74 replies to this topic

[Jon Isaacs]

Tony Flanders, on 22 Jun 2024 - 06:09 AM, said:

It seems to me that skyglow is pretty much of a red herring in this thread; in fact the main postings have barely mentioned it.

The proper title for the thread so far would be "Why Canadians Have Better Transparency than Americans."

The relationship between transparency and skyglow is interesting and complex, and probably deserves its own thread. However, poor transparency is a menace for deep-sky observers even at sites with zero artificial skyglow.

Being located in most southwest corner of the Continental United States, I am trying to make sense of all this.  My friends who live in Montreal have very few opportunities to observe and seem to envy my location..  The United States is a large area and generalizations over the entire nation seem likely to be fraught with errors..  To me, it all starts with clear skies.

 

I am looking at maps.. Rainfall, sunniest places in the world..  How often are the skies clear?

 

https://en.wikipedia...nshine_duration

 

The southwestern United States looks pretty good..  Yuma, Arizona has over 4000 hours of sunshine per year, more than any other city listed in the world, nearly double any city listed in Canada.  And 3 inches of rain,   Our place in the high desert, it's 100 miles from Yuma... 50 miles to the north is the Hale 200 inch, 120 miles to the south is the Mexican National Observatory.. 

 

I guess I am too simple minded.. 

 

Jon

Edited by Jon Isaacs, 22 June 2024 - 10:48 AM.

[CharLakeAstro]

 

The southwestern United States looks pretty good..  Yuma, Arizona has over 4000 hours of sunshine per year, more than any other city listed in the world, nearly double any city listed in Canada

 

The list omits the two sunniest cities in Canada, which are Victoria BC and Cranbrook BC, each around 2400 hours of sunshine. But nevertheless, the "nearly double" statement remains valid.

 

There are other factors also. These higher latitudes result in much later dusk and earlier dawn (shorter nights) in summer than lower latitudes. Summer nights in Canada are short, and the northern sky is annoyingly bright this time of year. This is true even at my 44.5N latitude, and the higher latitudes even more true.

 

If one was to compare total hours of astronomical darkness, the longer winter nights would balance out the shorter summer nights. The climate being quite moderate especially in Victoria, autumn, winter and spring are the best seasons for observing. For most of Canada, autumn is really the best season - longer nights and not yet very cold.

 

[Jon Isaacs]

Charles;

 

I had looked up to see that astronomical dark on these short nights is only about an hour in Montreal. And I did not mention the fact that in dry climates like the southwest there are typically no mosquitoes.

 

Jon

[GeorgeLiv]

This is fantastic info. For those of us who are not as savvy reading weather maps, which website would you recommend for looking at air masses, fronts, temperatures and so forth?

 

I live in the southeast US, not right on the Atlantic Coast but probably close enough to receive those tropical marine air masses.

 

This screen shot is from Wunderground Wondermaps. Not sure if this is a reputable website or maybe you can recommend better, but I like the graphics.

 

Thanks,

Tony

Hi, I made some time & checked out www.wunderground.com/wundermap. This is a great site for what we're looking for. Keep using it! Occasionally zoom out to see the bigger picture. Currently, continental-Polar is behind the cold front in northeast Quebec. The motion of the fronts are implied in the manner they're drawn (example: D for direction --> to the east). I marked the direction of the frontal boundaries shown with red & blue arrows. A stationary front may move in-line as drawn, but air circulation can be as I've marked. Thanks for the heads up!
 

[GeorgeLiv]

It seems to me that skyglow is pretty much of a red herring in this thread; in fact the main postings have barely mentioned it.

The proper title for the thread so far would be "Why Canadians Have Better Transparency than Americans."

The relationship between transparency and skyglow is interesting and complex, and probably deserves its own thread. However, poor transparency is a menace for deep-sky observers even at sites with zero artificial skyglow.

I posted what I know of the structure of our atmosphere, here on this forum, which discusses topics on light-pollution. If I wanted to discuss transparency, I'd post this in another forum.

 

Granted, the title is click-bait. But yes, I'm implying less sky-glow, and you should be inferring the same. It's very simple: When it clears, not when it snows, nor when it rains or remains cloudy, it simply can get darker because most of Canada is influenced by cold & shallower "continental polar" air-masses, more often, not always, especially not midsummer.

 

Happy to see that others here have understood.

[vsteblina]

The list omits the two sunniest cities in Canada, which are Victoria BC and Cranbrook BC, each around 2400 hours of sunshine. But nevertheless, the "nearly double" statement remains valid.

 

If Victoria and Cranbrook are the sunniest cities in Canada......good thing I left BC to go to California.

 

But I currently live, not to far away from both those cities and the weather is awful in winter.

 

I live in what use to be known as the Great Columbia Desert, until FDR got rid of it.

 

We are in a drought this year with five inches of precipitation in this water year.  It looks like we will not even approach our normal precipitation of eight inches.

 

Being a desert, we have great transparency and low relative humidities that go under 10% in the summer.  Between Thanksgiving and President's Day it is pure crap with 90% relative humidities and foggy, cloudy skies.

 

The NWS when new meterologists transfer into Spokane always has to watch them since in winter when a high pressure cell moves overhead they want to forecast SUNNY weather, instead of CLOUDS.

 

So how do you get CLOUDS in a desert in the middle of winter when a cold Canadian air mass moves in???
 

[GeorgeLiv]

 

Being located in most southwest corner of the Continental United States, I am trying to make sense of all this.  My friends who live in Montreal have very few opportunities to observe and seem to envy my location..  The United States is a large area and generalizations over the entire nation seem likely to be fraught with errors..  To me, it all starts with clear skies.

 

I am looking at maps.. Rainfall, sunniest places in the world..  How often are the skies clear?

 

https://en.wikipedia...nshine_duration

 

The southwestern United States looks pretty good..  Yuma, Arizona has over 4000 hours of sunshine per year, more than any other city listed in the world, nearly double any city listed in Canada.  And 3 inches of rain,   Our place in the high desert, it's 100 miles from Yuma... 50 miles to the north is the Hale 200 inch, 120 miles to the south is the Mexican National Observatory.. 

 

I guess I am too simple minded.. 

 

Jon

 

Why would anyone want to compare a light-polluted city like Montreal with any rural South-West location? Shouldn't you be comparing say Phoenix with Montreal instead? Vegas with Toronto? And why not compare dark-sky sites instead like Algonquin Provincial Park with the Grand Canyon?? Do you get it now?

 

Did I mention climatic statistics here? If I wanted to discuss which climate is better, frequency of cloudy/sunny days, or length of nights per latitude, I'd post this in another forum.

 

Again, it's quite simple: When it clears, not when it snows/rains or remains cloudy, it simply gets darker, more frequently, because most of Canada is under the influence of "continental polar" air-masses.
 

Charles;

 

I had looked up to see that astronomical dark on these short nights is only about an hour in Montreal. And I did not mention the fact that in dry climates like the southwest there are typically no mosquitoes.

 

Jon

Why are you veering into "other" topics in this particular light-pollution forum? Is there some sort of prior agenda? Are you being facetious??

 

Did anyone mention anything about Canada being better for Astronomy? On the contrary, it's horrible.
 

Edited by GeorgeLiv, 22 June 2024 - 10:21 PM.

[GeorgeLiv]

So how do you get CLOUDS in a desert in the middle of winter when a cold Canadian air mass moves in???
 

If you take a parcel of dry & exceptionally cold air, and move it over warm land and unfrozen lakes, you can get the following...

 

 

Not as extreme as this lake-effect image, but if you study the saturation vapor-pressure diagram of water I posted above, you can see that the moisture in the air on top of a dry dessert, say at 15° C & 20% RH, if you simply cool it to -5° C you get 100% RH, likely lots of low cloud of stratus form.

[Jon Isaacs]

Why would anyone want to compare a light-polluted city like Montreal with any rural South-West location? Shouldn't you be comparing say Phoenix with Montreal instead? Vegas with Toronto? And why not compare dark-sky sites instead like Algonquin Provincial Park with the Grand Canyon?? Do you get it now?

 

Did I mention climatic statistics here? If I wanted to discuss which climate is better, frequency of cloudy/sunny days, or length of nights per latitude, I'd post this in another forum.

 

Again, it's quite simple: When it clears, not when it snows/rains or remains cloudy, it simply gets darker, more frequently, because most of Canada is under the influence of "continental polar" air-masses.
 

Why are you veering into "other" topics in this particular light-pollution forum? Is there some sort of prior agenda? Are you being facetious??

 

Did anyone mention anything about Canada being better for Astronomy? On the contrary, it's horrible.
 

 

The reason I chose Montreal was because that is where you are located. 

 

I could have compared Las Vegas with Toronto.. 3825 hours per year to 2066 hours per year.  

 

You wrote:

 

"I rarely come here in summer months. But when I do, I find it alarming in how simplistic some amateurs can be, misunderstanding SQM-based LP maps & searching for some holy-grail dark site, yet won't consider the occasional & special circumstances that arise (or arrive) to darken any light-polluted town."

 

You are discussing "some holy grail dark site."  You did not mention climate statistics but obviously it is important in determining who experiences transparent skies most frequently.  Your analysis seemed to point to more transparent skies but in my simple minded thinking, one has to include clouds in that equation.

 

Again, it's quite simple: When it clears, not when it snows/rains or remains cloudy, it simply gets darker, more frequently, because most of Canada is under the influence of "continental polar" air-masses.

 

 

It seems that might be true for most of Canada but not for most Canadians. 

 

 

Did anyone mention anything about Canada being better for Astronomy? On the contrary, it's horrible.

 

 

That's good enough for me.  Do Canadians experience less sky glow than Americans? One could argue that they see less clear sky to glow.

 

What interested me what that my location in the extreme southwestern corner of continental US was being lumped with other parts of the US with very different conditions.  I couldn't find much about my region.  

 

Jon

[GeorgeLiv]

Too many off-topic replies obscuring my descriptions/arguments. But if we can veer way off-topic, let's change the words Canada with Siberia.

 

Siberia doesn't have better weather than any part of the USA nor any parts of Europe. True.

Siberia definitely has more black-flies and arguably an extended mosquito season. True.

Siberia has much more snow than any other parts of the planet. Probably true.

Siberia has midnight twilight centered around June 21st. True.

Siberia has 'round the clock Auroras on many winter nights. True.

Siberia is the worst place for Astronomy. Not necessarily true. This depends on your hardiness.

 

So what?!?! All of the above are irrelevant to my original description.

 

Like northern Canada, Siberia is a source for "continental Polar air-masses". The gist is that when it's clear over a lit-up Siberian town, it's darker than a similar town anywhere else on Earth.

 

The reasons are..

1: The column of air up to the stratosphere is only 8 km above the ground.

2: Cold air has a decreased capacity to hold water per unit volume. The probability of H₂0 molecules bonding with impurities to enlarge the total size & scatter light independently of wavelength is also decreased.

 

And that's it. How much darker is subject to calculation or estimation. You're welcomed to ask for one.

[vsteblina]

If you take a parcel of dry & exceptionally cold air, and move it over warm land and unfrozen lakes, you can get the following...

 

Lake-effect-squals.jpg

 

Not as extreme as this lake-effect image, but if you study the saturation vapor-pressure diagram of water I posted above, you can see that the moisture in the air on top of a dry dessert, say at 15° C & 20% RH, if you simply cool it to -5° C you get 100% RH, likely lots of low cloud of stratus form.

Thanks for the explanation.

 

The Great Columbia Desert had no lakes, no water, except for the Columbia River flowing through it. 

 

The locals swear that when the ENTIRE Columbia River was dammed in the 30's and 40's the weather changed in winter.  However, the dams on the Columbia with the one exception of Grand Coulee are pretty much run of the river dams.  Just slightly bigger than the "original" river.

 

One person did tell me that it was NOT the dams but the Columbia Basin Irrigation Project which converted almost a million acres from desert to farmland that changed the winter weather.  There is "official" National Weather Service data dating back to the 1880's.  The bulk of the land use change in the Columbia Basin was from the 1940's to 1970.  That might be an interesting graduate student project.

 

Did you see the UC Berkeley study on tule fogs in the Central Valley of California??  

 

The clean air regulations in California reduced the ;particulate levels in the Central Valley and as a result the number of "tule fog" events has gone done dramatically. 

 

It would be interesting to see the correlation between transparency and particulate levels.

 

It is an interesting example of how transparency was enhanced by reducing the level of particulates in the air.  Likewise on the flip side, increasing particulates in the atmosphere will result in a significant decrease in transparency.

Edited by vsteblina, 23 June 2024 - 10:31 PM.

[GeorgeLiv]

I have nightly records for clear/cloudy or partly cloudy skies from 1977 thru to about 1988. I can tell you that there's now about 2 fewer clear nights per week. That's for my skies, but I'd imagine that there's extra cloud everywhere on Earth except where air genuinely sinks. Extra cloud is likely due to increased evaporation of warmer oceans & lakes AND added condensation nuclei in the air, as well as in the Stratosphere now. Additionally, tropical flow from south to north has increased. Low pressure systems become widespread & huge and hurricanes extra deep. Occasionally, entrenched "Polar vortex" flow will inflict 1 or 2 areas on Earth, simply because the atmosphere needs to mix everything for equilibrium.

 

This afternoon's flow (Monday June 24 '24)..

 

 

What you currently have in the southern-tier States is essentially tropical flow. The SW particularly is in what we call "Monsoonal" flow.  With regards to sky-glow, lighting will strike air particles up until 18 km above sea-level where the Tropopause ends & Stratosphere begins. Cool but modified air is now way up in Northern Quebec.

 

I forgot to mention that a quarter of Hudson's Bay is still frozen! Thaws completely in July. A frozen Hudson Bay is great for creating cP air, especially in winter. And for those in the North-East, expect a palpable change in air quality and temperature by this Thursday June 27th.

 

 

Great site for following fronts. The dashed lines on the attached are troughs. Think of a hill, imagine the opposite of a ridge, which is a valley. Trough Lines (see marking above) are elongated areas of low pressure. Air generally rises in this area so clouds will form as well as precipitation. Also click on "Windstream" on the right, to visualize the Jet-streams.

Edited by GeorgeLiv, 24 June 2024 - 10:00 PM.

[deSitter]

This is all extremely interesting!

 

-drl

[gordtulloch]

The list omits the two sunniest cities in Canada, which are Victoria BC and Cranbrook BC, each around 2400 hours of sunshine. But nevertheless, the "nearly double" statement remains valid.

That surprised me - BC seems to get a lot more rain November - April than we do on the prairies, and I checked - Cranbrooke only gets 2229hrs of sun versus Calgary at 2396, my own Winnipeg at 2352 and Edmonton at 2345. Victoria makes the list at 2109hrs.  I do agree that autumn in Canada is the best observing time, with mild temps and the mosquitos are gone. Although to make maximum advantage of my observatory it's geared up to operate 365 days a year, including our -35C temps, generally when it gets dark before 4:30PM! Makes up for now when we have zero true night.

[GeorgeLiv]

Those of you in the North East, please try to enjoy this rare night under a (highly) modified continental polar air-mass. Judging from the color of my sky it's smoke free. It won't last for more than one night. There's a warm front moving in from Northern Ontario by noonish Friday the 28th local time.

 

 

This air is highly modified from Hudson's Bay, James Bay and the very warm waters of Lakes Ontario & Erie. But this type of weather I once enjoyed up here long ago on most summers.

Edited by GeorgeLiv, 27 June 2024 - 04:59 PM.

[GeorgeLiv]

Perhaps I spoke too soon because my NW sky at sunset (near8:40pm) didn't look "good". Too humid & orangy.

 

[Jon Isaacs]

That's me, down along the US-Mexico border, about 60 miles east of the Pacific Ocean... I'm not exactly sure what it all means but I'm expecting clear transparent skies.

 

 

Jon

[Tony Flanders]

Those of you in the North East, please try to enjoy this rare night under a (highly) modified continental polar air-mass. Judging from the color of my sky it's smoke free. It won't last for more than one night. There's a warm front moving in from Northern Ontario by noonish Friday the 28th local time.

 

Fri28-000UT to Sat29-12UT.gif

 

This air is highly modified from Hudson's Bay, James Bay and the very warm waters of Lakes Ontario & Erie. But this type of weather I once enjoyed up here long ago on most summers.

I had excellent transparency last night here in Amherst, MA. And the terrestrial transparency this morning was the best I've ever seen. Viewing from Mt. Norwottuck, the tower on Mt. Greylock 40 miles away was sharp in my 8x32 monocular. Normally I struggle to see it through the haze at 20X.

[mountain monk]

Just curious…

 

When I was planning a steelhead fishing trip to Vancouver Island I read that it was the rainiest place in North America. So how can Victoria be one on the sunniest places in Canada?

 

Dark skies.

 

Jack

[Tony Flanders]

When I was planning a steelhead fishing trip to Vancouver Island I read that it was the rainiest place in North America. So how can Victoria be one on the sunniest places in Canada?

Rain shadow. It's amazing what a few little mountains will do.

I remember hiking across Chilkoot Pass in Alaska. You go from dense rain forest to semidesert in 2 miles.

[Jon Isaacs]

Rain shadow. It's amazing what a few little mountains will do.

I remember hiking across Chilkoot Pass in Alaska. You go from dense rain forest to semidesert in 2 miles.

It's all relative.

 

I looked up the average rainfall in Victoria, BC.  By San Diego standards, it rains a lot.. 24 inches a year with 130 days a year with some rain..  San Diego is about 10 inches per year with 21-41 days of measurable rain depending on who you believe.  In the recent past, we have had years with about 3 inches of rain. 

 

Vancouver gets about 44 inches a year with 160 days of precipitation., 

 

https://en.wikipedia...ritish_Columbia

 

https://en.wikipedia...ne arid climate.

 

https://en.wikipedia...te_of_Vancouver

 

Squim, Washington is known at the Banana belt, it's in the shadow of the Olympics, it gets around 17 inches per year.

 

Jon

[GeorgeLiv]

IR loop for the night of Thur/Fri June 27/28, '24, from 6 pm (Jun27th) to 11am (Jun28th) EDT...

 

 

It's a negative of the infra-red displaying surface temperatures, ostensibly, the higher the cloud tops, the colder they are. Celsius scale is at bottom. The South West gets hotter than 30°C, so they show it going darker again (scale above 30°C is not shown, it's a Canadian website).

 

In the N.E., you can see an all too brief slot of cool air flow circulating from the NW to SE. Lowest sky-glow I've seen since last month, May of '24. In the 'burbs, 3.5 mag stars easy before moonrise, instead of typical 2.3 mag in soupy tropical air.

 

In the extreme South West US, you may think it's a similar flow, but this is mostly sinking air. Air is four dimensional. There's time of course, north-south & east-west flows, but there's also a small up-down component. Sinking air dries and heats-up (Santa-Anna winds have a large sinking component). This gives rise to the characteristic belt of arid zones near 30° north & south latitudes. In these areas, the temperature swing in cooling then heating is large, often more than 40°C in 12 hours.

 

Notice how the floor of the Grand Canyon remains warm relative to the higher plateaus.

 

 

Attached Thumbnails

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[Jon Isaacs]

An interesting measurement is IR from the ground. 

 

Jon

[GeorgeLiv]

Global Jet-Stream finder, useful for any part of the world, simply grab & rotate. Make sure to check the Southern Hemisphere

 

Half a billion citizens across North America are enjoying tropical & sub-tropical air.

 

IR loop starts @ 5am EDT July 7 & ends @ 7:30pm EDT, July 8th, '24. Red arrows mark the Sub-tropical jet, blue marks the Polar-jet.

 

Edited by GeorgeLiv, 08 July 2024 - 09:22 PM.

[Tony Flanders]

Half a billion citizens across North America are enjoying tropical & sub-tropical air.

Perhaps the word you intend is "experiencing." At least one of those half billion isn't enjoying it one little bit.

Edited by Tony Flanders, 09 July 2024 - 05:11 AM.