By Steff Gaulter
It’s good news for us in Doha! Autumn has now officially started, and this can only mean one thing: the weather will start to get cooler.
Many people would say that the first day of autumn is September 1, but if we follow astronomy, it officially started a bit later, on the autumn equinox. The exact time of the equinox varies slightly each year, this year it happened on September 23 at 0229 GMT, which was 05:29 in Qatar. It’s a very precise time, the moment that the sun crosses the equator as it moves southwards away from the northern hemisphere. The word equinox comes from the Latin meaning ‘equal night’, and is a time when day and night are nearly the same length, no matter where in the world you are.
The reason that we have an equinox is due to the way that the earth rotates around the sun. As you probably know, the sun doesn’t stay above the same position of the earth throughout the year. It moves to the north for the northern hemisphere summer, and southwards for the southern hemisphere summer.
The sun reaches its most northern point in June, when it is overhead at the Tropic of Cancer, shining directly above Muscat and Dhaka. For the northern hemisphere, this day is known as the summer solstice, the longest day of the year.
The most southerly point along the sun’s track is reached in December. At this point the sun will be directly overhead at the Tropic of Capricorn, above Sao Paulo and Alice Springs. For the northern hemisphere, this is the winter solstice, and the shortest day of the year.
If the sun tracks between the Tropic of Cancer in June and the Tropic of Capricorn in December, then logically it must travel past the equator twice each year. This happens in mid-March and mid-September and these are known as the equinoxes.
These important landmarks of the sun, the solstices and the equinoxes, traditionally mark the beginning of our four seasons, which at first may seem a little illogical. After all, it means that the longest day of the year is only the beginning of summer, and days immediately start to get shorter. People often ask me why the longest day of the year isn’t in the middle of the summer.
The reason that the solstices mark the beginning of the seasons is that there is a time lag between the position of the sun and the climate on the earth. The northern hemisphere continues to heat up after the longest day of the year, and likewise in winter, it continues to chill after the shortest day of the year in December, therefore the length of the day is considered largely irrelevant to meteorologists.
I think many people would agree that all of this is frankly rather confusing, Therefore despite astronomy, many Meteorological Offices in the northern hemisphere class summer as the three months of June, July and August and autumn as the following three months, from September until the end of November. This also avoids our having to remember exactly when the equinoxes and solstices occur, given that they aren’t on the same day every year.
Whichever method you use to determine the start of autumn, however, we’re definitely in the new season now. For Doha, the significance of the sun moving southwards away from the northern hemisphere is that we are finally leaving the summer heat.
As the sun moves south, it will shine on us at more of an angle. This means the rays will have to pass through more of the earth’s atmosphere and therefore will no longer be as strong. This will allow our temperatures finally to begin to ease. By the end of this month, the average temperature is normally 36C (97F), which is definitely still hot, but certainly not as hot as it was. As the temperatures ease, there is also the chance of seeing more cloud, some showers and generally a little more variety in our weather.
In other parts of the world, autumn brings rather a more dramatic change to the weather, with the change in Canada being more like a sledgehammer. This year on September 7, the locals of Calgary were basking in temperatures of 26C (79F), but just 24 hours later, the city was coated in snow and the temperatures didn’t manage to climb above 4C (39F). As the cold season is so long in Calgary, the locals don’t exactly celebrate the early arrival of snow.
Equally badly received was the recent long range forecast which predicted that this year would be colder and snowier than usual. The locals can draw some comfort that long range forecasts are still designed to be taken with a healthy pinch of salt, and also from the fact that the forecast is not backed by the national weather service, Environment Canada.
For Qatar, our autumnal changes are far more subtle than in Canada, which I think is a shame. Although it will be nice to see our heat gradually subside, it would certainly add an extra bit of excitement if it suddenly started to snow!
