Geography Reference
In-Depth Information
Table 1.2
SI Derived Units with Special Names
Property
Name
Symbol
Hz (s
−
1
)
Frequency
Hertz
N (kg m s
−
2
)
Force
Newton
Pa (N m
−
2
)
Pressure
Pascal
Energy
Joule
J (N m)
W (J s
−
1
)
Power
Watt
kilogram already is a prefixed unit, decimal multiples and submultiples of mass
are formed by prefixing the gram (g), not the kilogram (kg).
Although the use of non-SI units will generally be avoided in this text, there are
a few exceptions worth mentioning:
1. In some contexts, the time units minute (min), hour (h), and day (d) may be
used in preference to the second in order to express quantities in convenient
numerical values.
2. The hectopascal (hPa) is the preferred SI unit for pressure. Many meteo-
rologists, however, are still accustomed to using the millibar (mb), which
is numerically equivalent to 1 hPa. For conformity with current best prac-
tice, pressures in this text will generally be expressed in hectopascals (e.g.,
standard surface pressure is 1013.25 hPa).
3. Observed temperatures will generally be expressed using the Celsius tem-
perature scale, which is related to the thermodynamic temperature scale as
follows:
T
C
=
T
−
T
0
where T
C
is expressed in degrees Celsius (
◦
C),
T
is the thermodynamic temperature
in Kelvins (K), and T
0
=
273.15 K is the freezing point of water on the Kelvin scale.
From this relationship it is clear that one Kelvin unit equals one degree Celsius.
Table 1.3
Prefixes for Decimal Multiples and Submulti-
ples of SI Units
Multiple
Prefix
Symbol
10
6
Mega
M
10
3
Kilo
k
10
2
Hecto
h
10
1
Deka
da
10
−
1
Deci
d
10
−
2
Centi
c
10
−
3
Milli
m
10
−
6
Micro
µ
