I was the keynote speaker at Georgia State University recently. During that talk, I spoke about a few concepts that are often counterintuitive or confusing to the public. Since I wrote this 12 days into December, let’s explain 12 weather and climate concepts that can understandably be tricky if you are not trained as a meteorologist or climatologist.
Source: NASA and NOAA Scijinks page.
1. Moist air is less dense than dry air. If you live in Texas or parts of Plains, you may be familiar with the "dryline." It is a boundary that represents a difference between relatively dry and moist air. Moist air (less dense) can be lifted along the dryline to initiate storms. Wait, shouldn’t air with moisture in it be more dense? Moist air is actually less dense because for a given volume, water vapor has a molecular weight of about 18 grams per mole (atomic units) whereas dry air (mostly nitrogen and oxygen) has a molecular weight of 28.97 grams per mole. So when you add moisture to a volume, you are lowering the density. Feel free to review Avogadro’s Law if you have a headache by now (smile).
2. It is dangerous to take shelter under the tallest trees during lightning but people do it anyhow. The tree serves as a natural lightning rods. This illustration by the University Corporation for Atmospheric Research (UCAR).
3. It is very dangerous to shelter under a bridge overpass if you are trying to avoid a tornado. The Venturi Effect (describe in detail here) explains how a fluid’s velocity increases when it flows through a contracted channel or tube. The overpass provides an opportunity for the violent wind flow in a tornado to be constricted and perhaps accelerated.
4. Lightning associated with a thunderstorm is not spelled with an "e". Full disclosure: I just threw that in because it is a pet-peeve.
5. As long as we are getting my pet peeves out of the way, heat lightning is not a "thing" and it is not caused by the heat of the day. Here is a great explanation by The Weather Channel.
6. Some deserts are inherently cold. The American Meteorological Society’s Glossary of Meteorology defines a desert as "a region where precipitation is insufficient to support any except xerophilous (drought resistant) vegetation." Parts of Greenland are considered a desert. Here is a list of the 10 coldest deserts on Earth.