# Tag Info

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 ...

25

@gerrit provided a formula, but without stating the reasoning behind it. Radioactive decay is an exponential function. After $n$ half-lives, the amount of the original material remaining is $$\textrm{amount remaining after}\ n\ \textrm{half-lives} = \left(\frac{1}{2}\right)^n$$ Therefore, you want to solve \begin{align*} \left(\frac{1}{2}\right)^n &... 19 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 highest recorded temperature, exactly 90 years after it had been established at El Azizia, Libya, with a measurement of 58°C. The official highest recorded ... 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 ... 17 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 than mercury, so a water barometer requires a 10.3m tube. 1mbar is therefore roughly 1cm, and 0.1mbar measurement is clearly trivial using a ruler with 1mm ... 16 The other answers are entirely correct. But I like graphical representations. From http://en.wikipedia.org/wiki/Radioactive_decay we see the decay formula is:N(t) = N_0e^\frac{-t}{τ}$$Where N0 is the starting number of nuclides and τ is the mean lifetime. We also see that the half-life is$$t_{1/2} = τ ln(2)$$Substituting for τ, we get:$$N(t) = ...

16

Yes. Nearly global satellite and radar derived rainfall data are hosted by NASA Goddard Space Flight Center, namely: Tropical Rainfall Measurement Mission (TRMM) aboard the TRMM Microwave Imager (TMI), a multi-channel, dual polarized, conical scanning passive microwave radiometer designed to measure rain rates over a wide swath under the TRMM satellite. ...

16

I don't understand the last sentence about decimal places, but I can tell you about the relationship between lat, long and distance. Over two centuries ago, the meter was defined as one ten-millionth (1/10 000 000) of the length of a quadrant along the Earth's meridian; that is, the distance from the Equator to the North Pole. So, for latitude the number of ...

15

You can use simple logarithms to calculate the answer. The number of half-lives that have elapsed can be calculated with $$- \frac{\log{f}}{\log{2}}$$ where $f$ is the fraction that remains. So plugging in the numbers gives $$- \frac{\log(0.75)}{\log(2)} = 0.415 = 41.5\%$$

15

Challenger Deep (10.99km) in the Mariana's Trench is the deepest part of the ocean floor. This is probably close to the deepest theoretically possible ocean floor with the current thermal regime. With the current thermal regime, the deepest 'steady state' ocean floor depth is about 5.5-6km ( cooling curves at Muller et al ) - limit is reached as the ocean ...

14

This is a good question, and the basic answer is earthquake seismology. To answer this question, lets accept a fact: Waves propagate through the least time pathway, and not the least distance path. This property of physics is known as Fermat's principle. When an Earthquake occurs, energy propagates similar to a ripple of water, and spreads. Each point on ...

14

The width of a unit in a stratigraphic column, or 'log', sometimes represents the average grainsize of the rock. I can imagine it being keyed to some other property, but grainsize is common. You'll find lots of examples with a quick search for 'sedimentary log'. The height of a unit typically represents thickness if the vertical axis is length, height or ...

13

Images showing clouds mostly come from geostationary satellites. Geostationary satellites are at an altitude of about 36000 km, which allows them to monitor the same area of the Earth continuously. They stay in place relative to the Earth's surface above the equator thanks to balance between gravitational and centrifugal force. There are a few such ...

13

If you are looking for a dataset going back a bit further, but still sticking to satellite and radar data, GPCP (Global Precipitation Climatology Project) goes back to 1979. The limitation of certain TRMM datasets, in addition to the relatively short length of the project, is that they only cover the tropics and so you lack data in the mid-latitudes and ...

12

Before defining wind velocity, I think it is necessary to explain the continuum assumption. The basic idea is that even though gases are composed of discrete molecules occupying a small fraction of the total volume filled by the gas, gas flows are made up of many individual collisions between gas molecules. In most applications, the flow field is assumed to ...

12

I remember a comment on this by Rodney Calvert in the video lecture version of his SEG Distinguished Instructor Lecture "Insights and Methods for 4D Reservoir Monitoring and Characterization": http://shop.seg.org/OnlineStore/ProductDetail/tabid/177/Default.aspx?ProductId=1842 The comment was referring to the possibility of observing a pressure change front ...

12

One standard that has be used by the USA is to measure the distant between points on the coast at intervals of 30 latitude minutes, as measured on a 1:1,200,000 scale map. See chapter 5 of Measurements from Maps: Principles and Methods of Cartometry by D. H. Maling for further information and other standards that have been used.

12

Organic material (plants and animals) contains carbon. Carbon has three main isotopes: carbon 12, 13 and 14. Carbon 14 is radioactive, with a half life of 5730 years. Carbon 14 is continuously created in the atmosphere by cosmic rays hitting nitrogen. The nitrogen atoms lose a proton when struck by cosmic rays, turning the affected nitrogen atom into an ...

11

Most data we collect about weather is done regularly and for all altitudes of the troposphere. Kites, though, are at the mercy of the weather and do not fly high enough. So when there is ice or snow or other meteorological conditions that don't allow a kite to fly, you get no data. We now use methods to measure the weather that don't break in bad weather. ...

11

Tomography! In essence, we guess some velocities, compute the arrival times our guess implies, compare them with actual arrival times, tweak our answer, and repeat. Seismic tomography is an ill-posed, ill-conditioned inverse problem, and one upshot of this is that the solutions are non-unique — there are infinitely many answers! We have to choose one (or, ...

11

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 measurement at 6:00 in winter. (So if you do see a DST effect in the data, that would be due to traffic and other local anthropogenic effects shifting by an ...

10

You can calibrate anemometers from other anemometers, or loosely from a windsock if precision isn't that important. But per your question, how was the first anemometer calibrated? See my answer about wind and you'll see that we have equations that relate fluid velocity to factors like pressure gradients, friction, coriolis force, advection, etc. We could ...

10

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 instruments used for surface measurements. The second deals with instruments used for measuring vertical profiles, which have to deal with a larger range of ...

9

The only open and ongoing data source for in-situ ocean wave measurements I am aware of is the National Data Buoy Center. Though NDBC manages data service from plenty of moored buoys in the Gulf of Mexico and the Atlantic and Pacific coasts of North America, unfortunately there isn't much in your region of interest. The only buoys I have found that are ...

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 ...

9

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 invariably useful). If you read your definition carefully you will realise that specific gravity is defined as the ratio of the density of the material to that of ...

9

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 been a concern of merchants and those regulating them; in 1692, the standard would probably have been a brass prototype yard in the possession of the Royal Society....

8

The first problem to tackle is "what is an odor"? An odor is a chemical aerosol or gas, which are small molecules suspended in the atmosphere. To track the odors of pizza or burning wood you would first need to identify the molecules associated with the scent. One example is α-pinene, which is the molecule that gives pine trees their scent. Food cooking ...

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