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Aug 15, 2013 14:38:10   #
justkillingtime
 
The northern hemisphere has its shortest day of the year on the winter solstice in December. Then the northern hemisphere gets more and more sunlight every day until it has its longest day of the year at the summer solstice in June. But we have our coldest weather in January and February and our hottest weather in July and August. Why? Why does the weather not coincide with our periods of increasing and decreasing sunlight? Why is it hotter when we get less sunlight and colder when we get more?

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Aug 20, 2013 09:35:37   #
Zemirah (a regular here)
 
justkillingtime wrote:
The northern hemisphere has its shortest day of the year on the winter solstice in December. Then the northern hemisphere gets more and more sunlight every day until it has its longest day of the year at the summer solstice in June. But we have our coldest weather in January and February and our hottest weather in July and August. Why? Why does the weather not coincide with our periods of increasing and decreasing sunlight? Why is it hotter when we get less sunlight and colder when we get more?
The northern hemisphere has its shortest day of th... (show quote)



There is more involved than sunlight. Rather than my own words, there is a paragraph from one of my son's old meteorology textbooks that answers your question:

"At this point it is interesting to note that although sunlight is most intense in the Northern Hemisphere on June 21, the warmest weather in middle latitudes normally occurs weeks later, usually in July or August. This situation (called the lag in seasonal temperature) arises because although incoming energy from the sun is greatest in June, it still exceeds outgoing energy from the earth for a period of at least several weeks.

When incoming solar energy and outgoing earth energy
are in balance, the highest average temperature is attained. When outgoing energy exceeds incoming energy, the average temperature drops. Because outgoing earth energy exceeds incoming solar energy well past the winter solstice (December 21), we normally find our coldest weather occurring in January or February. As we will see later in this chapter, there is a similar lag in daily temperature between the time of most intense sunlight and the time of highest air temperature for the day.

[pg 63, Meteorology Today: An Introduction to Weather, Climate, and the Environment, 5th edition, C. Donald Ahrens]

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Aug 20, 2013 19:03:54   #
justkillingtime
 
Quote:
"At this point it is interesting to note that although sunlight is most intense in the Northern Hemisphere on June 21, the warmest weather in middle latitudes normally occurs weeks later, usually in July or August. This situation (called the lag in seasonal temperature) arises because although incoming energy from the sun is greatest in June, it still exceeds outgoing energy from the earth for a period of at least several weeks.


I realize this, but what causes the lag time? Why doesn’t the earth absorb and store solar energy in proportion to the intensity of that energy which reaches it? The spring should be our warmest period since we receive more and thus should store more in the spring because we get more as the sun comes closer and closer to us, but we seem to have more stored in the summer when we are actually getting less.

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Aug 21, 2013 02:44:34   #
Zemirah (a regular here)
 
justkillingtime wrote:
I realize this, but what causes the lag time? Why doesn’t the earth absorb and store solar energy in proportion to the intensity of that energy which reaches it? The spring should be our warmest period since we receive more and thus should store more in the spring because we get more as the sun comes closer and closer to us, but we seem to have more stored in the summer when we are actually getting less.


Earth's seasonal lag is largely caused by the presence of large amounts of water, which has a high latent heat of freezing and of condensation.

Seasonal lag is the occurrence whereby the date of maximum average air temperature at a geographical location on earth is delayed until after the date of maximum insolation ( the act or an instance of exposing to sunlight). The same applies to the minimum temperature being delayed until some time after the date of minimum insolation.

This is not because of the time required to warm the earth, but because of the time required for heat to exit the earth.

In addition, heat which is stored in rocks, sand and stone, loses temperature slower than the reduction in incoming energy, thus the heat stored during summer months is enough to shift the maximum temperature beyond the maximum solar influx.

Its length varies with opposing climates, with extremes ranging from as little as 15–20 days (in summer polar regions) to as much as 10 weeks (along low-latitude ocean fronts). In many locations, it is not "seasonally symmetric", as the time between the winter solstice and subsequent coldest temperature is not the same as between the summer solstice and the following hottest temperature. In low and middle latitudes, the summer lag is longer, while with the winter lag in polar areas the reverse is true. In mid-latitude continental climates, it ranges between 20–25 days in winter and 25–35 days in summer.

[Climate Near The Ground, Prof. Dr. Rudolf Geiger, Harvard University Press]

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Aug 21, 2013 07:35:46   #
justkillingtime
 
Zemirah wrote:
This is not because of the time required to warm the earth, but because of the time required for heat to exit the earth.


Am I right in thinking that:

1. From winter to summer the wavelengths of the solar heat grow in frequency and from summer to winter they decrease in frequency, i.e., the wavelengths change from season to season so the speed changes from season to season;

2. The wavelengths of the heat being released from the earth are always the same regardless of season so the speed of released heat stays the same.

3. From summer to winter the heat going out has a longer wavelength than the heat coming in so going out doesn’t travel as fast as coming in and you get more heat from the earth than you do the sun;

4. From winter to summer the heat coming in has a longer wavelength than the heat going out so coming in doesn’t travel as fast as going out and you get more heat from the sun than you do the earth?

But then how do you explain periods of temperatures that are colder or warmer than average?

And if stored heat has more do to with our weather than solar heat does, how does this affect the idea of global warming? Maybe humans aren’t trapping heat in the atmosphere with greenhouse gases. Maybe humans are changing how the earth’s surface stores heat by altering the landscape and paving over rural areas with urban sprawl. And if this is true we can deal with urban sprawl more easily than we can greenhouse gases.

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