1. Central California Circulation Study

2. Purpose Use Models, Surface Obs. and Pt Sur Data to:
Analyze low-level cyclonic feature on 28 January.
Study diurnal variations and their extent
Model performance evaluation

3. Cruise Weather Event 4 km IR from 03Z to 21Z 28 Jan

4. Synoptic Forcing 06Z Mountains obstruct flow of main low
Lower Pressure to the North
Mass Accumulation
Fr = U/hmN Ratio of KE to APE
U - 5 to 10 knots hm m N - high stability
- Therefore Ratio less than one, flow blocking

5. Low-Level Vorticity MM5 06Z 28 Jan. MM5 12Z 28 Jan MM5 15Z 28 Jan

6. Vertical Temperature (C)
MM5 09Z 28 Jan
MM5 12Z 28 Jan
- Cold low-level trough along coast
- Air-Sea temperature difference increased

7. Monterey Bay Circulation (18Z)
- Observations support model circulation
- Extremely Low-Level

8. Diurnal Circulation - Nocturnal Phase
Unusually Strong Land Breeze for this area
Land must be colder than water
Typically stable conditions
Nightime/early morning phenomena
Need light winds, clear skies and low moisture.

9. Synoptic Picture for 00Z 02 Feb.

10. MM5 Surface Temperature and Local Surface Observations 00Z 02 Feb (1600 LT 01 Feb)

11. MM5 Surface Temperature and Local Surface Observations 06Z 02 Feb (2200 LT 01 Feb)

12. MM5 Surface Temperature and Local Surface Observations 12Z 02 Feb (0400 LT)

13. MM5 Surface Temperature and Local Surface Observations 15Z 02 Feb (0700 LT)

14. MM5 Surface Temperature and Local Surface Observations 18Z 02 Feb (1000 LT)

15. MM5 Surface Temperature and Local Surface Observations 21Z 02 Feb (1300 LT)

16. Pt. Sur Surface Observations 02 Feb
Did this pressure drop occur everynight on Pt. Sur? No H L
Ocean
Land
- Average pressure drops per night at NOAA buoy (42) 1.1 mb
- Average pressure rise per night at Salinas 1.8 mb

17. Pt. Sur Vertical Sounding Observations 04Z 02 Feb (2000 LT 01 Feb)
NW wind above inversion offshore below
100m inversion
Cold Air advection over water

18. Pt. Sur Vertical Sounding Observations 1530Z 02 Feb (0730 LT)
Weak and variable winds above inversion strong offshore below
220m inversion

19. Pt. Sur Vertical Sounding Observations 1825Z 02 Feb (1025 LT)
Strong Subsidence Inversion
Lower Levels Well Mixed

20. Pt. Sur Observations No diurnal signature Offshore Diurnal Variation
In Bay

21. Pt Sur Observations 01 and 02 Feb
- Wind Shift
- Temperature Drop
- Wind speed change

22. Pt Sur Observations 03 and 04 Feb
- Weaker wind shift
- Lower temp. drop
- Favorable synoptic conditions weakening

23. MM5 Surface Temperature and Local Surface Observations 15Z 02 Feb.

24. Cold Air Drainage

25. Why are Diurnal Variations Capture so poorly by Models?
Good Thermodynamics
Coarse topography information
More uniform weak flow instead of localized intense valley flow

26. MM5 Surface Temperature Model Winds and Local Surface Observations 00Z 02 Feb.
Cold air not concentrated to valleys
- Umax = k g max ZI (Perturbation land breeze wind speed)
o (k2 + 2)
- Valley of cold air in wrong location

27. Questions?