Skill of ship‐following large‐eddy simulations in reproducing MAGIC observations across the northeast Pacific stratocumulus to cumulus transition region

Abstract

During the Marine ARM GPCI Investigation of Clouds (MAGIC) in October 2011 to September 2012, a container ship making periodic cruises between Los Angeles, CA, and Honolulu, HI, was instrumented with surface meteorological, aerosol and radiation instruments, a cloud radar and ceilometer, and radiosondes. Here large‐eddy simulation (LES) is performed in a ship‐following frame of reference for 13 four day transects from the MAGIC field campaign. The goal is to assess if LES can skillfully simulate the broad range of observed cloud characteristics and boundary layer structure across the subtropical stratocumulus to cumulus transition region sampled during different seasons and meteorological conditions. Results from Leg 15A, which sampled a particularly well‐defined stratocumulus to cumulus transition, demonstrate the approach. The LES reproduces the observed timing of decoupling and transition from stratocumulus to cumulus and matches the observed evolution of boundary layer structure, cloud fraction, liquid water path, and precipitation statistics remarkably well. Considering the simulations of all 13 cruises, the LES skillfully simulates the mean diurnal variation of key measured quantities, including liquid water path (LWP), cloud fraction, measures of decoupling, and cloud radar‐derived precipitation. The daily mean quantities are well represented, and daily mean LWP and cloud fraction show the expected correlation with estimated inversion strength. There is a −0.6 K low bias in LES near‐surface air temperature that results in a high bias of 5.6 W m−2 in sensible heat flux (SHF). Overall, these results build confidence in the ability of LES to represent the northeast Pacific stratocumulus to trade cumulus transition region.

Estimating the Decoupling Degree of Subtropical Marine Stratocumulus Decks From Satellite

“…Such a Cu-feeding phenomenon has been extensively observed (e.g., Albrecht et al, 1995;Klein et al, 1995;Martin et al, 1995) and simulated by large-eddy simulations (e.g., McGibbon & Bretherton, 2017;Sandu & Stevens, 2011;Stevens, 2000;Wyant et al, 1997). Such a Cu-feeding phenomenon has been extensively observed (e.g., Albrecht et al, 1995;Klein et al, 1995;Martin et al, 1995) and simulated by large-eddy simulations (e.g., McGibbon & Bretherton, 2017;Sandu & Stevens, 2011;Stevens, 2000;Wyant et al, 1997).…”

DNS and LES for Simulating Stratocumulus: Better Together

“…For a given grid, the relation between entrainment efficiency and stratocumulus thickness also varies between LES models with different advection schemes and subgrid‐scale turbulence models (e.g., Blossey et al, ; Pressel et al, ; Stevens et al, , , ), underlining that numerical convergence (in the sense of independence of simulated results from the choice of grid and numerical method) has not been achieved at these grid resolutions. Nevertheless, it is encouraging that one choice of LES grid can suffice to realistically simulate stratocumulus LWPs across a range of cloud regimes and inversion strengths (McGibbon & Bretherton, ) and that stratocumulus‐to‐cumulus transitions simulated by a variety of LES with the same grid resolutions all show similar and realistic evolutions (van der Dussen et al, ).…”

“…Since the pioneering works by Deardorff () and Moeng (), LES has often been used for process studies of the stratocumulus‐topped boundary layer. There is the consensus that LES is able to reproduce qualitatively many important properties, both when the cloud and subcloud layers are strongly coupled and the cloud cover is close to one (Kurowski et al, ; Stevens et al, ; Yamaguchi & Feingold, ; Yamaguchi & Randall, ), and when the cloud and subcloud layers start to decouple and the stratocumulus breaks into shallow cumulus (de Roode et al, ; McGibbon & Bretherton, ; Sandu & Stevens, ; van der Dussen et al, ). More recently, LES has also shown robustness in climate change sensitivity studies (Blossey et al, ; Bretherton & Blossey, ; Bretherton et al, ).…”

Estimates of entrainment in closed cellular marine stratocumulus clouds from the MAGIC field campaign

“…Here we describe the technique used to estimate entrainment rates and uncertainty using the observations collected during Leg 15A that started at 1200 UTC on 20 July 2013. This same case was also used by McGibbon and Bretherton () in their large‐eddy simulation study.…”