I aim to demonstrate in this series of posts that ever changing gravitational tides influence the flow of the polar Jet Stream thereby changing weather patterns at high latitudes. Such effects should be included in global circulation models to improve medium range weather forecasting.
Previously I described a proposal from Roberto Madrigali that tides acting on the Jet Stream affect high latitude weather (North and South). Robert Currie and others have reported long term coincidences of drought with Lunar Cycles (1). H. Yndestad reports lunar cycles in Arctic climates (2) and Li & Zong have reported lunar induced variations in global wind speed (3). Over 3000 years of folklore also links the moon to extreme weather on earth. Is all this just nonsense, or could atmospheric tides really be responsible for much of our weather in Europe and North America?
I decided to look into this in more detail and have spent the last few days calculating the horizontal tidal forces acting on the earth. To do this I used the JPL ephemeris to calculate the net tidal vector of the moon and the sun acting on the earth, and used the formulae derived previously to determine the horizontal tractional force for a given angular separation from the central net vector. In a north south direction this angular separation is the same as latitude. It is these tractional forces that cause the ocean currents that generate the two familiar tidal bulges. Although the forces are about 10 million times smaller than gravity they act perpendicular to gravity and cover vast regions of the earth. They also generate measurable winds in the upper atmosphere especially near the poles. The largest tractional forces occur at the extremes of latitude and can vary dramatically from month to month and year to year as the relative positions of the earth moon and sun change. The rotation of the earth then causes the familiar ~twice daily high tides. Their effect on the atmosphere is yet more complex also generating a small torque through the Coriolis effect.
The hypothesis presented here is that maximum tides induce meanders in the Jet Stream and mixing of warm and cold air masses which then trigger storm systems. I estimate that the horizontal force acting on a 1000km long stretch of the Jet Stream to be roughly half a billion newtons or the equivalent of 10,000 metric tonnes weight. My calculations for the year 2013/14 are shown below.
The animation shows a calculation of the horizontal tidal forces acting on the oceans and atmosphere as the moon and earth orbit both each other and the sun from 1 Oct 2013 until 30 September 2014. The daily variations are shown for a fixed longitude -30 deg. and show the maximum of either the lunar facing or the opposite tide. That is why the central bulge stays above the equator. Note that a series of severe storms hit the UK on Dec 5-6, Dec 23-24, Dec 26-27, Dec 30-31,Jan 3-6, Feb 4-5, Feb 12-14. This winter was a period of especially strong tides and this summer will see 3 super moons. The animation shows that the strongest tidal forces must affect the polar Jet Stream zone. Rapid changes in these tidal forces generate differential torques acting on the Jet Stream as the earth rotates by coriolis effects. Did these torques then trigger the destructive UK storms this winter ?
Meanders in the Jet Stream caused the extreme cold weather across North east America and also placed the UK directly in the firing line for Atlantic storms. Warm air sucked up from the Gulf created unstable conditions for storms to develop. The trigger for these storms seems likely to be rapid variations in atmospheric tides at the critical latitude. Judge for yourself.
Now we look more into the effects of the 18.6 year cycle, which is reported as being responsible for changes in rainfall across China and North America. In the following animation I just follow the lunar facing tide to show how strongly asymmetric the tides can get.
June 2006 saw a major lunar standstill. This is when the moon’s orbit reached its maximum declination of 28.5 deg. The tidal bulge moves from a latitude of -28.5 deg to + 28.5 deg in about 14 days. This animation shows the tractional tidal force field centered on a longitude of -30 deg. Only the lunar facing tide is shown. In reality there are 2 high tides every day as the earth rotates through the lunar facing tide and its mirror on the earth’s opposite side. Do such large changes in tidal forces tweak the Jet Stream mixing polar air with warm air thereby affecting weather systems ?
Ensemble model based forecasts are accurate over short terms. Would these be improved if tidal forces on the atmosphere were included? The evidence is that the answer is quite probably yes. Shown below is the 2 week prediction for London weather from today (August 4) by the Global Forecast System Ensemble of models prepared by Roberto Madrigali. A period of instability is expected exactly coincident with the largest “super-moon” tide this summer. Lets see what happens over the next 2 weeks.
We often hear the analogy that because our weather is chaotic, storms can be generated just by the flapping of butterfly’s wings. Well there is a prime candidate for that butterfly effect – the ever changing tides acting on the northern and southern Jet Streams! Perhaps its time now to take the moon more seriously !
1) Robert Currie, Periodic (18.6-YEAR) and cyclic (ll-YEAR) induced drought and flood in Western North America, JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 89, NO. D5, PAGES 7215-7230, AUGUST 20, 1984
2) H. Yndestad, The influence of the lunar nodal cycle on Arctic climate, ICES Journal of Marine Science, Vol 63,3 P 401-420.
3) GuoQing Li, HaiFeng Zong, 27.3-day and 13.6-day atmospheric tide, Science in China Series D: Earth Sciences September 2007, Volume 50, Issue 9, pp 1380-1395