Dynamics of Super Cloud Clusters, Westerly Wind Bursts, 30-60 Day Oscilations and ENSO: An Unified View

Lau, K.-M.; Li, Peng; Sui, Chung‐Hsiung; Nakazawa, Tetsuo

doi:10.2151/jmsj1965.67.2_205

Cited by 115 publications

(72 citation statements)

References 19 publications

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“…3) is a key for the cyclogenesis, consistent with the observations (Lau et al 1989;Chen et al 1996). Panel (d) indicates that the genesis marked by the black diamond is likely to be prompted by the trough (cyclonic vorticity; black lines) at 200 hPa that is present quasi-persistently in 15 20°N.…”

Section: Resultssupporting

confidence: 82%

A Simulated Preconditioning of Typhoon Genesis Controlled by a Boreal Summer Madden-Julian Oscillation Event in a Global Cloud-system-resolving Model

Oouchi

Noda

Satoh

et al. 2009

SOLA

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A preconditioning of a typhoon genesis over the North Western Pacific by an Madden-Julian Oscillation (MJO) event is simulated in a boreal summer numerical experiment conducted using a global cloud-systemresolving model. The simulation highlights the importance of the following processes in the typhoon genesis that were not clearly captured in the conventional general circulation models: as the MJO propagates over that region, the easterly shear (with an enhanced lowlevel westerly) of the western branch of the MJO's circulation moderates the climatological westerly shear that is otherwise persistent and inhibits cyclogenesis there. Meanwhile, its attendant cyclonic vorticity from the westerly region migrates northward, causing the genesis to occur. The trough in the upper troposphere at 15° 20°N is found to contribute to the genesis. The result demonstrates the performance of a global cloudsystem-resolving model at predicting tropical cyclogenesis associated with the MJO in the North Western Pacific during the active typhoon season in boreal summer. IntroductionImproving the prediction of tropical cyclogenesis has broad socioeconomic impacts. The need for improvement has been high in the weather forecasting field and will be higher in the future, greenhousewarmed climate condition, when tropical cyclones are projected to become more intense (IPCC 2007) and destructive. Our current understanding of the genesis process remains fragmentary despite the expanded observational network in the tropics after a seminal article (Yanai 1964) on the issue. It was in the past few decades that observational studies suggested a possible link between the MJO, a planetary-scale and quasi-periodic tropical weather event, and statistics of tropical cyclogenesis over some oceanic basins, including the North Western Pacific (Nakazawa 1986).In terms of the modeling approach, both the MJO (Lin et al. 2006) and tropical cyclogenesis are elusive factors. Clouds drive both phenomena, and difficulty in handling a cloud spanning less than the grid spacing of a given model has always hampered our understanding of the phenomena. Atmospheric general circulation models (GCMs) typically use a grid spacing of O (100 km) or so to cover the globe, and the simulated cloud disturbances are too fuzzy to pick up anything as small as a tropical cyclone in the genesis stage and the clouds embedded in an MJO. A way to avoid this difficulty is cumulus convection parameterisation, which was typically subject to uncertainties when implemented in conventional GCMs. The most compelling difficulty is its inability to represent mechanisms associated with mesoscale convection, a key convective element of O (10 km) scale in tropical cyclones (Yamasaki 1986(Yamasaki , 2006) and the MJO (Oouchi and Yamasaki 2001).Alternatively, a "global" cloud-system-resolving model (GCSRM) was suggested. The advent of the Earth Simulator facilitated this computationally intensive calculation. The Nonhydrostatic ICosahedral Atmospheric Model (NICAM) Tomita and Satoh 2004) i...

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Section: Resultssupporting

confidence: 82%

A Simulated Preconditioning of Typhoon Genesis Controlled by a Boreal Summer Madden-Julian Oscillation Event in a Global Cloud-system-resolving Model

Oouchi

Noda

Satoh

et al. 2009

SOLA

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“…These scales are similar to those from other observational studies (Nakazawa, 1988;Lau et al, 1989;Nitta et al, 1992). Thus, if the super clusters are organized in a wave structure, the wave period is<20 days.…”

Section: Discussionsupporting

confidence: 88%

Boundary Layer Radar Observations of the Passage of the Convection Center over Serpong, Indonesia (6°S, 107°E) during the TOGA COARE Intensive Observation Period

Hashiguchi

Fukao

Yamanaka

et al. 1995

Journal of the Meteorological Society of Japan

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“…Needless to say, non-linear models are required that can simulate, at least, cloud clusters embedded in SCC (Nakazawa, 1988;Lau et al, 1991) in order to clarify whether or not Kelvin wave-CISK needs surface friction. Numerical experiments with hydrostatic models that include parameterized convection (with or without surface friction) have been performed by, for instance, Itoh (1989), Lau et al (1989), Chao and Lin (1994), Wang and Li (1994), and Kuma (1994). On the other hand, studies with non-hydrostatic, two-dimensional cloud-resolving models have been made by Nakajima (1994, Doctoral thesis at Univ.…”

Section: Discussion and Remarksmentioning

confidence: 99%

Kelvin Wave-CISK Controlled by Surface Friction

Ohuchi

Yamasaki

1997

Journal of the Meteorological Society of Japan

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As a step toward an understanding of the mechanism of super cloud cluster (SCC), the effect of surface friction on the instability of Kelvin wave is discussed, together with the condition of the vertical profile of parameterized convective heating. In this paper (Part I), linear theory is developed with an equatorial beta-plane model in which the amount of convective heating is assumed to be proportional to the vertical velocity at the top of the boundary layer. Results from the eigenvalue problem suggest that the effect of surface friction is, at least under such parameterization, indispensable for essential understanding of SCC; this study is along the same line as Wang (1988) with respect to the importance of surface friction.Issue is focused on three unstable modes. One is a stationary mode excited with much heating at lower levels, and identified with conditional instability of the first kind (CIFK). The other two are Kelvin modes that contrast with each other; one is destabilized by enough heating at upper levels, even without surface friction (referred to as NFK: Non-Frictional Kelvin mode), and the other is destabilized by moderate heating at lower levels under the control of surface friction (FK: Frictional Kelvin mode). NFK has phase velocities of more than 10ms-1, and its growth rates are on the order of 10-3s-1 at small wavelengths. On the contrary, FK is characterized by smaller phase velocities of less than 10ms-l, and by only slight dependence of its growth rates on wavelength. In addition, the convergence in the boundary layer exhibits a phase shift slightly eastward relative to the convergence aloft; this is the key feature that induces effective feedback between convection and the wave.In view of the large phase velocity and the small preferred scale, NFK may be interpreted as a Kelvin mode of the type that has been treated in many previous studies on SCC. Difficulties in explaining the observed phase velocity and preferred scale of SCC are inherent in NFK. By contrast, FK can give a realistic phase velocity and preferred scale, and clear up major difficulties in the previous studies. Inclusion of surface friction is expected not only to serve as the missing link of the past linear theories of SCC, but also as a basis of future non-linear experiments with explicit moisture processes.

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Dynamics of Super Cloud Clusters, Westerly Wind Bursts, 30-60 Day Oscilations and ENSO: An Unified View

Cited by 115 publications

References 19 publications

A Simulated Preconditioning of Typhoon Genesis Controlled by a Boreal Summer Madden-Julian Oscillation Event in a Global Cloud-system-resolving Model

A Simulated Preconditioning of Typhoon Genesis Controlled by a Boreal Summer Madden-Julian Oscillation Event in a Global Cloud-system-resolving Model

Boundary Layer Radar Observations of the Passage of the Convection Center over Serpong, Indonesia (6°S, 107°E) during the TOGA COARE Intensive Observation Period

Kelvin Wave-CISK Controlled by Surface Friction

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Dynamics of Super Cloud Clusters, Westerly Wind Bursts, 30-60 Day Oscilations and ENSO: An Unified View

Cited by 115 publications

References 19 publications

A Simulated Preconditioning of Typhoon Genesis Controlled by a Boreal Summer Madden-Julian Oscillation Event in a Global Cloud-system-resolving Model

A Simulated Preconditioning of Typhoon Genesis Controlled by a Boreal Summer Madden-Julian Oscillation Event in a Global Cloud-system-resolving Model

Boundary Layer Radar Observations of the Passage of the Convection Center over Serpong, Indonesia (6&deg;S, 107&deg;E) during the TOGA COARE Intensive Observation Period

Kelvin Wave-CISK Controlled by Surface Friction

Contact Info

Product

Resources

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Boundary Layer Radar Observations of the Passage of the Convection Center over Serpong, Indonesia (6°S, 107°E) during the TOGA COARE Intensive Observation Period