## Monday 11 May 20 – Cumulus and Cumulonimbus

Herne Bay and Reculver.  Cold, near gale force wind with good sunny spells but some showers too.  Featured image shows cumulus with blue sky to the left but the onset of a shower to the right.  Note the reduction of visibility under the shower and the loss of a hard horizon.  I have no image of the vertical extent of the cloud but there are strong gusts and showers, so … cumulonimbus.  In between the showers are smaller cumulus clouds, but always in a cold blast.

This bitter north easterly across the North Sea has reset the seasons back to winter after some summer like days last week.

The satellite image for the same time shows a classic pattern of deep convection with separate convective cells dappled in the flow.

## September 2019 UK Weather Headlines

Source: UKMO Climate Summaries and Wetterzentrale Archives

### Summary

September 2019 started and ended with an unsettled westerly flow of fronts and depressions but enjoyed a more settled, high pressure dominated, spell in the middle. Slightly warmer than the long term (1981-2010) average, with a little more rain and sunshine than normal.

### Averages

 Mean Temperature 13.1 °C (0.5 °C above average) Rainfall 127% of average Sunshine 115% of average

### Extremes

 Max Temperature 27.7 °C Weybourne (Norfolk) on the 22nd Min Temperature -1.6 °C Aboyne (Aberdeenshire) on the 8th Max Rainfall 59.4 mm Fontmell Magna (Dorset) on 24th Max Wind Gust 61 kt (70mph) Baltasound (Shetland) on the 15th

## 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:

$latex y=mx+c &s=2$

with $latex y=storm\ intensity &s=2$ and $latex x=climate\ change &s=2$.

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 $latex \pi &s=2$ and $latex e &s=2$ 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:

and

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.

## 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.

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.

## Airbourne Desert Sands Mark Out Cold Front in Eastern Mediterranean

desert sands blow out of Africa on a conveyor belt of air ahead of a cold front

Cold fronts are normally identifiable from their cloud signature on satellite imagery.  Of course, air mass boundaries can exist without condensation: density changes and air flows can exist without clouds particularly in dry and hot air.  Summer front can cross the UK with just low strato-cumulus.  In the Mediterranean, cloudless density boundaries one day give potential for fierce thunderstorms the next.

The 23 Mar 2016 was a case in point.  Over the Eastern Mediterranean we note a conveyor belt of air dragging sand northwards from the African deserts.  No clouds but a cold front none the less.