mental4astro
08-08-2013, 12:19 PM
Hi all,
Ol' Wavytone, with his thing for flying, has put me onto a BOM page that gives the data that's gathered by those big silver weather balloons they release everyday. The data that they gather in shooting up through the sky reveals an amazing amount of information that is helpful to us observing through our scopes. Bringing up this page can help you also decide if pulling out a scope is worthwhile if you intend to do high magnification observing.
The chart in question is their Aerological Diagrams (http://www.bom.gov.au/aviation/observations/aerological-diagrams/). It brings up a map of Australia, and you just select the city/town you want. I am not across all the information that the chart shows, I'll leave that to others more informed than I, but I will note the information that is relevant to us. The chart shows various data entries versus altitude as the balloon rises. On the far right is a lot of 'arrows', these signify wind velocity and direction.
The most significant information is shown by the red line on the left hand side. It shows dew point against altitude. The more serrated the line is, particularly just below the 5,000m mark (noted in the chart as "5.0" as altitude is noted in 1000's), it means that there is an inversion layer (hot air trapped under cold), and this serration is the effective turbulence that's created as these two air masses pass over each other. The more drastic the serrations are, the greater the turbulence and the worse seeing conditions are. The smoother the line, the less, if any, turbulence, and the better the seeing. In an aircraft you notice this with the plane's dramatic and sometimes violent rise and fall and you poop your pants as you think you're about to fall out of the sky.
The serration is created by the dramatic rise and fall in temperature as the balloon rises travelling through the turbulence.
Here are two examples showing 'good' seeing and 'poor'. The first chart is from today for Sydney. It shows the red line without any significant wild variations in the dew point, just a single smooth steady line that shows the temperature is just consistently dropping as the balloon rises. All of this suggests seeing is good:
145012
This second chart shows a significant 'serration' of the left side red line reaching the 5,000m mark. The means a lot of turbulence and poor seeing:
145013
Being sceptical of anything Wavy tells me, :rolleyes:, :lol:, I thought I'd put this info to the test on several nights. Low and behold! it worked! Those nights that saw the aerological diagram give a smooth, steady temperature drop gave fantastic seeing conditions. Those nights that saw the red line very serrated were nights of poor seeing conditions.
On those night now when I'm contemplating doing a sketch of the Moon or planets, or some other high magnification work, I consult this chart before setting up. It's saved me time and frustration knowing in advance if it would be worth the while or not. But if high magnification is not my main fodder for the night, I don't bother with the chart.
Wavy mentioned to me how this information is gathered. The balloons gather primarily temperature and humidity readings (maybe altitude?). These balloons have attached under them as part of their ballast, a silvered reflective catseye prism that reflects the radar signal from the airport. It is this that gives the BOM the balloons direction and velocity (altitude too?). Other variations on weather balloons sees the ballast carry a transponder rather than a reflector, and other instruments.
Hopefully others here will find this chart useful.
Mental.
Ol' Wavytone, with his thing for flying, has put me onto a BOM page that gives the data that's gathered by those big silver weather balloons they release everyday. The data that they gather in shooting up through the sky reveals an amazing amount of information that is helpful to us observing through our scopes. Bringing up this page can help you also decide if pulling out a scope is worthwhile if you intend to do high magnification observing.
The chart in question is their Aerological Diagrams (http://www.bom.gov.au/aviation/observations/aerological-diagrams/). It brings up a map of Australia, and you just select the city/town you want. I am not across all the information that the chart shows, I'll leave that to others more informed than I, but I will note the information that is relevant to us. The chart shows various data entries versus altitude as the balloon rises. On the far right is a lot of 'arrows', these signify wind velocity and direction.
The most significant information is shown by the red line on the left hand side. It shows dew point against altitude. The more serrated the line is, particularly just below the 5,000m mark (noted in the chart as "5.0" as altitude is noted in 1000's), it means that there is an inversion layer (hot air trapped under cold), and this serration is the effective turbulence that's created as these two air masses pass over each other. The more drastic the serrations are, the greater the turbulence and the worse seeing conditions are. The smoother the line, the less, if any, turbulence, and the better the seeing. In an aircraft you notice this with the plane's dramatic and sometimes violent rise and fall and you poop your pants as you think you're about to fall out of the sky.
The serration is created by the dramatic rise and fall in temperature as the balloon rises travelling through the turbulence.
Here are two examples showing 'good' seeing and 'poor'. The first chart is from today for Sydney. It shows the red line without any significant wild variations in the dew point, just a single smooth steady line that shows the temperature is just consistently dropping as the balloon rises. All of this suggests seeing is good:
145012
This second chart shows a significant 'serration' of the left side red line reaching the 5,000m mark. The means a lot of turbulence and poor seeing:
145013
Being sceptical of anything Wavy tells me, :rolleyes:, :lol:, I thought I'd put this info to the test on several nights. Low and behold! it worked! Those nights that saw the aerological diagram give a smooth, steady temperature drop gave fantastic seeing conditions. Those nights that saw the red line very serrated were nights of poor seeing conditions.
On those night now when I'm contemplating doing a sketch of the Moon or planets, or some other high magnification work, I consult this chart before setting up. It's saved me time and frustration knowing in advance if it would be worth the while or not. But if high magnification is not my main fodder for the night, I don't bother with the chart.
Wavy mentioned to me how this information is gathered. The balloons gather primarily temperature and humidity readings (maybe altitude?). These balloons have attached under them as part of their ballast, a silvered reflective catseye prism that reflects the radar signal from the airport. It is this that gives the BOM the balloons direction and velocity (altitude too?). Other variations on weather balloons sees the ballast carry a transponder rather than a reflector, and other instruments.
Hopefully others here will find this chart useful.
Mental.