Vectorizing the wind Station Models Divergence/Convergence
We continue our discussion today with continued talk about analyzing and describing the wind.
Vectors
A vector is a way to represent the magnitude and direction of a given quantity, such as the wind. Vectors indicate both the magnitude and direction of a physical variable such as velocity or force.
To understand vectors, we will do a brief review of cartesian coordinate geometry.
In the above diagram, notice the vector, V. In component form, the vector is shown to have the representation 2i + 3j. The i direction in vector notation is the x direction from cartesian geometry and the j direction in vector notation is the y direc tion.
The resultant of the vector, V would be its length. To find its length, the pythagorean theorem is utilized and the square root of the sum of squares of the x-magnitude and the y-magnitude are calculated.
In this coordinate system, the direction of the vector is defined as an angular measurement. Starting at the origin and heading along the +x axis would be a 0 degree angle. The angular measurement increases counterclockwise. So a vector beginning at the origin following the +y axis would have a 90 degree measurement. In the case of vector V, the measure of the angle is defined as the arctangent of the y component divided by the x component.
Representing forces and velocities with vector notation is particularly convenient as it allows you to easily represent the magnitude and direction.
Vectors in Meteorology
The most frequently encountered vectors in meteorology are wind vectors. Since wind speed and direction are both critically important measurements, representing the wind in vector form is convenient and useful.
In meteorology, wind direction is determined by the direction the wind is coming from. North is defined as 0 degrees, East as 90 degrees, South as 180 degrees, and West as 270 degrees. Therefore, a 9 mph wind at 45 degrees would represe nt a northeast wind.
Station Models
Station models refer to the symbolic method of representing the meteorological conditions at a given location. Station models contain all the available surface meteorological obeservations.
Below is a sample station model that is interpreted for you:
Notice above how wind speed and direction is represented on a station model.
Click here to see some weather symbols used on station model plots.
Convergence/Divergence
Winds propagate around the world at all different speeds, directions, and levels of the atmosphere. Occasionally slower moving winds encounter faster moving winds and occasionally, winds cross paths. The result is convergence and divergence .
Convergence at the surface promotes vertical motion. Therefore, diagnosing and predicting regions of surface convergence is crucial in the prediction of precipitation and cloud formation and development. When air comes together at the surface, it has no choice but to rise upward vertically. However, when air comes together aloft above certain levels, it will not rise, however it will descend. Study the above diagrams representing convergence and divergence.
There are many methods used by professional meteorologists and computer programmers to estimate the magnitude of vertical motion (thus the likelyhood of cloud and precipitation) from the wind field which can help to diagnose regions that will experienc e convergence andthose that will experience divergence.
The Seven Fundamental Variables
In meteorology, there are a seemingly infinite number of variables and a seemingly infinite number of equations. All of these variables and expressions are used by the meteorologist to describe and predict the behavior of the atmosphere.
However, interestingly, all the variables and equations in meteorology can be traced back to seven fundamental variables which are described in the table below:
| Variable | Symbol |
|---|---|
| Temperature | T |
| Pressure | p |
| Specific humidity | q |
| Density | The Greek letter rho |
| Easterly wind component | u |
| Westerly wind component | v |
| Vertical wind component | w |
These above variables can be thought of as sort of the starting point for all of the many equations found in meteorology that are used to represent and predict the behavior of the atmosphere.