1. WESTERN DISTURBANCES: ROLE OF UPPER TROPOSPHERIC FEATURES IN THEIR DEVELOPMENT
GP CAPT RM SAXENA AND GP CAPT B NANDI
VATAVARAN, VOL 22, NO. 2, DEC 1998, PP
SCIENTIFIC REVIEW BY
FG OFFR SELJIN MATHEW
53 IFC, MET

2. SCOPE Introduction Aim Earlier Studies Discussion of Results
Conclusion
Critical Appreciation

3. AIM
This study is an attempt to dispel some myths about WDs and the role of upper tropospheric features in intensification or weakening of WDs.

4. EARLIER STUDIES
1. Bedi, Billa and Mukherjee (1981) has studied the interaction between northern mid-latitude and summer monsoon circulation and found out that the frequency and track of WDs during monsoon can determine whether it was a good monsoon year or vice versa.
2. Taneja RP (1978) has studied on some aspects of active and inactive western disturbances over nw india during winter season and has given some guidelines for demarcating active and inactive WDs.
3. Bhaskara Rao and Morey (1971) studied on cloud system associated with WDs.

5. MOVEMENT EXTRA TROPICAL DISTURBANCE EXTRA TROPICAL CYCLONES
SECONDARY CYCLONES WD
TERTIARY CYCLONES
INDUCED LOW

6. SOME MYTHS AND FACTS Need not be a surface system
Need not cause precipitation
Does not have fixed upper air extent
No fixed core charecteristics

7. DISCUSSION OF RESULTS WD A
9. THE FOLLOWING FEATURES ARE ASSOCIATED WITH THE APPROACH OF ACTIVE WDS (TANEJA, 1978):
11/20/2018 4:19:06 AM
37 SFC

8. DISCUSSION OF RESULTS WD
11/20/2018 4:19:06 AM
37 SFC

9. DISCUSSION OF RESULTS Points to be Considered.
Position of low level cyclonic circulation (lat/long)
Position of upper level trough (lat/long)
Tilt of the trough (+ve, -ve, or zero)
Slope of the system
Curvature of trough/ridge
Position of wind maxima

10. DISCUSSION OF RESULTS
1. The forward (+ve) or backward (-ve) tilt of upper air systems (trough) will determine whether barotropic instability is present or not.
2. Slope of the trough will decide the nature of the baroclinicity. Eastwards slope of the trough with height is favourable for weather development and vice versa. No slope signifies any further growth of the system.

11. DISCUSSION OF RESULTS Slope of the Trough SLOPE TO EAST SLOPE TO WEST
NO SLOPE

12. DISCUSSION OF RESULTS Role of Trough in Westerlies CONV DIV ZERO TILT
+VE TILT
-VE TILT

13. DISCUSSION OF RESULTS
Trough in Westerlies in Association with Jet/Wind Maxima
CONV
DIV
DIV
CONV

14. DISCUSSION OF RESULTS
JET

15. DISCUSSION OF RESULTS
JET

16. DISCUSSION OF RESULTS
Trough in Westerlies with Embedded Jet Axis and Jet/Wind Maxima
JET

17. DISCUSSION OF RESULTS
JET

18. DISCUSSION OF RESULTS
JET

19. DISCUSSION OF RESULTS
JET

20. DISCUSSION OF RESULTS

21. DISCUSSION OF RESULTS
NEW WIND MAXIMA

22. DISCUSSION OF RESULTS Low Level Systems
Leading Half of the Moving Cyclonic Circulation.
Northwest And Southeast Quadrant Of Elliptically Shaped Major Axis East-west Oriented Slow Moving or Near Stationary Circulation.
In Other Cases when the Major Axis is North-south Oriented then North East & South West Quadrants.

23. DISCUSSION OF RESULTS
LOW LEVEL SYSTEMS

24. CHECK LIST FOR LOCAL FORECASTING
Synoptic Features
Surface Position of WD.
Upper Air Extent of WD.
Position of Jet/Wind Maxima.
Position & Orientation of Trough in Westerlies (300 hPa)
Position of Low Level Anticyclone (850 hPa)

25. CHECK LIST FOR LOCAL FORECASTING
Local Parameters
Pressure tendency Ist & IInd order
Wind tendency at 850 hpa
Local wind veering with height
Rise in minimum temperature
Rise in surface dew point temperature
Dew point depression decreases at 850 hPa
Increase in temperature difference between Delhi & Jodhpur

26. CHECK LIST FOR LOCAL FORECASTING
LOCAL PARAMETERS
Lowering of freezing level
Space & time variation of precipitation to the west of station
Type of cloud mass as observed in satellite imageries associated with WD i.e. Overcast Mass (OM), Vortex (V), Latitudinal Band (LB), Meridional Band (MB) or Broken Amorphous clouded area as classified by Bhaskara Rao & Morey (1971).

27. CONCLUSION Critical analysis of prevailing situation
Use of integrated approach
Use of ojective Metohd

28. CRITICAL APPRECIATION
Importance of careful analysis of upper air features to identify the divergence sectors.
All the positions should have been supported by the actual observed cases.
The checklist adopted by the author in this paper can be extended to other places for local forecasting.
Use of satellite images would have enhanced the justification and acceptance.

29. ?