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The Journal Pioneer
Ah, Summer. We officially greeted the new season a little more than three weeks ago. Each year, following what always seems like a long winter, summer holds the promise of warm evenings and lingering light into the late hours.
Wouldn’t it be nice if both those things happened at the same time? They don’t.
I will use Halifax as an example:
The day of the summer solstice: June 20th
- Daylight: 15 hours and 34 minutes.
- Normal daytime high temperature: 19
Today, July 14
- Daylight: 15 hours and 14 minutes.
- Normal daytime high temperature: 22
Average warmest period: August 1:
- Daylight: 14 hours and 38 minutes.
- Normal daytime high temperature: 24
By the time we get to the warmest period of the summer, usually the last week in July to the first week in August, we will have lost almost one hour of daylight. We can blame it on something called seasonal lag.
The main reason for seasonal lag is that close to 71 per cent of the Earth is covered in water, which has a much higher heat capacity than land. Heat capacity is defined as the amount of heat that must be added to or removed from something to change its temperature. Because water has a relatively high heat capacity, it requires much more heat and takes a longer time than land to warm up.
Conversely, water takes a longer time to cool down than land. So even though the greatest amount of solar energy occurs on the summer solstice, the substantial water bodies on the Earth slow the heating process, which delays the hottest temperatures by about a month or so. This same concept applies to the winter solstice, where it takes longer for the temperature of the water to cool, so the coldest temperatures of the year are typically delayed to January.
Due to seasonal lag, the fall equinox is considerably warmer than the spring or vernal equinox.
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Cindy Day is the chief meteorologist for SaltWire Network