Convectively coupled Kelvin waves in aquachannel simulations: 2. Life cycle and dynamical‐convective coupling

Blanco, Joaquin; Nolan, David S.; Mapes, Brian E.

doi:10.1002/2016jd025022

Cited by 6 publications

(7 citation statements)

References 52 publications

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“…This means that for the subsequent identification, filtering, and classification of CCs, the precipitation intensity is not considered further. Details of the CC-tracking algorithm (including CC identification and CC properties) and its performance can be found in Blanco (2018). The approach is similar to that used by Wielicki and Welch (1986), Williams and Houze (1987), and Dias et al 2012, although here the tracking is on time-longitude space.…”

Section: A Local Approach: the Cc-tracking Algorithmmentioning

confidence: 99%

Nonlinear Zonal Propagation of Organized Convection in the Tropics

Blanco

Nolan

Mapes

2019

Journal of the Atmospheric Sciences

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A wide range of the observed variability in the ITCZ is frequently explained in terms of equatorially trapped modes arising from Matsuno’s linear shallow-water model. Here, a series of zonally constant, meridionally symmetric aquachannel WRF simulations are used to study the propagation of tropical cloud clusters (CCs; patches of deep cloudiness and precipitation) in association with eastward-moving super cloud clusters (SCCs), also called convectively coupled Kelvin waves (CCKWs). Two independent but complementary methods are used: the first, from a local approach, involves a CC-tracking algorithm, while the second uses Lagrangian trajectories in a nonlocal framework. We show that the large-scale flow in low to midlevels advects the CCs either eastward or westward depending on model climatology, proximity to the CCKW axis, and latitude. Moreover, for most analyzed cases, sequences of CCs oscillate, describing qualitatively sinusoidal-like paths in longitude–time space, although with sharp transitions from westward to eastward motion due to westerly wind burst activity associated with the CCKWs. We also find that the discrete precipitation elements (CCs) are embedded in continuous tracks of positive moisture anomalies, which are parallel to the Lagrangian trajectories themselves. A conceptual model of the nonlinear SCC–CC interaction is presented.

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Section: A Local Approach: the Cc-tracking Algorithmmentioning

confidence: 99%

Nonlinear Zonal Propagation of Organized Convection in the Tropics

Blanco

Nolan

Mapes

2019

Journal of the Atmospheric Sciences

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“…Other studies have also examined the representation of convectively coupled equatorial waves—particularly Kelvin waves—in general circulation and limited‐area models (e.g., Blanco, Nolan, & Mapes, 2016; Blanco, Nolan, & Tulich, 2016; Dias et al., 2018; Frierson, 2007; Frierson et al., 2011; Lin et al., 2006; Peatman et al., 2018; Seo et al., 2012; Straub et al., 2010). Most of those studies also emphasize the influence of deep cumulus schemes on the structure and variability of Kelvin waves.…”

Section: Introductionmentioning

confidence: 99%

Mean Climate and Tropical Rainfall Variability in Aquaplanet Simulations Using the Model for Prediction Across Scales‐Atmosphere

Ríos-Berríos

Medeiros

Bryan

2020

J Adv Model Earth Syst

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Aquaplanet experiments are important tools for understanding and improving physical processes simulated by global models; yet, previous aquaplanet experiments largely differ in their representation of subseasonal tropical rainfall variability. This study presents results from aquaplanet experiments produced with the Model for Prediction Across Scales-Atmosphere (MPAS-A)-a community model specifically designed to study weather and climate in a common framework. The mean climate and tropical rainfall variability simulated by MPAS-A with varying horizontal resolution were compared against results from a recent suite of aquaplanet experiments. This comparison shows that, regardless of horizontal resolution, MPAS-A produces the expected mean climate of an aquaplanet framework with zonally symmetric but meridionally varying sea-surface temperature. MPAS-A, however, has a stronger signal of tropical rainfall variability driven by convectively coupled equatorial waves. Sensitivity experiments with different cumulus parameterizations, physics packages, and vertical grids consistently show the presence of those waves, especially equatorial Kelvin waves, in phase with lower-tropospheric convergence. Other models do not capture such rainfall-kinematics phasing. These results suggest that simulated tropical rainfall variability depends not only on the cumulus parameterization (as suggested by previous studies) but also on the coupling between physics and dynamics of climate and weather prediction models. Plain Language Summary Continuous improvements of weather and climate models are necessary to advance both our understanding and ability to predict high-impact weather under present and future climates. One particular area requiring model improvements is the representation of tropical rainfall variability happening at subseasonal timescales. With this issue in mind, we produced experiments using a simplified version of a global model called an aquaplanet-an Earth-like water-covered surface devoid of land, topography, sea-ice, or seasons. We first demonstrate that the model used in this study, whichwas specifically designed to study weather and climate, simulates a mean climate that is consistent with other aquaplanet experiments. We also demonstrate that the model is able to capture tropical rainfall variability driven by phenomena called convectively coupled Kelvin waves. Because other models do not capture this variability, we show experiments changing various components of the model to explore the influence of those components on the representation of Kelvin waves. Those experiments demonstrate that, contrary to previous perceptions, the component that approximates deep cumulus clouds is not the only responsible component. Instead, the ability to produce a certain phasing between winds and rainfall appears to explain whether a model can capture Kelvin waves.

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“…In particular, the SCCs associated with the theoretical, nondispersive Kelvin mode were regarded as CCKWs. Recently, Blanco et al (2016) proposed a decoupling mechanism for idealized CCKWs (simulated under zonally homogeneous conditions) in which the SCCs originate and dissipate but the dynamical (Kelvin) component remains mostly unchanged.…”

Section: Introductionmentioning

confidence: 99%

Regional Differences in the Response of Rainfall to Convectively Coupled Kelvin Waves over Tropical Africa

et al. 2019

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The representation of convection remains one of the most important sources of bias in global models, and evaluation methods are needed that show that models provide the correct mean state and variability, both for the correct reasons. Here we develop a novel approach for evaluating rainfall variability due to convectively coupled Kelvin waves (CCKWs) in this region. A phase cycle was defined for the CCKW cycle in OLR and used to composite rainfall anomalies. We characterize the observed (TRMM) rainfall response to CCKWs over tropical Africa in April and evaluate the performance of regional climate model (RCM) simulations: a parameterized convection simulation (P25) and the first pan-Africa convection-permitting simulation (CP4). TRMM mean rainfall is enhanced and suppressed by CCKW activity, and the occurrence of extreme rainfall and dry days is coupled with CCKW activity. Focusing on regional differences, we show for the first time that there is a dipole between West Africa and the Gulf of Guinea involving onshore/offshore shifts in rainfall, and the transition to enhanced rainfall over west equatorial Africa occurs one phase before the transition over east equatorial Africa. The global model used to drive the RCMs simulated CCKWs with mean amplitudes of 75%–82% of observations. The RCMs simulated coherent responses to the CCKWs and captured the large-scale spatial patterns and phase relationships in rainfall although the simulated rainfall response is weaker than observations and there are regional biases that are bigger away from the equator. P25 produced a closer match to TRMM mean rainfall anomalies than CP4 although the response in dry days was more closely simulated by CP4.

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Convectively coupled Kelvin waves in aquachannel simulations: 2. Life cycle and dynamical‐convective coupling

Cited by 6 publications

References 52 publications

Nonlinear Zonal Propagation of Organized Convection in the Tropics

Nonlinear Zonal Propagation of Organized Convection in the Tropics

Mean Climate and Tropical Rainfall Variability in Aquaplanet Simulations Using the Model for Prediction Across Scales‐Atmosphere

Regional Differences in the Response of Rainfall to Convectively Coupled Kelvin Waves over Tropical Africa

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