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. ZapperZ

    PF PHOTO CONTEST - Singing In The Rain (9/6-9/12)

    Singing In The Rain This week, your pictures must show a rainy scene. It must be clear enough that one can tell that it is raining. Zz. Contest Rules: 1. Any digital photo or digitally-scanned photo relevant to the theme will be accepted within the contest period. In case there's a...
  2. D

    Kinematics of moving car and falling rain

    a man driving his car on a straight road at 25m/s looks through his side windows and sees rain fallling at 30 degrees. when he stops he sees the rain is actually falling straight down(0 degrees). what is the velocity of the rain, relative to the car a- when the car is moving b- when the car...
  3. wolram

    One Step from Rain to Dry: A Strange Encounter

    Driving home this morning the rain was teeming down, we often get teeming rain in periods of drought, but just at the edge of my property it stopped, i could literally take one step from rain to dry, i know a storm has to have boundaries but to be so abrupt was strange.
  4. M

    Water Distribution - Rain Barrel System

    I had an idea to collect rain in large amounts in rain barrels for use in irrigation for my lawn and garden. I want to create a network of 30 rain barrels at 55 gallons each. I will put one rain barrel at each of my down spouts on my gutters, to catch the rain. Then I will have the rest, 28...
  5. morrobay

    Electrocution in rain flooded streets

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  6. wolram

    New Evidence: Bacteria Causes Rain

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  7. P

    How Much Acid Rain Can Limestone Neutralize?

    Homework Statement Estimate the volume of acid rain in L that can be neutralized by 1.00 g of limestone. Assume the pH of rainwater collected in your rain gauge is a representative value for acid rain. Assume that acid rain contains sulfuric acid as the source of hydrogen ions. The molecular...
  8. T

    Please help me about Process of Clouds, Rain, and Struktur of Atmosphere

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  9. Math Jeans

    Unbelievable Phenomenon: Rain Falling in a 5 Foot Radius

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  10. M

    Does Running in the Rain Make You More or Less Wet?

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  11. G

    Work Done by Air Resistance on rain drops

    Homework Statement A 2.76 x 10^-5 kg raindrop falls vertically at constant speed under the influence of gravity and air resistance. After the drop has fallen 131m, what is the work done by gravity? After J is found for gravity, what is the work done by air resistance in units of J. Homework...
  12. B

    Power Generated by 2.5x10^10cc of Rain Falling 1000m in 1 Hour

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  13. wolram

    Rainy Day Blues: Wish for Sun to Shine Again

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  14. P

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  15. jambaugh

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  16. G

    Solving a Frictionless Cart Problem with Rain

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  17. P

    Is Rain Water Beneficial for Plant Growth?

    Some time again, my neighbour told me that rain water is better for the plants than tap water. Is this true? Both tap and rain water come from open sourse such as rivers or paddocks. Tap water has been treated and cleaned. But I guess rain water is pure H20 since heavier elements could not...
  18. S

    Why Michelson-Morley Were Wrong (Wind vs Rain)

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  19. A

    Acid rain affect on the environment

    Hi can someone help me out a little bit on this question How might acid precipitation threaten the fitness of the environment? I need to include molecular aspects such as pH.
  20. K

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    Hi, Can someone please check my work and tell me where I am going wrong? Rain is falling vertically downward with a velocity 25m/s. A cyclist is moving from North to South vith a velocity 15m/s. What is the velocity of the rain with respect to the cyclist? What is the direction the cyclist has...
  21. A

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  22. B

    Running in the Rain: Mythbusters Results & Sun Rays

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  23. B

    Rain in a train wagon - speed, momentum and KE

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  24. P

    Triple Point of Water: Hail Rain Explained

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  25. Astronuc

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  26. P

    Understanding the Effects of Acid Rain on Tree Leaves

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  27. Hootenanny

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  28. R

    A 4-Day Weekend Ruined by Rain: Now I'm Stuck at Home Bored

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  29. Ivan Seeking

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  30. E

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  31. Mk

    The Unknown Threat: Is Acid Rain Real or Just Hype?

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  32. S

    Air Resistance of falling rain

    So, here's the question: The speed of falling rain is the same 10m above ground as it is just before it hits the ground. What does this tell you about whether or not rain encounters air resistance? So here's my attempt: Since the speed of the falling rain is just the same 10m above ground...
  33. J

    Kinetic energy from rain drops

    Hi, I searched some websites with information about average size and average speed of rain drops, which I used to calculate the kinetic energy of the rain drop just before it hits the ground. My original question was: Is ALL this kinetic energy transferred to the ground (assume a non-elastic...
  34. T

    Find the velocity of the rain with respect to the car and the Earth

    I would like to confirm the answer to this question. 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 75.0° with the vertical. Find the...
  35. M

    Why is my TV better in the rain?

    Why is my TV better in the rain?? Ok, there is a TV channel that usually has really crappy reception. But dad noticed that it picks up whenever it rains. I looked at him funny the first time, but on a dry day he went and sprayed it with the hose and presto, reception instantly improves...
  36. wolram

    Rain clouds are gone and the birds are singing

    I am a happy chappie, though i can not tell you why, the rain clouds are gone and the birds are singing oh happy am i.
  37. B

    What is the volume of a rain drop?

    One of my physics H-work questions asks, If one inch of rain fell on an one arce field, how many rain driops hit that field. I figure that each rain drop has a volume of .5 mL. Does this sound about right?
  38. C

    Related rates and rain drops

    if a raindrop is a perfect sphere,and it accumulates moisture at a rate proportional to its surface area. Show that the radius increases at a constant rate. I know surface area of sphere = 4 * pi * r^2 dV/ dr = 4 * pi * r^2 I am not sure where to go from here Any help is appreciated...
  39. tandoorichicken

    The Mystery Behind 'Base Rain': Exploring the Unknown

    Why isn't there such a thing as base rain? Or do we just never hear about it?
  40. D

    Why Do Sweaters Shrink When Washed, But Sheep Don't When Caught in the Rain?

    how come sweaters shrink when you wash them, but sheep don't when they get caught in the rain my ap bio teacher asked us that in class, and nobody had an answer :confused:
  41. S

    Artificial rain cloud machine created by Israel scientists

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  42. S

    Rain producing machine invented this year

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  43. Monique

    Exploding black holes rain down on Earth

    http://www.newscientist.com/news/news.jsp?id=ns99994446 I am sorry if this was already dicussed earlier, but I thought it was pretty weird: black holes raining down on Earth :O
  44. Ivan Seeking

    Putin Orders Fine Weather for St Petersburg Celebration

    "PRESIDENT PUTIN has ordered fine weather for the St Petersburg summit and 300th anniversary festivities next week, and it is unlikely to rain on his parade"
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