Can We Use Single‐Column Models for Understanding the Boundary Layer Cloud‐Climate Feedback?

Abstract

This study explores how to drive Single‐Column Models (SCMs) with existing data sets of General Circulation Model (GCM) outputs, with the aim of studying the boundary layer cloud response to climate change in the marine subtropical trade wind regime. The EC‐EARTH SCM is driven with the large‐scale tendencies and boundary conditions as derived from two different data sets, consisting of high‐frequency outputs of GCM simulations. SCM simulations are performed near Barbados Cloud Observatory in the dry season (January–April), when fair‐weather cumulus is the dominant low‐cloud regime. This climate regime is characterized by a near equilibrium in the free troposphere between the long‐wave radiative cooling and the large‐scale advection of warm air. In the SCM, this equilibrium is ensured by scaling the monthly mean dynamical tendency of temperature and humidity such that it balances that of the model physics in the free troposphere. In this setup, the high‐frequency variability in the forcing is maintained, and the boundary layer physics acts freely. This technique yields representative cloud amount and structure in the SCM for the current climate. Furthermore, the cloud response to a sea surface warming of 4 K as produced by the SCM is consistent with that of the forcing GCM.

Investigating the Diurnal Evolution of the Cloud Size Distribution of Continental Cumulus Convection Using Multiday LES

“…The 24-h-long simulations are initialized and driven by time-varying boundary conditions and large-scale forcings derived from the Integrated Forecasting System (IFS) of ECMWF. The method as applied here to drive the LES model was first described by Neggers et al (2012), and was recently used in slightly modified form in the study by Gesso and Neggers (2018). All fields provided to the LES as input are based on two analysis fields per day, at 0000 and 1200 UTC, supplemented by short-range forecast fields to cover the intermediate time points at 3, 6, and 9 h. This effectively yields a forcing dataset covering 24 h at 3-h time resolution, which is assumed sufficient to resolve diurnal and synoptic signals in the large-scale forcing.…”

Insensitivity of the Cloud Response to Surface Warming Under Radical Changes to Boundary Layer Turbulence and Cloud Microphysics: Results From the Ultraparameterized CAM

“…A sensitivity test that isolates these microphysical impacts from UP's grid resolution confirms that the microphysical settings are mostly responsible for the differences between SP and UP cloud feedback.Recent global simulations have predicted mostly positive and occasionally negative low cloud feedbacks with different magnitudes (Bretherton, 2015). Other studies have focused on cloud feedbacks in regional/single-column models (Dal Gesso & Neggers, 2018) or on only a particular cloud type. Xu et al (2010) studied the low cloud feedback to a change in sea surface temperature (SST) in the range of +4 K to an extreme +14 K. In a limited-area simulation of subtropical boundary layer cloud, they showed that the cloud feedback simulated by their large eddy simulation (LES), for this large range of SST increases is negative and is in the range of −0.7 to −5.2 W/m 2 /K with mostly negative contribution (−1.5 to 0.5 W/m 2 /K) from clear-sky feedback.…”

A Library of Large‐Eddy Simulations Forced by Global Climate Models

“…cfSites includes high‐frequency output at different locations of instrumented sites and field campaigns, as well as a number of climate regimes where the inter‐model spread of cloud feedbacks is large (Bony et al., 2011). Dal Gesso and Neggers (2018) have used large‐scale forcings derived from the cfSites data to drive single column models and explored the boundary layer cloud response to climate change. The cfSites data has also been used to investigate the diurnal cycle of cloud feedbacks in GCMs (Webb et al., 2015).…”