Central California Circulation Study
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
Cruise Weather Event 4 km IR from 03Z to 21Z 28 Jan
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 - 3000m N - high stability - Therefore Ratio less than one, flow blocking
Low-Level Vorticity MM5 06Z 28 Jan. MM5 12Z 28 Jan MM5 15Z 28 Jan
Vertical Temperature (C) MM5 09Z 28 Jan MM5 12Z 28 Jan - Cold low-level trough along coast - Air-Sea temperature difference increased
Monterey Bay Circulation (18Z) - Observations support model circulation - Extremely Low-Level
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.
Synoptic Picture for 00Z 02 Feb.
MM5 Surface Temperature and Local Surface Observations 00Z 02 Feb (1600 LT 01 Feb)
MM5 Surface Temperature and Local Surface Observations 06Z 02 Feb (2200 LT 01 Feb)
MM5 Surface Temperature and Local Surface Observations 12Z 02 Feb (0400 LT)
MM5 Surface Temperature and Local Surface Observations 15Z 02 Feb (0700 LT)
MM5 Surface Temperature and Local Surface Observations 18Z 02 Feb (1000 LT)
MM5 Surface Temperature and Local Surface Observations 21Z 02 Feb (1300 LT)
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
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
Pt. Sur Vertical Sounding Observations 1530Z 02 Feb (0730 LT) Weak and variable winds above inversion strong offshore below 220m inversion
Pt. Sur Vertical Sounding Observations 1825Z 02 Feb (1025 LT) Strong Subsidence Inversion Lower Levels Well Mixed
Pt. Sur Observations No diurnal signature Offshore Diurnal Variation In Bay
Pt Sur Observations 01 and 02 Feb - Wind Shift - Temperature Drop - Wind speed change
Pt Sur Observations 03 and 04 Feb - Weaker wind shift - Lower temp. drop - Favorable synoptic conditions weakening
MM5 Surface Temperature and Local Surface Observations 15Z 02 Feb.
Cold Air Drainage
Why are Diurnal Variations Capture so poorly by Models? Good Thermodynamics Coarse topography information More uniform weak flow instead of localized intense valley flow
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
Questions?