Moon winds

“Winds rise at the times of the rising of the Sun and the Moon. If the Sun or Moon on its rising cause the wind to drop, it increases afterwards its force”.

- ‘Weather Signs’ by Theophrastus 335BC.

In February 2001 it occurred to me that the tide of the air may behave in a similar fashion to the sea tide. As the body of air above the horizon ‘went out’ it must hasten, as water does, and like water there may be less air above horizon and of lower height when the air tide diminished.

I resolved to prove the atmospheric tide if possible; and perhaps shed light on two major unsolved air crashes in NZ’s history, the 1963 NAC 21-death tragedy in the Kaimais and Ansett 708’s fatal crash in 1995 in the Tararuas.

Archival hourly wind-direction and wind-speed at a location with no hills to alter it and unaffected by the seatide (e.g. Hamilton), plotted against moonrise and moonset times would tell me if wind altered during the hours of moon rising or setting. Cause and effect could then be inferred and could show that air was tidal.

Initially I plotted 3 months of NIWA data for Hamilton from January 1st 2001 through March 31st 2001 covering 206 moonrises and sets. In all but 10 cases the wind daily alteredmore during and only duringeach moonrise andmoonset hour.On some occasions there was a complete lull just for that hour, some showed a new east/ west alignment just over that hour, some a decrease or increase in wind speed just over that hour, some a complete wind direction reversal in that hour and some showed an hour of variable confused winds. 

Each if the three months started with an air-speed increase at moonrise, then midway through the month this pattern reversed. The influence of moon on wind seemed established. I then looked at the two plane crash timings and they revealed the same results. 

Ansett 708 crashed in the TararuaRanges 16km east of PalmerstonNorthAirport, on June 9th, 1995. Initial moonset on 9th was at 0337hrs, wind speed 6.1m/s, and 24 hours later the next moonset was 0300 on 10 June, wind speed 3.6m/s. Midmoon directly underfoot was at 9.04am. The crash happened at 9am. In the hour prior to the crash the wind had increased in speed by 40%, the northerly wind had swung 20deg further to the west and exactly at the crash time switched back to north again.

Later that day moonrise was at 1431hrs, with wind-speed reaching 13.8m/s, more than double the speed at previous moonset, with the day’s velocity peak coming at the time of moonrise.  The moonrise itself held wind well to the west and on the following moonset it returned to a northerly aspect. Immediately after the next moonset on the 10th the wind switched to blow from due east. 

Similar results were obtained for the NAC crash. There was a two-fold increase in wind speed for the mid-moon position and another, almost as big increase on moonrise. When the crash occurred the wind had only just increased by half as much again. It was later that I discovered Theophrastus’s repeating of Aristotle’s observation 2300 years ago.

Anyone who races modern yachts will report that on full moon day the anemometer spins at a fast rate, but sails may frustratingly, not fill, necessitating extra sail, yet on other days with a same wind speed, there may be good billowing. Whilst the volume of the air is subject to changes, air of varying densities may still blow at the same speed. 

When the moon is full, the air density is at a maximum, because of the moon’s gravitational pull on the atmosphere. But as the full moon does not rise until sunset, the daylight hours of a full moon time will provide minimum air density because the air-tide is ‘out’. At midday of a full moon the moon is on the opposite side of the earth.

Much wind lore tied to the moon’s ever-changing declination cycle of approximately 27 days has been preserved. Airflows are pulled by the moon’s gravitational force, in the direction the moon is travelling. The moon moves 13 degrees per day around earth, attempting to drag weather systems eastward, and either north or south. The moon pulls from different points on the 27-day declination cycle, from SW to the NE, from NW to SE, and to the E.

Wind is caused by moving differences in masses of air. Where pressure is high air will move outwards to where pressure is lower. Pressure differences are created by the moon travelling between hemispheres, shifting ocean volumes that switch ocean currents and air-mass and creating temperature differences which help monitor when rain may form and fall.

Air-flows are not necessarily wind, but are potential for wind. Actual wind is monitored by local features, hills, bays and plains. The sea’s effect is by friction at interface of water and air, causing air to move with surface currents, which is why the wind is observed to change when the tide turns. The turn is also when rain may be dislodged.

Willis Eschenbach notes that before full moon, the moon wind is always an east wind. After full moon the moon rises at night, so during that time the moon wind is a west wind. After full moon, the west wind at moonrise opposes the underlying east wind, and is seen as a brief period of calm around the time of moonrise. But if the underlying wind is from the west, the wind at moonrise will reinforce that west wind and lead to a brief gusty period around moonrise.

On some pleasant day you may be out walking and suddenly notice trees rustling and clouds scurrying, before returning once more to calm. Check it out - the moon may be rising at the horizon.

Further reading: http://wattsupwiththat.com/2012/12/24/sailing-on-the-moon-wind/