More on Thermals (A perhaps scientific but important discussion)

It’s been a while since I’ve taken a radiation course but I am taking one at the graduate level this semester. I think you’ll find it amusing (and perhaps unsurprising) that various topics in my atmospheric science education often provoke thoughts of deer hunting. One of the recent topics that came up in my radiation course is solar absorption and how it can affect the surrounding air behavior. Before I get into it I want to give a quick (jargon free as possible) crash course on solar radiation and absorption:

A term that often comes up with this topic is “Albedo.” The albedo of a surface describes the amount of solar radiation that is either reflected or absorbed by that surface. The scale for characterizing albedo is from 0 to 1. With 0 meaning all solar radiation is absorbed and 1 being all solar radiation is reflected. Dark colors tend to have a lower albedo, while light colors have a higher albedo. You’ve probably experienced this when wearing a black shirt in the summer time, IT’S HOT. The reason for this is that the black color of your shirt is absorbing high amounts of solar radiation. The opposite can be said for why you feel cooler when you wear a white shirt in the summer, most of that radiation is being reflected.

Now, the way that this applies to a deer hunting situation is that different terrain features are going to have different albedos. Dark colored dirt is going to be absorbing high amounts of radiation and heating up. This leads to rising warm air over the surface of the dark dirt, or what we as hunters refer to as “thermals.” You can’t necessarily look at any given hunting location and know exactly what kind of albedos you’re going to be dealing with, but you can get an idea. If you’re hunting in a spot where there’s a lot of dark colored dirt, you can probably expect thermals to be more of an issue than they are in an area with lots of light colored grass or leaves. Does this mean there are no thermals in those spots? Absolutely not, and if you pay attention to these things I don’t think I need to tell you that. However, this is a piece of information you can take with you into the field and apply it in situations where it’s maybe more obvious.

One of the more interesting aspects of this discussion (to me) is that there is a very pronounced effect over water. Water is much more difficult to heat than land and thermals are close to zero over bodies of water (with possibly the exception of small bodies of stagnant water that have more time to heat up). There is an episode from “The Hunting Public” where Aaron Warbritton drops some milkweed from his stand and it floats over a creek next to them. The milkweed floats on thermals until it is over the water and it almost immediately sinks down. The water doesn’t necessarily “pull” it down, there’s just no rising air underneath it to keep it up. This is extremely advantageous to a hunter. As long is there isn’t a super strong wind to blow your scent well over the water before it has time to sink, it will sink down into the water. So, with the right wind, you could set up with your scent blowing out over a body of water and there is almost no way a deer will be able to pick up your wind scent unless they are standing in the middle of that water. Ground scent is another story of course.

So, as always do with this information what you see appropriate. I don’t necessarily believe in trying to “advise” people on how to hunt and apply information. I’m not an expert on deer or hunting. Maybe when I’m 60 with a room full of mature bucks I’ll entertain that notion, but probably not. I have a piece of paper that says I’m technically an “expert” in meteorology, but any wise man knows there’s always much more to learn.

Good luck.

Austin

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