Ground-Based Remote Retrievals of Cumulus Entrainment Rates

Journal Article · Fri Jul 26 00:00:00 EDT 2013 · Journal of Atmospheric and Oceanic Technology, 30(7):1460–1471

DOI:https://doi.org/10.1175/JTECH-D-12-00187.1· OSTI ID:1090177

Wagner, Timothy J.; Turner, David D.; Berg, Larry K.; Krueger, Steven K.

While fractional entrainment rates for cumulus clouds have typically been derived from airborne observations, this limits the size and scope of available data sets. To increase the number of continental cumulus entrainment rate observations available for study, an algorithm for retrieving them from ground-based remote sensing observations has been developed. This algorithm, called the Entrainment Rate In Cumulus Algorithm (ERICA), uses the suite of instruments at the Southern Great Plains (SGP) site of the United States Department of Energy's Atmospheric Radiation Measurement (ARM) Climate Research Facility as inputs into a Gauss-Newton optimal estimation scheme, in which an assumed guess of the entrainment rate is iteratively adjusted through intercomparison of modeled liquid water path and cloud droplet effective radius to their observed counterparts. The forward model in this algorithm is the Explicit Mixing Parcel Model (EMPM), a cloud parcel model that treats entrainment as a series of discrete entrainment events. A quantified value for measurement uncertainty is also returned as part of the retrieval. Sensitivity testing and information content analysis demonstrate the robust nature of this method for retrieving accurate observations of the entrainment rate without the drawbacks of airborne sampling. Results from a test of ERICA on three months of shallow cumulus cloud events show significant variability of the entrainment rate of clouds in a single day and from one day to the next. The mean value of 1.06 km-¹ for the entrainment rate in this dataset corresponds well with prior observations and simulations of the entrainment rate in cumulus clouds.

• Research Organization: Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC05-76RL01830
• OSTI ID: 1090177
• Report Number(s): PNNL-SA-90715; KP1701000
• Journal Information: Journal of Atmospheric and Oceanic Technology, 30(7):1460–1471, Journal Name: Journal of Atmospheric and Oceanic Technology, 30(7):1460–1471
• Country of Publication: United States
• Language: English