W06 - Wind Flashcards
Define Wind
Wind is air in motion. It represents the horizontal flow of air at a height of 10m.
Wind information is recorded in all surface weather reports and SHALL contain…
Both velocity (including direction) and character (variations in wind speed).
How is wind direction recorded?
Recorded as the direction the wind is coming from, in respect to True North. The direction recorded is the average direction during the TWO minute period ending at the time of observation
Define Wind Speed
The wind speed is rate of airflow past a fixed point. It represents average speed during the two-minute period ending at the time of observation. The term “calm” is used to describe winds less than 2 knots.
Define Wind Velocity
Wind Velocity is the combination of both Wind Speed and Wind Direction.
Define Gust
Gusts are sudden, rapid, and brief changes in wind speed. They are characterized by more or less continual fluctuations between the high (peak) and low (lull) speed.
Define Squall
Squalls are essentially gusts with longer duration and higher speeds.
Define Wind Shift
Wind Shift is a definite change in general direction from which the wind is blowing.
What are the criteria for reporting Gusts?
Gusts SHALL be recorded when:
1) The highest peak speed is atleast 5 kts higher than current two-minute average
2) The highest peak is atleast 15 kts
What are the criteria for reporting Squalls?
Squall speeds are recorded only by stations with a recording wind instrument and only by the following criteria:
1) The wind speed increases by 15 kts or more over the two-minute average speed that preceded the increase.
2) The duration of the peak speed period is atleast 2 min.
3) The wind speed attains a one-minute mean of atleast 20 kts
4) The wind speed diminishes by atleast 5 kts
The speed to be reported is the highest one-minute mean speed.
What are the criteria for reporting Wind Shift?
A Wind Shift SHALL be recorded when all of the following occur:
1) The direction changes by 45 degrees or more
2) The change of direction takes less the 15 minutes
3) The average wind speed at the completion of the shift is 10 kts or more.
The time of the Wind Shift SHALL be the time at which the wind begins to shift.
When is Wind Direction considered variable?
Wind Direction is defined as variable when the wind direction varies by 60 degrees or more and less then 180 degrees in the 10 minute period preceding the observation, and the mean wind speed is 3 kts or more.
When reporting variable wind, the two extremes SHALL be reported in a clockwise fashion.
How tall is the 78D Wind System tower?
30 feet (10m)
Is the 78D connected to a recorder?
No
What does the 78D record?
Wind Speed and Direction
Displayed as 2 and 10 minute means. Toggle switch to switch between 2 and 10 min means.
Gust information displayed when criteria met.
What is the minimum wind speed for a 78D to read other than calm?
Minimum of 2 kts
When recording wind direction in box 36 of the 2322, how would you record a direction of 132 degrees?
recorded as “13”.
The wind direction is rounded to the nearest 10 degrees, then only the first 2 digits are recorded.
eg. 132 becomes 130, then recorded as 13.
What would you record in box 36 of the 2322 if the wind was calm?
00
How is Wind Speed recorded in box 37 of the 2322?
If less then 2kts, enter “00” (calm), otherwise, enter speed in kts in 2 digits unless 100 kts or more, then record as 3 digits. eg. wind speed of 7 kts would be entered as 07, wind speed of 105 kts would be entered as 105.
If either the wind speed or direction was estimated and wind speed 2 kts or greater, then the entry in box 37 SHALL be followed by the letter “E”
When wind gusts observed, what is recorded in column 38?
The symbol “G” followed by the numerical value of the highest peak speed of the gust in the 10 minute period ending in the time of the observation.
How do you record gusts in column 38 when wind speeds are estimated?
Record the symbol “G” in column 38 if observer is confident criteria is met for gusts. Do NOT enter the speed. Never estimate the peak speed of a gust.
When squalls observed, what is recorded in column 38?
The symbol “Q” followed by the numerical value of the highest 1-minute speed observed or recorded during the squall period. Squall speeds SHALL be obtained from wind recording devices.
How do you record squalls in column 38 when wind recording devices unavailable?
Record the symbol “Q” in column 38 if observer is confident criteria is met for gusts. Do NOT enter the squall speed. Never estimate the speed of a Squall.
How is Wind direction recorded in box 36?
Enter the 2 minute mean direction from which the surface wind is blowing to the nearest 10 degrees.
Recorded as 2 digits (00-36)
Direction recorded as 00 if wind calm, 36 if from the North
