Shallow precipitation variability during the Aerosol and Cloud Experiments in the Eastern North Atlantic (ACE-ENA)

 

Authors

Pavlos Kollias — Stony Brook University
Bernat Puigdomenech — McGill University
Edward Luke — Brookhaven National Laboratory
Katia Lamer — Brookhaven National Laboratory
Bradley Isom — Pacific Northwest National Laboratory
Nitin Bharadwaj — Pacific Northwest National Laboratory
Jian Wang — Washington University in St. Louis

Category

Warm low clouds, including aerosol interactions

Description

The Atmospheric Radiation Measurement (ARM) Climate Research Facility operates a fixed observatory on Graciosa Island in the Eastern North Atlantic (ENA). This site hosted the two-phases Aerosol and Cloud Experiments in the Eastern North Atlantic (ACE-ENA) field campaign motivated by the need for comprehensive in-situ characterization of boundary layer structure, low clouds, and aerosols. Information on shallow precipitation representative of the conditions in the vicinity of the ENA site is essential for improving our understanding aerosol-cloud-precipitation interactions and for model validation. We present two methods for shallow precipitating rate retrieval from observations: i) A combination of vertically pointing 35-GHz radar and ceilometer backscattering observations are used to estimate light precipitation mass flux [10-4 to 3-5 mm hr-1] from the surface to cloud base height using a backscattering ratio technique and ii) 35-GHz scanning radar low-elevation surveillance observations are converted to domain rain rate using reflectivity-rain rate (Z-R) relationships produced from vertically pointing sensors. While targeting the same cloud systems, both techniques provide different views on shallow precipitation. Vertically pointing sensors collect information on weaker rain events (due to their higher sensitivity) at higher temporal resolution. On the other hand, while less sensitive and of coarser temporal resolution, scanning sensors document a larger number of heavier drizzle events and provide domain-representative estimates of shallow precipitation. The goal of the current study is to consolidate the information content of both retrievals to provide the best estimate of domain averaged shallow precipitation rate for the region around the ARM ENA site. The validity of this merging technique is evaluated using high-resolution model output and a sophisticated forward radar operator.