1. INTERPRETATION OF LARGE SCALE CIRRUS PATTERNS

2. LARGE SCALE CIRRUS PATTERNS
Large scale Ci cloud formations and dry zone boundaries are useful for locating:-
Axes of jet streams
Thermal and upper ridges
Upper anticyclones
Upper level turbulence

3. SCHEMATIC CLOUD AND MOISTURE PATTERNS OF COMMON UPPER CLOUD AND WV PATTERNS
Indicates Jet
Ci Cloud band & Jet Axis
Vortex Cloud shield
Indicates
Streamline
Deformation Boundary in Ely flow
Associated with Anticyclone
Deformation Boundary in NWly flow
Associated with Turbulence

4. MODEL OF CI PLUME ASSOCIATED WITH SUB TROPICAL JET

5. LOCATING THE SUB-TROPICAL JET STREAM
The sub tropical jet (STJ) lies along the poleward edge of the water vapour and cloud boundary. Usually there is a broad dry area in the water vapour image on the cold side of the jet
The jet is generally not reflected in the hpa thickness field.
The associated cloud boundary has some anti-cyclonic curvature
Moisture and clouds move pole wards in response to the amplification of a low latitude trough in westerlies, or the digging of a mid-latitude trough into the sub-tropics

6. EXAMPLE : IDENTIFICATION OF STJ
Continuous band of upper cloud
Usually 2000Km or more
Similar to the relationship between frontal cloud and polar jet
Originates in the tropics and extend 15 deg polewards
IR images of sub-tropical jet cloud from Meteosat at 1800 UTC on 09 Jan 91, with six-hour forecast of isotachs at 250 hPa in knots

7. JET AXIS DERIVED FROM THE WV IMAGE

8. MODEL SHOWING THE RELATIONSHIP OF TURBULENCE TO TRANSVERSE BANDS AND SCALLOPS IN A JET Ci BAND
Dashed lines enclose regions where moderate turbulence is likely
Transverse bands are wide, thick (bright in Vis), carrot shaped and are oriented across the flow
Scallop pattern appears as a ragged pole ward edge along a straight or anti-cyclonically curved Ci formation

9. LOCATING TURBULENCE ASSOCIATED WITH JET STREAMS
Empirical studies show that certain Ci boundaries and cloud patterns are often associated with moderate or severe upper level turbulence
Turbulence is identified with Jet streams accompanied by strong temperature gradients, shears, deformation in the upper flow, atmospheric waves and instability
Turbulence is usually confined to within 3° latitude of the cloud or moisture edge
Transverse bands, oriented across the direction of the upper wind flow, occur within both straight and anticyclonically curved jet Ci shields.
Transverse Ci bands, Ci scallops and billows are patterns, which may indicate moderate or possibly severe turbulence at the cruising altitude of jet aircraft

10. LOCATING TURBULENCE ASSOCIATED WITH JET STREAMS
Billow cloud patterns occur in strong wind shear and have a wavelength of a few kilometers
They are too small to depict in the model
The patterns are not terrain-related, but translate and are transitory
Large scale billows with a wavelength of 5 km or more nearly always indicates the presence of severe turbulence. Examples of these features are shown in imageries

11. TRANSVERSE BANDS AND SCALLOPS IN STRAIGHT FLOW
GOES VIS IMAGES SHOWING MODERATE OR SEVERE TURBULENCE AT 2030 UTC ON 26 MAR 87

12. BILLOW CLOUDS
2100 UTC ON 24 JAN 90

13. LEE WAVES AND OROGRAPHIC CLOUDS
Fig. 5(a): Vis image of Central
Europe on 07 Mar 83
Fig. 5(b): IR image of Central Europe on 07 Mar 83

14. MODEL SHOWING A BROAD SHIELD OF THICK CLOUD
ASSOCIATED WITH A THERMAL RIDGE AND WA
HPA THICKNESS
(RED DASHED LINES),
SURFACE ISOBARS
( CONTINUOUS LINES)

15. LOCATING THERMAL RIDGES
Solid, bright shields usually reflect a well- defined ridge
Ragged or fragmented shields usually reflect a weak, low amplitude thickness ridge
The model shows a broad cloud shield (over 500 km wide) around a high amplitude thermal ridge
The imagery next shown is an example of a broad shield of cloud B and the associated thickness pattern.

16. LOCATING THERMAL RIDGES
GOES IR image at 1800 UTC on 16 Mar 90, showing a broad of cloud B and : HPA thickness ( DASHED LINES IN M) , surface isobars ( in hPa) and the thermal ridge axis superimposed.

17. LOCATING RIDGES : SOME CHARACTERISTICS OF BROAD CI CLOUD SHIELDS
The Ci shield coincides with a broad thickness ridge of large amplitude, produced by a period of WA
Incase of narrow shield, it is associated with PVA and the WA is weak. in this case the thickness ridge is not discernible
The centre line of the cloud shield coincides with the axis of the thickness ridge
The leading edge of the cloud shield (oriented across the upper flow) is at, or a few degrees downstream of, the upper ridge axis (for example as shown by the 500 hpa wind barbs in fig.

18. WINDS AT 500 HPA THE LEADING EDGE OF THE MAIN CLOUD SHIELD (DASHED LINE) , AND THE 500 HPA RIDGE AXIS SUPERIMPOSED

19. LOCATING THERMAL GRADIENTS
The cloud shields are related to WA. Hence the upper winds are approx.ly parallel to the cloud edge
The thickness isopleths are usually not parallel to cloud edge but angle to it
With very strong jet the thickness isopleths near the rear edge may be nearly parallel
Near the striations the thickness isopleths are nearly parallel to the striations E
992
996
1012 E
GOES Vis image with hPa thickness lines
and surface isobar (hPa) superimposed. EE is the rear edge of frontal cloud

20. LOCATING TURBULENCE IN RIDGE
Near the ridge axis, the transverse bands are often oriented at an angle across the direction of upper flow
It can be either linear or curved
They are located east of the ridge line or axis of –ve vorticity
The orientation depends on tilt of ridge line
In the model the ridge is tilting eastward

21. LOCATING TURBULENCE IN RIDGE
Turbulence occurs close to the transverse bands but more likely with sharp curvature of the flow
However the likelihood and intensity is much lower than the transverse bands associated with jet axis
More the cloud shield angles across the wind less the turbulence threat
This is because the overall wind speeds are weakening in these regions

22. LOCATING UPPER LEVEL ANTICYCLONE

23. SCHEMATIC MODEL OF WV IMAGE PATERN OF WARM UPPER LEVEL CLOUD
WV imagery sometimes show distinctive pattern of curved moist and dry bands
Distinctive WV boundary forms when an upper anticyclone with a closed circulation develops with Ely winds on the equatorward side
The centre of the large scale anticyclone is defined by a band of moist (cloudy) air ‘WW’ rising to the west and north of anticyclone
A dark band denoting dry air spreading southwards from the north and east with a well defined dark edge DD on its forward side
Light shade denotes upper level moisture
Darker shade shows dry zone
Arrows show upper flow

24. UPPER ANTICYCLONE WV Image IR Image Moist and dry zones are clearly
Visible in WV image
In IR ‘WW’ is less homogeneous
than in WV imagery

25. LOCATING TURBULENCE IN DEFORMATION ZONES

26. SCHEMATIC MODEL : RELATIONSHIP OF TURBULENCE TO TRANSVERSE BANDS IN DELTA CLOUD FORMATION
Identification with Ci. Deformation zone can be identified in animated satellite imagery. Turbulence is associated with Transverse bands. The deformation zone in Ci formations and in comma clouds were found to be most reliable indicators of moderate-severe turbulence
Wide and thick bands are associated with stronger turbulence than narrow and long bands
WV Imagery Elongated dark bands, or large oval shaped grey regions in WV Imagery may become further darker. The portion of the image that is darkening most rapidly with time experiences frequent and intense turbulence

27. EXAMPLE : DEFORMATION ZONES