Meteorology PPL Question

[el_miguel42]

Hi guys

Im currently studying for my PPL ground exams and am focusing on met and nav. I like physics and so a lot of the stuff im reading makes perfect sense, but ive come across a question a couple of times that is really bugging me and im hoping someone would be able to shed some light on it.

its regarding incident solar radiation on the Earth and its subsequent reflection when reaching clouds and absorption by the surface. The questions mention "short wavelength radiation" and "long wavelength radiation" one being absorbed and the other being re-emitted.

This makes no sense, short compared to what? and long compared to what? Everything is short compared to radiowaves and everything is long compared to gamma.

Hope someone can clear this up for me

Cheers

Miguel

[mad_jock]

Visible light is the reference.

[PA28181]

Maybe this is what the re-think regarding TK for PPL's is about, by the CAA?


Proposals for new PPL training syllabus being developed | CAA Newsroom | About the CAA (http://www.caa.co.uk/application.aspx?catid=14&pagetype=65&appid=7&mode=detail&nid=2283)

[UV]

Yes, you will need to know all about that when you are flying your PA28 on your local Bimble (what an awful expression).

[el_miguel42]

Thanks for the replies guys,

Im a bit miffed at visible light being the reference. Correct me if im wrong but, the sun sends out a lot more IR and Radio than it does UV and xrays etc, additionally a large portion of the higher frequency radiation gets absorbed by our atmosphere.

So the majority of solar radiation that actually reaches the surface of the Earth is of UV and lower frequencies, therefore averaging it out it seems more longer wavelengths reach the surface than short...

[dubbleyew eight]

el_miguel a lot of the "theory" was developed without the sophisticated understanding of today. the best approach is to think of the simplest explanation possible without understanding all the detail and look at what the theory is based on that. some of this stuff dates from 50 years ago.

[LondonJ]

Hi el_miguel

Concept is straightforward, and well it seems like overkill, it's not a bad bit of foundation knowledge if you go on to learn about things like radiation fog etc.

Anyway, the electromagnetic spectrum is split up into groups by electromagnetic wavelength (X-ray, visible light, Ultraviolet etc). These wavelengths are measured in microns (or micrometers or 10^-6 metres). If the wavelength is less than 1 micron, it is shortwave and viceversa, it's long wave.

The sun emits Shortwave radiation, as it hits our atmosphere the very shortest wavelengths are absorbed by the Helium and Hydrogen high up, a lot of Ultraviolet is absorbed by 03 (i.e. Ozone) and of the remainder, some is absorbed by clouds and water vapour on the way down and the rest hits the ground, where it is either absorbed (and heats the ground in a process called insolation) or reflected. When it is reflected it becomes longwave radiation (i.e wavelength > 1 micron). This longwave radiation then exits our atmosphere.

Shortwave In Longwave Out (Mnemonic SILO)

[el_miguel42]

Cheers LondonJ,

Thats exactly what I was after, while I had read the general information of the model, none of the books I have actually tell me what the reference for "short" and "long" is. Without knowing that the reference for this terminology is 1 micrometer, its impossible to answer the question from first principles.

As you say, if we are talking shorter or longer than 1 micrometer then there is no problem at all; as that would include all visible light and a small band of IR which would certainly be the majority of the emitted radiation from the sun.

All this being said I think the biggest absurdity ive seen yet are the variances in the units of measurements, especially in the conditions for VMC.

Imperial units of measurement for height, knots used for airspeed and meters used for horizontal distance. Really made me cringe.

Cheers

Miguel

[PA28181]

Is that gas meters or electric. The word meters for distance makes me cringe also. (Metres please)

[el_miguel42]

Cant argue there, I do normally spell it correctly.

Unfortunately US spellings are in some cases being made international standard. Case in point being sulphur, which is now according to the international council for sciences officially spelt sulfur.

[UV]

UV and xrays
UV and lower frequencies
Earth is of UV

Tell me more...