Ryan Henning - Field guide to the weather : learn to identify clouds and storms, forecast the weather, and stay safe

METEOROLOGY AND THE BUILDING BLOCKS OF WEATHER

To understand the various phenomena you might see or experience when out in nature, it is important to understand the processes that bring those about. Where do you get rain? From clouds, of course. But how do you get clouds? Atmospheric updrafts are one way. And how are those caused? Sometimes by cold fronts, which are caused by cyclones, which are enhanced by the jet stream, which in turn is a process with roots in the revolution of Earth and its orbit around the sun, dictated by the rules of physics. That seems like a good place to start. In this first section, well try to narrow things down so we can really sink our teeth into those phenomenaand how they might affect us every day.

What Is Meteorology?

NOAA/GOES EAST, taken January 24, 2019

Defined simply, meteorology is the study of the processes and phenomena of the atmosphere. To a meteorologist, it is a bit more complicated than that. While most people are interested in the days forecast, if you want to learn how the weather works, its helpful to start with a top-down look from the perspective of a professional meteorologist.

At its rawest and most basic level, meteorology is one big math problem. The atmosphere is essentially a big basin full of fluids, such as water vapor and gases (which are considered fluids in physics). These fluids follow all the basic rules of physics, so in theory, the daily forecast is a solvable problem, if it werent for two issues.

1. Too many calculations are required to solve this equation, and the calculations are too complicated to be solved by the worlds fastest computers in time for the forecasts to be usable.
2. There are several equations, called primitive equations, that feed into all of the atmospheric models that meteorologists use for their forecasting, but there arent enough equations to calculate for the variables in question.

Fortunately, the science of fluid dynamics is well understood, as are the relationships between all the variables, enabling us to process enough of the calculations to get useful forecasts. Whats more, because we experience the weather every day and see the results of that big system of fluid dynamics, we understand the phenomena that result from these relationships and can explain how they come about.

Thats what meteorology is, in its essence. Its a riddle that is mostly solvable, and any forecast or definition you seeand even this bookis going to be, in its own way, a piece of the overall puzzle.

Planetary Motion

The atmosphere is a whirling mix of gases and water vapor, and it stays active thanks to a combination of the planets motion, its tilted axis, and its orbit around the sun. Without those factors, the atmosphere would remain sitting still on the Earths surface, almost like a big lake. Our atmosphere is ever-moving because the Earth itself is constantly in motion; the sun warms a new part of the planet every second.

Earths Axis and the Seasons

The progression of the seasons

Any study of the weather begins with Earths orbit and the planets tilt on its axis. It takes Earth about 365.25 days to orbit the sun; it takes the Earth 24 hoursone dayto rotate on its axis. (The calendar year is rounded down to 365 days, and every four years, we have a leap year, to make up for the difference.)

Earth has seasons because it is tilted 23.5 degrees on its axis. As the Earth orbits the sun over the course of a year, this tilt causes some parts of the Earth to get sunlight more directly in parts of the orbit than it does in others. For example, the northern hemisphere gets more direct sunlight in July and the height of summer than it does in February. We refer to this changing relationship with the sun as the changing of the seasons. There are four astronomical seasons in all: Winter, Spring, Summer, and Fall. December 21 marks the day that the Southern Hemisphere is angled most directly at the sun, while June 21 says the same about the Northern Hemisphere. March 21 and September 21 are the days in which night and day are nearly the same length for all latitudes. (These dates are approximate, and can change by about 24 hours in either direction.)