1. Analysis of SODAR Data during Wi-BLEx – Winter Boundary Layer Experiment Javier FOCHESATTO & John MAYFIELD Department of Atmospheric Sciences Geophysical Institute University of Alaska Fairbanks Air Quality Sulfur Workshop, FNSB-Fairbanks, May 26-28, 2010

2. Outline Wi-BLEx Objectives Observations sites, Instruments & Data Base Inversion Heights SODAR-RAOBS Drainage Flows-Micrometeorological influences on the SBL Elevated Inversion layers-hypothesis of recirculation in the Tanana Valley Synoptic Forcing & BL-States Summary

3. Wi-BLEx Objectives Wi-BLEx Phase I (08-09): Characterization of the structure and dynamics of the Winter BL SODAR + Sonics-UAF campus Wi-BLEx Phase II (09-10): Micrometeorological influences of small scale flows in the SBL: surface flux, momentum, energy exchange and stratification NWS & UAF campus Wi-BLEx Phase III (10-11). Formation of multiple inversion layers, stratification, breakup of inversions and intermittence. Synoptic forcing and BL structure. Micrometeorological effects of small scale flows in the SBL.

4. Observation Sites, Instruments & Data base UAF-Campus FARMNWS-NOAA Jan 27, 2009 10:03 Dynamic of the inversion over aprox. flat areas To determine the dynamic of the inversion layer under topography dominating flows

5. Wi-BLEx Data Base Dec. 08Jan. 09Feb. 09Mar. 09Apr. 09 UAF Oct. 09Nov. 09Dec. 09Jan. 10Feb. 10Mar. 10 NWS 02/ 12, UAF Nov. 10Dec. 10Jan. 11Feb. 11Mar. 11Apr. 11 UAF Phase I Phase II Phase III SODAR SONIC Tower FNSB-Unit Scintillometer Met. Stations LIDAR

6. Measured and Derivable Variables Acoustic Phased Array Doppler SODAR BL-Structure (CT2) m-2/3. K Inversion height Wind Speed (20-400 m) (m/s) Wind Direction (20-400m) (deg) Vertical velocity(cm/s) σw σθ Lapse Rate Inversion Height (By Remtech) Sonic Anemometers Tower Turbulent Temperature Turbulent U,V,W Kinematic heat, momentum and turbulent fluxes Turbulent surface variables Large Aperture Scintillometer Cn2 CT2, HS, Attenuation (980nm)

7. Inversion Heights SODAR-RAOBS

8. Wi-BLEx Phase I: Structure and Dynamics 08/09 Phase II: Surface and stratification Effects 09/10 Objectives: Determine the structure of the SBL and study the micrometeorological influences of small scale drainage flows on the surface exchanges Drainage Flows-Micrometeorological influences on the SBL

9. Experimental site for drainage flows Doppler SODAR LIDAR Sonics 300 m distance FNSB- Sampling unit Meteo tower 3 & 10 m LAS ~ 520 m Tx Rx

10. Dynamics of the Drainage Flow Small scale penetrative flows from NW - N No acceleration of the flow is verified away from the source of drainage

11. Effect on the SBL Although not conclusive the vertical velocity is positive at the onset of the flow penetration and returns to negative when intermittency reduces Formation of stratified layers, increase of surface inversion - detrainment

12. Intermittent drainage Drainage flow penetrates in a shallow layer < 100 m depth and over shorter periods of occurrence (intermittent)

13. Influences on the surface stratification Temperature Ranges: Feb 12/13/14 Max (-10 C) Min (-20 C) Mar. 01/02/03 Max (-15 C) Min (-27 C) SFC - Stratification: Mar 01 to 03: ~ 3 C; Feb 12 to 13 ~ 4 C

14. Drainage Flow Summary Drainage flow increases stratification in the SBL/or initiate the formation of the inversion Middle winter drainage is shallow < 100 m depth and intermittent while in the second part of the winter the drainage is deeper and persistent Penetrative conditions are regulated by stratification in the basin and temperature in the source During Wi-BLEx II we have verified the modifications of HS across the valley when the drainage occurs This mechanism although increases stratification, reduces the PM concentration by mixing “cold clean air” with “stagnant polluted air mass” from the floor of the valley. Occurrence of drainage modifies the radiation balance in the BL by increasing stratification, which in turns increases IR flux divergence. Occurrence of drainage flows clears ice-fog from the valley.

15. Elevated Inversion Layers Hypothesis of Low Level Recirculation / re-mixing in the Tanana Valley Elevated inversions occurs in the BL under moderated synoptic forcing when a colder and stagnant BL valley flow is present. In mid-latitudes under non-advective conditions over continental places the Nocturnal BL may experience Residual Layers as levated inversions Elevated layers are not consider (for some authors) part of the BL because their formation does not depend on the surface conditions Observations and modeling have demonstrated that elevated layers can effectively have a coupling through turbulent kinetic energy and or radiative processes. The presence of such elevated layer can carry important influences in the Air Quality because of it will drive downward mixing and low level recirculation of PM and gases in valleys setting

16. Synoptic Setup for Occurrence of an Elevated Inversion

17. SODAR Observation of an elevated Inversion LHElevated INV Weakening of SFC-INV Upper-level Subsidence

18. Tanana Valley Cross Section Synoptic Driven Wind N-NE North White Mountain Range ~ 550m Alaska Ranges ~1000 m Power Plants Increasing subsidence Pumping Mechanism Density Flows/Seiches Driving Recirculation Synoptic Driven Flow Initiating Secondary Inversion 160 km Elevated INV SFC-INV Study Area Effects on the Study Area : swaying flows at low level, increasing probably gases and PM Recirculation period can be variable and about ½ of a day

19. 1.- Flows in the BL and the Free Troposphere November 20, 2009 (NWS-PAFA) At 50 m within the SBL the wind direction tends to be out of the NE At 200 m above the SBL the wind direction tends to be out of the E-SE Synoptic Forcing & Winter BL-States “Synoptic Driven High Latitude Stable Boundary Layer States in the Interior Alaska”. J. Mayfield and J. Fochesatto – Paper Presented at the 2010-Alaska Weather Symposium, Fairbanks, AK. HSBL = 180 mHSBL = 226 m

20. Decoupling of flows in the BL and free troposphere Wind Direction in the SBL unrelated to the Synoptic flow March 02, 2009 (UAF-Experimental Farm) At 50 m within the SBL the wind direction tends to be out of the NW- NNW At 200 m above the SBL the wind direction tends to be out of the SW Areas close to topography verifies flow decoupling (BL/FT) while areas of moderate-flat land experience inversions without decoupling with a moderate synoptic forcing

21. December 18 2008 1800 LST - December 22 2008 0000 LST During this period Dec 18-22, 2008 the flow in the BL and the free troposphere is synoptically driven The L-pressure system in the Gulf slowly moves SE weakening BL-State under changing synoptic forcing

22.  Moderate winds speed, BL and free troposphere verifies same wind direction.  Statistical distribution of wind direction verifies no dominant direction  Inversion weakens and disappears as the Low weakens and slowly (~ 3 days) moves south east  Inversion re-appears as the H pressure system dominates low level flows. – This inversion may be difficult to capture by modeling although the forcing is remains synoptically dominated.

23. Occurrence of Low Level Jets, January 16, 2009 NWS 6 hr Surface Analysis Chart shows a Low-Level Jet developing in the Fairbanks area LLJ- channeling through low topography – orientation SE-NW Reduced aerodynamic roughness Weakening of inversion strength-warming by compression Source of PM2.5 from North Pole?

24. Summary Wi-BLEx captured BL structures and the effect of the small scale drainage flows on the surface inversion, surface exchanges and the inversion structure through the winter Wi-BLEx observed elevated inversions in the Tanana Valley and we hypothesize that this mechanism can have potential for Air Pollution when combined with recirculation in the valley BL states respond to synoptic forcing in periods ranging from one-day to several days depending on the flow orientation and time of the winter Strong synoptic forcing (e.g., LLJ) where measured in certain occasions and can be a test scenario for mesoscale simulations and for evaluation of potential for regional Air Pollution transport e.g. North Pole /EAFB sources.