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?
这取决于每个气象气球测量什么;他们在捕捉什么数据。< / p >
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.
像飞机的下投式探空仪系统一样，使用漂移探空仪的现场实验涉及巨大的成本，需要大量的提前计划。了解可能的飞行路线并获得飞越许多国家的许可可能需要几个月的时间。如果气球飘过的区域没有获得飞越许可，那么它就必须被砍掉。< / p >
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.
- 新闻中的气球不是一个典型的气象气球。典型的气象气球被用来快速(在几小时内)测量大气热廓线(以及一些与高度有关的其他数据)，然后它们爆裂并下降。它们也小得多，通常在2公斤或更少的范围内。它们的电子有效载荷的电源是一个小电池，只能维持预定的任务，所以没有必要让它们升空。把它们变得更大更重只会让它们更危险，没有明显的好处
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.
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:
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.