initiating rotor chop. Rotor chop is a difficult to control,
sometimes hazardous, up and down oscillation of the
rotor blades. The peak wind speed or peak gust is the
highest instantaneous wind speed or gust speed greater
than 25 knots observed since the last METAR
Variable winds occur when the wind direction
fluctuates by 60° or more. While this condition occurs
most frequently when the winds are very light, wind
direction fluctuations are most significant when the
wind speeds are higher (greater than 6 knots). For
observation purposes, the wind direction may be
considered variable anytime the observed 2-minute
mean wind speed is 6 knots or less.
Certain wind phenomena are included in an
observation even though the events did not occur during
the 2- or 10-minute period during which the winds were
being observed. These phenomena or events may be
included in the observation if they occurred within the
past hour and were not reported in a previous
observation. The events include squalls and wind shifts.
A squall is a sudden large increase in wind speed
(usually accompanied by a change in wind direction)
that lasts several minutes and then suddenly dies. For
observation purposes, the wind speed must increase by
16 knots or more and the sustained wind speed after the
increase must be 22 knots or more for at least 1 minute.
Squalls are usually caused by large convective cells,
like those that produce strong rain showers and
thunderstorms. Squalls may also be produced by dry
frontal passages; the presence of precipitation is not a
requirement. At sea, strong rain showers at a distance
away from the ship are called "squalls" because squall
winds are usually present. When lines of thunderstorms
form on or move out ahead of a cold front, the line may
be called a "squall line" because of the squall winds
associated with the thunderstorms.
A wind shift is any change in wind direction by 45°
or more during a 15-minute time period. The change in
direction may or may not be accompanied by a change
in wind speed. However, wind shifts are only recorded
when the mean wind speed is 10 knots or greater during
the shift. A wind shift may be very sudden, occurring
within a minute or so, or it may occur gradually over the
15-minute period. The most common cause of wind
shifts is frontal passage, especially a cold-frontal
passage. The onset of a sea breeze may cause a wind
shift, as may other locally produced wind conditions.
Foxtrot Corpin is the term used to identify the best
course and speed a ship should come to to bring the
relative wind into the proper window for the launch and
recovery of aircraft.
For departures and recoveries
aboard different classes of ships, the most desirable
relative wind speed, acceptable minimum and
maximum wind speeds, the most desirable relative
wind direction, and the acceptable wind direction
variations are specified in the NATOPS Flight Manuals
for each type of aircraft.
Foxtrot Corpin is routinely provided by
Aerographers Mates aboard aircraft carriers and
amphibious assault ships and is computed by using the
CP-264/U true wind computer. Detailed instructions
for the procedure are printed on the reverse side of the
CP-264/U. The procedure uses the true wind and the
desired wind to find required ships course and speed.
Explain the difference between True North and
Winds blowing directly off the starboard beam
are coming from what relative direction?
How can relative winds be manually converted
to true winds?
How is the mean wind speed determined?
How would the observed wind speed on a ship be
affected by winds blowing from dead astern?
Define the term "gust."
Define the term "squall."
SEA AND SWELL WAVES
LEARNING OBJECTIVES: Explain the
importance of sea conditions to naval
operations. Define duration limited seas and
fetch limited seas. Define wave height, wave
length, and wave period, and wave direction.
Define and distinguish the difference between
sea waves and swell waves. Define Romeo