This post will present evidence that strong tides were a primary cause of the December 5/6 storm that surged down the North Sea last winter. The first observation to be noted is the remarkable coincidence that all of the UK December storms coincided with maxima in tidal forces, as shown below.
The December 2013 storms. This slide was prepared by Roberto Madrigali and shows how each successive storm coincided with maximum tidal forces. The strongest tide of all coincided with the December 5-6 storm.
So now let’s look in detail at the first of these – 5/6 December storm. This first December storm also had the strongest tides of the year. The Met office writes the following description:
The first storm of 5 December brought very strong winds to Scotland and northern England, and a major storm surge affecting North Sea coasts. A week of quieter weather then followed, but from mid-December there was a succession of further major winter storms which continued into early January.
On the 3rd December a low depression system had already just passed north of the UK and appeared to be weakening. However for some reason it stalled and then strengthened on the 4th and 5th December while it descended south along the east coast of the UK. The associated storm surge caused extensive coastal flooding. This storm was very similar to the devastating 1953 storm which killed 300 people in the UK and over a thousand in the Netherlands. This experience led to the strengthening of coastal defenses and the eventual construction of the Thames barrage. This 1953 storm also coincided with a high spring tide and extensive storm surge.
Next we look at the evidence that it was these same strong tides that actually caused the storms. This evidence is based on the weather plots below shown below which track both the development of the storm and changes in the Jet Stream over the 3 day period beginning on the 4th December. All these charts are taken from meteociel.fr(2). These charts have been overlaid with arrows resulting from my calculations of the tractional vector tidal forces at the times shown. For comparison a deep red arrows correspond to a tidal acceleration of about 0.3*10-6 g.
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By midday on 4th December a depression had just passed over the UK and stalled to the North East of Scotland. The Jet Stream lay further south looping over the UK. The tides were increasing rapidly and strong tractional tidal forces were concentrated over northern polar latitudes tending to drag air south. These tidal forces are always changing as the earth rotates but during this period the moon’s position was over the southern hemisphere causing asymmetric tides over the UK with one major tide effecting polar air masses every 24 hours. The net effect was to drag air down in a South-Easterly direction.
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One day later on the 5th December the depression had now deepened and turned downwards towards Scotland bringing very strong winds to the north east coast. Tides still remained very high but now the Jet stream shows a southerly kink pulling to the east of the UK with very strong velocities. The arrows show the focussing effect of the tidal forces acting directly on the Jet Stream. The storm is now well underway and moving down the North Sea.
The Jet Stream remained strong for the next 24 hours and lay further south than is normal during the winter period. At the same time very cold polar air was drawn down over the east coast of the US.
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By 6th December there was a strong easterly flow of the Jet Stream driving the storm down the North Sea. This was then exacerbated by high maritime tides in the North Sea to create a storm surge similar to that in 1953. However this time there was far better warning, flood protection and preparation, but still hundreds were evacuated from their homes. By midday on the 6th December the storm center had moved off further to the east of the UK still leaving strong north easterly winds.
The BBC reported the effects of the this first storm of the winter as follows:
The tidal surge which hit the east coast of Britain has been described as the “most serious” for 60 years.
Thousands were forced to abandon their homes as tides in parts of the North Sea reached higher levels than the devastating floods of 1953.
Flood waters have receded in many areas but authorities are warning that high tides later on Friday could cause further damage.
Maxima in spring tides only last a few days as the moon rapidly moves out of phase with the sun during its 28 day orbit. Possible effects on weather at high latitudes are stronger in winter because a) there is often a strong asymmetry between the two tidal bulges and b) there are far less thermal tides in polar regions due low to zero solar radiation.
Horizontal tidal forces may appear to be weak because they are about 2 million times less than the earth’s gravitational force. However there is no opposing force parallel to the earth’s surface. It is these tractional forces that generate the tidal bulges in the oceans and coastal tides. They act over vast areas and their effects are strongest at high latitudes.
In summary the first major storm of lhen ast winter on 5-6th December corresponded to the largest spring tides of the year. These tidal forces were strongest north of the Jet Stream and appear to have drawn down a passing depression and in the process strengthened it into a major storm hitting the east coast of the UK.
Future posts we will look at the other UK storms during the winter of 2013/14 and investigate whether they too show any causal connection with changing atmospheric tides.
1. Roberto Madrigali was one of the first to propose a connection between lunar tides and weather.
2. All jet stream images and weather maps are produced curtesy of meteociel.fr
3. I am not a meteorologist !