# Tag Info

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You get fog when the relative humidity at ground level goes above 100%. This is easily achieved by a drop in temperature without a lot of airflow. Looking at the saturated vapor pressure in the range of 25 - 35 C gives us a sense of what temperature drop you would need to go from 80% RH (muggy but not unusual) to "fog". This plot (raw data from http://www....

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Water boils at $100 ^\circ~\mathrm C$. $30$-$45^\circ~ \mathrm{C}$ is not nearly enough to boil water, but the constant heat of the sun is enough to evaporate water over time. It takes about $4.314~\mathrm{J/K}$ to evaporate 1 kg of water (under normal atmospheric pressure). The can slowly evaporate the water on the ground, but $30$-$45 ^\circ~\mathrm{C}$ is ...

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According to this website, A Birkeland current is a set of currents that flow along geomagnetic field lines connecting the Earth’s magnetosphere to the Earth's high latitude ionosphere. These then are driven by solar wind in the Earth's magnetosphere. Birkeland currents are caused by the movement of plasma perpendicular to the magnetic field. They ...

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To know whether a column of fluid is in equilibrium, you take a fluid element anywhere in the column, displace it by a small amount (compared to column height) in any direction, and see what forces come to act on it; if the forces are such that they push (or pull) the fluid element back to its initial position, then the fluid column may be said to be in ...

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CAVEAT - I am giving a possible calculation, but I believe the answer may be off by a factor 2x (compared to the lapse rate observed in the atmosphere). I am leaving it here for you to ponder. Perhaps it can inspire you to find the correct solution yourself. Or perhaps the difference is due to the fact that this calculation doesn't assume convection - so ...

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But I just had a thought coming to my mind, thinking about that in the mornings and evenings, we mostly see red light here, the higher end of the visible spectrum not getting through. It does get through, at least to some extent. You see a very blue sky when the Sun is at its reddest. That blue sky can give you a sunburn if you go skiing in the mountains ...

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The reddening of the sun has to do with Rayleigh scattering as the sun passes through more atmosphere. (see picture). This is in a sense, related to less energy but not the primary cause. The reason we get less solar energy per square meter is that the angle of the sun in the sky affects how spread out the light is. (see updated picture). Ignoring ...

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For a definition of the UV index and a rough discussion of influencing factors see e.g. https://en.wikipedia.org/wiki/Ultraviolet_index. You can compare the model shown there against actually measured data for the US: http://www.cpc.ncep.noaa.gov/products/stratosphere/uv_index/uv_annual.shtml. Both sources will support your statement that UV exposure in ...

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The Earth "compells" an aircraft to rotate with it through the fluid drag of its atmosphere. So a practical answer to your question is then "above the atmosphere", which is at about a $100{\rm km}$ height. This is the von Kármán line, which is often taken as the definition of the edge of space. The definition is made because at this height, a standard ...

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As soon as you get above the atmosphere (about 100 km off the surface of Earth, give or take), then there's nothing in particular that compels you to follow the Earth's rotation. Of course, once you get there, you will probably already be moving to some degree, depending on which mechanism you use to get yourself up. If you do, however, you can bring along ...

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It doesn't depend on the height. Now you are on the rotating Earth, so you rotate with it (around the axe of Earth's rotation). Its speed is between 0 (on the poles) and around 1.5 Mach on the Equator (1 Mach = the sound of speed). If you want to compensate this rotation, there are many ways, for example, you can simply sit on an airplane capable to go ...

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If you were at the equator, your ground speed, due to the rotation of the Earth, is around 460 m/s (1 000 mph) so you are really moving. Now say you jump into the air and somehow you delay your fall by 10 secs. Will the earth have rotated a bit under you? No, because you have the same horizontal speed as you had on the ground. This is why rockets are ...

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@Zero is correct in their explanation, and I just wanted to add a few points. Temperature, pressure, and relative humidity all play a part in the formation of clouds. Both temp and pressure decrease with height. As air ascends it expands due to the lessening pressure at higher altitudes. When a fluid expands in volume, its temperature also decrease. (...

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You must know that atmospheric temperature decreases with height. As a moist air parcel rises it is thus continuously cooled and beyond a certain height water begins condensing and droplets are formed. A large ensemble of such droplets are what we call clouds. If conditions are right then clouds form close to the ground too. These are called stratus clouds.

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@Flojo1 - I know more about RF atmospheric refraction than optical, so this won't give you anywhere near a complete answer. But I can say a few things that may be of some use. First, looming is no more than enough vertical refraction in the earth atmosphere that an object on the surface looks like it is above the surface. Sinking is the opposite. There's ...

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Based on this article on the website American Scientist Clouds and UV, clouds pass more UV light than you would imagine, which suprised me, as where I live it is cloudy on most days and I thought I received some UV protection as an upside to gloomy weather. Several studies suggest that reflection off the sides of cumulus clouds is one mechanism by which ...

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