Stratosphere and Climate Group

Strat-hour

Strat-hour is a meeting on stratospheric research for scientists and PhD students at the Department of Meteorology and beyond. It is generally held as an informal oral presentation of 45 minutes plus questions. You can subscribe to the Met-strathour mailing list to be kept up-to-date with the schedule.

Interested in presenting some work at Strat-hour? Please e-mail Angus or Andrew using the addresses in the right hand panel.

Current Schedule:

25th May 2012 2 pm 1L61

Isla Simpson (University of Toronto) Understanding climate model biases in Southern Hemisphere mid-latitude variability. The Southern Annular Mode (SAM) represents a latitudinal shifting of the Southern Hemisphere (SH) jet stream and is the dominant mode of variability in the SH mid-latitude circulation. A common bias among global climate models is that they tend to exhibit SAM variability that is much too persistent, particularly in the summer season. Many climate forcings such as ozone depletion/recovery and increasing greenhouse gas concentrations result in tropospheric circulation changes that project strongly onto the SAM and therefore the inability of models to simulate natural SAM variability correctly is of concern for the ability of such models to accurately predict future circulation changes. Here, specifically targetted experiments with one global climate model, the Canadian Middle Atmosphere Model (CMAM), will be used to investigate the cause of this bias in SAM variability. The role of biases in stratospheric variability and climatological tropospheric jet structure will be assessed. It is found that even in the absence of stratospheric variability the SAM timescales are biased long relative to the observations, suggesting a role for a bias in internal tropospheric dynamics. Furthermore, it is found that this bias is not alleviated when the climatological tropospheric jet structure is improved in an artificial way. An analysis of eddy-mean flow feedbacks reveals that the strength of planetary scale wave feedbacks differ between the model and observations leading to the enhanced SAM persistence.

16th November 2012

Peter Hitchcock (University of Cambridge)

Previous Strat-hour seminars:

16th March 2012	Blanca Ayarzagüena (Freie Universitaet Berlin) Study of stratospheric sudden warmings in the Northern Hemisphere: tropospheric forcing and climate change
4th November 2011	Gavin Esler (University College London) The nonlinear self-tuning resonance theory of stratospheric sudden warmings A range of simple experiments using idealised models of the stratospheric vortex demonstrate a mechanism for generating vortex splits and vortex displacement events. The modelled events are shown to share key features with observed stratospheric sudden warmings. The key point about the generation mechanism is that, unlike in previous experiments (following e.g. Matsuno 1970), a large change in forcing at the model lower boundary is not required to initiate the vortex split or displacement. Instead it is shown that a small change can initiate a subsequent event by crossing a nonlinear bifurcation point in parameter space. The existence of the bifurcation curve is implicit in the nonlinear self-tuning resonance idea of Plumb (1982).
21st October 2011	Kerry Day (University of Bath) Planetary wave dynamics of the Stratosphere, Mesosphere and Lower Thermosphere Planetary waves are large global-scale meandering waves in the atmosphere. We can observe them by the winds and temperatures in the atmosphere. The focus of my studies is on the 5- and 16-day wave planetary waves in the stratosphere, Mesosphere and Lower Thermosphere (MLT), together the middle atmosphere. Planetary waves are important in transporting energy, momentum and chemical species. They can help explain the dynamics and coupling of the atmosphere in a region which is still, on the whole, poorly understood. Only in the last ~20 years have techniques to observe this region been developed and deployed. Here the studies use meteor radars and satellite to observe the winds and temperatures, respectively, of the middle atmosphere. An overview of my studies to date will be presented including major conclusions from the 4 papers produced.

Latest update: May 2012