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I was reading about weather balloons and the articles said that weather balloon flights usually last about two hours. When I looked up why, some articles said that when the balloons get high enough in the atmosphere, the balloons pop from the low pressure causing the hydrogen or helium inside the balloon to expand until the balloon popped.

My question is: if weather balloons always pop when they reach a certain altitude, why don’t they just make sure the balloon is carrying a payload that is too heavy for the balloon to reach that altitude (or put less hydrogen). If these are used by meteorologists and the like, wouldn’t it be cheaper to just leave the balloons in the sky instead of constantly putting new ones up?

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    $\begingroup$ The balloon wouldn't rise high or fast enough if it were too heavy to reach popping height. Automatic ballast-release mechanisms are expensive and heavy themselves. Not worth it for a usually very very cheap balloon. Why spend 50k making a not popping balloon (whose battery will run out) if you can just get 50 1k$ balloons? $\endgroup$
    – Hobbamok
    Feb 15 at 14:52
  • $\begingroup$ this makes me wonder is there like satellite thing for replacement of weather balloon? $\endgroup$
    – encryptoferia
    Feb 16 at 1:47
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    $\begingroup$ @encryptoferia satellites are great but balloons carry instrumentation through the air we want to know about, measuring various parameters as a function of altitude. Satellite measurements can have produce some altitude-dependent data for some parameters, but not for everything and not with anything like the resolution $\endgroup$
    – Chris H
    Feb 16 at 14:36
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    $\begingroup$ Because then what would the tame American press have to get fake worked up about? $\endgroup$
    – Valorum
    Feb 16 at 19:38
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    $\begingroup$ @encryptoferia There are weather satellites. There are also weather rockets (no satellites, the rocket radios sensor readings before crashing back to earth - they're called sounding rockets) and there are also weather drones (cheap RC planes equipped with GPS control system - same logic as weather balloons and sounding rockets). The one thing balloons do that none of the other things do is drift with the wind for a very-very long distance. Scientists use different equipment to measure different things on different budgets. $\endgroup$
    – slebetman
    Feb 17 at 1:12

6 Answers 6

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In addition to radiosondes that do a single ascent over a few hours, there are also driftsondes that stay in atmosphere for days or weeks, typically with their buoyancy set up to track a particular pressure level. They commonly carry a payload of dropsondes that they can deploy periodically to do sampling on the way down, much like a radiosonde does on the way up. Because these are much larger and more expensive platforms than radiosondes, they are typically used for targeted field campaigns, particularly in places where it would be difficult to launch lots of radiosondes. For a summary, see Cohn et al (2013) https://doi.org/10.1175/BAMS-D-12-00075.1 and, having been peripherally involved in one of the campaigns they mention, I echo their comment:

Like aircraft dropsonde systems, field experiments using driftsondes involve significant cost and require much advance planning. It can take months to understand likely flight paths and obtain permissions to overfly many countries. If a balloon drifts near a region where overflight permissions have not been granted, then it must be cut down.

In additional to that difficulty, general reasons why driftsondes can’t stay aloft permanently include,

  • All balloons leak, so they can’t stay aloft indefinitely
  • Balloon materials deteriorate, particularly in extreme temperatures
  • Instruments need power, and solar panels add to weight and complexity
  • Finite number of dropsondes aboard, although that’s not the only type of payload

I notice that (but don’t know much about) the more recent STRATEOLE-2 driftsonde (Haase et al, 2018; https://eos.org/science-updates/around-the-world-in-84-days) can stay aloft for around three months, which means it can circle the equator about three times.

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    $\begingroup$ "air balloons leak" and of course helium (pesky monatomic stuff that passes through almost anything) leaks far faster than air. Hydrogen is somewhere in between. $\endgroup$
    – Chris H
    Feb 16 at 14:39
  • $\begingroup$ @chrisH I think you got those two backwards $\endgroup$
    – Kai
    Feb 16 at 17:28
  • $\begingroup$ @Kai hydrogen is a bigger molecule being H2, but it does seem on further reading like it can be even worse than He (which I have worked with, unlike H2) $\endgroup$
    – Chris H
    Feb 16 at 17:48
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    $\begingroup$ @ChrisH I have no doubt that air balloons do leak, but the answer here says that all balloons leak; this of course already encompasses both helium balloons and air balloons $\endgroup$
    – Will
    Feb 17 at 16:46
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    $\begingroup$ @Will I could have sworn it said "air balloons" - but I must be wrong because it hasn't been edited. $\endgroup$
    – Chris H
    Feb 17 at 18:18
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It depends on what each weather balloon is measuring; what data they are capturing.

Most weather balloons are released as specific times during a 24 hour cycle. Such balloons measure altitude, temperature, air pressure, humidity, etc. as they rise through the atmosphere. This data is used to get a data cross-section through the atmosphere. This allows meteorologists to obtain a better idea of what is occurring with the atmosphere during the course of the day.

Once the balloons have provided this data they've done their job. Constantly supplying data for a specific horizon within the atmosphere, once the balloons have reached their ultimate height is not as useful as knowing the data at various altitudes.

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There are several reasons for this. One of them is air traffic concerns. The parts of the atmosphere that are interesting for weather (namely, the troposhere and lower stratosphere) also happen to be the ones in which nearly all aircraft fly. This is why air traffic control is informed and NOTAMs (Notices to Airmen or, as the U.S. now calls them, Notices to Air Missions) are issued when weather balloon operations will take place. For a normal balloon launch, the balloon will only remain at potentially-hazardous altitudes for a matter of minutes (and only a few minutes at the altitudes with the most air traffic density,) so planning air traffic around the launches isn't too big of a deal. However, if the balloon were staying continuously at altitudes where it was collecting useful information, it would also be continuously a hazard to air traffic.

An additional reason, as other answers have mentioned, is that the point of weather balloon launches is to collect data for all altitudes from the surface up to at least the lower portions of the stratosphere, not just one altitude. So, the balloon's flight consisting primarily of a climb phase followed by termination is a feature, not a bug. The radiosonde attached to the balloon collects data such as ambient temperature, dew point, air pressure, wind magnitude, and wind direction for all altitudes. This information then aids meteorologists in determining all kinds of useful information, such as precipitation amount forecasts, potential for thunderstorm development, what type (if any) of precipitation would be expected at the surface, as well as at higher altitudes (for aviation weather forecasting,) depth of different air masses during frontal passage, winds aloft, jet stream position, direction, and magnitude, etc. The data collected by the radiosonde looks like this:

Radiosonde data from weather balloon
Recent Radiosonde data from NWS weather balloon launched from Nashville, TN.
Units on the left are air pressure in millibars (with kilometers altitude in red.)
Source: National Weather Service

Additionally, balloons are subject to wind. A lot of wind. Making them stay put in one spot relative to the ground is not so easy, especially in the portions of the atmosphere that are interesting for weather observations, which usually have non-trivial winds aloft, even when the wind is mostly calm at the surface. As seen in the radiosonde data in the picture above, winds aloft were measured up to about 118 knots (136 mph or 219 km/h) in this particular launch. According to the U.S. National Weather Service, even its normal balloon launches can drift as much as 125 miles (200 km) during flight. If you just let the balloons free-float indefinitely, then they won't stay where you want them for long, at least not in the interesting parts of the atmosphere. In order to produce reliable, comparable records, the balloons need to be launched at the specified times from the same positions on the ground. Of course, you can tether balloons to the ground in order to make them stay in a mostly-fixed position, but tethers long enough to reach up to 20 km / 65,000 ft or so are not exactly practical and would also greatly magnify the risk posed to air traffic.

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The vast majority of weather balloons are designed to collect vertical profiles of the nature of the Earth's atmosphere. That would not be possible with a balloon that stays aloft at more or less constant altitude. The US alone launches hundreds of weather balloons every day that rise and rise and rise, but then pop. The popping is intentional. While the payload might need a parachute, the bursted balloon itself does not. Its job is done at the point of popping.

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There are such things as zero pressure balloons, they are thin, pliable, and are not a continuous enclosed space, so they auto equalize pressure and work much such like a helium filled parachute.

In theory if you could make a material 100% impermeable to helium atoms, and make it in the zero pressure form factor, AND prevent any turbulence at the open end that may scatter and lose helium, you would have a perpetually floating balloon.

Such material would also have to be able to withstand extremes in temperature and radiation. Also since they would hover so close to space small debris puncturing it would be a real threat as well as the particles would not have to go through much atmosphere and therefore have less chance to burn up prior to hitting the balloon.

So impossible? No. Cost effective? Not even close.

Also what happens if you have any equipment malfunction and or want it to come down as new tech evolves? Sure you could have it have a mechanically driven device to cause deflation, provided that is not what malfunctioned ;

All in all impractical on all levels.

But again, NOT impossible.

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  1. There is no balloon that can stay up indefinitely. The gas will leak from the balloon and the balloon will slowly sink into the air traffic band and then all the way down, going with the wind in the meantime.

Bigger balloons made of better materials will stay longer, but one should design them for some controlled descent in order to prevent air traffic interference.

  1. The balloon from the news is not a typical weather balloon.

The typical weather balloons are used to quickly (in a matter of hours) measure the atmospheric thermal profile (and some other data related to altitude) and then they pop and fall down. They are much, much smaller as well, generally in the range of 2kg or less. The power source for their electronic payload is a small battery that has only so much juice to sustain the intended mission so there is no point of leaving them up.

Making them bigger and heavier will simply make them more dangerous for no apparent gain.

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