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51 votes

What does a mm of rain mean?

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 ...
jeffB's user avatar
  • 798
23 votes

How is rainfall measured when the news speaks of "two inches of rain"

A wheelbarrow is usually considerably wider at the top than at the bottom, so the accumulated water at the bottom will likely be deeper than what actually fell. However, rainfall can also have ...
damp_civil's user avatar
22 votes

What does a mm of rain mean?

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 ...
trond hansen's user avatar
  • 1,878
20 votes

How is rainfall measured when the news speaks of "two inches of rain"

Weather stations measure the depth of rain that falls over a small, set area by setting an open topped cylinder of precise diameter in the open at a standard height above the ground and measuring how ...
Ken Fabian's user avatar
  • 2,120
19 votes

What does a mm of rain mean?

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 ...
JeopardyTempest's user avatar
19 votes
Accepted

What was the highest temperature ever recorded on the surface of Earth?

The record the article is referring about seems to be the same as registered at Guiness World Records: On 13 September 2012 the World Meteorological Organisation disqualified the record for the ...
Camilo Rada's user avatar
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17 votes

How are barometric pressure measurements traceable over centuries to 100 parts per million accuracy?

Mark's answer about mercury barometers is correct - but it is not the complete story. Barometers were initially constructed using water, not mercury, on the manometer principle. Water is lighter ...
Graham's user avatar
  • 437
11 votes
Accepted

Are average daily temperatures affected by DST?

They compensate for DST. That is, for any daily measurement, they use the same universal time every day of the year. If they take a measurement at 7:00 local time in summer, they will take the same ...
gerrit's user avatar
  • 11.7k
10 votes

What does a mm of rain mean?

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 ...
thomasrutter's user avatar
10 votes
Accepted

Unwarranted claim of higher degree of accuracy in zircon geochronology

I can't be entirely sure but I'll make an informed guess: That value doesn't come for a single measurement. Therefore, if the error in the age of a single sample is $\pm125$ kyr, you just need to ...
Camilo Rada's user avatar
  • 17.7k
10 votes

How do the pros measure humidity?

The WMO report Instruments and Methods of Observation has a chapter on Measurement of humidity and a separate chapter on Measurement of upper-air pressure, temperature, humidity. The first deals with ...
M Juckes's user avatar
  • 772
9 votes
Accepted

Is there a difference between Density and Specific Gravity?

It is different to density but they are closely related. This is easily seen by considering the dimensions of the two quantities (side note: always consider the dimensions of quantities - it is ...
bon's user avatar
  • 2,211
9 votes

How are barometric pressure measurements traceable over centuries to 100 parts per million accuracy?

A mercury barometer is a simple, easy-to-build barometer that turns the problem of calibrating a pressure standard into one of calibrating a length standard. Accuracy of length standards has long ...
Mark's user avatar
  • 1,261
8 votes

How is rainfall measured when the news speaks of "two inches of rain"

In addition to what others have mentioned, sometimes measurements are simply wrong, in particular where measurements are automated. Some weeks ago, two weather stations in Germany reported over 60 mm ...
gerrit's user avatar
  • 11.7k
7 votes

Is there any way to measure the amount of radiation the earth receives from the sun?

Your understanding is half correct. Yes, we can measure the amount of radiation the Earth receives from the Sun. Yes, it is difficult to get an extremely precise measure of how much radiation the ...
410 gone's user avatar
  • 4,080
7 votes
Accepted

How is the distribution of Argo floats managed over the Earth's oceans?

I think, there are two factors which prevent the forming of clusters of floats: The floats' lifespan. Batteries supposedly last for four years, then the floats become debris which sink to the bottom ...
Erik's user avatar
  • 756
7 votes

If the accuracy of measurement of the earth's volume is not known, how can scientists assert that the earth is not expanding?

In short, the current volume of the earth is known to great precision and modern measurements show no significant expansion at meaningful scales. Facing 20th century evidence that points on the globe ...
jeffronicus's user avatar
  • 3,487
7 votes

How is relative humidity determined from a wet and dry bulb readings?

Edit: 1 May 2021 The following procedure uses the less accurate method from page 455 onward from the scanned sections of the book pictured below, from the original answer. The procedure is a ...
Fred's user avatar
  • 24.7k
6 votes
Accepted

How to Interpret this set of Latitude and Longitude?

It looks like your coordinates are written in decimal degrees but with the decimal points omitted. 34.144442 -118.654084 corresponds to 34°08'40.0"N 118°39'14.7"W. Google maps shows this to be a ...
bon's user avatar
  • 2,211
6 votes
Accepted

How does ice-penetrating radar "see" through kilometers of ice without being absorbed?

Water molecules do interact with microwaves and in microwave ovens that operate at 900MHZ- 2.5GHz. This Radar instrument operates using Very High Freq Radio Waves at 193MHz [1]. At lower-than-...
potatasbravas's user avatar
6 votes

What was the highest temperature ever recorded on the surface of Earth?

The Hadean era covers the time from the formation of the Earth until 4bn years ago. It was characterized by a surface of molten rock, due to repeated meteor strikes, volcanism and radioactive decay. &...
Boodysaspie's user avatar
6 votes

What was the highest temperature ever recorded on the surface of Earth?

Note that in addition to Camilo's answer, Wikipedia links to a peer reviewed BAMS article noting that: Satellite measurements of ground temperature taken between 2003 and 2009, taken with the MODIS ...
JeopardyTempest's user avatar
6 votes

How are barometric pressure measurements traceable over centuries to 100 parts per million accuracy?

I don't think they are using that level of accuracy for the old readings. Reporting pressure, in hPa, to one decimal place is being done for recent measurements. There are no values given for very ...
Fred's user avatar
  • 24.7k
6 votes
Accepted

What is the second thermometer in the image from the Esperanza Antarctic temperature record?

Doing a quick calculation that looks to be around the wet-bulb temperature at the time of observation so that thermometer on the right side should be a hygrometer. Hygrometers measure the level of ...
Wxboyajm's user avatar
  • 426
6 votes

How do the pros measure humidity?

We use something like an Onset HOBO electronic sensor. They've got logging (and in some cases, networking) built in. They'll typically log both temperature and relative humidity at regular intervals ...
410 gone's user avatar
  • 4,080
6 votes
Accepted

Measuring the circumference of the earth - revisited

You can use the fact that the Earth's rotation period is known. Then divide that period (use the solar day of 24 hrs 00 minutes instead of the sidereal day of 23 hrs 56 minutes) by the actual amount ...
Oscar Lanzi's user avatar
  • 3,906
6 votes

How did they know that there was a "desert tsunami" in a Death Valley cave after a 7.6 magnitude earthquake near the southwest of Mexico?

The news section of the Death Valley National Park website has the story: Mexican earthquake sloshes Devils Hole. There is footage of the waves at the end of the page. Here is a screenshot from the ...
Jean-Marie Prival's user avatar
6 votes

How is rainfall measured when the news speaks of "two inches of rain"

Properly designed rain gauges can give accurate results for a given location or point in space, but the problem is that it's hard to have enough of them packed densely enough in an area to give the ...
anjama's user avatar
  • 161
5 votes
Accepted

Where can I get historic hourly precipitation data for Italy?

The US NCDC has this link to surface hourly global data which I was indeed able to find Napoli on. It appears, based upon this page describing the World Data Center For Meteorology, that there may be ...
JeopardyTempest's user avatar

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