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View Full Version : Why are sun angle and seasons out of sync?



Nicolas
2007-Sep-10, 04:11 PM
I assume the maximum sun angle (closest to perpendicular) occurs on the 21st of june here in the northern hemisphere. This is also the longest day.

How come 21st of june isn't in the middle of summer, but before summer starts? Is the earth system rigid and does that cause the delay between sun angle and average temperature (and hence seasons), or did I totally misunderstand something?

I'm talking about my situation, Belgium, northern hemisphere.

01101001
2007-Sep-10, 04:21 PM
How come 21st of june isn't in the middle of summer, but before summer starts?

While incoming energy maxes out for your latitude at that time, the average temperature takes some weeks more to max out, as it takes a while to warm the ground, water, and atmosphere around you. Wikipedia: Seasonal lag (http://en.wikipedia.org/wiki/Seasonal_lag)

But, for some cultures, 21 June is midsummer's day. It depends on how a culture defines the seasons.

Bad Astronomy: The seasons begin at the time of the solstice or equinox.
(http://www.badastronomy.com/bad/misc/badseasons.html)


The definition of when the seasons begin is at the moment of solstice or equinox; that is, winter (in the north) starts on December 22nd and summer starts on June 22nd. I feel instead that the midpoint of the seasons are really at these times. The seasons themselves start a month and a half before then.

Delvo
2007-Sep-10, 06:32 PM
That's when solar energy is coming in at the highest rate, but it's STILL coming in at a pretty high rate the next week, and the week after that, so more energy is still getting absorbed on top of what was absorbed on the day of solstice.

Jerry
2007-Sep-10, 06:37 PM
For some of us, there are only two seasons: Winter and construction. Expect delays.

astromark
2007-Sep-10, 07:26 PM
Why are sun angle and seasons out of sync?

They are not... Its always been this way.
The surface of Earth is slow to absorb the warmth of sun.
Weather patterns take a while to respond to change.
Ocean temperatures are very stable and,
dampen the weather changes.
The different sunrise, set. Times are very similar for weeks
Mid spring and autumn has a greater daily difference.

Nicolas
2007-Sep-10, 07:26 PM
So it is what I called the rigidity of the system, ie maximum temperature of soil, water etc is not reached immediately when max sun angle is reached, result is that (overhere) the real summer is delayed compared to the sun angle.

Thanks!

Impressive how a lesser sun angle but more warming up being done already can cause 30C+ temperatures in july and august here, while that is quite rare in june.

Nicolas
2007-Sep-10, 07:29 PM
Why are sun angle and seasons out of sync?

They are not... Its always been this way.
The surface of Earth is slow to absorb the warmth of sun.
Weather patterns take a while to respond to change.
Ocean temperatures are very stable and,
dampen the weather changes.
The different sunrise, set. Times are very similar for weeks
Mid spring and autumn has a greater daily difference.

With out of sync I meant that there was a (constant) phase difference, not that suddenly something has changed compared to the (distant) past. But thanks for the explanation.

Nicolas
2007-Sep-10, 07:31 PM
Re the BA's comment on the solstices being the midpoint of the seasons: that will depend on where you live. Here, they are somewhere between the start and the mid of the season IMO.

Saluki
2007-Sep-10, 07:51 PM
One simple thermodynamic concept explains it. Specific heat. It takes energy to raise the temperature of matter. It takes time for this energy to build up in the matter.

Specific heat is the thermodynamic equvilant of inertia. As inertia is the reason objects don't instaneously jump from one velocity to another, specific heat is the reason objects don't instantaneously jump from one temperature to another.

Nicolas
2007-Sep-10, 07:52 PM
That was what I assumed to be the cause, but the fact that temperatures can rise or drop an awful lot in the course on one day made me doubt it, and therefore ask this question :).

Saluki
2007-Sep-10, 08:29 PM
That was what I assumed to be the cause, but the fact that temperatures can rise or drop an awful lot in the course on one day made me doubt it, and therefore ask this question :).

That is an effect of the movement of air masses, not the sudden warming or cooling of the existing mass around you.

neilzero
2007-Sep-10, 09:33 PM
When I lived in Jamestown, NY, I wondered why May 21 was cooler than August 21, but here in Florida, the Gulf Steam makes the temperatures about the same. I'm now too far South for still frozen Northern Canada to affect the Florida weather, but Jamestown frequently had cold days in May and June, because of snow pack a few hundred miles farther North.
One year, we got one of the heaviest snow storms of the season on May 5 in Jamestown, NY, so the Arctic snow pack is definately a factor in delaying the coming of hottest days.
Here in Florida, The coldest days of the year more often occur in December instead of January, so Florida is in sync, but closer to the poles and possibly near mountain glaciers the seasons are delayed a month or more, most years. Neil

astromark
2007-Sep-11, 10:45 AM
Yes Nicolas., you have it... If you live in a region that has off shore winds from a warm ocean currant. Then any local air temperature changes will not effect your weather as dramatically. I live in a very moderate climate area. On the centigrade scale we seldomly dive below 10deg., and only top out at 30 once in ten years. I to have wondered why the warmest weather is later than the solstice as is the depth of winter after the shortest day... We have the answer. It takes weeks for the ambient temperature of the landscape to rise. Its a cumulative effect.

Tobin Dax
2007-Sep-11, 01:16 PM
For some of us, there are only two seasons: Winter and construction. Expect delays.
Could be worse. If you live in the Pacific NW, there's only one season: rain.

To answer the OP another way, it's like using a stove burner. You turn on the burner, but it still has to heat up before you can boil a pot of water. If you turn it off, it is still hot enough to boil the water for a while. The on/off knob is the sun, and the burner is the earth. There a lag there due to specific heat, as Saluki says. (I just thought of the burner analogy, though, so I had to post it. :) )

laurele
2007-Sep-15, 04:54 PM
This is also interesting as it relates to ocean temperatures. Many people don't realize that in the mid-Atlantic region (I live in NJ), the ocean water stays warm throughout September and is warmer then than in May or June. While the tourist industry may consider Labor Day the end of beach season, a trip to the beach in September, when water temperatures are still about 72 degrees, can be a wonderful experience.

mugaliens
2007-Sep-18, 05:45 PM
That was what I assumed to be the cause, but the fact that temperatures can rise or drop an awful lot in the course on one day made me doubt it, and therefore ask this question :).

Air temps vary significantly around a locus of water temps, usually due to varying weather patterns. But it's the water temps which anchor seasonal averages.