Extended Abstract (1.9M)11.1
Lagrangian Coherent Structures and Turbulence Detection near the Hong Kong International Airport based on LIDAR Measurements
Wenbo Tang, Arizona State University, Tempe, AZ; and G. Haller and P. W. Chan
Terrain-disrupted turbulent airflow brings windshear to aircraft at the Hong
Kong International Airport (HKIA). Better knowledge of the structures of
the turbulent airflow would be very useful to detection of the windshear and
understanding of the effects of the shear on aircraft. A methodology is
developed to identify Lagrangian coherent structures (LCS) from the
turbulent airflow sampled by Doppler velocity measurements of LIght
Detection And Ranging (LIDAR) systems at HKIA. As a demonstration of the
methodology, strong southerly flow associated with a tropical cyclone in
April 2008 is analyzed. In this methodology, a variational method is first
applied to the conical scans of the radial velocity from the LIDAR to derive
the 2D wind field. Lagrangian airflow analysis is then used to identify the
LCS in the airflow as revealed in the 2D wind data. The Lagrangian flow
field is integrated backward and forward in times to determine the updraft
and downdraft of the flow respectively, and the results are compared with
the vertical scans of the LIDAR which have not been used in the Lagrangian
flow analysis. It is found that the updraft and downdraft identified from
the Lagrangian flow analysis of the LIDAR conical scans are generally
consistent with the airflow convergence and divergence as analyzed from the
LIDAR vertical scans. The Lagrangian flow analysis presented in the study
provides a way to infer the vertical air motion from the conical scan data
of the LIDAR. This could bring a significant progress in LIDAR based
windshear detection as both the vertical and horizontal components of the
air motion account for the windshear effects to aircraft, but so far, the
vertical component could not be measured directly by the LIDAR or other
ground-based weather sensors.
Session 11, Mixing within the Ocean and Atmosphere
Thursday, 11 June 2009, 1:50 PM-3:30 PM, Pinnacle BC
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