theweather club newsletter · 2020-05-14 · mid-october then saw tropical cyclone gonzalo affect...

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Winter 2014:

Issue 8 Winter 2014theWeather Club Newsletter

Weather Report Weather news stories from around the world during the last three months

Weather Watch Geoff Jenkins takes a look at setting up your own weather station plus we take a look at some rare clouds

World Weather A traveller’s guide to Tuscany

Science Lesson Probabilistic Weather Forecasting

And finally.......Weather Facts

My Weather Les Darlow talks about his passion for painting the weather

Weather and Climate view

Paul Hardaker and Ellie Highwood comment on weather and climate

info@theWeatherClub.org.ukwww.theWeatherClub.org.ukwww.facebook.com/RMetSoc@RMetS

Research News An update on recent scientific research


www.theWeatherClub.org.uk2

+WeatherReport

Welcome As 2014 draws to a close it’s interesting to look back at the weather over the last 12 months. Cast your mind back to the start of the year when the UK was battered by frequent winter storms which led to the wettest winter in the UK since the 1910 records began and the wettest in the long running England and Wales records that go back to 1766. However the year started off on a mild note and that theme was to continue throughout the year. 2014 is on course to be the hottest year on record, not just in the UK but globally and you’ll find out more about this in the Weather Report.

Talking of weather records - if you are interested in keeping your own weather records from your back garden then Geoff Jenkins explains how to set up a weather

Ozone levels improved...

In September 2014 it was announced that the Earth’s protective shield, the ozone layer, is on track to recover over the next few decades. This is due to combined international action against ozone depleting substances. The Scientific Assessment of Ozone Depletion 2014, produced by the United Nations Environment Programme (UNEP) and the WMO, includes assessments by 300 scientists and is the first comprehensive update in four years.

Prof Liz Bentley Founder of theWeather Club

September 2014

1981 - 2010

Actual AnomalyAverage Max 18.2°C (+1.7°C)Average Min 9.7°C (+0.9°C)Mean Temp 13.9°C (+1.3°C)Sunshine 124.1 hrs (100 %)Rainfall 22.1 mm (23 %)

UK Weather

The stratospheric ozone layer is a shield of gas that protects the Earth from harmful UV radiation. Total column ozone declined over most of the globe during the 80s and early 90s, remaining relatively unchanged since 2000. The Antarctic ozone hole still occurs each spring, however this recent assessment indicates it is in recovery and should reach the 1980 benchmark level – the time before significant ozone depletion – by the middle of the century.

The Montreal Protocol, agreed in 1987, and subsequent treaties have seen atmospheric levels of ozone depleting substances - such as CFCs (chlorofluorocarbons) and halons, once used in products such as refrigerators, spray cans, insulation foam and fire suppression - steadily decreasing. Without these agreements, models show that concentrations could have increased tenfold by 2050, leading to 2 million cases of skin cancer annually by 2030, damage to human eyes, immune systems, wildlife and agriculture.

...Whilst Greenhouse Gases reached highest levels in 2013

According to the World Meteorological Organization’s (WMO) annual Greenhouse Gas (GHG) Bulletin released In September 2014, GHG levels reached a new record high in 2013 as carbon dioxide (CO2) levels in the atmosphere reached 396 parts per

station in Weather Watch, so that you can keep a record of how the weather changes day-by-day and how it compares with last month or last year.

It just leaves me to wish you all a Merry Christmas and a Happy New Year.

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Atmospheric Gases: The Good News and the Bad News @RMetS

million, 142% of the pre-industrial era (ca. 1750), and methane and nitrous oxide reached 253% and 121%, respectively. At the current rate of increase, the global annual average CO2 concentration is set to cross the symbolic 400 parts per million threshold in 2015 or 2016.

The measurements made by WMO’s Global Atmosphere Watch network showed that CO2 levels increased more between 2012 and 2013 than during any other year since 1984, with preliminary data linking this with reduced CO2 uptake by the earth’s biosphere in addition to the steadily increasing CO2 emissions.

The Bulletin also showed that between 1990 and 2013 there was a 34% increase in radiative forcing (the warming effect on our climate) because of long-lived GHGs such as CO2 (which accounted for 80% of this increase), methane and nitrous oxide

WMO Secretary-General Michel Jarraud said,

“International action on the ozone layer is a major environmental

success story…This should encourage us to display the same level of urgency and unity to tackle

the even greater challenge of climate change.”



A Tale of Two Storms: Ex-Hurricane Cristobal brought Autumn Warmth to UK whilst Ex-Hurricane Gonzalo brought StormsSeptember and October 2014

Weather Report

Despite a fairly quiet 2014 Atlantic hurricane season, there were two systems that bought very contrasting weather to the UK in the autumn.

Whilst August saw ex-Hurricane Bertha draw the UK summer to an untimely end (see Issue 7), September saw ex-Hurricane Cristobal bringing hot and humid air to the UK for the start of autumn. Temperatures reached the mid-twenties as Cristobal dragged warm air in from the continent.

Cristobal moved northwards towards Iceland, staying northwest of the UK. However, it brought stronger winds to northwestern parts of Scotland and rain to the UK on Monday 1st September 2014. High pressure then developed to the south of the UK which brought settled conditions from the 2nd September onwards, particularly across southern parts.

Mid-October then saw tropical cyclone Gonzalo affect several Caribbean islands before rapidly strengthening into a strong category 4 hurricane. It was the strongest hurricane to hit the area for more than a decade and the strongest Atlantic hurricane since Igor in 2010. Gonzales brought rain and strong winds up to 110 mph to Bermuda causing damage to power lines, trees and buildings.

Gonzalo then transitioned into a mid-latitude depression as it travelled northeastwards across cooler waters towards the UK. The ex-hurricane brought strong winds, gusts of over 70 mph in some coastal areas and torrential rain on 21st October 2014, resulting in flood warnings and travel disruption across many regions. Road, rail and air passengers suffered disruption due to fallen trees and high winds, and one pedestrian died after being hit by a falling tree in London.

October 2014

1981 - 2010

Actual AnomalyAverage Max 14.2°C (+1.5°C)Average Min 7.9°C (+1.7°C)Mean Temp 11.1°C (+1.6°C)Sunshine 83.8 hrs (91 %)Rainfall 158.7 mm (125 %)

2014 on Course to be One of Hottest on Record

The WMO has issued its provisional statement on the status of the climate, stating that 2014 is likely to be one of the hottest, “if not the hottest”, years on record.Global average temperature over land and ocean surfaces for the entire period, January to October 2014, were the highest since records began in 1880. The combined global land and ocean average surface temperature for this period was 0.57°C above the average of 14.0°C for 1961-1990.

The high temperatures have occurred in the absence of a full El Niño-Southern Oscillation (ENSO). Latest reports indicate that there is a 70% chance of a weak El Niño developing across the central and eastern equatorial Pacific by end of February 2015.

If November and December maintain this trend, then 2014 will likely be the hottest

on record, ahead of 2010, 2005 and 1998. This provisional information means that fourteen of the fifteen warmest years on record have occurred in the 21st century.

Closer to home, this year the UK had the wettest winter in over 250 years, the driest September and warmest Halloween on record. In fact, all months except August have been above average. Provisional data from the Met Office also suggests autumn is likely to have been the third warmest on record.

The UK’s mean temperature from 1st January to 25th November was 1.6oC above the 1961-1990 average, making it currently the warmest since 1910. Unless December is exceptionally cold, 2014 will be the warmest on record – exceeding 1995, 2006, 1990 and 2011 – with England potentially having the hottest year in over 350 years.

UK Weather

NASA satellite imagery of Hurricane Gonzalo in the vicinity of Bermuda on 16th October 2014

November 2014



+Weather Report

A number of extreme rainfall events have been experienced across south-western parts of Europe during autumn.

Montpellier, in southern France, was inundated by heavy rain twice in seven days at the start of October 2014. The first event brought record-breaking rainfall, with 252 mm of rainfall falling in just 3 hours and rainfall totals reaching nearly 50% of the city’s annual total! The rainfall quickly flooded streets and highways, and River Lex exceeded its banks in the city centre forcing 4,000 people to evacuate.

Later in the season, parts of the Canary Islands experienced torrential downpours and flash flooding. On 20th November 2014, Los Rodeos airport on Tenerife recorded 31.0 mm of rain in 24 hours - the majority of which fell in less than 6 hours - with other locations recording 50 to 75 mm of rain.

This intense rainfall was due to a large southwards perturbation of low pressure systems over the northeastern Atlantic which were being blocked by a high pressure ridge over northeast France. These merged with a very large, stationary high pressure system over Scandinavia. The location, shape and movement of these weather systems across southwestern Europe can be traced back to the meandering jet stream - which has become more super-charged as a result of the large contrast between the very cold air over North America (see below) and the warm seas off the eastern seaboard of the USA.

Snowstorm Hit the US

Extreme Rainfall Events in Southwest Europe

November 2014

1981 - 2010

Actual AnomalyAverage Max 10.3°C (+1.3°C)

Average Min 4.8°C (+1.5°C)Mean Temp 7.6°C (+1.4°C)Sunshine 53.2 hrs (93 %)Rainfall 122.8 mm (101 %)

UK Weather

October - November 2014

November 2014

Parts of northeast USA were struck by up to 2.4 m of snow in November 2014, as Arctic air swept southward to the east of the Rocky Mountains breaking temperature records in some places. High winds exacerbated conditions, and temperatures dropped below freezing across most of the US, particularly in Illinois, Wisconsin and Nebraska. At least thirteen people were killed as a result of the snowstorm – mostly from exposure and heart attacks - and many others were stranded in vehicles for over 24 hours.

So what caused this event? Similar to last winter, an unusually meandering jet stream allowed Arctic air from the polar vortex - which normally circles the North Pole – to drift southwards over a large proportion of the US, as far as Pensacola, Florida. This ‘ripple’ in the jet stream is in part is due to the impact of the remnants of Super Typhoon Nuri, which resulted in one of the deepest low pressure systems (924 millibars) ever recorded over the Bering Sea and warmed the seas west of Alaska ten days previously.

To exacerbate matters, some parts of far western New York experienced ‘lake effect snow’. Areas to the east of Lake Erie received over a metre of snow, with some towns receiving several cm of snow in an hour. To put this into context, the 1981-2010 average snowfall for November

in Buffalo is around 20 cm, and the city is estimated to have received as much snow in three days as it normally gets in a year!

As cold, dry Arctic air swept southwards over Lake Erie and the other Great Lakes which are still relatively warm at this stage of season, it picked up moisture and heat, and dumped it as snow in ‘bands’ on the downwind shoreline of western New York. Lake effect snow has been increasing around the Great Lakes as the climate warms.

Montpellier floods

Historic lake effect snow in Buffalo, New York (Source: Anthony Quintano)



Does the Atlantic hold the answer to the Temperature Hiatus?

Arctic Melting could lead to harsher European Winters

Research News

The Arctic is one of the fastest warming regions of the planet, and scientists have warned that this area could be free of ice by the summer of 2050. Previous work has indicated that this could result in severe winters in northeastern parts of North America whilst new research indicates this could also have major implications for parts of Eurasia.

New work published in Nature Geoscience has found that distinct patterns of winds and pressure systems which can transport cold air south, creating severe winters in Eurasia, can be linked to a decline in Arctic sea ice. This would mean than parts of Europe and Asia are twice as likely to experience harsh winters due to a reduction in Arctic ice, particularly in the Barents-Kara Sea.

Despite continued increasing levels of atmospheric CO2 and the link with increasing global temperatures, the rate of global warming has slowed in recent years, commonly referred to as the ‘temperature hiatus’. Researchers have been searching for the underlying cause of this slowdown, with natural cycles such as La Niña, weaker solar irradiance, trade winds, Pacific ocean sinks and incomplete measurements all providing possible explanations. However, a recent study may hold the key.

Scientists in China and the US may have found an answer as to where the extra heat is going: to the bottom of the Atlantic and Southern Oceans. The paper, published in the journal Science, analysed millions of ocean measurements of temperature and salinity since 1970 and tracked the heat pathways since the early 21st Century. They argue that a sudden shift in ocean salinity could have triggered the transfer of heat to very deep waters, since this corresponds with the slowdown in increasing global temperatures. Since water with a higher salinity is more dense, it sinks faster thereby taking heat with it as is falls to a lower depth. The work also suggests that the ‘cooling period’ associated with this heat-sequestration mechanism could last 20-35 years.

Oceans cover 70% of the planet and are capable of storing 90% of the planet’s heat. It has long been known that heat cycles naturally within the ocean, eventually rising back to the surface. The novelty with this piece of research is that the Pacific Ocean was originally thought to be the main ‘hiding place’ for heat - the role of the Atlantic and Southern Oceans were not previously the main suspects. Of course, as for all scientific research, more analyses and studies will be required before it is fully accepted, but it certainly adds more evidence for the role of ocean circulation in global climate.

Researchers at the University of Tokyo ran 200 different simulations of global atmospheric circulation forward into the 21st century to explore the impacts. They found that as sea ice declined, persistent circulation patterns - blocking high pressure systems - developed, transporting cold air further south. Although the findings are still provisional, the results support earlier studies.

Peter Wadhams, who heads the Polar Ocean Physics Group at the University of Cambridge in the UK, said: “Annual average global temperatures continue to rise, but the distribution of temperature through the year is giving us more extremes... As ice continues to retreat, we can expect these weather extremes to continue to occur, and maybe worsen.”

It is a frequent misconception that global warming will bring higher temperatures to all parts of the globe, but this is not the case; more extreme weather is to be expected. Indeed, over the past decade there have been frequent severe winters in parts of Europe.

Despite a slow-down in the mean global surface warming since 2000, the Arctic has continued to warm at a rapid rate – and this will have knock-on effects globally.

According to new research, the number of lightning strikes across the UK has been significantly affected by solar activity. The study – published in in the journal Environmental Research Letters - found that the Sun’s magnetic field affects our own, thus increasing our exposure to cosmic rays which increase the number of thunderclouds and trigger lightning bolts.

Current theories suggest that high energy particles, ‘galactic cosmic rays’, play an important role in the generation of lightning, whilst this latest work suggests that the orientation of the Sun’s magnetic field is playing a significant role in the number of strikes

“What we found was there is significantly more lightning in the UK when the field is pointing towards the Sun than when its pointing away which was surprising,” said Dr Matt Owens from the University of Reading, the lead author on the study.

“What we think is happening is that the Sun’s magnetic field is pulling or pushing on the Earth’s field and that’s letting energetic charged particles down into the atmosphere at different locations and the idea is that these actually trigger lightning. For lightning, you need a thin conducting channel like a wire, and galactic cosmic rays can provide this thin column of ionisation in the atmosphere.”

The study found 50% more strikes when the Earth’s magnetic field is affected by the sun, with far higher rates in the summer. As the nature of the Sun’s magnetic fields is well known, there may be scope for incorporating this information into weather forecasts in the future.

Sun’s Magnetic Field could increase Lightning Strikes across the UK



+Weather Watch

Linda Bonskowski snapped the cloud seen here in Martinsburg, West Virginia, but had no idea what she was looking at, so she contacted the Royal Meteorological Society to find out.

We, like many others, initially thought it may have been a contrail created by some kind of aerial vehicle that had completed a loop-the-loop manoeuvre, but it is difficult to determine from just this static photo without knowing more about the weather conditions at the time. Further research and discussion via social media channels now suggest that it may be a very rare ‘moustache cloud’.

Moustache clouds – or ‘horseshoe vortex clouds’ – form in a region of rotating air. These vortices usually form vertically and can lead to funnel clouds, or even tornados. If, however, they develop horizontally, and under the right wind conditions, the updraught may result in a gently rotating crescent of cloud.

As seen in this video (http://wap.weather.com/video/mustache-clouds-54418), when a cumulus cloud travels over a weak updraught, it may bend and form a rotating moustache

Rare Cloud Types Explored

There have been lots of ‘fallstreak’ or ‘punch hole’ clouds appearing on social media channels recently, but what are they?

Essentially they form when a high- or mid-level cloud of supercooled cloud droplets - liquid water that exists at sub-zero temperatures - are disturbed by something like an aeroplane that introduces ice crystals into the cloud struc-ture. These act as ‘ice nuclei’ causing the supercooled droplets to spontane-ously freeze in a process known as ‘seeding’. These frozen droplets then fall below the cloud forming the ‘fallstreak clouds’ we see.

Occasionally an iridescent rainbow can also be seen in these clouds, similar to what is often seen in soap bubbles. This type of iridescence occurs in high level clouds due to diffraction of light by the cloud droplets.

A video from University of Manchester demonstrating nucleation of supercooled water can be found at https://www.youtube.com/watch?v=O0uwGlgkgfY. In fact, you can do similar experiments at home and there are many vid-eos on YouTube demonstrating this (e.g. https://www.youtube.com/watch?v=ph8xusY3GTM)

Moustache Clouds: The ‘Goldilocks’ of Cloud

cloud (named after its handlebar moustache-like appearance).

According to the Cloud Appreciation Society, “such a movement of air seems to happen when an updraught is sent into a spin upon reaching shearing horizontal winds. Rarely are conditions right for a cloud to appear within the spin.”

One of the best times to spot such a cloud is in the vicinity of a supercell storm, or a thunderstorm with a continuously rotating updraught. However, such clouds appear for just a minute or so before evaporating away, so if this was indeed a moustache cloud, Linda was very lucky to capture it in a photograph!

Fallstreak or Punch hole clouds

A Moustache Cloud or Hourseshoe Vortex Cloud by Linda D Bonowski

Image: A fallstreak hole that was seen over Oklahoma City on 2nd January

2010 [By Pfranson]



+Weather Watch

In the last newsletter, I talked about buying your own automatic weather station. But many people will be put off doing this because they have read that you need to have access to a large open area for the observations to be worthwhile. The good news is this isn’t true. Of course an open area away from buildings and trees is the ideal situation, with all the separate instruments put at their correct heights above ground: 10 m for the anemometer and wind vane, 1.2 m for temperature and humidity sensors and 30 cm for the rain gauge. This is what Met Office stations, and indeed any official station worldwide, have to aim to achieve. But the space available to most amateur observers will be very different from that ideal; it is often a “pocket-handkerchief” back garden on a housing development in a city suburb or small town. So the rule is: do the best you can. Try to get your weather station as far away as you can from obstructions and put the sensors

somewhere near the correct heights, but don’t worry too much if they are far from ideal.

Other non-meteorological criteria may affect your decision: is it safe from vandalism or damage by animals? Does it get in the way of enjoying your garden or look intrusive? Quite often, what you may end up with is what many other amateurs and schools have done, and that is to attach the weather station to the side of a garage, outbuilding or existing post with the anemometer up as high as you (safely) can and the other instruments perhaps 2 m above the ground, out of harm’s way. The photos below, taken from the web, are typical of what many amateur observers do.

The observations you make will not, of course, represent those in open conditions, and hence cannot be used by the Met Office for establishing long-term climate of the area or its extremes, but they will be representative of many locations similar to your own – after all, some 80% of people in the UK are estimated to live in suburban areas. In the next edition of the newsletter, I will talk about how to get your weather data on the web by connecting to the WOW website; when you look at wind speed and direction (probably the measurements more likely to

Setting up your Weather Station

Geoff Jenkins explains why you don’t need to move to a cliff top or the middle of a field to get useful weather observations.

Keep a record of how the weather

changes day-by-day and how it compares with last

month or last year.

Images (left to right): Grant Gibson’s weather station at Elderslie, Scotland, Alistair Sargent’s at Hatfield, one at the University of Ulster, and the author’s own in Hampshire.

be affected by poor exposure) from amateur observers on WOW over a local area, the surprising thing is how similar the observations are, rather than how different they are. And even if it is only representative of your own back garden, you can still keep a record of how the weather changes day-by-day and how it compares with last month or last year.



+WorldWeather

Visitors to Tuscany come for a whole plethora of reasons; for a romantic city break to take in the medieval città di arte (cities of art); a gastronomic tour of the many delicious eateries; a relaxing summer holiday along the coast; to ramble or cycle in the picturesque Tuscan hills; for an educational experience to learn the beautiful Italian language, rich history and culture; or indeed to take advantage of the Tuscan weather!

The climate of Tuscany is mainly influenced either by the sea which bathes the west, or by the dorsal of the Apennines Mountains which close the territory at north and east. Flows of air which influence the climate of Tuscany often present differences between north and the south of the Island of Elba which behaves like a sort of a weather “watershed”.

Overall, Tuscany has a humid subtropical climate that is generally very mild with year-round rainfall. However, there can be significant differences over

A traveller’s guide to TuscanyA view over Florence (Photo by A.R.Heath)

This map shows the provinces of the Italian region of Tuscany (Created by NormanEinstein, 2005. Accessed vi WikiCommons)

small distances due to the changeable geography of the region.

The most enjoyable times of the year to visit Tuscany – both in terms of climate and avoiding crowds – are spring and autumn. The summer months are hot, humid and busy, particularly July and August; intense heat and thunderstorms are commonplace during the summer months. There is less rain in spring and these months are still warm and sunny. November is the wettest month, but autumn can still be a pleasant time to visit the region since the foliage in the Tuscan countryside can be breathtaking. Winters are relatively mild, but sometimes it can get rather cold, particularly at night and in hilly areas which also experience snow – a bonus for skiers!

The valleys and coastal areas to the west, such as Pisa, Grosetto and Livorno, experience hotter summers than the hilly, mountainous regions, as temperature decreases with height, though the coasts do benefit from pleasant sea breezes making them popular with tourists. Many farmhouses and villas are intentionally located at the tops of hills surrounded by



Climate of Tuscany Average min temperature range: 2°C in January to 19°C in July

Average max temperature range:11°C in January to 32°C in July

Average driest month: July with 31.5 mm and 5 rain days

Average wettest month: November with 133 mm and 15 rain days

Average daily sunshine: 3 hours in December to 11 hours in July

‘Tuscany, like a fine wine, has

been some time in the making.’

The narrow

streets of Lucca

woodland, and are built with thick stone walls that help to keep the houses cool in summer and warm in winter. Perfect for the unacclimatised tourist!

From the Etruscans to the Romans to the Renaissance, Tuscany is possibly the greatest repository of art in the world, from extraordinary paintings and sculpture to frescoes and architectural masterpieces.

Tuscan countryside

Siena’s hulking Gothic cathedral

The city of Florence (Firenze) is located in the north of Tuscany. It is famed for its art and architecture: The Uffizi which houses masterpieces such as Botticelli’s Birth of Venus, Pitti Palace once the residence of the Medici family, Florence’s majestic cathedral with its panoramic perches, and of course, Michaelangelo’s David in Galleria dell’Accademia.

To the south of Florence lies Siena, with its hulking Gothic cathedral and Piazza del Campo (“Il Campo”) where crowds gather to stroll, eat and socialise. The Palio di Siena, a horse race, is held twice a year in July and August.

Another area definitely worth visiting is Lucca, a genteel, 16th century walled city of opera, Romanesque churches and hidden gardens, that lies north of Pisa. In recent years it featured on an episode of Top Gear, in which the team found themselves ‘trapped’ whilst driving within the city walls – if you ever visit this city, you’ll understand why! Similar to many other Italian cities, its narrow streets lined by tall buildings and high walls, interspersed with wide piazzas, give rise to ‘microclimates’ and you can experience a range of temperatures, humidity, winds and sunlight whilst wandering through the city. On a hot day this means there is always a shaded corner to escape to …but failing that there are gelaterias and cafeterias aplenty!

Surrounding these towns and cities you’ll find the breathtaking Tuscan countryside. Between Florence and Sienna lies Chianti, a picture-perfect landscape of vineyards, olive groves, castles and market towns – once experienced it is easy to understand why artists were compelled to paint! This region is so popular with the English that it has earned the nickname Chiantishire. Head to Pienza, interior hills located to the south of Tuscany, to escape the urban heat of the cities and take in the stunning views.

And of course, we cannot mention Italy without reference to the cuisine; the food across the whole of Italy is world-famous, but it is particularly appetising in this region. From gelato to gnocchi, you won’t be disappointed, and if you’re a meat-eater, the local dish ‘Steak Florentine’ is certainly not to be missed!

This article has only touched-on a few of the regions in Tuscany – there are plenty more places to visit in this extraordinary region of Italy. It is certainly one you’ll want to return to again and again, whatever the weather.

Gelato!



+ScienceLesson

The following science lesson has been written with school students in mind, but should be informative and fun for everyone.

Weather forecasts have improved over the years, but we can all think of occasions when the forecast did not turn-out to be correct. Forecasting remains a popular target for jokes, but have you ever wondered why forecasts can have errors? Forecasts are made with super-computers that run weather “models” to approximate and solve the laws of physics. While approximations are necessary, they are one source of error in the forecasts. A second source of uncertainty in forecasts arises from the growth of ‘chaos’ (sometimes known as the “Butterfly Effect”), whilst a third factor is that some weather situations (e.g. fast-growing cyclones) are harder to forecast than others (e.g. slowly changing high-pressure systems). In general, weather forecasters do not mention these sources of error, but sometimes indicate these uncertainties by replacing the phrase “it will be” with phrases such as “it is likely to be” and “chances of”. It is probabilistic weather forecasting that takes into account these sources of uncertainty, and provides the forecaster with information about how certain they can be when presenting the weather.

What is ‘chaos’ and how are probabilistic weather forecasts made?

Here is an experiment that demonstrates the part ‘chaos’ plays in forecast uncertainty. It shows us why we need probabilistic forecasts, and how they are made. The numbered points below correspond to the panel numbers in the diagram.

1. You will need: some paper (not card) preferably four different colours, a ruler, scissors, string, a pen or pencil, and a coin.

2. Cut-out 2x2 cm squares: Write “T” (‘truth’) on both sides of one of the squares and “F” (‘single forecast’) on both sides of a different coloured square. Cut ten squares from another colour and write “P” (‘probability forecast experiment one’) on both sides of each, and ten squares from the last colour and write “Q” (‘probability forecast experiment two’) on both sides.

3. Find a clear area of floor, away from draughts. Put the coin in the centre of the area and stretch the string from the coin in a straight line. Write “sun” and “rain” on two pieces of paper and put these either side of the string.

4. Put the “F” (‘single forecast’) square in the palm of your hand.

Probabilistic Weather Forecastingby Dr Mark Rodwell, European Centre for Medium-Range Weather Forecasts, Reading, UK.

5. Stand next to the coin, facing along the line of the string. Stretch your arm straight out level with your shoulder, parallel to the string and one shoulder-width to the side of it. Turn your hand over quickly so the square flutters to the floor. We can think of the place where the “F” square lands as the forecast for tomorrow: rain or sunshine, depending on where it fell. What did your forecast predict?

6. Next, put the “T” (truth) square in the palm of the same hand.

7. Stand as before with your hand in the same position. Turn your hand quickly so that this square also flutters to the floor. We can think of where it lands as what the weather was really like. Did the truth square fall on the sunny or rainy side of the string? Was your forecast correct?



8. Next, put the “P” (probability forecast) squares in a small pile in the palm of the same hand.

9. Stand as before and turn your hand quickly so that all the squares flutter to the floor. Did they spread-out much? How many fell on the sunny side of the string? If seven fell on the sunny side, you could have made a probability forecast that there was a 7 in 10 chance (70% probability, or odds of 70:30) that it would be sunny. This prediction method is often called an “ensemble forecast” because it involves an ensemble of lots of individual forecasts. Why do you think the “P” squares separated? One reason is that each square was in a slightly different position on your palm before you turned it over. In reality, we do not know the present state of the weather perfectly. The slightly different positions of the squares in your hand before you dropped them represents our uncertainty in the present weather state, and the spreading-out of the squares on the floor is an example of chaos.

10. Over the years, more observations of the present weather have become available (from weather stations, satellites, weather balloons, aircrafts), and as these observations become more accurate and as methods for combining these observations improve, uncertainty in the present weather state is getting smaller. We can look at how uncertainty in

the present weather affects our probability forecasts by doing an experiment involving larger uncertainty. To do this, spread the “Q” (second probability forecast) squares as widely as possible over your hand.

11. Stand as before and turn your hand over quickly so that all the squares flutter to the floor. Did they land more spread-out than the “P” squares? What probability do the “Q” squares predict for sunny weather? Usually the “Q” squares are more spread-out, but you might like to try the experiment several times or draw-up a table to compare results with others. Do you find that the “Q” probabilities are closer to 50% (50:50)? Although reducing uncertainties in the present weather state can help improve weather forecasts, chaos is a fundamental aspect of the atmosphere which will always lead to the growth of forecast errors. Another source of uncertainty is the approximations made in our weather models. What feature of this simple experiment might represent these model approximations? How could we investigate uncertainty in forecasts for twice as far into the future (e.g. forecasts for the day-after-tomorrow)?

How can we use probabilistic weather forecasts?

Instead of the weather forecaster using phrases such as “it is likely to be”, many industrial forecast users (e.g. in

the renewable energy sector) can make better use of the raw probabilities from the ensemble forecasts. The “then and now” cartoon below explores how we might also benefit from using the raw probabilistic forecasts (“P”) instead of the traditional single forecasts (“F”). Two pairs of friends are trying to organise a weekend trip. One pair were doing this in 1984 and used the traditional forecast, and the other pair were doing this in 2014 and used the probabilistic forecast. This cartoon puts our two couples into their era of communication to show how probabilistic forecasts might help us achieve a better outcome.

Of course, we would prefer to be told for certain if it will be sunny or rainy but forecasters will never be able to completely eliminate the effects of chaos. Meteorologists are still trying to determine the best way to communicate probabilistic weather forecasts. Perhaps you have ideas about the presentation and use of probabilistic forecasts?

There is still a lot of exciting work left for future physicists and mathematicians in order to improve the computer models that forecast the weather. And this job is becoming increasingly important.

If you conducted the experiment above, or have any other comments or results, we would love to hear from you.



+Weather View Prof Paul Hardaker

Chief Executive ofThe Institute of Physics

In the early 1800s Frederic ‘the ice king’ Tudor founded the Tudor Ice Company. He had the idea of bringing ice down from the New England lakes to the Caribbean, then eventually on to Europe and as far away as India. He even invented the American Ice brand which became very fashionable after Queen Victoria said that she preferred it in her drinks.

Whether harvested locally or shipped direct from the ice king, the ice needed to be stored and so the big houses and community centres built ice cellars. I visited one recently in the canal museum in London, a fascinating place where canal boats used to load and unload in the Paddington basin of the Grand Junction Canal. The ice cellar became host for a few months to an installation piece, formed from a collaboration between physicist Ben Still and artist Lyndall Phelps; a quite spectacular representation of an underground neutrino detector.

Some of the more exotic designed ice cellars can be found in the Middle East. These Yakhchal (literally translated means ice pit) were built across Persia. They had a very clever design. Water was channelled in to the shade and down in to the underground pits where it was frozen during the cold, clear sky nights. The evaporation from the surface of the ice up through the chimney cooled the surrounding air and kept the ice frozen. That is, the air around the ice is heated through the day by heat from the sun (known as sensible heat). The ice absorbs this heat, cooling the air temperature, and releases it as latent heat, melting the ice. If the gradient in temperature is large enough the ice can sublimate, that is go directly from ice to water vapour, missing out the liquid water phase. This process can be so efficient that it can cool the air using much less energy than an average household refrigerator.

We take it very much for granted that Earth has the right conditions for water to exist on the planet as ice, liquid water and water vapour, that is in solid, liquid and gas phases. The ranges of pressure and temperature have to be just right to allow that to happen. In fact this is what astronomers use to look for planets around other stars in what they call the habitable zone – a search for planets that support life. We know that in our solar system, Venus, Mars and Earth are in that zone and that at one time Venus and Mars would have also been able to support water in all three phases.

If you can have all three phases then at some point there must be a transition between these phases, where they all come together. And sure enough there is, we call that the triple point of water. In fact we use this to define the Kelvin, our standard (SI) unit of measure for temperature. We set 273.16 K at the thermodynamic temperature of the triple point of water, 0.01oC.

We talk about the three phases of water but, as usually turns out to be the case, it’s much more complicated in practice. In fact ice has 15 different phases, to do with the different ways in which the hydrogen and oxygen atoms can arrange themselves, although the vast majority of ice occurs in the hexagonal crystalline phase. Whichever phase it forms in the structures are incredibly beautiful and intricate even if we don’t like having to walk or drive through it.

Ice is important to both our weather and climate system. The ice in our glaciers is a very important storage mechanism. Their melting (and growth) cycles form some of our most important river systems, bringing water to large numbers of communities. Ice also has a very significant effect on what goes on inside clouds. For

example the distribution and behaviour of ice particles strongly influence the electrification process within a cloud, and the ice affects the characteristics of the cloud precipitation. Indeed, more than half of the rainfall on the planet starts off in clouds as ice.

The ice on the surface (land and sea) helps to reflect the incoming short wave radiation from the sun and is part of the process that keeps the planetary temperature in balance. We call the ratio of reflected incoming solar radiation the albedo. The albedo of the earth is around 30 to 35%, depending, in part, on changes in the ice cover through the season and also what levels of cloud cover we have, as clouds, being water and ice, also help to reflect or trap the solar radiation depending on their height. The melting of land ice also plays a part in the circulation in the oceans because the fresh water can weaken the salinity.

Water can trap gases like carbon dioxide and methane when it freezes and hold these in the ice. This forms what we call clathrate structures which act as natural sinks for these greenhouse gases in the frozen tundra. You may have seen the trick on the TV where the presenter melts the frozen patch of ground and sets light to the methane that is being released with their lighter.

So the next time it snows or freezes over, try not to get too cross about the travel disruptions. Enjoy the ice crystal structures, think about the important role the ice is playing and how lucky we are to live on a planet where we have ice, just not all of the time!

Ice, Ice Everywhere but not a Drop to Drink The thermodynamic temperature of the

triple point of water [is] 0.01oC.



+ClimateView

Prof Ellie HighwoodProfessor of ClimatePhysics at theUniversity of Reading

Global Implications of Ice MeltThis term I have been teaching cloud physics to our undergraduates. I have thoroughly enjoyed immersing myself (not literally!) in ice formation over the past couple of weeks. We’ve learnt about how ice crystals grow faster at -5°C and -15°C (diffusion of water vapour onto ice crystals is much faster than on to liquid water droplets at -15°C and changes in shape alter the efficiency of growth), and what kind of clouds are more likely to produce hail (vigorous convective clouds).

I am however, more used to thinking about ice on the Earth’s surface. Ice is a key part of our climate system. The bright surface of ice and snow covered regions reflects around 80% of the sunlight falling on it back to space. This reflection helps determine the balance between energy entering and leaving the climate system, giving a push towards globally lower temperatures. Changes in ice and snow lead to an important

positive feedback in the climate system (a positive feedback is an amplification of an initial change). In the snow/ice albedo feedback, an initial warming of the climate system (it doesn’t matter what causes it) leads to melting of ice and snow. This decrease in snow and ice reveals a darker land surface, i.e. the planetary albedo is decreased. Less sunlight is reflected back to space and more is absorbed by the darker surface leading to further warming. The original warming is amplified. The more rapid warming in the Arctic compared to other parts of the Northern Hemisphere is often attributed in part to this feedback. Recently there has been much attention on the additional possibility that black carbon aerosol from fossil fuel burning can also accelerate ice melting when it lands on surface snow and ice.

When ice melts, the water has to go somewhere! With ice on land, this can mean an increase in run-off into rivers

and eventually the sea, contributing to sea-level rise. Melt water from ice floating on water does not lead to significant sea-level rise (you can test this at home by floating an ice cube in a jar of water, marking the level, waiting for it to melt, and then checking the level again – for salty seawater there might be a small increase due to the density difference between saline and non-saline water, but it is tiny compared to increases due to thermal heat expansion of liquid water). However, melting sea ice may lead to changes in the global water circulation because these are driven largely by salinity (density) differences and meltwater is less salty than sea water.

So what is observed to be happening to ice? The latest report of the Intergovernmental Panel on Climate Change (IPCC) states that both extent and thickness of Arctic sea ice have decreased since 1980s, and that almost all glaciers globally have continued to shrink The Greenland ice sheet and floating Antarctic ice shelves have also lost mass over the past two decades and snow extent in the Northern Hemisphere has decreased. These changes at sea and on land can have multiple impacts on us and our surroundings. Aside from the much publicised effects on polar bears, the melting of Arctic sea Ice during summer months is opening up new sea routes that could be exploited for commercial gain. Loss of ice from inland glaciers may affect water supply for high altitude regions (e.g. central Asia), although water use and precipitation patterns may likely have a bigger impact. And thus I return to where I started this article and the atmospheric part of the water cycle, ice formation in clouds and resulting effects on precipitation!

Ice is a key part of our climate system. The bright

surface of ice and snow covered regions reflects

around 80% of the sunlight falling on it back to space.



+My Weather

As an artist I am truly inspired by our wonderful countryside, remarkable skies, and of course, our diverse and incredible weather which shapes and lights the landscape so beautifully, so, as artists we can interpret this in our paintings.

Weather plays an enormous part in my work as an artist, and I feel that skies in particular have formed a fascination for me that transcends into most of my paintings. I will quite often take off into the countryside in the wildest of weather conditions, just to experience this, so I can better portray this in my work. A good friend of mine is a pilot, and we often fly around the Lancashire area, so I can study clouds from a different perspective.

Storms

One of my favourite paintings, entitled “The Hand of God”, was inspired by Hurricane Sandy in 2012. Sometimes before and after a storm, the sky can be almost celestial in its appearance, and my inspiration came from the build up of this storm through the media channels leading me to begin the thought process of putting the painting together.

I was actually quite shocked to realise that New York could be affected by a Hurricane, and began thinking that global warming and it’s effects would considerably change what we think of as being normal when it comes to the weather.

Inspiration is essential for me to paint as an artist, and sometimes even when bad things happen through storms and weather events, I feel drawn to these things, even if it is just to document it in an art form for the future, just as artists have done for thousands of years.

“Riverdance”: The Riverdance Ferry had set sail from Ireland on its route to Heysham, and during an exceptional storm and winds that reached up to 80 mph she was ‘broadsided’ by a huge wave, which made the cargo shift and the ferry list, and it then started to run aground at Anchorsholme, which is at the northern end of Blackpool seafront, on the boundary with Cleveleys.

The RNLI and helicopter rescue were mobilised that night into weather which they later described as some of the worst that they had ever seen. During the course of the night everyone aboard including the crew and few passengers were taken off and to safety and by 4am the ferry had been evacuated – and amazingly for the

conditions, with no loss of life. The ferry was left alone that night – and stayed there on the beach for months.

Snow

This is a real obsession for me, a love, a passion. It can literally change the appearance of our world in minutes, a soft cushion of delicate, incredible, beautiful frozen flakes which reflect the light in a magical way. A real artists dream to be honest.

“Kirkstone Pass”: My wife thinks I am crazy! It’s 7.30pm, Tuesday evening, winter, the fire is on, the central heating is on, it’s very cosy in the lounge and I get a call from my niece in Shap, Cumbria to say it is snowing. Within 10 minutes, I have my Landrover packed with shovels, blankets, camera equipment and emergency supplies, just in case, and I set off for a 1 hour journey to Kirkstone Pass in the Lake District just to experience the feeling of blizzard conditions on the mountain; the result of this trip can be seen above.

A Professional Artist, Tutor and Demonstrator with a Passion for Painting the Weatherby Les Darlow, UK Ambassador for Canson - World Leaders in Fine Art Paper Manufacturewww.lesdarlow.com

“The Hand of God” Inspired by Hurricane Sandy in 2012

“Riverdance” Inspired by Local Shipwreck



“The Golf Course” was inspired by the winter of 2012. Blackpool, where I live, does not get snow, or very rarely. I remember one year, the whole country was covered with snow apart from literally an 8 mile radius around the Fylde Coast. But in 2012, nobody played golf on our golf course for months.

Clouds

Ever since I began painting with pastels, I have had a fascination for clouds, storms and weather events, following all my favourite Storm Chasers in the United States. As an artist, I collect cloudscapes, taken on my camera, wherever I go in the world and then use those in my paintings locally. Below is a painting of Fleetwood, from Knott End in Lancashire, with a sky I took whilst on holiday in Florida.

Kirkstone Pass, Cumbria The River The Golf Course

Weather plays an enormous part in my work as an artist, and I feel that

skies in particular have formed a fascination for me that transcends into

most of my paintings.

As a tutor, I am constantly running workshops throughout the UK and Europe, and most people who attend give the same feedback, that they want to be able to paint magnificent skies.

The sky in a landscape is everything, and I feel blessed that I have both the vision and passion to use my skills as an artist to document and paint the light that transmits through the clouds and lights our landscape with unbelievable beauty.

+Weather Facts

At any one time there are over

2,000 active thunderstorms

producing 100 lightning flashes

every second

Each year in the UK about

20 people are injured by lightning and

4 people are killed

* * * HAVE YOUR SAY * * * We are interested to hear what you think about theWeather Club newsletter. What features do you particularly like/dislike? Are there any items you’d like to see covered in the newsletter in the future or do you have ideas for a new type of article you’d like to see included?

Let us know at [email protected]

A blizzard is a severe snow storm with winds

over

35 mph & visibility of less than

400 mfor more than 3 hours

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The coldest & snowiest Christmas day on record

in the UK was in

2010 with a minimum temperature of

–18.2°C

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