Evidence week, or why I chatted to politicians about evidence.

Email: a.w.bateson@pgr.reading.ac.uk

Twitter: @a_w_bateson

On a sunny Tuesday morning at 8.30 am I found myself passing through security to enter the Palace of Westminster. The home of the MPs and peers is not obvious territory for a PhD student. However, I was here as a Voice of Young Science (VoYS) volunteer for the Sense about Science Evidence WeekSense about Science in an independent charity that aims to scrutinise the use of evidence in the public domain and to challenge misleading or misrepresented science. I have written previously here about attending one of their workshops about peer review, and also here about contributing to a campaign aiming to assess the transparency of evidence used in government policy documents.

The purpose of evidence week was to bring together MPs, peers, parliamentary services and people from all walks of life to generate a conversation about why evidence in policy-making matters. The week was held in collaboration with the House of Commons Library, Parliamentary Office of Science and Technology and House of Commons Science and Technology Committee, in partnership with SAGE Publishing. Individual events and briefings were contributed to by further organisations including the Royal Statistical Society, Alliance for Useful Evidence and UCL. Each day had a different theme to focus on including ‘questioning quality’ and ‘wicked problems’ i.e. superficially simple problems which turn out to be complex and multifaceted.

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Throughout the week both MPs, parliamentary staff and the public were welcomed to a stand in the Upper Waiting Hall to have conversations about why evidence is important to them. Photo credit to Sense about Science.

Throughout the parliamentary week, which lasts from Monday to Thursday, Sense about Science had a stand in the Upper Waiting Hall of Parliament. This location is right outside committee rooms where members of the public will give evidence to one of the many select committees. These are collections of MPs from multiple parties whose role it is to oversee the work of government departments and agencies, though their role in gathering evidence and scrutiny can sometimes have significance beyond just UK policy-making (for example this story documenting one committee’s role in investigating the relationship between Facebook, Cambridge Analytica and the propagation of ‘fake news’). The aim of this stand was to catch the attention of both the public, parliamentary staff, and MPs, and to engage them in conversations about the importance of evidence. Alongside the stand, a series of events and briefings were held within Parliament on the topic of evidence. Titles included ‘making informed decisions about health care’ and ‘it ain’t necessarily so… simple stories can go wrong’.

Each day brought a new set of VoYS volunteers to the campaign, both to attend to the stand and to document and help out with the various events during the week. Hence I found myself abandoning my own research for a day to contribute to Day 2 of the campaign, focusing on navigating data and statistics. I had a busy day; beyond chatting to people at the stand I also took over the VoYS Twitter account to document some of the day’s key events, attended a briefing about the 2021 census, and provided a video roundup for the day (which can be viewed here!). For conversations that we had at the stand we were asked to particularly focus on questions in line with the theme of the day including ‘if a statistic is the answer, what was the question?’ and ‘where does this data come from?’

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MP for Bath, Wera Hobhouse, had a particular interest in the pollution data for her constituency and the evidence for the most effective methods to improve air quality.  Photo credit to Sense about Science.

Trying to engage people at the stand proved to be challenging; the location of the stand meant people passing by were often in a rush to committee meetings. Occasionally the division bells, announcing a parliamentary vote, would also ring and a rush of MPs would flock by, great for trying to spot the more well-known MPs but less good for convincing them to stop to talk about data and statistics. In practice this meant I and other VoYS members had to adopt a very assertive approach in talking to people, a style that is generally not within the comfort zone of most scientists! However this did lead to some very interesting conversations, including with a paediatric surgeon who was advocating to the health select committee for increasing the investment in research to treat tumours in children. He posed a very interesting question: given a finite amount of funding for tumour research, how much of this should be specifically directed towards improving the survival outcomes of younger patients and how much to older patients? We also asked MPs and members of the public to add any evidence questions they had to the stand. A member of the public wondered, ‘are there incentives to show what doesn’t work?’ and Layla Moran, MP for Oxford West and Abingdon, asked ‘how can politicians better understand uncertainty in data?’

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Visitors to the stand, including MPs and Peers, were asked to add any burning questions they had about evidence to the stand. Photo credit to Sense about Science.

The week proved to be a success. Over 60 MPs from across parliamentary parties, including government ministers, interacted with some aspect of evidence week, accounting for around 10% of the total number of MPs. Also, a wider audience who engaged with the stand included parliamentary staff and members of the public. Sense about Science highlighted two outcomes after the event: one was the opening event where members of various community groups met with over 40 MPs and peers and had the opportunity to explain why evidence was important to them, whether their interest was in beekeeping, safe standing at football matches or IVF treatment; the second was the concluding round-table event regarding what people require from evidence gathering. SAGE will publish an overview of this round-table as a discussion paper in Autumn.

On a personal level, I had a very valuable experience. Firstly, it was great opportunity to visit somewhere as imposing and important as the Houses of Parliament and to contribute to such an exciting and innovate week. I was able to have some very interesting conversations with both MPs and members of the public. I found that generally everybody was enthusiastic about the need for increased use and transparency of evidence in policy-making. The challenge, instead, is to ensure that both policy-makers and the general public have the tools they need to collect, assess and apply evidence.

The Role of the Cloud Radiative Effect in the Sensitivity of the Intertropical Convergence Zone to Convective Mixing

Email: j.f.talib@pgr.reading.ac.uk

Talib, J., S.J. Woolnough, N.P. Klingaman, and C.E. Holloway, 2018: The Role of the Cloud Radiative Effect in the Sensitivity of the Intertropical Convergence Zone to Convective Mixing. J. Climate, 31, 6821–6838, https://doi.org/10.1175/JCLI-D-17-0794.1

Rainfall in the tropics is commonly associated with the Intertropical Convergence Zone (ITCZ), a discontinuous line of convergence collocated at the ascending branch of the Hadley circulation, where strong moist convection leads to high rainfall. What controls the location and intensity of the ITCZ remains a fundamental question in climate science.

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Figure 1: Annual-mean, zonal-mean tropical precipitation (mm day-1) from Global Precipitation Climatology Project (GPCP, observations, solid black line) and CMIP5 (current coupled models) output. Dashed line indicates CMIP5 ensemble mean.

In current and previous generations of climate models, the ITCZ is too intense in the Southern Hemisphere, resulting in two annual-mean, zonal-mean tropical precipitation maxima, one in each hemisphere (Figure 1).  Even if we take the same atmospheric models and couple them to a world with only an ocean surface (aquaplanets) with prescribed sea surface temperatues (SSTs), different models simulate different ITCZs (Blackburn et al., 2013).

Within a climate model parameterisations are used to replace processes that are too small-scale or complex to be physically represented in the model. Parameterisation schemes are used to simulate a variety of processes including processes within the boundary layer, radiative fluxes and atmospheric chemistry. However my work, along with a plethora of others, shows that the representation of the ITCZ is sensitive to the convective parameterisation scheme (Figure 2a). The convective parameterisation scheme simulates the life cycle of clouds within a model grid-box.

Our method of showing that the simulated ITCZ is sensitive to the convective parameterisation scheme is by altering the convective mixing rate in prescribed-SST aquaplanet simulations. The convective mixing rate determines the amount of mixing a convective parcel has with the environmental air, therefore the greater the convective mixing rate, the quicker a convective parcel will become similar to the environmental air, given fixed convective parcel properties.

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Figure 2: Zonal-mean, time-mean (a) precipitation rates (mm day-1}$) and (b) AEI (W m-2) in simulations where the convective mixing rate is varied.

In our study, the structure of the simulated ITCZ is sensitive to the convective mixing rate. Low convective mixing rates simulate a double ITCZ (two precipitation maxima, orange and red lines in Figure 2a), and high convective mixing rates simulate a single ITCZ (blue and black lines).

We then associate these ITCZ structures to the atmospheric energy input (AEI). The AEI is the amount of energy left in the atmosphere once considering the top of the atmosphere and surface energy budgets. We conclude, similar to Bischoff and Schneider, 2016, that when the AEI is positive (negative) at the equator, a single (double) ITCZ is simulated (Figure 2b). When the AEI is negative at the equator, energy is needed to be transported towards the equator for equilibrium. From a mean circulation perspective, this take place in a double ITCZ scenario (Figure 3). A positive AEI at the equator, is associated with poleward energy transport and a single ITCZ.

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Figure 3: Schematic of a single (left) and double ITCZ (right). Blue arrows denote energy transport. In a single ITCZ scenario more energy is transported in the upper branches of the Hadley circulation, resulting in a net-poleward energy transport. In a double ITCZ scenario, more energy is transport equatorward than poleward at low latitudes, leading to an equatorward energy transport.

In our paper, we use this association between the AEI and ITCZ to hypothesize that without the cloud radiative effect (CRE), atmospheric heating due to cloud-radiation interactions, a double ITCZ will be simulated. We also hypothesize that prescribing the CRE will reduce the sensitivity of the ITCZ to convective mixing, as simulated AEI changes are predominately due to CRE changes.

In the rest of the paper we perform simulations with the CRE removed and prescribed to explore further the role of the CRE in the sensitivity of the ITCZ. We conclude that when removing the CRE a double ITCZ becomes more favourable and in both sets of simulations the ITCZ is less sensitive to convective mixing. The remaining sensitivity is associated with latent heat flux alterations.

My future work following this publication explores the role of coupling in the sensitivity of the ITCZ to the convective parameterisation scheme. Prescribing the SSTs implies an arbitary ocean heat transport, however in the real world the ocean heat transport is sensitive to the atmospheric circulation. Does this sensitivity between the ocean heat transport and atmospheric circulation affect the sensitivity of the ITCZ to convective mixing?

Thanks to my funders, SCENARIO NERC DTP, and supervisors for their support for this project.

References:

Blackburn, M. et al., (2013). The Aqua-planet Experiment (APE): Control SST simulation. J. Meteo. Soc. Japan. Ser. II, 91, 17–56.

Bischoff, T. and Schneider, T. (2016). The Equatorial Energy Balance, ITCZ Position, and Double-ITCZ Bifurcations. J. Climate., 29(8), 2997–3013, and Corrigendum, 29(19), 7167–7167.

 

It’s a #GlobalHeatwave

Email: simonhaydnlee@outlook.com

Sometimes a simple tweet on a Sunday evening can go a long way.

This summer’s persistent dry and warm weather in the UK has led to many comparisons to the summer of 1976, which saw a lethal combination of the warmest June-August mean maximum temperatures (per the Met Office record stretching back to 1910) and a record-breaking lack of rainfall (a measly 104.6 mm – since bested by 1995’s 103.0 mm –  compared with the record-wettest 384.4 mm in 1912). When combined with a hot summer the year before and a dry winter, water shortages were historic and the summer has become a benchmark to which all UK heatwaves are compared. So far, 2018 has set a new record for the driest first half of summer for the UK (a record stretching back to 1961) but it remains to be seen whether it will truly rival ’76.

All these comparisons made me wonder: what did global temperatures look like during the heatwave of 1976? Headlines have been filled with news of other heatwaves across the Northern Hemisphere, including in AfricaFinland and Japan. Was the UK heatwave in 1976 also part of a generally warm pattern?

So I had a look at the data using the plotting tool available on NASA’s Goddard Institute for Space Studies (GISS) site, and composed a relatively simple tweet which took off in a manner only fitting for a planet undergoing rapid warming:

At the time of writing, it’s been retweeted over 8,800 times in under 48 hours and featured as part of a Twitter Moment. Even Héctor Bellerín, a footballer for Arsenal, retweeted it!

Once the tweet had taken on a life of its own, I was also well aware of so-called “climate change deniers” (I don’t like the term, but it’s the best I can do) lurking out there, and I was somewhat apprehensive of what might get said. I’ve seen Paul Williams have many not-so-pleasant Twitter encounters on the subject of climate change. However, I was actually quite surprised. Aside from a few comments here and there from ‘deniers’ (usually focusing on fundamental misunderstandings of averaging periods and the interpolation used by NASA to deal with areas of low data coverage), the response was generally positive. People were shocked, frightened, moved…and thankful to have perhaps finally grasped what global warming meant.

I endeavoured to keep it cordial and scientific, as the issue is too big to make enemies over – we all need to work together to tackle the problem.

So, maybe now I have some idea how Ed Hawkins felt when his global warming spiral went viral and eventually ended up in the 2016 Olympics opening ceremony. I guess the biggest realisation for me is that, as a scientist, I’m familiar with graphics such as these showing the extent of global warming, but the wider public clearly aren’t – and that’s part of the reason I believe the tweet became so popular.

I can’t say that the 2018 UK heatwave is due to global warming. However, with unusually high temperatures present across the globe, it takes less significant weather patterns to produce significant heatwaves in the UK (and elsewhere). And with the jet streams that guide our weather systems already feeling the effects of climate change (something which I researched as an undergraduate), we can only expect more extremes in the future.

Royal Meteorology Conferences

From 3rd-6th July 2018 the Royal Meteorological Society (RMetS) held two national conferences at the University of York. The Atmospheric Science Conference, joint with NCAS, started off the week and brought together scientists to present and discuss the latest research findings in weather, climate and atmospheric chemistry. The following two days brought the RMetS Student Conference. Both events were well attended by PhD students from Reading and provided a great opportunity to share our work with the wider scientific community.

For a summary of the work presented by Reading students, stick around until the end of the blog!

Atmospheric Science Conference 2018

Weather, Climate and Air Quality

Many of the presentations focused on seasonal forecasting with Adam Scaife (Met Office) giving a keynote address on “Skilful Long Range Forecasts for Europe”. He presented an interesting analysis on the current progress of predicting the North Atlantic Oscillation showing that there is skill in current predictions which could be improved even further by increasing ensemble size. Adam was also awarded the prestigious Copernicus Medal at the conference dinner. Another notable talk was by Reading’s own Ed Hawkins, who presented the benefits of using citizen scientists to rescue weather records. A summary of Ed’s presentation can be accessed below, and you can read more about research involving Citizen Science in Shannon Jones’ blog.

The poster sessions at the conference also gave a great opportunity to look at the breadth of work going on in institutions around the UK. It was also a great time to catch up with colleagues and forge new academic connections.

One of the highlights of the conference was having the conference dinner in the National Railway Museum. This was a fantastic yet surreal location with dining tables set up in the station hall overlooking a suite of old steam trains . The event was made even better by watching England‘s quarter-final world cup game!

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Evolution of Science: Past, Present and Future

Students & Early Career Scientist Conference

The student conference is open to all students with an interest in meteorology, from undergraduate to PhD and early career scientists. The conference aimed to give students the opportunity to meet each other and present their work at an early stage in their career before attending other academic conferences. For many of those attending from Reading this was their first time presenting research at an event outside of the department and provided a great experience to communicate their work with others. Work presented varied from radiative forcing to normal empirical modes (summaries of talks are below). There were also a number of keynote speakers and workshops aimed at addressing the current challenges in atmospheric sciences and skills that are important for researchers.

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Rory Fitzpatrick, presenting on skills for writing as an academic. “I have the Best Words” – How to write articles that impact bigly”

Of course there was also time for socialising with an ice-breaker dinner and pub quiz  and a formal Conference dinner on the Thursday. This was the second student conference I have attended and it was a really great place to discuss my work and meet other students from around the country. I have also attended other academic events with several people that I met at the conference last year, it’s always great to see a friendly face!

The student conference is organised by a committee of students from around the UK. Being on the committee was a great opportunity to learn more about how conferences work and to practice skills such as chairing sessions. It has also been great to get to know lots of different people working within meteorology. If you’re interested in helping organise next year’s conference please do get in touch with Victoria Dickinson at RMetS (Victoria.Dickinson@rmets.org) or if you’re thinking about attending then you can start by joining the society where you’ll hear about all the other great events they host.

Highlights of the work presented by Reading students:

Godwin Ayesiga presented work on the convective activity that connects Western and Eastern equatorial Africa. Investigating how intraseasonal modes of variability influence intense rainfall.

Matt Priestley presented an assessment of the importance of windstorm clustering on European wintertime insurance losses. More details of this work can be found here.

Lewis Blunn presented his work looking into the ‘grey zone’ of turbulence at model grid scale lengths of 100 m – 1 km. At these scales turbulence is partially resolved by the grid but still needs to be partially parameterised. Lewis finds that spurious grid scale features emerge at scales where turbulence is partially resolved. Model results are poorer in this ‘grey zone’ than when turbulence is fully resolved or fully parameterised.

Alec Vessey presented his work evaluating the representation of Arctic storms in different reanalysis products. He found that there is a difference between different reanlysis and so care should be taken when using these products to analyse Arctic storms.

Dominic Jones presented a technique for extracting modes of variability from atmospheric data, and a test dataset that has been developed to use this technique to examine the relationship of modes of variability associated with the jet-latitude.

Rachael Byrom presented a motivation for quantifying methane’s shortwave radiative forcing. Her work demonstrated a need to use a high resolution narrow-band radiation model to accurately calculate forcings in atmospheric models.

Andrea Marcheggiani presented a poster on the role of resolution in predicting the North Atlantic storm track. An energy budget of the winter climatology (DJF 1979-2018) was presented.

Sally Woodhouse presented her work on the impact of resolution on energy transports into the Arctic. She has found that increasing atmospheric resolution increases the energy transport in the ocean to better agree with observations.

Kaja Milczewska presented work on evaluating the inaccuracies of predicting air quality in the UK.

Having recently passed her viva, Caroline Dunning’s presentation was on precipitation seasonality over Africa under present and future climates. Caroline has developed a new methodology for determining the beginning and end of the wet season across Africa. This has been applied to CMIP5 model output to look at future changes in wet seasons across Africa under climate change.

How the Earth ‘breathes’ on a daily timescale

Email: J.Gristey@pgr.reading.ac.uk
Web: http://www.met.reading.ac.uk/~fn008822/

As the Earth rotates, each location on its surface is periodically exposed to incoming sunlight. For example, over London at the beginning of September, the intensity of incoming sunlight ranges from zero overnight, when the sun is below the horizon, to almost 1000 W m–2 at noon, when the sun is highest in the sky (Fig. 1).

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Fig. 1. Top-of-atmosphere incoming sunlight over London (51.5° N, 0° E) for the first three days in September 2010. Data is from the Met Office numerical weather prediction model.

Earth’s atmosphere and surface respond to this repeating daily cycle of incoming sunlight in ways that can change the amount of energy that is emitted or reflected back to space. For example, the increased amount of sunlight in the afternoon can heat up the surface and cause more thermal energy to be emitted to space. Meanwhile, the surface heating can also cause the air near the surface to warm up and rise to form clouds that will, in turn, reflect sunlight back to space. The resulting daily cycle of the top-of-atmosphere outgoing energy flows is therefore intricate and represents one of the most fundamental cycles of our weather and climate. It is essential that we can properly represent the physical processes controlling this daily variability to obtain accurate weather and climate forecasts. However, the daily variability in Earth’s outgoing energy flows is not currently well observed across the entire globe, and current weather and climate models can struggle to reproduce realistic daily variability, highlighting a lack of understanding.

To improve understanding, dominant patterns of the daily cycle in outgoing energy flows are extracted from Met Office model output using a mathematical technique known as “principal component analysis”.

The daily cycle of reflected sunlight is found to be dominated by the height of the sun in the sky, or the “solar zenith” angle, because the atmosphere and surface are more reflective when the sun is low in the sky. There is a lesser importance from low-level clouds over the ocean, known as “marine stratocumulus” clouds, which burn off during the afternoon, reducing the amount of reflected sunlight, and tall and thick clouds, known as “deep convective” clouds, which develop later in the afternoon over land and increase the amount of reflected sunlight. On the other hand, the daily cycle of emitted thermal energy is dominated by surface heating, which increases the emitted energy at noon, but also by deep convective clouds that have very high and cold tops, reducing the emitted energy later in the afternoon. These dominant processes controlling the daily cycle of Earth’s outgoing energy flows and their relative importance (summarised in Fig. 2) have not been revealed previously at the global scale.

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Fig. 2. A schematic diagram showing the first (top) and second (bottom) most important processes controlling the daily cycle in emitted thermal energy (left) and reflected sunlight (right).

The physical processes discussed above are consistent with the daily cycle in other relevant model variables such as the surface temperature and cloud amount, further supporting the findings. Interestingly, a time lag is identified in the response of the emitted thermal energy to cloud variations, which is thought to be related to changes in the humidity of the upper atmosphere once the clouds evaporate.

The new results highlight an important gap in the current observing system, which can be utilized to evaluate and improve deficiencies in weather and climate models.

Gristey, J. J., Chiu, J. C., Gurney, R. J., Morcrette, C. J., Hill, P. G., Russell, J. E., and Brindley, H. E.: Insights into the diurnal cycle of global Earth outgoing radiation using a numerical weather prediction model, Atmos. Chem. Phys., 18, 5129-5145, https://doi.org/10.5194/acp-18-5129-2018, 2018.

Estimating the Effects of Vertical Wind Shear on Orographic Gravity Wave Drag

Orographic gravity waves occur when air flows over mountains in stably stratified conditions. The flow of air creates a pressure imbalance across the mountain, so a force is exerted on the mountain in the same direction as the flow. An equal and opposite force is exerted back on the atmosphere, and this is gravity wave drag (GWD).

GWD must be parametrized in Global Circulation Models (GCMs), as it is important for large-scale flow. The first parametrization was formulated by Palmer et al. (1986) to reduce a systematic westerly bias. The current parametrization was formulated by Lott and Miller (1997) and partitions the calculation into 2 parts (see figure 1):

  1. The mountain waves. This is calculated by averaging the wind, Brunt-Väisälä frequency and fluid density in a layer between 1 and 2 standard deviations of the subgrid-scale orography above the mean orography.
  2. The blocked flow. This is based on an interpretation of the non-dimensional mountain height.
Fig 1
Figure from Lott and Miller (1997).

The parametrization does not include the effects of wind shear. Wind shear is a change in the wind with height and it alters the vertical wave length of gravity waves and so alters the drag. It has been shown (Teixeira et al., 2004; Teixeira and Miranda, 2006) that a uniform shear profile (i.e. a change in the magnitude of the wind with height) decreases the drag whereas a profile in which the wind turns with height increases the drag. This effect was seen by Miranda et al. (2009) to have the greatest impact over Antarctica, where drag enhancement was seen to occur all year with a peak of ~50% during JJA. Figure 2 shows this.

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Figure 2: Annual mean linear GWD stress (1992-2001). Vectors show the surface stress with shear. Shading indicates the anomaly of the modulus of the surface stress due to shear. Computed from ERA-40 data. Taken from Miranda et al. (2009).

The aim of this work is to test the impact of the inclusion of shear effects on the parametrization. The first stage of this is to test the sensitivity of the shear correction to the height in the atmosphere at which the necessary derivatives are approximated. We carry out calculations using 2 different reference heights:

  1. The top of the boundary layer (BLH). This allows us to avoid the effects of boundary layer turbulence, which are not important in this case as they are unrelated to the dynamics of mountain waves.
  2. The middle of the layer between 1 and 2 standard deviations of the sub-grid scale orography (SDH). This is the nominal height used in previous studies and in the parametrization.

All figures shown below focus on Antarctica and are averaged over all JJAs for the decade 2006-2015. We are interested in Antarctica and the JJA season for the reasons highlighted above. All calculations are carried out using ERA-Interim reanalysis data.

We first consider the enhancement assuming axisymmetric orography. The advantage of this is that it considerably simplifies the correction due to terms related to the anisotropy becoming constant (see Teixeira et al, 2004). Figure 3 shows this correction calculated using both reference heights. We can see that the enhancement is greater when the SDH is used.

Fig 3
Figure 3: Drag enhancement over Antarctica with shear corrections computed at the BLH (left) and SDH (right), during JJAs for the decade 2006-2015, using axisymmetric orography.

We now consider the enhancement using mountains with an elliptical horizontal cross-section. This is how the real orography is represented in the parametrization. Again, we see that the enhancement is greater when the SDH is used (figure 4).

Fig 4
Figure 4: Drag enhancement (left) and enhancement of drag stress (in Pa) (right) over Antarctica with shear corrections calculated at the BLH (top) and SDH (bottom), during JJAs for the decade 2006-2015, using orography with an elliptical horizontal cross-section.

It is interesting to note that at both heights the enhancement is greater when axisymmetric orography is used. This occurs because, in the case of elliptical mountains, the shear vector is predominantly aligned along the orography, resulting is weaker enhancement (see figure 5).

Fig 5
Figure 5: Histograms of the orientation of the shear vector relative to the short axis of the orography over Antarctica for JJAs during the decade 2006-2015, using the BLH (left) and SDH (right).

We also investigate the fraction of times at which the terms related to wind profile curvature (i.e. those containing second derivatives) dominate the drag correction. This tells us the fraction of time for which curvature matters for the drag. We see that second derivatives dominate over much of Antarctica for a high proportion of the time (see figure 6).

Fig 6
Figure 6: Fraction of the time at which terms with second derivatives dominate the drag correction relative to terms with first derivatives over orography with an elliptical horizontal cross-section, for JJAs during the decade 2006-2015, calculated using the BLH (left) and SDH (right).

In summary, the main findings are as follows:

  • The drag is quantitatively robust to changes in calculation height, with the geographical distribution, seasonality and sign essentially the same.
  • The drag is considerably enhanced when the SDH is used rather than the BLH.
  • Investigation of the relative magnitudes of terms containing first and second derivatives in the drag correction indicates that second derivatives (i.e. curvature terms) dominate in a large proportion of Antarctica for a large fraction of time. This leads to an average enhancement of the drag which is larger over shorter time intervals.
  • Use of an axisymmetric orography profile causes considerable overestimation of the shear effects. This is due to the shear vector being predominantly aligned along the mountains in the case of the orography with an elliptical horizontal cross-section.

These results highlight the need to ‘tune’ the calculation by identifying the optimum height in the atmosphere at which to approximate the derivatives. This work is ongoing. We expect the optimum height to be that at which the shear has the greatest impact on the surface drag.

References:

Lott F. and Miller M., 1997, A new subgrid-scale orographic drag parametrization: Its formulation and testing, Quart. J. Roy. Meteor. Soc., 123: 101–127.

Miranda P., Martins J. and Teixeira M., 2009, Assessing wind profile effects on the global atmospheric torque, Quart. J. Roy. Meteor. Soc., 135: 807–814.

Teixeira M. and Miranda P., 2006, A linear model of gravity wave drag for hydrostatic sheared flow over elliptical mountains, Quart. J. Roy. Meteor. Soc., 132: 2439–2458.

Teixeira M., Miranda P. and Valente M., 2004, An analytical model of mountain wave drag for wind profiles with shear and curvature, J. Atmos. Sci., 61: 1040–1054.

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…

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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!

Olivia