Weather Observation and Analysis
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Chapter 3. SPACE, TIME, AND MOTION
3.1 Wind Observations
We can divide weather elements into scalars and vectors.
Anything that can be represented as a single value is a scalar.
observed atmospheric quantities are scalars.
pressure, rainfall, infrared radiation, concentration .
.. all of these are things
whose value is specified by a single number.
The one important exception
to the ubiquity of scalars is wind.
Wind, like all vectors, has a magnitude and a direction.
is defined as the motion of the air at a particular location, averaged over
some period such as two or ten minutes.
According to normal convention,
the wind is a two-dimensional vector.
Strictly speaking, air moves in three
dimensions (east-west, north-south, and up-down), and sometimes the
velocity vector is taken to be the full three-dimensional wind, but it is
more common in normal use to work with the vector horizontal wind and
treat the vertical component of air motion as a separate scalar.
air parcel might be said to have a wind vector of 16 m/s from 130 degrees
and also be ascending at 2.4 cm/s.
Remember that wind directions are
expressed as the direction the wind is coming from, not the direction it is
As with all vectors, the wind can be described in terms of its
components as well as a speed and direction.
There’s no law that requires
it, but you are probably accustomed to the three cartesian coordinates
being designated as
By similar inviolate convention, the three
components of air motion (toward the
are represented as
When the air motion was described as 16
m/s from 130 degrees and ascending at 2.4 cm/s, that 2.4 cm/s was the
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