Unseasonably Cold April Weather in UK

UKMO climate information for April give average temperatures for Kent at 12-13 ^{o} C for coasts and more inland.

Current, April 2016, temperatures are several degrees lower.

We should be used to variability in this part of the world and unseasonable weather is the norm in the UK.  What would we talk about otherwise?

The physical processes of the atmosphere mix cold air at the pole with hot air at the equator with the overall aim of evening out the temperature everywhere.  Atmospheric thickness between standard pressure levels is the way the average heat content of the atmosphere is represented by meteorologists.  Current situation is indicated in the featured image above.

Blue is thin, dense and cold.  Orange is thick, rarefied and warm.  One rule of thumb says that anywhere on the blue side of the white 528 line is subject to greater than 50% probability of snow/sleet in any precipitation.

Current UK weather is currently subjected to a cut off area of cold air being mixed down from the pole: meteorologists call this a cold pool.

Weather is a zero sum game: if there are losers then there are also winners.  Note that Russia has relatively warm air being mixed north.  Anyone to the north of Norway (North Cape to Murmansk) is enjoying unseasonably warm weather.

Tornadoes and Storms hit Central USA, 26 Apr 16

A vigorous storm brought tornadoes and massive hail stones the central USA yesterday, 26 Apr 16.

Cloud top pressure, courtesy of EOSDIS, computed from satellite imagery shows pressure of highest cloud visible to the sensor; the lower the pressure the higher the cloud.

Desktop meteorologists can get a quick view of the tornadoes and convective storms that hit central USA yesterday, 26 Apr 16, by using NASA’s EOSDIS presented as the featured image to this blog.  The purple mass in the top right hand area of the picture is very high cloud associated with this active storm system.

Visual imagery is presented below.

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EOSDIS Satellite 26 Apr 16

A look at the wind flow at 250 mb /30,000ft ish, using the Earth website, shows the region overlain by the exit of a powerful jet stream.  Mathematical dynamics predict this to be aan area of strong divergence the result of which being the air is literally sucked up through the atmosphere from the surface causing these vigorous storms.

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250mb flow 26 Apr 16

Heat Wave in India

Current news reports present fears of deaths in the heat wave that currently bakes the sub continent.  Dark pink/maroon on above image (Earth website) indicates maximal temperatures above 40 degrees Celsius.

India’s hottest months are usually May and June.  Weather reports indicate that some areas have the highest April temperature since 2006.

India experiences a wide range of weather and climate across her vast and varied landscape but is mainly subjected to a tropical regime.  The seasons follow the pattern of winter in January and February, summer in March to May, monsoon rains in June to September and a post monsoon period from October to December.

China wants ships to use Arctic routes

This Reuters release caught my eye.  One economic benefit of climate change is the possibility of cheaper shipping routes between China and the Atlantic.  It is, perhaps, a small positive in an impending global disaster.

“China wants ships to use faster Arctic route opened by global warming.”

There are some problems though.  The Canadian section is claimed as ‘Internal Waters’ and the map shows why.

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North West Passage

Sea ice still extends over these waters in winter but the National Snow and Ice Data Centre reports on 28 Mar 16, that ‘The Arctic sets yet another record low maximum extent” … of sea ice.  So this story will be a theme in Geopolitics in the future.

EOSDIS sourced imagery for 20 Apr 16 shows the area north of Alaska to be fast with sea ice at the moment, so no shipping possibilities on this route at the moment.  (Polar view, so north is towards the top right hand corner.)

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Polar Sea Ice – MODIS via EOSDIS, 20 Apr 16

 

 

The same area, without sea ice overlay gives an impressive view of the ice flows even if the perspective of the polar regions makes a good featured image to this blog.

 

Saharan dust over the Mediterranean near Tripoli

The 18th of April 2016 sees a minor dust plume event over the Mediterranean near Tripoli.  The satellite picture from NASA’s EOSDIS is beautiful and shows quite a lot going on here.

In fact a depression is forming in the Gulf of Gabes (Tunisia) and it is this weather system that is driving the wind here.  As a small scale feature it is not well represented by internet available NWP and is very much on the edge of UKMO Atlantic analysis.  No low pressure is registered here until 20/4/16.

The dust wind on this picture would seem to indicate that this is a significant event in the location though.

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UKMO analysis 194/16
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UKMO analysis 20/4/16

Are recent storms the consequence of climate change?

This is always a hot media topic when we experience severe weather.

Since weather is the result of the Earth system trying to breakdown temperature gradients between equator and pole, it does not follow that and overall increase in global temperature will lead to more vigorous weather.  Downhill skiers go fast because of the gradient they ski on, the same gradient could be found high in the mountains as well as near the valley bottom.

Sadly, the issue if complex and not understood fully yet.

There is no school maths correlation equation:

y=mx+c

with y=storm\ intensity and x=climate\ change .

It was never going to be that simple yet byte size media demands such simplicity.  Contemplation of the equations of dynamics on the surface of a rotating sphere subject to chaotic dynamics make this unsurprising.  Computed calculations use curtailed floating point numbers, numerical weather prediction  cannot even work with true values for irrational numbers like \pi and e and the departure from such values could trigger a ‘butterfly effect’.  Sometimes a better maths and science education is required to understand how much we don’t know.

Recent work has been done to try and define the meaning of questions and develop a framework for answers:

http://www.nap.edu/catalog/21852/attribution-of-extreme-weather-events-in-the-context-of-climate-change

and

http://link.springer.com/article/10.1007/s40641-016-0033-y/fulltext.html

As an operational meteorologist and synoptic weather watchers, I warm to Shepherd’s ‘storyline’ approach to analysis.   Successful application in this area would lead to communicable cause and effect discussions.

The conclusion on the question posed, for now, is that we have low confidence in ‘Understanding of physical mechanisms that lead to changes in extremes as a result of
climate change’ as well as in sufficient ‘Quality/Length of the observational record’ to make the judgments anyway.

Anthropomorphic climate changes is accepted, but this particular question remains unanswered.

 

 

Tephigram or Skew T log p diagram

A whole lot of physics happens very quickly in meteorology and nowhere more so than in understanding the output of a weather balloon.  The basic measurements which are plotted are temperature, dew-point temperature and pressure but these are plotted on a complicated graph with many background curved lines.  These diagrams are often call ‘Tephigrams’ (in UK) or ‘skew T log p’ graphs (US).

Much calculation happens on top of the basic measurements and an example is given below.

160414Tephi1

The basic idea is to compare the measured atmosphere with a theoretical one and then to deduce whether displaced or heated air will rise (giving cloud and rain) or fall giving sunshine.  Behind this is the assumption that heat energy is not added or taken away from a region of air as it rises or falls, that is to say in scientific terms that these processes are ADIABATIC.

The laws of thermo dynamics tell us that change in heat leads to a change in temperature and work done in terms of expansion of contraction.  This complicated equation leads us to predict how the temperature should change with height.  The conclusion is that the rising air should cool in such a way that it’s graph follows the ‘dry adiabat’ (see diagram below).

When air becomes saturated (clouds form) latent hear is released and thus cooling is reduced.  When this is the case the graph should follow the ‘saturated adiabat’ (see diagram below).

160414Tephi2

The diagrams I am using on this blog compare the actual graph of the weather balloon with these theoretical lines.  If the theoretical lines lie to the right of the actual lines then there is instability and trouble with heavy showers and cumulonimbus clouds.

The extent of the trouble can be eyeballed by judging the area between the theoretical atmosphere and the actual atmosphere because areas of these graphs indicate energy.

Going back to the example diagram above, the blue area indicates that there is much instability and the potential for heavy showers.

spiral low near Greenland, 8 Apr 16

Eyes in the sky, courtesy of Dundee Satellite Receiving Station bring this image of a spiral depression near Greenland.

Such perfectly represented spiral lows happen when the vortex is present through all layers of the atmosphere: surface streamlines as well as wind aloft trace out the same pattern circular pattern.  This is often not the case in the mid-latitudes.  See following images from Earthnullschool which show that the surface low is located at the same position as the upper low.

The trailing cold front has a marked wind veer on it.

UKMO analysis for same day follows, which shows the somewhat complicated structure of the frontal system.  Bands of airflow are sucked up from the south and gradually wind upwards and around the vortex thereby mixing warm northwards.  There is a noticeable change in air mass because behind the front we can see convective cells in the polar airflow which pours down from the Davis Straits between Greenland and Canada.

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Spirals, and in particular logarithmic spirals often occur in nature.  The dynamics are complicated here so there is no simple equation; circular motion on the surface of a spinning sphere moving in an elliptical orbit.  There seems to be an undeniable approximation to the following.

160412LogarithmicSpirala1bthreequarters.PNG