Saturday, 20 September 2014

All Quiet on the Urban Front

Where has the time gone? I have certainly been neglecting this blog.

So with the new term imminent I am going to make a conscientious effort to post more!

Watch this space for an update on the old PhD, Meteorology Department seminar reviews and random urban news.

Monday, 24 March 2014

Re-entering the Matrix

   Whilst I won't be donning a pair of black glasses and a large trench coat to enter a parallel universe via a phone line, I have returned to the world of matrices after a 10 year hiatus.

   It has been a while since my last post, and after giving myself a kick up the backside I am back to it. After a period of reading (note to self update online bibliography) focused on urban surface models of varying degrees of complexity and how they treat vegetation (if at all), I have started the first modelling phase. After discussions with the Prof. during a period of disillusionment (first of many I am sure over the next few years) it was decided that it is time to get practical and put into practice some of the topics I have been reading about. 

   So as a first exercise I am focusing on modelling radiation exchange within a 2D urban canyon using the method of Sparrow and Cess (1970) as applied by Harman et al. (2004), in which shapefactors are determined for a chosen canyon geometry and used to calculate the exchange of diffuse radiation between surfaces. This scheme was chosen as it is shown by Harman et al. (2004) to be more accurate than two commonly utilised approximations to determine the net radiation balance of a canyon used in a number of models and the scheme is utilised (in a simplified form) within the MORUSES model (Porson et al. 2010) that I plan to adapt to include urban vegetation.

  The 2D urban canyon alluded to earlier has four facets (roof, road, wall 1 and wall 2), with the road having width, W, the building walls having height H and the canyon is of infinite length (Figure 1). The canyon geometry is then described by the height to width ratio of the canyon (H/W) which from inference identifies the magnitude of the surface area within it for radiative transfer and emission (radiation trapping). In this modelling exercise the surfaces considered are the road, two walls and the sky (s) at the top of the walls which forms a closed system. The roof is treated separately as a flat surface and not considered in this initial exercise. 
Figure 1. Schematic of urban canyon system (Harman et al. 2004)

   The aims of the modelling exercise are to recreate the results of Harman et al (2004), to look deeper at the underlying geometry and mathematics used in determining the solution, as a starting point in the coding of my model, and to begin to consider the impact of additional facets such as trees from a coding and theoretical prospective.   

   So where do matrices come into this I hear you say? It is possible to describe the exchange of radiation within the above defined closed system by a set of three equations (see below) that consider the emitted (Sigma), total incoming (Lambda) and total outgoing (B) radiation for each facet (i) and the other facets (j) within the system and the net radiative balance (Q). 
Equations 6, 7 and 8 from Harman et al. (2004) 

The solutions for the 3 equations can be determined using a matrix that considers the interactions between the 4 facets (sky, road, wall1, wall2) in terms of calculated shapefactors (Fij), facet emissivity (epsilon) and the identity matrix (deltaij ,not shown). From this matrix the outgoing radiant density for each facet (B) is then determined using a set of 4 simultaneous equations solved using Gaussian Elimination (a.k.a. LU Factorization). Results to follow... 

References
Harman, I. N., Best, M. J., and Belcher, S. E.: 2004, Radiative exchange in an urban street canyon. Boundary Layer Meteorology, 110, 301-316.

Porson, A., Clark, P. A., Harman, I. N., Best, M. J., and Belcher, S. E.: 2010, Implementation of a new urban energy budget scheme in the MetUM. Part I: Description and idealized simulations. Quarterly Journal of the Royal Meteorological Society, 136, 1514-1529.

Sparrow, E. M., and Cess, R. D.: 1970, Radiation Heat Transfer, Chapters 3-4, Appendices A & B, Thermal Science Series, Brooks/Cole, pp.75-136, 300-313.  

Thursday, 20 February 2014

Good Times, Bad Times


Good times...

   Exciting times! My work is going to be published in a journal (my first first author paper) has been accepted. Coming to a journal near you (Journal of Atmospheric and Oceanic Technology in fact) will be work from my HiTemp days up in Brum entitled 'A low-cost wireless air temperature sensor: Evaluation for use in environmental monitoring applications'.

  Very thankful for the help of my co-authors Lee, Cat, Sue and Xiaoming and the 3 reviewers for their constructive (not too nasty thankfully) comments. Also I really appreciate the support and congratulations from my friends on Facebook, never had so many likes :-)

Bad times... (but not all bad)


   As with many things with the good comes the bad. Nothing too bad thankfully just frustrations. I nearly slipped into old habits ( they do say they die hard) this week after a not very constructive (from my point of view at the time) meeting with the Prof. I left the meeting feeling like knew very little in sufficient detail and that I had read the wrong stuff. Throughout the rest of the day I got frustrated and began to question what I was actually looking at am I really cut out for this? In the past that would probably spiral into anxiety and today I would be lying if I didn't say I was feeling it a little.

   However I funnelled that frustration into some thing positive. It was time to re-evaluate what I was doing and re-visit my short term plan (6 month plan). I concluded that a) I hadn't wasted my time with the reading, b) I didn't need to feel like I knew very little, I know a lot but not as much as the Prof and not in the subjects we discussed, and c) I was perhaps procrastinating a little out of worry about models and have re-focused my reading to more relevant papers for the long term goals of the thesis (details can be studied when required).

   The moral to this story is to use the times of frustration and doubt to re-evaluate where you are at. It often turns out that you are doing a lot better than you thought you were.

Tuesday, 4 February 2014

Finding the positives out of an unpleasant surprise

   Into my 4th week and I have just found two papers (same author) in my initial literature search that contains lots of the things I have discussed with The Prof and thought about for my work over the last few weeks. It does not fill you full of confidence to find out things like this as it could threaten your original contribution to science.
 
   However I am not going to be downbeat for too long! Firstly, I am only a month into this journey and even after that period of time I realise that there are many questions to answer about the modelling problem of representing urban vegetation in weather and climate models, so no end of original contributions to make. Secondly, I can critique their work. Have they missed something? Is there something I can improve? Is it better to model something they did in a different way?

Tuesday, 21 January 2014

"The power to surprise"

   To borrow Kia's phrase "The power to surprise", I am certainly not referring to their latest SUV but a meeting today with my supervisor. Even at this early stage of the PhD I had an idea of what I was going to be working on over the next few years and a plan in my head as to how things might pan out. That was until today... during the meeting I presented a tentative work plan for the coming three years and a more detailed plan for the next 12 months, as I saw it. Two hours later work plan version 1.0 mais well be consigned to the recycle bin (not all that bad as can use to to develop version 2).

   The Prof (will call my supervisor that from now on) suggested (and we discussed) a whole new way of looking at the problem of representing vegetation in urban areas that was not restricted to a single modelling framework. In fact the production of a final operational model as it turns out (in the Profs view) should not be the overall aim of the PhD, it is more important to ensure the science is correct, implementation can wait as it is a trivial coding exercise. That means that I have greater freedom when developing and testing the model I chose to construct on close consultation with the literature and what question I want to answer. This flexibility would then allow additional coupling with a range of models that are not restricted by the the frameworks of operational numerical prediction models (although an overall aim would be to implement my findings within them if possible). So tomorrow it is time to have a re-think of the key reading I need to undertake and start to formulate those initial questions.

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Departmental Seminar (Monday 20th July)
'Chemtrails, carbon tragets and methane burps: Climate science communication in the UK government'
Tyrone Dunbar (Met Office Hadley Centre/ DEFRA/ DECC - formally at Reading)

   Something a little different for a seminar, with a focus on how to communicate often complex scientific theories in a correct and concise manner to the UK government. Tyrone gave an overview of his role in this process for DEFRA (Department for Environment, Food & Rural Affairs) and DECC (Department of Energy & Climate Change) where he produces science statements to aid policy and law makers (Members of Parliament and House of Lords) from the latest meteorology and climate research.
   One of the most worrying aspects of his job was the need to explain the headlines of the Daily Mail and Express (other papers too) are not scientifically accurate to MPs! He produces a briefing note that summaries the true science behind the headline (if there is any) in three easy to remember soundbites that unsuspecting MPs can then use if they are questioned on the headlines by journalists. However this task is not limited to spurious press stories but also includes scientific papers that make the news. The example he presented was a paper on 'Methane Burps' that highlighted the potential financial impact of a sudden mass release of methane from the tundra and sea floor. In this case Tyrone contacted the experts in the relevant field whether that be in other government funded research institutes (e.g. Met Office) or academic specialists to get consensus/facts before producing the a response and guidance. It turned out some of the assumptions made in the paper were extremely unlikely in reality meaning that some the underlying science was questionable.
   Other aspects of his work included producing responses to freedom of information requests from the public and questions asked in parliament. He informed the audience of a scheme that matches up academics with civil service personnel to see how DECC and DEFRA operate and how science is used in the formulation of policy.
   From this talk I certainly will take away the need to be able to explain your research concisely and in terms that are understandable to a wider audience and to ensure that pictures used to describe your work are chosen carefully.        
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Thursday, 16 January 2014

Meetings, Seminars and Coffee Breaks

  The first week is nearly coming to an end and so far so good. Getting settled in at my desk and making it feel homely with my old name tag from the door in Birmingham, a selection of mugs, a pint glass for my orange squash and my second sun to help on those dark overcast winter days. Slowly remembering names of people I meet (takes me a while) and have met many who I working in my subject area which will hopefully lead to many a useful conversation on the ins and outs of the Met Office Unified Model (UM), but not all the time I hope.  

   Unfortunately the Meteorology Department is very spread out these days due to rapid growth over the last decade meaning it has out grown the Met Building (I remember them building the last extension) with my office not in it :( This however has aided my new year fitness regime no end as I have to scuttle across campus to various buildings in double quick time. Couple this with the 113 steps up to the 5th floor of the Lyle building and I will be back in shape in no time!    

   It may be week one but I have already come to the conclusion that a PhD is clearly just a series of meetings, seminars and coffee breaks. Just need to make sure I fit some work in between them!!!!

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Urban Met Group Seminar

Comparisons of observations in central London with the UM 
Sian Lane (Uni of Reading)

   They must have known I was joining the department as this gave me a brief introduction to the UM model that I will be working with! Sian has been comparing observations from a number of urban heat island (UHI) events in London with model output from the UM (single tile JULES urban surface scheme).

   As people may know (or not) London and Britain as a whole are not renowned for our scorching temperatures and clear skies (even in summer a bit of fair weather cumulus likes to make an appearance), so the number of 'classic' UHI events is few and far between in the dataset she was using. To account for this she looked at the UHI intensity using average temperatures from a number of MetOffice synoptic stations inside the M25 for urban and stations outside it for rural observations, making clear that many of the so called urban stations were located in grassed areas (e.g. airports and parks) so were not necessarily giving the true urban temperature. Selecting UHI intensity events in the upper quartile led to her having about 90 days of data. Quite surprisingly the days with the largest magnitude UHI intensity were distributed fairly evenly across the year, not with the majority in the summer as would be expected.

   The comparison focused mainly on turbulent fluxes of heat and moisture (comparison was also made for urban air temperatures with a difference between observed and modeled of ~ 1 K - plotted results not shown) determined using Eddy Covariance (EC) techniques from two flux tower sites in central London. One on the top of BT Tower (within the Mixing Layer) and a second site located on top of the offices of Westminster City Council on Marylebone Road (within the Surface Layer). Results for all days for turbulent sensible heat flux (H) compared with UM output showed the model captured the diurnal variation in the H fluxes but under estimated the magnitude. Unfortunately there seemed to be a problem with the modeled latent heat flux which fluctuated barely above zero, Sian noted that she will need to investigate this further as one would expect higher modeled latent heat fluxes even in central London which is highly urban.

   As this was a Urban Met Group seminar they are designed to be less formal and more interactive than departmental seminars so lots of discussion was made of the results and suggestions were made for possible further analysis, statistical techniques and possible reasons for the differences in model output and observed fluxes that will hopefully aid Sian as she moves forward with her research.

This style of seminar is of great use to all concerned as it gives a relaxed setting to discuss results, techniques and the finer points of urban met theory. I intended to make the most of such opportunities throughout my PhD.    

Tuesday, 14 January 2014

Day One & First Seminar

Day one was spent doing the usual first day things, getting an ID card, filling in forms, getting use to Linux and meeting lots of friendly new people. Despite little work been done I attended my first departmental seminar (first since back in the day) which had some relevance to the ceilometer remote sensing I did in a previous life.

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East East Asian Pollution Observed with Multiwavelength 
Raman Lidar in South Korea
Dr. Detlef Muller - University of Hertfordshire

   An interesting talk on how to use a specially designed Raman Lidar (Light detection and radar) to observe vertical profiles of aerosols in the heavily polluted air of Asia. Dr Muller and his team made observations up to 15km above the surface of the so called Asian Brown Cloud (ABC) which forms as a result of forest fires, un-regulated industry and windbourne dust from the deserts of central Asia. In this region the atmospheric circulation coupled with nearly constant emissions and long settling time results in wind transport of pollutants across international boundaries impacting on air quality far from source.
  Unlike traditional Lidar that are used in boundary layer research that report backscatter coefficient to identify concentrations of aerosols, the Raman Lidar's data can be used to determine the extinction coefficient of the atmosphere (useful for global climate modellers) and to derive the particle depolarization ratio which can be used to infer the shape of the particle. Using all three properties Dr Muller's team were able to identify qualitatively possible source areas/regions of the observed air pollution at different heights in the atmosphere based on known properties about the size of certain aerosols. A common observation made by the team was a low level layer of local air pollution above which was a layer of 'clean' aerosol free air capped at around 5 km with windborne dust from the deserts of central Asia or industrial emissions from China. However there is a degree of uncertainty when multiple sources of aerosol may be present over the Lidar. An interesting finding was that the optical depth of the atmosphere in East Asia from observations in South Korea and China ranges from 1 to 1.5 which is incredible when compared with the values ~0.2 observed in Europe where much stricter air pollution controls are in force.
   The final section of the seminar focused on using the data to infer even more information about the types of aerosol observed (e.g. Quartz dust from deserts using SiO2 (Silicon dioxide)) by using complex mathematical analysis techniques. This early research (Dr Muller estimated that to improve techniques and reduce uncertainty to the levels required by modellers could take 10-15 years) showed that by using distinct Raman lines (the signature of some aerosol have a distinct wavelength that they scatter at) that they could also determine the elemental composition of the observed aerosol layers.
   In summary (and in response to questions) Dr Muller stated that to improve the algorithms there needed to be advances in numerical analysis and dedicated observation campaigns, to get in-situ data to verify the Raman Lidar observations and numerical solutions used to identify aerosol species, in which remote sensors and sampling teams needed to work in close unison to a set of common goals.

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I am aiming to take away one lesson from each seminar that I attend over the coming years. Today I learnt that I need to embrace uncertainty and accept the limitations of techniques used. This is especially true as I am to learn many new techniques over the coming years and may revisit subjects of old (Mixing Layer Height determined using Ceilometers) in which my thinking was influenced by negativity towards the accuracy and uncertainty of the techniques used.