1 / 21

CESAR Science Day, 19 June 2013 Albert Oude Nijhuis

Dynamics of turbulence in precipitation: Unravelling the eddies. CESAR Science Day, 19 June 2013 Albert Oude Nijhuis. Contents. UFO project Retrieval of wind field with IDRA Retrieval of the Eddy Dissipation Rate The Inertia Effect Outlook. UFO Project. UFO Project. UFO Project.

calum
Download Presentation

CESAR Science Day, 19 June 2013 Albert Oude Nijhuis

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Dynamics of turbulence in precipitation: Unravelling the eddies CESAR Science Day, 19 June 2013 Albert Oude Nijhuis

  2. Contents • UFO project • Retrieval of wind field with IDRA • Retrieval of the Eddy Dissipation Rate • The Inertia Effect • Outlook

  3. UFO Project

  4. UFO Project

  5. UFO Project

  6. UFO Project • The combination of LIDAR and RADAR can be used to detect wake vortices in all weather conditions. • Quantitative information on turbulence, e.g. the eddy dissipation rate, can be retrieved from the Doppler moments, velocity and spectral width, from LIDAR and RADAR instrument.

  7. Retrieval of wind field with IDRA In contours: Doppler velocitiesHorizontal wind vectors areobtained via a least sqaures fit.

  8. Retrieval of wind field with IDRA Model from Doviak and Zrnic (1992)

  9. Retrieval of wind field with IDRA

  10. Retrieval of the eddy dissipation rate The eddy dissipation rate (EDR) is based on the assumption of homogenous isotropic frozen turbulence. In the inertial sub-range the dissipation goes with a -5/3 power. Figure from O'Connor (2010).

  11. Retrieval of the eddy dissipation rate The eddy dissipation rate (EDR) is based on the assumption of homogenous isotropic frozen turbulence. In the inertial sub-range the dissipation goes with a -5/3 power. Several retrieval methods are possible: • 1. Use the Doppler spectral width. Subtract the fall speed distribution and compute the turbulence spectral width. Then calculate the EDR. • 2. Use a sequence of Doppler velocities and compute the variance. Use an analytic relation to compute the EDR. • 3. Use a sequence of Doppler velocities, and compute the vertical velocity energy density spectrum (FFT). Fit the slope from the loglog plot, which can be used to compute the EDR.

  12. Retrieval of the eddy dissipation rate TARA (S-band RADAR) measures the vertical Doppler verlocity at Cabauw. EDR from Doppler spectral width LSF method 1 LSF method 2 O'Connors method(from the variance) EDR from Doppler velocitiy sequence Different retrieval methods lead to different answers!

  13. Retrieval of the eddy dissipation rate EDR from the spectral width is quite a challenge, as it is depending on the drop size distribution! EDR from Doppler spectral width

  14. Retrieval of the eddy dissipation rate The basics O'Connors method(from the variance) EDR from Doppler velocitiy sequence

  15. Retrieval of the eddy dissipation rate Figure from O'Connor (2010). Power spectrum for a LIDAR instrument. Power spectrum from TARA (S-band RADAR). +/- 60 min. of data. For the RADAR the -5/3 power law seems not to be satisfied for the shorter spatial scales.

  16. The inertia effect • Large droplets have inertia. They need some time to participate in the turbulent motion. A very simple model can be used (Gorelik, 1964):- For each drop size there is a minimum length scale Lmin.- For turbulent motions larger than Lmin the drop is a perfect tracer.- For turbulent motions smaller than Lmin the drop will not participate in the motion.- For Lmin we use the approximation:

  17. The inertia effect • Large droplets have inertia. They need some time to participate in the turbulent motion. Power spectrum from TARA (S-band RADAR). +/- 60 min. of data. Theoretical power spectrum,with and without the inertia effect. Inertia effect??

  18. Benchmark: plot vs. height From variance, method from (O'Connor, 2010) Spectral width Spectrum lsf method 2 Spectrum lsf method 1

  19. Comparing retrieval methods LSF 1 (y-axis) vs. O'Connor LSF 2 (y-axis) vs. O'Connor

  20. Outlook • Benchmark / validate EDR retrieval methods • Investigation of the inertia effect. Potentially it may be possible to retrieve the drop-size distribution. • The addition of a Doppler LIDAR on CESAR would be helpfull. Then the LIDAR+RADAR combination performance for all weather conditions can be assessed.

More Related