Visiting Scientist 2018

With thanks to Kaja Milczewska

Every year the PhD students in the Meteorology Department invite a distinguished scientist to spend a few days with us. This year, the students voted for the Visiting Scientist to be Prof. Olivia Romppainnen-Martius, who came to the Department from 4th-7th June 2018.

Prof. Romppainen-Martius is based at the University of Bern, in Switzerland, as an Associate Professor researching climate impacts.

Olivia’s research interests broadly covers mid-latitude atmospheric dynamics, with topics from how blocking events are precursors Sudden Stratospheric Warming events, to more impact based work on heavy Alpine precipitation and extreme hail in and around Switzerland. Her main research areas can be summarised as dynamics of short-term climate variation, forecasting and statistics of high-impact weather events and mid-latitude weather systems. More about her research and publications can be found here.

As is usual for the start of our distinguished visitor’s stay, Prof. Romppainen-Martius’s visit began with an introduction from Prof. Sue Gray during the coffee reception. This was immediately followed by a special seminar, titled “Recent hail research in Switzerland – the challenges and delights of complex orography and crowd-sourced data”. Her talk covered various probabilistic measures for predicting hail in the mountainous region that is Switzerland and how the climatology of these identified events is strongly linked with these mountainous areas. Verification of these predictions has recently been achieved through observer reports via the MeteoSwiss app, where observers record the time, location, and size of the hail they have observed.

The day was rounded off with a social at Zero Degrees, with Olivia and many PhD students engaging in fruitful conversation over pizza and beer.

After a busy first day, the second day of her visit included individual meetings with both research staff and students, and attending the Mesoscale and HHH (Hoskins-Half-Hour) research groups. On Wednesday 5th July, some PhD students presented their research to Olivia to showcase the breadth of topics covered in the Meteorology department. Interestingly, one of the talks ‘reliably’ informed us that Arctic sea-ice melting meant it was now possible to go on holiday cruises to see penguins. Clearly these penguins are on holiday too…


At the weekly PhD Group meeting, Prof. Romppainen-Martius gave some useful advice on careers in academic research and the pathway to her current position – which of course includes lots of skiing. Additionally, she advertised some post-doctoral funding opportunities in Switzerland and Germany, which was sure to encourage the keen skiers in the crowd. This was an engaging open discussion about the realities of research life, and attendance was made all the better by biscuits from the group leaders Beth and Liam.

On the last day of her visit (Thursday 8th June), Olivia gave her second departmental seminar titled “Periods of recurrent synoptic-scale Rossby waves and associated persistent moderate temperature extremes”. The seminar was followed by a well-attended leaving reception, which concluded Olivia’s visit to our department. The students prepared a photo frame and other England themed items as a gift, to thank our distinguished scientist for accepting the invitation to spend an inspiring week with us.  Unfortunately, Olivia could not stay for the ‘world-renowned’ annual Met BBQ and Barn Dance on the Friday, but nonetheless we hope that she enjoyed her visit as much as we did!


Understanding the dynamics of cyclone clustering

Priestley, M. D. K., J. G. Pinto, H. F. Dacre, and L. C. Shaffrey (2016), Rossby wave breaking, the upper level jet, and serial clustering of extratropical cyclones in western Europe, Geophys. Res. Lett., 43, doi:10.1002/2016GL071277.


Extratropical cyclones are the number one natural hazard that affects western Europe (Della-Marta, 2010). These cyclones can cause widespread socio-economic damage through extreme wind gusts that can damage property, and also through intense precipitation, which may result in prolonged flood events. For example the intensely stormy winter of 2013/2014 saw 456mm of rain fall in under 90 days across the UK; this broke records nationwide as 175% of the seasonal average fell (Kendon & McCarthy, 2015). One particular storm in this season was cyclone Tini (figure 1), this was a very deep cyclone (minimum pressure – 952 hPa) which brought peak gusts of over 100 mph to the UK. These gusts caused widespread structural damage that resulted in 20,000 homes losing power. These extremes can be considerably worse when multiple extratropical cyclones affect one specific geographical region in a very short space of time. This is known as cyclone clustering. Some of the most damaging clustering events can result in huge insured losses, for example the storms in the winter of 1999/2000 resulted in €16 billion of losses (Swiss Re, 2016); this being more than 10 times the annual average.

Figure 1. A Meteosat visible satellite image at 12 UTC on February 12th 2014 showing cyclone Tini over the UK. Image credit to NEODAAS/University of Dundee.

Up until recently cyclone clustering had been given little attention in terms of scientific research, despite it being a widely accepted phenomenon in the scientific community. With these events being such high risk events it is important to understand the atmospheric dynamics that are associated with these events; and this is exactly what we have been doing recently. In our new study we attempt to characterise cyclone clustering in several different locations and associate each different set of clusters with a different dynamical setup in the upper troposphere. The different locations we focus on are defined by three areas, one encompassing the UK and centred at 55°N. Our other two areas are 10° to the north and south of this (centred at 65°N and 45°N.) The previous study of Pinto et al. (2014) examined several winter seasons and found links between the upper-level jet, Rossby wave breaking (RWB) and the occurrence of clustering. RWB is the meridional overturning of air in the upper troposphere. It is identified using the potential temperature (θ) field on the dynamical tropopause, with a reversal of the normal equator-pole θ gradient representing RWB. This identification method is explained in full in Masato et al. (2013) and also illustrated in figure 2. We have greatly expanded on this analysis to look at all winter clustering events from 1979/1980 to 2014/2015 and their connection with these dynamical features.

Figure 2. Evolution of Rossby waves on the tropopause. RWB occurs when these waves overturn by a significant amount. H: High potential temperature; L: Low potential temperature (Priestley et al., 2017).

We find that when we get clustering it is accompanied with a much stronger jet at 250 hPa than in the climatology, with average speeds peaking at over 50 ms-1 (figures 3a-c). In all cases there is also a much greater presence of RWB in regions not seen from the climatology (Figure 3d). In figure 3a there is more RWB to the south of the jet, in figure 3b there is an increased presence on both the northern and southern flanks, and finally in figure 3c there is much more RWB to the north. The presence of this anomalous RWB transfers momentum into the jet, which acts to strengthen and extend it toward western Europe.

Figure 3. The dynamical setup for clustering occurring at (a) 65°N; (b) 55°N; and (c) 45°N. The climatology is shown in (d). Coloured shading is the average potential temperature on the tropopause, black contours are the average 250 hPa wind speeds and black crosses are where RWB is occurring.

The location of the RWB controls the jet tilt; more RWB to the south of the jet acts to angle it more northwards (figure 3a), there is a southward deflection when there is more RWB to the north of the jet (figure 3c). The presence of RWB on both sides extends it along a more central axis (figure 3b). Therefore the occurrence of RWB in a particular location and the resultant angle of the jet acts to direct cyclones to various parts of western Europe in quick succession.

In our recently published study we go into much more detail regarding the variability associated with these dynamics and also how the jet and RWB interact in time. This can be found at

This work is funded by NERC via the SCENARIO DTP and is also co-sponsored by Aon Benfield.


Della-Marta, P. M., Liniger, M. A., Appenzeller, C., Bresch, D. N., Köllner-Heck, P., & Muccione, V. (2010). Improved estimates of the European winter windstorm climate and the risk of reinsurance loss using climate model data. Journal of Applied Meteorolo

Kendon, M., & McCarthy, M. (2015). The UK’s wet and stormy winter of 2013/2014. Weather, 70(2), 40-47.

Masato, G., Hoskins, B. J., & Woollings, T. (2013). Wave-breaking characteristics of Northern Hemisphere winter blocking: A two-dimensional approach. Journal of Climate, 26(13), 4535-4549.

Pinto, J. G., Gómara, I., Masato, G., Dacre, H. F., Woollings, T., & Caballero, R. (2014). Large‐scale dynamics associated with clustering of extratropical cyclones affecting Western Europe. Journal of Geophysical Research: Atmospheres, 119(24).

Priestley, M. D. K., J. G. Pinto, H. F. Dacre, and L. C. Shaffrey (2017). The role of cyclone clustering during the stormy winter of 2013/2014. Manuscript in preparation.

Swiss Re. (2016). Winter storm clusters in Europe, Swiss Re publishing, Zurich, 16 pp., Accessed 24/11/16.