What Season is it? Meteorological vs. Astronomical

Mark SpencerNational, Ohio, USLeave a Comment

Its that time of year again where we found ourselves in one astronomical season but a different meteorological season. You may have heard your local meteorologist talking about March 1st as the start of spring but if you go according to astronomical seasons, its still winter. The recent weather in Ohio has proven that no season is perfect as we went from spring warmth and severe weather to cold and snow in just a day or two. So if neither system delineates the weather of each season, why do we have two systems?

Before we delve into this debate, let’s look into why we have seasons to begin with. In ancient times, cultures would use Gods and myths to explain complex scientific ideas. The Greeks have a story to explain the seasons and its one of my personal favorite myths. This myth revolves around the Goddess Persephone who was the daughter of Zeus and Demeter. Demeter was the Goddess of Agriculture and was very close to her daughter. They lived in a world where it was summer every day and harvests always flourished. Once day while Persephone was picking flowers, she was abducted by Hades, the lord of the Underworld. This devastated Demeter who at once forbade anything to grow and the planet turned cold. Persephone knew that if she ate or drank anything that she would be trapped in the Underworld forever. Her location was eventually discovered and Zeus demanded her return. Hades relented but upon her departure, he offered Persephone a pomegranate or which she ate six seeds. Because she ate the seeds, it was decided she would living in the Underworld with Hades for six months every year. It was during that time that the world would again grow cold and nothing would grow due to Demeter’s sadness.

In modern times we know what causes the change in our weather and our astronomical seasons are defined based on this process. Our planet revolves around the Sun and while doing this also rotates around its axis. This rotation is why we have a day-night cycle. The length of day is not constant from place to place or day to day. This is because our axis is tilted by 23.5 degrees. This tilt means that the Northern Hemisphere spends six months of the year tilted towards the sun (longer days) and six months away from it (shorter days). In the mid-latitudes we have what we call a four season climate with each season having its own changes in temperature, weather, flora, and fauna. We have a season of warmth and one of cold with two transitionary periods on either side. The day that the Northern Hemisphere receives the most sunlight (longest day) is called the Summer Solstice while the day of least sunlight (shortest day) is the Winter Solstice. The two days where the planet receives equal sunlight are called the vernal and autumnal equinoxes. Astronomers define the seasons by the exact moment these events occur and the start day and time therefore vary by hours and often days from year to year making seasons between 89 and 93 days in length.

So why do meteorologists choose a different system for their seasons? The answer is actually fairly straightforward. Meteorologists define their seasons to start on the first of the month that a solstice or equinox occurs (March, June, September, and December) meaning it has little to do with the weather of a given location. These chosen months often have weather associated with both seasons as shown in Ohio last week. The reason behind choosing the first is because the exact day and time the astronomical seasons start varies making it difficult to compare one season to another. By grouping our seasons by calendar month, winters are always 90 days long (91 in a leap year), spring and summer each have 92 days, and autumns are 91 days long. So this system was developed simply as a means of convenience for meteorologist and climatologists and has little to do with the weather itself. Our atmosphere is a chaotic system and we will always have weather events “native” to one season occur outside of its assigned domain. But instead of worrying about the fact that we are technically in both winter and spring, rejoice that the cold weather associated with winter will soon come to an end.

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