ppl_04_e2
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C H A P T ER 2 0 : W O R L D A R EA F O R EC A S T S IG
Figure 20.12 Tropopause heights are reported as flight levels inside small rectangular boxes,
(a). The highest Tropopause levels are reported as ‘H’, (c). The lowest Tropopause levels are reported as ‘L’, (b).
TROPOPAUSE LEVELS
Tropopause levels are included on the high level significant weather charts. The levels shown indicate the start of the Tropopause, and are calculated by finding the coldest temperature in the Troposphere. The height of the Tropopause, therefore, is defined by the height in the atmosphere at which the temperature becomes constant, rather than declining with altitude. These Tropopause levels are indicated at a number of spot locations across the high level charts. Tropopause levels are presented as flight levels in a rectangular box. (See Figure 20.12, ( a.) )
When more than one Tropopause level is present in the atmosphere, either an “H” or an “L” is added to the Tropopause box, to indicate whether the uppermost or lowest Tropopause height is displayed. In these cases, the rectangular box is expanded to include the additional symbol, and the box looks more like an arrow head pointing up or down. In Figure 20.12, above, the lowest Tropopause level is marked (b), and the highest Tropopause level is marked (c).
The flight level
given for a jet stream on the
WAFS High
Level SIGWX chart is the level for the maximum wind in that jet stream.
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C H A P T ER 2 0 : W O R L D A R EA F O R EC A S T S IG NIF IC A NT
JET STREAMS.
Jet streams are identifiable on the charts by black solid lines, which have wind “barbs”, indicating jet stream speeds at various spot points, with the flight level at which the maximum speed occurs written underneath. (See Figure 20.13.) The arrow head on the end of each jet stream line indicates the direction of movement of the flow. Any changes in speed along the length of the jet stream of 20 knots or more are indicated by either an additional set of wind “barbs”, or, if there is little space on the chart, two parallel lines perpendicular to the direction of flow of the Jet Stream.
(See Figure 20.13.)
Figure 20.13 Jet Streams are indicated by solid black lines accompanied by a flight level and speed. Usually, the Jet Stream has an associated Clear Air Turbulence region indicated by a dashed line with an identifying number in it.
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Customer: Oleg Ostapenko E-mail: ostapenko2002@yahoo.com
C H A P T ER 2 0 : W A F S S IG
R e p r e W A F S
s e n t a t i v e q u e s t i o n s t o t e s t y o u r t h S IG W X.
1.On WAF significant weather charts, jet streams are given flight levels. To what does this flight level refer?
a.The flight level of the mean wind in the jet stream
b.The flight level of the maximum wind in the jet stream
c.The highest flight level where the winds are more than 60 knots
d.The average height of the jet stream
2.At what times are WAF significant weather charts produced?
a.At 0000, 0600, 1200, 1800 UTC
b.At 0000, 0600, 1200, 1800 LMT
c.At 0000 and 1200Z
d.At midnight and midday only
3.What is the validity time for a WAF significant weather chart?
a.6 hours
b.3 hours
c.30 minutes
d.For a fixed single time only
4.When are WAF significant weather charts produced?
a.Every 3 hours
b.Every 6 hours
c.Every 12 hours
d.At midnight and midday only
5.On WAF significant weather charts what do the letters CB imply?
a.Moderate icing and turbulence
b.Moderate to severe icing and turbulence
c.Moderate to severe icing and turbulence and hail
d.Severe icing and turbulence and hail
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Customer: Oleg Ostapenko E-mail: ostapenko2002@yahoo.com
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CHAPTER 21
THE SIGMET
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C H A P T ER 2 1 : T H E S IG M ET
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C H A P T ER 2 1 : T H
INTRODUCTION.
The code SIGMET stands for Significant Meteorological Information. A SIGMET is an abbreviated, plain language message, which concerns the occurrence, and/or expected occurrence, of significant weather which may affect the operational safety of aircraft.
There are two classifications of basic SIGMETS: convective and non-convective.
Convective SIGMETS concern the occurrence of thunderstorms, and non-convective SIGMETS warn of severe turbulence and/or icing. A SIGMET is valid for 4 hours.
SIGMETs are issued from designated meteorological watch offices each of which has a responsibility to the many Flight Information Regions around the world.
You will already have met many of the abbreviations used in the SIGMET, in Chapter 19 on Low Level Forecast Charts, but a full list of abbreviations is given in Figure 21.1, for your reference.
SIGMET stands for Significant Meteorological Information.
A SIGMET informs pilots
of actual or forecast
significant weather phenomena concerning the safety of flying operations. In general, SIGMETs refer to thunderstorms, severe turbulence and icing.
Figure 21.1 Abbreviations used in SIGMET messages.
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C H A P T ER 2 1 : T H E S IG M ET
DECODING THE SIGMET.
Figure 21.2 shows an example of a SIGMET message. The first item is the location indicator of the Air Traffic Services Unit (ATSU) serving the Flight Information Region
(FIR) or Control Area to which the SIGMET message refers. The ATSU which issued our example SIGMET is EGTT, (a), which is the London FIR. EGTT is followed by the code SIGMET, (b), which is the message identifier.
Figure 21.2 An example of a SIGMET.
After the identifier, the sequence number is given next, (c). In this example, the sequence number is 02, which corresponds to the number of SIGMET messages issued for the London FIR since 0001 UTC on the day of issue.
The next item is the date and time groups, (d), indicating the period of validity of the SIGMET message in UTC. In this example, the SIGMET is valid on the 28th of the month from 1400 UTC to 1900 UTC.
The first line of the SIGMET ends with the location indicator of the meteorological watch office which issued the SIGMET. Here, it is EGRR, (e), which is the UK Met Office. EGRR is followed by a hyphen which separates the SIGMET preamble from the next line of text.
At the beginning of the second line, is the name of the FIR or control area for which the SIGMET is issued; so the code EGTT is repeated, (f), but now is also decoded as the London FIR.
Next comes the name and description of the weather phenomenon which is the reason for the issuing of the SIGMET. The weather phenomenon is given in abbreviated plain language, using the abbreviations given on the previous page. In our example, the warning is of severe mountain waves, (g), with a vertical speed of 600 feet per minute.
Following the weather phenomenon, there is an indication of whether the information is observed or forecast, using the abbreviation “OBS”, or “FCST”, (h). If relevant, the time of observation in UTC will also be given.
The next group of information relates to the location and altitude of the observed or forecast phenomenon, in this instance between Flight Levels 60 and 120, (i).
Where possible, reference is made to latitude and longitude, locations or well-known geographical features. In our example SIGMET, the location of the mountain waves is given as: South of a line from a position at 52º 20’ N, 5º 30’ W to a position at 53º N, 3º E, (i). This is a line from a point on the FIR boundary in Cardigan Bay to a point in the North Sea, some miles North East of Yarmouth.
Movement or the forecast movement of the weather phenomenon is normally indicated
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C H A P T ER 2 1 : T H
by reference to one of the eight points of the compass; however, this SIGMET does not contain such a reference.
The speed of displacement of the weather phenomenon is given in kilometres per hour or knots. But if the weather phenomenon is stationary, as in this example, the code STNR, (k), is used. Finally, an indication is made of any change in intensity of the weather phenomenon, using the abbreviation INTSF for intensifying, WKN for weakening or NC for no change, as in this example, (l).
The SIGMET is ended, as with the METAR, with an equals sign (m).
COMPLETE SIGMET MESSAGE.
The complete SIGMET message in Figure 21.2 decodes as follows:
The message is for the London FIR, EGTT; the message is a SIGMET, the second to be issued for the FIR since 0001 UTC. It is valid for the 28th of the month from
1400 UTC until 1900 UTC and was issued by the UK Met Office, EGRR. In the
London FIR, severe mountain waves, whose vertical speed is 600 feet per minute, are forecast from FL60 to FL120, South of a line from 52º 20’ N 5º 30’ W to 53º N 3º E; the phenomenon is stationary and no change is expected.
Figure 21.3 Sample SIGMET.
A further SIGMET is shown in Figure 21.3, below. This SIGMET decodes as follows:
The message is for the Scottish FIR, EGPX; it is the first SIGMET issued since
0001 UTC, and is valid for the 28th of the month from 0900 UTC to 1300 UTC, being issued by the UK Met Office, EGRR. In the Scottish FIR, severe turbulence is forecast below FL70, South of a line from 58º N, 10º W to 57º N, 5º W to 55º N, 0º E/W; it is moving North North East at 35 knots, and no change is expected.
The position line given in the SIGMET in Figure 21.3 translates roughly as extending from a point on the Western boundary of the FIR, 90 miles West of Benbecula to a point at the South end of Loch Ness and, thence, to a point in the North Sea, 60 miles East of Newcastle.
SPECIAL SIGMETS.
There are two other specialised types of SIGMET valid for up to 6 hours. These are the VOLCANIC SIGMET, issued to notify pilots of volcanic ash, due to volcanic eruptions, and the TROPICAL CYCLONE SIGMET, used to notify pilots of hurricane or cyclone activity.
SIGMETs for volcanic ash clouds or tropical cyclones include an additional line of text. This line contains a brief outlook forecast beyond the period of validity specified earlier in the message. In a Volcanic SIGMET, the outlook will include a direction of travel for the ash cloud. For a Tropical Cyclone SIGMET, the position of the tropical cyclone centre is included.
SIGMETs are
valid for 4 hours, except
for special
SIGMETs concerning volcanic or cyclonic activity which are valid for 6 hours.
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C H A P T ER 2 1 : T H E S IG M ET Q U ES T IO NS
R e p r e s e n t a t i v e P P L - t y p e q u e s t i o n k n o w l e d g e o f T h e S IG M ET .
1.What do the first four letters of the SIGMET message identify?
a.The issue number
b.The ICAO identifier for the relevant airport
c.The name of the Air Traffic Services Unit
d.The validity time
2.EGTT SIGMET 1 VALID 310730/311130 EGRR LONDON FIR ISOL CBFCST TOPS FL370 ROUTES W OF W00400 NC=
In the above SIGMET, what is the nature of the forecast significant weather?
a.Hail
b.Cumulonimbus with tops approximately at the Tropopause
c.Trans-Atlantic routes at Flight Level 370 closed
d.No change
3.EGTT SIGMET 1 VALID 310730/311130 EGRR LONDON FIR ISOL CB FCST TOPS FL370 ROUTES W OF W00400 NC=
What is the expected change in the weather intensity indicated by this SIGMET?
a.Weakening
b.Strengthening
c.Dissipating
d.No change
4.How would a severe mountain wave be coded in a SIGMET message?
a.+ MTW
b.SEV MTW
c.SEV MNTW
d.SEVERE MNTW
5.LFFF SIGMET 1 VALID 310600/311100 LFPWUIR FRANCE MOD TURB FCST BLW FL420 W of 04W MOVE E 30KT NC=
In the SIGMET message shown above, what is the hazard forecast?
a.Moderate turbulence at 42 000 ft West of 4 degrees West and moving Eastwards
b.Moderate turbulence below 42 000 ft West of 4 degrees West and moving from the East
c.Turbulence at 42 000 ft West of 4 degrees West and moving at 30 kts
d.Moderate turbulence below 42 000 ft West of 4 degrees West and moving Eastwards
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