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Heatwaves and heavy snow

Some think weather occurs at random, as if God spins a roulette wheel or throws an imaginary dice. Those who claim that weather is the function of chaos or bad luck may simply have not done enough study into the nature of cycles and the cycles of nature. Something is only a mystery to one who has not yet realised a secret, whether a magic trick, mathematical formula or the undiscovered workings of a scientific process.

There should not be too much surprise at northern hemisphere summer heatwaves because we warned of them in our Ireland Almanac for 2013. We suggested heatwaves would be widespread in Canada, USA, France, Italy, UK and Ireland between June and August. In the NZ almanac we called for icy wintry blasts south of the Central Plateau that could break cold temperature records. Some Australian states like South Australia are also likely to succumb.

At first glance there should be no connection between severe cold and severe heat, the two hemispheres being on opposite sides of the globe. But the current severity of summers and winters is no coincidence. What causes one also causes the other according to lunar weather science. To understand this we need to revisit what causes weather.

There is a tide in the atmosphere, whereby the air varies in height daily according to the position of the moon. There are two things trying to get through our insulating air barrier; heat from the sun during daylight hours and the cold from space at night. The varying height of the air allows more or less of either of these through.

We can map the air tide pattern and then extrapolate forward, asking what factors would vary the air tide the most, much as we can ask what varies the height of the sea. When we have worked out the timing of main variables we can calculate forward for seasons in the future. Then we can predict which months of which years the air tide might be susceptible to increased heat coming through to the ground for summer, or when more ground heat is likely to be lost in winter.

One moon cycle is the daily one we observe when the moon appears to come up and over us, rising on the horizon, reaching a highest point, then setting below the horizon, this repeating 48 minutes later the following day. This is an illusion because the moon is not really going around us – the whole earth is rotating under the moon once every 24-hours.

We also notice the moon changes its shape from one day to the next as it works its way through the sky, orbiting planet Earth once a month. This is another illusion as it is always spherical and only changes its angle to the sun as seen from earth. So we are turning under the moon daily, and it is going around us monthly.

The moon is not equidistance from earth at all times in the month. This distance varies over 27-days. There is a closest-distance day, called perigee, and 14 days later a furthest-away day called apogee. Not all perigees are created equal. Some are closer than others and over a season, averagely closer than during other seasons. Closer perigees may span a summer, spring, autumn or winter and may span both a summer and the following winter.

The effects of perigees are to exaggerate seasonal temperatures because they magnify the air tide. Closer perigees always bring more extreme weather. Winters are colder and summers hotter due to the closeness of perigees about every four years. But there is still more.

Orbiting earth once a month the moon also slowly drifts (currently) 20 degrees of earth’s latitude north of the equator then 13 days later 20 degrees south of equator. This is called ‘declination’ and is also a 27-day turnabout. We call moon-furthest-south southern declination. Southern declination days June to August give warmth to the northern hemisphere and can bring polar blasts to us.

These three cycles, moon phase, perigee and declination are out of synch with each other, but occur together on or near the same day approximately twice per year, and collectively every 9-years right smack in the middle of summer and winter months. Northern summer heatwaves and southern severe cold will be expected when closer perigee and southern declination days combine between June and August.

Perigee+declination is not the only factor that can bring heat or cold to a season, but can be the one that breaks previous records. The solar cycle can also play a part as in 2010 when all countries had colder winters due to solar minimum, when the sun was “asleep”.

The extent of northern heat and southern cold depends on how close in days southern declination is to close perigee June to August. During the washout summer in 2010 (the much touted “BBQ summer” that didn't eventuate), perigee and southern declination days were well apart. Northern hemisphere heatwaves again began when perigee and declination came together in July of 2011.

The northern hemisphere summer of 2012 was hot and the southern hemisphere cold because perigee and southern declination happened on same days during June and July then started to move apart in late August. It is the same situation this year. But next year will possibly not be so hot and cold, because perigees in June through August occur not on southern declination but a few days past it.

Nine years ago saw the last time closer perigees and southern declinations came on same days between June and August. In 2003 and 2004 heatwaves in Europe were record-breaking. Our 2003 and 2004 winters brought savage cold at times. Nine years before that in 1995 heatwaves came to the northern hemisphere and we had a good ski season until mid September. This particular cycle comes around again in 2022.

Ken Ring of www.predictweather.com is the author of Weather Almanac for NZ for 2013