Cloud-radiation feedback and atmosphere-ocean coupling in a stochastic multicloud model

Abstract

a b s t r a c tDespite recent advances in supercomputing, current general circulation models (GCMs) have significant problems in representing the variability associated with organized tropical convection. Furthermore, due to high sensitivity of the simulations to the cloud radiation feedback, the tropical convection remains a major source of uncertainty in long-term weather and climate forecasts. In a series of recent studies, it has been shown, in paradigm two-baroclinic-mode systems and in aquaplanet GCMs, that a stochastic multicloud convective parameterization based on three cloud types (congestus, deep and stratiform) can be used to improve the variability and the dynamical structure of tropical convection, including intermittent coherent structures such as synoptic and mesoscale convective systems. Here, the stochastic multicloud model is modified with a parameterized cloud radiation feedback mechanism and atmosphere-ocean coupling. The radiative convective feedback mechanism is shown to increase the mean and variability of the Walker circulation. The corresponding intensification of the circulation is associated with propagating synoptic scale systems originating inside of the enhanced sea surface temperature area. In column simulations, the atmosphere ocean coupling introduces pronounced low frequency convective features on the time scale associated with the depth of the mixed ocean layer. However, in the presence of the gravity wave mixing of spatially extended simulations, these features are not as prominent. This highlights the deficiency of the column model approach at predicting the behavior of multiscale spatially extended systems. Overall, the study develops a systematic framework for incorporating parameterized radiative cloud feedback and ocean coupling which may be used to improve representation of intraseasonal and seasonal variability in GCMs.

Improving synoptic and intraseasonal variability in CFSv2 via stochastic representation of organized convection

“…One major concern of CFSv2 climate is an unrealistically cold middle troposphere [ Saha et al , ] arguably due to the lack of proper stratiform cloud radiative forcing feedback [ Frenkel et al , ]. Figures Ig and Ih show the bias in the two simulated (zonally averaged) temperature fields.…”

“…Primarily, we would like to investigate the simulation of convectively coupled equatorial waves in the CFSsmcm. Also, interactive radiation at the subgrid scale will be considered following the work of Frenkel et al []. The fact that SMCM is built on a robust mathematical framework makes model improvements more transparent.…”

Implementation and calibration of a stochastic multicloud convective parameterization in the NCEP Climate Forecast System (CFSv2)

“…A notable feature of the CFSsmcm is the resilience of its mean climate, with respect to changes in parameter values, as evidenced from the overlapping temperature and moisture cycles in Figure 1. We suspect that the systematic cooling/drying of the midtroposphere in CFSsmcm is perhaps due to the lack of radiation feedback due to the stratiform clouds [Frenkel et al, 2015]. The fact that all the temperature and moisture annual means in Figure 1 are grouped together separate from the observed (reanalysis) profiles indicates that the convective parameterization is not the only factor responsible for all the climate model biases.…”

“…The fact that all the temperature and moisture annual means in Figure 1 are grouped together separate from the observed (reanalysis) profiles indicates that the convective parameterization is not the only factor responsible for all the climate model biases. We suspect that the systematic cooling/drying of the midtroposphere in CFSsmcm is perhaps due to the lack of radiation feedback due to the stratiform clouds [Frenkel et al, 2015]. Figure 2 shows the annual mean precipitation distributions for TRMM and the 5 year CFSv2 and CFSsmcm runs listed in Table 3.…”

Seasonal Synchronization of a Simple Stochastic Dynamical Model Capturing El Niño Diversity

“…In addition to the above processes, current theory emphasizes the role of convective activity and cloud cover as a main contender for explaining the ENSO seasonal synchronization (Zebiak and Cane 1987;Jin et al 2006;Dommenget and Yu 2016). The convective response to ENSO SST anomalies in the tropical Pacific can significantly affect the SST in return through exchanges in radiative and turbulent heat fluxes, mainly incoming solar shortwave radiation as well as outgoing latent heat flux (Lloyd et al 2012;Frenkel et al 2015). This so-called cloud radiative feedback usually tends to dampen the ENSO variability, as was analyzed in a number of studies (e.g., Waliser et al 1994;Wang and McPhaden 2001;Dommenget et al 2014), but is however strongly state dependent and seasonal.…”