Not quite yet, but as everyone else is wishing happy New Years that seems covered. On the 3rd (usually at least) of January we are closest to the sun. That the calendar year starts near then is coincidence. Due to orbital variations (Milankovitch cycles), our date of closest approach varies through the calendar year. This is the longitude of perihelion.
Back with the simplest climate model posts we looked some at how our distance to the sun could affect the global mean temperature. In honor of our passage, a project to see how much difference our being 0.0167 astronomical units closer to the sun than normal (i.e., we'll be at 0.9833 AU instead of the average 1.0000) would make. At least, would make if the assumptions of the simplest model were all true.
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Thoughts and notes on science from another blogging Grumbine.
Welcome
I'll be trying what seems to be an unusual approach in blogs -- writing to be inclusive of students in middle school and jr. high*, as well as teachers and parents (whether for their own information or to help their children). To that end, comments will have to pass a stricter standard than I'd apply for an all-comers site. It shouldn't be onerous, just keep to the topic and use clean language.
I expect it to be fun for all, however, as you really can get quite far in understanding the world, even climate, by understanding this sort of fundamental. If I get too much less fundamental, let me know where I went astray.
* Ok, I concede that not many middle school students will get everything. Even a fair number of adults will find some parts hard to follow. Still, some middle school kids will have fun. And almost everyone will follow a number of posts just fine.
Please see the comment policy for details. And the link policy for details about that. The latter is more open than you might expect.
I expect it to be fun for all, however, as you really can get quite far in understanding the world, even climate, by understanding this sort of fundamental. If I get too much less fundamental, let me know where I went astray.
* Ok, I concede that not many middle school students will get everything. Even a fair number of adults will find some parts hard to follow. Still, some middle school kids will have fun. And almost everyone will follow a number of posts just fine.
Please see the comment policy for details. And the link policy for details about that. The latter is more open than you might expect.
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About Me
- Robert Grumbine
- In my day job I work on the oceanography, meteorology, climatology, glaciology end of my science interests, but I'm interested in everything, science or not. So I've also been on stage in a production of Comedy of Errors, run an ultramarathon, and been to Epidaurus, Greece, to see a production of Euripides' Iphigenia among the Taurians Prior to starting the current job, I was a post-doc in oceanography in the UCAR ocean modelling program, and earned my doctorate from the Department of the Geophysical Sciences at the University of Chicago (1989). My undergraduate degree involved Applied Math, Engineering, Astrophysics, and Glaciology. Of course I don't speak for my employer, whoever that may be.
2 comments:
Great Blog and topic.
Only conicidentally, I've started a blog of my own on Earth Climate a did a bit on this subject. Albedo and emissivity should be included to get results resembling actual surface temperatures.
http://climateearth.blogspot.com/2008/12/perspective.html
Albedo is indeed included.
The emissivity you refer to is something I intentionally did not use -- it is not an observed quantity. In the simplest meaningful model, everything is observable -- earth's albedo, solar constant, and earth's blackbody temperature. It matches up well given any two of the three observables.
The emissivity you refer to is a kludge* to cover the fact that what we care about (more) is the earth's surface temperature, rather than blackbody temperature. The only way to determine that figure is to first observe everything else, and then say that the emissivity is whatever is needed to make the equation balance. This doesn't tell us how the emissivity comes about. It does give the right sense of things -- adding greenhouse gases to the atmosphere decreases the surface emissivity, which leads to warming. So it's ok in that sense.
Good luck with the blog. The more of us trying to explain things, each in our different way, the better chance that one of us will do it in a way useful for a given reader.
*kludge: Used by scientists and engineers. It means a fix that works, but is not pretty and may not be working for the right reason. As we're not all scientists and engineers, it occurs to me that a kind of vocabulary guide would be a good idea here. More later.
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