Wikipedia:Reference desk/Archives/Science/2023 May 9

= May 9 =

Washington Metro
Would a lineside signal have prevented the June 2009 Washington Metro train collision? Or would the same parasitic oscillations which fooled the automatic systems have also given Train 112 a false green light on the lineside signal as well? 73.162.86.152 (talk) 00:36, 9 May 2023 (UTC)
 * You are asking for speculation as to how a lineside signal would have been controlled if there had been one. We can't do that. --174.89.12.187 (talk) 03:57, 9 May 2023 (UTC)


 * According to the NTSB report (which I didn't read completely), the cause of the accident was faulty train detection. Train detection is separate from signalling. Choosing lineside signals instead of automatic control doesn't imply a different type of train detection, nor does automatic control imply this particular type of train detection. So, no, a lineside signal wouldn't have prevented this accident. Axle counters instead of track circuits might have, or a different type of track circuits. PiusImpavidus (talk) 18:43, 9 May 2023 (UTC)


 * You are concluding that if there had been lineside signals, they would have used the same train detection as in the actual system. We can't do that. --174.89.12.187 (talk) 03:46, 10 May 2023 (UTC)
 * In fact, there is also an implicit assumption in the devout and intrepid editor's contribution that if there had been lineside signals, there would have been trains running on that day. The absence of trains would have meant no collision, so. But IMO it is fair to conclude that, everything else having been the same, the change of control from ATC to signalling control would not have prevented this accident. What might (and likely would) have prevented the accident is not another type of control, but an alternative type of detection. Ultimately, though, all devices can fail, including axle counters. --Lambiam 07:20, 10 May 2023 (UTC)
 * Thanks! So, the answer is, it would not have prevented the wreck -- right?  (Which is what I thought, too.) 73.162.86.152 (talk) 21:30, 10 May 2023 (UTC)

Largest storm
What was the largest storm? Typhoon Tip is the result that comes up when I look up the question. This is despite the fact | this source said that extratropical cyclones can stretch 3000 km and the | WMO says the largest tropical cyclones only get to 1000 km. ✶Mitch  199811  ✶  17:17, 9 May 2023 (UTC)
 * Depends on how you define the words "largest" and "storm". That's the problem with superlatives; you can get different answers depending on how you tweak the parameters.  Typhoon Tip is the largest tropical cyclone ever recorded, but those have fairly well-defined parameters; once you get outside of those parameters, into the realm of Extratropical cyclone, you run into issues that many of these cyclones are not reasonably well defined, nor are many of them "storms" under normal understandings of the word.  The strongest (not geographically largest, though) non-tropical storm was the Braer Storm of 1993, but if you just want to know "What is the largest extratropical cyclone ever recorded in terms of geographic extent?" that's probably harder to determine; many if not most of such features are unremarkable weatherwise, bringing some rain and wind, maybe, but nothing you'd call a "storm".  Additionally, they don't have well-defined boundaries the way that a hurricane does.  Any time you watch the weather on the TV, every one of those big red "L" symbols is the center of an extratropical cyclone.  Whatever continent you're on right now there's probably 3-4 over it as we speak. -- Jayron 32 17:52, 9 May 2023 (UTC)
 * Are extratropical cyclones the largest storms if they are to be counted as singular storms? ✶Mitch  199811  ✶  18:06, 9 May 2023 (UTC)
 * Let's start again. Most extratropical cyclones are not storms, under any reasonable definition of the term.  They are rotating masses of air (cyclones) centered on a low-pressure area.  That's all they are.  Some may have stormy weather, most might have clouds and light showers associated with them.  Also, unlike tropical cyclones like hurricanes/typhoons, most are not as well organized and thus don't have well-defined boundaries.  We can define the size of something like Typhoon Tip because it is highly organized, and has clearly defined boundaries that we can measure.  Most extratropical cyclones are not easily defined, don't have complete cloud coverage, and lack clear boundaries we could even delineate a size of.  In summary: we don't define "largest storm" for an extratropical cyclone because 1) most aren't "storms" in the sense that a hurricane is and 2) they aren't as easy to define in terms of extent anyways.  -- Jayron 32 18:44, 9 May 2023 (UTC)
 * Now, if we're talking mid-latitude storm events, you probably want to look for squall lines, though a quick google search turns up no records kept for "longest squall lines" or anything like that. Continent-spanning squall lines of thousands of kilometers are somewhat rare, but not unheard of.  Such squall lines aren't given names like hurricanes or typhoons, and there are no records kept on their size, but they are probably the largest mid-latitude synoptic scale weather systems one could reasonably call "a storm" in the same way you think of a hurricane or a typhoon.  -- Jayron 32 18:52, 9 May 2023 (UTC)
 * In the winter, nor'easters can get very large, the Ash Wednesday Storm of 1962 is often cited as among the most intense such storms, but I don't know if the cloud cover was bigger than, say, Typhoon Tip. -- Jayron 32 18:56, 9 May 2023 (UTC)
 * Now, if Mitch199811 wants to know examples of long squall lines, some of them can be from just an organized line (say, August 2020 Midwest derecho) of storms capable of producing wind damage spanning a couple hundred miles long to QLCS' that span over a thousand miles long. What's neat about extratropical cyclones (especially in the Northeast U.S.,) is that they can drop +24 millibars in order to be classified as a bomb cyclone. About the distance? I would say in terms of distance, Typhoon Tip may be a large storm, but as Jayron32 noted, we can't define it because it is highly organized. Tip was definitely an intense typhoon, though! But in meteorology terms, we don't classify most systems as "storms", like Mesoscale Convective System or Low Pressure Area. Tails   Wx  19:25, 9 May 2023 (UTC)
 * @Mitch199811: Adding to @Jayron32's helpful contributions, you should note that "storm", as well as being a general term for unpleasant weather, has a specific meaning in meteorology. In the part of the world I am in, there are several a year and they are named. Bazza (talk) 18:59, 9 May 2023 (UTC)
 * And of course there is always the Great Red Spot. Shantavira|feed me 19:04, 9 May 2023 (UTC)
 * Or geomagnetic storms. ✶Mitch  199811  ✶  19:08, 9 May 2023 (UTC)