What can we learn from The American President?

December 12, 2018

The American President

I love the American President. It’s a weakness of mine of which I am not proud. No. Not that one: the film.

The American President was an Oscar-nominated film made in 1995 starring Michael Douglas as the eponymous hero and Annette Bening as a lobbyist who comes to Washington to campaign for a 20% cut in US greenhouse gas emissions.

The film is unremarkable in many ways. But the fact that cutting greenhouse gas emissions was a mainstream idea 25 years ago (albeit in a light-hearted romantic comedy-drama) puts into perspective just how slowly political reality has changed.

Constant

During the period from the fictional 1995 American President to the present 2018 incumbent, one thing has remain constant: the science.

Since 1981, when James Hansen and colleagues wrote a landmark paper in Science, the complexity of our models of the Earth’s climate has increased dramatically.

And our understanding of the way our Climate System works has improved, increasing our confidence in future projections.

But the core science has barely changed. Indeed, it hasn’t changed that much since Svante Arrhenius’ insight back in 1896.

Climate Change: My part in its downfall

I have been speaking and writing about Climate Change since 2004 or so. I think I have spoken to a few thousand people directly, and I guess each web article has been read a few hundred times. So perhaps I have helped a little to ‘raise consciousness’.

But regular readers will have noticed that recently I haven’t written about Climate Change as often as I used to. The reason is that I am lost for words.

Back in 2004, (9 years the American President) I thought there was a genuine public education requirement. But now, I don’t believe any rational human on Earth seriously doubts the reality of Climate Change or its causes.

[But just in case: if there is a rational human out there who doubts the reality of Climate Change, please drop me a line: I am happy to discuss any questions you have.]

Political Science

I still believe that despite The American President (yes that one, not the film) and his supporters, humanity will act collectively and decisively on Climate Change. Eventually.

I expect this because ultimately I think we will collectively understand that the alternative is in nobody’s best interest.

The ‘Natural Sciences’ have identified the existence of Climate Change, worked out its causes, laid out clear paths for how to combat it, and estimated the consequences of inaction.

But the path to action involves what Charles Lane writing the Washington Post has called ‘Political Science’. He identified the impasse as arising from the fact that we are asking the rich world (us) to pay now to solve a problem which will (mainly) occur in the future.

  • If the spending is effective, then the worst aspects of Climate Change will be abated and that expenditure may then appear to be a waste – the disaster was averted!
  • But if it the spending is ineffective, then the worst aspects of Climate Change will be experienced anyway!

This (and many other difficulties) are real and they are readily exploited by people who are acting – frankly – in bad faith.

So I expect we will act, but too late to avoid bad consequences for communities world-wide. And the political path we will take to action is not at all clear to me.

Reasons to be hopeful

But there are plenty of reasons to be hopeful. Renewable energy alternatives to fossil fuels are now feasible in a large and growing number of sectors. And once the transition begins, I think it will move quickly.

The speed with which coal has been (and is is continuing to be) phased out in the UK has shocked and surprised me. You can check current grid generating mix at Gridwatch.

The chart below shows the last 12 months of generation on top and the previous 12 months below that. You can see that coal use has almost disappeared in summer and is now only used on the coldest darkest days.

This year UK Yearly generating mix

UK Yearly generating mix

UK Electricity Generating Mix for the last 12 months. Notice that coal generation – in black – is only significant for a few months of the year, and has declined this year (top) compared with last year (bottom)

Science is our greatest cause for hope.

Imagine if we were observing changes in climate and had no idea what was happening? We would be doomed to confusion and inaction. This has been the situation in which humanity has existed since the dawn of time.

But now, our collective scientific understanding  has allowed us quantify Climate Change, to discover its root cause, and to identify the practical steps we can take minimise the harm.

Humanity has never been in this position before. We have never previously known in advance the hand which nature will deal us.

So I see our inability to act collectively – as exemplified by the slowness of progress in the 23 years since the debut of the celluloid American President – as a temporary state.

I take hope from the fact that we when the political reality permits, science will guide us to the best available solution in the circumstances.

I just wish I could figure out what I can do to make that happen faster.

Links

On this site:

On Variable Variability

On IPCC web site

Refrigerators: Part#1

December 2, 2018

A month ago our refrigerator stopped working. A repair didn’t seem possible, so we headed to the shops to search for something as similar as possible to what we had just lost.

Thankfully, the snappily-named Bosch KGN33NW3AG fridge-freezer has proved to be entirely adequate.

Of course a new refrigerator requires testing (obviously) and an assessment of how close to specification it is performing. So…

How much energy should a fridge use?

Fridge Freezer Pictures

I made a ‘guess-timate’ by estimating the rate at which heat which would flow into the fridge. My thought was that this should be similar to rate at which the fridge would use energy.

[Aside: the actual calculation is tricky, but I’ll come back to it in a later post]

To estimate the heat flow into the fridge I measured the size of fridge and freezer compartments and the thickness of the insulation.

Then I calculated the area of each compartment that faced the room which I assumed to be at a nominal 20 °C.

Heat will constantly flow from the room, through the insulation, into the cold compartments and a simple rule (called Fourier’s Law) allows me to calculate the rate at which energy flows (watts).

I assumed that a perfect ‘heat pump’ – the scientific name for a refrigerator – would pump all this heat back out again, but would (unrealistically) not require any energy to operate.

By multiplying the rate of energy flowing into the refrigerator (in watts) by an amount of time (in seconds) I could work out how much energy (in joules) even a perfect refrigerator of this size must use.

I could then convert the energy used (in joules) into kilowatt-hours – the charging unit used by electricity companies – by dividing by 3.6 million (the product of 3600 seconds in an hour and 1000 watts in a kilowatt).

My calculations indicated that heat flows would be:

  • About 16.4 W into the refrigerator, amounting to around 144 kW-h over a year.
  • About 14.8 W into the freezer, amount to around 130 kW-h over a year.

So if the device were perfect, I calculated it would use 274 kW-h per year.

EU Label

The specification for the fridge says that it will use 290 kW-h per year, just 6% more energy than I estimated a perfect fridge would use. This indicates a fridge performing surprisingly well.

I assume that Bosch’s estimated consumption is realistic. So how wrong could my estimate be?

Well I assumed that the thermal insulation around the fridge had a thermal conductivity of 0.03 W/K/m – just three time greater than that of still air. This is exceptionally good insulation. But my estimate could easily be wrong by 10% or so if improved insulation had been used.

Opening the door.

Many people think that opening the door of the fridge will affect its energy consumption, but my calculations indicate that it is not really a very big problem.

I assumed that at worst, opening the door could replaces all the air in the fridge with room temperature air. If this were the case then:

  • opening the fridge door 10 times a day every day would use an additional 3.7 kW-h of energy per year which is just over 1% of the annual expected usage.
  • opening the freezer door once a day would use an additional 0.4 kW-h of energy per year which is much less than 1% of the annual consumption.

So my calculations indicate that as long as door is not left open for many minutes at time, perhaps by careless children tired of their parents nagging, then it will have relatively little effect on the energy consumption of the fridge.

Data

I logged data at four locations in the fridge/freezer over a day or so last weekend.

The figure below shows a composite view of the data from the top of the fridge and the freezer over a period from 7 p.m. on Saturday to 4:30 p.m. on Sunday.

Composite Data

I’ll analyse this data more in the next article, but here I will just note that the data show:

  • The basic cycle of the heat pump which switches on around once every 45 minutes.
  • The more rapid cycling of the air within the fridge – every 10 minutes or so.
  • The effect of leaving the door open.

It is pretty clear that when my son and his friend arrived home at approximately 5 a.m. on Sunday morning (!) they contrived to leave the door open for the best part of an hour!

Composite Data Close up

I thought this was impressive detective work on my part and it could well be the start of a new mode of behaviour analysis: Forensic Thermometry.

Perhaps I should propose °CSI Teddington. 😉

Anyway. More on the temperature and humidity data in the next article.

Ignorance: Eggs & Weather Forecasts

November 26, 2018

Every so I often I learn something so simple and shocking that I find myself asking:

How can I possibly not have known that already?“.

Eggs

Eggs

Eggs

While listening to Farming Today the other morning, learned that:

Large eggs come from old hens

In order to produce large eggs – the most popular size with consumers – farmers need to allow hens to reach three years old.

So during the first and second years of their lives they will first lay small eggs, then medium eggs, and finally large eggs.

On Farming Today a farmer was explaining that egg production naturally resulted a range of egg sizes, and it was a challenge to find a market for small eggs. Then came the second bomb’shell’.

The yolk is roughly same size in all eggs

What varies between small and large eggs is mainly the amount of egg white (albumen).

How could I have reached the age of 58 and not  known that? Or not have even been curious about it?

Since learning this I have become a fan of small eggs: more yolk, less calories, more taste!

But my deep ignorance extends beyond everyday life and into the professional realm. And even my status as ‘an expert’ cannot help me.

Weather Forecasts & Weather Stations

Professionally I have become interested in weather stations and their role in both Numerical Weather Prediction (NWP, or just weather forecasting) and in Climate Studies.

And as I went about my work I had imagined that data from weather stations were used as inputs to NWP algorithms that forecast the weather.

But in September I attended CIMO TECO-2018 (Technical Conference on Meteorological and Environmental Instruments and Methods of Observation) in Amsterdam.

And there I learned in passing from an actual expert, that I had completely misunderstood their role.

Weather station data is not considered in the best weather forecasts.

And, on a moment’s reflection, it was completely obvious why.

Weather forecasting work like this:

  • First one gathers as much data as possible about the state of the atmosphere ‘now’. The key inputs to this are atmospheric ‘soundings’:
    • Balloon-borne ‘sondes’ fly upwards through the atmosphere sending back data on temperature, humidity and wind (speed and direction) versus height.
    • Satellites using infrared and microwave sensors probe downwards to work out the temperature and humidity at all points in the atmosphere in a swathe below the satellite’s orbit.
  • The NWP algorithms accept this vast amount of data about the state of the atmosphere, and then use basic physics to predict how the state of the entire atmosphere will evolve over the coming hours and days

And then, after working out the state of the entire atmosphere, the expected weather at ground level is extracted.

Visualisation of the amount of moisture distributed across different heights in the atmosphere based on a single pass of a 'microwave sounding' satellite. Image credit: NASA/JPL-Caltech

Visualisation of the amount of moisture distributed across different heights in the atmosphere based on a single pass of a ‘microwave sounding’ satellite. The data gathered at ground level is just a tiny fraction of the data input to NWP models. Image credit: NASA/JPL-Caltech

Ground-based weather stations are still important:

  • They are used to check the outputs of the NWP algorithms.
  • But they are not used as inputs to the NWP algorithms.

So why did I not realise this ‘obvious’ fact earlier? I think it was because amongst the meteorologists and climate scientists with whom I spoke, it was so obvious as to not require any explanation.

Life goes on

So I have reached the age of 58 without knowing about hen’s eggs and the role of weather stations in weather forecasting?

I don’t know how it happened. But it did. And I suspect that many people have similar areas of ignorance, even regarding aspects of life with which we are totally familiar – such as eggs – or where one is nominally an expert.

And so life goes on. Anyway…

This pleasing Met Office video shows the importance of understanding the three-dimensional state of the atmosphere…

And here is a video of some hens

 

Mug Cooling: Salty fingers

November 23, 2018

You wait years for an article about heat transfer at beverage-air interfaces and then four come along at once!

When I began writing these articles (1, 2, 3) I was just curious about the effect of insulation and lids.

But as I wrote more I had two further insights.

  • Firstly the complexity of the processes at the interface was mind-boggling!
  • Secondly, I realised that cooling beverages are just one example of the general problem of energy and material transfer at interfaces.

This is one of the most important processes that occurs on Earth. For example, it is how the top layer of the oceans – where most of the energy arriving on Earth from the Sun is absorbed – exchanges energy with the deeper ocean and the atmosphere.

But in the oceans there is another factor: salinity.

Salinity 

Sea water typically contains 35 grams of salt per litre of water, and is about 2.4% denser than pure water.

So pure water – such as rain water falling onto the ocean surface – will tend to float above the brine.

This effect is exacerbated if the pure water is warm. For example, water at 60 °C is approximately 1.5% less dense than water at around 20 °C.

Video 

In the video at the top of the article I added warm pure water (with added red food colouring) to a glass of cold pure water (on the left) and a glass of cold salty water (on the right).

[For the purposes of this article I hope you will allow that glasses are a type of mug]

The degree to which the pure and salty water spontaneously separated surprised me.

But more fascinating was the mechanism of eventual mixing – a variant on ‘salt fingering‘.

Salt Fingers Picture

The formation of ‘salty fingers’ of liquid is ubiquitous in the oceans and arises from density changes caused by salt diffusion and heat transfer.

As the time-lapse section of the movie shows – eventually the structure is lost and we just see ‘mixed fluid’ – but the initial stages, filmed in real time, are eerily beautiful.

Now I can’t quite explain what is happening in this movie – so I am not going to try.

But the web has articles, home-made videos and fancy computer simulations.

 

Mug Cooling: Visualising complexity with peanut butter

November 20, 2018

I hope you’ve enjoyed the last couple of articles (1, 2)  about mug cooling. I have enjoyed writing them, but I am having trouble stopping.

My problem in trying to finish this investigation is the sheer complexity of the physics involved in the cooling of beverages.

Complexity? Yes, mind-boggling complexity. In the liquid, the air, and the profoundly mysterious ‘boundary layer’ between them.

First there is the liquid.

When one looks at a cup of tea or coffee, its opacity hides the complexity of the flow patterns in the liquid.

But with different fluids, such as the mixture of Marmite™, Peanut Butter, and hot water shown in the movie at the top, the turgid flows become visible.

[ASIDE: Some might ask: “Michael, what made you think of mixing Marmite™, Peanut Butter, and hot water?”.  Sadly, the answer is confidential, but I urge readers: please: do try this at home, but please don’t blame me!]

These flows are driven by the convective instability of the liquid.

  • The hot liquid near the surface cools as its fast-moving molecules either evaporate or lose energy by colliding with the slower-moving air molecules.
  • As the liquid cools, its density increases until it begins to sink beneath the liquid layer below.
  • This lower layer is now lifted to the surface, cools, and then sinks in turn.
  • And so a circulating flow pattern can be established and sustained by a liquid cooling at a surface.

In the case of the  Marmite™  and Peanut Butter concoction in the movie above, matters are further complicated by oil from the peanut butter which appears to have formed a stable surface layer below which the convective flow takes place.

This roiling turmoil can also be measured quantitatively.

I repeated the cooling measurements from the previous articles, but this time I placed all four thermocouples close to the surface.

Thermocouples near the surface

Four thermocouples measuring the temperature close to the surface of hot water in an insulated mug.

Looking in detail at the data from just two of the thermocouples one can see apparently random heating and cooling events.

These temperature fluctuations are caused by rising and falling convecting liquid .

Slide 11

Then there is the air.

Analogous processes also occur in the air above the liquid. 

These are harder to visualise, but I have created a simulation of the process in the amazing (and free!) Energy2D application – more details at the end of this article.

Large Gif
Animated GIF made from selected frames of an Energy2D simulation of the  air cooling of a liquid in insulated mugs with a lid (left) and without (right).

In the simulationthe flow patterns in the air quickly develop a breathtaking fractal complexity that is completely familiar.

The simulation is not entirely realistic. It is only in two-dimensions, does not include the effects of evaporation, does not include convection in the ‘liquid’ (so it is more like a solid), and yet some how, when the data is exported, it looks qualitatively similar to that which I observed experimentally in a real 3-D mug!

Slide 10

Graph of data exported from the Energy 2D simulation showing the cooling of an insulated beverage cup with and without a lid.

 

Underlying the ‘simple’ beverage cooling curves are processes in both the liquid and the air which are at the limit of what can be realistically modelled.

And as we approach the interface between the liquid and the air and look in ever more detail, matters only get more complex.

At this apparently ‘static’ interface there are multiple dynamic processes:

  • The liquid is evaporating, cooling and convecting away from the surface.
  • Air molecules and liquid molecules are interacting strongly.
    • The air is dissolving in the liquid
    • The liquid is evaporating and re-condensing both as droplets in the air (steam) and back into the liquid.
  • The air is warming and convecting away from the surface.

And yet all we just notice is that our coffee is getting cold!

Energy 2D

Energy2D is a wonderful FREE application that carries out complex two-dimensional calculations based on real physics.

I have found it difficult to get exact numerical matches between simulations and real world situations, but the physics which the software simulates is deeply insightful.

I strongly recommend that you waste several hours playing with its example demonstrations.

 

Mug Cooling: The Lid Effect

November 12, 2018
IMG_7906

Droplets collect near the rim of a mug filled with hot water.

During my mug cooling experiment last week, I was surprised to find that taking the lid off a vacuum insulated mug increased its initial cooling rate by a factor 7.5.

Removing the lid allowed air from the room to flow across the surface of the water, cooling it in two ways.

  • Firstly, the air would warm up when it contacted the hot water, and then carry heat away in a convective flow.
  • Secondly, some hot water would evaporate into the moving air and carry away so – called ‘latent heat’.

I wondered which of these two effects was more important?

I decided to work out the answer by calculating how much evaporation would be required to explain ALL the cooling. I could then check my calculation against the measured mass of water that was lost to evaporation.

Where to start?

I started with the cooling curve from the previous blog.

Slide5

Graph#1: Temperature (°C) versus time (minutes) for water cooling in an insulated mug with and without a lid. Without a lid, the water cools more than 7 times faster.

Because I knew the mass of water (g) and its heat capacity (joule per gram per °C), I could calculate the rate of heat loss in watts required to cool the water at the observed rate.

In Graph#2 below I have plotted this versus the difference in temperature between the water and the room temperature, which was around 20 °C.

Slide6

Graph#2: The rate of heat flow (in watts) calculated from the cooling curve versus the temperature difference (°C) from the ambient environment. The raw estimates are very noisy so the dotted lines are ‘best fit lines’ which approximately capture the trend of the data.

I was struck by two things: 

  • Firstly, without the lid, the rate of heat loss was initially 40 watts – which seemed very high.
  • Secondly:
    • When the lid was on, the rate of heat loss was almost a perfect straight line This is broadly what one expects in a wide range of heat flow problems – the rate of heat flow is proportional to the temperature difference. But…
    • When the lid was off, the heat flow varied non-linearly with temperature difference.

To find out the effect of the lid, I subtracted the two curves from each other to get the difference in heat flow versus the temperature of the water above ambient (Graph#3).

[Technical Note: Because the data in Graph#2 is very noisy and irregularly spaced, I used Excel™ to work out a ‘trend line’ that describes the underlying ‘trend’ of the data. I then subtracted the two trend lines from each other.]

Slide7

Graph#3: The dotted line shows the difference in power (watts) between the two curves in the previous graph. This should be a fair estimate for the heat loss across the liquid surface.

This curve now told me the extra rate of cooling caused by removing the lid.

If this was ALL due to evaporative cooling, then I could work out the expected loss of mass by dividing by the latent heat of vaporisation of water (approximately 2260 joules per gram) (Graph#4).

Slide8c

Graph#4. The calculated rate of evaporation (in milligrams per second) that would be required to explain the increased cooling rate caused by removing the lid.

Graph#4 told me the rate at which water would need to evaporate to explain ALL the cooling caused by removing the lid.

Combining that result with the data in Graph#1, I worked out the cumulative amount of water that would need to evaporate to explain ALL the observed extra cooling (Graph#5)

Slide9

Graph#5: The red dashed line shows the cumulative mass loss (g) required to explain all the extra cooling caused by removing the lid. The green dashed lines show the amount of water that actually evaporated in each of the two ‘lid off’ experiments. The green data shows additional measurements of mass loss versus time from a third experiment.

In Lid-Off Experiments#1 and #2, I had weighed the water before and after the cooling experiment and so I knew that in each experiment with the lid off I had lost respectively 25 g and 31 g of water –  just under 10% of the water.

But Graph #5 really needed some data on the rate of mass loss, so I did an additional experiment where I didn’t measure the temperature, but instead just weighed the mug every few minutes. This is the data plotted on Graph#5 as discrete points.

Conclusions#1

In Graph#5, it’s clear that the measured rate of evaporation can’t explain all the increased cooling rate loss, but it can explain ‘about a third of it‘.

So evaporation is responsible for about a third of the extra cooling, with two thirds being driven by heat transfer to the flowing air above the cup.

It is also interesting that even though the cooling curves in Graph#1 are very similar, the amount of evaporation in Graph#5 is quite variable.

The video below is backlit to show the ‘steam’ rising above the mug, and it is clear that the particular patterns of air flow are very variable.

The actual amount of evaporation depends on the rate of air flow across the water surface, and that is driven both by

  1. natural convection – driven by the hot low-density air rising, but also by…
  2. forced convection – draughts flowing above the cup.

I don’t know, but I suspect it is this variability in air flow that caused the variability in the amount of evaporation.

Conclusions#2

I have wasted spent a several hours on these calculations. And I don’t really know why.

Partly, I was just curious about the answer.

Partly, I wanted to share my view that it is simply amazing how much subtle physics is taking place around us all the time.

And partly, I am still trying to catch my breath after deciding to go ‘part-time’ from next year. Writing blog articles such as this is part of just keeping on keeping on until something about the future becomes clearer.

P.S. Expensive Mugs

Finally, on the off-chance that (a) anybody is still reading and (b) they actually care passionately about the temperature of their beverages, and (c) they are prepared to spend £80 on a mug, then the Ember temperature-controlled Ceramic mug may be just thing for you. Enjoy 🙂

 

Mug Cooling: Initial Results

November 7, 2018

One of life’s greatest pleasures is a nice cup of tea or coffee.

  • But what temperature makes the drink ‘nice’?
  • And how long after making the beverage should we wait to drink it?
  • And what type of mug is optimal?

To answer these questions I devised a research proposal involving temperature measurements made inside mugs during the cooling process.

I am pleased to tell you that my proposal was fully-funded in its initial stage by the HBRC*, having scored highly on its societal impact.

Experimental Method

The basic experiment consisted of pouring approximately 300 ml of water (pre-stabilised at 90 °C) into a mug sitting on a weighing scale. The weighing allowed low uncertainty assessment of the amount of water added.

The temperature of the water was measured every 10 seconds using four thermocouples held in place by a wooden splint. The readings were generally very similar and so in the graphs below I have just plotted the average of the four readings.

Experiments were conducted for a fancy vacuum-insulated mug (with and without its lid) and a conventional thick-walled ceramic mug. The results for the vacuum-insulated mug without its lid were so surprising that I repeated them.

This slideshow requires JavaScript.

Results

The average temperature of the water in the mugs is shown in the two graphs below.

The first graph shows all the data – more than 8 hours for the vacuum insulated mug – , and the second graph shows the initial behaviour.

Also shown are horizontal lines at various temperatures that I determined (in a separate series of experiments) to be the optimal drinking range.

Slide1

The average temperature of the water in the mugs versus time.

Slide2

The first 120 minutes of the cooling curves. The water was poured in at 4 minutes.

Discussion

The most striking feature of the cooling curves is the massive difference between the results for the vacuum insulated mug with, and without, its lid.

As I mentioned at the start, the result was so striking that I repeated the measurements (marked as #1 and #2) on the graphs.

The table below shows how many minutes it took for the water to cool to the three states highlighted on the graphs above:

  • Too hot to drink, but just sippable
  • Mmmm. A nice hot cuppa.
  • I’ll finish this quickly otherwise it’ll be too cold.

Minutes to reach status

  Vacuum-Insulated Mug

Ceramic Mug

 No Lid

 With Lid

Just Sippable

2

10

66

Upper Drinkable Limit 12 24

151

Lower Drinkable Limit

28

53

296

Conclusion

The insulating prowess of the vacuum insulated mug (with lid) is outstanding.

But the purpose of a mug is not simply to prevent cooling. It is to enable drinking! 

So to me this data raises a profound question about the raison d’être for vacuum insulated mugs.

  • Who  makes a cup of coffee and then thinks “Mmm, that’ll be just right to drink in two and a half hours time!”

Admittedly,  the coffee will then stay in the drinkable range for an impressive two hours. But still.

In contrast, the ceramic mug cools the hot liquid initially and allows it to reach the optimal drinking temperature after just a few minutes.

Further work

The review committee rated this research very highly and suggested two further research proposals.

  • The first concerned the explanation for the very large effect of removing the lid from the vacuum insulated mug. That research has already been carried out and will be the result of a further report in this journal.
  • The second concerned the effect of milk addition which could significantly affect the time to reach the optimal drinking temperature. That research proposal is currently being considered by HBRC.

==============================

*HBRC = Hot Beverage Research Council

Where have I been all this time?

October 26, 2018

It’s been almost two months since I last wrote an article for this blog. In the 10 years since I began writing here, that is the longest gap ever.

What’s up?

Broadly speaking, I have been very busy and very unhappy at work.

My unhappiness at work is nothing new. Regular readers may remember my article on ‘Coping by Counting‘ back in February 2017 where I extolled the virtue of counting down the time to retirement month-by-month.

Colleagues will know that I have been able to immediately tell them how many months, weeks  and days (and occasionally hours!) until my planned retirement date.

This technique really helped me through the last 20 months, but recently it became apparent that I would not last another 86 months and two weeks.

The only possibility seemed to be to resign, and a couple of weeks ago that is what I decided to do. But after talking with friends, family and colleagues, I was ‘talked down’ from this precipitous step and urged to look for alternatives.

So I have been negotiating to work part-time, and happily this seems to be achievable. This is due in no small part to my exceptionally kind line manager. So from January 2019 I will begin working three days a week. Hopefully this will be sustainable.

Perspective & Reflections

At the moment, this step feels like a humiliating defeat. Being unable to cope in a 21st Century working environment feels like a very personal failure. But I hope these feelings will fade.

Firstly, when I have told colleagues of my decision, they have reacted with a mixture of empathy and envy. They too are feeling the strain. So I have sense that it is not ‘just me’.

Secondly, looking at my career more broadly, in my 18 years at NPL I have managed to achieve a thing or two.

  • I was part of the team that made the second most accurate measurement of the Boltzmann constant ever.
  • I was part of the team that made the most accurate temperature measurements ever.
  • I have affected the lives of many people with my outreach work.
  • In 2009 I met the Queen and she gave me a medal!

And importantly I have managed to earn money, stay married, and bring up two children.

So from this wider perspective, reducing the amount of work I do and focusing more on writing and general pottering seems reasonable and not really a sign of defeat and failure.

So…

Over the next few months I will hand over (or drop) the responsibilities that  fitted into the previously normal 6/7 working days, and find a package of work projects that I can achieve in 3.00 working days.

  • Did you notice the decimal point?

This will require a change in perspective on my part. I will need to let  go of some projects which I have been holding onto in the hope that I would be able to find some time to move them forwards. This won’t be easy.

But on the other hand, the prospect of several days a week on which I have no agenda items whatsoever already feels exhilarating.

 

 

 

Hydraulic jumps in the kitchen

September 1, 2018

It has been a difficult summer for me.

Putting on the Royal Society Summer Science Exhibition was utterly exhausting, and even two months on, I have not been able to catch up on all the extra days and hours I worked. And I fell behind on every other project on which I am working.

So every day as I enter work I have to catch my breath, staunch my sense of panic, and force myself to stay calm as I begin another day of struggling through tiredness to avoid failure on all the projects on which I am way behind.

But earlier this week my colleague caught me staring at the water flowing down the sink in the kitchenette where we prepare tea.

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I was staring at a phenomenon I have been fascinated by since childhood – the way water falling from the tap onto the bottom of the kitchen sink forms a smooth flat circle for a few centimetres around where the water lands – and then forms a ‘wavy wall’ around this circle.

My colleague said to me: “It’s great isn’t it. It’s called a hydraulic jump“. Learning that this phenomenon had a name lifted my spirits enormously and made me more curious about what was going on.

So today (Saturday) I have wantonly avoided catching up with my weekly tide of failure, stupidly neglected to pack for my week long conference in Belfast starting tomorrow, and spent the afternoon playing at the kitchen sink. I have experienced transitory happiness.

Hydraulic jump

Naming a phenomenon is stage#1 of the process of understanding it. Knowing this name allowed me to read a number of  – frankly confusing – articles on the web.

But after reading and playing for a while I think I am now beginning to understand what makes the circle form. There are two parts to my understanding:

The first insight arises from comparing:

  • the flow speed of the water with,
  • the speed at which waves travel on the surface of the water.

Inside the circle, the flow is faster than the speed at which waves can travel in the water.  So surface disturbances are swept outwards – the waves are not fast enough to travel ‘upstream’, back towards the centre.

As one moves further away from the centre, the flow speed falls and at the edge of the circle, the flow speed is just equal to the speed of water waves. So water waves travelling back towards the centre of the circle appear stationary – this what makes the circle appear to be ‘fixed’ even though it is a dynamically created structure.

Outside the circle, the flow slows sufficiently that water waves can travel upstream (towards the middle) but they can never travel into ‘the circle’. (There is actually a scientific paper in which this circle is used as an analogy to the ‘Event Horizon’ in a putative ‘White hole’!)

Hydraulic Jump Illustration

The second insight, arises from considering turbulence.

Once waves can travel in both directions in the water, turbulence builds up which slows the speed of the flowing water dramatically.

So in the steady state, the depth of the water builds up suddenly and the ratio of the depth of water inside the circle to the depth outside the circle is simply the ratio of the speeds of water flow just outside and just inside the circle.

So if the speed of flow is 10 times slower outside the circle, then the water will be be 10 times deeper outside the circle.

In the picture above and the video below, you can see the very strikingly different nature of the liquid surfaces. Shallow and perfectly smooth within the circle, and deeper and turbulent outside the circle.

Experiments

I began playing by finding a better surface than the bottom of a sink. I used an upside down baking tray and adjusted it to be as level as I could manage.

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Not knowing what to do, I began by measuring the diameter of the circle formed for different flow rates:

  • I measured the diameter roughly with a ruler
  • I measured the flow rate by timing how long it took to fill a measuring jug which I weighed before and after filling.

This produced a pleasing graph, but no real insight. An increased flow rate meant made the circle larger because it took more time (and distance) for the flowing water to slow down to the speed of water waves.

Graph

Looking at the algebra, I realised I really needed to know the speed of the water and depth of the water. But how could I measure these things?

I tried estimating the speed of the water by injecting food colouring into the flow and making a movie using the slow-motion mode of my iPhone camera.

Knowing the circle was about 8.8 cm in diameter, this allowed me to estimate the speed of flow as roughly 1.5 ± 0.5 metres per second in the centre zone. However I couldn’t think how to estimate the thickness (height) of the flowing layer.

By sticking a needle in I could see that it was much less than 1 mm and appeared to be less than a tenth of the thickness of the water outside the circle. But I couldn’t make any meaningful measurements.

Then I realised that I could I estimate the speed of the water in a different way. If I placed a needle in the moving water, it produced an angular ‘shock wave’.

This is similar to way an aeroplane travelling faster than the speed of sound in air produces a ‘sonic boom’.

  • For an aeroplane, the angle of the shock wave with respect to the direction of motion is related to the ratio of the speed of the plane to the speed of the sound.
  • For our flowing water, the angle of the shock wave with respect to the direction of motion is related to the ratio of the speed of the water to the speed of the water waves.

Unfortunately the angle changes very rapidly as the ratio of flow speed to wave speed approaches unity and I found this phenomenon difficult to capture photographically.

Graph 2

But as the photographs below show, I could convince myself qualitatively that the angle was opening out as I placed the obstacle nearer the edge of the circle.

Hydraulic Jump Pictures

Observations of the shock wave formed when an obstruction is placed in the water flow. The top row of photographs shows the effect of moving the obstruction from near the centre to near the edge of the circle. The bottom row of photographs are the same as the top row but I have added dotted lines to show how the shock angle opens up nearer the edge of the circle.

Summary

  • My work remains undone.
  • I still have to pack in order to leave for the conference at 8:30 a.m. on Sunday morning: less than 8 hours away as I finish this. (Perhaps I will have a chance to complete some tasks at the airport or on Sunday evening?)
  • I have understood a little something about one more little thing in this beautiful world, and that has lifted my spirits. For now at least.

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Hot dry summers

August 10, 2018

Apparently its been hot all around the northern hemisphere this summer.

And that got me thinking about the long hot summer of 1976 when I was 16.

I have the general impression that summers now are warmer than they used to be. But I am aware that such impressions can be misleading.

Being the age I am (58), I fear my own mis-remembering of times past.

So was 1976 really exceptional? And will this year (2018) also prove to be really exceptional?

I decided to download some data and take a look.

Heathrow Data.

I popped over to the Met Office’s Climate pages and downloaded the historical data from the nearby Heathrow weather station.

I had downloaded this data before when looking at long-term climate trends, but this time I was looking for individual hot months rather than annual or decadal trends.

When I plotted the monthly average of the daily maximum temperature, I was surprised that 1976 didn’t stand out at all as an exceptional year.

Heathrow Monthly Climate Data July Maxima Analysis

The monthly average of the daily temperature maxima are plotted as black dots connected by grey lines. I have highlighted the data from July each year using red squares. Notice that since 1976 there have been many comparable July months.

In the graph above I have highlighted July average maximum temperatures. I tried similar analyses for June and August and the results were similar. 1976 stood out as a hot year, but not exceptionally so.

Ask an Expert

Puzzled, I turned to an expert. I sent an e-mail to John Kennedy at the UK’s Met Office  and to my astonishment he responded within a few hours.

His suggestion was to try plotting seasonal data.

His insight was based on the fact that it is not so unusual to have a single warm month. But it is unusual to have three warm months in a row.

So I re-plotted the data and this time I highlighted the average of daily maximum temperatures for June, July and August.

Heathrow Monthly Climate Data June July August Maxima Analysis

The monthly average of the daily temperature maxima are plotted as black dots connected by grey lines as in the previous figure. Here I have highlighted the seasonal average data (from June July and August) using red squares. Notice that 1976 now stands out as an exceptionally warm summer.

Delightfully, 1976 pops out as being an exceptional summer – in line with my adolescent recollection.

More than just being hot

But John suggested more. He suggested looking at the seasonal average of the minimum daily temperature.

Recall that in hot weather it is often the overnight warmth which is particularly oppressive.

In this graph (below) 1976 does not stand out as exceptional, but it is noticeable that warming trend is easily visible to the naked eye. On average summer, summer nights are about 2 °C warmer now than they were at the start of my lifetime.

Heathrow Monthly Climate Data JJA Minimum Analysis

The monthly average of the daily temperature minima are plotted as black dots connected by grey lines. Here I have highlighted the seasonal average data (from June July and August) using red squares. Notice that 1976 does not stand out exceptionally.

John also suggested that I look at other available data such as the averages of

  • daily hours of sunshine
  • daily rainfall

Once again seasonal averages of these quantities show 1976 to have been an exceptional year. Below I have plotted the Rainfall totals on two graphs, one showing the overall rainfall, and the other detail of the low rainfall summers.

Heathrow Monthly Monthly Rainfall

The monthly average of the daily rainfall total are plotted as black dots connected by grey lines. Here I have highlighted the seasonal average data (from June July and August) using red squares. Notice that 1976 was a dry summer. The data below 50 mm of rainfall are re-plotted in the next graph.

Heathrow Monthly Monthly Rainfall detail

Detail from the previous figure showing the low rainfall data. The monthly average of the daily rainfall total are plotted as black dots connected by grey lines. Here I have highlighted the seasonal average data (from June July and August) using red squares. Notice that 1976 was a dry summer.

de Podesta ‘Hot Summer’ Index

Following on from John’s suggestion, I devised the ‘de Podesta Long Hot Summer Index‘. I defined this to be:

  • the sum of the seasonal averages of the minimum and maximum temperatures (for June July and August),
  • divided by the seasonal average of rainfall (for June July and August).

Plotting this I was surprised to see 1976 pop out of the data as a truly exceptional hot dry summer – my memory had not deceived me.

But I also noticed 1995 ‘popped out’ too and I had no recollection of that being an exceptional summer. However this data (and Wikipedia) confirms that it was.

Now I just have to wait until the end of August to see if this year was exceptional too – it most surely felt exceptional, but we need to look at the data to see if our perceptions are genuinely grounded in reality.

Heathrow Hot Dry Summer Index

The de Podesta Hot Dry Summer (HDS) index as described in the text.  Construct an ‘index’ in this way really flags up the exceptional nature of 1976, and also 1995.

John Kennedy’s blog

In typical self-deprecating manner, John calls himself a ‘diagram monkey’ and blogs under that pseudonym. 

His is one of just two blogs to which I subscribe and I recommend it to you highly.


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