I noticed this interesting article about polynya on the Phys.org website (you might what to add this to your favourites because it looks a great site) that might interest some of you out there. I was thinking, it’s only because the upwelling of warm water occurs under an ice sheet that we realise that they’re happening at all. They must happen all the time in the worlds oceans, but we just don’t see them, apart I suppose from anomaly charts of very sensitive SST satellite sensor data.
The Guardian must have known they were onto a winner with this article from the great Michael Mann about Hurricane Harvey, who states categorically in the article that Hurricane Harvey was made more deadly due to climate change (fig 1). I wonder just how many comments this article will attract?
Michael Mann states that one of the main factors why it was more deadly was due to higher than average SST in the Gulf of Mexico. So I thought that I’d have a quick look and see what the latest anomalies were across the North Atlantic, Caribbean and Gulf of Mexico to see if what he was saying was correct. Courtesy of NCOF, here are the SST (fig 2), on which I’ve drawn a very approximate track for the path of tropical cyclone Harvey, which as far as I can see from the NHC records, sprang into life as a cyclone at around 54° west on Thursday the 17th of August. Harvey has had a very fitful life, it ‘died’ as a tropical storm as it entered the Caribbean late on Saturday the 19th, before being reborn again as a tropical depression on Wednesday the 23rd as a tropical depression in the Bay of Campeche, the rest as they say is history.
All that you can say about the SST anomalies along the path of Harvey was that they were generally in the slightly warm category +0.5 to +1.0°C for much of its life. Interestingly these ‘higher’ than average SST in the Caribbean didn’t seem to stop it from dying for four days though, and it wasn’t till it entered the Bay of Campeche that it was reinvigorated. Because the SST anomalies in the above chart (fig 2) are in a bit of a turmoil after the passage of what was a category four hurricane, I have included an extra chart (fig 3) from the 23rd and before the waters got churned up. The SST anomalies in that chart show anomalies between +0.5°C and 1.5°C, generally across coastal regions of Texas extending eastward to Florida, with negative anomalies of the coast of the Yucatan peninsula.
So what caused Harvey to reform and quickly turn nasty as she entered the Gulf of Mexico? I personally don’t think it was ‘more deadly’ because the waters of the Gulf of Mexico were slightly warmer than average, I think it was more to do with the atmospheric mechanics that were driving Hurricane Harvey, of which the SST, although important are just one factor. Anyway now that I have provided one piece of the evidence you can make your own minds up.
Not surprisingly, the sea surface temperatures in the Mediterranean, are generally well above the average for this time in August, no doubt helped by the recent hot and sunny weather of the last week or so, with anomalies of +3°C above average in parts of the Adriatic, and off the Costa Calida in Spain. There’s also a curious tongue of colder water that seems to project westward into the northern Aegean sea. The SST in the coastal waters around the UK, are above average in the west and the southeast, but cooler than average in the southwest, and along the east coast from Fraserburgh down to the Humber.
July continues it a mood of being mobile and often quite cyclonic at times, in fact that’s how it’s been since the end of May across the British Isles, as this graph of zonality shows (fig 2). The simple answer of why has it been so mobile is that mean pressure in the first three weeks of July 2017, has been 8 hPa below average across Baffin Island, and there has been a band of lower than average mean pressure extending westward across Iceland, before arching around Scandinavia and into eastern Russia. South of that the mean pressure across much of the central Atlantic has been higher than average (+3 hPa), and between the two the W’SW gradient has been tightened.
It’s very likely that this is all driven by temperature of the atmosphere at all levels. The SST is well below average around Baffin Island (-4°C), and the central mid Atlantic remains generally cooler than average (-1.5°C), although there is now a band of warmer water (+1.5°C) extending westward from America at ~38° north. It’s interesting to see the SST down the east coast of Greenland being colder than average, probably from fresh water from the summer melt of the glaciers.
This may help explain the very intense lows for July’s that we are seeing. Here’s the forecast for this Wednesday (26 July) from the Met Office, which shows an intense low of 973 hPa low at 19° west, throwing a frontal system across the British Isles. This low in turn, will spawn a series of secondary lows that will dumbbell around it before the week is out maintaining the mobility.
Finally, I thought that I would look at a virtual barograph that I would sit at 57.5° north and 22.5° west (where hopefully it won’t get too wet). As you can see (fig 4) the anomalies there have been mainly negative there for long periods, and this is in an area of low pressure anyway and generally close to where the Icelandic low is found on mean pressure charts.
No change in the SST in the central Atlantic this month (fig 1), any changes in SST would be very slow anyway, but when comparing it to last September’s chart (fig 2) there is little difference apart from the appearance of a massive negative anomalies at 43N 50W, and the almost complete disappearance of the intense warm clusters south of Nova Scotia in last years chart. If these charts from NCOF are accurate, then I wonder what’s responsible for producing that massive area of violet-coloured negative anomalies SW of Newfoundland? You can imagine that they are mostly responsible for fueling the cooling further that s occurring further east.
Chilly down the east coast of England today with a moderate or fresh northeasterly straight of a relatively cold North Sea (fig 2) keeping temperature at around 9 or 10°C (fig 1).
Meanwhile in comparison, the west of Scotland has seen temperatures as high as 20°C in some places this afternoon, on what’s been another generally sunny day in the north, although with a bit of cirrus (fig 3) and a keen breeze at times.
I thought that I would compare changes in the North Atlantic SST by using two charts, one from the 14th March 2017 (fig 2), and one from the 13th of March last year (fig 1). It looks to me that in the last year sea surface temperatures seem to have warmed by 1 or 2°C in many areas where the North Atlantic has influence. The cold pool that has been resident in the central Atlantic for so long, now seems to have shrunk and become less well organised as it once was. Waters around the British Isles and for much of the North and Norwegian Seas have predominantly positive SST anomalies. I have no idea what the current SST setup in the Atlantic might mean for the weather in our part of the world for the rest of this year.
Fresh doubt has now been cast into the ‘pause’ in global warming after the release of a study in which it was found that SST from ocean buoys have been underestimated for the last 20 years. Interestingly the report says that the NOAA ERSST series used in their global temperature series was correct with its much faster rate of warming than the HadISST series with its colder bias used in the CRUTEM4 global temperature series from our own Met Office.
The Met Office slant on things
The Met Office don’t seem to want to dwell too much on the comments of Zeke Hausfather, the new paper’s lead author in their reaction to the paper on the Met Office Blog (fig 2). They seem to be taking a more pragmatic view on the various biases involved in the ways of measuring SST that they use in constructing their own HadISST series, and the differences between it and the NOAA ERSST series. Apparently they hosted an international workshop in 2015 about this very subject, but are still waiting for the results of a peer-reviewed paper before
adding a fudge factor implementing any changes.
You really couldn’t make this up! It looks to me like a pretty sneaky way of getting rid of the pause and boosting global temperatures in one fell swoop to me – and I’m an agnostic! I can imagine this causing a massive storm in the global warming debate during 2017.
As regards finding an alternative and accurate method of measuring SST from ships, why don’t they simply trail behind the ship a thin cable with a weighted temperature sensor at the end of it (similar to the trailing earth cable that you used to see on cars years ago)? Surely in these days of high-tech, someone could develop an accurate sensor and wireless transmitter that could be towed behind a ship. Perhaps that idea has been discounted because the wake left by the ship could minutely increase the SST.
It’s no wonder that there are moves afoot* to update the nursery rhyme the “north wind doth blow”
The North wind doth blow and we
shallmay possibly have snow over high ground in the north,
And what will poor robin do then, poor thing?
He’ll sit in a barn and keep himself warm
and hide his head under his wing, poor thing.
Take a look at this morning’s 06 UTC synoptic chart (fig 1) in what is a classic northerly just to see what I mean.
Have a look at the plotted observations from Lerwick (fig 2) for the last 24 hours or so, and even with a partial 1000-500 hPa thickness of 5209 M in the midnight ascent there, the wintry showers have not managed so far to put down a covering there. And yes, I do know that there are multiple severely contorted occlusions in the UKMO analysis, but then again when aren’t there?
The main reason why a northerly is not as cold as it used to be apart from the fact that global temperatures are that bit warmer than they were 40 years ago, is all down to the temperature of the ocean between here and the pole. At the moment if you trace the trajectory back north and then northeast across Svalbard (fig 3) you’ll see how the SST anomalies en route are all positive and as high as +3°C or more.
Not only that the sea ice at this time of year has not reformed for a huge section of the Barents sea east of Svalbard (fig 4), as it hasn’t done for the last few winters in that area. That in itself allows the surface temperatures to be around 20°C warmer than they would have been over pack ice.
Classic northerlies are not that common, and are usually very fleeting affairs, but to whet your appetite I did find one from the 15th of January 1981 in my archives (fig 5), although it’s a little bit west of north, it did have a bit more bite than the one that just ushered in 2017. It would be interesting to see some research done in this area, just to see how cold northerlies may have been modified in the last 40 years, unfortunately I don’t have access to the kind of observational and climate data any research like that would require.
*As I’m sure you realised I made that line up in the first sentence for the sake of a punchy title!
The stage is now set for the New Year of 2017, with ocean temperature anomalies in most of the world’s oceans starting the year in a decidedly positive state, even though the El Niño event of 2015/16 has now finished. Figure 2 for example shows the latest North Atlantic Ocean SST, and the cold anomalies that seem to have been around for so long in the central Atlantic at around 50°N and 40°W are now much reduced in size and squeezed further north. The other thing to notice is the exceptionally warm anomalies of +3°C and +4°C wrapped around three sides of Svalbard in the Arctic Ocean, and to a lesser accent in the Denmark Straits between Iceland and Greenland.
Figure 3 is a detailed look at the SST along the eastern seaboard of North America in more detail, and that never-ending stream of anomalously warm water that’s spilling into the Western Atlantic as if someone’s left the warm tap on and forgot about it.
Don’t mix up these SST anomaly charts with the Gulf Stream (or more accurately with the North Atlantic drift), SST anomalies and ocean currents are not the same thing, but it does look like the Gulf stream has pushed bodily further north, and the cold Labrador current that runs south along the North American coast does seem to be having a torrid time of it maintaining the ‘cold wall’ south of Nova Scotia.
There are a number of different methods to fix the exact position of the Gulf Stream and they are:
- The Global Real Time Ocean Forecast System model [RTOFS]
- The Navy Coastal Ocean Model [NCOM]
- The Naval Oceanographic Office [NAVO] Gulf Stream analysis.
The position of the north wall of the Gulf Stream is estimated from the 12°C isotherm at 400 meters of the various global ocean models, but the NAVO Gulf Stream north wall is estimated by analysts using satellite AVHRR SST, ship and buoy data. Figure 5 shows the results from the three methods, and as you will notice none of them align with the SST anomalies in figure 3.
Figure 6 shows the strength of the Gulf Stream at the moment, and it looks pretty healthy, moving along at around 3 knots. The OPC site is not one you may visit that often, but is very useful nonetheless. So we can keep on hold any thoughts of any ‘Day after tomorrow‘ scenario for the time being.