Wikipedia:Reference desk/Archives/Science/2022 March 29

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March 29

Name of a common weather pattern

In the Northern Hemisphere mid-latitudes, where I live, it is quite common that a low-pressure area is accompanied by a warm front extending southeast and a cold front extending southwest. The diagram shows an example: in this case the (blue) cold front has caught up with the (red) warm front to form a section of (purple) occluded front, but that's not important to my question. If the low passes north of us, we get both fronts in rapid succession, causing a short period of warmer weather, lasting maybe a day or so. For example, look at maximum temperatures recorded here in Toronto this month, on the left side of this table: on March 6, the temperature spiked to 16°C, much higher than the day before or after. And there was a similar but less intense spike on March 24.

My question is simply this: Is there a name for this phenomenon, either the underlying phenomenon of a moving low with two fronts extending from it, or the resulting rapid two-way temperature change? --184.144.97.125 (talk) 11:46, 29 March 2022 (UTC)

This is a cyclone, more specifically an Extratropical cyclone. The red and blue lines represent warm fronts and cold fronts, which are literally the front edge of an air mass whose temperature differs significantly from the neighboring air masses. --Jayron32 11:58, 29 March 2022 (UTC)

For completeness, in the occluded front the cold front has caught up with the warm front and is driving underneath it. The marked front is similar to the bottom of a V shaped valley higher in the atmosphere as the warm air is pushed upwards. Martin of Sheffield (talk) 12:07, 29 March 2022 (UTC)

Yes, I know, "cyclone" is another name for a low-pressure area. I'm talking about the cyclone together with two fronts, the whole thing moving along with the prevailing winds to create a tongue of warmer air that gives a day or of warmer weather. --184.144.97.125 (talk) 01:17, 30 March 2022 (UTC)

In the northern hemisphere the polar front marks the division between cold polar air and warm, moist air coming from the south. A disturbance in the upper atmosphere allows some warm air to start to push north which creates a toungue with cold air behind it. As the low develops the coriolis force ensures that the rotation is anti-clockwise and that brings the cold air down behind the low. You can always tell where things are: Buys Ballot's Law states that if you stand with the wind behind you, the Low is on your Left. The wind will angle about 10-15 degrees inwards from the isobars over the sea, and as much as 30° over land. The cold air travels significantly faster than the warm, and so the cold front eventually catches up with the warm, lifts it (occluded front) and the low fills and dissipates. The rotating winds around a low are called a cyclone (think: cycle). Cyclones are always associated with fronts, there is no special name for a cyclone with fronts anymore than there is a special name for people with fronts! Martin of Sheffield (talk) 08:42, 30 March 2022 (UTC)

Earth is expelled from solar system, how far away from the Sun can we maintain the same global temperature by injecting greenhouse gases into the atmospere?

Suppose that due to some freak event like an encounter with a rogue planet that enters our solar system, the Earth is propelled out of the solar system. Temperatures will then drop as we get farther away from the Sun, But we can try to compensate for that by injecting greenhouse gasses such as CO2, methane into the atmosphere. There exist extremely powerful greenhouse gases like HFC-23 that have about 12,000 times the global warming potential compared to CO2. How far away from the Sun can the current ambient temperature be maintained by injecting these sorts of greenhouse gasses into the atmosphere? Count Iblis (talk) 19:26, 29 March 2022 (UTC)

Maybe you will be able to figure it out yourself after reading Inverse-square law. 178.208.99.186 (talk) 07:34, 30 March 2022 (UTC)

At a first approximation, no further (and probably rather less less) than the outer extent of the Sun's Circumstellar habitable zone (aka "Goldilocks zone"), which is based on atmospheric compositions compatible with life (of any kind) rather than Earth's current exact atmospheric composition and biosphere.

As you will see (Section 2.1), there are a range of estimates of what the furthest extent of the zone (in our Solar system) is, which the article tabulates: the estimates range from 1.004 to 10 AU, but the latter predicates a high-pressure hydrogen atmosphere probably unobtainable by any amount of terrestrial planetary engineering and incompatible with virtually all terrestrial life (perhaps some microbes could survive in it).

(I notice with amusement that the next most generous estimate of 3.0 AU was made by Martyn J. Fogg, an old friend of mine.)

While this doesn't directly address your question, it may give you some parameters within which to work and some references for further investigation. {The poster formerly known as 87.81.230.195} 90.209.233.48 (talk) 10:27, 30 March 2022 (UTC)

A similar idea occurs in the sci-fi novel Project Hail Mary: the sun's output is temporarily reduced by (something alien), and humans avoid a new and permanent Ice Age by releasing large amounts of methane into the atmosphere, countering the reduction in solar energy coming in by reducing the amount of energy radiated out. If you want to do computations, probably best to start from something like Earth's energy budget. —Kusma (talk) 10:58, 30 March 2022 (UTC)

Could such gases be introduced to the atmosphere in quantities sufficient to hold in enough heat without reaching levels inimical to human life? --User:Khajidha (talk) (contributions) 11:29, 30 March 2022 (UTC)

That's the rub, isn't it? Methane and CO2 and other greenhouse gases are not necessarily inert with regards to life on earth. High enough CO2 levels, for example, lead to Hypercapnia in animals. --Jayron32 12:13, 30 March 2022 (UTC)

Not to mention the forces needed to remove the earth from its orbit are likely to make the question of human reaction moot, due to our going extinct from various effects. --User:Khajidha (talk) (contributions) 12:29, 30 March 2022 (UTC)

The force that keeps the Earth in its orbit is something like 35 × 10²¹ N. This does not appear to bother us much.  --Lambiam 15:29, 30 March 2022 (UTC)

Yes, but the additional forces needed to overcome that force over a short enough time for us to notice it would likely cause accelerations that are unfriendly to our soft internal organs. --Jayron32 15:44, 30 March 2022 (UTC)

If a planet with a mass like Jupiter passes by the Earth at a distance of 360 000 000 m (360 000 km), it will exert a gravitational force of about 5.83 × 10²⁴ N on the Earth, which will result in an acceleration of the Earth with its inhabitants of less than 0.1 g. This is survivable. But if the hyperbolic trajectory of the rogue planet near perigee comes close to the Earth's orbit, while the Earth is near at that time, this mild acceleration over a longer period of time may be enough to result in a significantly altered orbit. Compare the slingshot effect.  --Lambiam 22:56, 30 March 2022 (UTC)

There's a mismatch in your calculation. The force and acceleration are correct if a Jupiter-mass planet is 360 thousand km from Earth, which is about the same as the Earth-Moon distance. At 360 million km, both are smaller by a factor of one million. (The actual closest approach of Jupiter to Earth is about 588 million km.) --Amble (talk) 23:34, 30 March 2022 (UTC)

Thanks, now corrected.  --Lambiam 13:09, 31 March 2022 (UTC)

Gravity acting on the entire human body will cause the same acceleration everywhere and therefore no forces in the human body. The large acceleration is no problem. There could be a problem with tidal forces, but those are more likely to rip the Earth apart than to rip humans apart. But then, ripping the Earth apart would be pretty bad for those humans living there. PiusImpavidus (talk) 12:22, 31 March 2022 (UTC)

Extreme tidal forces – much stronger than a mere planet can give rise to – can lead to spaghettification, which would be a serious health problem.  --Lambiam 10:59, 1 April 2022 (UTC)

I've wondered about that. It's not like stretching the body though, the structures, cells, atoms and even fundamental particles and fields would be distorted in the same manner. Would the putative astronaut actually perceive anything at the event horizon? Martin of Sheffield (talk) 11:40, 1 April 2022 (UTC)

Yes, tidal forces cause a real, physical stretching and squashing that you would feel. This is what heats the interiors of Io and Europa, and the spaghettification near a black hole is just a more extreme instance of the same physical effect. But it is not connected to the event horizon in particular. See Spaghettification#Inside_or_outside_the_event_horizon. If you fell through the event horizon of a supermassive black hole, as far as we know, you would not feel anything special, and the tidal forces would still be very small at that point. Note that the equivalence principle only applies locally; a body feels tidal forces when it is too big to count as "local" in some setting.--Amble (talk) 16:20, 1 April 2022 (UTC)

Thermal equilibrium is reached when the incoming heat from solar radiation equals the outgoing heat radiated by Earth into space. The former is easily computed as a function of the distance to the Sun. The latter depends on the temperature distribution, the composition of the atmosphere, and the albedo (mainly but not only a matter of cloud cover). Without formulas and tables of constants for computing this, it is not possible to determine the answer to the hypothetical question.  --Lambiam 15:42, 30 March 2022 (UTC)

It's really only the surface and atmosphere that will cool down on a relevant timescale. The interior can stay quite hot for a long time. If you can surround the planet with enough layers of multi-layer insulation, the Earth's internal heat budget will be enough to keep up a cozy temperature at the surface. Of course, it will still be dark and there will be nothing to eat. --Amble (talk) 16:52, 30 March 2022 (UTC)

Hard to give an exact answer, but the distance would be of the order of one astronomical unit. Given the speed at which the Earth has to move to be ejected from the solar system, that would only take months, so no time to add enough greenhouse gas to the atmosphere to make a significant difference. PiusImpavidus (talk) 12:22, 31 March 2022 (UTC)