Eight Miles High

The title is actually not a reference to the song by the Byrds (although I’m a fan, particularly of David Crosby).  Rather its a reference to a part of what you are looking at above.

And before we get to much further into this, I should warn you that this is one of those philosophical, perhaps melancholy, not so much about engineering posts that I do sometimes.  Some may find them really annoying, so you may want to just wait for the next one, which will be the third part of the VSD series.  But for those who are more patient with my occasional ramblings to the other side of life (which is actually a part of my techie side in the bigger picture), read on.

The picture is from the International Space Station (the topic of a previous somewhat melancholy post), Expedition 24 and is looking through the atmosphere.  The cloud layer that the sun is glinting off of is the top of the troposphere, which is between about 5.5 miles thick at the poles and 10 miles thick at the equator as I recall;  an average of about 8 miles, hence the title (O.K. the average is really 7.75, but I really like David Crosby, so I rounded it up).

You are also looking at the stratosphere and the mesosphere.  I encountered the picture while reading Weatherwise, a magazine I subscribe to.  Its in a side bar where they discuss the various layers you are looking at in the picture.

The picture reminded me of how thin a veil the atmosphere is relative to the earth. There are a lot of numbers out there that talk about how thick it actually is;  if you include the exosphere, then you are talking over 6,000 miles;  pretty big relative to earth.  But, if you consider where the ISS operates as being space, then the thickness is about 250 miles give or take.

If you think about atmospheric thickness in terms of the protection it provides for life on earth, then you are probably talking about 60 to 70 miles from what I can tell.  For instance, the aurora borealis, generated by the collision of charged particles from the sun with our magnetic field takes place at about 62 miles.

Meteors tend to glow and burn up between 40 and 70 miles up, depending on their arrival speed and the angle they hit the atmosphere at.   The ozone layer, which protects us from ultraviolet radiation and is the focus of a lot of attention these days –  is part of the stratosphere which runs from the troposphere up to about 30 miles or so.

And 70-80% of the atmosphere’s mass and water are contained in the troposphere which, as I said above, averages about 8 miles high, in round numbers.  That’s about 0.1%  of the earth’s diameter (8,000 miles in round numbers).   On most commercial airline flights, you are looking down at most of it.  Even if you compare 70 miles – the level below which most of the protection that makes life possible is provided –  to the earths diameter, you get a number that is a bit under 1%;  that seems pretty thin to me.

This shot, also from the same ISS mission is perhaps an even better view of the “thinness” perspective.

Here is a similar one with a perhaps more romantic angle on things.

(Incidentally, that particular picture (and maybe some of the others) was taken by Douglas Wheelock, an astronaut with an artistic and poetic eye  – my opinion.   There are a lot of really amazing pictures on his Twitpic page if you like this kind of stuff.)

The concept that seeing earth from altitude reveals how thin the atmosphere is relative to the earth is not particularly new to me; I’ve thought about it a lot over the years and am reminded of it every time I fly.  But, realizing that the images above were available from NASA and that I could download them and use them in classes (or on this blog) when I talk about the impact energy conservation might have on the atmosphere in general and global warming in particular was a new one to me (I know, “well Duh…).

I found the one of the aurora particularly thought provoking since in effect, it is an image that is taken looking down on the atmosphere doing its thing.  Not only can you see the interactions of charged particles with the magnetic fields in the atmosphere that create the Northern Lights (the link takes you to a pretty cool book),  you see the clouds that are the manifestation of the complex atmospheric circulation patterns that occur in the troposphere.  Those patterns are responsible for the various climate zones and the water cycle (among other things), and they are a big part of making life as we know it here on earth possible.

I mentioned global warming above.  That’s a  controversial subject as I discovered when I responded to a comment on an article in HPAC a while back.  The reality is (I think) that we probably don’t really know what is going on right now nor do we know specifically how much we did or did not have to do with it.   I think there is a lot of evidence that strongly suggests relationships between human activity and changes in the atmosphere.  But its so complex and long term that I’m not sure we will ever really understand it other than in hindsight.

But that’s my point;  I think there is a bigger perspective to consider, that being …

The earth’s climate is driven by heat flow, but it is not a machine we understand well enough to control. We ignore the thermodynamics of climate at our own peril.

That’s how David Bruderly put it when he responded to the responses to my comments in HPAC.

So, I guess that’s the reason I decided to do this post.  I was thinking about it all and discovered these pictures, which gave me some new insights and perspectives.  So, I thought I would share them with you.

Maybe they will give you something to think about the next time global warming or climate change comes ups, or maybe not.  But at a minimum, I figure I’ve shared some interesting perspectives on the beautiful place we call home.  And I can’t help but believe that having an appreciation of that is good for everyone and everything.

David Sellers
Senior Engineer – Facility Dynamics Engineering

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