Adelaides seeing issues

[rumples riot]

Not entirely certain this is the right forum for this thread but I figure it is science related.

Spent a considerable time today reading up on the causes of bad seeing from a topographical point of view, and have discovered the cause of my bad seeing on the South side of Adelaide. See Damien Peaches site and Bureau of Meteorology.

According to the experts seeing conditions are particularly dictated by topographical features such as hills, mountains and the prevailing wind. In particular where they are located in relation to your seeing position. In my case I am on the south eastern side of Adelaide and just behind the peak of a hill (well within a kilometre).

As it turns out the prevailing wind comes from the north west which runs across the city up the hills face on directly over my position. This apparently will create unstable eddies in the atmosphere and directly make seeing quite unpredictable. No wonder I only rarely get 7/10 seeing and even then I am not sure of this. The reality is that when I think it is 7/10 it is more likely 4/10. This makes me wonder if I have ever seen 9/10 here at all.

Apparently the best position to be in is on the windward side of the hills or mountains if your prevailing wind travels over you and up over the mountain. Stable air currents are more common and therefore much more stable seeing. Wish I had known this before spending the money on my unit.

The only time this works for me is when the wind comes from the South East or when the winds abate all together and the inversion remains stable. In other words; very rarely. If you know Adelaides topography, then you know that the wind 9/10 comes from the west, northwest or south west.

Anyway just thought some of you guys would like to know this information.

Paul

[RB]

Very interesting,

Thanks.

:)

[rumples riot]

Yeah I was shocked when I saw the effects. :scared: And then it all started to make sense.

[fringe_dweller]

yeah but at least your nice and cool in summer on the south side Paul :) and get plenty of rain - I wonder do many cities have such radical different temp. max's and min's climates ie elizabeth/gawler can be 5º warmer than the south side in summer (Adelaide sprawls for 90 klm N-S) . I have often thought about immediate local conditions affecting seeing just as much as jetstreams ect. In my case I am in a built up area with a lot of concrete/bituman/gravel/tin roofs (with no lawn to speak of) which on warm to hot days of course absorbs the heat and radiates it all night!! So it can be hard to tell if bad seeing is caused by local conditions or the sky conditions. I have found when visiting friends just having a small amount of lawn makes the world of diff in seeing!
I can tell you a lot about the local hills - on one side it can total cloud and on the other side it is totally clear :) same with wind. I have observed a few times from the hills near you years ago ie bridgewater and Blackwood and I dont like the average local conditions up there very much at all - specially in the hollows - to much fog for one thing. to many tree's as well, even if it is darkish. Give me the rain shadow country anytime, Slice is actually really is in paradise - he's not exaggerating there - but being on TOP of the hills is better again - the softly undulating mount lofty ranges actually steadies the seeing for the prevailing northerlies - there is a name for that effect, i cant remember it tho - and they look for that effect when building observatories i have read.

[rumples riot]

Hmmm, that interesting, wonder where this effect is? Like to know myself, so that when I am in the buying market again I know where to look.

[fringe_dweller]

AHA! Laminar airflow is the term! and i guess topographical ordinance maps would be the go :)

"MacRobert's (1995) suggestions:

"Geography is critical. Smooth, laminar airflow is the ideal sought by observatory siting committees worldwide. The best sites on Earth are mountaintops facing into prevailing winds that have crossed thousands of miles of flat, cool ocean. You don't want to be downwind of a mountain; the airstream breaks up into turbulent swirls after crossing the peak. Nor do you want to be downwind of varied terrain that absorbs solar heat differently from one spot to the next. Flat, uniform plains or gently rolling hills extending far upwind can be almost as good as an ocean for providing laminar airflow. You may learn to predict which wind direction brings you the smoothest air."
http://www.saao.ac.za/assa/html/doc_selecting_an_observing_sit.html

[slice of heaven]

Yeah, but the grass is always greener........

The true rain shadow country is great, no doubt about it.
But I'd rather be down here on the flats than up in the hilly sections. The summer nights viewings are absolutely brilliant. We can be in the mid 40's in the day, and the 15-20 knot sea breeze will strip that back and stabilize it to around 18-20degs by midnight and dead calm, while the hills and Adelaide are still in the high 20s-30s.
Same during the winter, the winds off the ocean keep the temp stabilized and the clouds dont bank up, they just roll on by.
The downside... early morning mist.
East of the Callington hills and Palmer hills is probably the best bet, how far north?, maybe Mannum would be a cutoff?, depending on what time of year you favour.
This time of year is the only time you'll cop a fair few s/easterly winds Paul, thats IF a normal late spring weather pattern develops.

[slice of heaven]

You posted while I was typing Kearn :)
Does what I said compare to your post?

[Striker]

Sounds like it's time to move Paul......lol

[rumples riot]

Yeah, all confirmed, glad I bought my block over on Parsons. The seeing there is great. I am 150m from the beach. Gets a bit dewy there, but nice seeing. Just have to wait till armageddon to get my house approved. Maybe I will buy down at Clayton. On the water.

[fringe_dweller]

Yes still applies Slice - the orientation of the mt lofty ranges still would do that to the skies above you re the prevailing winds. the only tricky thing about MB would be Lake Alexandrina and the river causing morning fog/mist as you say- and from experience, it translates all the way up the ranges on the mid to eastern side. Just the lack of cloud is worth it as far as astronomy goes - the Murray can cause a few problems if you get to close re morning mist. but then the hills can produce their own sort of localised cloud/fog of course - its not always perfect :)

[slice of heaven]

That's true, Spring absolutely Sux here, the clouds seem to go around in circles overhead. But 3 out of 4 aint bad ;)

[fringe_dweller]

Slice: late summer/autumns are my favourite times - and mild to severe drought year winters are pretty impressive for astronomy. Springs not that great on this side of hill either mate ;( i have come to associate (normal) springs with cirrus and wind after being a skywatcher for a while. At least we dont get all the horrible longlasting bushfire and cloud trouble they get in the eastern states in summer some years - very fortunately :prey: nothing much to really burn in the way of dense forestation most areas here eh

Paul: I hope your scope doesnt rust up there on the coast - what about sea breezes/hurricanes? good for cooling down - but not for steady astronomy? :confuse3: at least its REALLY dark there and it is nice and in the cloud freeish north -
thats ok I am just jealous ;)

[rumples riot]

If I ever get my house built I will invite you over there. Seeing is very good, not much wind either. No hurricanes to speak of.

[fringe_dweller]

thnx dude - sounds like a plan :)

[Jonathan]

Interesting information.
Is it just me, or has the seeing in general been pretty ordinary for the last couple of months in Adelaide? That is of course on those rare cloudless nights we've been getting.

[Darkplague]

Yep Its been pretty lousy these last few months.

Planet hunting, pffft, forget about it, nothing but wobbly blobs to look at.
I had a semi decent night last monday, maybe 5/10.
The highlight was 47 Tucanae and Tarantula Nebula. Mars looked very poor.

Also saw a massive fireball which broke up into 3 seperate fireballs coming in!!!! :o Covered about 1/4 of the sky. I guess its part of the Taurid shower?? Saw plenty of smaller meteors as well.