The Stratosphere – why do we care?

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I study the stratosphere, the layer of atmosphere that extends above the troposphere from about 10-50 km. Friends and colleagues of mine often joke (I hope…) that “nobody cares about the stratosphere” *, primarily because it contains no real ‘weather’ – such as what happens in the troposphere. With little to no water vapour, it can’t be seen on visible satellite imagery – unlike the huge and beautiful weather systems in the troposphere. To visualise the stratosphere, we rely primarily on computer-generated graphics – and it’s not like you can walk outside and experience it, either. So, why do we care? What follows is a relatively simple (I hope!) explanation.

Weather forecasts, particularly on TV, often explain that our weather is “all down to the position of the jet stream” (the band of fast flowing air high in the troposphere that forms on the boundary between warmer and cooler airmasses). Now, that’s almost always true in the UK, but it’s particularly potent in winter – when the temperature contrasts either side of the jet become enhanced thanks to the Polar Night. One of the main driving factors behind the speed and position of the jet stream (particularly the Atlantic jet stream) in winter is… the stratosphere!

Rather like the jet streams we know and love/loathe in the troposphere that guide the development and evolution of weather systems, in the stratosphere there exists another jet stream – the Polar Night Jet (Figure 1). This encircles the Stratospheric Polar Vortex (SPV). Both of these form as the pole tilts away from the Sun in winter, leading to intense cooling. The strong temperature gradient then forms a jet stream and cyclonic vortex, which isolates the air within the vortex, and it cools further…etc. The Polar Vortex is a normal phenomenon which forms each winter – nothing sensational like some headlines suggest.

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Figure 1: GFS zonal wind analysis from February 4th 2018. Reds indicate westerly winds. A strong Polar Night Jet exists in the stratosphere, associated with a strong tropospheric jet.

Through a process known as stratosphere-troposphere coupling, the stratosphere and the troposphere beneath can ‘talk’ via the influence of planetary/Rossby waves. These very large waves in the mid-latitude westerly flow can propagate vertically from the troposphere into the stratosphere and influence the circulation there – a process known as wave-mean flow interaction. Sometimes, this is strong enough to strongly disrupt the SPV, and when that happens, the isolated reservoir of cold air is broken down and the temperature sky-rockets… by as much as 50C in only a few days. This is known as a Sudden Stratospheric Warming (SSW). Very strong SSWs – called major SSWs – occur in approximately 6 winters per decade, and result in a reversal of the Polar Night Jet to easterlies. The Polar Vortex is either displaced, split up, or destroyed (2018’s SSW is shown in Figure 2).

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Figure 2: The February 2018 Major SSW, as told through daily analyses from the GFS of 10 hPa wind (filled) and geopotential height (contours). This is classified as a ‘split’ SSW, for obvious reasons.

This has implications for our weather, because anomalies in the strength and position of the SPV and the Polar Night Jet can propagate downwards and influence the tropospheric jet stream. A stronger than normal SPV is associated with a strengthened tropospheric jet stream – and for us in the UK, that means Atlantic westerlies and generally mild winter weather. In contrast, following a major SSW, the easterlies propagate downwards (Figures 3 and 4) – resulting in a reduction in strength of the Atlantic westerlies. Sometimes, there can be a complete reversal of circulation – this happened in March 2018 with the infamous ‘Beast from the East’, bringing cold and snowy weather.

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Figure 3: As in Figure 1, but for February 17th, following the major SSW. Note the weaker tropospheric jet and surface easterlies as the ‘Beast from the East’ developed in response.

Thus, being able to predict the state of the Stratospheric Polar Vortex is a source of skill for wintertime forecasts. Moreover, because there tends to be some lag between the events in the stratosphere and their maximum impact at the surface (~2 weeks), stratospheric predictability can provide increased predictability on the sub-seasonal timeframe (~15-30 days). Additionally, anomalies associated with a major SSW tend to persist in the lower stratosphere for even longer – which again, is a source of skill.

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Figure 4: Anomalies in geopotential height for January-March 2018. Note how anomalies associated with the major SSW (red blob in the centre) propagate downwards like ‘dripping paint’.

And that is why we care about the stratosphere!

Further reading:

Kidston et al., 2015: Stratospheric influence on tropospheric jet streams, storm tracks and surface weather. Nature Geoscience, 8, 433-440.

*A tongue-in-cheek quote from Reading Meteorology’s weekly ‘Weather and Climate Discussion’ a few years ago that stuck with me was “the stratosphere – nothing of interest lies therein”. I plan to use that in my thesis…

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Careers ‘Advice’? Follow your dreams!

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Sara Thornton (co-owner of Weathertrending) recently shared an article highlighting how one particular careers adviser in her past told her to ‘give up on her dreams’ of presenting the weather on TV. Now, clearly that didn’t stop Sara! But it got me thinking about careers advice from my past – especially since meteorology is a relatively niche subject which extends far beyond what some assume it to be.

I have pretty much always wanted to be a meteorologist – well, I can trace it back to about the age of 6. It didn’t take long before I started to find out for myself what you needed to do and be good at to do meteorology… it turned out that was Maths and Physics. I quickly found out that the Department of Meteorology at the University of Reading was one of the best in the world, and offered undergraduate courses in the subject. So, I had worked out what I needed to do to pursue my dream.

Naturally, you’d imagine that careers advisers and teaching staff during my time at school were helpful and encouraging – seeing as I had a definite dream in a very realistic career. Think again. The following is a genuine quote from a school careers adviser during a compulsory visit around the time I did GCSEs:

“Hmm. Have you ever considered becoming an actuary? They earn a lot of money.”

I have never forgotten that because the meeting had nothing to do with how I could pursue my dream or what I needed to or could do, but focused instead on the adviser rattling off as many careers as she could think of that weren’t in atmospheric science – including actuary because they earn a lot. Not because it might be something I wanted to do or had anything to do with my dreams.

It extends beyond that. These are quotes from teachers in my past:

“I checked, you don’t need Further Maths to do Meteorology. So you should do French!”

Choosing A-levels is hard enough. It can define your life before you’ve really worked out what you wanted to do. It’s even more difficult when teachers want you to do their subject instead of what’s right for you. It’s true, you don’t need Further Maths, but it has helped me far more than French ever would. Plus… I love maths!

“But I’m so disappointed you’re not doing Physics, you’re very good at that.”

The thing is I am doing Physics – it’s just all applied to the atmosphere and oceans! That’s something I could never seem to make this teacher, or many others, understand.

There were several other quotes which I can’t remember precisely enough to replicate. My overall point is that I had to stand my ground and just do what I wanted to do, and it often felt that this was going against the wishes of others. I’m not sure if this has something to do with a poor knowledge of what meteorology entails, or whether its snobbery towards the highest-ranked universities (instead of departments…which is what really matters, right?).

I don’t know whether I would have ended up where I am now if I didn’t have such a strong desire to go and study Meteorology at Reading, because I was never properly encouraged by those who should have done so. If you’re a young person who loves weather, go and study it. Words can’t express how happy my undergraduate degree, and now this PhD, has made me.

There’s never a dull day in weather.

“They get it wrong 90% of the time”

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I was on a long train journey a few days ago, and ended up in conversation with the person next to me. When I explained what I’m doing (a PhD project looking to improve sub-seasonal forecasting), I was greeted with the all-too-familiar response of “oh, that’s good because they get it wrong 90% of the time”. Doing my utmost to supress just how much that sentence annoyed me with its factual inaccuracy, I responded with a comment about how there is still so much to learn about the atmosphere-ocean system, and ‘things can only get better’ (perhaps that song by D:Ream should be the soundtrack to NWP – or is it still too tainted by Tony Blair?). I also recently saw a post on Reddit’s ‘showerthoughts’ saying “Forecasting the weather is the only job where you can get it wrong every day and still have a job” – I refrained from responding to that!

Of course, “they” don’t get it wrong 90% of the time (you could easily argue the reverse is true) and a forecaster won’t still be in the job if they’re getting it wrong every day.

In the last few days we have seen a spectacular example of what NWP is capable of with the forecast of Hurricane Florence. We knew days in advance that the storm would reach category 4 status. The track into the Carolinas is now without doubt (though the exact motion when the storm makes landfall remains uncertain). So how is it that a forecast of a huge, turbulent, dynamic vortex can be so incrediby accurate to an extent that even amazes meteorologists – and yet the general public can have such a different opinion about their experiences of weather forecasts? How is it that this perception is so ubiquitous?

I had noticed over the summer that there were noticeable issues with app forecasts – and noticeable failures – but there is often good reason. Showers are difficult to predict to postcode-level accuracy, and, sometimes, “shit happens”. A great example of the latter occurred earlier in 2018 in Reading, in perhaps the only time I’ve really experienced the forecast go completely wrong. The forecast: a dry, cloudy day. However, the inversion mixed out, resulting in clear, sunny skies. That in turn lead to unexpected solar heating and thus unexpected instability, which generated a heavy (but very isolated) shower over Reading (perhaps its localised nature was a response to additional urban heating – yet another complexity!). A wonderful non-linear response – and something which as a meteorologist made sense. However, to a member of the public, it was unexpected rain that may have left them irritatingly soaked – and perhaps fostered a resentment of weather forecasters.

Forecast accuracy has come on in leaps and bounds over the last 30 years, but it seems public’s trust has not increased accordingly. I think part of this is how quickly one adjusts to a ‘new normal’ – I can draw a parallel to Internet connection speeds (remember when 1 Mbps was fast, yet now seems painfully slow?). I think a large part comes down to a lack of understanding as to why a forecast may go wrong. Rather like a medical diagnosis, it may make logical sense as to why a Doctor misdiagnosed, but the patient’s response may be filled with anger and confusion. And part of that comes down to the human body seeming naiively simple (because we all have one!) in the same way forecasting the weather may seem simple (just some fancy graphics and looking at clouds, right?). Both are hugely complex, but its usually only the experts who truly comprehend that.

Thus, it’s my conclusion that the more meteorology we can get out there, the better the public will trust the forecasts we make.

Edit: after writing this post, I received a wonderful tweet which showed that, for some, the incredible accuracy of weather forecasts is understood.
 

Why deny climate science?

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Imagine you are an astronaut who has just returned from the International Space Station and you meet a Flat-Earther… how would you even go about that argument? 

Climate science and evolution are two sciences denied by many. In the case of evolution-denial, a creationist view is faith-based. Those who believe that God made the Universe 6,000 years ago (or equivalent) at least get a religious ‘kick’ out of it. I’m not saying that belief is a good thing (far from it – I think evolutionary science is an incredible human achievement and filled with beauty), but at least I can somewhat understand the mindset that leads to it (or the root of the belief – a religious text).

I cannot say the same for climate science denial. I just don’t understand what motivates it. What is the benefit to the individual? Does it make you feel good to think that all the experts are wrong?

Now, I do what I can to help the environment. I could do much more – I’m aware of the scale of the problem. But I don’t refuel a diesel car or use a petrol lawn-mower and feel riddled with guilt. My scientific opinion on climate change doesn’t follow me around like a dark cloud. I don’t overuse fuel in order to save money, primarily.

When the World Health Organization listed bacon (and other processed meats – of which you probably consume more than you think!) as definitely carcinogenic, I didn’t deny it – I’m not a medical scientist, and I’m sure good science was done in order to reach that conclusion. Equally, when we meteorologists and climate scientists announce that greenhouse gases are causing global warming, I don’t expect non-experts to take issue with that. Whether you act on it is something else, but don’t turn around and say, “Ha! Have you even considered the urban heat island?“. An every-day equivalent would be responding to an F1-trained mechanic informing you that your car needed a new engine by saying “Really? Did you check the oil?”. 

Of course they checked the oil.

In truth, what deniers say to climate scientists is often hurtful, and sometimes very difficult to respond to, purely because of the extent of the misunderstanding – not because we can’t support our science. It’s also plain baffling what some deniers say. When you’re just an excited or concerned scientist doing your thing, experiencing people thowing wild accusations at you is just…bizarre.

So, to all climate scientists – from those currently braving the harsh Antarctic winter, to those dealing with difficult questions from the media, to those who have been sitting coding for two days straight (or more!) – I salute all of you, for everything you deal with.

Going Viral: Some thoughts one week later

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Sunday, July 22, 2018, 9:31 PM BST. I put out a relatively simple tweet comprising of two NASA GISS global temperature anomaly graphics – one for June 1976, and one for June 2018. After listening to the media and meteorologists alike comparing and contrasting the current UK heatwave with that of 1976 (something which I had earlier written about here), I felt it necessary to put it into some global context: the planet as a whole is far warmer than it was in 1976 – meaning that regardless of the final ranking of the 2018 heatwave in the UK, it occurred with a different climate background. The heatwave, alongside record-breaking heatwaves across the Northern Hemisphere, is symptomatic of climate change. It has a different meaning in today’s world.

I did not in any way expect the response the tweet gained – with close to 14,000 likes a week later. Initially, I thought it might rile up a few ‘climate change deniers’ (I had a genuine interest in what might get said in response…) but after it surpassed by previous highest like/retweet count within a few hours, I knew something special was happening! I have no real idea of how far and wide the comparison went, as some didn’t relay any credit back to me for the original idea (e.g. a BBC News special “Feeling the Heat” which aired on July 26, and Met Office blog post using their HadCRUT data). Not that it bothers me – they are NASA’s graphics, after all, and I’m just happy to get a conversation going. Special thanks to Leo Hickman of Carbon Brief for helping me keep track of the various media appearances!

I’ve been looking at NASA’s GISS maps for years – the plotting tool on their website is a fantastic way to play around with climate data. Seeing a comparison like 1976 vs 2018 wasn’t surprising to me, but it occurred to me that the public don’t regularly see imagery like that – especially in such a relevant and meaningful way. It told a story. Telling the general public that the globe is X degrees warmer than it was 100 years ago, or showing them a line graph doesn’t really work – hence the success of my tweet and other novel visualisation ideas, such as the ‘climate spiral’ and ‘warming stripes’ by Professor Ed Hawkins – the original climate science viral sensation from the University of Reading! As I stated in the tweet thread, graphics like those I posted shouldn’t be surprising – global warming isn’t new, and the planet has been much warmer (relative to normal) than it is currently (try plotting February 2016 for a real shock).

Perhaps initiated by my tweet, or perhaps a coincidentally, the media – and scientists – quickly began widely discussing the relationship between climate change and the heatwaves across the Northern Hemisphere. The tweet seems to be the reason why the phrase ‘global heatwave’ gained so much use – I have seen it used before my tweet, but my use of that as a hashtag seems to have made it mainstream. It is not meant to suggest everywhere is under heatwave conditions – just that this heatwave is part of something bigger; that the planet itself is warmer than normal (i.e., a ‘heatwave’). It’s perhaps a bit of flippant phrasing which I can understand disagreement with.

However, whilst this has been the best-reported and most clear-cut example of linking climate change to ongoing weather, it did strike me that in some cases it was reported as though this was, in some way, new. A BBC News article from August 2003 (“Heatwave part of global trend”) could have been extracted word-for-word and used in 2018. The story then: a heatwave in the UK, but also deadly heatwaves around the world as global temperatures rose. 15 years later, and the story is the same. Yes, we have come a long way in 15 years in terms of our understanding of the climate, but the story is the same and the expectations are (broadly) the same. How long until it is accepted that the future we predicted is now happening? How long until we stop speaking of ‘heatwaves are expected to become more common due to climate change’? Climate change isn’t something we should continuously speak of in the future tense – it has happened and it is happening.

If you’ve read this far and are still with me, I added some of my ‘in the moment’ thoughts on July 24 to my first post on Reading’s Meteorology PhD blog site, “The Social Metwork”.

Right. What do I tweet next?

Heatwave Summers: There’s more than 1976 & 1995

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2018 has been a remarkable summer. On the back of the warmest May on record (since 1910) for the UK, we saw the 3rd warmest June (featuring the 2nd warmest daytime maxima) which was also the 5th sunniest and 9th driest (3rd driest for England). The first half of this summer has been the driest on record for the UK. Temperatures have remained consistently very warm, with localised regions seeing prolonged and sometimes record-breaking dry spells. Were it not for a wet spring, we might have more concerns than we already do about water supplies (with only United Utilities so far issuing a hosepipe ban). 2018 has yet to see a very hot spell, though that may change in the coming few weeks – climatologically the warmest time of the year (for example, the UK’s record temperature of 38.5°C was set on August 10th 2003).

But will this heatwave be remembered?

I pose this question because the manner in which this summer has been reported would seem to suggest we’ve only ever had one heatwave in the UK: 1976. At a push, maybe 1995 too. But the truth is, of course, far from that.

Even just last year featured a memorable heatwave. June 2017 saw 5 consecutive days of temperatures exceeding 30°C somewhere in the UK, with a peak of 34.5°C on June 21 marking the highest temperature recorded in June since…yes, you guessed it…1976.

Until this year, the driest first half of a summer was 2013, which also featured a 19-day streak of temperatures exceeding 28°C somewhere in the country during July (which was the 3rd warmest and 3rd sunniest). Yet, aside from the astute meteorological observer, no-one I speak to seems to remember it happening – something I find astonishing because of the contrast after the 2007-2012 spell of very wet summers!

Other remarkable summers have occurred in recent times. July 2006 is the warmest month on record for the UK, and set the warmest July maximum temperature record (later beaten in 2015). 2003 saw a severe heatwave across Europe which resulted in setting the UK’s all-time maximum temperature record of 38.5°C on August 10th, a month which went on to become the UK’s 5th warmest August. August 1997 was the 2nd warmest on record for the UK, only slightly behind 1995. And before 2006, July 1983 was the warmest month on record for the UK.

In terms of mean temperatures for the UK, 1976 is only 3rd (tied with 2003) with 2006 taking pole position. However, 1976 and 1995 are the top 2 in terms of maximum temperatures, followed by 2006 and 2003. Rainfall wise, the driest summers are 1995 and 1976, followed by 1983.

I can’t deny that the string of hot temperatures, and the truly “flaming” June of 1976, were incredible. The water shortages caused by the preceding hot summer of 1975 (even more forgotten, with a hotter August than 1976!) and dry 1975-6 winter, were historic. But other historic heatwaves have happened since.

So, will people look back and remember the dry and hot summer of 2018? Only time will tell, but the evidence of “forgotten” recent heatwaves seems to suggest it won’t get the recognition it deserves.

Perhaps it’s a generational thing.

Perhaps people don’t spend as much time outside anymore – as someone who’s outside a lot (aside from being a meteorologist) I have always noticed the warmer spells even in a poor summer.

Perhaps, because the summers preceding 1976 were so much poorer (the 1960s lacked anything that could be called a ‘heatwave’ summer), we’ve just become accustomed to warmer summers and there’s less of a ‘wow’ factor when a heatwave does come along.

Despite all of that, I’d like to think people will remember this summer due to England’s performance in the World Cup and how well it timed with the peak (so far) of the heatwave. If only we’d won it, then it would really be a magnificent combination!

I’ll close with this thought: has anyone ever said “Summer weather was so much worse when I was a child!”.

Thoughts upon finishing the MMet

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Yesterday (May 11), at about 10:50am, I completed my Master’s Degree in Meteorology and Climate (MMet) at the University of Reading.

The exam – Oceanography (perhaps not the most typical way to end a meteorology degree, but I guess it highlights the diversity of the subject).

The way I finished it? Ending a question on the thermohaline circulation with, “And with that, I’ve finished my degree!”.

It’s a surreal feeling when it’s a moment that’s been coming for the last four years. It’s been a long slog. Like everyone who studies meteorology at university, I can confirm it’s a tough subject – full of concepts and equations that (for me at least!) have required a caffeine addiction (thanks, Taylors of Harrogate) and a lot of head scratching to understand to the required level. From linear algebra and differential equations, to fluid dynamics in the laboratory, boundary layer fieldwork… and hours of programming. The Reading degree is thorough, to say the least. But it was everything I could have wanted, and more. I finally have the understanding of the atmosphere (and, apparently, the oceans as well!) which I so craved when I first became interested in the clouds above my head.

What’s worth more, though, is the understanding of the sheer scale of the atmospheric science discipline, and just how much I don’t know. The most challenging class I took was Advanced Synoptic at the University of Oklahoma (taught by Howie Bluestein, all-round meteorology legend and someone who can plaster the whiteboard with the semi-geostrophic equations and make the whole thing less daunting than it should be!). I’d probably show the notes I made in this class to anyone who thinks that meteorology is just about standing in front of a weather map saying it might rain tomorrow. Here’s a brief look at them:

Deciding to study the MMet degree at Reading was the best decision I ever made, and it’s opened up a world of opportunities for me – both here and in Oklahoma, where I spent my third year. I’ll be studying for a PhD in Meteorology from September, sharing my time between Reading and Oklahoma yet again (which I’m super excited about).

Thank you to all the staff at Reading and OU for making it all worth it, and for sharing your knowledge in a consistently entertaining and passionate way. Thank you to all my fellow students and friends, who sufferred and celebrated through the degree with me. And, thanks to everyone on #WxTwitter – I’ve learnt a great deal from all of you!

I couldn’t recommend the MMet strongly enough to anyone with an interest in the atmosphere. You won’t regret it!