Resources for the Resourceful; Understanding Warm and Cold Fronts

Welcome back and Happy New Year! I hope everyone had a pleasant holiday.

I took some time off and then spent the past week doing the recovering from taking time off thing. Its all been good though. The time off gave me a chance to work on a few home projects and enjoy time with Kathy and family. And the time this week hasn’t been bad either because I’ve been working out on the Oregon coast where the storms have given way to a couple of pretty days and a very pretty sunset last night.

One of the things that I tend to do when I have free time is read and one of the things I tend to do when I’m at the coast is watch the weather. Those to things kind of merged the past couple of weeks.

During my time off, I started read a book called Air Apparent, which is a history of the evolution of the weather map.  I didn’t finish it, so I have been continuing to read it here at the coast where, as I indicated previously, I tend to watch the weather a lot.

As those of you who visit the site occasionally know, I am a big fan of understanding and monitoring climate patterns. For one thing, its pretty interesting stuff that impacts us on day to day basis.  And, in the broader sense, if you are involved with HVAC and trying to control the built environment, one of the challenges you are faced with is the impact of the ambient climate on the environment you are trying to control.

The coast is a great place to watch the weather, at least in my opinion because the large expanses of open horizon really let you get a big picture perspective on things. And people flying kites and chimney caps that rotate with the wind give you a pretty good perspective on wind direction and speed.

It was at the coast, at the very place I am currently staying that:

  • I was able to show Kathy, the kids, and my grandson green flash two nights in a row a couple of summers ago (pretty rare in general and particularly along the coast here).
  • I first recognized with certainty the cloud and wind patterns associated with an approaching warm front, and the subsequent frontal passage and cold front. In other words, I went from an intellectual understanding to a practical understanding of a fairly common phenomenon in this part of the world.

In fact, as I took the picture at the beginning of the post, I suspected that the clouds I was looking at were the precursors to an approaching front, a fact that the weather maps and increasing cloud cover tended to confirm when I looked at them this morning.

We are staying near the tip of the red arrow on the map and as you can see, at the time I checked the weather maps, there was a warm front (the red line with red half circles) just to the north of us.   While the low pressure system and fronts associated with it did not pass directly over us, it did pass close enough to the North of us to cause our sunny sky to disappear and generate some light rain by the time Kathy and I went out to dinner.

The picture below illustrates the “plan view” and “sections” through a typical frontal system with the section at the top representing whats going on north of the low pressure center that generates the fronts and the lower section representing what’s going on south of the low pressure center.

Most folks today probably have a passing familiarity with warm and cold fronts as they are common topics in most TV weather broadcasts. But it if you go back in time less than a hundred years, you will discover that something we take for granted was something that folks did not really know about or understand.

The illustration above was taken from one of two fairly ground-breaking paper published in 1918 and 1922 by a Norwegian physicist named Jacob Bjerknes, who was affiliated with the Bergen School, a band of Norwegian meteorologists headed by his father, Vilhelm Bjerknes.

The first paper, published in 1918 is titled On the Structure of Moving Cyclones and it discussed the authors application of  hydrodynamic analysis based on the climate observations from multiple stations to develop some general conclusions about the structure of low pressure systems and the squall lines (cold fronts) and steering lines (warm fronts) associated with them.

The second paper, titled Life Cycle of Cyclones and the Polar Front Theory of Atmospheric Circulation , written in conjunction with a Mr. H. Solberg, built on the information presented in the first and presented a complete picture of an atmospheric phenomenon that we take for granted, that had been likely occurring since the time the earth first formed an atmosphere, and that had and has a direct impact on our day to day lives.

Prior to this, a number of people had recognized the phenomenon we now associate with warm and cold fronts. For instance, a gentleman named Heinrich Dove had recognized the the “battle” occurring between cold air from the polar regions and warm air from the equatorial regions in the late 1820’s. And in the 1840’s, Elias Loomis presented a diagram very similar to the cold front portrayed above.

But from what I can tell from my reading and research so far, nobody put together the complete picture of what was happening until Jacob Bjerknes published his papers with the support of others from the Bergen School. Just goes to show you the potential for having an impact on things that exists when you have a small group of energetic folks with a passion for what they are doing. Kind of inspiring when you think about it.

So if your interest in HVAC and in controlling the built environment has led you to an interest in the uncontrolled ambient environment, take a few minutes to download and read Mr. Bjerknes and Mr. Solberg’s papers. If nothing else, they will give you some insight into a phenomenon that has a direct impact on what you do every day. And they may even inspire you to follow your passion and share what you learn.

David Sellers
Senior Engineer – Facility Dynamics Engineering

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