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: zvecenaj@gfz.hrzvecenaj@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