1. Observations and modelling of IOP6: response of the valley winds to the upstream profile R. Burton 1, S. Vosper 2, P. Sheridan 2, S. Mobbs 1 1 Institute for Atmospheric Science, School of Earth and Environment, University of Leeds, U.K. 2Met Office, Exeter, U.K. School of Earth and Environment INSTITUTE FOR ATMOSPHERIC SCIENCE

2. Introduction IOP6: severe winds in the valley Relating the winds in the valley to the upstream flow Further work School of Earth and Environment INSTITUTE FOR ATMOSPHERIC SCIENCE

3. Photo: A. Doernbrack T-REX IOP6: 24 th – 26 th March 2006 “A full temporal evolution of a trapped-lee-wave rotor event was captured in this IOP. There was a strong and well defined wave/rotor event with wave clouds, roll clouds, cap cloud over the Sierra, and a dust storm in Owens Valley.” (Mission Summary) Kuettner 1959

4. Locations of the AWS:DRILeeds

5. Comparing winds from UM and AWS is difficult: instead we seek a statistical parameter to describe the effect of severe winds. From Mobbs et al. 2005 (“Observations of downslope winds and rotors in the Falkland Islands”, QJRMS, 131, 2839-2860 σ 2 = σ u 2 ++ σ v 2 |U| = average wind speed

6. It is thought that the stratification and the shear of the upstream profile are important parameters in determining the nature of the downstream response. From Hertenstein and Kuettner, “Rotor types associated with steep lee topogreaphy: influence of the wind profile”, Tellus A, 57, 117-135

7. It is known that the stratification and the shear of the upstream profile are important parameters in determining the nature of the downstream response. Can the wind effect parameter be linked to the upstream profile? From Hertenstein and Kuettner, “Rotor types associated with steep lee topogreaphy: influence of the wind profile”, Tellus A, 57, 117-135

8. UM configuration

9. UM: Principal components analysis of the upstream profile between 3 and 5 km These are the dominant structures in the N and dU/dz profiles for all upstream profiles (sample size: 6840) Maximum in both shear and stability at 4250m

10. Time series of principal components; wind effect parameter: UM

11. Wind starts to veer to the south: another mechanism?

12. Time series of principal components; wind effect parameter: AWS

13. Correlations: UM wind effect parameter with upstream profile structure UM winds

14. Correlations: AWS wind effect parameter with upstream profile structure AWS winds Insert pic here

15. Summary The dominant structure in the UM profiles between 3km and 5km is a peak in shear and a peak in stability at z = 4250m There is a very strong ( r = 0.95; r = 0.87) correlation between the UM winds in the valley and the shape of the upstream N and dU/dz profiles for all of IOP6; The correlation is not as strong for the observed winds. But then the model is reacting to the model profiles, which may differ slightly to the observed profiles. Is this behaviour unique? Or does it apply to other IOPs? Ongoing. School of Earth and Environment INSTITUTE FOR ATMOSPHERIC SCIENCE

16. Correlations between first PC score for N and dU/dz