Seeing

[Solanum]

I was out with the scope last night after a couple of weeks of fairly poor weather and was a little surprised to find the seeing was pretty poor, despite the evening being fairly still and not a spot of cloud all day. My 6 mm was useless, whereas the other day when there had been high haze all day and wind, it was better than I expected.

Presumably, air movement in the upper atmosphere has more effect than down here in the troposphere. I've seen links to satellite maps of the jetstream before, could someone repost here and more importantly, tell me what I'm actually looking for in those maps.

[Dez]

G'day Everard

You're lucky to get out at all! Cloudy continuously here, although looking clear this morning.

If you click on "Resources" in the menu bar on the left hand side, there is another link to Weather Resources. Think you may find what you are looking for there

Cheers

[kljucd1 (Daniel)]

Hi,

Yeah those maps don't really mean much to me either, some pointers on how to read them would be useful.

Daniel...

[Gargoyle_Steve (Steve)]

Ok down below I've inserted a typical jet stream map image, the kind you see on most of the links. Jetstream is the high atosphere FAST winds that circle around the world (one "jet" in each hemisphere) and that tend to stuff up the seeing if they are above you - the faster the winds, the worse the seeing. The strongest jetstream seen in this image is around 110 to 120mph.

http://www.wunderground.com/auto/vir...JetStream.html

If you have a look at this you'll see that at this particular point in time Hobart and Sydney are suffering under the strongest/fastest jetstream, Brisbane and Melbourne are both slighty better off ie not quite so buried, and Perth, Adelaide and Darwin are unaffected by any jetstream winds at all.

That doesn't mean that the seeing in those latter 3 will still be perfect, other factors will affect it as well, but if you've got stronger jetstream overhead you will have degraded seeing.

Jetstream is the one factor luckily that you can very quickly and easily check.

Hope that helps.

[Solanum]

Thanks Steve, I figured that faster probably meant worse seeing, but was confused as the highest speed on there is only a fraction of the full scale. So basically, not only the faster the worse, but anything coloured (over about 25 m/s I guess) = bad.

[Gargoyle_Steve (Steve)]

From what I've been able to tell by comparing my own local seeing to those maps it seems that once you pass the 30-40 m/s mark it will have some effect, though with the bulk of my observing done from suburban skies (though not "big city" suburban) it may be that a good dark sky will be visibly affected by even less wind.

Things definitly deteriorate rapidly as the speed increases past and over that 50 m/s (100mph) mark, and I suspect it affects astro imaging more than it does visual observing.

All I can say is I pity anyone who suffers those 200+ mph winds!

[Gargoyle_Steve (Steve)]

As an example of how things change have a look at this image.
I wouldn't like to be on the receiving end of this load!

[Solanum]

Hmmm, looks like it's the Kiwi's rather than us that are going to get it! The only problem with those figures is that they seem to be at least 12 hours+ out of date, so I guess you need to have an idea of where they'll be going next.... I know a guy who is a weather forecaster from an unrelated email list, perhaps I'll quiz him.