Recorded presentation5.6
Water vapor variability within the atmospheric boundary layer using Raman Lidar and sounding measurements
Mariana Adam, Howard University, Washington, DC; and M. Hicks, T. Dejene, M. Robjhon, B. B. Demoz, J. D. Fuentes, E. Joseph, D. Venable, and R. Connell
The water vapor mixing ratio and the aerosol backscatter coefficient are determined on regular basis from a Raman lidar. The atmospheric boundary layer attributes, such as mixed layer or stable boundary layer height, are currently determined using various approaches, mostly based on the altitude where the largest gradient is found in the vertical profiles of aerosol backscatter signals. Theoretically, above the top of the mixed layer, the mean virtual potential temperature, horizontal wind speed, and various scalar fluxes exhibit strong gradients. In contrast, these quantities have a maximum at the top of the stable boundary layer. If one applies the same methodology to determine the boundary layer height (to either mixed layer, stable boundary layer, or residual layer) using water vapor mixing ratio profiles, the results can be different. To derive such boundary layer attributes, we have applied the same procedure (using wavelets analysis) to determine boundary layer height using both water vapor mixing ratio and aerosol backscatter coefficients for data sets obtained during WAVES (Water Vapor Variability – Satellite / Sondes experiment) 2006 and 2007 campaigns. Comparison of the mixed layer height and stable boundary layer height retrieved from both data sets is discussed. The results are compared against boundary layer heights derived using profiles of virtual potential temperature as determined from radiosondes. Special attention is given to the cases with least agreement among the two methods. An interesting subset of these cases is the post sunset decay of the mixed layer. While the aerosol backscatter coefficient decreased monotonically (suggesting the mixed layer decreased), water vapor mixing ratio gradients post-sunset changed slowly due to the lack of both convection dry air entrainment. As a result, the water vapor field is not well defined as convective boundary layer transitioned to the residual layer. Meteorological conditions for such cases are discussed in order to explain unique water vapor mixing ratio distribution patterns within and above the boundary layer. Wind profilers as well as meteorological tower data will be presented for the different conditions.
Session 5, Lidar Application Studies in The Boundary Layer and Lower Troposphere - II
Tuesday, 13 January 2009, 3:30 PM-5:00 PM, Room 122A
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