Lapse Rates
So why is it cooler in the mountains than in the flatlands? Well, it has to do with gravity and something called the temperature lapse rate.
As one gets nearer the center of the earth, the ball of air surrounding the earth becomes more dense. The greater the density of the air, the greater the thermal activity — temperature — from solar heating it is able to sustain. (I'll spare you the physics and the math.) For dry air, this amounts to about 9°F per 1000 feet in altitude change. With Air Bellows at 3650 feet and RDU at 450 feet, that comes to a dry air temperature difference of about 29°F!
Adding moisture to the air lowers the temperature lapse rate. That varies from 3°F per 1000 feet for saturated air to 9°F per 1000 feet for dry air. For Air Bellows and RDU, that's a difference of between 10 and 29°F.
Exactly what the lapse rate is at any time depends, then, on both elevation and relative humidity. If it's raining in both places, the temperature difference is closer to 10°F but if it's nose-bleed dry both places, it could be as much as 29°F. The actual is called the environmental lapse rate. Because moisture is usually present to some extent at both places, the typical temperature differential is about 15°F between RDU and Air Bellows.
And, that's why it is always cooler on the mountain!
As one gets nearer the center of the earth, the ball of air surrounding the earth becomes more dense. The greater the density of the air, the greater the thermal activity — temperature — from solar heating it is able to sustain. (I'll spare you the physics and the math.) For dry air, this amounts to about 9°F per 1000 feet in altitude change. With Air Bellows at 3650 feet and RDU at 450 feet, that comes to a dry air temperature difference of about 29°F!
Adding moisture to the air lowers the temperature lapse rate. That varies from 3°F per 1000 feet for saturated air to 9°F per 1000 feet for dry air. For Air Bellows and RDU, that's a difference of between 10 and 29°F.
Exactly what the lapse rate is at any time depends, then, on both elevation and relative humidity. If it's raining in both places, the temperature difference is closer to 10°F but if it's nose-bleed dry both places, it could be as much as 29°F. The actual is called the environmental lapse rate. Because moisture is usually present to some extent at both places, the typical temperature differential is about 15°F between RDU and Air Bellows.
And, that's why it is always cooler on the mountain!
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