Spatial and Temporal Features of Mountain Wave Related Turbulence

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Spatial and Temporal Features of Mountain Wave
Related Turbulence

• Željko Vecenaj, Stephan de Wekker Vanda
  Grubišic
• 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 zvecenaj_at_gfz.hr
• .

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CONTENT

1. INTRODUCTION
2. DATA ANALYSIS
3. RESULTS
4. CONCLUSIONS

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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

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• Richardson number
• We are interested in following situations
• Ri gtgt 0 Stable situation
• Ri ltlt 0 . Convectively produced
  turbulence
• Ri 0 ... Turbulence produced by
  wind stress

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I.1. ESTIMATION OF e

• For evaluation of e, the Inertial Dissipation
  Method (IDM) provided by the Kolmogorovs 1941
  hypotheses can be employed
• Condition Taylors Hypotheses (TH) of frozen
  turbulence must be valid (transformation from
  time to space domain)
• Criterion (e.g.
  Stull, 1988)
• M.........Mean horizontal wind
  speed
• sM........Standard deviation

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• Power spectrum density in inertial subrange
• (1)
• Using TH, e can be evaluated from (Champagne et
  al., 1977)
• (2)
• ..........mean streamwise
  velocity component
• Su(f) ......power spectrum
  density
• ..........Kolmogorovs
  constant

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II. DATA ANALYSIS
Figure 1. The map of the area of interest along
with the towers locations.
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• 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)

• Ggccc

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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.
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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).
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III. RESULTS
Figure 4. Time series of 1 minute dissipation
rate values
Figure 5. Time series of 15 minute dissipation
rate values
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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.
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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