posted
You probablly have a much better idea than I. But I wonder, wouldn't the 60 degree air be less dense? Wouldn't the 30 degree air, having a higher density move in?
Posts: 1275 | Registered: Mar 2004
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posted
its not about temperature its about pressure.
Air moves from high pressure to low pressure. Generally warmer means higher pressure.
The weather effects of an instantly heated area would be immediate. It would take 10-15 minutes for thunderheads to be actively pouring freezing rain into the surrounding area.
There is no way that a plane would be landing near the edge of the phenomenon you describe. You just created a very short lived reverse hurricane.
As soon as you heat the air, the air at the edge will rise over the surrounding cold air, sucking that air under it - Wind is blowing at low levels into the circle, probably in a clockwise direction. At high levels its blowing outward and cooling fast, causing condensation and thus rain - which would freeze when hitting the 30 degree area, depending on whether it freezes in the air (sleet) or on the ground (frozen rain). This all assumes a transplant of air, taking out the 60 mile area of cold air and popping in a similar area of warm air.
If you just heated the existing air, forget the condensation, the air would not saturate to create rain since the air could already sustain the water vapor before it was heated. Still the wind effects would be in place.
The air moving in opposite directions (high out, low in) would cause numerous tornadoes at the fringe. No planes near those.
[This message has been edited by pantros (edited January 31, 2006).]
posted
It's also going to depend a lot on the moisture in the area. You can almost think ofit as the air over Phoenix in the summertime, though the surrounding air isn't 30 degrees cooler, it is cooler. We get very violent storms localized in very small areas. I suspect that your small area would have extremely violent storms with hurricane strength winds, especially if this is sudden.
Posts: 2 | Registered: Aug 2010
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posted
A difference of thirty degrees Fahrenheit is pretty big, so there will be a significant effect. But 60 miles isn't all that big, so the effect won't be on the order of a hurricane. Not a big one, at least.
Near the edge, sudden downdrafts would be a pretty significant danger to an aircraft. Precipitation would depend on humidity and such, wind speeds would depend on how long the phenomenon was in place.
From the point of view of an observer on the ground near the edge of the phenomenon, a strong breeze will probably be noticible immediately, flowing out from the center of the circle (assuming that the phenomenon has a sudden "start" at a defined moment). In only a few minutes, that breeze will reverse itself and begin flowing inwards. There probably won't be much initial turbulance unless there are unusual ground features, but sooner or later things will get complicated at the boundry. And if the temperature difference is simply maintained in a column of air several miles high, the amount of energy being pumped into the system is just going to keep on increasing as the convection drives wind speeds higher and higher. It's impossible to say exactly what the top speed would be without having a lot of detailed information on local humidity, barometric pressure, exact ground conditions, etc. but it would be significant if air could move across the boundry freely.
1) Your circle must really be a cylinder. How tall is it? Does it stretch all the way to space? Does it have a "top?"
2) How is the temperture difference maintained? 2nd law of thermodynamics teaches that, all other things being equal, energy will move between bodies in contact (like the cold air and hot air in your question) until they reach equilibrium. If the air inside of your cylinder is in contact with the air outside (can move or transfer energy across the boundary), then you have to add or remove energy to maintain a temperature difference. If the air inside the cylinder is not in contact with the air outside of the cylinder, then you have to maintain some kind of barrier. If there's some kind of barrier, then I can't see how there would be any appreciable effect on the weather (it would be the same as having a huge climate controlled building) unless the cylinder is shorter than the atmosphere. Then the barrier would trap warm air, making the cold air directly over the cylinder even colder.
1) Your circle must really be a cylinder. How tall is it? Does it stretch all the way to space? Does it have a "top?"
2) How is the temperture difference maintained? 2nd law of thermodynamics teaches that, all other things being equal, energy will move between bodies in contact (like the cold air and hot air in your question) until they reach equilibrium. If the air inside of your cylinder is in contact with the air outside (can move or transfer energy across the boundary), then you have to add or remove energy to maintain a temperature difference. If the air inside the cylinder is not in contact with the air outside of the cylinder, then you have to maintain some kind of barrier. If there's some kind of barrier, then I can't see how there would be any appreciable effect on the weather (it would be the same as having a huge climate controlled building) unless the cylinder is shorter than the atmosphere. Then the barrier would trap warm air, making the cold air directly over the cylinder even colder.
posted
I am reminded of the fact that microwave heating was discovered as a consequence of radio transmission experiments. Which is why there was an early model called a "radar range".
Posts: 366 | Registered: Sep 2006
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posted
Wow -- this is great information. I certainly came to the right place! Any ideas where I can find more info, in case y'all run out of patience?
Now, to answer J's questions: it's a sphere 60 miles in radius with a center at ground level. I am supposing that in effect this means a cylinder, because I don't think the upper reaches would be very different.
The mechanism for creating this odd situation is time travel: a sphere from a warm day in October is transferred to a nippy day in February, centuries away. The sphere is modern, so we'll have planes and airports. I'm picturing the airport as being maybe 10 miles from the boundary, but it doesn't matter as long as it's not immediately adjacent (I want an airplane to see the changes, and return to a landing).
...so there's nothing to *maintain* the situation; it's a one-shot deal.
So you *can* get downdrafts, which as I understand are one of the biggest dangers. (I suppose that's from turbulence? I get the air moving laterally at the border, up in the center, but I don't understand the downdraft yet.) I was picturing this, don't know if it's realistic:
Pilot finds he can't radio any place but the local airport. (The power's out -- of course -- but I'm assuming airports would have generators.) He returns; wind is picking up; as he lands, a sudden lateral gust causes the plane to tip over sideways slightly, so that the wing touches the ground. Problem: I think this causes plane to go up in a huge fireball, since the wings contain fuel (right?), and I want survivors, possibly everyone. A rotational twist (realistic?) might cause the plane to spin around, so the landing gear breaks off, and the plane skids to a halt (possibly same result). A downdraft, I'll have to look up.
Originally I had an uneventful landing, but it occurred to me that nasty danger might happen, so naturally I'd like to use it. Also OSC said not enough happened in that scene. A plane crash should change that...
No initial outwelling of air, no major weather system, just a pocket of light, warm comparitively humid air. This air will immediately begin to rise relative to the surrounding air, so there will be a noticible breeze at ground level moving towards the center of the circle, and equivalent downdrafts around the perimeter. There will also be fog and possibly a minor sleet as the warm air near the boundry cools rapidly below the freezing point of water.
The downdrafts wouldn't be really dangerous, but they would be very alarming, particularly combined with the fog (which is nearly a dead certainty unless the airport was in the middle of a desert). Certainly combined with a radio blackout, it would be enough to cause a pilot to turn back. But probably not enough to force a landing in unsafe conditions. The more realistic danger would be if the plane initially flew across the barrier, and became encumbered with ice, a potentially severe problem. This could damage or hamper some of the control mechanisms, and it would change the flight characteristics to make a crash landing plausible.
Airports do tend to have their own emergency power, yes. But a wing touching the ground won't result in a fireball. Jet fuel (I assume you're describing a passenger jet here) is less volitile than gas, it won't burn just with a spark and exposure to air. Substantial heat and pressure are needed for combustion. Modern jet fuel is specifically formulated to not burn unless it is injected into a jet engine (or something similar). That doesn't mean that you can't get a fireball (like if an explosive device hits the wing), but modern jet planes can break off both wings by smashing them against burning telephone poles and generally the jet fuel should put out the fires rather than igniting (don't try this at home, kids, chemistry is wonderful but it has limits).
quote:In 1940, Percy Spencer was walking by an experimental high frequency radio wave communications device when the chocolate bar in his pocket melted. Ten years later, microwave ovens came onto the market. Sometime after that, the following anomaly was observed. If a grape is placed in a microwave oven, sliced in two and spread (butterflied in such a way that the two hemispheres are directly beside each other and just touching, ideally with a small flap of skin still connecting them) and then the microwave is turned on, within seconds a spark/flame appears between the two halves. This seems bizarre, but has been observed by many different people and documented several places: on the Internet, on science question-and-answer periods on CBC, and probably by others, who haven’t bothered to publish their observations.
This is just from a geocities page so I don't know how accurate it is.
posted
You can get the same effect with pretty much any citrus fruit (unless it's a really not sour kind). The acidity of the juice allows it to conduct electricity across the cut surface. This isn't a large problem because the conductivity isn't high enough to allow the cut surface to reflect the microwaves enough to present a danger (the way metal would), but it is certainly enough to create visible electro-luminesence at times. You can probably do the same thing with a large pickle.
Of course, why exactly you'd want to microwave a grapefruit in the first place is beyond me.
posted
So a sphere of matter is transported from time A to time B? Did it leave a huge vaccuum in time A? What happened to the matter in time B that occupied the space to be occupied by the sphere of matter from time A? If you try hard enough to force two bits of matter (two air molecules, let's say) to occupy the same space at the same time, you get a huge release of energy--this is the principle that underlies a nuclear fusion bomb.
If all you need is for the plane to turn back and land at the local airport, why does the bad weather need to be caused by the time jump? What if, at the time of the jump, it was a clear day in time A, and a violently stormy one in time B? The pilot is flying through clear weather in time A, when all of the sudden and out of nowhere, there is time B's massive storm dead ahead.
posted
I didn't say that. I said that the amount of turbulence you'd get wouldn't be enough to jepoardize a landing, and that it wouldn't be much of a storm. But icy rain (sleet, as we call it some places) and attendent difficulties potentially resulting in a crash landing would be very probable.
I would presume the matter from one time period was transposed with matter from the other time period (by the way, have you read...um...1632?). Even if it weren't, normal air (and even soil, water, and most rocks) lack the potential to release nuclear energy just because you suddenly doubled the local density. But certainly any animal life or complex technology would be rendered...inoperative.
But the idea of having a nice storm waiting on the 30F side of the boundry is probably something to consider as an option, if you really need it.
I actually like the scenario of having just a really cold sleet and fog occur near the boundry as a result of the two atmospheres mixing. The pilots turn back because of the strange weather and lack of radio contact, but they don't realize the severity of the temperature difference so they aren't able to compensate for the rapid buildup of ice on their wings. When they get back, they have a hard landing (perhaps not quite a crash, but bad enough to break their landing gear somehow and shake things up) due to the extra weight and reduced aerodynamic performance.
when the characters are looking over the plane, they wonder "how did they get three inches of ice on the wings in 60F weather?" That leads you right into the story...maybe.
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