Another Look at the Wind

#2009 "Algonquin Rock Lake Turbulent Sunrise"
Looking back at this plein air painting, I see
that I painted my Coriolis hand into the
cold advection, turbulent stratocumulus. 

The geostrophic and gradient wind balance equations can be a challenge even for meteorologists. The fundamental forces that move the air around the Globe are not something that we think about every day. There is no time during any shift to go back to first principles when preparing a forecast for the next week for large areas of Canada. 

To be clear, what I am attempting to do in these Art and Science Blogs, is explain nature in a way so that even the most challenging concepts are understandable. It is a task I have set for myself and I link the ideas with phenomena that I observe in my artwork. Science should make sense and if I can’t explain something, then I must not really understand it well enough. Being naturally curious can be a full-time occupation - even when retired I need to brush up on the science and learn it better. 

I rely on visual aids when explaining things. Many of these explanations, especially meteorological ones, are hand-waving exercises. I do not go anywhere without my Coriolis Hand! The Coriolis Hand can be used to explain much about living on a rotating planet. 

Gaspard-Gustave de Coriolis of Paris (1792-1843) was an engineer and mathematician who first described motions on a rotating body deflected by an apparent force that now bears his name. If you place your Coriolis hand palm down and point your thumb in the direction of the motion, the moving substance will be deflected in the direction of your fingers. Your right hand is your Coriolis Hand in the Northern Hemisphere while south of the equator, it is your left hand. 

We can also use the Coriolis Arm which is attached to your Coriolis Hand, to explain the geostrophic and gradient wind balances detailed in the last Science Tuesday. I keep trying to elucidate things in different ways until the concepts connect. Everyone learns in their own unique way. 

The Geostrophic and Gradient Wind Balance Graphics

Instead of analysing the vector diagrams like we did last week, align your Coriolis Arm with the gradient wind at the top of the planetary boundary layer (PBL) - where there is no friction. Hold your Coriolis Hand outward with your fingers pointing in the direction of the gradient wind, your palm facing down. If you stretch your Coriolis thumb at 90 degrees to your fingers, your thumb must point toward lower pressure and in the direction of the pressure gradient force (PGF).  The Coriolis force deflects every moving thing to the right in the Northern Hemisphere. The centrifugal force always points way from the centre of curvature. 

The following graphic summarizes these three forces - pressure, Coriolis and centrifugal using your own Coriolis Arm. It also explains that due to the centrifugal force, the gradient wind is weaker than the geostrophic wind balance in a trough but stronger in a ridge.  My Coriolis arm only bends cyclonically when I am relaxed and one would expect the gradient wind in a trough to be more calm as well. 

Understanding the Wind Using you Coriolis Arm
View looking down from space

You can use your Coriolis Arm in reverse as well. Point your Coriolis fingers in the direction of an observed wind revealed by gravity waves, swells or Langmuir Streaks. Your stretched thumb must point toward lower pressure. If the wind is strong, the pressure gradient is also steep. All of these facts can tell you something about the weather. 

Next Science Tuesday we will add in the fourth important force of friction so that we might better understand the wind in the planetary boundary level as well. Bring your Coriolis arm too. 

Warmest regards and keep your paddle in the water,

Phil the Forecaster Chadwick