TY - JOUR

T1 - Turbulent Transport in the Gray Zone

T2 - A Large Eddy Model Intercomparison Study of the CONSTRAIN Cold Air Outbreak Case

AU - de Roode, Stephan R.

AU - Frederikse, Thomas

AU - Siebesma, A. Pier

AU - Lesage, Andrew T.

AU - Chylik, Jan

AU - Field, Paul R.

AU - Fricke, Jens

AU - Gryschka, Micha

AU - Hill, Adrian

AU - Honnert, Rachel

AU - Krueger, Steve K.

AU - Lac, Christine

AU - Tomassini, Lorenzo

N1 - Funding Information: The PALM simulations with DALES including ice were performed with resources provided by the North-German Supercomputing Alliance (HLRN) and the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation)?Projektnummer 268020496?TRR 172, within the Transregional Collaborative Research Center ?ArctiC Amplification: Climate Relevant Atmospheric and SurfaCe Processes, and Feedback Mechanisms (AC)3.? DHARMA simulations used resources provided by the NASA High-End Computing (HEC) Program through the NASA Advanced Supercomputing (NAS) Division at Ames Research Center. The case specifics are posted at the Met Office website (http://appconv.metoffice.com/cold_air_outbreak/constrain_case/home.html). The simulation data in this study are stored at the EUCLIPSE website (www.euclipse.nl/CONSTRAIN/model.tar), with model the (case sensitive) model name, DALES, DHARMA, MONC, Meso-NH, PALM, SAM, or UCLA.

PY - 2019/4/21

Y1 - 2019/4/21

N2 - To quantify the turbulent transport at gray zone length scales between 1 and 10 km, the Lagrangian evolution of the CONSTRAIN cold air outbreak case was simulated with seven large eddy models. The case is characterized by rather large latent and sensible heat fluxes and a rapid deepening rate of the boundary layer. In some models the entrainment velocity exceeds 4 cm/s. A significant fraction of this growth is attributed to a strong longwave radiative cooling of the inversion layer. The evolution and the timing of the breakup of the stratocumulus cloud deck differ significantly among the models. Sensitivity experiments demonstrate that a decrease in the prescribed cloud droplet number concentration and the inclusion of ice microphysics both act to speed up the thinning of the stratocumulus by enhancing the production of precipitation. In all models the formation of mesoscale fluctuations is clearly evident in the cloud fields and also in the horizontal wind velocity. Resolved vertical fluxes remain important for scales up to 10 km. The simulation results show that the resolved vertical velocity variance gradually diminishes with a coarsening of the horizontal mesh, but the total vertical fluxes of heat, moisture, and momentum are only weakly affected. This is a promising result as it demonstrates the potential use of a mesh size-dependent turbulent length scale for convective boundary layers at gray zone model resolutions.

AB - To quantify the turbulent transport at gray zone length scales between 1 and 10 km, the Lagrangian evolution of the CONSTRAIN cold air outbreak case was simulated with seven large eddy models. The case is characterized by rather large latent and sensible heat fluxes and a rapid deepening rate of the boundary layer. In some models the entrainment velocity exceeds 4 cm/s. A significant fraction of this growth is attributed to a strong longwave radiative cooling of the inversion layer. The evolution and the timing of the breakup of the stratocumulus cloud deck differ significantly among the models. Sensitivity experiments demonstrate that a decrease in the prescribed cloud droplet number concentration and the inclusion of ice microphysics both act to speed up the thinning of the stratocumulus by enhancing the production of precipitation. In all models the formation of mesoscale fluctuations is clearly evident in the cloud fields and also in the horizontal wind velocity. Resolved vertical fluxes remain important for scales up to 10 km. The simulation results show that the resolved vertical velocity variance gradually diminishes with a coarsening of the horizontal mesh, but the total vertical fluxes of heat, moisture, and momentum are only weakly affected. This is a promising result as it demonstrates the potential use of a mesh size-dependent turbulent length scale for convective boundary layers at gray zone model resolutions.

KW - cold air outbreak

KW - gray zone

KW - large eddy models

KW - stratocumulus

UR - http://www.scopus.com/inward/record.url?scp=85062351037&partnerID=8YFLogxK

U2 - 10.1029/2018MS001443

DO - 10.1029/2018MS001443

M3 - Article

AN - SCOPUS:85062351037

VL - 11

SP - 597

EP - 623

JO - Journal of Advances in Modeling Earth Systems

JF - Journal of Advances in Modeling Earth Systems

SN - 1942-2466

IS - 3

ER -