Modes of Tropical Variability under Convective Adjustment and the Madden–Julian Oscillation. Part II: Numerical Results

Yu, Jia‐Yuh; Neelin, J. David

doi:10.1175/1520-0469(1994)051<1895:motvuc>2.0.co;2

Cited by 96 publications

(124 citation statements)

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“…While the pressure velocity is centered around the base point in each case (where the precipitation is maximum), the temperature anomaly is shifted eastward with longer relaxation time. This phase shift of the temperature anomalies is in accordance with the prediction of Emanuel (1993) (see also Emanuel et al 1994;Neelin and Yu 1994;Yu and Neelin 1994), which shows that an increased convective relaxation time acts as a damping for evaporation-wind feedback modes. At small convective relaxation time, the temperature is nearly in quadrature with the pressure velocity (and is actually slightly positively correlated with the upward motion); however at higher relaxation time this phase relationship is disrupted in such a way that the temperature is more anticorrelated with the upward motion.…”

Section: Varying Convective Relaxation Timesupporting

confidence: 90%

Convectively Coupled Kelvin Waves in an Idealized Moist General Circulation Model

Frierson

2007

J. Atmos. Sci.

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The dynamics of convectively coupled Kelvin waves and their dependence on convection scheme parameters are studied within a simplified moist general circulation model. The model consists of the primitive equations on the sphere over zonally symmetric aquaplanet, slab mixed layer ocean boundary conditions, and idealized physical parameterizations including gray radiative transfer and a simplified Betts-Miller convection scheme. This framework allows the authors to study the dependence of Kelvin waves on quantities such as the gross moist stability in a clean manner.A control simulation with the model produces convectively coupled Kelvin waves that are remarkably persistent and dominate the variability within the Tropics. These waves propagate with an equivalent depth of Ϸ40 m. Linear regression analysis with respect to a Kelvin-filtered time series shows that the waves are driven by evaporation-wind feedback and have structures broadly consistent with theoretical predictions for Kelvin waves.Next, the determination of the speed and structure of the Kelvin waves is studied by examining the response of the waves to changes in convection scheme parameters. When the convective relaxation time is lengthened, the waves are damped and eventually are completely eliminated. The propagation speed additionally increases with longer relaxation time. Then changes to a convection scheme parameter that essentially controls the fraction of convective versus large-scale precipitation are examined. When some large-scale precipitation occurs, the waves increase in strength, propagate more slowly, and move to larger scales. However, when mostly large-scale precipitation occurs, the Kelvin wave disappears, and the Tropics are dominated by tropical storm-like variability. The decrease in speed is related here to the gross moist stability of the atmosphere, which is reduced with increased large-scale precipitation.

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Section: Varying Convective Relaxation Timesupporting

confidence: 90%

Convectively Coupled Kelvin Waves in an Idealized Moist General Circulation Model

Frierson

2007

J. Atmos. Sci.

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“…This result is contrary to the wave-CISK mechanism (Hayashi, 1970), through which tropical transient waves coupled with moist convection become unstable, even in the absence of evaporation-wind feedback. It is, however, consistent with convective cancellation (Emanuel, 1987) based on the convective-neutrality hypothesis and EWF instability theory (Neelin and (c)1997, Meteorological Society of Japan Yu and Neelin, 1994) based on the BettsMiller parameterization (Betts and Miller, 1986). As schematically illustrated in Fig.…”

Section: Introductionsupporting

confidence: 85%

United Mechanisms for the Generation of Low- and High-Frequency Tropical Waves. Part II

Hayashi¹,

Golder²

1997

Journal of the Meteorological Society of Japan

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It is assumed that low-and high-frequency tropical waves are generated by the united mechanisms consisting of the evaporation-wind feedback (EWF), saturation-triggering (ST), and lateral-triggering mechanisms. Through the EWF mechanism, some waves become unstable owing to evaporation-wind feedback. Through the ST mechanism, other waves are triggered by the intermittent onset of moist convection, upon saturation, to neutralize any pre-existing conditionally unstable stratification. These mechanisms are theoretically interpreted by partitioning moist connective adjustment into two consecutive processes of diagnostic and prognostic adjustments. The two processes respectively restore and maintain convective equilibrium, and are crucial to the ST and EWF mechanisms.As a step to toward a unified theory, EWF instability is examined by the use of a theoretical Kelvin-wave model, which incorporates only the prognostic-adjustment process in the linearized perturbation equations, thereby excluding the ST mechanism. The solutions indicate that wave instability results from the EWF mechanism and not from the wave-CISK mechanism. For a plausible choice of adjustable parameters, one strongly unstable mode corresponds to the observed 40-50-day oscillation, while two weakly unstable modes correspond to the observed 25-30-day and 10-20-day oscillations.These results are compared with those from the numerical experiments conducted in Part I, using a nonlinear model incorporating the original moist convective adjustment scheme. It is then speculated that the 40-50-and 25-30-day modes can strongly grow through the linear and nonlinear EWF mechanisms respectively, while the 10-20-day mode can strongly amplify through the ST mechanism.

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“…Based on the analytical solutions derived from the Betts-Miller moist convective adjustment scheme (Betts and Miller 1993), typical vertical structures of temperature, moisture, and winds for deep convection are used as leading basis functions for a Galerkin expansion (Neelin and Yu 1994;Yu and Neelin 1994). The resulting primitive equation model makes use of constraints on the flow by quasi-equilibrium thermodynamic closures and is referred to as QTCM1 (a quasi-equilibrium tropical circulation model with a single vertical structure of temperature and moisture for deep convection).…”

Section: B Modelmentioning

confidence: 99%

“…In (6), hv› p hi is roughly proportional to the rising motion associated with convection (e.g., Yu and Neelin 1997). Based on (6), the convergence of the columnintegrated MSE, 2hv› p hi 2 hv Á = (T 1 q)i, must be balanced by the net heat flux into the atmospheric column, F net (Chou et al 2001;Chou and Neelin 2003).…”

Section: The Wet Phase a The Moisture And Moist Static Energy Budgetsmentioning

confidence: 99%

Annual Cycle of Rainfall in the Western North Pacific and East Asian Sector

et al. 2009

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The annual cycle of precipitation over the western North Pacific and East Asian (WNP-EA) sector has five major periods: spring, the first and second wet periods, fall, and winter. In this study, processes that induce precipitation in each period are examined from a large-scale point of view. The wet phase over this sector has two distinct periods, which are dominated by the Asian summer monsoon circulation induced by the land-ocean contrast of net energy into the atmospheric column (F net ). In the first wet period, the pre-mei-yu/mei-yu rainband is directly associated with a moisture flux convergence caused by the southwesterly Asian summer monsoon flow and the southeasterly trade winds, and indirectly associated with a dynamic feedback induced by this horizontal moisture convergence. The tropical convection, in the meantime, is associated with a rising motion that is induced by positive F net . In the second wet period, the WNP summer monsoon gyre dominates the rainfall of this region, which is partially associated with warmer local sea surface temperature (SST) via positive F net . The land-sea contrast of F net and the atmosphere-ocean interaction also play an important role in establishing the monsoon gyre. The dry phase over the WNP-EA region is the winter period in which precipitation is associated with winter storm activities and large-scale lifting associated with a pressure surge. In the two transition phases, due to a difference in heat capacity, the atmosphere and ocean have distinct impacts on precipitation, albeit similar solar insolations during the two periods. In the spring period, the atmospheric condition is favorable for convection, while the ocean surface is relatively colder, so the horizontal moisture advection associated with the westward extent of the Pacific subtropical high, which is different from a typical winter frontal system, is a major source for the spring rain. In the fall period, however, the atmospheric conditions dominated by the Asian winter monsoon circulation suppress convection, while relatively warmer SST still maintains tropical convection over the southern part of the WNP-EA region. Over the northern part of the WNP-EA region, the fall precipitation is associated with frontal systems, similar to those in winter.

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Modes of Tropical Variability under Convective Adjustment and the Madden–Julian Oscillation. Part II: Numerical Results

Cited by 96 publications

References 0 publications

Convectively Coupled Kelvin Waves in an Idealized Moist General Circulation Model

Convectively Coupled Kelvin Waves in an Idealized Moist General Circulation Model

United Mechanisms for the Generation of Low- and High-Frequency Tropical Waves. Part II

Annual Cycle of Rainfall in the Western North Pacific and East Asian Sector

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