Multiple and spin off initiation of atmospheric convectively coupled Kelvin waves

Baranowski, Dariusz B.; Flatau, Maria; Flatau, Piotr J.; Schmidt, Jerome M.

doi:10.1007/s00382-016-3487-7

Cited by 5 publications

(3 citation statements)

References 51 publications

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“…Flood onset and termination times were identified automatically using a surge in tweets, that is, extremes in tendencies of tweet number time-series. Floods which occurred within 3 days of one another were considered part of a single event, a limit imposed by the minimal re-occurrence time of a CCKW 36 and also close to the duration of the MJO precipitating phase affecting a single location 15 . Flood events identified using this technique match the rapid increase in tweets at the beginning of a flood (red lines in Fig.…”

Section: Resultsmentioning

confidence: 99%

Social-media and newspaper reports reveal large-scale meteorological drivers of floods on Sumatra

Baranowski

Flatau

et al. 2020

Nat Commun

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Floods are a major contributor to natural disasters in Sumatra. However, atmospheric conditions leading to floods are not well understood due, among other factors, to the lack of a complete record of floods. Here, the 5 year flood record for Sumatra derived from governmental reports, as well as from crowd-sourcing data, based on Twitter messages and local newspapers’ reports, is created and used to analyze atmospheric phenomena responsible for floods. It is shown, that for the majority of analyzed floods, convectively coupled Kelvin waves, large scale precipitation systems propagating at ∼12 m/s along the equator, play the critical role. While seasonal and intraseasonal variability can also create conditions favorable for flooding, the enhanced precipitation related to Kelvin waves was found in over 90% of flood events. In 30% of these events precipitation anomalies were attributed to Kelvin waves only. These results indicate the potential for increased predictability of flood risk.

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Section: Resultsmentioning

confidence: 99%

Social-media and newspaper reports reveal large-scale meteorological drivers of floods on Sumatra

Baranowski

Flatau

et al. 2020

Nat Commun

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“…The next step is to choose the possible initiation location of the MJO events (Zhang and Yoneyama 2017). With an exclusive preference over the warm ocean, the MJO initiation may occur over the tropical IO, MC, EWP, and the tropical Atlantic (M08; Baranowski et al 2017). We examine the three-dimensional (3-D) distribution of the variance associated with the 90-day highpass-filtered specific humidity, with a tacit assumption that the role of low-frequency (> 90 days) basic state is minor in triggering the large-scale deep convective initiation on the intraseasonal time scale (20-90 days).…”

Section: Assuming That Moisture Triggers Primary Mjo Initiationmentioning

confidence: 99%

Nonlinear optimal moisture perturbations as excitation of primary MJO events in a hybrid coupled climate model

Wei

Ren

et al. 2019

Clim Dyn

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Although the moisture feedback has been well known to be essential in the Madden-Julian Oscillation (MJO) dynamics, whether its pre-moistening effect plays a key role in exciting the onset of primary MJO events, as has been confirmed in the successive initiation, remains elusive. In this study, using a hybrid coupled climate model that has a good fidelity in simulating the intraseasonal variability, we develop a new framework of methodology to investigate the nonlinear excitation of primary MJO event, of which the key achievement is the successful implementation of the conditional nonlinear optimal perturbation (CNOP). In an application of this new framework, the CNOP-type moisture perturbations are calculated for the pre-chosen non-MJO reference states and generally favor a moistening in the equatorial region while drying in the poleward. Comparisons of the model simulation with observation give credibility to the existence of moisture signals several weeks before some primary MJO events. A suite of numerical experiments confirms that the CNOPs of moisture can contribute to the excitation and propagation of strong primary MJO events while random perturbations cannot. The moisture budget analysis further reveals the central importance of the horizontal moisture advection, especially the nonlinearly upscaled moisture transports associated with the high-frequency disturbances on the quasi-3-4-day and 6-8-day synoptic time scales, in supporting the nonlinear excitation of the primary MJO events. The subgrid-scale processes of evaporation, condensation and eddy transport of moisture are found to be critical for the pre-moistening effect in the boundary layer as well. This study directly supports the vital importance of the moisture perturbations, which are characterized by a particular pattern concentrated at low levels, to the nonlinear growth and propagation of the primary MJO events.Publisher's Note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

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“…CCKWs are responsible for high‐impact weather (Ferrett et al ., 2020; Lubis and Respati, 2021), including major flooding incidents (Baranowski et al ., 2020; Latos et al ., 2021). They can be identified and skilfully forecast in real time in atmospheric models (Yang et al ., 2021), but also have a significant, possibly two‐way, interaction with the underlying ocean (Baranowski et al ., 2016a; Baranowski et al ., 2017).…”

Section: Introductionmentioning

confidence: 99%

Dynamical propagation and growth mechanisms for convectively coupled equatorial Kelvin waves over the Indian Ocean

Matthews

2021

Quart J Royal Meteoro Soc

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Convectively coupled equatorial Kelvin waves (CCKWs) are high-impact tropical weather systems that can lead to severe flooding over the Maritime Continent. Here, a vorticity budget for CCKWs over the Indian Ocean is constructed using reanalysis data, to identify the basic mechanisms of eastward propagation and growth. The budget is reasonably well closed, with a small residual/subgrid-scale term. In the lower troposphere, CCKWs behave like strongly modified theoretical equatorial Kelvin waves. Vortex stretching, from the divergence of the Kelvin wave acting on planetary vorticity (the −fD term), is the sole mechanism by which the vorticity structure of a theoretical Kelvin wave propagates eastward. In the lower and middle troposphere, this term is also the key mechanism for the eastward propagation of CCKWs but, due to subtleties in its structure and phasing linked to a combination of modal structures, it also contributes to growth. Unlike in the theoretical Kelvin wave, other vorticity source terms also play a role in the propagation and growth of CCKWs. In particular, vortex stretching from relative vorticity (the −𝜁D term) is the largest source term, and this leads strongly to growth, through interactions between the background and perturbation vorticity and divergence. Horizontal vorticity advection by the background flow contributes to propagation, and also acts to retard the growth of the CCKW. The sum of the source terms in this complex vorticity budget leads to eastward propagation and growth of CCKWs. The structure and vorticity budget of CCKWs in the upper troposphere is quite unlike that of a Kelvin wave, and appears to arise as a forced response to the lower-tropospheric structure. The implications for numerical weather prediction and climate simulations are discussed.

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Multiple and spin off initiation of atmospheric convectively coupled Kelvin waves

Abstract: off equatorial circulation. In addition a theoretical study of the sequential Kelvin waves is performed using a shallow water model. Finally, conceptual models of these two types of initiations are proposed.

Cited by 5 publications

References 51 publications

Social-media and newspaper reports reveal large-scale meteorological drivers of floods on Sumatra

Social-media and newspaper reports reveal large-scale meteorological drivers of floods on Sumatra

Nonlinear optimal moisture perturbations as excitation of primary MJO events in a hybrid coupled climate model

Dynamical propagation and growth mechanisms for convectively coupled equatorial Kelvin waves over the Indian Ocean

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