1. Observations of cold air pooling in a narrow mountain valley Allison Charland, Craig Clements, Daisuke Seto Department of Meteorology and Climate Science San José State University San José, CA

2. Overview Introduction Experimental Design Observations Preliminary Results

3. Introduction Experiments were designed as part of an undergraduate meteorological instruments course to provide students with hands-on experience working in the field. Designed and implemented field experiment as part of undergraduate thesis 23 April-6 May 2010

4. Goal To observe wind and temperature structure during the formation and breakup of cold pools in a mountain valley: –Temperature structure across the valley –Wind and turbulence statistics –Surface energy balance on the valley floor

5. Experimental Site San Jose San Francisco Diablo Range Santa Cruz Mountains

6. Instrumentation –3 Remote Automated Weather Stations (RAWS) –10-m Micromet Tower (floor) 2 Sonic Anemometers (10 Hz) Temperature & RH 10 Type-E Thermocouples (5 Hz) 4-component net radiometer –3-m Micromet Tower (gully) 3 Cup Anemometers Sonic Anemometer (10 Hz) 4 Type E Thermocouples (5 Hz)

7. Instrumentation –Atmospheric Systems Corporation (ASC) miniSoDAR 10 min, 20-200 m AGL –10 HOBO ProSeries Temperature Dataloggers –Tethersonde System GRAW GS-E Vertical profiles of temperature & humidity to heights of 120-200 m –Smoke tracers and time- lapse photography

8. Hall’s Valley Santa Clara County, CA Instrument Platforms: 3 RAWS 2 Micrometeorological Towers Tethersonde SODAR 10 HOBO temp sensors Constriction Zone Joseph D. Grant County Park Hall’s Valley Upper Valley Lower Valley Experimental Design

9. Synoptic Conditions 300mb Heights and Isotachs

10. CloudyClear Timeseries of Temperature (HOBO cross-section, 2 min) Time (PST) Temperature ( o C)

11. Time (PST) Temperature ( o C) Timeseries of Temperature (HOBO cross-section, 2 min) ~0.1 K m -1

12. Tethersonde Soundings Potential Temperature Mixing Ratio

13. SODAR Wind Profiles Wind Speed Wind Direction

14. Winds from 10-m Tower Time (PST)

15. Winds from 3-m Tower

16. Night 1Night 2 Wind rose

17. Surface Energy Balance QHQH QEQE

18. Cold Pool Turbulence Structure u * (m s -1 ) Time (PST) TKE (m 2 s -2 )

19. Summary A cold pool developed in the valley during clear nights with an observed temperature gradient of 0.1 K m -1 compared to 0.2 K m -1 from the cold pool study in Peter Sinks, UT (Clements et al. 2003). Winds of 1.0-3.5 ms -1 and TKE values of 0.2-0.4 m 2 s -2 were observed during the first night and weak drainage flow(0-1.0 ms -1 ) and lower TKE values between 0.1-0.2 m 2 s -2 during the second night. Slight increase of negative sensible heat flux during the first night was due to higher wind speeds and increased turbulent mixing. Cooling during the first night was reduced due to increased winds

20. Future Work Investigate moisture transport between the upper and lower valley Conduct spectral analysis of the turbulence data Planning to operate the CSU-MAPS during the PCAPS campaign Doppler lidar measurements of inter-basin moisture transport in cold pools

21. Acknowledgements METR 163 class of 2009 and 2010 Q

22. Questions?