Why the afternoon Sun is the hottest? (lawn, systems)
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I am a gardener so I pay attention on sun intensity. I've always known that sun is hottest in the afternoon but just the other day I began to think why that is. I have my theory but want to hear others.
Location: East of Seattle since 1992, 615' Elevation, Zone 8b - originally from SF Bay Area
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In my experience, the sun is not hotter in the afternoon, it's just that the temperature is hotter then. Here, the temperature on a sunny day peaks about 5pm, when it's actually going down behind the big trees to the west of us. What I noticed one day was that in my front yard which is mostly lawn, it was comfortably hot. When I went to the store less than a mile away, and got out of the car, it was almost unbearably hot. Thinking about it, I formed my theory, it's the buildup of heat on the ground, especially concrete during the day. By afternoon, you have the sun still providing heat, but in addition, the heat coming up from the ground.
In my experience, the sun is not hotter in the afternoon, it's just that the temperature is hotter then. Here, the temperature on a sunny day peaks about 5pm, when it's actually going down behind the big trees to the west of us. What I noticed one day was that in my front yard which is mostly lawn, it was comfortably hot. When I went to the store less than a mile away, and got out of the car, it was almost unbearably hot. Thinking about it, I formed my theory, it's the buildup of heat on the ground, especially concrete during the day. By afternoon, you have the sun still providing heat, but in addition, the heat coming up from the ground.
Is your grill/oven/stove the hottest immediately after turning it on or after it's been running for a while?
Same reason
.
Bingo. Heat is additive.
If you keep heating a fluid, it is going to get hotter and hotter as you add more heat. Even after it's mid-day apogee, the sun is still at sufficient angle to keep on heating the atmosphere and the surface. At some point, the setting sun in your location is so low in the sky, it can't add significant heat and the air cools down. And then, there is sunset...
Ignoring for a moment seasons and axial tilt, there are a couple of things happening. As mentioned above both the atmosphere and the surface are heating throughout the day. And as you reach mid-day, the sun is its most direct with the least amount of atmosphere between you and it to impact the intensity you feel. As you move on through the day, the atmosphere keeps heating while the sun angle gets lower and hence more atmosphere to protect you. Eventually it starts radiating and cooling off. Of course, there are a significant number of weather effects that change the actual results in any one area from day to day.
Then why do they say "Only mad dogs and Englishmen go out in the noon day sun," instead of five pm sun?
Because the sun is strongest mid day, even if the temperature keeps rising.
Here in Arizona, I go for a walk before 6am, while it's only in the 80s. It's been 105°+ every afternoon for weeks.
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