Wikipedia:Reference desk/Archives/Science/2009 August 22

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August 22

Tropical Cyclone Crossing the Equator

Track map of all known tropical cyclones to crossover Central America. –Juliancolton | ^Talk 02:01, 22 August 2009 (UTC)

I understand that winds almost never blow across the equator, and to my knowledge no hurricane has ever crossed the equator, but pretending that a hurricane did end up travelling across the equator, what would happen? Would it destroy itself in an attempt to spin the other way, or would it keep spinning the same way?

Also, on a semi-related note, why do hurricanes not cross Central America and keep going? Also, to my knowledge that has never happened, and I can't think of a good reason why.

Thanks,

Falconus^{p t c} 00:06, 22 August 2009 (UTC)

On the first point, winds certainly do blow across the equator. The trade winds from the northern and southern hemispheres meet at the Intertropical Convergence Zone, which moves around; thus they blow across the equator if the zone isn't on the side of it that they start from.

If you google on "hurricane" and "crossing the equator" you will find some sites that say it isn't likely to happen because they don't form near the equator in the first place, and hasn't ever been known to happen. But if it did happen, the storm would probably be able to preserve its original rotation.

Finally, hurricanes do cross Central America occasionally. The convention is that when this happens they get a new name. See Hurricane Cesar-Douglas for one example. --Anonymous, 01:55 UTC, August 22, 2009.

Yeah - the coriolis effect is not very strong near to the equator (which may be a part of the reason hurricanes don't form there to start with). Mathematically, the "coriolis coefficient" is proportional to the sine of your latitude. At the equator (zero degrees latitude) - the sine of zero is zero - so there is no coriolis force whatever. As hurricanes move towards the equator the coriolis force gradually decreases. If one ever did cross the equator, the coriolis force counteracting its rotation would get gradually stronger the further it went - eventually (presumably) disrupting the storm and causing it to fizzle out. But it would have to move a long way past the equator for that to happen. SteveBaker (talk) 02:11, 22 August 2009 (UTC)

Ah, alright. That all makes sense. Thank you, Falconus^{p t c} 04:50, 22 August 2009 (UTC)

Global Tropical Cyclone Tracks between 1985 and 2005, indicating the areas where tropical cyclones usually develop

It just does not happen. See Tropical_cyclogenesis#Unusual_areas_of_formation, which includes a global track picture. If somehow it did happen, the storm's rotation would slow and then cease as it neared the equator, and then restart in the opposite direction. Apparently there have been two storms that did get close to the equator. Remember that the atmosphere is a gas. A hurricane does not have rotational inertia in the same sense that a spinning top has roatational inertia. gass molecules can push on each other, put they cannot pull on each other. The corriolis effect is the only thing that causes the circular motion. -Arch dude (talk) 13:02, 22 August 2009 (UTC)

Once a storm got going, its intrinsic tendency to amplify its spin rate would probably allow it to survive crossing the equator; see this link for a somewhat authoritative explanation. And you can look at this pdf for an account of an exceptional typhoon that formed less than 2 degrees from the equator in 2001. Looie496 (talk) 19:05, 22 August 2009 (UTC)

Agreed. The coriolis effect is extremely tiny, and just enough to get a bit of rotation in a tropical depression. Once started, however, the energy from the rising steam off the water and the cold air dropping from the stratosphere into the eye greatly magnifies the rotational energy. I believe there are even rare cases where a hurricane or cyclone rotates the opposite direction it should, due to some local wind condition where it formed which was stronger than the coriolis effect. StuRat (talk) 21:50, 22 August 2009 (UTC)

Do you have a citation for this? Alternatively, can you describe a physical reason for this effect? I cannot think of any effect that would result in an "intrinsic tendency to amplify its spin rate." I think that the hurricane amplifies the latidudinal relative velocity differences as it pulls each packet of air radially toward itself. The hurricane's heat engine does not impart any rotation, instead the pre-existing horizontal velocity differences remain constant as each air packet moves toward the eye. -Arch dude (talk) 23:14, 22 August 2009 (UTC)

LOL@latiDudinal, is that really cool latitudes ? The concept is that, as the steam rises off the water and into higher altitudes, it creates a low-pressure area at the surface. This causes air to rush in from outside the hurricane, which has a tendency to compact the storm. As the rotational center of gravity of any rotating body is moved in towards the center, the rotational speed must increase to conserve rotational momentum. The low pressure in the center of the hurricane eventually leads cold air to be drawn down from the stratosphere in the center to form the eye, pushing the hurricane away from the center. This results in the highest rotational velocity (and therefore winds) at the eye wall. StuRat (talk) 09:10, 23 August 2009 (UTC)

Then you agree that the rotation at the eye is "merely" the concentrated rotation of the more distant atmosphere in general: your description is the same as mine. But the large-scale (i.e., Hurricane-scale) angular momentum of the atmosphere is completely dominated by the coriolis effect. So I ask again: what would cause a hurricane to carry the "wrong" rotation across the equator? I do not believe this will occur. -Arch dude (talk) 12:09, 23 August 2009 (UTC)

No, there's also something else going on that increases the rotation speed. The energy of rising heat is redirected into rotation, much like water going down the drain is redirected into rotation. The coriolis effect gets the rotation started and the previous effect I mentioned concentrates this rotation, but, once established, this redirected energy is the real powerhouse of rotation. And I didn't say that hurricanes are carried the wrong direction across the equator, my point was only that, if the steering winds pointed one that way, it could probably survive, with only a slight weakening from the coriolis effect (now rotating in the opposite direction). However, the steering winds just don't seem to point that way, and the cross-equator winds we do get just aren't strong enough to move a hurricane. StuRat (talk) 13:56, 23 August 2009 (UTC)

You may be miss-remembering the fact that tornados ocasionally (roughly 1 out 1000) spin the "wrong" way and thinking that this also applies to hurricanes. But the coriolis force is an essential part of a hurricane dynamics and there can be no hurricanes spinning the wrong way. In a hurricane coriolis and Pressure Gradient Force (PGF) always opose each other on a quisi-equilibrium. Unlike a hurricane, in a tornado the coriolis plays very little role on the dynamics which is an quasi-equilibrium between centripetal force and the PGF matching more closely your description of rotational movement getting concentrated by the tightening of the storm due to air lift at its center. Dauto (talk) 15:28, 23 August 2009 (UTC)

The story I heard was about reverse-spin "cyclones", but some in the US do mistakenly call tornadoes by that name, so I suppose they might have meant that. However, I still maintain that the sum of the rotational energy in a hurricane does not all come from the coriolis effect. If the coriolis effect were that great, then all storms would have rotation, but they don't if they lack another rotational energy source (or an energy source which can be redirected into rotation). StuRat (talk) 23:36, 23 August 2009 (UTC)

Two points: First Point: Being always perpendicular to the velocity means that the coriolis force does no work and cannot provide any energy at all to the hurricane. The energy is provided by the PGF. What the coriolis force does is to deflect the radial movement created by the PGF creating a circular movement. Second Point: All Tropical Storms, Cyclones, Typhoons, and Hurricanes DO HAVE rotation. In those storms the coriolis force is about as strong as the PGF and they are in a quasi-equilibrium. Dauto (talk) 05:22, 24 August 2009 (UTC)

To your first point, since the pressure-gradient force is itself created by rising steam off the water, as I described earlier, then the rotation is due to this heat engine, so we appear to be in agreement. As for your second point, yes, many storms have rotation, but not all. Specifically, those lacking the heat engine I described tend to also lack rotation. This is common over land, where most storms lack rotation, but can also occur over water during some tropical depressions, etc. StuRat (talk) 14:09, 24 August 2009 (UTC)

The question is about tropical cyclones. They all do rotate, they all do rotate the 'right' direction, they never rotate the 'wrong' direction and they cannot possibly rotate the 'wrong' direction and still be tropical cyclones, because there would not be any quasi-equilibrium between the PGF and the coriolis force. Dauto (talk) 15:39, 24 August 2009 (UTC)

And I'm not arguing with you about any of that, am I ? My comment that "not all storms rotate" was to illustrate that the coriolis effect can't be the sole cause of all storm rotation, because, if it was, all storms would rotate (except those on the equator). I don't go as far as you in saying the coriolis effect "cannot provide any energy at all to the hurricane", however. StuRat (talk) 22:11, 24 August 2009 (UTC)

As to the point of the coriolis force being in a different direction than the storm rotation, forces are frequently redirected, as in the case of sailboats redirecting the force of the wind to go in just about any direction they wish. StuRat (talk) 16:26, 26 August 2009 (UTC)

Actually the Coriolis effect is velocity-dependent too .... and remember, upper-level winds are really really really strong. John Riemann Soong (talk) 05:34, 23 August 2009 (UTC)

For the record, the tropical cyclone that (recently) formed closest to the equator was Tropical Storm Vamei. ~AH1^(TCU) 11:17, 24 August 2009 (UTC)

Microsleep and discontinuity

Why doesn't the brain notice a discontinuity upon waking from microsleep, as it would when watching a scratched DVD that suddenly jumped forward a few seconds? NeonMerlin 03:36, 22 August 2009 (UTC)

Why do you think the brain does not notice discontinuity? If you've ever dozed off, your personal reaction may vary; but the waking-up part is often jarring, even disproportionately so compared to the amount of time that was actually slept through. Nimur (talk) 05:09, 22 August 2009 (UTC)

...I'm exactly the opposite to what Nimur describes. When I doze off, I drift back into consciousness without ever knowing I was asleep (until I notice the clock says it's an hour and a half after my appointment). So I, too, am curious as to why this is...Although I've never microslept. Vimescarrot (talk) 18:18, 22 August 2009 (UTC)

The brain is tuned to attend to things that have implications for behavior, meaning mainly things in the external world. There are loads of discontinuities happening all the time that we never notice unless we attend to them, for example blinking and rapid (saccadic) eye movements. Also, I think that the event Nimur describes is not actually related to waking from sleep -- many people have a tendency to drift into half-sleep and then abruptly jerk into full wakefulness. These events are sometimes called hypnic jerks, and their causes and function (if any) are not well understood. Looie496 (talk) 18:45, 22 August 2009 (UTC)

If nothing much has changed while you were asleep (at least, nothing your brain considered worth paying attention to), then there is no discontinuity to notice. --Tango (talk) 19:46, 23 August 2009 (UTC)

Naga Fireballs

Is there any scientific answer for this the Naga fireballs. I mean it seems interesting that no one has apparently bothered to even look into them, or is it just soldiers firing stuff? —Preceding unsigned comment added by 58.111.132.76 (talk) 07:14, 22 August 2009 (UTC)

It's not clear that they have ever even been observed; so it's hard to have a scientific explanation of them. Like many "fringe" areas, the scientific community can't make any kind of explanation until there is good recorded observational evidence; and that kind of evidence usually comes only from well-funded scientific study by properly trained specialists. The result is a positive-feedback loop - minimal evidence, so minimal investigations, so even less evidence ... . If an amateur video existed, and the phenomenon is shown to be more than a local legend, it'll probably be looked into. Unfortunately, this is what we have - and the only thing unexplained in that video is, "why did he videotape an empty, dark sky?" Nimur (talk) 07:21, 22 August 2009 (UTC)

Are you sure it's not clear they've ever been observed? Our article suggests they're well-known:

The number of fireballs is variable, being reported at between tens and thousands per night.

The fireballs have been seen for centuries and are most often reported around the night of Wan Awk Pansa — the end of the Buddhist rains retreat — in October, although displays have also been reported in March, April, May, June, and September.

The fireballs are even being promoted as a tourist attraction: Previously known as the ghost fireballs, the event has now had its name changed and is being promoted as a festival to attract tourists. I get the impression that unlike the Ness or the Sasquatch, anybody who wants to see these fireballs can easily do so. --99.237.234.104 (talk) 12:25, 22 August 2009 (UTC)

Though it is striking how few pictures of them are on the internet. Seems like there are about three that get repeated everywhere. For a tourist phenom, you'd expect a lot more tourist photos. --98.217.14.211 (talk) 14:00, 22 August 2009 (UTC)

There are also purported photographs of Bigfoot; I'm still skeptical that a Great Forest Ape has ever actually been observed in the Pacific northwest. Evidence of extraordinary claims needs to be extraordinarily convincing. Nimur (talk) 15:19, 22 August 2009 (UTC)

There's also this less-than-convincing musical number. Nimur (talk) 07:28, 22 August 2009 (UTC)

Experiment variables

I'm considering doing an experiment. I plan to test two different cars (a heavy one and a light one) on three different surfaces (bitumen, gravel, dirt) with three different speeds (20km/h, 40km/h, 60km/h). The idea is to contrast the performance braking distance of the two cars with respect to the speed and surface variables. My question is whether one could reasonably draw a meaningful conclusion from such an experiment. Are there too many variables for anything of substance to be derived? Would any conclusion made be non-rigourous and inherently iffy? Should I perhaps consider operating with only a single variable, and axe two of the others? —Anonymous Dissident^Talk 08:02, 22 August 2009 (UTC)

• You need to define performance in order to design a meaningful test. Once the test is performed you could rigorously say that car A is better than car B, provided the data supported that conclusion. You could not imply that light cars are better than heavy ones for example. Noodle snacks (talk) 08:55, 22 August 2009 (UTC)

"performance" is an error on my part. I mean to contrast braking distance. —Anonymous Dissident^Talk 09:10, 22 August 2009 (UTC)

That sounds like a reasonable experiment. There are a few confounding variables you can consider: are the brake systems equivalent on the different vehicles (probably not). Are they reasonably equal in age? The brake pads wear out, so even testing the same car with new vs. old brake pads would result in different braking distances. How will you account for variations by the driver? Do you have a plan to slam the brakes to maximum (this can be dangerous, especially on gravel)? If not, how will you ensure consistency in the experiment? Nimur (talk) 09:17, 22 August 2009 (UTC)

Brakes will be slammed to a maximum. WRT to the other factors, you're completely right – they'd be entirely necessary to consider for something professional. But this is just an amateur experiment, and I'll just be counting such factors as the driver's variations as negligible. Nonetheless, I have an interest in drawing some kind of conclusion about the experiment – maybe something along the lines of how the lighter car's results contrast with the heavier car's and why. Thanks for the input. —Anonymous Dissident^Talk 09:42, 22 August 2009 (UTC)

Slamming on brakes is a good way to go off the road, so you might consider doing this stuff in parking lots. --Sean 12:28, 22 August 2009 (UTC)

Do both cars have anti-lock brakes? Will this be on or off? Or will you conduct experiments with on and off? Exxolon (talk) 15:13, 22 August 2009 (UTC)

And the key is to be careful about extrapolating your results. You definitely can't use this experiment to say "light cars are better than heavy cars in breaking on gravel". You also can't really say "this model is better than this model", if you want to be really rigorous, you are only allowed to say "this particular car is better than this particular car (in these particular conditions)". That's fine though, it's still a conclusion. Aaadddaaammm (talk) 17:17, 22 August 2009 (UTC)

Better yet, you could test the same car with different braking methods (anti-lock engaged vs. non-engaged; pumping the brakes vs. slamming, etc. etc.) on different surfaces. By using ONE car, and testing the methods, you can control for all of the hidden variables mentioned above. That may be a far more controlable experiment. If you are attempting to make a meaningful conclusion about car weight vs. braking distance, two cars is FAR too small a sample size, you'd have to use literally hundreds of cars, and plot some sort of graph of weight vs. stopping distance, and also try to do a proper statistical analysis to confirm the validity of the results. --Jayron32 17:32, 22 August 2009 (UTC)

Having run an experimental laboratory myself, here are my main suggestions. First, the most critical thing, you need to find drivers who are blind to the purpose of the experiment, so that you can be sure their expectations don't influence the results. Second, you need to randomize the order of tests, so that changes in conditions don't alter the results. Third, you need sufficient sampling of each condition, I would guess 5 trials for each would be enough. Whether you can handle the number of variables you mentioned is a function of whether you have enough resources to do multiple trials for each combination. Looie496 (talk) 18:34, 22 August 2009 (UTC)

(20km/h, 20km/h, 60km/h) is only 2 different speeds. Cuddlyable3 (talk) 20:23, 22 August 2009 (UTC)

Being a psychic, I've read the OP's mind and determined that they meant to say 40km/h for the middle speed. :-) StuRat (talk) 21:39, 22 August 2009 (UTC)

Scientifically, the problem is that the two cars you're using don't differ only in their weight. There are guaranteed to be lots of other differences (different sized brake disks, different brake pad materials, different braking forces, better tires, different ABS strategies, different drag coefficients, different power-assisted braking designs...heck different seats and brake-pedal-travel could make a difference). So if (say) the heavier car takes a shorter distance to come to a stop - all you can really say is that this model of car stops better than that model of car. You can't make any conclusions about the weight alone because it might be that the bigger car has bigger brake disks and that could be the reason for the difference.

What I think you need to do is to stick with just one car - and alter the weight it carries. Try it with just the driver, with one, two, three and four passengers (weigh them!) - load the thing down with sandbags or other weights. Plot a graph of weight versus stopping distance. If you have another car, then you can try the same experiment and see if the curve you get is similar in shape. If you can show that all kinds of car show the same shape of weight-versus-stopping-distance then perhaps you have learned something that's generally applicable. Of course, even that isn't 100% rigorous because the distribution of that weight (all at the front, all at the back, divided 50/50, etc) could also make a difference. In the end, the depth of your experimentation depends on the importance of the results for whatever practical purpose they are intended. If it's for something like a high-school science fair - then the experiment I describe ought to be enough to get you good marks. If you are going to use the results to design the next Ford super-monster-Uber-wagon...you're going to need to do a lot more work! One word of warning...doing this on gravel, or with ABS disabled, can cause you to fish-tail and even skid/spin-out. Be really careful about what's to either side of the car when you do this. SteveBaker (talk) 20:20, 23 August 2009 (UTC)

I ended up doing the experiment. I decided to use only one vehicle with different speeds on different surfaces. I figured that making any generalisations about one type of car vs. another was unwise with so few samples on hand, and that a conclusion about something meaningful could be more readily drawn with just two variables. It certainly made my job easier – 27 tests (3 for each speed to calculate a rough average) take much less time than 54. I didn't have any problem with skidding on the gravel – as it happened, the gravel consistently had the shortest braking distance. Is it possible the gravel had the opposite effect to what might have been expected, and actually retarded the speed faster rather than skidding it? How does the result of gravel's having the shortest braking distance fit in with the typical traction of such a surface? Is it possible the result can best be explained by some flaw in the test or by human factors? An interesting thing was that even though the gravel had a shorter braking distance than the bitumen, the gravel's braking time was longer. Thanks all for chipping in. —Anonymous Dissident^Talk 14:35, 24 August 2009 (UTC)

With gravel, you probably expected it to reduce friction by rolling between the tires and ground, but they may have actually dug into both the tires and the ground. However, smaller abrasives, like rock salt, definitely do increase braking distances by rolling between the tires and road. StuRat (talk) 22:03, 24 August 2009 (UTC)

At slower speeds, the gravel may actually pile up in front of a locked wheel and make a wedge-like thing that would stop the car quicker. It's a complicated business though. Certainly cornering on gravel is much tougher than on tarmac or concrete...not good. (And I speak from bitter experience!) SteveBaker (talk) 22:49, 24 August 2009 (UTC)

Oxidant Scavenging Systems

Hello, will someone kindly explain, how oxidant scavenging systems may be useful in cancer therapy? Many Thanks,in advance. —Preceding unsigned comment added by 59.93.214.236 (talk) 15:19, 22 August 2009 (UTC)

I assume you mean antioxidants ?83.100.250.79 (talk) 15:46, 22 August 2009 (UTC)

Perhaps they aren't useful. See http://arstechnica.com/science/news/2009/08/duplicitous-antioxidants-tumor-suppression-and-promotion.ars

For a fuller picture I recommend searching for "antioxidant" + tumor/cancer therapy etc.83.100.250.79 (talk) 15:46, 22 August 2009 (UTC)

Neanderthals

In the local train station, there's a display on evolution. It includes a model of a Neanderthal in what appears to be a crude shelter made of mammoth ribs or tusks or something. Did Neanderthals really make buildings out of mammoth bones? Aaadddaaammm (talk) 17:13, 22 August 2009 (UTC)

Mammoth bone houses are well known, and Neanderthals are contemporary with mammoth, I can't find anything as yet to prove what type of human lived in mammoth bone houses. I'm sure some archaeologist has examined mammoth bone houses in detail, and pinned them on a specific culture.. someone else will know..83.100.250.79 (talk) 17:51, 22 August 2009 (UTC)

Such dwellings have been found, amongst other places, in the Ukraine and Russia. Particularly in areas of poor forestation (the ice age had turned large areas into tundra / steppe), the bones were a valuable means of building shelter. Ivory was used for arrow heads and carved into artifacts. As to the name of the associated culture, it would depend on the "sophistication" of he stone tools unearthed on these sites. Micoquian or Mousterian may be options, but an anthroplogist will know better. --Cookatoo.ergo.ZooM (talk) 20:17, 22 August 2009 (UTC)

There's also the option of examining butchery marks on the bones, which to someone with a microscope and expertise reveals the type of knife tool used to carve up the mammoth - as I understand it Neanderthals used the simplest type of flint tool. I'm sure someone will have researched this - though if the research has been published in cyrillic text this may prevent a google search bringing in its usual rewards.83.100.250.79 (talk) 20:34, 22 August 2009 (UTC)

Wow OK I was sure this model just came from someone who'd watched too much The Flintstones. Thanks for educating me! Aaadddaaammm (talk) 20:36, 22 August 2009 (UTC)

Mammoth bone deposits and subsistence practices during Mid-Upper Palaeolithic in Central Europe: three cases from Moravia and Poland (which is unfortunately not free) seems to discuss the use of mammoth remains as a living-structure. It's not clear whether the humans were Homo sapiens or Neanderthals. Nimur (talk) 22:01, 22 August 2009 (UTC)

Tiny flies in the kitchen

My kitchen is full of tiny little flies. They are concentrated near the sink and the window above it. I know this is pretty common because I have some friends who have them too, but mine are getting out of hand.

I keep it very clean, and there is little to no food lying around exposed. There's nothing clogging the sink drains, no other obvious source.

1) What are these things called? (I live in the northeastern USA so they aren't "exotic"). People call them "fruit flies" but are they really?

2) How do I get rid of them? What am I missing?

Gohome00 (talk) 21:47, 22 August 2009 (UTC)

I'm pretty sure this has been asked before. They're likely Drosophila species, frequently Drosophila melanogaster. They way I deal with them in my kitchen is to put some wine vinegar diluted 50% in water in a small glass (although straight vinegar should work; they seem to prefer non-white vinegars. you can also use some old wine or beer). Cover the cup with plastic wrap and poke some smallish holes (roughly the size of the flies or a bit larger). The flies are attracted to the vinegar and crawl through the holes and get trapped. Then they have unfortunate swimming accidents and drown. Two such traps are usually good. Also I suggest ensuring that you have rinsed out any beverage containers or cans that contained fruit that you have in your kitchen. Beer bottles with a small amount of beer (or "empty" wine bottles) are like buffets to the fruit flies. Oh, and feel free to kill any that you can clap your hands on. I find that wet hands seem to be more effective at getting them. Good luck! -- Flyguy649 ^talk 23:58, 22 August 2009 (UTC)

Spanish flying insects

For several years we have seen what appears to be a "moth"like insect whilst on holiday in Southern Spain. Closer inspection when the insect lands on a flower reveals a birdlike face with a long probe that appears to be extracting nectar. Does anyone know what these insects are?Huscroft (talk) 21:54, 22 August 2009 (UTC)

Hmm. Feeds on nectar, has a bird-like face, about the size of a big flying insect – sounds a lot like a hummingbird, except that hummingbirds aren’t found in Spain. Red Act (talk) 22:25, 22 August 2009 (UTC)

Perhaps it’s the hummingbird hawk-moth, which is found in Spain? Red Act (talk) 22:32, 22 August 2009 (UTC)