Temperature



The cold wet August of 1912 and the Novarupta eruption

Figure 1 – Courtesy of Wetterzentrale

The coldest August since 1910 was that of 1912. It was both wet, cold and dull. At many coastal stations around the UK the sea temperature was higher than the air temperature. In the monthly weather report for 1912 the review of the month concludes by saying

Observers in various parts of the United Kingdom noticed in the rare intervals of fine weather the sky seldom assumed its ordinary blue tint, but appeared to be covered with a hazy film “producing grey whiteness of the unclouded sky, and extreme weakness of all sunshine”. A similar appearance was noted by several continental observers.

The mean temperature for the UK was just 11.7°C which is 3.26°C below the 1981-2010 long-term average. The mean maximum anomaly for the month was even lower at 3.94°C below average. Looking at the regional temperature anomalies (fig 2), the cold was across the board.

Figure 2 – August 1912

As well as being very cold, it was also very wet, especially in more southern regions, and particularly in East Anglia which saw over three times the monthly average rainfall (fig 3).

Figure 3 – August 1912

In fact August 1912 was and still is the wettest August in the entire EWP rainfall series that started in 1766 (fig 4).

Figure 4

As you probably noticed in the daily charts for the month (fig 1), August 1912 was a very cyclonic month as you can see in the Lamb Circulation types for the month (fig 5).

Figure 5

As regards the CET for the month, I can’t remember ever seeing a summer month as cold as this one (fig 6). August 1912 was, and still is the coldest August on record back to 1659, beating even the cold year of 1695 into second place.

Figure 6

Not only was it the coldest August on record, it was also ushered in the start of a three-month cold spell in central England, with a cold September (mean anomaly -2.5°C) and October (mean anomaly -2.4°C) to follow (fig 7).

Figure 7

At this point I would like to produce some statistics to show that August 1912 was also the dullest on record, but I can’t, the Met Office maintain that they only began measuring sunshine from 1929. The MWR comes to the rescue though, because it says about sunshine:

Sunshine was very deficient, a large number of stations situated in nearly all parts of the kingdom recording considerably less than half the average amount. In the Channel Isles and at a few places in the extreme southeast of England the mean daily duration ranged between 4 and 4½ hours, and was equal to about 30 percent of the possible. Over Central and Southern Scotland and at a few places in the northeast of England the daily duration was less than 2 hours; at Crathes, Glasgow and Eskdalemuir it amounted to only 1o percent of the possible.

What caused it?

Here’ a graph of 12 month rolling CET values for around that time, forget the date in the subtitle, another bug for the programmer to fix. I’ve overlaid the volcanic dust index events that were greater, or equal to 4, on the VEI on top of the line series, and as you can see the Novarupta event (VEI 6) looks like it may well have been responsible for global cooling that also affected our own CET series back in 1912 across, and fits well with the reports of a greyish white haze from the Monthly Weather Report for August 1912.

Figure 8

Novarupta

Figure 9 – Novarupta’s lava dome in July 1987

I had never heard of the Novarupta eruption until I started researching this article today. I never even realised it was the most powerful volcanic eruption of the 20th century, here’s what the Wikipedia article had to say about it:

The eruption of Novarupta in the Aleutian Range began on June 6, 1912, and culminated in a series of violent eruptions. Rated a 6 on the Volcanic Explosivity Index, the 60-hour-long eruption expelled 13 to 15 cubic kilometers (3.1 to 3.6 cu mi) of ash, 30 times as much as the 1980 eruption of Mount St. Helens. The erupted magma of Rhyolite, Dacite, and Andesite resulted in more than 17 cubic kilometers (4.1 cu mi) of air fall tuff and approximately 11 cubic kilometers (2.6 cu mi) of pyroclastic ash-flow tuff. During the 20th century, only the 1991 eruption of Mt. Pinatubo in the Philippines were of a similar magnitude; Pinatubo ejected 11 cubic kilometers (2.6 cu mi) of tephra. At least two larger eruptions occurred in the 19th century: the 1815 eruption of Tambora (150 km3 (36.0 cu mi) of tephra), and the 1883 eruption of Indonesia’s Krakatoa (20 km3 (4.8 cu mi) of tephra).

Figure 10 – Novarupta map: Approximate location of the June 6th, 1912 eruption. Ash fell on the town of Kodiak for three days, and although the town was about 100 miles from the volcano, it was covered with over one foot of ash which collapsed many buildings. Courtesy of Geology.com and MapResources.

There’s a interesting article on the Geology.com website about the eruption that you might find useful.

The latitude of the Novarupta eruption was just about perfect at 58° north for maximum effect across the northern hemisphere, as was the timing of the 6th of June to coincide with the cold months of August, September and October of 1912 in the CET series. I should imagine that the ash from the eruption would have taken at least a month or so to completely encircle the northern hemisphere and reduce the amount of sunlight. I am of course completely guessing that this was the cause of the cold August of 1912, I’ll have to spend some more time looking at NCEP reanalysis surface temperature data for 1912 to see just what affect it had on other countries across the northern hemisphere to completely be sure of my assertion.

Finally here are the daily CET values for the Summer of 1912 (fig 11), which I think says it all. This is one of the better articles that I’ve put together for my blog, I found little evidence of any link between the cold August of 1912 and Novarupta in any of my climate and weather books, and even though Philip Eden does mention the poor summer of 1912 in his book ‘Great British Weather Disasters’, he doesn’t make the link with the volcanic ash of Novarupta. August 1912 does get a short mention as the worst on record in the book ‘The Wrong Kind Of Snow’, but again no mention of why. So if you thought that August 2017 has been cool in its first ten 10 days, the mean temperature for the first 10 days of August 1912 was 2.5°C colder still.

Figure 11

Summer 2017 failed on the 20th of July

Figure 1

Temperatures in the summer of 2017 in the UK crashed on the 20th of July and have never recovered in the almost three weeks since it’s been since then. You can see clearly how the temperature has almost flat lined in the NCEP reanalysis data for the grid point 52.5° north and 2.5° west (just to the west of Birmingham), with almost all the 6 hour anomalies negative since then, negative (fig 1). I remarked in a blog only yesterday about how unusually flat the daily CET values had been since the 20th of July. Its probably all tied up with that ‘ribbon of high wind speed high in the atmosphere‘ that we like to call the jet stream.

Meanwhile in stark contrast to the UK, just to the northeast of Rome in Italy, at the 42.5° north 12.5° east grid point, things have been slightly different. A part from three short cold spells, the temperature anomalies there have all been well above average since early June (and before), with the recent heatwave this month clearly evident.

Figure 2

 

Coldest start to an August in 30 years

Figure 1

I notice that the latest provisional mean maximum daily temperature for the first eight days of August in Central England of 18.89°C (-1.38°C) are the lowest for that period since 1987 (fig 2). The 10 year average mean temperature for this period, has been on a downturn since 2000, and even the linear trend shows only limited warming since 1772 (fig 1).

Figure 2

A cool start to August

Figure 1

A cool start to August in most places, but particularly so across southern areas, with daytime maximum temperature anomalies typically 2°C or more below the long-term average for the first eight days of the month. The chart is from the mean maximum temperatures [06-18] for the 1st to the 8th of August 2017 compared with the 1981-2010 daily averages than I’ve calculated from the SYNOP records that I have (fig 1). I think the low value for St Catherine’s point is probably due to missing data.

Calvi and the sea breeze

Figure 1

It’s been an interesting week at Calvi in northwest Corsica weather wise. In the heatwave that’s been going on in that part of the world, there’s been a constant battle going on between the sea breeze from the north, and the foehn wind from over the mountains to the south (fig 3). The effect of the sea breezes arrival must be very noticeable at times, and must come as a welcome relief to the town (fig 1). It looks like the flip-flop between the two can happen at anytime of the day judging by the plot grid (fig 2), and the land breeze – sea breeze, must obviously be very finely balanced. Yesterday evening for example, the sea breeze which had set in earlier was quickly replaced by a land breeze that kicked in at 22 UTC and increasing the temperature from 26.3 to 31.6°C. The land breeze then failed early this morning at 02 UTC, and the temperature dropped again from 32.5 to 27.8°C, eventually the land breeze set back in at 10 UTC this morning as daytime heating cancelled out the sea breeze. I have marked out some other sharp fluctuations in the plot grid (fig 2).

Figure 2

The observing station at Calvi is located at the airport, in a valley a few kilometres to the southeast of the town itself (fig 3), with the Mediterranean sea to the north, and ringed by high ground to the south, east and west (fig 3).

Figure 3 – Courtesy of Google Maps

Cool out last night

Figure 1

Quite a cool night in places across the country last night under clearing skies and cool air for August (fig 2). Marked contrast between the coastal stations and the more rural inland stations as you would expect with SST around the coast of 16 or 17°C. Exeter with a min of 5.1°C and Portland 14.1°C is just one example (fig 1).

Figure 2

A cool night was well anticipated by the BBC, but it was a little colder than they thought in the south of Scotland, the west Midlands and Devon. They never can quite anticipate just how cold it can get at Exeter airport, with a grass minimum of just 2°C (fig 3), and the Met Office supercomputer just a couple of miles up the road.

Figure 3 – Courtesy of the BBC on the 5 August at 1pm

The crafty Met Office

Of course the Met Office and the BBC are very crafty, and since the demise of the magnetic weather charts, they now always quote a spot value for a particular time as the minimum temperature, rather than the true ‘minimum’ temperature for the whole night, which in my opinion is much more useful, and less misleading. It’s my belief that they don’t display a minimum or maximum temperature chart to hinder any verification of their forecasts, and prevent smart Alec’s like me from saying just how far their forecasts were out by.

Sitting in an English garden waiting for the sun…

Figure 1 – Courtesy of EUMETSAT

Summer seems to have taken a bit of a holiday and gone south this August, with cool, showery air over the UK, and clear skies top to toe across Italy again this morning (fig 1). I bet there would be many Italians who would be thankful to swap a day with maximum temperatures of 20°C that we will see in the UK today, with the 40°C many of them are likely to see again today in Italy (fig 2).

Figure 2 – WMO Block #16

Baking hot

The baking hot weather over southern Europe continues for another day with little sign in the short-term of any relief, here are the 12 UTC temperatures for that part of the world (fig 1), and as you can see that there are a number of stations already reporting 40°C or higher on it.

Figure 1

Alghero in Sardinia is one of the hottest places on the chart, with a temperature of 41°C at 12 UTC. This is a coastal site but these observations are from the airport which is a short distance inland, here are the temperature stats for Alghero for the last month (fig 2).

Figure 2

So today makes five days in a row that the temperature has exceeded 40°C. Here are this week’s plotted 3 hourly observations for Alghero (fig 3).

Figure 3

You would have thought than a 12 knot wind from 200° would have brought a cooling sea breeze into that part of Sardinia and cooled things down at the airport (fig 4), but of course there is very little in the way of gradient over the Mediterranean, so I suppose the low-level flow could be from more of an easterly point.

Figure 4 – Courtesy of Google

It’s not till this time next week before the hot air looks like it loses its grip in that part of the world, according to the GFS model (fig 5), and this hot weather will only exacerbate the severe and very serious drought conditions that are affecting a large part of Italy at the moment.

Figure 5

 

 

Today’s heatwave numbers

There are quite a few stations reporting air temperatures above 40°C, in today’s 12 UTC observations, right from North Africa, across Italy and into the Balkans.

Figure 1

Tropical Heatwave continues

Figure 1

The heatwave continued yesterday over much of central and eastern Europe, and was particularly intense over parts of SE France, Italy and the Balkans, with temperatures in excess of 40°C in places (fig 1). In the above chart of maximum temperatures for yesterday the temperature at Alghero in Sardinia reached 41.9°C. Yesterdays overnight minimum at Capo Caccia never fell below 30.4°C (fig 2).

Figure 2

I didn’t quite believe this one, because of course Capo Caccia is a cape that’s stuck out in the sea, but on closer scrutiny it does seem to agrees well with the hourly temperatures (fig 3). The station is at 204 M, so it’s not exactly on the beach, and may well explain why it stayed so warm overnight. Then it all came back to me that I’ve actually been to Capo Caccia, because at the bottom of a series of concrete stairs built into the cliff face, is a series of sea caves called Neptune’s Grotto, that my wife and I visited on our first holiday abroad in 1985, over 30 years ago!

Figure 3

Here’s a picture of Capo Caccia with its lighthouse that I never thought to capture in a picture back in 1985, perhaps because Kodachrome 25 was very expensive back then (fig 4). All I can imagine is that somewhere on the site is an AWS, it’s very similar to Berry Head in Devon, but a lot more dramatic.

Figure 4 – Courtesy of an unknown Italian drone pilot