The Role of Moisture–Convection Feedbacks in Simulating the Madden–Julian Oscillation

Hannah, Walter M.; Maloney, Eric D.

doi:10.1175/2011jcli3803.1

Cited by 104 publications

(123 citation statements)

References 79 publications

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“…The experience with the MJO in GISS Model E2 is consistent with effects that can be produced in many other GCMs by increased entrainment, a stronger trigger for deep convection initiation, or increased rain evaporation (Kim et al 2009;Hannah and Maloney 2011). Why, then, do so many operational GCMs have dry middle tropospheres and poor MJOs?…”

Section: Parameterizing Entrainment In General Circulation Modelssupporting

confidence: 69%

Representing the Sensitivity of Convective Cloud Systems to Tropospheric Humidity in General Circulation Models

Genio

2011

Surv Geophys

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Convective cloud variability on many times scales can be viewed as having three major components: a suppressed phase of shallow and congestus clouds, a disturbed phase of deep convective clouds, and a mature phase of transition to stratiform upper-level clouds. Cumulus parameterization development has focused primarily on the second phase until recently. Consequently, many parameterizations are not sufficiently sensitive to variations in tropospheric humidity. This shortcoming may affect global climate model simulations of climate sensitivity to external forcings, the continental diurnal cycle of clouds and precipitation, and intraseasonal precipitation variability. The lack of sensitivity can be traced in part to underestimated entrainment of environmental air into rising convective clouds and insufficient evaporation of rain into the environment. As a result, the parameterizations produce deep convection too easily while stabilizing the environment too quickly to allow the effects of convective mesoscale organization to occur. Recent versions of some models have increased their sensitivity to tropospheric humidity and improved some aspects of their variability, but a parameterization of mesoscale organization is still absent from most models. Evidence about the effect of these uncertainties on climate change projections suggests that climate modelers should make improved simulation of high and convective clouds as high a priority as better representations of low clouds.

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Section: Parameterizing Entrainment In General Circulation Modelssupporting

confidence: 69%

Representing the Sensitivity of Convective Cloud Systems to Tropospheric Humidity in General Circulation Models

Genio

2011

Surv Geophys

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“…This tilt is seen in observations (e.g., Benedict and Randall 2007) and is generally attributed to shallow convection in advance of the precipitation maximum, leading to a moistening of the lower troposphere and preconditioning the atmosphere for deep convection. The importance of the tilt is unclear, and its appearance with the MJO is irregular in models (Hannah and Maloney 2011). Hannah and Maloney found that the tilt decreases as a function of convective entrainment rate and rainfall reevaporation, and note that it does not appear in an aquaplanet version of the conventional CAM.…”

Section: Moist Static Energy Budgetmentioning

confidence: 99%

Enhanced MJO-like Variability at High SST

2013

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The authors report a significant increase in Madden-Julian oscillation (MJO)-like variability in a superparameterized version of the NCAR Community Atmosphere Model run with high sea surface temperatures (SSTs). A series of aquaplanet simulations exhibit a tripling of intraseasonal outgoing longwave radiation variance as equatorial SST is increased from 268 to 358C. The simulated intraseasonal variability also transitions from an episodic phenomenon to one with a semiregular period of 25 days. Moist static energy (MSE) budgets of composite MJO events are used to diagnose the physical processes responsible for the relationship with SST. This analysis points to an increasingly positive contribution from vertical advection, associated in part with a steepening of the mean vertical MSE profile in the lower troposphere. The change in MSE profile is a natural consequence of increasing SST while maintaining a moist adiabat with a fixed profile of relative humidity. This work has implications for tropical variability in past warm climates as well as anthropogenic global warming scenarios.

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“…The version we use has a minimum fractional entrainment threshold that has been documented to substantially improve intraseasonal variability with Arakawa-Schubert style convective parameterizations (e.g., Tokioka et al 1988;Lin et al 2008;Hannah and Maloney 2010). All other physical parameterizations of the NCAR CAM3.1 remain unchanged (Collins et al 2006).…”

Section: Model Descriptionmentioning

confidence: 99%

Effect of SST Distribution and Radiative Feedbacks on the Simulation of Intraseasonal Variability in an Aquaplanet GCM

Landu

Maloney

2011

Journal of the Meteorological Society of Japan

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An aquaplanet atmospheric general circulation model with prescribed sea surface temperatures (SST) is used to provide insight on tropical intraseasonal variability. Previous work showed that a zonally asymmetric SST distribution that resembles observations but with the meridional SST gradient reduced to one-quarter of its observed value poleward of 10 • , could produce a robust Madden-Julian oscillation (MJO) with 50-day periodicity and amplitude greater than observations in this model. Wind-evaporation feedback was shown to be necessary to destabilize the model MJO. This present work extends these aquaplanet sensitivity experiments to examine the impact of other SST basic states on intraseasonal variability, and also determines whether cloud-radiative and moisture-radiative feedbacks are important for destabilizing the model MJO.A zonally symmetric model with reduced meridional SST gradient produces dominant intraseasonal power at too short of timescale (∼30 days) and reduced amplitude relative to the zonally asymmetric simulation, suggesting that basic state zonal asymmetries and surface mean westerlies are important for producing a realistic MJO. The intraseasonal mode in the zonally symmetric model resembles the WISHE mode of linear theory, with wind speed and latent heat flux anomaly maxima occurring in surface easterly anomalies to the east of maximum convection, unlike the zonally asymmetric model in which latent heat fluxes maximize near and to the west of convection like in observations. An experiment with in which longwave radiative heating is prescribed to be near climatology suggests that both radiative and wind-evaporation feedbacks may help to destabilize the model MJO.

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The Role of Moisture–Convection Feedbacks in Simulating the Madden–Julian Oscillation

Cited by 104 publications

References 79 publications

Representing the Sensitivity of Convective Cloud Systems to Tropospheric Humidity in General Circulation Models

Representing the Sensitivity of Convective Cloud Systems to Tropospheric Humidity in General Circulation Models

Enhanced MJO-like Variability at High SST

Effect of SST Distribution and Radiative Feedbacks on the Simulation of Intraseasonal Variability in an Aquaplanet GCM

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