3sixbits, I consulted a friend who has a PhD in Physics and Astrophysics as I disagreed with some of your conclusions. Below is his thoughts:
Greetings, I have a Ph.D. in physics so let's walk through these concepts and see if we can un-confuse ourselves.
According to Webster's Dictionary, "mirage" is any "optical phenomenon, especially in the desert or at sea, by which the image of an object appears displaced above, below, or to one side of its true position as a result of spatial variations of the index of refraction of air." However, because we are discussing long-range hunting, we can limit our interest to the effects in the atmosphere which occur within approximately 8 feet of the planet's surface.
During the day, light from the Sun warms the surface of the Earth. The air near the ground can then absorb some of this heat. Since hot air rises, this newly warmed air moves upward. Light reflecting off the target you are trying to hit passes through this rising air and is slightly deflected. This displacement of light due to heated, rising air is what hunters usually refer to as mirage.
Mirage can occur on hot or cold days. All that is required is for the Sun to warm the ground above the temperature of the air.
Following are my comments addressing the previous posting of others:
Comments from one person:
>> "From a physics standpoint, you must have a heat source present to warm the air. Warm air rises or moves in relationship to its cooler surrounding air, and it is the rising air that we call mirage. Regardless of the outside temperature, a heat source (like the sun) is necessary. Mirage can be worse in cold temperatures since the sun can cause a slight temperature difference easier in cold weather which
causes the slightly warmer air to rise."
These statements are correct. The only addition I would make would be to point out that, while the Sun is the ultimate source of the heat, the air is being warmed by the heated ground.
Comments from a second person:
>> OK Your kidding right? You didn't know that the planet we live on has an internal heat source?
The Earth does have an internal heat source in the form of a molten core. However, this has almost nothing to do with atmospheric phenomenon. The heat from the center of the Earth is released through geological phenomenon like volcanoes, geysers, and sea-floor spreading zones. It has a large affect on the inside of the Earth, BUT at the surface of the Earth, the Sun provides 20,000 times more energy than geothermal energy of the Earth. The Sun is the primary source of energy for both the atmosphere and the oceans.
>> You did know that outside the earth atmosphere that space is at absolute zero?
The fact that the space is colder than the surface of the Earth is correct. However, weather phenomenon happen in the troposphere (the bottom 10 kilometers of the atmosphere). You don't reach space until you climb to an altitude of over 400 kilometers.
Additionally, deep space is actually at 2.7 degrees above absolute zero. Because the Earth is fairly close to the Sun, the space above Earth is not even quite as cold as deep space.
Absolute zero is the temperature at which ALL motion stops – even the motion of electrons moving within atoms.
>> You must know that the law of thermal dynamics still apply when the sun is shining on the other side of the planet and you are in beddy-by? Heat still travels to cold!
Actually, our atmosphere is very complex due to the motions of warm and cold fronts, the jet stream, the effects of varying land and water masses, etc. The fact that the Sun is heating the other side of the Earth during the night has very little effect on the weather experienced by the people on the night side; it takes considerable time for heat to travel 12,500 miles (1/2-way around the globe).
In addition, heat is only guaranteed to travel towards cold when you are discussing the concept of conduction (heat transfer due to physical contact – this is what occurs when you place your hand on a hot surface). Conduction is of little consequence when discussing large-scale atmospheric movement. Heat in the air is moved primarily by the motion of large masses of air (convection). If this were not the case, a cold front could never move over a location that was experiencing weather due to a pleasant warm front.
I hope all of that helps. Have a good evening!
