What is Rain: Definition and 144 Discussions

Rain is liquid water in the form of droplets that have condensed from atmospheric water vapor and then become heavy enough to fall under gravity. Rain is a major component of the water cycle and is responsible for depositing most of the fresh water on the Earth. It provides suitable conditions for many types of ecosystems, as well as water for hydroelectric power plants and crop irrigation.
The major cause of rain production is moisture moving along three-dimensional zones of temperature and moisture contrasts known as weather fronts. If enough moisture and upward motion is present, precipitation falls from convective clouds (those with strong upward vertical motion) such as cumulonimbus (thunder clouds) which can organize into narrow rainbands. In mountainous areas, heavy precipitation is possible where upslope flow is maximized within windward sides of the terrain at elevation which forces moist air to condense and fall out as rainfall along the sides of mountains. On the leeward side of mountains, desert climates can exist due to the dry air caused by downslope flow which causes heating and drying of the air mass. The movement of the monsoon trough, or intertropical convergence zone, brings rainy seasons to savannah climes.
The urban heat island effect leads to increased rainfall, both in amounts and intensity, downwind of cities. Global warming is also causing changes in the precipitation pattern globally, including wetter conditions across eastern North America and drier conditions in the tropics. Antarctica is the driest continent. The globally averaged annual precipitation over land is 715 mm (28.1 in), but over the whole Earth it is much higher at 990 mm (39 in). Climate classification systems such as the Köppen classification system use average annual rainfall to help differentiate between differing climate regimes. Rainfall is measured using rain gauges. Rainfall amounts can be estimated by weather radar.
Rain is also known or suspected on other planets, where it may be composed of methane, neon, sulfuric acid, or even iron rather than water.

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  1. Vanadium 50

    Chance of Rain: Interpreting Probabilities

    What exactly does a chance of rain me? Tonight there is a 15% of rain. At one hour tonight, it's a 55% chance of rain. How exactly does this work out? How do I interpret these probabilities?
  2. PhanthomJay

    Probability of Rain in weather forecasts

    I am trying to settle a debate over two definitions of the 'probability of rain' in a weather forecast area. Definition 1 states that for example there is a 50% averaged probability of rain at some point in the forecast area over a given duration of time, that is, there is a 50-50 chance that I...
  3. Drakkith

    Cartoon Spider Walking a Dog in the Rain and Other AI Generated Images

    So I just discovered DALL*E, an AI that generates images based on text descriptions input by the user. And it is FANTASTIC. Fantastically amusing, that is. The images are generated in blocks of 9, and are VERY strange. The full version is a commercial product I believe, but there's a 'mini'...
  4. H

    How can I differentiate between monsoon rains and cyclonic rain?

    In my country, we get yearly rainfall from South-West Monsoon. But from time to time, there is something called cylonic (or western) disturbances which bring rain in my country. I have myself observed that though disturbances are cylconic, yet we (at my particular location and about 50km radius)...
  5. T

    Why Does Rain Create Waves on My Street? - Investigating Fluid Mechanics

    Hello (Perhaps this should be in physics, but perhaps it should be mechanical engineering (fluid mechanics). I attach a picture of water running down the street near my house. The street is a nearly constant 15 degree incline that goes on for about 1 kilo-meter with no speed bumps. The...
  6. B

    Block diagram showing how to turn white noise into rain

    So I have been looking and trying different thing to synthesize rain noise like this: https://mynoise.net/NoiseMachines/campingRainNoiseGenerator.php but I cannot get it. and the graph that this sound makes did not help at all: can some make a block diagram of how to do this?
  7. Hamiltonian

    Velocity of a cart moving in the rain as a function of time

    At time t = 0, the mass of the cart is ##M_0## and velocity is ##v_0## in a time interval ##dt## let a mass of ##dm## be added to the cart due to the pouring water and let the reduction in speed be ##dv## ##\lambda = dm/dt## applying conservation of momentum from the ground frame gives $$M_0...
  8. karush

    MHB -find probability it will rain both days

    ok I still don't know where the (0.2) comes from
  9. binbagsss

    How Can You Redefine Healing in November Rain Lyrics?

    Okay I want the November rain lyric - "but If you could heal a broken heart, wouldn't time be out to charm you..." But I want to replace the ' If you could heal a broken Heart ' with something that doesn't really refer to heartT break but along the lines of something that means letting the...
  10. G

    Change in Mass of Hurricane Harvey's Rain

    First I have to explain that this is not actually a homework problem. It is a problem I created to use in a sort of game. If I made a mistake, it tends to ball up the game. So I am looking for someone to double check my answer, and to point out any errors in my statement about physics. I prefer...
  11. L

    Automotive Are some car glasses more resistant to acid rain?

    I have two cars, one an early 2000 Honda CRV and second one a 2016 Subaru Forester. The Subaru Forester is prone to acid rain marks in the windshield and side windows and rear. But the CRV didn't seem to have obvious acid rain after more than 14 years parked in open air. Are some glass more...
  12. davenn

    Coronal Rain -- an interesting article

    For all you solar astronomers out there An interesting new article from Emily Mason at the NASA’s Goddard Space Flight Centre in Greenbelt, Maryland continue reading at ... https://www.nasa.gov/feature/goddard/2019/unexpected-rain-on-sun-links-two-solar-mysteriesDave
  13. T

    Cars rounding a slippery banked corner in the rain

    Homework Statement The question is from Fundamental Physics 10th Edition, Walker Resnik Holiday: A banked circular highway curve is designed for traffic moving at 60 km/h. The radius of the curve is 200 m. Traffic is moving along the highway at 40 km/h on a rainy day.What is the minimum...
  14. I

    Find the velocity of the rain drops with respect to the man?

    [Mentors' note: No template, as this post was moved from the technical forums] Q. A man is walking on a level road at a speed of 3.0 km/h. Raindrops fall vertically at a speed of 4.0 km/h. Find the velocity of the raindrops with respect to the man, A. The explanation is below: Here I don't...
  15. B

    Catching cold when wet in rain

    Whenever I got wet in the rain. I always get cold (running nose, etc.) I know I'm not catching the virus in the rain. Is the explanation because one's body thermo regulation (hypothalamus) gets affected which lowers the immune system that makes the existing virus in the body multiply? Right now...
  16. Suppaman

    B Cosmic Rain: Exploring the Mysteries of High-Energy Particles

    I was just reading the article about “cosmic rain” here and they talk about these very high energy particles striking a detector. But as I understand things, these have to be waves, not particles, put up a double slit and these things will go through both as waves (and since they do not know...
  17. Hawksteinman

    B Calculating Probability of Rain This Weekend

    I was reading a book about innumeracy and one of the chapters was on probability. This weather woman said 'there is a 50% chance of rain on Saturday, and a 50% chance of rain on Sunday, so the chance of rain this weekend is 100%' Obviously she was wrong, but it got me thinking how would one...
  18. kyphysics

    Why don't wood construction sites get damaged in the rain?

    They're building new condos across from my parents house right now (adjacent neighborhood). I see this site everyday and it's growing. Right now, they've got a lot of the framework up for the condos and it's all wood (as far as I can tell). It's also raining a lot here. Question - why...
  19. M

    MHB What is the Probability of No Rain Tomorrow?

    There is a 30 percent chance of rain tomorrow. What is the probability of no rain tomorrow. Solution: Let P = probability P(no rain tomorrow) = 1 - P(rain tomorrow) P(no rain tomorrow) = 1 - 0.30 P(no rain tomorrow) = 0.70 or 70 percent Right?
  20. D

    Is generating electricity from rain water efficient?

    From small generators attached to the gutters of your house to large ones in the storm sewers, is it efficient enough to make the effort?
  21. B

    Lightning discharge's effect on rain fall velocity?

    When stopped at a red light during a thunder storm, I notice this: - I hear the intensity of the rain hitting the roof of the car - there is a lightning flash - for a couple of seconds the rain intensity eases up noticeably, then resumes - then the thunder clap follows a little bit later It is...
  22. ChloeYip

    Angle of Rain on Earth: Investigating Relative Velocity

    Homework Statement When a cart travel to the left at v=-10m/s, the angle of rain come towards it is 50o from normal. When the cart travel to the right at v=10m/s, the angle of rain water come is perpendicular to it. What is the angle of rain come to the earth? Homework Equations relative...
  23. kipup123

    Relative Velocity (Man walking in rain question)

    Homework Statement A stationary person observes that rain is falling vertically down at 30km/hr. A cyclist is moving on the level road, at 10km/hr. In which direction the cyclist should hold his umbrella to prevent himself from the rain? 2. The attempt at a solution I used triangle law to...
  24. P

    How does rainwater compare to home water in terms of potential harm?

    I've heard people say that if you come back from the rain and you're soaking wet (because of the rain water), you should take a bath to prevent any kind of illness. However, how can it be that rainwater can cause you harm, but the water in your home cannot? Or maybe, how does your home water...
  25. TheSodesa

    Calibrating a rain gauge (problem interpreting question)

    Homework Statement We wish to make a precipitation meter shaped like a paraboloid ##z = x^2 + y^2, 0 \leq z \leq 10##. Devise a scale on the z-axis that tells you the amount of precipitation in cm. In other words, at what height ##z = h## is the surface of water in the dish when there has been...
  26. P

    Falling Rain Drop (Variable Mass)

    Homework Statement Suppose a rain drop with mass ##m_0\neq 0## is falling due to gravity with initial velocity ##v_0##, assume ##\frac{dm}{dt}=k=##constant. Solve the differential equation and determine the velocity as ##t\to\infty## Homework Equations ##F=\frac{dp}{dt}=\dot{m}v+m\dot{v}## The...
  27. Edison Bias

    B Understanding the Science Behind Water Vapor and Cloud Formation

    Hi! I wonder how water vapour can reach the sky while its temperature is far from the boiling point? I have learned that water is lighther than air and this is said to be the reason for water vapour to reach the sky. The trick question is however, how does water become vapour in the first...
  28. J

    Saturn: Helium Rain, or non-indigenous planet?

    I'm using Chaisson'/McMillan's "Astronomy, a Beginner's Guide to the Universe"/7th Edition In Chapter 7, it describes the gas giants, and says that Jupiter, Uranus, and Neptune all have "86% Hydrogen, 14% Helium" in their atmospheres, while Saturn has about 92% hydrogen, and 7% Helium, in its...
  29. MattRob

    Proper Time in Rain Frame: Exploring GR

    So, I've been working through "Exploring Black Holes: Introduction to General Relativity" by Taylor and Wheeler, and I'm somewhat puzzled by a term in the "Rain Frame." The "Rain Frame" is meant to be a frame of reference of an object initially released from rest at infinity as it free-falls...
  30. Muthumanimaran

    Why there is no rain when clouds are scattered?

    Raining only occurs when there are dense clouds in the sky, when they are scattered the raining is stopped, why?
  31. T

    Optimizing Velocity on Incline for Vertical Rain Perception

    Homework Statement Rain falls with velocity of 20m/s parallel to an incline which is at an angle of 37 degrees from the ground. A man starts running down the incline with a velocity 'v' . Find 'v' such that the rain appears to be falling vertically on the man( from his perspective). Homework...
  32. T

    Can I Reach the End of a Rainbow with a Shovel?

    I'm interested in rainbows. I'm talking about good old fashioned arc/halo rainbows like those you see in the sky. Sometimes you see rainbows from lawn sprinklers. How small would the smallest rainbow arc conceivably possible to view be? Could I make a rainbow at night using a sprinkler with a...
  33. P

    How Does a Rain Catchment System Affect Water Levels in a Tank?

    I am volunteering at an orphanage in Guatemala. There is no well, and the city water is a relatively expensive. I would like to install a rain catchment system on our roof for use in the outhouse bathroom and garden. I've diagrammed it and attached the image. My question is this: Will the...
  34. nsaspook

    What is causing the dirty rain and animal attacks in the Northwest?

    I've no idea what the cause is but it fell over a wide area. http://www.kboi2.com/news/local/Mysterious-dirty-rain-falling-in-Eastern-Washington-Oregon-291094521.html http://www.kxly.com/news/spokane-news/31142818
  35. M

    Momentum/Impulse- Calculating Average Force of Raindrops

    Homework Statement The problem says: "A record rainstorm produced 304.8 mm (approximately 1 ft) of rain in 42 min. Estimate the average force that the rain exerted on the roof of a house that measures 10 m * 16 m. Indicate any assumptions you made. (Note: density of water is 1000 kg/m3"...
  36. S

    Slowly walking in the rain or running fast?

    Who will get more wet? The one who is slowly walking in the rain or the who is running fast? What is the physics behind it? Thanks in well advance
  37. Simon Bridge

    [paper] Run or walk in the rain

    I am looking for other opinions on the following that has come to my attention: Seongtaek Seo (2013) Orthogonal Projection & Run or Walk in the Rain? European Journal of Scientific Research ISSN 1450-216X / 1450-202X Vol. 113 No 4 October, 2013, pp.560-570 Abstract: In this paper, we will find...
  38. Hijaz Aslam

    Is relative velocity confusing in multiple vector systems?

    Are the vectors resolved correctly? I get a different answer to this question(well my diagram itself is different). How can ##\beta## be greater than ##\alpha##? Isn't it that here ##\alpha## should be in place of ##\beta## and ##\beta## in place of ##\alpha## and both ##V(rain,woman)## and...
  39. K

    How the velocity of rain relative to the driver in car increases?

    How does the velocity of the rain with respect to the car get added up? Velocity of rain with respect to man is given by the (velocity of rain wrt ground - the velocity of car wrt ground). Here it's not being added up!
  40. S

    How many days does it rain in May?

    Homework Statement A survey concludes that it in average rains 15 of 30 days in may. Thusly P(R|M) = 1/2 Where M is May and R is rain. The Weatherservice forcasts fits 2/3 of the time. Thus it does not rain 2/3 of the time. I bring umbrella with me every day the promise and...
  41. B

    Wind and rain sounds -- how to make from basic sources?

    ok I have a FFT filter ( lowpass and highpass), white, brown, and pink noise generators. How do I use all these things to make wind ,rain, and ocean noise ? I am told there is a way.
  42. C

    Maximizing Flow in a Rain Gutter: 3-sided vs Semicircular Cross Section

    A long piece of sheet metal w inches wide is to be bent into a SYMMETRIC form with three straight sides to make a rain gutter. A cross section is shown below. \_____/ The base is w-2x and the angled side lengths are both x with a theta between top horizontal. A. Determine dimensions that...
  43. E

    Effect of rain on velocity of sound

    I was suddenly asked this question by a friend... How a 'cats & dogs' rain would affect the velocity of sound through air?(as we know velocity of sound through water is five times than in air) I just couldn't be sure how to answer it... The raindrops are really small but there's a lot of...
  44. L

    What is the relationship between wet bulb temperature and rain temperature?

    If the external DBT is 20 deg C and it is 50% RH, then it rains, what temperature is the liquid rain? I am trying to calculate the heat transfer from a surface when it is raining. I have a set of climate data which will give me external ambient DBT, RH and precipitation. So how can i predict...
  45. A

    How Do You Model Rainfall and Runoff on a Flat Surface?

    I would like to model rain hitting a surface and then running off of the surface. The surface would be a square, such as a slab of concrete, and the concrete would not be at any angle, so the rain would run off of all sides equally. This is a starting point for a small research project I am...
  46. P

    Harnessing kinetic energy from impact of rain water

    I read in a science magazine that you would be able to generate more energy by collecting a mass of water and tipping it through a turbine than from generating energy from the impact of that mass of water as individual raindrops. Now this may simply be to do with the technology we have that...
  47. P

    What Causes the Velocity of a Cable Car to Change in the Rain?

    Hi, Homework Statement A cable car slides without any friction along a horizontal wire with initial velocity v0. The car is half filled with water and its mass (with the water) is m. At t=0 it starts raining (perpendicular to the ground). The rate at which water is collected in the car is k...
  48. Monsterboy

    Exploring Red Rain Mysteries: Is DNA-less Life Possible?

    Is discovery science's "Unexplained files" more believable than say ,History channel's "Ancient aliens" ? http://science.discovery.com/.../red-rain-in-sri-lanka.htm http://en.wikipedia.org/wiki/Red_rain_in_Kerala Mod note: Inappropriate links removed They said the red rain 'cells' did not...
  49. U

    Calculating Power from rain flow

    Homework Statement As we have seen, energy can be extracted from moving water. When it rains, water that lands on roofs is collected in gutters and carried to the ground via downspouts. In a typical heavy rain in your city, how much power could be harnessed from the rain flowing out of your...
  50. C

    Classic rain falling on a car's window problem doubt

    A car travels due east with a speed of 50.0 km/h. Raindrops are falling at a constant speed vertically with respect to the Earth. The traces of the rain on the side windows of the car make an angle of 60.0° with the vertical. Find the velocity of the rain with respect to (a) the car and...