Long-term Observations of Daytime Fair-Weather Cumuli at the ARM Southern Great Plains Facility during Summer months

Time-height plots of Doppler lidar moments at the SGP ARM Facility. Squares indicate cloud base detections and hourly LCL values

Hourly diurnal composites during fair-weather cumuli conditions from the period 1997-2010.

A long data record (14-year) of ground-based observations at the Atmospheric Radiation Measurement (ARM) program Southern Great Plains (SGP) site is analyzed to document the macroscopic and dynamical properties of summertime fair-weather cumuli clouds. First, a fuzzy-logic based algorithm is developed to eliminate insect radar echoes in the boundary layer that hinder our ability to develop representative cloud statistics. The refined dataset is used to document the daytime composites of fair-weather cumuli clouds properties. Doppler velocities are processed for lower reflectivity thresholds that contain small cloud droplets having insignificant terminal velocities; thus Doppler velocities used as tracers of air motion. The algorithm is implemented to process the entire 14 yr dataset of cloud radar vertical velocity data. Composite diurnal variations of the cloud vertical velocity statistics, surface parameters and profiles of updraft and downdraft fractions, updraft and downdraft velocity, and updraft mass flux are calculated. Statistics on the cloud geometrical properties such as, cloud thickness, cloud chord length, cloud spacing and aspect ratios are calculated on the cloud scale. The present dataset provides a unique insight into the daytime evolution and statistical description of the turbulent structure inside fair-weather cumuli over land.

About the Author

Arunchandra Chandra is currently a PhD Student working with Prof. Pavlos Kollias. His research interests are mainly focused on atmospheric boundary layer, shallow convection and ground-based remote sensing.

The main focus of his thesis is to better understand the turbulence structure of clear and cloud-topped boundary layers using long-term observations, mainly from cloud radars, along with the supplemental measurements at the ARM (Atmospheric Radiation Measurement) climate research facility. Another main focus is to use Doppler lidar observations to test some of the aspects of existing mass-flux parameterization schemes over land.

He previously obtained M.Sc (Engg) from Indian Institute of Science in 2007, and B.E in Mechanical Engineering from VTU in 2004.