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 ...
- 798
23
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 ...
- 1,886
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 ...
- 905
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 ...
- 2,110
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 ...
- 8,822
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 ...
- 17.7k
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 ...
- 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 ...
- 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 ...
- 200
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 ...
- 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 ...
- 772
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 ...
- 1,291
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 ...
- 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 ...
- 4,080
7
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-...
- 326
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 ...
- 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 ...
- 3,464
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 ...
- 24.8k
6
votes
How does ice-penetrating radar "see" through kilometers of ice without being absorbed?
When electromagnetic waves travel through a medium, it can interact with the medium in question. But that interaction depends on the electric properties of the medium.
Ice, being a dielectric medium, ...
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 ...
- 2,201
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.
&...
- 169
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 ...
- 8,822
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 ...
- 24.8k
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 ...
- 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 ...
- 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 ...
- 4,041
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 ...
- 8,151
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 ...
- 161
5
votes
Accepted
How does one interpret negative geopotential height values?
This likely means that the surface MSLP is less than 1000 mb.
If you are looking at a 1000 mb geopotential height, and the MSLP at a point is 995 mb, then the height of the 1000 mb geopotential ...
- 8,809
Only top scored, non community-wiki answers of a minimum length are eligible