M3MC Meeting MinutesDoppler Lidar Measurements of Vertical Velocity Spectra, Length Scales, and Coherence in the Convective Planetary Boundary Layer
Lidar Radar images Lidar time-height cross-sections of W with the same aspect ratio (AR ~ 7.8) comparing a light-wind day (top: U = 2.2 m/s) with a moderate-wind day (bottom: U = 7.2 m/s). The upper-right panel shows integral scales normalized by the CBL depth in the vertical (triangles) and the along-wind directions (squares). The dashed line was obtained from airplane observations of the along-wind integral scale in a marine CBL.
During August 1996, the National Center for Atmospheric Research's Atmospheric Technology Division (NCAR/ATD) and NOAA's Environment Technology Laboratory (ETL) deployed three lidars at a University of Illinois field site near Champaign, Illinois, USA, to observe the high resolution structure of aerosol, winds and ozone in the lowest few kilometers of the atmosphere as the convective boundary layer (CBL) evolved from early morning to late evening. Airplane observations show an increasing horizontal integral scale with height. The site for Lidars In Flat Terrain (LIFT) was chosen because of the flat terrain, good aerosol scattering, and nearby UHF radar wind profilers operated by the NOAA Aeronomy Laboratory. Drs. Marie Lothon (MMM visitor from Toulouse, France), Don Lenschow, and Shane Mayor (EOL) are publishing a paper that analyzes vertical velocity W statistics throughout the CBL from the NOAA High Resolution Dopplar Lidar (HRDL). The figure shows cross-sections from two of the eleven analyzed cases; the upper-right panel shows the integral scales. They found that the W eddies are squashed in the middle of the CBL, with the vertical integral scale decreasing somewhat with height and the horizontal integral scale nearly constant. Airplane observations show an increasing horizontal integral scale with height. The difference might be due to the heterogeneity of the LIFT site. The coherence for vertical displacements is larger than predicted for isotropic turbulence, while the phase angle shows negligible tilt of the eddies with height.
