Between the 11th-16th March myself and four other PhDs and post docs attended the Ocean in Weather and Climate (OiWC) course at the Met Office, Exeter. This NERC advanced training course was aimed at PhDs, postdocs and beyond. It provided a great opportunity to spend a week meeting other Oceanography researchers at varying stages of their career, and to expand your understanding of the oceans role in climate beyond the scope of your own work.
The week kicked off with an ice breaker where we had do some ‘Scientific speed dating’, chatting to other participants about: Where are you from? What do you work on? What is your main hobby? What is the biggest question in your field of research? This set the tone for a very interactive week full of interesting discussions between all attendees and speakers alike. Course participants were accommodated at The Globe Inn situated in Topsham, a cute village-sized town full of pastel-coloured houses, cosy pubs, art galleries, and beautiful riverside walks to stretch your legs in the evenings.
The days consisted of four 1.5 hour sessions, split up by caffeine and biscuit breaks to recharge before the next session.
Topics covered in the lecture-style talks included…
Modelling the Ocean
High Resolution Ocean modelling in coupled forecast systems
The Meridional Overturning Circulation
The Southern Ocean in climate and climatic change
Climate variability on diurnal, seasonal, annual, inter-annual, decadal timescales
Climate sensitivity, heat uptake and sea level.
All the talks were very interesting and were followed by some stimulating discussion. Each session provided an overview of each topic and an indication of the current research questions in each area at the moment.
In the post lunch session, there were group practical sessions. These explored observational ARGO float data and model output. The practicals, written in iPython notebooks, were designed to let us play with some data, giving us a series of questions to trigger group discussions to deepen understanding of topics covered that morning.
The course also included some ‘softer’ evening talks, giving research career advice in a more informal manner. Most evenings were spent exploring the lovely riverside walks and restaurants/pubs of Topsham. The final evening was spent all together at the Cosy Club in Exeter, rounding off a very interesting and enjoyable week!
The Volcanic and Magmatic Studies Group (VMSG) held a conference from the 3-6th of January in Leeds. The Centre for Observation and Modelling of Earthquakes, Volcanoes and Tectonics (COMET) held a student conference from 8-9th January in Cambridge. It was a conference double-whammy about all things volcanic – heaven!
VMSG is a joint special interest group of the Mineralogical Society of Great Britain and Ireland and the Geological Society of London. The VMSG conference is a fairly small affair, with about 200 in attendance, and it brings together research in geochemistry, seismology, volcanology and related fields. Because of its size, it’s a nice informal space where there is a focus on students presenting their work to the VMSG community, but anyone is free to present their research.
Talks ranged from how tiny fossils, called diatoms, became trapped in a pyroclastic density current, to modelling of lava domes, to how local people interact with the volcano they live on at Masaya, to every aspect of volcanology you can think of. The final talk was definitely a highlight – with everyone in 3D glasses to look at volcanic plumes across Russia, it really brought the satellite images to life (and we got to keep the glasses).
90 posters on a variety of topics were presented, the majority of which were by students (I was one of them). There was of course an obligatory dinner and disco to round off the second day of talks, and a great chance to network with other people from VMSG.
The conference also provides workshops on different aspects of research, with sessions on writing papers, diffusion modelling and InSAR to name a few. These were hosted on the 6th at the University of Leeds Environment and Earth Sciences Department, and comprised a full day of talks and labs so you could get to grips with the techniques you were being shown. I attended the InSAR workshop, which gave a good introduction to the topic of comparing two satellite images and seeing where the ground had moved. There was also a session on deformation modelling in the afternoon and playing with bits of code.
Then it was onto the second leg of the conferences, which took the action to Cambridge, where students that are part of COMET met up to discuss work and attend talks from 8-9th January.
COMET is a National Environment Research Council Centre of Excellence, it comprises a group of researchers that uses remote and ground sensed data and models to study earthquakes and volcanoes. They also work with the British Geological Survey and the European Space Agency, and fund PhD projects in related fields.
The meet-up of students comprised two days of talks from students, with some keynote speakers who had been past members of COMET that had gone on to careers outside of academia. The talks from second and third years included: remote sensing and InSAR being used to examine tectonic strain in the East African Rift Valley and slip (movement) rates along faults in Tibet, modelling how gas bubbles in magma change the more crystals you add to the magma, and using cosmogenic isotopes to work out slip rates on a fault in Italy.
First years are also given the chance to give a talk lasting 5 minutes, so I filled people in on what I’d been up to in the past four months – lots of data collection! My project will be using satellite data to look at the varied eruption behaviour of Bagana volcano in Papua New Guinea, with a view to modelling this behaviour to better understand what causes it. Bagana has a tendency to send out thick lava flows in long pulses and let out lots of gas, and occasionally then violently erupt and let out lots of ash and hot pyroclastic density currents. But it is very understudied, as it is so remote – so there’s lots still to be learnt about it!
The meet-up also included a fancy meal in Pembroke College’s Old Library, with candles and it felt a bit like being at Hogwarts! Then it was back to Reading, thoroughly worn out, but with lots of ideas and many useful contacts – VMSG2019 is in St. Andrews and I can’t wait.
Over the past ~decade, extended-range forecasts of river flow have begun to emerge around the globe, combining meteorological forecasts with hydrological models to provide seasonal hydro-meteorological outlooks. Seasonal forecasts of river flow could be useful in providing early indications of potential floods and droughts; information that could be of benefit for disaster risk reduction, resilience and humanitarian aid, alongside applications in agriculture and water resource management.
“Ultimately, the most informative forecasts of flood hazard at the seasonal scale are streamflow forecasts using hydrological models calibrated for individual river basins. While this is more computationally and resource intensive, better forecasts of seasonal flood risk could be of immense use to the disaster preparedness community.”
Over the past months, researchers in the Water@Reading* research group have been working with the European Centre for Medium-Range Weather Forecasts (ECMWF), to set up a new global scale hydro-meteorological seasonal forecasting system. Last week, on 10th November 2017, the new forecasting system was officially launched as an addition to the Global Flood Awareness System (GloFAS). GloFAS is co-developed by ECMWF and the European Commission’s Joint Research Centre (JRC), as part of the Copernicus Emergency Management Services, and provides flood forecasts for the entire globe up to 30 days in advance. Now, GloFAS also provides seasonal river flow outlooks for the global river network, out to 4 months ahead – meaning that for the first time, operational seasonal river flow forecasts exist at the global scale – providing globally consistent forecasts, and forecasts for countries and regions where no other forecasts are available.
The seasonal outlook is displayed as three new layers in the GloFAS web interface, which is publicly (and freely) available at www.globalfloods.eu. The first of these gives a global overview of the maximum probability of unusually high or low river flow (defined as flow exceeding the 80th or falling below the 20th percentile of the model climatology), during the 4-month forecast horizon, in each of the 306 major world river basins used in GloFAS-Seasonal.
The second layer provides further sub-basin-scale detail, by displaying the global river network (all pixels with an upstream area >1500km2), again coloured according to the maximum probability of unusually high or low river flow during the 4-month forecast horizon. In the third layer, reporting points with global coverage are displayed, where more forecast information is available. At these points, an ensemble hydrograph is provided showing the 4-month forecast of river flow, with thresholds for comparison of the forecast to typical or extreme conditions based on the model climatology. Also displayed is a persistence diagram showing the weekly probability of exceedance for the current and previous three forecasts.
Over the coming months, an evaluation of the system will be completed – for now, users are advised to evaluate the forecasts for their particular application. We welcome any feedback on the forecast visualisations and skill – feel free to contact me at the email address below!
To find out more, you can see the University’s press release here, further information on SEAS5 here, and the user information on the seasonal outlook GloFAS layers here.
*Water@Reading is “a vibrant cross-faculty centre of research excellence at the University of Reading, delivering world class knowledge in water science, policy and societal impacts for the UK and internationally.”
Full list of collaborators:
Rebecca Emerton1,2, Ervin Zsoter1,2, Louise Arnal1,2, Prof. Hannah Cloke1, Dr. Liz Stephens1, Dr. Florian Pappenberger2, Prof. Christel Prudhomme2, Dr Peter Salamon3, Davide Muraro3, Gabriele Mantovani3
1 University of Reading 2 ECMWF 3 European Commission JRC
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!
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”.
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).
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!
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).
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.
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.
For many Africans, the timing of the wet season is of crucial importance, especially for those reliant upon subsistence agriculture, who depend on the seasonal rains for crop irrigation. In addition, the wet season recharges lakes, rivers and water storage tanks which constitute the domestic water supply in some areas. The timing of the wet season also affects the availability of energy from hydroelectric schemes, and has impacts upon the prevalence of certain disease carrying vectors, such as mosquitoes.
Climate change is already threatening many vulnerable populations, and changes in the timing or intensity of the wet season, or increasing uncertainty in the timing of the onset, may lead to significant socio-economic impacts. But before we consider future projections or past changes in the seasonality, we need to go back a few steps.
The first step is to find a method for determining when the wet season starts and ends (its ‘onset’ and ‘cessation’). In order to look at large-scale shifts in the timing of the wet season and relate this to wider-scale drivers, this method needs to be applicable across the entirety of continental Africa. Most previous methods for determining the onset focus on the national to regional scale, and are dependent on the exceedance of a certain threshold e.g. the ﬁrst week with at least 20mm of rainfall, with one rainfall event of more than 10mm, and no dry spell of more than 10 days after the rain event for the next month. While such definitions work well at a national scale they are not applicable at a continental scale where rainfall amounts vary substantially. A threshold suitable for the dry countries at the fringes of the Sahara would not be suitable in the wetter East African highlands.
In addition to a vast range of rainfall amounts, the African continent also spans multiple climatic regimes. The seasonal cycle of precipitation over continental Africa is largely driven by the seasonal progression of the ITCZ and associated rain belts, which follows the maximum incoming solar radiation. In the boreal summer, when the thermal equator sits between the equator and the Tropic of Cancer, the ITCZ sits north of the equator and West Africa and the Sahel experience a wet season. During the boreal autumn the ITCZ moves south, and southern Africa experiences a wet season during the austral summer, followed by the northward return of the ITCZ during the boreal spring. As a consequence of this, central African regions and the Horn of Africa experience two wet seasons per year – one as the ITCZ travels north, and a second as the ITCZ travels south. A method for determining the onset and cessation at the continental scale thus needs to account for regions with multiple wet seasons per year.
In our paper (available here) we propose such a method, based on the method of Liebmann et al (2012). The method has three steps:
Firstly, determine the number of seasons experienced per year at the location (or grid point) of interest. This is achieved using harmonic analysis – the amplitude of the first and second harmonic were computed, using the entire timeseries and their ratio compared. If the ratio was greater than 1.0, i.e. the amplitude of the second harmonic was greater than the amplitude of the first harmonic then the grid point was defined as having two wet seasons per year (biannual), if the ratio was less than one then it was defined as having an annual regime. Figure 1 shows the ratio for one African rainfall dataset (TARCATv2). Three regions are identified as biannual regions; the Horn of Africa, an equatorial strip extending from Gabon to Uganda and a small region on the southern West African coastline.
Secondly the period of the year when the wet season occurs was determined. This was achieved by looking for minima and maxima in the climatological cumulative daily rainfall anomaly to identify one or two seasons.
The third and final stage is to calculate the onset and cessation dates for each year. This is done by looking for the minima and maxima in the cumulative daily rainfall anomaly, calculated for each season.
Figure 2 shows the seasonal progression of the onset and cessation, with the patterns observed in agreement with those expected from the driving physical mechanisms, and continuous progression across the annual/biannual boundaries. Over West Africa and the Sahel, Figure 2a-b shows zonally-contiguous progression patterns with onset following the onset of the long rains and moving north, and cessation moving southward, preceding the end of the short rains. Over southern Africa Figure 2c-d shows the onset over southern Africa starting in the north-west and south-east, following the onset of the short rains, reaching the East African coast last, and cessation starting at the Zimbabwe, Mozambique, South Africa border and spreading out radially into the cessation of the long rains.
As well as testing the method for compatibility with known physical drivers of African rainfall, agreement across multiple satellite-based rainfall estimates was also examined. In general, good agreement was found across the datasets, particularly for regions with an annual regime and over the biannual region of East Africa.
The advantage of having a method that works at the continental scale is the ability to look at the impact of large-scale oscillations on wider-scale variability. One application of this method was to investigate the impact of El Niño upon both the annual rains and short rains (Figure 3). In Figure 3 we see the well-documented dipole in rainfall anomaly, with higher rainfall totals over 0–15°S and the Horn of Africa in El Niño years and the opposite between 15°S and 30°S. This anomaly is stronger when we use this method compared with using standard meteorological seasons. We can also see that while the lower rainfall to the south is colocated with later onset dates and a consequentially shorter season, the higher rainfall over the Horn of Africa is associated with later cessation of the short rains, with only small differences in onset date.
In addition to using this method for research purposes, its application within an operational setting is also being explored. Hopefully, the method will be included within the Rainwatch platform, which will be able to provide users with a probabilistic estimate of whether or not the season has started, based on the rainfall experienced so far that year, and historical rainfall data.
For more details, please see the paper detailing this work:
Dunning, C.M., E Black, and R.P. Allan (2016) The onset and cessation of seasonal rainfall over Africa, Journal of Geophysical Research: Atmospheres, 121 11,405-11,424, doi: 10.1002/2016JD025428
Liebmann, B., I. Bladé, G. N. Kiladis, L. M. Carvalho, G. B. Senay, D. Allured, S. Leroux, and C. Funk (2012), Seasonality of African precipitation from 1996 to 2009, J. Clim., 25(12), 4304–4322.
In 2016 the United Nations (UN) Sustainable Development Goals (SDGs) officially came into force to tackle key global challenges under a sustainable framework.
The SDGs comprise 17 global goals and 169 targets to be achieved across the next 15 years. As part of the ‘2030 Agenda’ for sustainable development, these goals aim to address a range of important global environmental, social and economic issues such as climate change, poverty, hunger and inequality. Adopted by leaders across the world, these goals are a ‘call for action’ to ensure that no one is left behind. However, the SDGs are not legally binding. The success of goals will rely solely on the efforts of individual countries to establish and implement a national framework for achieving sustainable development.
As part of the NERC funded ‘Innovating for Sustainable Development’ programme, students here in the Department of Meteorology were given the opportunity to explore and find solutions to key environmental challenges as outlined in the UN’s SDGs.
Run by the SCENARIO and SSCP doctoral training partnerships, the programme challenged students from a variety of disciplines and institutions to re-frame the SDGs from a multi-disciplinary perspective and to develop tangible, innovative solutions for sustainable development.
The programme began with an ‘Interdisciplinary Challenges Workshop’ where students participated in activities and exercises to review the importance of the SDGs and to consider their multi-disciplinary nature. Students were encouraged to think creatively and discuss issues related to each of the goals, such as: ‘Is this SDG achievable?’, ‘Are the goals contradictory?’ and ‘How could I apply my research to help achieve the SDGs?’
Following this, three ‘Case Study’ days explored a handful of the SDGs in greater detail, with representatives from industry, start-ups and NGOs explaining how they are working to achieve a particular SDG, their current challenges and possible opportunities for further innovation.
The second Case Study day focused on SDG 6 – Clean Water and Sanitation. Experts from WaterAid, De-Solenator, Bear Valley Ventures, UKWIR and the International Institute for Environmental Development outlined the importance of confronting global sanitation and water challenges in both developing and developed nations. Alarmingly, it was highlighted that an estimated 40% of the global population are affected by water scarcity and 2.4 billion people still lack access to basic sanitation services, with more than 80% of human activity wastewater discharged into rivers without going through any stage of pollution removal (UN, 2016).
The programme finished off with a second workshop. Here students teamed up to develop innovative business ideas aimed at solving the SDG challenges presented throughout the Case Study events. Business coaches and experts were on hand to offer advice to help the teams develop ideas that could become commercially viable.
On the 16th March the teams presented their business ideas at the ‘Meet the Cleantech Pioneers’ networking event at Imperial’s new Translation and Innovation Hub (I-HUB). An overview of the projects can be found here. This event, partnered with the Climate-KIC accelerator programme, provided an excellent platform for participants to showcase and discuss their ideas with a mix of investors, entrepreneurs, NGOs and academics all interested in achieving sustainable development.
Overall the programme provided a great opportunity to examine the importance of the SDGs and to work closely with PhD students from a range of backgrounds. Fundamentally the process emphasised the point that, in order for the world to meet the 2030 Agenda, many sustainable development challenges still need to be better understood and many solutions still need to be provided – and here scientific research can play a key role. Furthermore, it was made clear that a high level of interdisciplinary thinking, research and innovation is needed to achieve sustainable development.
UN, 2016: Clean Water and Sanitation – Why it matters, United Nations, Accessed 05 March 2017. [Available online at http://www.un.org/sustainabledevelopment/wp-content/uploads/2016/08/6_Why-it-Matters_Sanitation_2p.pdf]
Small-scale rainbands often form downwind of mountainous terrain. Although relatively small in scale (a few tens of km across by up to ~100 km in length), these often poorly forecast bands can cause localised flooding as they can be associated with intense precipitation over several hours due to the anchoring effect of orography (Barrett et al., 2013). Figure 1 shows a flash flood caused by a rainband situated over Cockermouth in 2009. In some regions of southern France orographic banded convection can contribute 40% of the total rainfall (Cosma et al., 2002). Rainbands occur in various locations and under different synoptic regimes and environmental conditions making them difficult to examine their properties and determine their occurrence in a systematic way (Kirshbaum et al. 2007a,b, Fairman et al. 2016). My PhD considers the ability of current operational forecast models to represent these bands and the environmental controls on their formation.
What is a rainband?
A cloud and precipitation structure associated with an area of rainfall which is significantly elongated
Stationary (situated over the same location) with continuous triggering
Can form in response to moist, unstable air following over complex terrain
Narrow in width ~2-10 km with varying length scales from 10 – 100’s km
To examine the ability of current operational forecast models to represent these bands a case study was chosen which was first introduced by Barrett, et al. (2016). The radar observations during the event showed a clear band along The Great Glen Fault, Scotland (Figure 3). However, Barrett, et al. (2016) concluded that neither the operational forecast or the operational ensemble forecast captured the nature of the rainband. For more information on ensemble models see one of our previous blog posts by David Flack Showers: How well can we predict them?.
Localised convergence and increased convective available potential energy along the fault supported the formation of the rainband. To determine the effect of model resolution on the model’s representation of the rainband, a forecast was performed with the horizontal gird spacing decreased to 500 m from 1.5 km. In this forecast a rainband formed in the correct location which generated precipitation accumulations close to those observed, but with a time displacement. The robustness of this forecast skill improvement is being assessed by performing an ensemble of these convection-permitting simulations. Results suggest that accurate representation of these mesoscale rainbands requires resolutions higher than those used operationally by national weather centres.
Idealised numerical simulations have been used to investigate the environmental conditions leading to the formation of these rainbands. The theoretical dependence of the partitioning of dry flow over and around mountains on the non-dimensional mountain height is well understood. For this project I examine the effect of this dependence on rainband formation in a moist environment. Preliminary analysis of the results show that the characteristics of rainbands are controlled by more than just the non-dimensional mountain height, even though this parameter is known to be sufficient to determine flow behaviour relative to mountains.
This work has been funded by the Natural Environmental Research Council (NERC) under the project PREcipitation STructures over Orography (PRESTO), for more project information click here.
Barrett, A. I., S. L. Gray, D. J. Kirshbaum, N. M. Roberts, D. M. Schultz, and J. G. Fairman, 2015: Synoptic Versus Orographic Control on Stationary Convective Banding. Quart. J. Roy. Meteorol. Soc., 141, 1101–1113, doi:10.1002/qj.2409.
— 2016: The Utility of Convection-Permitting Ensembles for the Prediction of Stationary Convective Bands. Mon. Wea. Rev., 144, 10931114, doi:10.1175/MWR-D-15-0148.1.
Cosma, S., E. Richard, and F. Minsicloux, 2002: The Role of Small-Scale Orographic Features in the Spatial Distribution of Precipitation. Quart. J. Roy. Meteorol. Soc., 128, 75–92, doi:10.1256/00359000260498798.
Fairman, J. G., D. M. Schultz, D. J. Kirshbaum, S. L. Gray, and A. I. Barrett, 2016: Climatology of Banded Precipitation over the Contiguous United States. Mon. Wea. Rev., 144,4553–4568, doi: 10.1175/MWR-D-16-0015.1.
Kirshbaum, D. J., G. H. Bryan, R. Rotunno, and D. R. Durran, 2007a: The Triggering of Orographic Rainbands by Small-Scale Topography. J. Atmos. Sci., 64, 1530–1549, doi:10.1175/JAS3924.1.
Kirshbaum, D. J., R. Rotunno, and G. H. Bryan, 2007b: The Spacing of Orographic Rainbands Triggered by Small-Scale Topography. J. Atmos. Sci., 64, 4222–4245, doi:10.1175/2007JAS2335.1.
Showers are one of the many examples of convective events experienced in the UK, other such events include thunderstorms, supercells and squall lines. These type of events form most often in the summer but can also form over the sea in the winter. They form because the atmosphere is unstable, i.e. warm air over a cooler surface, this results in the creation of thermals. If there is enough water vapour in the air and the thermal reaches high enough the water vapour will condense and eventually form a convective cloud. Convective events produce intense, often very localised, rainfall, which can result in flash floods, e.g. Boscastle 2004.
Flash floods are very difficult to predict, unlike flood events that happen from the autumnal and winter storms e.g. floods from Storms Desmond and Frank last winter, and the current floods (20-22 November). So often there is limited lead time for emergency services to react to flash flood events. One of the main reasons why flash floods are difficult to predict is the association with convective events because these events only last for a few hours (6 hours at the longest) and only affect a very small area.
One of the aspects of forecasting the weather that researchers look into is the predictability of certain events. My PhD considers the predictability of convective events within different situations in the UK.
The different situations I am considering are generally split into two regimes: convective quasi-equilibrium and non-equilibrium convection.
In convective quasi-equilibrium any production of instability in the atmosphere is balanced by its release (Arakawa and Schubert, 1974). This results in scattered showers, which could turn up anywhere in a region where there is large-scale ascent. This is typical of areas behind fronts and to the left of jet stream exit regions. Because there are no obvious triggers (like flow over mountains or cliffs) you can’t pin-point the exact location of a shower. We often find ourselves in this sort of situation in April, hence April showers.
On the other hand in non-equilibrium convection the instability is blocked from being released so energy in the system builds-up over time. If this inhibiting factor is overcome all the instability can be released at once and will result in ‘explosive’ convection (Emanuel, 1994). Overcoming the inhibiting factor usually takes place locally, such as a sea breeze or flow up mountains, etc. so these give distinct triggers and help tie the location of these events down. These are the type of situations that occur frequently over continents in the spring and often result in severe weather.
It’s useful having these regimes to categorise events to help determine what happens in the forecasts of different situations but only if we understand a little bit about their characteristics. For the initial part of my work I considered the regimes over the British Isles and found that we mainly have convective events in convective quasi-equilibrium (showers) – on average roughly 85% of convective events in the summer are in this regime (Flack et al., 2016). Therefore it is pertinent to ask how well can we predict showers?
To see how well we can predict showers, and other types of convection, the forecast itself is examined. This is done by adding small-scale variability into the model, throughout the forecast, to determine what would happen if the starting conditions (or any other time in the model) changed. This is run a number of times to create an ensemble.
Using ensembles we can determine the uncertainty in the weather forecast, this can either be in terms of spatial positioning, timing or intensity of the event. My work has mainly considered the spatial positioning and intensity of the convection, and is to be submitted shortly to Monthly Weather Review. The intensity in my ensemble shows similar variation in both regimes, suggesting that there are times when the amount of rainfall predicted can be spot on. Most of the interesting results appear to be linked to the location of the events. The ensembles for the non-equilibrium cases generally show agreement between location of the events, so we can be fairly confident about their location (so here your weather app would be very good). On the other hand, when it comes to showers there is no consistency between the different forecasts so they could occur anywhere (so when your app suggests showers be careful – you may or may not get one).
So I’ll answer my question that I originally posed with another question: What do you want from a forecast? If the answer to this question is “I want to know if there is a chance of rain at my location” then yes we can predict that you might get caught by a shower. If on the other hand your answer is “I want exact details, for my exact location, e.g. is there going to be a shower at 15:01 on Saturday at Stonehenge yes or no?” Then the answer is, although we are improving forecasts, we can’t give that accurate a forecast when it comes to scattered showers, simply because of their very nature.
With forecasts improving all the time and the fact that they are looking more realistic it does not mean that every detail of a forecast is perfect. As with forecasting in all areas (from politics to economy) things can take an unexpected turn so caution is advised. When it comes to the original question of showers then it’s always best to be prepared.
This work has been funded by the Natural Environmental Research Council under the project Flooding From Intense Rainfall, for more project details and project specific blogs visit: www.met.reading.ac.uk/flooding
Arakawa, A. and W. H. Schubert, 1974: Interaction of a Cumulus Cloud Ensemble with the Large-Scale Environment, Part I. J. Atmos. Sci., 31, 674-701.
Emanuel, K. A., 1994: Atmospheric convection, Oxford University Press, 580 pp.
Flack, D. L. A., R. S. Plant, S.L. Gray, H. W. Lean, C. Keil and G. C. Craig, 2016: Characterisation of Convective Regimes over the British Isles. Quart. J. Roy. Meteorol. Soc., 142, 1541-1553.
Over the past two weeks 25,000 delegates have been gathering in Marrakech to discuss mitigation and adaptation for climate change. On the 4th November 2016 the Paris Agreement came into force and as a result discussions during the conference debated its implementation. The Walker Institute and the Department of Meteorology (University of Reading), with the support of the NERC SCENARIO doctoral training partnership and an UNFCCC partnership, supported two PhD students to be official UN observers at COP22, and enabled remote participation with students back at Reading University. To find out more about our work with COP22 continue reading this blog post and check out:
Today (18/11/16) the UK government are set to announce that the United Kingdom has ratified the Paris Agreement. Yesterday, Boris Johnson (UK foreign secretary) signed the Paris Agreement after no objections were raised by the House of Commons or House of Lords. The United Kingdom in accordance with the Intended Nationally Determined Contributions (INDCs) of the European Union, are set to reduce greenhouse gas emissions by 40% by 2030 relative to 1990 emission levels. Today also marks the end of the 22nd Conference of the Parties (COP) for the United Nations Framework Convention on Climate Change and here are some quick summary points that PhD students took away from observing the process in Marrakech:
1) The significance of the Paris Agreement.
“Now that we have Paris, we need to take action immediately”
Teresa Anderson, ActionAid UK.
The Paris Agreement marks a change in the intentions during the COP process. Due to the success and ratification of the Paris Agreement more discussions can be based on the adaptation and mitigation against climate change, rather than negotiating global targets on climate change prevention. The Paris Agreement states that a global response is needed to respond to the threat of climate change and that global temperature rise should be kept well below 2°C and that efforts should be pursued to limit the global temperature rise to 1.5°C. COP22 Marrakech, began by stating that this is the “COP of Action”, and therefore the focus seen during side events, negotiations, dignitary speeches and press conferences was on the need for action.
“Countries have strongly supported the [Paris] Agreement because they realize their own national interest is best secured by pursuing the common good. Now we have to translate words into effective policies and actions.”
Mr Ban Ki-Moon, Secretary General of the United Nations.
2) A continued effort is needed to concentrate on the individual.
As SCENARIO PhD students we were challenged to understand the process that takes place during a UNFCCC conference. To do this we interviewed many conference delegates including policymakers, research organisations, industry experts, entrepreneurs, environmental consultants and funding sources to name a few. A common theme that ran through most of our interviews is that action is needed to prioritise the individual as well as thinking in terms of national- and community-level. To ensure the successful mitigation and adaptation to climate change, strategies need to come into place that protect the rights of the individual. This poses a global challenge, stretching from protecting the livelihoods of indigenous cultures and those impacted by sea level rise on low-lying islands, to supporting workers who rely on the non-renewable energy industry. In terms of climate research we need to ensure that we make our scientific conclusions accessible on an individual-level so that our work has a greater impact.
“a key goal for us is making climate change research accessible to the user community”
3) Action is needed now, however the Paris Agreement only implies action post-2020.
Throughout our attendance in plenary meetings and side events there was an emphasis that whilst the Paris Agreement is an important stepping stone to combatting climate change, action is needed before 2020 for the Paris Agreement to be reached. Currently INDCs are proposed for between 2021-2030, however for the intended global temperature targets to be achieved it was argued that action is needed now. Although, pre-2020 action raises much contention, with the most popular argument against pre-2020 action being that more time and effort is needed for negotiations to ensure that a better understanding of national efforts to climate change mitigation is determined.
“We need to take action before 2020. Working for action post-2020 is not going to be enough. We need to start acting now.”
Honduras Party Representative.
“We need more time to work on the rule book for the Paris Agreement. Discussions on this should continue.”
Switzerland Party Representative.
4) There is a difference in opinion on whether 1.5°C can be reached.
For me the most interesting question we asked conference delegates was “do you think the target of 1.5°C can be reached?” This question brought a difference of opinion including some party members arguing that the change in our non-renewable energy dependence is far too great for the target to be achieved. Meanwhile, other political representatives and NGO delegates argued that accepting the target is unachievable before even trying makes negotiations and discussions less successful. There was also anticipation for the future IPCC report titled, Special Report on Global Warming of 1.5°C above pre-industrial levels and related global greenhouse gas emission pathways.
“Of course we want to fight for 1.5°C, why fight for 2°C? It just makes sense to fight for 1.5°C”
Martina Duncan, Party Representative for Grenada.
COP22 has been a fantastic opportunity for PhD students in our department to interact and understand the process that takes place during a UNFCCC conference. Whilst the past couple of weeks have been dominated by the results of the US election and the associated uncertainties, there has been an increasing global recognition of climate change and that action should be taken. In the next few years the challenge to mitigate and adapt towards climate change will be an increasing priority, and let us hope that these annual UNFCCC conferences are key stepping stones for climate change action.
“This is a problem people are recognising, and that it is time to change”
Jonathan Pershing, US Climate Envoy
Thank you all those who have supported our work at COP22 this year. Thank you to the Walker Institute, NERC SCENARIO doctoral training partnership and UNFCCC for this brilliant opportunity. Thank you to all those who have supported us with publicity including NERC, Royal Meteorological Society, members of staff and PhD students at the University of Reading and Lucy Wallace who has ensured the appropriate communication of our project. Plus a huge thanks to all delegates and staff at COP22 who volunteered their time to talk to us.