Boundary Layer, Urban Meteorology and Land-Surface Processes

Observation of water vapor turbulence profiles in stationary and well mixed convective boundary layers over the ARM Tropical Western Pacific site

Dr. Mohammed Osman

CIMMS/NSSL

09 December 2016, 2:00 PM

National Weather Center, Room 5600
120 David L. Boren Blvd.
University of Oklahoma
Norman, OK

The high temporal and vertical resolution and the ability to operate continuously under most atmospheric conditions make Raman lidars outstanding tools for studying turbulence in the convective boundary layer (CBL). Raman lidars have been used to study the turbulent structure of the CBL and the entrainment zone; however, previous studies have been in general based on a limited number of cases, which restricts the representativeness of the results for different atmospheric conditions. This study uses data from the autonomous Raman lidars that measure water vapor over the Tropical Western Pacific (TWP) site located at Darwin (Australia) as part of the Atmospheric Radiation Measurement (ARM) program. The data from TWP used here spans 5 years from December 2010 to December 2015. The vertical profiles of turbulent fluctuations have been derived using an auto covariance technique to separate out the instrument random error from the atmospheric variability over a set of 2-h period time series during which the CBL is quasi-stationary and well mixed. The temporal and vertical resolutions of water vapor are 10 s and 37.5 m, respectively. The error analysis of the Raman lidars observations demonstrates that the lidars are capable of resolving the vertical structure of turbulence in the CBL, and the small noise errors allow us to thoroughly examine different moments up to the third-order. The seasonal variations of the vertical profiles of variance, structure function coefficient, skewness and integral scale have been carefully analyzed. We particularly highlight noticeable differences in water vapor turbulence in the CBL during monsoon and non-monsoon seasons. These results are also compared with previous findings obtained from the Southern Great Plains (SGP) site located at Lamont, Oklahoma (USA).

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