Many calculations in meteorology and
oceanography use the Kelvin, or Absolute, temperature
scale. A kelvin is exactly equal to a Celsius degree in
scale, but the starting point of measurement on the
Kelvin scale (0 kelvin) is absolute zero, or -273.16°C.
That is the temperature at which, theoretically, all
molecular motion would stop. Water freezes on the
Kelvin scale at 273.16 K and boils at 373.16 K.
Conversions may be easily made between the Kelvin
and the Celsius scales by addition or subtraction using
the following formulas:
C = K 273.16
K = C + 273.16,
where K is kelvin and C is Celsius degrees.
Though the hour, minute, and second convention is
universally used in keeping time, various time zones are
also used. In North America, eastern standard time
(EST), central standard time (CST), mountain standard
time (MST), and Pacific standard time (PST) are used.
Standard time zones generally cover strips of the globe,
extending north and south parallel to the longitude lines.
Each time zone covers about 15° longitude centered on
0° longitude, with all longitudes evenly devisable by 15.
Time zone boundaries that cross land masses have been
adjusted by local agreement, and often zig-zag.
Standard time zones for the world are provided in
Appendix III. Throughout most of the world, standard
time is 1 hour earlier for each time zone to the west and 1
hour later for each time zone to the east. A list of
countries, provinces, and states, with their local
standard time departure from the 0° longitude standard
zone is provided in the Nautical Almanac, published
each year by the U.S. Naval Observatory. When
standard time is used, it is referred to as local standard
time (LST) or by a standard zone designation, such as
Eastern Standard Time (EST) or Ppacific Sstandard
Daylight savings time or summer time is the
convention adopted by most regions in North America.
On the first Sunday in April at 0200, the clocks are set
ahead 1 hour. On the last Sunday in October at 0200,
they are set back 1 hour. During the summer, time in
these regions is called daylight time; for example,
Eastern Daylight Time (EDT) or Pacific Daylight Time
(PDT). Other regions of the world have also adopted
Another measurement of time sometimes used is
local mean time (LMT). Local mean time is time
measured in 24-hour days relative to the movement of
the sun. When the sun is highest in the sky, local mean
time is 1200 noon. Within a time zone, local mean time
may be off standard time by up to several hours. Local
mean time changes by 4 minutes for every degree of
To prevent confusion between the different zones
and types of time, meteorological and oceanographic
records, charts, and reports use Coordinated Universal
Time (UTC). UTC time is kept by using the 24-hour
clock. UTC is the local mean time at the Royal
Greenwich Observatory in East Sussex, England, at 0°
longitude. This time is the same all over the world,
regardless of local time conventions. All times in UTC
are suffixed with a Z for identification. Because of this,
UTC time is sometimes referred to as "Zulu Time." The
term Coordinated Universal Time and the abbreviation
UTC, by international agreement, have replaced the
older term Greenwich mean time and the older
ORDER OF OBSERVATION
Surface weather observations are completed and
transmitted every hour. The various weather elements
are actually observed from 5 to 15 minutes before the
hour, for routine observations. The time to begin
monitoring the elements should be adjusted as the
observer gains speed and experience.
As a general rule, first observe the elements from
outside the weather office, and then from the equipment
inside the office. Pressure elements and those elements
changing quickly should be observed last. Even when
automatic observation equipment is used, these general
rules apply. Most of the necessary observation data will
come from equipment located within the office spaces,
but outside measurements, such as cloud type and
visibility, should be done first.
Although many observation records and reporting
codes are in use, the formats have many elements in
common. For example, all surface weather
observations include data for state-of-the-sky,
visibility, and temperature. Some observation formats
require additional data, such as sea condition, seawater
temperature, and sea ice conditions. The following
sections cover the various data types and the methods
used to obtain the data. These data types are not
arranged in any particular code format, but are generally
arranged in observation order.