Chapter 13

What is wind? What is humidity?

Wind is simply the movement of air. Humidity is a measure of the amount of H2O(v) that is in the air.

What is air made of and in what proportions? What is the valuable message here regarding the *minority of gasses in the ATM?

Air is made of N2 (78%), O2 (21%), and 1% of absolutely everything else! Within this 1% category includes CO2, O3 (ozone), CH4 (methane), H2O(v), etc, etc. The point tough is that so many of the interesting things that happen in our atmosphere revolve around changes in this 1%. It might in the minority, but these gases can influence global patterns so much!

How is rising air generally linked to clouds and possibly precipitation? How is the converse of this (sinking air) generally liked to clear skies and low chances of precipitation?

As air rises then it moves into a lower pressure environment because it is moving into an area where there is less air above it and thus less air pushing down on it. Hence "low pressure" as elevation *increases! However, given P = nT/V, when P drops then T *also* decreases, which is why the atmosphere is cooler at higher elevations. This decrease in temperature then cools the air, including any water vapor in the air, thus increasing the chance that water vapor will condense and form clouds (potentially including precipitation). Conversely, sinking air is air that is moving closer to the earth and thus entering an environment with more overlying air that is pushing down upon it. Thus, there is more pressure at the surface. Given P = nT/V, since P is increasing then temperature also increases, and when temperature increases then any liquid water (in the form of clouds) will likely evaporate, clouds then disappear, the sky clears, and the chance of precipitation plummets.

How is the vertical movement of air linked to the density of air? How is density in turn linked to the temperature and humidity of air? Explain.

Less dense air rises and denser air sinks. We already basically know this. However, the nuances here are linked to temperature and humidity. Temperature-wise, hotter air rises and colder air sinks (which again, we are familiar with). But what about the patterns with humidity? As discussed above, water vapor is in the 1% of all atmospheric gasses. The interesting point is that water vapor is relatively LIGHT compared to the many other gasses in the atmosphere. Thus, when there is more of it in the air (i.e., the air is humid) then that air is lighter. By contrast, when the air is more dry (i.e., less water vapor — less humidity) then that means that more of the heavier gasses are in the air instead, and the air is more dense. In short, hot n' humid air is the least dense (rises); cold n' dry air is the most dense (sinks).

In chemistry there is an equation that captures what is called the "ideal gas law." It states that PV = nRT. What do each of these variables mean (ignoring R, which is the ideal gas constant), and when you solve for P, how can this equation provide you with an understanding of the relationship among these variables as they relate to pressure?

P = pressure; V = volume; n = # of molecules or ~density; T = temperature; ALL In reference to what is happening to a gas and how these variables relate to one another in the context of gasses. Solving for pressure, P = nT/V. Conceptually, this means that the equation is also equivalent to P/1 = nT/V. That is, since both P and n and T are in a numerator separated by an equals sign, they are directly proportional/related. If "n" increases then so does pressure; if temperature increases then so does pressure. Conversely, since volume is in the denominator, volume and pressure are inversely related. When the volume of a gas increases then the pressure *decreases! We know this relationship from basic life experience if you've ever let the air free flow out of a bike tire. When this happens, the pressure drops (duh!). However, if you feel the air then you will notice that it is cold (temperature also drops) and the density of air that is crammed into the bike tire is also decreasing because the air in the tire is escaping. Furthermore, since the air is escaping, the volume of that air (now in the rest of the world, and not crammed into a tire) can expand, and when it does, then the volume increases! These relationships (up vs down) are exactly the same as is illustrated by P=nT/V.

Distinguish between weather and climate. How do they relate?

Weather is the condition of the atmosphere locally, day-to-day; whereas climate includes the regional and global patterns of weather played out over months-to-years. On the short term, weather may seem stochastic and changeable (and it certainly can be!), but larger patterns emerge when you take a step back and look at the bigger picture —spatially and temporally —and this is exactly what climate is. Climate takes the "narrow time" and "narrow place" of the atmosphere (i.e., weather) and broadens it out to larger geographic areas over much longer time scales.

Why is the sky blue? How does knowing that help you understand why the sun is yellow from the perspective of the earth and white from the perspective of space?

he earth's sky is blue because blue light is scattered *out of the ROYGBIV spectrum as sunlight enters the earth's atmosphere. This means that the other colors remain as light that we see when we look at the sun, and the combination of these other colors produce a *yellow (not white) light. The reason why the sun looks white from space is because ALL of the ROYGBIV colors are striking your eyes from space... and the complete reflectance of colors in the visible spectrum produces a white color. However, when blue is scattered out by the earth's atmosphere, a yellow sun is what remains.