ARM Remote Sensors Reveal Higher Frequency of Occurrence of Clouds and Drizzle in the Eastern North Atlantic: How ground-based observations can complement CloudSat/Calipso

 
Poster PDF

Authors

Katia Lamer — Brookhaven National Laboratory
Pavlos Kollias — Stony Brook University
zeen zhu — Brookhaven National Laboratory

Category

Warm low clouds, including aerosol interactions

Description

Continuing gaps in both the representation and our understanding of low-level cloud processes motivated the collection of additional observations. While CloudSat continues to collect global observations of cloud and precipitation attributes, ARM’s ground-based remote sensors, with their different sampling configuration, could add-to/change our current perspective. Three-years of backscattering observations collected by the ground-based Ka-band Zenith ARM Radar and ceilometer lidar are combined, using the O’Connor et al. [2005], to quantify the frequency of occurrence and microphysical properties of clouds and precipitation forming at different heights within the marine boundary layer. These observations indicate that a vast majority (98%) of the marine boundary layer precipitation in the ENA falls at a rate below 1 mm hr-1; This represents 90% more drizzle than reported in CloudSat’s 2C-PRECIP-COLUMN drizzle product. Histograms of precipitating cloud attributes, including reflectivity, thickness, locations and liquid water path, and drop sizes are constructed from ground-based remote sensing observations to help explain the observed discrepancies. Beyond helping to reconcile ARM and CloudSat observational records, these statistical summaries could also serve to guide the configuration (e.g., sensitivity, vertical resolution or deadzone extent) of future spaceborne missions. By revealing, among other things, a higher frequency of occurrence of drizzle, this ground-based study also offers an alternative perspective for previous model evaluation studies that concluded on an overproduction of low-level precipitation based-on CloudSat observations.