing our AMIP II simulation which used the Unified Model, while Julian Elliott is the new Coordinator of Unified Model usage in UGAMP, taking over Colin's role. Julian's background is in stellar convection and he is one of those lucky enough to have worked and lived in Boulder Colorado (not at NCAR or CIRES, but at JILA, the Joint Institute for Laboratory Astrophysics, a name that conjures up images of test-tube stars!). In March, Pete Inness will be joining us from the Met. Office College to work on climate variability in the tropics.
We have been busy on the "transfer market" too, the result being that Buwen Dong has joined the coupled ocean-atmosphere modelling project, Andrew Gregory will soon begin looking at impacts of the "new dynamics" in the Unified Model and Rich Neale will be looking at ENSO and ENSO-related teleconnections, also in the UM. In March, Robin Glover will formally join CGAM as Coordinator of the palaeoclimate project.
Mike Blackburn
CGAM, University of Reading
M.Blackburn@rdg.ac.uk
Coupled Ocean-Atmosphere Modelling News
The last year has been an exciting one in coupled ocean-atmosphere modelling. Various new projects have got underway and a new member of staff has recently joined the group.
The 1997/1998 period saw one of the largest El Niño events of the century, and also posed many questions for coupled ocean-atmosphere modellers. We have been addressing three of the most important of these questions.
First, we are attempting to determine which features of the atmospheric circulation from this period were definitely caused by changes in sea surface temperature (SST), and how well this response can be simulated by the atmospheric component of the Unified Model (UM). In particular, we have been assessing what predictability there might have been over Europe at different times during the El Niño event.
Secondly, we have been looking at the effect of El Niño on the Atlantic Ocean. Historical records shows us that El Niño is usually followed by a warm sub-tropical Atlantic, and that was also the case during 1998. By using a model which is coupled in the Atlantic but is forced to follow a realistic El Niño cycle in the Pacific, we can see whether the UM coupled model can simulate this response, and also what other SST patterns in the Atlantic might have been caused by El Niño.
Thirdly, we have been looking to see whether the anomalous SSTs present in the Atlantic during 1998 (some of which were caused by El Niño, and some of which were not) also had an impact on the atmospheric circulation. The answer seems to be that they do, and that perhaps half of the predictable signal over Europe may be due to Atlantic SST anomalies (for more information see the article elsewhere in this issue).
Other projects which are just getting under way include a collaboration with the Hadley Centre in which we continue the AMIP 2 ensemble integration up to the present day, and beyond. This will provide a control ensemble against which we can compare a whole variety of experiments looking at the atmospheric response to SST anomalies.
We are pleased to announce a new member of the group. Buwen Dong has moved over from palaeoclimate modelling in the Reading Meteorology Department to CGAM. Initially he will be working on CGAM's contribution to coupled modelling within the international SINTEX project.
Steve Jewson, Rowan Sutton, Buwen Dong
CGAM, University of Reading
steve@met.reading.ac.uk
Low Frequency Group
Adam Scaife (UKMO external PhD student) has successfully completed his PhD on low frequency variability of the stratospheric flow. His thesis demonstrated the critical effect of the amplitude of the tropospheric forcing on the low frequency variability and spring breakdown of the polar night vortex. He also investigated the effects of ENSO tropospheric anomalies on aspects of stratospheric flow, such as the timing of the spring warming. A paper has been submitted to QJ Roy. Met. Soc.
Gilles Garric (BAS Research Fellow) has come to the end of his contract. He has modified the SGCM to include dynamical interactions between sea ice cover and low level winds, depending on whether leads in the sea ice are opened, allowing intense heating of the low level air, or closed, shutting off the surface heat flux. The effect of interactive sea ice is to move the midlatitude storm zone polewards, with more depressions taking a high latitude trajectory. The feedback between sea ice and atmospheric cyclones can, in some circumstances, generate low frequency variability of both the ice cover and the atmospheric flow, with periods in excess of 50 days and large spatial scales. A paper is being submitted to the QJ Roy. Met. Soc.
Ulrike Burkhardt (NERC Research Fellow) is studying the suppression of storm track activity over North America and the interactions between the Pacific and Atlantic storm tracks using observational and model data. She has carried out preliminary integrations of a version of the IGCM modified to include various configurations of the Pacific and Atlantic and of the Rocky mountains (Len Shaffrey, 1997). This model simulates fairly realistic storm tracks. Analysis of the differences between the storm tracks and of the connection between the two storm tracks in these various versions of the model and in observational data is being carried out.
Antonia Valente (PhD student sponsored by the Portuguese government) is using a mesoscale non-linear non-hydrostatic model to simulate the effect of a weak directional wind shear on orographic gravity wave drag. The results show that directional wind shear should be taken into account in parametrizations of GWD. Linear regimes (low mountains) are well represented by the linear theory for directional shear, and high drag regimes (breaking waves) retain some of the characteristics of linear flows, but low drag regimes (high mountains) are not described by the linear theory.
Sylvia Hare (NERC PhD student) is looking at the effect of the meridional overturning, found in the atmosphere in association with zonal acceleration at tropospheric jet entrance and exit regions, on the lifecycles of baroclinic waves. Simmons and Hoskins (e.g. 1978) type lifecycle calculations have been made, initialised with a normal mode perturbation. Meridional overturning has a dramatic effect on the lifecycle, both in terms of eddy magnitude and structure, particularly in the non-linear and decay phases of the lifecycle. The calculations are being extended to allow the basic state to evolve, in order to represent the passage of evolving disturbances along the jet.
Ian James
Meteorology Dept., University of Reading
I.N.James@rdg.ac.uk
