Interaction between dynamics and thermodynamics during tropical cyclogenesis

Gjorgjievska, Saska; Raymond, David J.

doi:10.5194/acpd-13-18905-2013

Cited by 27 publications

(73 citation statements)

References 34 publications

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“…Based on previous work on tropical cyclone formation, e.g., Gjorgjievska and Raymond [2014], the dimensionality of the causal parameter space is vastly reduced by assuming that the saturation fraction and instability index (both defined in section 2) characterize the temperature and humidity profiles. Journal of Advances in Modeling Earth Systems 10.1002/2015MS000595…”

Section: Resultsmentioning

confidence: 99%

“…In this section, we compare the predictions derived from the model to observations of convection in 37 cases of tropical disturbances in the western Pacific (Tropical Cyclone Structure experiment (TCS08)) [Elsberry and Harr, 2008] Journal of Advances in Modeling Earth Systems 10.1002/2015MS000595 Caribbean (Pre-Depression Investigation of Cloud-Systems in the Tropics (PREDICT)) [Montgomery et al, 2012]. These observations are taken from dropsonde grids over domains a few degrees in diameter with resolution of order one degree and are described by Gjorgjievska and Raymond [2014]. In these cases rainfall was not actually measured.…”

Section: Tcs08 and Predictmentioning

confidence: 99%

“…This dependence is important for the development of both tropical cyclones and intraseasonal oscillations. Komaromi, 2013;Gjorgjievska and Raymond, 2014;. In particular, increased saturation fraction (a kind of column-averaged relative humidity) and decreased low to midlevel moist convective instability (characterized by the instability index) are associated with an increase in the mean convective precipitation rate in developing tropical storms.…”

Section: Introductionmentioning

confidence: 99%

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Predicting convective rainfall over tropical oceans from environmental conditions

Raymond

Flores

2016

J Adv Model Earth Syst

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A cloud resolving model in spectral weak temperature gradient mode is used to explore systematically the response of mean convective rainfall to variations tropical environmental conditions. A very large fraction of the variance in modeled rainfall is explained by three variables, the surface moist entropy flux, the instability index (a measure of low to midlevel moist convective instability), and the saturation fraction (a kind of column-averaged relative humidity). The results of these calculations are compared with the inferred rainfall from 37 case studies of convection over the tropical west Pacific, the tropical Atlantic, and the Caribbean, as well as in the NCEP FNL analysis and the ERA-Interim reanalysis. The model shows significant predictive skill in all of these cases. However, it consistently overpredicts precipitation by about a factor of three, due possibly to simplifications made in the model. These calculations also show that the saturation fraction is not a predictor of rainfall in the case of strong convection. Instead, saturation fraction covaries with the precipitation as a result of a moisture quasi-equilibrium process.

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Section: Resultsmentioning

confidence: 99%

Section: Tcs08 and Predictmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Predicting convective rainfall over tropical oceans from environmental conditions

Raymond

Flores

2016

J Adv Model Earth Syst

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“…In this framework, a layer emerges where a prototype vortex is protected from dry air intrusion, able to concentrate vorticity and convective heating, and eventually split from its parent wave and grow into a mature TC. Several theories focus on the role of a preceding midlevel vortex in facilitating development of vorticity at lower levels, including ideas presented by Bister and Emanuel (), Ritchie and Holland (), Raymond et al (), and Gjorgjievska and Raymond (). These studies differ on the dominant mechanisms by which a midlevel vortex leads to spin‐up at lower levels, differences as fundamental as whether dynamic or thermodynamic factors play a leading order role.…”

Section: Introductionmentioning

confidence: 99%

Tropical Cyclogenesis From Self‐Aggregated Convection in Numerical Simulations of Rotating Radiative‐Convective Equilibrium

Carstens

Wing

2020

J Adv Model Earth Syst

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In a modeled environment of rotating radiative-convective equilibrium (RCE), convective self-aggregation may take the form of spontaneous tropical cyclogenesis. We investigate the processes leading to tropical cyclogenesis in idealized simulations with a three-dimensional cloud-permitting model configured in rotating RCE, in which the background planetary vorticity is varied across f -plane cases to represent a range of deep tropical and near-equatorial environments. Convection is initialized randomly in an otherwise homogeneous environment, with no background wind, precursor disturbance, or other synoptic-scale forcing. We examine the dynamic and thermodynamic evolution of cyclogenesis in these experiments and compare the physical mechanisms to current theories. All simulations with planetary vorticity corresponding to latitudes from 10 • -20 • generate intense tropical cyclones, with maximum wind speeds of 80 m s −1 or above. Time to genesis varies widely, even within a five-member ensemble of 20 • simulations, indicating large stochastic variability. Shared across the 10 • -20 • group is the emergence of a midlevel vortex in the days leading to genesis, which has dynamic and thermodynamic implications on its environment that facilitate the spin-up of a low-level vortex. Tropical cyclogenesis is possible in this model at values of Coriolis parameter as low as that representative of 1 • . In these experiments, convection self-aggregates into a quasicircular cluster, which then begins to rotate and gradually strengthen into a tropical storm, aided by strong near-surface inflow that is already established days prior. Other experiments at these lower Coriolis parameters instead self-aggregate into a nonrotating elongated band and fail to undergo cyclogenesis over the 100-day simulation. Plain Language SummaryDespite decades of research on tropical cyclones, we still do not have a universal agreement on how they form. Current theories agree that some sort of disturbance must exist beforehand, but our knowledge of the processes leading to a surface-based cyclone remains limited. To address this, we examine idealized numerical simulations in which convection is allowed to spontaneously cluster together on its own due to interactions between clouds, moisture, and radiation. Using this framework, we obtain a complete view of the tropical cyclone formation process, including the formation of the precursor disturbance. New to this study is the use of lower values of background rotation to simulate the formation of hurricanes at lower latitudes. Overall, simulations are run to represent latitudes from 0.1 • -20 • . Every simulation corresponding to latitudes between 10 • and 20 • produces a major hurricane, a few days after a vortex emerges a few kilometers aloft and affects its surrounding environment. Some simulations at 1 • and 2 • lead to formation of a weaker tropical cyclone, after cloud s have first organized into one circular cluster. In other low-latitude cases, this cluster of storms is instead a long band and fa...

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“…While the analysis of data obtained is still in progress, there have been already several studies examining the dynamical and thermodynamical structure of some of the genesis events documented (e.g. Davis and Ahijevych, ; Smith and Montgomery, ; Wang, ; Wang et al , ; Fritz and Wang, ; Komaromi, ; Gjorgjievska and Raymond, ; Melhauser and Zhang, ). These studies provide a motivation for further modelling work.…”

Section: Introductionmentioning

confidence: 99%

A unified view of tropical cyclogenesis and intensification

Kilroy

Smith

Montgomery

2016

Quart J Royal Meteoro Soc

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Idealized high-resolution numerical simulations of tropical cyclogenesis are presented in a model that represents deep convection by a warm rain process only. Starting with an initially weak, cloud-free, axisymmetric warm-cored vortex (maximum wind speed 5 m s −1 at a radius of 100 km), rapid vortex intensification begins after a gestation period on the order of 2 days. From a three-dimensional perspective, the genesis process is similar to that in the rotating convection paradigm for vortex intensification starting with a much stronger initial vortex (V max = 15 m s −1 ). The patterns of deep convection and convectively amplified cyclonic relative vorticity are far from axisymmetric during the genesis period. Moreover, the organization of the cyclonic relative vorticity into a monopole structure occurs at relatively low wind speeds, before the maximum local wind speed has increased appreciably. Barotropic processes are shown to play an important role in helping to consolidate a single-signed vorticity monopole within a few hours near the intensification begin time.The rotating convection paradigm appears adequate to explain the basic genesis process within the weak initial vortex, providing strong support for a hypothesis of Montgomery and Smith that the genesis process is not fundamentally different from that of vortex intensification. In particular, genesis does not require a 'trigger' and does not depend on the prior existence of a mid-level vortex.

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Interaction between dynamics and thermodynamics during tropical cyclogenesis

Cited by 27 publications

References 34 publications

Predicting convective rainfall over tropical oceans from environmental conditions

Predicting convective rainfall over tropical oceans from environmental conditions

Tropical Cyclogenesis From Self‐Aggregated Convection in Numerical Simulations of Rotating Radiative‐Convective Equilibrium

A unified view of tropical cyclogenesis and intensification

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