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Averaging Wind Speed and Direction
Name: John
Status: other
Grade: N/A
Location: WY
Country: N/A
Date: 11/29/2005
Question:
Given :
Wind speed and wind direction for different heights like 3000m ,
4000m , 5000m etc ...for a definite time and definite date for the past
ten years (The data are accurate and taken from a radiosonde reports ) .
example :
Date Height wind/Dir Wind/Speed
2/11/2005 5000m 240deg 23.4 m/sec
2/11/2005 5000m 286deg 9.2 m/sec
2/11/2005 5000m 291deg 23.7 m/sec
2/11/2005 5000m 277deg 11.11m/sec
Question :
1.Can we make an average for the direction of the wind for this height
in this date and time ?
2.Can we make an average for the speed of the wind for this height in
this date and time ?
In another way :
Is there any meteorological formula for calculating wind direction and
speed in upper air?
Replies:
You are on some rather thin statistical ice. The data provide an
instantaneous (altitude,direction,speed). However, one has to be careful
about "averages" because these three variables are not independent of one
another. While "altitude" I'd assume you mean the distance from the
earth's surface perpendicular to the surface. But that is going to change
from place to place. Also, because of turbulence, either from temperature
differences or terrain, "direction" and "speed" may each be vector
quantities. So it is difficult to know just what one is averaging. Also
the data do not include a time variable. That is, the wind may blow in one
direction/speed for a certain time period and another direction/speed for
a certain different time period even at the same place. So somehow a time
weighting factor would have to be folded into the averaging.
It is a real tough problem.
Vince Calder
John,
Climatologically speaking, one could determine such an
average for both wind direction and speed for a single
date, time, and height for a ten year period, but
it may not mean as much as, say, average surface temperature
or precipitation.
Upper level winds are constantly changing and have a
periodicity that can vary tremendously from one
latitude and longitude to another, as well as seasonally.
Determining wind speed and direction is operationally
done using radiosondes, as you know, as well as
radar, sodar, or lidar profilers that make remote measurements
from the ground. Furthermore, the complicated upper atmospheric
computer models used by the National Weather Service and other
country's weather services have become quite good at
predicting the upper level wind speeds and directions.
There is no simple formula or easy way to make these
calculations/predictions; measurements and/or computer
models are required.
David R. Cook
Climate Research Section
Environmental Science Division
Argonne National Laboratory
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