Re: Balloon Ascent Rate and Rising and Falling Air


Now that I reread your question you said ascent, not descent.

My first reason probably doesn't have much affect on ascent.  My second does but I think it will show up as a step function.  A few readings will be off while they go through a station that has a bad timestamp.

If you look at the paper associated with the ASTRA prediction site they describe the stuff that sets the ascent rate.  It is back to drag calculations and Reynolds numbers. If you plot their ascent rate predictions against Time it is not as linear as the other prediction tools.  From my brief looks at these they tend to be less linear than actual balloon flights.

All of the simulations rely on the drag calculations that use Reynolds numbers based on spheres.  I have seen a lot of balloons that are a long way from a sphere at launch.

I guess I should give up and say that while vertical wind does have an affect, it is probably not the only reason it exists.

Jerry Gable
Balloon Flights from APRS-IS

From: "Jerry Gable jerrygable@... [GPSL]"
To: "GPSL@..."
Sent: Thursday, May 4, 2017 1:51 PM
Subject: Re: [GPSL] Balloon Ascent Rate and Rising and Falling Air

My guess is it is mostly GPS and report time errors.  Mark Conner can probably give a more definitive answer but from what I have seen the vertical wind component is relatively small except in storm conditions.  Of course we have all experienced clear air turbulence in planes so it does exist.

My bet would be variations come from a couple of things related to reporting.

1. From what I have seen, at high altitudes the payload tends to toss and turn a lot. My guess is this affects the GPS fix and increases the vertical error in the reading.

2. The timestamps you see in APRS-IS can be pretty large.  I have seen > 30 seconds of variance in timestamps.  When you see altitude plotted against this time it will appear that the descent speed is varying greatly.

Or I could be completely wrong:)

Jerry Gable
Balloon Flight Prediction tools

From: "'L. Paul Verhage' nearsys@... [GPSL]"
To: GPSL@...
Sent: Thursday, May 4, 2017 12:12 PM
Subject: [GPSL] Balloon Ascent Rate and Rising and Falling Air

I see small and frequent variations in a balloon's ascent rate. I thought the variation was due to GPS errors.
But now I wonder how much might be due to air rising and falling. In the first example, if air streams collide and compress the air, does the air rise or fall in response (I can see that it will speed up or slow down). In the second case, can an air parcel be significantly cooler or warmer than the surrounding air and then fall or rise in response?
Is there another reason why air might rise or fall? Can any of these impact the ascend rate of a balloon enough to show up in the APRS data?

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