Coding lessons for the newly initiated

Better coding skills and tooling enable faster, more useful results. 

Daniel Ayers – d.ayers@pgr.reading.ac.uk

This post presents a collection of resources and tips that have been most useful to me in the first 18 months I’ve been coding – when I arrived at Reading, my coding ability amounted to using excel formulas. These days, I spend a lot of time coding experiments that test how well machine learning algorithms can provide information on error growth in low-dimensional dynamical systems. This requires fairly heavy use of Scikit-learn, Tensorflow and Pandas. This post would have been optimally useful at the start of the year, but perhaps even the coding veterans will find something of use – or better, they can tell me about something I am yet to discover!  

First Steps: a few useful references 

  • A byte of python. A useful and concise reference for the fundamentals. 
  • Python Crash Course, Eric Matthes (2019). Detailed, lots of examples, and covers a wider range of topics (including, for example, using git). There are many intro to Python books around; this one has certainly been useful to me.1 There are many good online resources for python, but it can be helpful initially to have a coherent guide in one place. 

How did I do that last time? 

Tip: save snippets. 

There are often small bits of code that contain key tricks that we use only occasionally. Sometimes it takes a bit of time reading forums or documentation to figure out these tricks. It’s a pain to have to do the legwork again to find the trick a second or third time. There were numerous occasions when I knew I’d worked out how to do something previously, and then spent precious minutes trawling through various bits of code and coursework to find the line where I’d done it. Then I found a better solution: I started saving snippets with an online note taking tool called Supernotes. Here’s an example:  

I often find myself searching through my code snippets to remind myself of things. 

Text editors, IDEs and plugins. 

If you haven’t already, it might be worth trying some different options when it comes to your text editor or IDE. I’ve met many people who swear by PyCharm. Personally, I’ve been getting on well with Visual Studio Code (VS Code) for a year now. 

Either way, I also recommend spending some time installing useful plugins as these can make your life easier. My recommendations for VS Code plugins are: Hungry Delete, Rainbow CSV, LaTeX Workshop, Bracket Pair Colorizer 2, Rewrap and Todo Tree

Linters & formatters 

Linters and formatters check your code for syntax errors or style errors. I use the Black formatter, and have it set to run every time I save my file. This seems to save a lot of time, and not only with formatting: it becomes more obvious when I have used incorrect syntax or made a typo. It also makes my code easier to read and look nicer. Here’s an example of Black in anger:  

Some other options for linters and formatters include autopep, yapf and pylint. 

Metadata for results 

Data needs metadata in order to be understood. Does your workflow enable you to understand your data? I tend to work with toy models, so my current approach is to make a new directory for each version of my experiment code. This way I can make notes for each version of the experiment (usually in a markdown file). In other words, what not to do, is to run the code to generate results and then edit the code (excepting, of course, if your code has a bug). At a later stage you may want to understand how your results were calculated, and this cannot be done if you’ve changed the code file since the data was generated (unless you are a git wizard). 

A bigger toolbox makes you a more powerful coder 

Knowing about the right tool for the job can make life much easier.2 There are many excellent Python packages, and the more you explore, the more likely you’ll know of something that can help you. A good resource for the modules of the Python 3 standard library is Python Module of The Week. Some favourite packages of mine are Pandas (for processing data) and Seaborn (a wrapper on Matplotlib that enables quick and fancy plotting of data). Both are well worth the time spent learning to use them. 

Some thoughts on Matplotlib 

Frankly some of the most frustrating experiences in my early days with python was trying to plot things with Matplotlib. At times it seemed inanely tedious, and bizarrely difficult to achieve what I wanted given how capable a tool others made it seem. My tips for the uninitiated would be: 

  • Be a minimalist, never a perfectionist. I often managed to spend 80% of my time plotting trying to achieve one obscure change. Ask: Do I really need this bit of the plot to get my point across? 
  • Can you hack it, i.e. can you fix up the plot using something other than Matplotlib? For example, you might spend ages trying to tell Matplotlib to get some spacing right, when for your current purpose you could get the same result by editing the plot in word/pages in a few clicks. 
  • Be patient. I promise, it gets easier with time. 

Object oriented programming 

I’m curious to know how many of us in the meteorology department code with classes. In simple projects, it is possible to do without classes. That said, there’s a reason classes are a fundamental of modern programming: they enable more elegant and effective problem solving, code structure and testing. As Hans Petter Langtangen states in A Primer on Scientific Programming with Python, “classes often provide better solutions to programming problems.”  

What’s more, if you understand classes and object- oriented programming concepts then understanding others’ code is much easier. For example, it can make Matplotlib’s documentation easier to understand and, in the worse caseworst case scenario, if you had to read the Matplotlib source code to understand what was going on under the hood, it will make much more sense if you know how classes work. As with Pandas, classes are worth the time buy in! 

Have any suggestions or other useful resources for wannabe pythonistas? Please comment below or email me at d.ayers@pgr.reading.ac.uk. 

Organising a virtual conference

Gwyneth Matthews – g.r.matthews@pgr.reading.ac.uk

A Doctoral Training Programme (DTP) provides funding, training, and opportunities for many PhD students in our department. Every year three environmentally focused DTPs: the SCENARIO NERC DTP, the London NERC DTP, and the Science and Solutions for a Changing Planet (SSCP) DTP, combine forces to hold a conference bringing together hundreds of PhD students to present their work and to network. As for many conferences in 2020, COVID19 disrupted our plans for the Joint DTP conference.  Usually the conference is hosted at one of the universities involved with a DTP however, this year it was held virtually using a mixture of Zoom and Slack. 

The decision to go virtual was difficult. We had to decide early in the pandemic when we didn’t know how long the lockdown would last nor what restrictions would be in place in September. If possible, we wanted to keep the conference in-person so that attendees got the full experience as it’s often the first time the new cohort meet and one of the few chances for the DTPs to mingle. However, as meeting and mingling was, and is, very much discouraged, making the decision to go virtual early on meant we had time to re-organise.  

Figure 1 – It was initially planned to hold the conference at the University of Surrey campus, which is located in Guildford, Surrey and hosts some students from the SCENARIO NERC DTP. The conference was instead held on Slack, an online communication platform that allows content to be divided into channels, and presentation sessions were hosted on Zoom.

When we thought we were organising a conference to be held at the University of Surrey, the main theme was “Engaging Sustainability” with the aim of making the conference as sustainable as possible. Since one of the often-made criticisms of conferences, especially those within the environmental fields, is the impact of large numbers of people travelling to one place, a virtual conference has obvious environmental benefits. An additional benefit was that we could invite guest speakers, such as Mya-Rose Craig (aka Bird Girl @birdgirluk), who may not have been able to attend if the event was held in person. It was also easier for some participants who had other commitments, such as childcare, to attend, although poor internet connection was an issue for others. 

The pandemic exposed, and often enhanced, many issues within academia and society in general. A questionnaire sent out before the event showed that most attendees were finding working from home and all other pandemic induced changes exhausting and mentally challenging. The recent Black Lives Matter protests around the world and the disproportionate impact of COVID on ethnic minority communities highlighted both the overt and systemic racism that is still prevalent in society. The UK Research and Innovation COVID funding controversy, and an increased focus on the challenges faced by the LGBTQ+ researchers emphasised the inequalities and poor representation specifically experienced in academia. Scientists working at the forefront of the pandemic response faced the challenge of providing clear information to enable people and policy makers to take life-disrupting actions before they are directly impacted; a challenge familiar to climate and environmental scientists. These issues gave us our topics for the external sessions which focused on wellbeing, inclusivity and diversity in academia, and communicating research.  

Barring technical difficulties, oral presentations are easy to replicate online, however, virtual conferences held earlier this year often had issues with recreating the poster sessions. Attempting to learn from these snags, instead of replicating an in-person poster session and possibly producing a poor-quality knock-off, participants were asked to create an animated “Twitter poster”. These were required to describe the key points of their research in a simple format that could be shared on social media and that was accessible to a non-expert. The posters were available for comments and questions throughout the two days in one easy-to-find location. Many of the participants shared their posters on Twitter after the conference using the conference hashtag #JointDTPCon.  

Another issue we faced was how to run a social and networking event. We kept the social event simple. A quiz. A pandemic classic with a fantastic double act as hosts. Randomly assigned teams meant that new connections could be made. However, the quiz was held online and after a full day of video calls most people didn’t want to spend their evenings also starring at a screen.  

Fig 2 – Jo Herschan and Lucinda King, members of the SCENARIO DTP and on the conference organising committee, hosted an entertaining quiz on the first night of the conference. An ethical objects photo round linked the quiz to the conference’s main theme.

With everyone having stayed at home and everything being conducted virtually for a few months by the time of our conference, Zoom fatigue was an issue we were aware could occur and tried to counter as much as possible during the day without losing any of the exciting new research being presented. In the weeks running up to the conference we had several discussions about how to encourage people to move throughout the two days without missing any of the sessions they wanted to attend. We decided on two ideas: a yoga session and a walking challenge. The yoga session was a success and not only gave participants an opportunity to stretch in the middle of the day but also linked strongly to our theme of researcher wellbeing. The walking challenge was not as successful. The aim was that collectively the conference participants would walk the distance from Land’s End to John O’Groats. We did not make it that far; but we did make it out of Cornwall. 

Fig 3 – Using World Walking to track the distance, we intended to collectively walk the 1576km (or 2,299,172 steps) from Land’s End to John O’Groats. This may have been an optimistic endeavour as we only achieved 235km (343, 311 steps).  

Helping to organise a virtual conference as part of an enthusiastic committee was a lot of fun and attending the conference and learning about the research being undertaken (from fungi in Kew Gardens to tigers in North Korea) was even more fun. There is still enormous room for improvement in virtual conferences, but since they aren’t as well established as traditional in-person conferences there’s also a lot of flexibility for each conference to be designed differently. Once we’re through the pandemic and in-person conferences return it’d be nice for some of these benefits to be maintained as hybrid conferences are designed.   

My journey to Reading: Going from application to newly minted SCENARIO PhD student

George Gunn – g.f.gunn@pgr.reading.ac.uk 

Have you been thinking ‘I’ll never be good enough for a PhD’? Or perhaps you’ve been set on the idea of joining those who push the bounds of knowledge for quite some time, but are feeling daunted by the process? Well, keep reading. 

I started university with the hopes of stretching myself academically and gaining an undergraduate degree. As the degree progressed, I found myself increasingly improving in my marks and abilities. I enjoyed the coursework – researching a topic and the sense of discovery brought about by it. I became deeply interested in climate change and the impact humans have on the environment and was able to begin my dissertation research a year early because I was so motivated within my subject. 

In my final year of undergraduate studies, much of my time was pre-occupied with my role as Student President. Attending social events, board meetings, and lots of other things that didn’t involve a darkened room and a pile of books. I was very much a student who turned up, put the effort in, and then spent the rest of my time as I wished.  

Giving a speech at the Global Youth Strike for Climate, Inverness, as Student President. Extracurricular activities are a worthwhile addition to your application and were considered a lot during the interview! 

I began to look for opportunities for research degrees online, as well as asking almost anyone and everyone I knew academically if they had any ideas. Nothing came to fruition. That was until I received a Twitter notification from my lecturer drawing my attention to what looked to be an ideal PhD studentship. The snag? Applications were due to close within 3 hours of me checking the notification. 

By the time I had read the project particulars, accessed the cited literature and paced around my living room more than a few times, I had around 2 hours to submit an application. Due to my prior unsuccessful searches, I hadn’t previously submitted a PhD application and so had nothing to refer to – but proceed I did.  

Thankfully, the application was relatively straightforward. Standard job application information, details of the grades I had achieved and was predicted to achieve, and two academic references (for me, my personal academic tutor and climate change lecturer). What took time (I would advise anyone considering an application to prepare these earlier than I did!) was the statement of research interest and academic CV. My university careers service had excellent advice and resources to assist in that regard. 

Within minutes of the deadline, my application was in. I had almost forgotten about it by the time a week-or-so later I received an e-mail inviting me to Reading for an interview day. Shocked and excited were the emotions – little old me from the Highlands of Scotland, who hadn’t yet finished his undergraduate degree, was somehow being invited to one of the best Meteorology departments in the world to interview for a PhD studentship.  

No time to spare, my travel to and from Reading was booked. For the next couple of weeks, all I now had to worry about was how to do a PhD interview – though as will become clear, I need not have worried. I sought the advice of academic friends and colleagues (a calming influence for sure) and countless websites and forums (generally a source of unnecessary worry). 

Given the level of conflicting advice on PhD interviews, on arrival at Reading I wasn’t sure what to expect. At the front door I was provided with all the information that I needed for the day. I then made my way to a room with all the other candidates for a welcome talk and the opportunity to learn more about other projects on offer over lunch. 

The interview itself was very relaxed. No ‘stock’ PhD interview questions here – it was very much an opportunity to discuss my previous work and abilities, and how that might fit with the project. Importantly, it was an opportunity to meet my potential supervisors and ‘interview’ them too. If you’re going to spend 3-4 years working together, the connection needs to work well both ways. So, whilst the 30-minute interview slot seemed daunting on paper, the time flew by and it was soon time to leave. 

Fast forward a week or so and I was very surprised to receive an e-mail offering me the studentship that I had applied for: Developing an urban canopy model for improved weather forecasts in cities. And the rest, as they say, is history. 

At my desk in the Department of Meteorology, University of Reading. 

I hope that this blog post has helped you to feel less daunted to begin your PhD journey. Please feel free to get in touch with me by e-mail if you would like to chat further about beginning a PhD, or indeed to let me know how your own interview goes. Good luck! 

Life on Industrial Placement

Email: holly.turner@reading.ac.uk

I finished my PhD last year, and since the start of this year I’ve been doing something rather different. Courtesy of SCENARIO DTP funding, I am doing a 3-month post-doc placement with JBA Consulting in Skipton, North Yorkshire. After spending 3.5 years researching in an academic setting, it is great to be able to apply my knowledge to real-world problems.

Working in industry has a very different feel to working in academia. The science being done has an immediate purpose for the company, rather than being done purely to extend knowledge. In the case of my placement, the work that I am doing is ultimately to benefit the end users of the product.

The field that I am now working in is rather far removed from my PhD project: I have gone from gravity waves to surface water flooding. Whilst it has been quite a steep learning curve to bring myself up to speed with the current science in this area, it is great to branch out. I would urge anyone interested in doing an industrial placement not to be put off by going outside of your subject area. You might find something else that suits you better. It might even be the best step you ever make.

The choosing and setting up of the placement has all been fairly easy for me. SCENARIO had a range of placements available and I chose the one that most interested me. I had to send an application to the company, who then called me for an interview. Once they decided to offer me the placement, SCENARIO did the setting up with both JBA and the university. All I needed to worry about was finding accommodation for the 3 months.

To anyone considering doing an industrial placement: do it! I am currently 3 weeks in and have really enjoyed it so far. Everybody has been welcoming and helpful. I felt like part of the team by the end of my first day.

On relocating to Oklahoma for 3.5 months

Email: s.h.lee@pgr.reading.ac.uk

From May 4th through August 10th 2019, I relocated to Norman, Oklahoma, where I worked in the School of Meteorology in the National Weather Center (NWC) at the University of Oklahoma (OU). I’m co-supervised by Jason Furtado at OU, and part of my SCENARIO-funded project plan involves visiting OU each summer to work with Dr. Furtado’s research group, while using my time in the U.S. to visit relavant academics and conferences. Prior to my PhD, I studied Reading’s MMet Meteorology and Climate with a Year in Oklahoma degree, and spent 9 months at OU as part of that – so it’s a very familiar place! The two departments have a long-standing link, but this is the first time there has been PhD-supervision collaboration.

The National Weather Center in Norman, Oklahoma – home to the School of Meteorology.

The National Weather Center (NWC) [first conceived publicly in a 1999 speech by President Bill Clinton in the aftermath of the Bridge Creek-Moore tornado] opened in 2006 and is a vastly bigger building than Reading Meteorology! Alongside the School of Meteorology (SoM), it houses the Oklahoma Mesonet, the NOAA Storm Prediction Center (SPC) (who are responsible for operational severe weather and fire forecasting in the U.S.) and the NOAA National Severe Storms Laboratory (NSSL). SPC and NSSL will be familiar to any of you who have seen the 1996 film Twister. You could think of it as somewhat like a smaller version of the Reading Meteorology department being housed in the Met Office HQ in Exeter.

Inside the NWC.

The research done at SoM is mostly focussed on mesoscale dynamics, including tornadogenesis, thanks to its location right at the heart of ‘tornado alley’. It’s by no means a typical haunt of someone who researches stratosphere dynamics like I do, but SoM has broadened its focus in recent years with the inception of the Applied Climate Dynamics research group of which I’m a part. Aside from the numerous benefits of being able to speak face-to-face with a supervisor who is otherwise stuck on a TV screen on Skype, I also learnt new skills and new ways of thinking – purely from being at a different institution in a different country. I also used this time to work on the impact of the stratosphere on North America (a paper from this work is currently in review).

I also visited the NOAA Earth System Research Laboratory (ESRL) in Boulder, Colorado to present some of my work, and collaborate on some papers with scientists there. Boulder is an amazing place, and I highly recommend going and hiking up into the mountains if you can (see also this 2018 blog post from Jon Beverley on his visit to Boulder).

As for leisure… I chose to take 2 weeks holiday in late May to, let’s say, do “outdoor atmospheric exploration“. This happened to coincide with the peak of one of the most active tornado seasons in recent years, and I just so happened to see plenty of them. I’m still working on whether or not the stratosphere played a role in the weather patterns responsible for the outbreak!

An EF2-rated wedge tornado on 23 May near Canadian, Texas.

Presenting in Ponte Vedra, Florida – 33rd Conference on Hurricanes and Tropical Meteorology

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

You’ve watched many speak before you. You’ve practised your presentation repeatedly. You’ve spent hours, days, months, and sometimes years, understanding your scientific work. Yet, no matter the audience’s size or specialism, the nerves always creep in before a presentation. It’s especially no different at your first international conference!

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Between the 16th and 20th April 2018, me, Jonathan Beverley and Bethan Harris were fortunate enough to attend and present at the American Meteorological Society 33rd Conference on Hurricanes and Tropical Meteorology in Ponte Vedra, Florida. For each of us, our first international conference!

Being a regular user of Instagram through the conference, especially the Instagram Story function, I was regularly asked by my friends back home, “what actually happens at a scientific conference”? Very simple really – scientists from around the world, from different departments, universities, and countries, come to share their work, in the hope of progressing the scientific field, to learn from one another, and network with future collaborators. For myself, it was an opportunity to present recently submitted work and to discuss with fellow researchers on the important questions that should be asked during the rest of my PhD. One outcome of my talk for example, was a two-hour discussion with a graduate student from Caltech, which not only improved my own work, but also helped me understand other research in global circulation.

Recordings of the presentations given by University of Reading PhD students can be found at:

Alongside presenting my own work, I had the opportunity to listen and learn from other scientific researchers. The conference had oral and poster presentations from a variety of tropical meteorology subject areas including hurricanes, global circulation, sub-seasonal forecasting, monsoons and Madden-Julian Oscillation. One of the things that I most enjoy at conferences is to hear from leading academics give an overview of certain topic or issue. For example, Kerry Emanuel spoke on the inferences that can be made from simple models of tropical convection. Through applying four key principles of tropical meteorology including the weak temperature gradient approximation and conservation of free-tropospheric moist static energy, we can understand tropical meteorology processes including the Intertropical Convergence Zone, Walker circulation and observed temperature and humidity profiles.

Of course, if you’re going to fly to the other side of the pond, you must take advantage of being in the USA. We saw a SPACEX rocket launch, (just at a distance of 150 miles away,) experienced travelling through a squall line, visited the launch sites of NASA’s first space programs, and explored the sunny streets of Miami. It was a great privilege to have the opportunity to present and attend the AMS 33rd Conference on Hurricanes and Tropical Meteorology, and I am hugely thankful to NERC SCENARIO DTP and the Department of Meteorology for funding my work and travel.

 

The 2017 SCENARIO Conference: Frontiers in Natural Environment Research

Every year students from the SCENARIO (Science of the Environment, Natural and Anthropogenic Processes, Impacts and Opportunities) Doctoral Training Partnership organise an annual conference. Those invited include SCENARIO students, NERC employees and industrial partners. This year, after last year’s successful collaboration with the University of Oklahoma, it was decided that we would run the conference (Frontiers in Natural Environment Research) with the Science and Solutions for a Changing Planet (SSCP) and London NERC DTPs, led by a variety of universities and institutions in London.

A similar conference was organised last year (Perspectives on Environmental Change) between SSCP and the London NERC DTP, which was a rousing success. This year, with the addition of Reading and Surrey, we had almost 200 delegates attending with a healthy proportion of supervisors and industry partners, with over 40 oral presentations and 40 posters from students at the various institutions. The conference was held in the Physics building at Imperial College, a literal stone’s throw away from the Royal Albert Hall.

Organising the conference was a daunting task; there was a lot of work involved between the nine PhD students on the committee! One of the challenges, (but also one of the most exciting parts of the conference), was the sheer variety of research being presented. Many of the attendees were from the Met department, but there were also students from Chemistry and Geography from SCENARIO, and students from the London institutions doing topics as varied as sociology, ecology, biology, materials science and plate tectonics. This made for a really interesting conference since there was so much on offer from such a wide range of fields, but made our lives quite difficult when trying to organise keynote speakers and sort abstracts!

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As well as the student presentations we also ran workshops and panel discussions, and had two invited keynote speakers. The workshops were about communicating science through social media, and also on getting published in one of the Nature journals (similar to the successful workshop ran by SCENARIO here at Reading). The panel discussions were themed around “Science and Development” and “Science in a post-truth world”, looking at ways in which science (particularly that within the NERC remit) can help to solve the UN’s Sustainable Development Goals, and how we communicate science in a time of “fake news”.

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Perhaps my favourite part of the conference were the two keynote speakers. Finding speakers who would appeal to the majority of people attending the conference was no easy task, given the huge range of disciplines!

Opening the conference, Marcus Munafo, Professor in Biological Psychology at Bristol University spoke about the “reproducibility crisis” and how incentive structures affect the scientific process. I can honestly say it was one of the most thought-provoking lectures I’ve ever been to. His main argument was that ultimately science is done by people who have an incentive to do certain things, (e.g. publish in high impact journals), for the benefit of their careers. However, this incentivisation means that often one “big result” can mean more for the career of someone than all the work they’ve done previously, even if that result ended up being retracted or proven false later on, (he went on to demonstrate that happens a lot). One of the statistics he presented was that the higher the impact factor of a journal, the higher the chance of retraction, which I thought was really interesting and certainly made me re-evaluate the way in which I approach my own work.

The other keynote speaker was Lucy Hawkes, Senior Lecturer in Physiological Ecology at Exeter, talking about her work and career, particularly “biologging” of animals and looking at their migratory patterns. Aside from all the great anecdotes and stories (like swimming with sharks in order to plant bio-tags on them), from a meteorologist’s perspective it was interesting listening to her talk about how these migratory patterns change with the climate.

Of course any conference worth its salt has entertainment and things outside work. A BBQ was hosted in the courtyard underneath the Queen’s Tower, and drinks and comedy (the Science Showoff) in the wonderfully titled hBar at Imperial. The Science Showoff in particular was really good, hosted by a professional comedian but with most of the material coming from PhD students at the various institutes (although shamefully no-one from Met volunteered).

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One of the other really useful parts was meeting students from disparate fields at the other institutions. As Joanna Haigh (director of the SSCP DTP) said in her closing speech, the people we meet at these conferences will be our colleagues for our entire careers, so it’s really important to get to know people socially and professionally. In the end I think it went really well, and I’m certainly looking forward to seeing the London students again at next year’s conference!

Should we be ‘Leaf’-ing out vegetation when parameterising the aerodynamic properties of urban areas?

Email: C.W.Kent@pgr.reading.ac.uk

When modelling urban areas, vegetation is often ignored in attempt to simplify an already complex problem. However, vegetation is present in all urban environments and it is not going anywhere… For reasons ranging from sustainability to improvements in human well-being, green spaces are increasingly becoming part of urban planning agendas. Incorporating vegetation is therefore a key part of modelling urban climates. Vegetation provides numerous (dis)services in the urban environment, each of which requires individual attention (Salmond et al. 2016). However, one of my research interests is how vegetation influences the aerodynamic properties of urban areas.

Two aerodynamic parameters can be used to represent the aerodynamic properties of a surface: the zero-plane displacement (zd) and aerodynamic roughness length (z0). The zero-plane displacement is the vertical displacement of the wind-speed profile due to the presence of surface roughness elements. The aerodynamic roughness length is a length scale which describes the magnitude of surface roughness. Together they help define the shape and form of the wind-speed profile which is expected above a surface (Fig. 1).

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Figure 1: Representation of the wind-speed profile above a group of roughness elements. The black dots represent an idealised logarithmic wind-speed profile which is determined using the zero-plane displacement (zd) and aerodynamic roughness length (z0) (lines) of the surface.

For an urban site, zd and z0 may be determined using three categories of methods: reference-based, morphometric and anemometric. Reference-based methods require a comparison of the site to previously published pictures or look up tables (e.g. Grimmond and Oke 1999); morphometric methods describe zd and z0 as a function of roughness-element geometry; and, anemometric methods use in-situ observations. The aerodynamic parameters of a site may vary considerably depending upon which of these methods are used, but efforts are being made to understand which parameters are most appropriate to use for accurate wind-speed estimations (Kent et al. 2017a).

Within the morphometric category (i.e. using roughness-element geometry) sophisticated methods have been developed for buildings or vegetation only. However, until recently no method existed to describe the effects of both buildings and vegetation in combination. A recent development overcomes this, whereby the heights of all roughness elements are considered alongside a porosity correction for vegetation (Kent et al. 2017b). Specifically, the porosity correction is applied to the space occupied and drag exerted by vegetation.

The development is assessed across several areas typical of a European city, ranging from a densely-built city centre to an urban park. The results demonstrate that where buildings are the dominant roughness elements (i.e. taller and occupying more space), vegetation does not obviously influence the calculated geometry of the surface, nor the aerodynamic parameters and the estimated wind speed. However, as vegetation begins to occupy a greater amount of space and becomes as tall as (or larger) than buildings, the influence of vegetation is obvious. Expectedly, the implications are greatest in an urban park, where overlooking vegetation means that wind speeds may be slowed by up to a factor of three.

Up to now, experiments such as those in the wind tunnel focus upon buildings or trees in isolation. Certainly, future experiments which consider both buildings and vegetation will be valuable to continue to understand the interaction within and between these roughness elements, in addition to assessing the parameterisation.

References

Grimmond CSB, Oke TR (1999) Aerodynamic properties of urban areas derived from analysis of surface form. J Appl Meteorol and Clim 38:1262-1292.

Kent CW, Grimmond CSB, Barlow J, Gatey D, Kotthaus S, Lindberg F, Halios CH (2017a) Evaluation of Urban Local-Scale Aerodynamic Parameters: Implications for the Vertical Profile of Wind Speed and for Source Areas. Boundary-Layer Meteorology 164: 183-213.

Kent CW, Grimmond CSB, Gatey D (2017b) Aerodynamic roughness parameters in cities: Inclusion of vegetation. Journal of Wind Engineering and Industrial Aerodynamics 169: 168-176.

Salmond JA, Tadaki M, Vardoulakis S, Arbuthnott K, Coutts A, Demuzere M, Dirks KN, Heaviside C, Lim S, Macintyre H (2016) Health and climate related ecosystem services provided by street trees in the urban environment. Environ Health 15:95.