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RACORO Case Studies of Continental Boundary Layer Clouds

 

Authors

David D. Turner — NOAA- Global Systems Laboratory
Minghua Zhang — Stony Brook University
Andrew M. Vogelmann — Brookhaven National Laboratory
Shaocheng Xie — Lawrence Livermore National Laboratory
Yangang Liu — Brookhaven National Laboratory
Greg McFarquhar — University of Oklahoma
Jian Wang — Washington University in St. Louis
Ann M. Fridlind — NASA - Goddard Institute for Space Studies
Andrew Ackerman — NASA - Goddard Institute for Space Studies
Yunyan Zhang — Lawrence Livermore National Laboratory
Robert Jackson — Argonne National Laboratory
Tami Fairless — Pacific Northwest National Laboratory
Wuyin Lin — Brookhaven National Laboratory
Satoshi Endo — Brookhaven National Laboratory
Zhijin Li — University of California
SHA FENG — The Pennsylvania State University
Marat Khairoutdinov — Stony Brook University

Category

General Topics – Cloud

Description

As part of the FAst-physics System TEstbed and Research (FASTER) Project, case studies have been constructed to assess and improve model representation of continental boundary-layer clouds (stratus, stratocumulus, cumulus) using Atmospheric Radiation Measurement (ARM) ground-based remote-sensing observations and aircraft data from the RACORO Campaign [Routine ARM Aerial Facility (AAF) Clouds with Low Optical Water Depths (CLOWD) Optical Radiative Observations]. Three 60-hour case study periods are selected that capture the temporal evolution of cumulus, stratiform and drizzling boundary layer cloud systems. Cases are included that are more mixed or transitional in nature compared to purely canonical cases. Collectively, the case studies include: daytime stratus, stratocumulus, and cumulus formation and breakup under varying aerosol conditions, strong and weak nocturnal jets, and nighttime stratus formation and deepening within a residual layer. The aircraft data include aerosol number size distributions in a wide range of aerosol loadings fit to lognormal distributions for concise representation in models. Aerosol hygroscopicity (kappa) is determined from observations for the lognormal modes for use in models. The low kappa values observed (0.05-0.30) suggest a large aerosol organic fraction. The case studies are developed to run side-by-side using large eddy simulations (LESs) and single-column models (SCMs). Large-scale forcing conditions are obtained: from the ARM continuous forcing for the standard domain and a reduced domain, derived from ECMWF for a standard domain and a reduced domain, and derived from a Multi-Scale Data Assimilation System. The goal is to provide a diverse set of observationally constrained cases of cloudy boundary layer evolution for use by the general modeling communities to improve our understanding of continental cloudy boundary layers, aerosol influences upon them, and their representation in cloud-scale and global-scale models. These continental case studies offer an important complement to previous boundary layer case studies, which mainly focus on marine boundary layer clouds. Overall, the periods sample a wide range of cloudy boundary-layer conditions but they use a modular specification, which makes it easy for modelers to use.