Interaction of tropical cyclone-like vortices with sea-surface temperature anomalies and topography in a simple shallow-water atmospheric model
TL;DR: In this paper, the authors show how the thermal effects affect trajectories, intensity, and formation of secondary structures during the passages of strong tropical cyclone-like vortices over oceanic warm and cold pools as well as over an island-type topography.
Abstract: In this paper, we show how the thermal effects affect trajectories, intensity, and formation of secondary structures during the passages of strong tropical cyclone-like vortices over oceanic warm and cold pools as well as over an island-type topography. Our results are obtained using the moist-convective thermal rotating shallow-water atmospheric model recently developed in [A. Kurganov et al., “Moist-convective thermal rotating shallow-water model,” Phys. Fluids 32, 066601 (2020)]. This model introduces thermodynamics of the moist air and moist convection in the standard rotating shallow-water models and allows to include in the latter atmosphere–ocean interactions in an elementary way.
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TL;DR: In this article , a detailed analysis of the redistribution and variation of angular momentum is given, and it is shown that intensive cyclonic motion with velocity exceeding initial values substantially (ten or more times) is a result of accumulation in the centre of a small fraction of global angular momentum of a fluid layer.
Abstract: ABSTRACT Numerical simulations of a laboratory model of a tropical cyclone are carried out for different rotation rates. Particular attention is paid to the non-stationary stage of intensive cyclonic vortex formation. The transfer of angular momentum plays a key role in the formation of cyclonic and anticyclonic flows; therefore, a detailed analysis of the redistribution and variation of angular momentum is given. The time evolution of angular momentum fluxes and total angular momentum strongly depend on the rotation rate. It is shown that intensive cyclonic motion with velocity exceeding initial values substantially (ten or more times) is a result of accumulation in the centre of a small fraction of global angular momentum of a fluid layer (from 0.25% at fast rotation to 2% at slow rotation). The integral angular momentum of the anticyclonic flow is significantly larger than that of the cyclonic flow, mainly because of the relatively large fluid volume of the anticyclonic flow. Another important result is that the rotating fluid layer very quickly adapts to new boundary conditions (heating and cooling). Approximately two rotation periods are required to reach a quasi-stationary state. The application of the obtained results to the evolution of real tropical cyclones is discussed.
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TL;DR: In this paper , a new multilayer pseudo-spectral moist-convective thermal rotating shallow water (mcTRSW) model was proposed to explain the genesis and dynamics of the Madden-Julian oscillation (MJO).
Abstract: By means of a new multilayer pseudo‐spectral moist‐convective thermal rotating shallow‐water (mcTRSW) model in a full sphere, we present a possible equatorial adjustment beyond Gill's mechanism for the genesis and dynamics of the Madden–Julian oscillation (MJO). According to this theory, an eastward‐propagating MJO‐like structure can be generated in a self‐sustained and self‐propelled manner due to nonlinear relaxation (adjustment) of a large‐scale positive buoyancy anomaly, depressed anomaly, or a combination of these, as soon as this anomaly reaches a critical threshold in the presence of moist convection at the Equator. This MJO‐like episode possesses a convectively coupled “hybrid structure” that consists of a “quasi‐equatorial modon” with an enhanced vortex pair and a convectively coupled baroclinic Kelvin wave (BKW), with greater phase speed than that of dipolar structure on an intraseasonal time‐scale. Interaction of the BKW, after circumnavigating the entire Equator, with a new large‐scale buoyancy anomaly may contribute to excitation of a recurrent generation of the next cycle of MJO‐like structure. Overall, the generated “hybrid structure” captures a few of the crudest features of the MJO, including its quadrupolar structure, convective activity, condensation patterns, vorticity field, phase speed, and westerly and easterly inflows in the lower and upper troposphere. Although moisture‐fed convection is a necessary condition for the “hybrid structure” to be excited and maintained in the proposed theory in this study, it is fundamentally different from moisture‐mode theories, because the barotropic equatorial modon and BKW also exist in “dry” environments, while there are no similar “dry” dynamical basic structures in moisture‐mode theories. The proposed theory can therefore be a possible mechanism to explain the genesis and backbone structure of the MJO and to converge some theories that previously seemed divergent.
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TL;DR: In this paper, the basic mechanism of tropical cyclones was investigated by constructing a numerical-dynamical model on such a model, and the model showed that the energy required for driving the vortex comes from the latent heat of condensation released by tall convective clouds around the center, and that the frictionally induced inflow in the vortex plays a major role in supporting the continued activity of convective cloud.
Abstract: The tropical cyclone is a solitary creature of the tropical oceans accompanied by violent rotating winds and torrential rain. Observational studies and diagnostic analyses leave little doubt that the energy required for driving the vortex comes from the latent heat of condensation released by tall convective clouds around the center, and that the frictionally induced inflow in the vortex plays a major role in supporting the continued activity of convective clouds. This dual character with respect to important scales of motion poses a great difficulty in investigating the dynamics of tropical cyclones as time-dependent phenomena. However, in order to understand the large-scale aspects of tropical cyclones, one may formulate the role of convective clouds in terms of cyclone-scale variables with only implicit consideration of the dynamics of individual clouds. The present study is an attempt to understand the basic mechanism of tropical cyclones by constructing a numerical-dynamical model on such a ...
698 citations
TL;DR: In the case of Hurricane Opal, the maximum heat loss of approximately 24 Kcal cm22 relative to depth of the 268C isotherm was a factor of 6 times the threshold value required to sustain a hurricane as discussed by the authors.
Abstract: On 4 October 1995, Hurricane Opal deepened from 965 to 916 hPa in the Gulf of Mexico over a 14-h period upon encountering a warm core ring (WCR) in the ocean shed by the Loop Current during an upper-level atmospheric trough interaction. Based on historical hydrographic measurements placed within the context of a two-layer model and surface height anomalies (SHA) from the radar altimeter on the TOPEX mission, upperlayer thickness fields indicated the presence of two warm core rings during September and October 1995. As Hurricane Opal passed directly over one of these WCRs, the 1-min surface winds increased from 35 to more than 60 m s21, and the radius of maximum wind decreased from 40 to 25 km. Pre-Opal SHAs in the WCR exceeded 30 cm where the estimated depth of the 208C isotherm was located between 175 and 200 m. Subsequent to Opal’s passage, this depth decreased approximately 50 m, which suggests upwelling underneath the storm track due to Ekman divergence. The maximum heat loss of approximately 24 Kcal cm22 relative to depth of the 268C isotherm was a factor of 6 times the threshold value required to sustain a hurricane. Since most of this loss occurred over a period of 14 h, the heat content loss of 24 Kcal cm22 equates to approximately 20 kW m22. Previous observational findings suggest that about 10%‐15% of upper-ocean cooling is due to surface heat fluxes. Estimated surface heat fluxes based upon heat content changes range from 2000 to 3000 W m 22 in accord with numerically simulated surface heat fluxes during Opal’s encounter with the WCR. Composited AVHRR-derived SSTs indicated a2 8‐38C cooling associated with vertical mixing in the along-track direction of Opal except over the WCR where AVHRR-derived and buoy-derived SSTs decreased only by about 0.58‐18C. Thus, the WCR’s effect was to provide a regime of positive feedback to the hurricane rather than negative feedback induced by cooler waters due to upwelling and vertical mixing as observed over the Bay of Campeche and north of the WCR.
693 citations
TL;DR: In this article, a 212-layer, thermodynamic numerical model is used to study the dynamics, thermodynamics and mixed-layer physics of Indian Ocean circulation, and a surface mixed layer of temperature Tm is imbedded in the upper layer of the model, and entrainment and detrainment in the mixed layer are determined by wind stirring and surface cooling.
659 citations
TL;DR: In this article, an investigation of the interaction between Supertyphoon Maemi, the most intense tropical cyclone in 2003, and a warm ocean eddy in the western North Pacific was presented.
Abstract: Understanding the interaction of ocean eddies with tropical cyclones is critical for improving the understanding and prediction of the tropical cyclone intensity change. Here an investigation is presented of the interaction between Supertyphoon Maemi, the most intense tropical cyclone in 2003, and a warm ocean eddy in the western North Pacific. In September 2003, Maemi passed directly over a prominent (700 km 500 km) warm ocean eddy when passing over the 22°N eddy-rich zone in the northwest Pacific Ocean. Analyses of satellite altimetry and the best-track data from the Joint Typhoon Warning Center show that during the 36 h of the Maemi–eddy encounter, Maemi’s intensity (in 1-min sustained wind) shot up from 41 ms 1 to its peak of 77 m s 1 . Maemi subsequently devastated the southern Korean peninsula. Based on results from the Coupled Hurricane Intensity Prediction System and satellite microwave sea surface temperature observations, it is suggested that the warm eddies act as an effective insulator between typhoons and the deeper ocean cold water. The typhoon’s self-induced sea surface temperature cooling is suppressed owing to the presence of the thicker upper-ocean mixed layer in the warm eddy, which prevents the deeper cold water from being entrained into the upper-ocean mixed layer. As simulated using the Coupled Hurricane Intensity Prediction System, the incorporation of the eddy information yields an evident improvement on Maemi’s intensity evolution, with its peak intensity increased by one category and maintained at category-5 strength for a longer period (36 h) of time. Without the presence of the warm ocean eddy, the intensification is less rapid. This study can serve as a starting point in the largely speculative and unexplored field of typhoon–warm ocean eddy interaction in the western North Pacific. Given the abundance of ocean eddies and intense typhoons in the western North Pacific, these results highlight the importance of a systematic and in-depth investigation of the interaction between typhoons and western North Pacific eddies.
284 citations
TL;DR: In this article, the authors considered the two-dimensional barotropic evolution of thin annular rings of enhanced vorticity embedded in nearly irrotational flow and found that these highly unstable annuli rapidly break down into a number of mesovortices.
Abstract: The present work considers the two-dimensional barotropic evolution of thin annular rings of enhanced vorticity embedded in nearly irrotational flow. Such initial conditions imitate the observed flows in intensifying hurricanes. Using a pseudospectral numerical model, it is found that these highly unstable annuli rapidly break down into a number of mesovortices. The mesovortices undergo merger processes with their neighbors and, depending on initial conditions, they can relax to a monopole or an asymmetric quasi-steady state. In the latter case, the mesovortices form a lattice rotating approximately as a solid body. The flows associated with such vorticity configurations consist of straight line segments that form a variety of persistent polygonal shapes. Associated with each mesovortex is a local pressure perturbation, or mesolow. The magnitudes of the pressure perturbations can be large when the magnitude of the vorticity in the initial annulus is large. In cases where the mesovortices merge to...
227 citations