Dominant Oscillation Research Articles

Mode decomposition to identify oscillation patterns of flexible aeroshell

Flexible aeroshells, featuring deformable membrane surfaces supported by pressurized gas, offer a novel re-entry system for high-altitude deceleration during re-entry. The flexibility of structural components introduces unique challenges in predicting aerodynamic behavior, as deformations can significantly alter the flow field, affecting pressure distribution and potentially causing aerodynamic instabilities. Therefore, coupled analysis is crucial to ensure the performance reliability of inflatable aeroshells. This study investigates the unsteady aerodynamic behavior, considering structural deformation in a two-way partitioned coupled manner in transonic flow. The dominant deformation patterns are identified using dynamic mode decomposition and the greedy compressive sensing algorithm. The findings reveal that the primary deformation pattern combines axial deformation and swing oscillation. The dominant oscillation frequencies remain different from the eigenfrequencies, indicating that the aerodynamic force is the primary driving force of such oscillations. The time evolution of these dominant modes indicates purely oscillatory behavior rather than increasing or decreasing trends. These insights are critical for the design and reliability assessment of inflatable aeroshells in varying aerodynamic environments.

Investigation of Viscor and Methanol Spray Dynamics using Proper Orthogonal Decomposition in Siemens Energy Industrial Atomisers

Abstract The demand to reduce carbon emissions has prompted research into alternative fuels that can replace conventional fuels like diesel in industrial gas turbines. Among different potential biofuels and e-fuels, methanol emerges as a sustainable and high-performance alternative to diesel for gas turbine applications. It is well established that the fuel physical properties, spray dynamics and degree of atomisation are strongly correlated and affect the engine performance. In this study, Proper Orthogonal Decomposition (POD) was applied on spatio-temporally resolved images to characterise Viscor, here used as diesel surrogate, and methanol sprays of pressure-swirl atomisers employed in Siemens Energy industrial gas turbine (SGT-400) combustors. The methanol experimental results were then compared against Viscor results at analogous operating conditions, including density adjusted atomiser pressure drop and ambient pressures. Results confirmed that the methanol spray cone angle is slightly wider than Viscor at corresponding operating conditions. The POD analysis allowed to identify dominant spatial oscillation modes and characterise them in terms of oscillation amplitude, wavelength and onset distance from the atomiser edge for both fuels. Oscillation wavelengths and maximum amplitudes were found to correlate with Weber number, average SMD and axial jet velocities.

A New Paradigm for Active–Break Cycle in the Indian Summer Monsoon

Abstract A multichannel singular spectrum analysis of 121 years of daily rainfall over India and 43 years of outgoing longwave radiation and horizontal wind has revealed two dominant intraseasonal oscillations (ISOs) that describe the space–time variability of monsoon rainfall. The two nonlinear oscillations are not perfectly periodic but exhibit broadband spectra centered at 45 and 28 days. These modes have coherent and near-regular spatial structure and temporal variations. This study posits that the two nonlinear oscillations provide a consistent and comprehensive framework to study the variability and predictability of intraseasonal rainfall variations. The active and break cycles of monsoon rainfall over India have been traditionally defined by using an arbitrarily chosen duration of persistence of arbitrarily chosen amount of rainfall averaged over an arbitrarily chosen area. This study shows that the phases of the two objectively derived modes of variability provide an objective method for defining the active and break cycles. The two ISOs are further shown to make negligible contribution to the seasonal mean rainfall and its interannual variability. This study proposes that the investigations of the origins of these nonlinear modes, and modulations of their amplitudes and phases, provide a new paradigm for future research on validation and predictability of intraseasonal variations in climate models.

The Supplementary Damping Method for CLCC HVDC Based on Projective Control Theory

This paper proposes a design method for an additional damping reduced-order controller based on the projective control theorem. Improvements are made to the projective theorem to achieve additional damping control through Controllable-Line-Commutated Converter (CLCC)-based High Voltage Direct Current (HVDC), which suppresses low-frequency oscillations. Using small disturbance identification techniques, the system’s linear model is first identified, and the state feedback control law of the system is then determined using the state-space pole assignment control method. Then, by retaining the dominant oscillation modes of the closed-loop system through the improved projective theorem, the state feedback is converted into output feedback. Ultimately, the sixth-order state feedback controller is reduced to a second-order one and applied in the CLCC HVDC additional damping strategy to suppress low-frequency oscillations. Simulation results based on the electromagnetic transient simulation software PSCAD demonstrate that the designed CLCC HVDC additional damping reduced-order projective control exhibits good suppression performance, strong robustness, and low order, which are of significant importance for engineering practice.

Thermal structure variations and influence factors in a subtropical reservoir, China: explanations from multiple research methods

ABSTRACT Revealing the subtle variations in thermal structure in a reservoir is crucial for accurately understanding the interaction between water and the carbon cycle. This study provides a detailed description of the thermal structure of Dalongdong reservoir, a representative subtropical stratified reservoir in Guangxi, China. It unveils the three stable state changes in water – mixing, microstratification, and stratification – along with their influencing factors. The study emphasizes air temperature (AT) as the primary factor influencing water temperature (WT) stability, followed by water level. Cross-correlation analysis shows that adjacent WTs experience a prolonged response hysteresis during the stratification period, while the mixing period exhibits a shorter hysteresis. Wavelet analysis revealed that AT and surface-layer WT exhibited a dominant oscillation period of 16–32 h. The periodicity of other water layers is not obvious. This framework can help to enhance our understanding of material cycles and protection of the water environment.

Determination of dominant oscillation section in power system based on MSSA algorithm and dissipated energy

The identification of dominant oscillation paths is one of the key aspects in studying the stability of inter-area power grids. This paper proposes an improved multi-channel singular spectrum analysis (MSSA) algorithm combined with dissipative energy to identify dominant oscillation section in power systems. First, an improved MSSA method is introduced, which determines the order using the singular value energy spectrum and can effectively identify inter-area oscillation modes in power systems. Second, an energy function analysis method is proposed, which is well-suited for determining dominant oscillation section in power systems. This method is minimally affected by time-varying and nonlinear factors and allows for the visualization of generator states. Finally, the IEEE 68-bus system is used to construct an equivalent model, demonstrating the method's versatility. Simulation results validate the noise resistance, computational efficiency, and applicability to topology change scenarios of the proposed method. This method can accurately analyze inter-area oscillation modes and help to establish the dominant oscillation section.

Experimental study on dynamic characteristics of shock train in an isolator with different types of incident shocks

The hypersonic mixed-compression inlet, operating in an off-design state, can be categorized into low-speed and over-speed regimes based on whether the external compression shock is incident into the internal flow channel. In this study, we investigate the movement process of the shock train within an inlet/isolator under both low-speed and over-speed conditions by generating various incident shocks using wedges installed in a direct-connected ground wind tunnel. Experimental investigations are conducted to examine the dynamic characteristics of the shock train in an isolator subjected to different types of incident shocks at an incoming Mach number of 2.7. The findings reveal that varying levels of backpressure resistance for the shock train are observed with different types of incident shocks. Through the movement trajectory of the shock train leading shock (STLS) and power spectral density analysis, it is found that unilateral incident shocks result in a more intense oscillation process for the shock train with a lower dominant oscillation frequency. The dynamic mode decomposition method identifies different oscillation structures within the unsteady shock train flow field and highlights that dominant mode energy primarily concentrates at the STLS, while its symmetry is influenced by the type of incident shock. Specifically, the symmetric bilateral incident shock tends to promote a higher degree of symmetry in the STLS structure while reducing its oscillation strength; however, when the STLS passes over the reflection point of the incident shock, the rapid upstream movement of the shock train still occurs in this situation, thereby inducing inlet unstart and compromising engine safety.

Propagation and Maintenance of the Quasi-Biweekly Oscillation over the Western North Pacific in Boreal Winter

Abstract This study investigates the propagation and maintenance mechanisms of the dominant intraseasonal oscillation over the western North Pacific in boreal winter, the quasi-biweekly oscillation (QBWO). The wintertime QBWO over the western North Pacific is characterized by the westward-northwestward movement from the tropical western Pacific to the western North Pacific and resembles the n = 1 equatorial Rossby wave. Its westward migration is primarily driven by the seasonal-mean zonal winds that advect vorticity anomalies in the lower–middle troposphere and moisture anomalies in the lower troposphere. Its northward movement is preconditioned by the vorticity dynamics of the beta effect, the low-level vertical moisture variation, and the local air–sea interaction. The latter involves the atmospheric forcing on the underlying ocean by changing the surface heat flux fluctuations and the sea surface temperature feedback on the low-level atmospheric instability. Its maintenance is primarily through atmospheric external energy sources from diabatic heating, which first generates eddy available potential energy and then converts it to eddy kinetic energy. Significance Statement Atmospheric quasi-biweekly oscillation (QBWO) is an important climate phenomenon over the western North Pacific in boreal winter. It can trigger significant influences both in the tropical and extratropical regions. Given the importance, it is necessary to investigate the propagation and maintenance mechanisms of the QBWO over the western North Pacific in boreal winter. The QBWO usually propagates northwestward from the tropical western Pacific to the western North Pacific. The westward propagation is driven by the seasonal mean zonal winds that advect vorticity anomalies in the lower–middle troposphere and moisture anomalies in the lower troposphere. The northward propagation is caused jointly by several processes, including the atmospheric forcing on the ocean via the surface heat flux fluctuations, the feedback of ocean on the low-level atmospheric instability, the vorticity dynamics of the beta effect, and the vertical variation of low-level moisture. In addition, converting from eddy available potential energy to eddy kinetic energy is essential in maintaining the QBWO’s development. The disclosure of these crucial processes deepens the dynamics of the QBWO over the western North Pacific in boreal winter.

Correlating analysis and optimization between hydropower system parameters and multi-frequency oscillation characteristics

This paper aims to study the relationship between multi-frequency oscillation characteristics and parameters of hydro-turbine governing systems (HTGS), as well as improve the system oscillation quantification accuracy and primary frequency regulation performance. Firstly, an HTGS model with multi-frequency oscillation characteristics is established using an actual hydropower system as the object. Then, system oscillation components and the sources of each oscillating link are identified using eigenvalue and correlation analysis. To address the issue that sub-wave interference with dominant oscillation quantization, we innovatively incorporate correlation and frequency indexes into quantification process, and the dominant oscillations of complex HTGS are accurately quantified. On this basis, the detailed partitioning of control parameters is established to obtain the guide graph quickly reflecting the relationship between control parameters and system oscillations. Finally, an integrated optimization strategy with ultra-low frequency oscillation (ULFO) safety and regulation performance constraints is constructed, and control parameters are further optimized under two typical parameter setting methods. The results indicate over 90 % of the stable parameters enable the system to enter ULFO mode, and optimized control parameters utilizing proposed strategy increase regulation speed by 46 % while effectively suppressing ULFO. This paper provides a powerful tool and novel ideas for complex HTGS oscillation analysis and parameter optimization.

Studying the Optimal Frequency Control Condition for Electric Vehicle Fast Charging Stations as a Dynamic Load Using Reinforcement Learning Algorithms in Different Photovoltaic Penetration Levels

This study investigates the impact of renewable energy penetration on system stability and validates the performance of the (Proportional-Integral-Derivative) PID-(reinforcement learning) RL control technique. Three scenarios were examined: no photovoltaic (PV), 25% PV, and 50% PV, to evaluate the impact of PV penetration on system stability. The results demonstrate that while the absence of renewable energy yields a more stable frequency response, a higher PV penetration (50%) enhances stability in tie-line active power flow between interconnected systems. This shows that an increased PV penetration improves frequency balance and active power flow stability. Additionally, the study evaluates three control scenarios: no control input, PID-(Particle Swarm Optimization) PSO, and PID-RL, to validate the performance of the PID-RL control technique. The findings show that the EV system with PID-RL outperforms the other scenarios in terms of frequency response, tie-line active power response, and frequency difference response. The PID-RL controller significantly enhances the damping of the dominant oscillation mode and restores the stability within the first 4 s—after the disturbance in first second. This leads to an improved stability compared to the EV system with PID-PSO (within 21 s) and without any control input (oscillating more than 30 s). Overall, this research provides the improvement in terms of frequency response, tie-line active power response, and frequency difference response with high renewable energy penetration levels and the research validates the effectiveness of the PID-RL control technique in stabilizing the EV system. These findings can contribute to the development of strategies for integrating renewable energy sources and optimizing control systems, ensuring a more stable and sustainable power grid.

Statistical Investigation of Wave Propagation in the Quiet-Sun Using IRIS Spectroscopic Observations

In this analysis, we use spectroscopic observations of the quiet Sun made by the IRIS instrument and investigate wave propagation. We analyze various spectral lines formed in different atmospheric layers, such as the photosphere, chromosphere, and transition region. We examine the Doppler velocity time series at various locations in the quiet Sun to determine the dominant oscillation periods. Our results executing statistical analysis resemble those of the classical physical scenario, indicating that the photosphere is mainly characterized by the dominant 5 minute period, while the chromosphere is primarily associated with the 3 minute oscillation period. In the transition region, we observe a variety of oscillation periods, with dominant periods of 3, 8, and 12 minutes. We estimate the cutoff frequency by deducing the phase difference between two Doppler velocity time series obtained from spectral line pairs in different atmospheric layers formed at different temperatures. This reveals a significant correlation between 3 minute periods in the transition region and photospheric oscillations, suggesting that these oscillations in the transition region might propagate from the photosphere. Additionally, we analyze the phase difference between chromospheric oscillations and photospheric oscillations, demonstrating that only the 3 minute oscillations propagate upward. Based on the statistical analyses, we suggest the presence of magnetoacoustic waves in the solar atmosphere, some of which are propagating from the lower solar atmosphere upward, while some others are propagating downward. The transition region carries both long-period oscillations generated in situ and some photospheric oscillations that are also able to reach there from below.

Effect of slug characteristics on the nonlinear dynamic response of a long flexible fluid-conveying cylinder

Hydrocarbon flows in a marine riser may appear in multiple phases with varying flow patterns, among which, slug flows are known to exhibit complex flow characteristics due to fluctuations in multiphase mass, velocities, and pressure changes. Bulk of the literature concerning internal single and two-phase flow induced vibrations have largely focused on the use of a linearized tension beam model. In this study, the fluid-structure interaction phenomena of a submerged long flexible cylinder conveying two-phase slug flows is investigated taking into account the geometric and hydrodynamic nonlinearities. A semi-empirical theoretical model which consists of nonlinear structural equations of coupled out-of-plane, in-plane and axial structural motions is presented for the analysis and prediction of two-phase slug flow induced vibrations (SIV). The model includes equations involving centrifugal and Coriolis forces to capture mass variations in the slug flow regime. A numerical space-time finite difference approach combined with a frequency domain analysis is used for analyzing the highly nonlinear three-dimensional responses. The model assumes constant geometric properties across the span of the cylinder and utilizes an idealized slug unit concept, wherein slug properties are considered to be fully developed and undisturbed by pipe oscillations. Model validations are performed through comparisons with published experimental internal flow-induced vibration results. Parametric study captures the effects of several key slug characteristics on the vibration responses of a fluid-conveying cylinder. The results demonstrate amplitude-modulation response, mean displacements, three-dimensional cylinder displacements due to geometric nonlinear couplings and the influence of internal flow velocities. Higher dominant modes and oscillation frequencies were observed when the cylinder experiences large amplitude motions at specific slug formations. A new dimensionless parameter is introduced to predict scenarios of high amplitude oscillations for long flexible cylinders carrying two-phase slug flows.

Research on the mechanism and transmission path of the oscillation in DFIG-connected flexible DC transmission system

Concerning the oscillations in DFIG (doubly-fed induction generator)-connected flexible DC transmission system caused by large disturbances, an analysis method based on subsystem partitioning and dynamic energy modeling is put forward. Firstly, the complex high-order system is partitioned into several low-order subsystems, and the dynamic energy model of each subsystem is built using the first integration method. Then, by analyzing the directions and variation patterns of the interaction energy flows between different subsystems in the oscillation process, the redistribution of the primary flow paths of the system’s oscillation energy after large disturbances occur is determined. And then, an oscillation tracing method based on the response characteristics of the oscillation energy links of the subsystems is proposed. In the oscillation process, the interaction energy links between different subsystems are categorized into 'oscillation gaining links', 'oscillation maintaining links' and 'oscillation damping links', according to the contribution of each interaction energy link to the system’s oscillation energy. By analyzing the ‘oscillation gaining links’ corresponding to the dominant interaction energy links of different subsystems, the transmission paths by which the dominant oscillation energy links keeps gaining can be obtained, and the energy source that induces oscillation can be located. Finally, hardware-in-loop tests are conducted on the RTLAB semi-physical simulation platform, the results of which verify the effectiveness of the proposed method. This research paper can provide theoretical support for suppressing the oscillation by adding compensation branches between the subsystems (i.e. damping control strategies based on supplementary compensation branches).

Numerical Study on the Self-Pulsation Characteristics of LOX/GH2 Swirl Coaxial Injector

To investigate the self-pulsation characteristics of a liquid-centered swirl coaxial injector with liquid oxygen (LOX) and gas hydrogen (GH2) as the working mediums under supercritical condition, a numerical simulation was employed. The transient simulation of the flow and injection process of cryogenic propellant was carried out using the RNG k−ε turbulence model, VOF model, and Peng-Robinson equation of state. The frequency spectrum of calculated pressure oscillation agreed with the experimental data. The amplitude-frequency characteristics of recess region, LOX, and GH2 paths when self-pulsation occurs were analyzed. The effects of operating parameters, such as the flow rate of LOX or GH2 and the initial GH2 temperature, on the self-pulsation, were evaluated specifically. Results reveal that the self-pulsation results from the periodic variation of pressure and velocity caused by the periodic blocking of annular gas by the liquid sheet. The dominant frequencies of pressure oscillation in the recess region, upstream of LOX, or GH2 path are diverse. But for the points in each region, the dominant frequency is about the same. When the LOX/GH2 mixing ratio increases, the liquid sheet thickness and the number of liquid filaments increase. The position where filaments are massively broken into droplets moves further downstream. For the same mixing ratio, the flow rate of LOX has a greater impact on the atomization features. The pressures corresponding to low or high frequency increase when the initial GH2 temperature raises. The higher temperature would shift the dominant oscillation between the low and high regimes.

A comprehensive localization and assessment method for SSO in power systems with wind power

Subsynchronous Oscillation (SSO) is a common dynamic stability issue in power systems that integrate wind power. This paper proposes a comprehensive method for assessing the localization of SSO in wind power integrated systems. The localization method applies the transient energy flow approach to identify SSO sources in systems with wind power. Additionally, a relevant SSO index system is established where the value of each index is calculated. By using the Fuzzy Inference System (FIS) to judge the index, the SSO disturbance source contribution rating of each area is obtained. Simulation cases demonstrate that the localization method of the transient energy flow approach can effectively identify the SSO disturbance source. Moreover, the SSO disturbance source contribution rating method based on FIS can determine the SSO contribution degree of each area, thus identifying the dominant oscillation disturbance sources. The proposed method can provide valuable insights for formulating emergency control measures.

An empirical model for the tropical Indian region using in-situ and space-borne observations taking into account of tropical oscillations

An empirical model of temperature is developed using long-term observations of radiosonde (52 years), M-100 Rocket (17 years), and Sounding of the Atmosphere by Broadband Emission Radiometry (SABER) (22 years) data. The dominant oscillations such as Annual Oscillation (AO), Semi-Annual Oscillation (SAO), Terr-Annual oscillation (TAO), and Quasi-Biennial Oscillation (QBO) variability has been incorporated into the temperature to obtain the empirical atmosphere. The monthly mean of temperature obtained from radiosonde from 0 to 25 km, M-100 rocket from 26 to 80 km and SABER from 26 to 109 km has been subjected to the Fast Fourier Transform technique to retrieve the amplitudes and phases of AO, SAO, TAO, and QBO. The amplitudes and phases obtained are put in an empirical formula along with the temperature obtained from the observations to retrieve the empirical temperature. The empirical model is developed for two epochs (1971–1990, and 2002–2023). The amplitude is similar in both epochs for the TAO, and it is high in the first compared to the second epoch for SAO, AO, and QBO. The peak in the amplitude (3–4 K) is obtained between 80 and 90 km for TAO, and between 70 and 80 km (2–3 K) for SAO. The amplitude is less than 1 K for AO in both the epochs. The peaks in the QBO are observed between 20 and 30 km (2–3 K), another between 60 and 70 km (3–4 K) in the first epoch and above 80 km (2–3 K). Downward phase propagation is dominant for all the oscillations observed below 50 km, and upward propagation above. The empirical temperature obtained compares well with the observations below 20 km (RMSE <1 K) and shows differences above it (RMSE ∼ 4–6 K). This is due to the fact, that the amplitude of the oscillation is more in the stratosphere and mesosphere which results in perturbation of the background temperature.

Characterization of Out-of-Plane Curved Fluidic Oscillators

A novel fluidic oscillator design, in which the oscillator is curved along the primary flow direction, was evaluated. The effects of mass flow rate, hydraulic diameter, aspect ratio, curvature radius, surface roughness, inlet orientation, and nonconstant curvatures were experimentally investigated. Measurements of the oscillation Strouhal number, discharge coefficient, spreading angle, and sweeping angle were used to characterize the jet. The resulting oscillators were found to fall into one of three categories: oscillated at the same frequency and sweep angle as conventional flat oscillators; oscillated at a slightly higher frequency and lower sweep angle than flat oscillators; or no dominant oscillation frequency detected and with no sweeping action. An unsteady Reynolds-averaged Navier–Stokes computational fluid dynamics simulation revealed fundamental differences in the internal flow mechanisms between flat and curved oscillators that drive the sweeping jet. The curvature between 37.5 and 62.5% of the total length, or the region from the inlet nozzle to halfway through the main chamber, was a primary factor influencing the response type of a design. Due to the curvature of these oscillators, they have the ability to be used in geometrically constrained spaces, such as the leading edge of wings and turbine vanes.

Numerical study on dominant oscillation frequency of unstable steam jet under heaving condition

With its advanced efficiency in heat transfer, the steam direct contact condensation method is now extensively employed in many areas. The pressure oscillation characteristics of unstable steam jets under heaving conditions were investigated numerically in this study. The dominant oscillation frequency gradually rose with the decrease of the heaving period and the increase of the heaving amplitude. The dominant oscillation frequency under the heaving condition was higher than that under the static condition, with a maximum increase of 27.4%. The inertia and condensation dominated the evolution of steam bubbles at the necking stage under heaving conditions. With the decrease of the heaving period and the increase of heaving amplitude, the additional force induced by heaving movement increased, contributing to the condensation heat transfer enhancement. A dimensionless correlation predicting the dominant oscillation frequency at a low flow rate under heaving conditions was fitted, and the maximum error was within ±6.2%.

Effect mechanisms of leading-edge tubercle on blade cavitation control in a waterjet pump

The bio-inspired leading-edge tubercles (LET) are specifically designed and exploited to control the blade cavitation dynamics under the inlet guide vans (IGVs) wake impacts in a waterjet pump. The experiments, numerical simulation, and modal analysis are jointly carried out to elaborate on the effects mechanisms and cavitation oscillations of the LET pump. It is observed that the tubercle blade cavitation is stably confined in the troughs with a tubular-like pattern and the spanwise coherent development is broken. The tubercles drive the flow turbulent and then form low pressure in the troughs to give rise to cavities. Weak counter-rotating vortex pairs can be identified in the tubercle trough. The analysis of vortex transportation demonstrates that vortex stretching and dilatation would be induced by tubercle cavitation. The loading instabilities obtained by Dynamic Mode Decomposition (DMD) indicate that the dominant oscillations emerge around the tubercles in the blade middle part regarding heavy loading. Due to the large-scale cavities depression by the tubercles, the thrust extremes in some revolutions could be efficiently avoided. In comparison with smooth and tubercle pumps, the thrust energy regarding the tonal and broadband frequency for a single blade and impeller are closing, which need to be further studied to degrade excited force instabilities. This work fundamentally investigates the cavitation instabilities and mechanisms in a tubercle waterjet pump, which could provide a guide on pump design to stabilize cavitation oscillations under uncertain inflow perturbations.

Increase in optimal configuration of 25–60-day atmospheric circulations for Yangtze heavy rainfall under global warming background

In summer, the middle and lower reaches of the Yangtze River (MLYR) often suffers from severe floods as a result of a dominant intraseasonal oscillation (ISO) of rainfall with the quasi-period of 25–60 days. 75% of flooding events during summers of 1961–2022 are found to occur following wet phases of the 25−60-day ISO in rainfall. This study objectively extracts the optimal configuration (OC) of 25−60-day atmospheric ISOs for the wet phase of MLYR rainfall. The OC is characterized by the quadruple pattern of tropical convection configuring with the 25−60-day Silk Road Pattern (SRP) in the mid−high latitudes. The 25−60-day SRP in cooperation with tropical ISO over the western Pacific induces dipolar vertical cells over eastern China, with ascending branch between the vertical cells providing the vitally dynamical condition for MLYR rainfall. With topographic blocking of the Tibetan Plateau, the northward-propagating tropical ISO over the Indian Ocean enhances maintenance of the 25−60-day SRP via upper-tropospheric divergent flows, thus anchoring anomalous ascents to the MLYR. Numerical experiments further verify the remarkable tropical-extratropical interaction around the Tibetan Plateau in this OC. Under the global warming background, the tropical 25−60-day ISO tends to strengthen, leading to an increase in the occurrence frequency of strong OC through tropical-extratropical interaction, and thus the severe flood events doubled in summers of 1991–2020.