Geoscience Reference
In-Depth Information
surface pressure variations) and wind fields. The determination is again affected by
the oceanic response to atmospheric pressure variations (Sect. 2.8 ) and atmospheric
tides (Sect. 2.7 ) .
2 Neutral Atmosphere
The first subsections here are meant as review and summary of basic physical and
meteorological relations which should serve as introduction for students in geodesy
who are not very familiar with those aspects but can be skipped by more experienced
readers in that field.
2.1 Physical Terminology
To conclude from the mechanical properties, which describe the behavior of single
molecules and atoms of a gas or gas mixture, to the behavior of a macroscopic
quantity of fluid, it would be necessary to count the number of particles. However,
this is not possible, and the total amount of substance n is used instead of the number
of particles. This amount of substance n is proportional to the number of particles
N , independent of the substance, and it can be measured with methods of continuum
physics. It holds that n
10 23
=
/
N A when N A =
.
·
/
mol is Avogadro's
number. The unit of the amount of substance is 1mol, and it is defined as the amount
of carbon of pure nuclide C 12
6
N
6
02252
of the exact mass 12g, 12 being the molecular weight
of this form of carbon.
Several relations can be introduced here: If the proportion of the amount of sub-
stance n to the unit amount of substance n p of a prototype is known, then the pro-
portion of the number of particles N and N p is known as well with N
/
N p =
n
/
n p .
If m is the mass of an amount of substance n , then M m
=
m
/
n is the molar mass
with the unit g/mol or kg/kmol. If
is the mass of a single particle of an amount
of substance and N is the number of particles, then m
μ
=
N
· μ
is the mass of the
amount of substance and
N A .
The numbers of the molar masses of various substances are the relative masses of
the molecules and atoms of the substances related to that of the fictitious substance
with
μ =
M m /
M m . They are only proportions, and they are identical to those
numbers in the periodic table, which are called weight of the molecules and atoms .
1mol is the amount of substance which has that mass in grams that is shown by the
atomic or molecular weight.
If V is the volume of an amount of substance, then V m
μ/μ
=
M m /
=
V
/
n is the molar
volume with units, e.g., cm 3
mol, and it is dependent on pressure and temperature.
The Loschmidt's number N S =
/
m 3 is the specific number of molecules
of ideal gases at 0 C and 1013.25hPa. At this pressure and temperature, 1mol of a
gas takes a volume of 22414 cm 3 .
10 25
2
.
687
·
/
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