spatial and temporal features of mountain wave related turbulence
DESCRIPTION
Spatial and Temporal Features of Mountain Wave Related Turbulence. * Ž eljko Ve č enaj, # Stephan de Wekker & + Vanda Grubi š i ć * Department of Geophysics, Faculty of Science, University of Zagreb, Croatia # Department of Environmental Sciences, University of Virginia, Virginia - PowerPoint PPT PresentationTRANSCRIPT
Spatial and Temporal Features of Spatial and Temporal Features of Mountain Wave Related Mountain Wave Related
TurbulenceTurbulence
**ŽŽeljko Veeljko Veččenaj, enaj, ##Stephan de Wekker & Stephan de Wekker & ++Vanda GrubiVanda Grubiššiićć*Department of Geophysics, Faculty of Science, University of Zagreb, Croatia#Department of Environmental Sciences, University of Virginia, Virginia+Division of Atmospheric Sciences, Desert Research Institute, Reno, Nevada
Email: Email: [email protected]@gfz.hr
..
CONTENTCONTENT
I. INTRODUCTION
II. DATA ANALYSIS
III. RESULTS
IV. CONCLUSIONS
I. INTRODUCTION
• OBJECTIVE:– To study the horizontal and vertical structure of TKE generation and
destruction in a variety of weather situations during T-REX– To combine aerosol lidar data and towers data
• TURBULENT KINETIC ENERGY BALANCE EQUATION:
• Richardson number
• We are interested in following situations:
Ri >> 0 ……… Stable situation
Ri << 0 ………. Convectively produced turbulence
Ri ≈ 0 ………... Turbulence produced by wind stress
22
z
v
z
u
zgRi
I.1. ESTIMATION OF ε
• For evaluation of ε, the Inertial Dissipation Method (IDM) provided by the Kolmogorov’s 1941 hypotheses can be employed
• Condition: Taylor’s Hypotheses (TH) of frozen turbulence must be valid (transformation from time to space domain)
• Criterion: (e.g. Stull, 1988)
M.........Mean horizontal wind speed
σM........Standard deviation
5.0MM
• Power spectrum density in inertial subrange:
(1)
• Using TH, ε can be evaluated from (Champagne et al., 1977):
(2)
..........mean streamwise velocity component
Su(f) ......power spectrum density
..........Kolmogorov’s constant
2/33/5 )(2
fSf
Uu
U
3/53/2)( kkSu
II. DATA ANALYSIS
Figure 1. The map of the area of interest along with the towers locations.
• Ggccc
• Height of towers: 35 m
• 6 vertical levels: 5, 10, 15, 20, 25 and 30 m
• CSAT3 ultrasonic anemometers
• Sampling rate: 60 Hz
• The data are averaged down to 10 Hz for further analysis
• period of interest: 02 March 00 UTC to 04 March 00 UTC (IOP1)
Figure 2. East (first row) and north (second row) 10 Hz wind speed components of the observed 6 hr episode (black curve). White curve is the 5 min moving average. Vertical dashed lines denote a period of interest.
Figure 3. The time series of the Bulk Richardson number in the layer between 5 & 30 m (for the west tower between 5 & 25 m).
Figure 4. Time series of 1 minute dissipation rate values
Figure 5. Time series of 15 minute dissipation rate values
III. RESULTS
Figure 6. Vertical distribu-tion of 15 minutes averages of the 1 min TKE dissipation rate in time for all three towers.
Figure 7. Vertical distribu-tion of 15 minutes averages of the 1 min mechanical term in time for all three towers.
IV. CONCLUSIONS
• We have started to analyze turbulence data from the three NCAR towers
• Independence of the averaging period is present
• Balance of the mechanical term and the TKE dissipation rate is present
• Next steps:
(1) To extend this work to the other two towers and to other IOPs/EOPs to investigate spatial and temporal structure in a
variety of stability and wind conditions
(2) Comparison with estimates/observations from other instruments (wind profiler/lidar/aircraft)
Acknowledgments: we would like to thank Steve Oncley for providing turbulence data