# Tag Info

130

You were right to question whether the atmosphere really held that much water. It comes nowhere close! We use precipitable water to track this, which is the measure of all moisture in the entire column of air in the troposphere. We can get good widespread estimates from remote observations. This animation shows current amounts of precipitable water ...

45

It's confusing to measure liquid in units of length instead of volume, isn't it? Here's how it works. "One millimeter of rain" is actually one cubic millimeter per square millimeter. On average, over the area you're talking about, each square millimeter has received one cubic millimeter of rain. If you divide n mm3 by 1 mm2, you get -- n mm! The field of ...

28

Short answer: humidity is not a proxy for rain starting and no, it does not start raining automatically when 100% humidity is reached (haze or clouds can form though). The onset of rain is dependent on many things including humidity, but a specific value of humidity is not a sufficient condition for rain. Water vapor is a gas and invisible. The amount of ...

24

I invite correction if I missed any details, the column of air above you, at any one time, at 100% humidity can hold maybe 3-6 inches (75-150 mm) of water depending on temperature and it's likey to rain only a percentage of that, not all of it. If air remained stationary, which, of-course it doesn't, then we'd get much less downpours. The hurricane is ...

18

It is the amount of rain that it takes to cover the ground X milimeters deep. It is normally measured in 24 hours and is measured each morning at a fixed time like 0900. But now the measurements are fully automatic, so the meteorological service gets the data more often and can provide data for each hour of the day. Total rainfall is still measured from ...

17

Does it mean that 3mm per square meter was experienced in a specific area, or does it mean that the total amount of rain had a volume such that if it was spread over all of Hong Kong the height would be 3mm. Or is it referred to in terms of per square meter? They're really the same idea. Fundamentally it means that it filled a rain gauge (of some ...

16

If you're open to a more mechanical solution, I'd suggest building a "tipping bucket rain gauge", best explained by a picture (source: https://www.researchgate.net/figure/Sideview-of-tipping-bucket-Rain-Gauge_fig4_304297354): This should be relatively easy to build and it's trivial to read this electronically by detecting the time it takes to tip. ...

14

The intensity of a rainstorm does not actually cause the duration of the precipitation to be shorter. There is a strong correlation, but not in the sense you may be implying here (let me get back to that in moment). First you have to dispel the model that a cloud is a big container of water, and if it "rains harder", the cloud will run out of water ...

13

Harvey is almost stationary and is rotating new gulf moisture up the "dirty" side (east of the center). I am outside the main path and have 10+ inches (250 mm) in 30 hours (emptied the rain gauge twice). It has been reported that affected areas have exceeded the "500 year" rainfall level. I guess they need a 1000 year level. The atmosphere is pretty big and ...

12

One way to do that is to estimate how much water is changing. If you can ignore the spill over, then that is approximately how much the puddle is changing. Another idea you can use is to measure the changing weight of a rain gauge (that will need to be emptied daily, unless you can rig something that will do that for you). The faster the weight increases, ...

12

Upon reading the question my first thought was, please define what is meant by "how hard is it raining?". The answers to the question Is there a consensus on the “heaviness” of rain? list rain intensity units as being L/m2 or mm/h, which are effectively the same thing (mm/h can be converted to L/m2) and I'm not disagreeing about either. My initial ...

12

It's not perfect, but a simple solution to the issue of a puddle building up on the resistance plate is to tilt the plate a bit, so that instead of the water building up on the plate it runs off. Your device would then look for sudden drops in resistance, indicating that a droplet has formed on the device, followed by the resistance rising again after the ...

11

For rain to fall, water vapour must exist in sufficient quantities in the atmosphere. The main source of atmospheric water vapour is evaporation from oceans. However, evaporation from large bodies of water such as lakes and dams also contributes. Another significant contributor, on a local level, is transpiration from forests. the Amazon alone creates 50-...

11

The rivers are generally fed by water that percolated into the ground, it takes longer for that water to work its way down to the stream so the streams and rivers keep flowing long after the initial rain. https://water.usgs.gov/edu/rivers-contain-groundwater.html

9

The Tropical Rainfall Measuring Mission (TRMM) satellite is a single satellite, carrying multiple instruments on board, as described here. It makes a total of 16 orbits/day at a low altitude of 400 km, with different swath widths for each instrument. Thus, the measurement product that you get is not a "continuous" measurement of a single atmospheric ...

8

A quick literature search seems to confirm Gordons estimation, even at the scale of a whole bucket: [T]he annual mean pH, based upon samples collected weekly during 1970-1971 and weighted proportionally to the amount of water and pH during each period of precipitation, was 4.03 at the Hubbard Brook Experimental Forest, New Hampshire; 3.98 at Ithaca, ...

8

Given any container with straight sides, 3 millimeters of rainfall will fill up that container to 3 millimeters in depth. The size of the container does not affect this. It holds whether the container is the size of a tennis court, or the size of a small beaker or a test tube with a flat bottom. As long as its sides are vertical and uniform. It is also ...

7

When it rains the raindrops nucleate around aerosol particles of salt, dust, clay, soot, dimethyl sulphide, etc. In addition a falling raindrop may pick up any particulate matter that may be in its trajectory. The net result is that rain 'scrubs' the atmosphere clean. Without all these polluting particles to diffuse different wavelengths of the spectrum, the ...

7

Robert Cartanio's answer makes very good points, and I'll accentuate them with some examples. Thunderstorms tend to produce "hard rain" and larger scale organized convection will have areas of hard rain and areas of weaker rain. Air-mass thunderstorms are the type of daily convection you see in Florida and elsewhere. These tend to appear somewhat ...

7

Without water in the air, clouds cannot form and evaporate quickly if they do and so a sudden drop in evapotranspiration that resulted in low humidity could decrease the prevalence of rain. But, in simulations, there's not usually much of a measurable effect (http://www.sciencedirect.com/science/article/pii/0273117787902900?np=y). This is because there's a ...

7

Raindrops gain a small amount of acidity as they fall through carbon dioxide in the air, but that's not what this question is about. Raindrops commonly start off as ice crystals which have to nucleate around something, usually an aerosol particle such as soot, clay, bacteria, sulphur dioxide , dimethyl sulphide, etc. If a small raindrop nucleates around an ...

7

Rain in a climate such as Ireland is most often stratiform. That is, it is created when moist air is lifted by a front, or by divergence in the upper troposphere. Thunderstorms involve buoyant air, which rises on its own due to its being warmer than its surroundings. Typically solar radiation is involved in heating the surface such that the air near it warms ...

7

Erratic Climate Lets take Broome, Australia as our example. Broome gets 615mm of rain a year (24 inches), including 58/182/180/102mm in Dec through March. Coupled with average highs in the low 90s, this would be fine for the sort of agriculture you see in South Texas. However, Broome's rainfall is very erratic. For example, in 2016, the rainy season started ...

6

This is an El Nino summer, and a very strong one and a very weird one at that. Weather patterns are messed up world-wide. Apparently a stable high pressure cell has set up that oscillates back and forth between just east of Barcelona to eastern Europe. France suffers when that high pressure cell is just east of Barcelona. That high pressure cell off ...

6

Sounds like your question, like most questions about historical data, might be a little challenging to find the right source, as it often is around the world. But seeing you said Atlanta brightened my eyes! For if one is seeking information for a US climate observation sites (most big cities, and a fairly reasonable web across the US... there's about 2-6 ...

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The atmosphere can "hold" only maximum 75mm worth of precipitation at any given locality, this is true. However, this particular hurricane Harvey was a very slowly moving structure. The vortex would carry the warm water-saturated masses from Gulf of Mexico, which essentially collided with colder air from the North, generating rainfall. It is the continuous ...

6

It literally means that the water depth will be 0.5mm. For example, if you place a container under the rain and it fills up to 0.5mm, then the precipitation is 0.5mm. Despite the fact that a wide container requires more rain to fill up than a narrow container, the larger surface area allows it to collect the right amount of rain water to fill up to the same ...

5

There are two solutions using the least square method for calculating $C$ and $D$. Both methods yield different results for your constants. There is no correct method. Method of least Squares We define the least square error as follows: $$\text{lse} = \sum_{i}{\left(y_i - f(x_i)\right)^2}$$ The $y_i$ and $x_i$ are our data through that we want to fit a ...

5

We define rain events in terms of the probability of reccurrence. For example, we call a certain rainfall the "10-year rain event," meaning that this amount of rain would only be expected to occur once every 10 years. We usually like to have at least 30 years of data before calculating recurrence intervals. Note: Just because we call something the 100-year ...

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