A perfect summer’s day…

Figure 1

I realise it’s not the same thing as UV, but the hourly solar radiation figures in the SYNOP reports do give you a very good idea of the sun’s strength at the moment, which is extremely strong across most areas. I know that down here in Devon, I’m starting to burn in less than 5 minutes sat out in it. It’s a funny thing, you wait patiently for the first hot sunny summers day to arrive, but then when it does, you have to hide from the sun.

Figure 2

The fair weather cumulus across East Anglia, has pegged solar radiation values down there a touch (fig 2), but in many other places it’s well in excess of 3000 kJ/m² (fig 1) this lunchtime.

Figure 3

The usual culprits are at the top of warmest places from the SYNOPs, but Exeter is doing quite well with 25.9°C at 13 UTC. It’s almost 4 degrees warmer than that here, about 8 km to the north of the airport, but my Vantage Pro is far too well sheltered, and at the moment is covered in splashes of Ambre Solaire.

Recent sunshine – a comparison

Figure 1

Figure 2

A little unfair of me perhaps, but this is a comparison of the last weeks sunshine from Kinloss on the Moray Firth in the north (fig 1), and Exeter in deepest darkest Devon in the south (fig 2). I’ll let the graphics do the talking. I’m sure that the balance will be redressed as the summer goes as they usually do. The GFS forecast still looks good, but thundery showers might be a problem for some areas next week.

A simple summer index: 1929 – 2016

One of the very first articles that I read in the Weather Magazine as a young outstation assistant was entitled “A simple summer index with an illustration for summer 1971” by R. Murray which was published in April 1972. Now over forty years later as a retired programmer with the Met Office, I have decided to revisit the summer index and update his record.

I have a number of advantages that Murray could only dream of, and they are a powerful personal computer, up to date freely accessible climate data, and of course the Internet to access that data from. The Met Office provide the data in the form of monthly regional and national gridded climate data back to 1910. This provides you with all the temperature, rainfall and sunshine that you require to calculate a summer index, and the advantage of this data is that you can generate a summer index not only for the UK, but for England, Wales, Scotland, Northern Ireland as well as any of the other twelve other regional areas.

All that was required to access the latest climate data from the Met Office website was internet access. The program converted the text files I downloaded into a data structure to hold each month’s mean temperature, total rainfall and sunshine values necessary to compute each year’s summer index. The slightly tricky bit was to calculate the quintiles of each month’s mean maximum temperature, and the terciles of the total sunshine and rainfall that the formula requires.

The summer index [SI]

SI = 3T + 5S – 5R – 9m

where:-

  • m = number of months
  • T = sum over m months of quintiles of monthly mean temperature
  • S = sum over m months of terciles of monthly sunshine
  • R = sum over m months of terciles of monthly rainfall

Quintiles and terciles are statistical terms used with any series of data arranged in order of magnitude. Rainfall is conventionally divided into three equal classes; the driest third being tercile 1, and the wettest tercile 3. With temperature the data is divided into five equal classes; quintile 1 refers to the coldest and quintile 5 to the warmest. There is a drawback in using the climate data series from the Met Office, although the temperature and rainfall series extend back to 1910, the sunshine series is only available from 1929, so I was unable to reach back quite to 1881 as Murray did originally. Using Murray’s formula the absolute best ‘meteorological’ summer can score a maximum SI of 48, and the absolute worst a SI of -48.

A simple summer index

The summer index was first proposed by Davis in 1968, its beauty lies in its simplicity, but a good summer can be ruined by a wet last week in Autumn, so the index is far from perfect. You could dream up a summer index that looked more closely at daily values of temperature, rainfall and sunshine, but at the moment the Met Office do not make daily regional climate data available, so for now monthly data will have to suffice.

How do you define what constitutes a ‘good’ summer? It is very subjective, and as we grow older, it may have less to do with weather, and more to do with other things that are going on in our lives. Keeping it strictly meteorological, and if you’re older than 70, you probably look back at the summer of 1959 as being the best, older than 50 and it’s highly likely that 1976 will be your perfect summer, younger still and it may well be the summer of 1995 or 2003. The worst summer in contrast is not so easy to quantify, and many people if asked will struggle to name the worst summer that they have experienced in their lifetime.

The ‘best’ summers

As you can see from the table of best summers (fig 1), 1976 tops the Summer index back to 1929 for the UK which probably comes as no great to surprise to many. In fact its score is the perfect maximum of 48.

Figure 1

The extended summer index

The beauty of the algorithm is that you can also calculate an extended Summer index (May through to September), which gives an entirely different slant on what was the best summer. The table below (fig 2) shows that 1959 has the highest extended summer index of 62 (out of a possible 80), and that 1976 is only eleventh in the rankings, with an index of 28. So why was the extended summer of 1976 so much worse? If you compare the various quintiles and terciles for 1976 and 1959, you will see that 1976 was in fact duller and wetter than 1959 in May and September so the extended index score was reduced.

Figure 2

Because the data is also split into regional as well as national values, it’s easy to compare what kind of summer other parts of the UK experienced. As you can see in the breakdown of the extended summer of 1959 (fig 3), the northeast of England and the Midlands score a very high 72, whilst somewhat lower down the rankings came the north and west of Scotland.

Figure 3

The ‘worst’ summer

The summer of 1954 has the lowest summer index -48 of all summers in the UK since 1929 (fig 4), you just can’t get a summer index lower than -48. 1954 was the very antithesis of 1976, it was not only wet, it was cold and dull. Even if you compare 1954 using the extended summer index, it’s still has the lowest index of -64 for the UK. Just to show you how poor that summer was, here are the headlines for each month of the extended summer of 1954 that I’ve copied from the Monthly Weather Report.

  • May 1954 mainly dull and wet, with frequent thunderstorms; large variations of temperature.
  • June 1954 mainly dull and cool; periods of rain, heavy at times.
  • July 1954 notably cool and dull; wet in some areas.
  • August 1954 cool and dull, mainly wet in England, Wales and southern Scotland.
  • September 1954 cool and unsettled; wet in most areas; sunny on the whole.

Figure 4

What about summer 2016?

To a lot of people, especially those in the south and east, summer 2016 was very good, and the eagle-eyed amongst you will have noticed that it ranked joint 19th in the table of meteorological summers, and joint 11th in the table of extended summers, just behind 1976 and on a par with 1947. But how did the extended summer of 2016 look nationally and regionally? According to the extended summer index East Anglia fared best in 2016 with a summer index of 42 (fig 5), closely followed by southern England and the Midlands.

Figure 5

Graphical view

Finally, here is a graphical way of looking at the summer’s since 1929 as a whole by means of two scatter graphs. The first graph plots temperature against rainfall (fig 6), whilst the second graph plots temperature against sunshine (fig 7). They show at a glance just how each summer compares with each other, for instance although 1995 was very slightly drier than 1976, it was slightly less sunny and not as warm.

Figure 6

Figure 7

 

Are summers getting any better?

The one remaining question is – are summers getting better? Well with the help of another chart (fig 8) I’ve plotted the summer index and overlaid it with a five-year centred moving average (dashed line with a yellow outline). I’ve also added a simple linear trend (dashed black line), although climatologically this may be frowned upon (because any trend certainly wouldn’t be linear), it does help to highlight the increase in summer index that there has been since 1929. So the short answer to that question is yes, the summer index has increased over the last 87 years, whether that equates to better summers, I will leave that for you to decide.

Figure 8

References

Davis, N. E.1968. An optimum summer index. Weather 23: 305-317.

Murray, R.1972.A simple summer index with an illustration for summer 1971.Weather 45:161-169.

Footnote

Many of my regular readers may remember that I wrote an article about the ‘Summer Index’ last July. I fully intended to get a fuller version of it published in the Weather Magazine of the Royal Met Society. I lost heart in the end, I don’t think I write in the way that they like, and I’m not good at writing in any other way. I went to a bit of trouble in putting the article together, so instead of it just languishing in a folder named ‘Weather Magazine’ in my Google drive account, I thought that I’d publish it in my blog just for posterity. The other thing that I like about a blog is that you can always fix typo’s or mistakes which you can’t do in a printed magazine, hopefully there are not too many of those.

Today’s alternative list of warmest places

The warmest place may have been Heathrow with a high of 24.3°C (anomaly +3.0°C) today, but in the alternative ‘anomaly’ top ten they only finished in joint 10th place, and it was Ballypatrick in County Antrim, that topped the list with an anomaly of +5.7°C anomaly (fig 1).

Figure 1

Spare a thought for those in the west and north…

Quite a temperature contrast going on in the last week between places in the south and east, and places further north and west, here’s a chart of the mean maximum temperature for the last 7 days across WMO block 03 (fig 1). Mean temperatures range from just over 15°C on the coastal fringes of western Ireland, and western and northern Scotland, to as high as 23.8°C in the heat island of London and Heathrow airport. I should imagine that the gap may widen even more in the coming week.

Figure 1

 

We’re all going on a summer holiday…

The next eight days, particularly in the southwest of England look set fair, summer has finally arrived and with 1000-500 hPa thicknesses never falling below 564 dm temperatures will be in the very warm category if not hot. Of course you have to faith in the latest NWP guidance from the GFS model, but let’s throw caution to the wind and believe it will happen. It’s not all plain sailing, there will be some thundery showers scattered across some other parts of the country, and someone has forgotten to invite the north or west of Scotland to the party.

Wind power can provide energy on coldest days

Some interesting news from the Met Office about a study (The relationship between wind power, electricity demand and winter weather patterns in Great Britain) that found rather surprisingly, that even on the very coldest days wind energy supply started to recover (fig 1). That does sound fairly obvious when you think about it, a very cold spell of weather does usually end on an anticyclonic note, before the high collapses, winds pick up ahead of the next approaching frontal system or low pressure, wind power would also increase. As usual, I’m writing about a study that I haven’t read yet, but I promise I will now that I’ve printed it out! The article for once, is free to download from the IOP Science website, which looks like it contains a lot of other very interesting articles about climate and weather, and one which I’ve bookmarked.

I wonder just how much energy wind turbines would have provided on the 12th of December 1981 (fig 2)? Back then of course, there were no wind turbines (or mobile phone masts come to that) strewn across the country.

Figure 2

Why do we never hear very much about energy generated from the tides around our Islands? I can guarantee that the tide will never let you down, even in the very coldest or hottest of weathers. I’m sure that if IKB was around today, he would have loved to have a crack at engineering a solution for the Severn Barrage, and I’m sure there would be Great Western trains running along the top of it!

The named storms of 2016-17

I know that there were only five named storms in the 2016-17 season, and one of them was aka as the ‘Irish Storm’, so which one is the odd man out?

Angus 20 November 2016
Barbara 23 – 24 December 2016
Conor 25 – 26 December 2016
Doris 23 February 2017
Ewan 26 February 2017 (Ireland)

Déjà vu

Another couple of large CB’s forming over the same part of central southern France as they did yesterday afternoon (fig 2). I looked for any impacts from yesterday’s thunderstorm and eventually found an article about it on The Watcher’s website. The article describes the storm as intense, and caused severe flash floods, with at least one person missing, presumed dead. I find it incredibly difficult these days, even with the help of powerful search engines, to find news articles about severe weather from a neighbouring European country. One good thing that did come out of my search is The Watcher’s website, which looks very informative.

Figure 2

Weather buoy observations

Figure 1

There are a number of weather buoys and light vessels scattered around the British Isles and in the eastern Atlantic (fig 1). The markers in the map of the North Sea are from oil or gas rigs. I thought that I’d just look at some of the data that they collect over a year and graph it. The sensors typically collect the following hourly information:

  • Air Pressure
  • Wind Speed
  • Wind maximum gusts
  • Wind Direction
  • Temperature
  • Dewpoint
  • Sea Surface Temperature

At times the onboard sensors do go U/S, which can be for extended periods, because repairs have to wait for the quieter summer months to get done, but usually they are very reliable. This is a record of the SST at K7 (64045) which is tethered at 59.1° north 11.7° west (fig 2), and as you can see the SST doesn’t vary that much 500 miles out to the west of the Hebrides, peaking at just over 14°C in early September and dropping to just over 9°C by March.

Figure 2

This chart is of the instrumental wave height measured by the K7 buoy, the vertical pink bands on the graph are for the named storms of last Winter (fig 3). I’ve plotted this 6 hourly, which still means processing almost 1500 files. The maximum wave height measured by the K7 buoy, was 11.7 metres (38 feet) at 18 UTC on the 23rd of December 2016 during Storm Barbara.

Figure 3

Closer to land the range in the SST is much higher, here is the graph for the Sandettie Lightship in the eastern end of the English Channel (fig 4). SST range from a high in September of over 19°C to a very early low of just over 6°C in the last week of January.

Figure 4

 

The application can access and visualise weather data from any weather buoy in the world, and that includes not only all the worlds oceans, but also the Great Lakes as well (fig 5).

Figure 5

As far as I know all weather buoys deployed on the Great Lakes are taken in for the Winter during November because the lakes can ice up, and put out again at the beginning of June. An amazing amount of warming goes into the Great Lakes in just a few short months, I’m sure people must have thought of turning them into some kind of huge heat pump to generate electricity with. These are the SSTs, or should that be the LSTs, from weather buoy 45006 in Lake Superior, ENE of Duluth (fig 6).

Figure 6

Occasionally a weather buoy will get in the way of the occasional hurricane, as was the case with 42058 last October with Hurricane Matthew (fig 7)

Figure 7

Weather buoys are also very handy for monitoring ENSO conditions in the central Pacific. Having said that, I think most of the ones strung out along the equator don’t report a SYNOP, the closest buoy with SST that I could find was 51004, southeast of Hawaii (fig 8) but 17.6° north of the equator, and seems to show the final stages of the above average SST from the recent El Niño event which ended last year.

Figure 8

The UK weather buoy network is far from perfect as I pointed out in an article I wrote in January, even at the best of times the coverage to the west is quite thin, the Americans in comparison make extensive use of weather buoys to monitor their coastline from the threat of hurricanes, and seem to freely dot weather buoys across the Caribbean and Pacific.