Canonical Transfer Research Articles

Multiscale interaction underlying 2022 concurrent extreme precipitation in Pakistan and heatwave in Yangtze River Valley

Unprecedentedly extreme precipitation occurred in Pakistan (PAK), and mega heat waves persisted along the Yangtze River Valley (YRV) from July to August 2022. Using the advanced multiscale window transform-based canonical transfer attribution framework, we quantitatively delineated intra-scale and inter-scale interactions leading to record-breaking spatially concurrent extremes in 2022 and comprehensively revealed differences in dynamic processes affecting extreme events in July and August. The basic flow scale window lost the available potential energy (APE), and through APE canonical transfers to the intraseasonal-scale and synoptic-scale windows, the inter-scale dynamic processes and barotropic instability of the basic flow scale preserved the concurrent extreme in July. In August, the eruptive synoptic-scale kinetic energy convergence provided dynamic conditions for the sinking motion of the YRV and its advection to PAK from the Indian Ocean. Consequently, the interaction between high- and low-frequency processes drove atmospheric circulation in summer, but the high-frequency process in August played a vital role in extreme events. Additionally, the heat source in the tropical western-central Pacific is considered one of the key drivers for localized repetitive bursts of energy. This study emphasizes both the interactions between multiple scales of atmospheric dynamics and reveals the driving mechanisms behind the impacts of warming on extreme events, linking the external forcing issue with the free problem of atmospheric internal instability.

Efficient parameter estimation for second order plus dead time systems in process plant control

AbstractDesigning a controller for a process plant typically modeled as a first or second‐order system with dead time involves an efficient and accurate estimation of its parameters. Since many process plants are characterized as second‐order plus dead time (SOPDT) overdamped or critically damped systems, this study presents a straightforward parameter estimation method using transient response data from a step input at three specific time instants. Two‐time domain performance indices (PIs), (= for system dead time = 0 and for system dead time ≠ 0; , and are respectively the times at which the response reaches 5%, 10% and 90% of the steady‐state response) and (reciprocal of rise time ) are proposed in this work. Correlations are established between these PIs and the parameters of the SOPDT system. The first correlation establishes that is a function of the damping ratio only and is independent of the undamped natural frequency which means that the evaluation of from the time response data is sufficient to estimate . The second correlation establishes that for a given , is a function of . Thus the evaluation of from the time response data and an estimate of from the first correlation is sufficient to estimate . The proposed algorithm estimates the parameters of the canonical transfer function of the plant by these correlations from the three specific time instants, as mentioned above, of the step response of the plant. Comparisons with four methods existing in the literature reveal that the method is also effective with higher order systems that may be approximated by SOPDT dynamics, and robust even with measurement noise, making it useful for implementing control strategies, not only in process plants but also in other systems having similar time responses.

Energetics of eddy-mean flow interactions in the western tropical Pacific Ocean

The eddy-mean flow interactions are critical processes in the ocean energy cycle. This study investigated the energetics of eddy-mean flow interactions in the western tropical Pacific Ocean using the multiscale window transform (MWT) and MWT-based canonical transfer theory, based on 16-year numerical outputs from the Ocean General Circulation Model for the Earth Simulator and two mooring measurements. Energy analysis revealed that prominent eddy kinetic energy (EKE) appears in the upper layer of the Sulawesi Sea and the source region of North Equatorial Countercurrent (NECC), and in the subsurface layer along the Philippine coast. The kinetic energy in the upper layer is mainly transferred from the mean flow to the eddy field through barotropic instability. Below the thermocline, the prominent subsurface EKE is not only caused by barotropic conversion, but also by baroclinic one. Subsurface mesoscale eddies east of the Mindanao Island extract energy from mean flow through barotropic instability, and those further north seem to release their kinetic energy to the mean flow of North Equatorial Undercurrent, indicating inverse energy cascades. Our results highlight that the advection effect plays a key role in the horizontal distribution of EKE, which generally shifts the high EKE area a few degrees downstream from the eddy formation region. Particularly, in the source region of NECC, the advection term shifts the EKE center 5° eastward from ∼132°E to ∼137°E.

The Role of Multiscale Interaction in the Maintenance and Propagation of MJO in Boreal Winter

Abstract The multiscale interaction and its role in the maintenance and propagation of the Madden–Julian oscillation (MJO) has been investigated using the newly developed multiscale window transform (MWT), the theory of canonical transfer, and the MWT-based multiscale energetics analysis (here particularly for this study, dry energetics analysis). The field variables are reconstructed/filtered with MWT onto three scale windows, namely a high-frequency window, intraseasonal window, and low-frequency window. Compositing the intraseasonal fields with respect to the real-time multivariate MJO (RMM) index unambiguously shows that the zonal extents of the easterlies and westerlies of MJO vary with the RMM phases, among which phases 4 and 2 are representative. In the former phase, the MJO has easterlies and westerlies within the same extent, while in the latter their extents are quite different. In phase 4, besides the previously discovered mechanisms such as pressure work and buoyancy conversion, the MJO is also energized by the canonical kinetic energy (KE) transfer from the low-frequency window to the intraseasonal window (signifying barotropic instability) on the west of its convection. But on the eastern side, MJO loses KE to the low-frequency window. The KE transport also functions like an energy sink. In phase 2, the MJO variabilities can be divided into an eastern part and a western part. The former is essentially the same as that in phase 4; for the latter, barotropic instability dominates. On the available potential energy (APE) budget, baroclinic instability and intraseasonal APE transport help produce and maintain the temperature anomalies. In contrast to previous energetics studies, our findings highlight the essential role played by multiscale interactions.

Characteristics and Dynamics of the Interannual Eddy Kinetic Energy Variation in the Central Pacific Sector of the Southern Ocean

AbstractMesoscale eddies play a crucial role in the dynamical balance of the Southern Ocean (SO) circulation. Yet, it remains unclear why the SO transient eddy activity has significant variations on interannual time scales, and to what extent these low‐frequency variations are attributed to wind forcing changes. Here we use a functional analysis tool, namely, the multiscale window transform (MWT), the MWT‐based theory of canonical transfer and a time‐dependent energetics framework to investigate these issues. Our focus is on the central Pacific sector of the SO in which there is a significant time‐mean and interannual variability of the eddy kinetic energy (EKE). It is found that wind stress does not directly contribute to the interannual EKE variability through wind power injection to the eddies; instead, the influence is fulfilled indirectly through two internal pathways. First, the baroclinic pathway in which the wind‐generated mean kinetic energy (MKE) is converted to the mean available potential energy (APE), and is further released to eddy APE and finally to EKE through baroclinic instability, is the dominant one. Second, the barotropic pathway, in which MKE directly fuels EKE through barotropic instability, is faster but secondary, and its influence is only concentrated along the axis of the Antarctic Circumpolar Current. Our results highlight the dynamical connections between the internal and external processes in the SO energy system, and provide insights into the predictability of the SO eddies on interannual time scales.

Mechanisms for generating and connecting the Yanai-mode and Rossby-mode tropical instability waves in the equatorial Pacific

It is generally believed that both barotropic and baroclinic instabilities may account for the tropical instability wave (TIW) variabilities in the equatorial Pacific Ocean. However, the coupling mechanisms between the two different meridional TIW modes, i.e., the Yanai-mode at the equator and the Rossby-mode around 5°N, and the associated vertical connections, are yet to be clarified. This is done here using a recently developed multiscale decomposition tool, multiscale window transform (MWT), and the MWT-based theory of canonical transfer and TIW-scale eddy kinetic energy (EKE) budget analysis, based on the (1/12.5)∘ HYCOM reanalysis data. In the subsurface layer (30–200 m), barotropic instability is the primary energy source for the Yanai-mode TIWs, while baroclinic instability dominates the EKE generation of the Rossby-mode TIWs. In contrast, the two TIW modes in the surface layer (0–30 m) are largely modulated by nonlocal mechanisms through pressure work, which functions to transport EKE upward from the subsurface to the surface layer, and southward from the Rossby-mode region to the Yanai-mode region. The pressure fluxes substantially couple the two TIW modes in both the meridional and vertical directions, leading to significant coherence between EKE in different vertical layers and regions of the TIWs. In addition, the prevailing vertical pressure flux identified north of the equator explains why the EKE signal is more vertically coherent in the Rossby-mode region than the Yanai-mode region. This nonlocal energy pathway, as well as the well-known instability processes, undergoes strong seasonal variations that determine the seasonal cycles of the TIWs in the equatorial Pacific Ocean.

On the intensification of typhoon Damrey with the monsoon gyre

AbstractTyphoon Damrey, the first named tropical cyclone (TC) of the year 2000 in the western North Pacific, was embedded in a monsoon gyre (MG) during its intensification period. We explored the mechanisms of its rapid development and the contribution of the MG using a localized, instantaneous energetics diagnostic tool: the multiscale window transform (MWT) and MWT‐based multiscale energetics analysis. We used the ERA5 reanalysis dataset to obtain the fields on three temporal scales: TC‐scale fields; MG‐scale fields; and large‐scale background fields. The canonical transfer of kinetic energy from the large‐scale background fields to the tropical cyclone was negligible, whereas the MG increased the TC‐scale kinetic energy in the precipitation active quadrant and weakened its kinetic energy in the precipitation inactive quadrant. Barotropic canonical transfer therefore did not contribute to the development of this tropical cyclone. Kinetic energy was produced in Damrey mainly through buoyancy conversion and pressure work. In the upper troposphere, the available potential energy converted to TC‐scale kinetic energy, but this was mostly offset by the negative work done by the pressure gradient force with the updraught near the eyewall. In the lower troposphere, TC‐scale kinetic energy was produced by horizontal pressure work due to the inflow. This new finding helps us to understand the impact of the MG on the TC intensification and the underlying mechanisms governing TC evolution.

Nexus of ambient flow and squall line via turbulence in the March 2018 meso-scale convective system over Southeast China

On March 4, 2018, an extremely strong squall line occurs suddenly over Southeast China, incurring devastatingly strong surface winds. In this study, we first present a high-resolution model simulation, then apply the recently developed theory of canonical transfer, which bears a form reminiscent of the Poisson bracket in Hamiltonian mechanics, to investigate the underlying dynamical processes. Using a recently developed functional analysis apparatus, multiscale window transform, the fields are reconstructed onto three scale windows, namely, ambient flow window, squall line-scale window, and turbulence window, which for convenience are denoted as windows 0, 1, 2, respectively. It is found that, among all the canonical transfers of kinetic energy (KE), only that between windows 0 and 2, and that between windows 1 and 2, are significant, and the two correspond remarkably well in space, except for opposite signs. Specifically, at the leading edge, KE is first transferred from the ambient flow over the spectrum all the way to the turbulence scale processes, and then goes to window 1 to form the squall line. At the trailing edge, this process is reversed. While the downscale cascading at the leading edge and upscale transfer at the trailing edge are expected in the classical shock hypothesis of squall lines, the existence of the secondary upscale and downscale transfers, respectively, at the leading and trailing edge, are not seen before. Most importantly, these secondary canonical transfers make the turbulence-scale window function like a hub, bridging the ambient flow and the squall line. To our knowledge, such an energetic scenario, i.e., the nexus of two adjacent scales in a spectrum via a “remote mediator” is not seen before in the literature. This study testifies to the importance of turbulent flows in the maintenance of squall lines, and may yield a clue to a better simulation.

On the Genesis of the South China Sea Mesoscale Eddies

The climatology of the mesoscale eddies in the upper layer of the South China Sea (SCS) is investigated for an understanding of its genesis using the outputs from a 1/12.5° ocean reanalysis. Employed is a recently developed multiscale energetics formalism on the basis of a multiscale window transform (MWT) and the theory of canonical transfer. Three scale windows, namely, background flow, mesoscale eddy and synoptic eddy, are differentiated, and fields on different scales are reconstructed henceforth. Diagnosis of the mesoscale eddy energy budget reveals that barotropic and baroclinic instabilities, wind work, advection and pressure work are essential ingredients of the eddy energy sources and sinks in the SCS, but their contributions vary from region to region. In the southwestern part of the SCS, the regional mesoscale eddy energy is mainly generated by barotropic instability, while in the northeastern SCS, baroclinic instability and the wind working directly on the eddies are the two dominant eddy generation processes. The eddies southwest of Taiwan are damped by outward energy transport via advection, while the decay of those southeast of Vietnam is due to pressure work. The three-scale framework also reveals that the interaction between the mesoscale eddies and higher-frequency synoptic eddies mainly serves as a sink for the mesoscale eddy energy in the SCS, except for the northeastern SCS, where significant inverse cascade of kinetic energy is found.

Multiscale Interactive Processes Underlying the Heavy Rainstorm Associated with a Landfalling Atmospheric River

The heavy precipitation in Northern California—brought about by a landfalling atmospheric river (AR) on 25–27 February 2019—is investigated for an understanding of the underlying dynamical processes. By the peaks in hourly accumulation, this rainstorm can be divided into two stages (Stage I and Stage II). Using a recently developed multiscale analysis methodology, i.e., multiscale window transform (MWT), and the MWT-based theory of canonical transfer, the original fields are reconstructed onto three scale windows, namely, the background flow, synoptic-scale and mesoscale windows, and the interactions among them are henceforth investigated. In both stages, the development of the precipitation is attributed to a vigorous buoyancy conversion and latent heating, and besides, the instability of the background flow. In Stage I, the instability is baroclinic, while in Stage II, it is barotropic. Interestingly, in Stage I, the mesoscale kinetic energy is transferred to the background flow where it is stored, and is released back in Stage II to the mesoscale window again, triggering intense precipitation.

Different mechanisms for the seasonal variations of the mesoscale eddy energy in the South China Sea

Using a recently developed functional analysis tool, Multiscale Window Transform (MWT) and the MWT-based theory of canonical transfer, this study investigates the dynamical processes responsible for the seasonal variability of the mesoscale eddies in the South China Sea (SCS). A three-scale energetics framework is employed, in which the original fields are decomposed into subfields on a nonstationary background flow window, a mesoscale eddy window and a high-frequency synoptic eddy window. Three local regions of high mesoscale eddy kinetic energy (EKE) levels, namely, the southwest of Taiwan Island (SWT), the southeast of Vietnam (SEV) and the northeast of the Natuna Island (NEN), are identified. The seasonal cycles of the mesoscale EKE in the three regions are not in phase, with peaks occurring around January, October and December, respectively. By diagnosing the canonical transfers between the background flow and the mesoscale eddies, we find that the seasonal cycle of the eddy variability in the SWT region is due to a mixed instability (baroclinic and barotropic instabilities), while barotropic instability plays a dominant role in determining the EKE seasonality in the SEV and NEN regions. This is quite different from the previous argument that baroclinic instability dominates the seasonal EKE in the SCS. The three-scale framework further reveals that high-frequency synoptic motions act to dissipate the lower-frequency mesoscale eddies through forward energy cascades. Besides the internal processes, external wind forcing is also found to influence the seasonal eddy variability, but is only limited to the NEN region. Our results highlight different mechanisms controlling the seasonal modulations of the mesoscale eddies in different regions of the SCS.

A viral RNA hijacks host machinery using dynamic conformational changes of a tRNA-like structure

A tricky mimicry RNA viruses use dynamic, multifunctional folded elements to hijack host cellular machinery. Bonilla et al . used cryo–electron microscopy (cryo-EM) to explore an RNA element from Brome mosaic virus that tricks host cell tyrosine transfer RNA synthetase (TyrRS) into adding a tyrosine to the viral genome’s 3′ end. Visualizing this RNA both in isolation and bound to a cellular TyrRS revealed a bound structure unlike the canonical transfer RNA L-like shape and conformational rearrangements in the RNA upon binding to the TyrRS, which suggests a multistep process of enzyme recognition. This study highlights the power of cryo-EM to illustrate dynamic processes involving small structured RNAs and RNA-protein complexes. —DJ

Drastic change in dynamics as Typhoon Lekima experiences an eyewall replacement cycle

Why does the 1909 typhoon, Lekima, become so destructive after making landfall in China? Using a newly developed mathematical apparatus, the multiscale window transform (MWT), and the MWT-based localized mutliscale energetics analysis and theory of canonical transfer, this study is intended to give a partial answer from a dynamical point of view. The ECMWF reanalysis fields are first reconstructed onto the background window, the TC-scale window, and the convection-scale window. A localized energetics analysis is then performed, which reveals to us distinctly different scenarios before and after August 8–9, 2019, when an eyewall replacement cycle takes place. Before that, the energy supply in the upper layer is mainly via a strong upper layer-limited baroclinic instability; the available potential energy thus-gained is then converted into the TC-scale kinetic energy, with a portion to fuel Lekima’s upper part, another portion carried downward via pressure work flux to maintain the cyclone’s lower part. After the eyewall replacement cycle, a drastic change in dynamics occurs. First, the pressure work is greatly increased in magnitude. A positive baroclinic transfer almost spreads throughout the troposphere, and so does barotropic transfer; in other words, the whole air column is now both barotropically and baroclinically unstable. These newly occurred instabilities help compensate the increasing consumption of the TC-scale kinetic energy, and hence help counteract the dissipation of Lekima after making landfalls.

Network Architecture of Gap Junctional Coupling among Parallel Processing Channels in the Mammalian Retina.

Gap junctions are ubiquitous throughout the nervous system, mediating critical signal transmission and integration, as well as emergent network properties. In mammalian retina, gap junctions within the Aii amacrine cell-ON cone bipolar cell (CBC) network are essential for night vision, modulation of day vision, and contribute to visual impairment in retinal degenerations, yet neither the extended network topology nor its conservation is well established. Here, we map the network contribution of gap junctions using a high-resolution connectomics dataset of an adult female rabbit retina. Gap junctions are prominent synaptic components of ON CBC classes, constituting 5%-25% of all axonal synaptic contacts. Many of these mediate canonical transfer of rod signals from Aii cells to ON CBCs for night vision, and we find that the uneven distribution of Aii signals to ON CBCs is conserved in rabbit, including one class entirely lacking direct Aii coupling. However, the majority of gap junctions formed by ON CBCs unexpectedly occur between ON CBCs, rather than with Aii cells. Such coupling is extensive, creating an interconnected network with numerous lateral paths both within, and particularly across, these parallel processing streams. Coupling patterns are precise with ON CBCs accepting and rejecting unique combinations of partnerships according to robust rulesets. Coupling specificity extends to both size and spatial topologies, thereby rivaling the synaptic specificity of chemical synapses. These ON CBC coupling motifs dramatically extend the coupled Aii-ON CBC network, with implications for signal flow in both scotopic and photopic retinal networks during visual processing and disease.SIGNIFICANCE STATEMENT Electrical synapses mediated by gap junctions are fundamental components of neural networks. In retina, coupling within the Aii-ON CBC network shapes visual processing in both the scotopic and photopic networks. In retinal degenerations, these same gap junctions mediate oscillatory activity that contributes to visual impairment. Here, we use high-resolution connectomics strategies to identify gap junctions and cellular partnerships. We describe novel, pervasive motifs both within and across classes of ON CBCs that dramatically extend the Aii-ON CBC network. These motifs are highly specific with implications for both signal processing within the retina and therapeutic interventions for blinding conditions. These findings highlight the underappreciated contribution of coupling motifs in retinal circuitry and the necessity of their detection in connectomics studies.

Spatiotemporal Variability of the Global Ocean Internal Processes Inferred from Satellite Observations

AbstractUsing a new analysis tool, namely, multiscale window transform (MWT), and the MWT-based theory of canonical transfer, this study investigates the spatiotemporal variations of the nonlinear interactions among the mean flows, interannual variabilities, quasi-annual fluctuations, and eddies in the global ocean. It is found that the canonical kinetic energy (KE) transfers are highly inhomogeneous in space, maximized in the western boundary current (WBC), Southern Ocean, and equatorial regions. In contrast to the equatorial and WBC regions where the temporal KE cascades are mainly forward, the Southern Ocean is the very place where coherent large-scale patterns of inverse KE cascade take place. The canonical transfers are also found to be highly variable in time. Specifically, in the Kuroshio Extension, the transfer from the mean flow to the interannual variability is in pace with the external winds from the eastern North Pacific; in the subtropical gyre, the mean flow-to-eddy transfer is responsible for the variability of the eddy kinetic energies (EKE) at both interannual and seasonal scales; in the tropics, the downscale transfers to the eddies from the other three scales all contribute to the interannual modulation of the EKE, and these transfers tend to decrease (increase) during El Niño (La Niña) events. In the Southern Ocean, the high-frequency eddies are found to feed KE to the low-frequency variability through temporal inverse cascade processes, which have been strengthened due to the enhanced eddy activities in the recent decade. Also discussed here is the relation between the seasonal EKE variability and the eddy–quasi-annual fluctuation interaction.

New Perspectives on the Generation and Maintenance of the Kuroshio Large Meander

AbstractThe internal dynamical processes underlying the Kuroshio large meander are investigated using a recently developed analysis tool, multiscale window transform (MWT), and the MWT-based canonical transfer theory. Oceanic fields are reconstructed on a low-frequency mean flow window, a mesoscale eddy window, and a high-frequency synoptic window with reference to the three typical path states south of Japan, that is, the typical large meander (tLM), nearshore non-large meander (nNLM), and offshore non-large meander (oNLM) path states. The interactions between the scale windows are quantitatively evaluated in terms of canonical transfer, which bears a Lie bracket form and conserves energy in the space of scale. In general, baroclinic (barotropic) instability is strengthened (weakened) during the tLM state. For the first time we found a spatially coherent inverse cascade of kinetic energy (KE) from the synoptic eddies to the slowly varying mean flow; it occupies the whole large meander region but exists only in the tLM state. By the time-varying multiscale energetics, a typical large meander is preceded by a strong influx of mesoscale eddy energy from upstream with a cyclonic eddy, which subsequently triggers a strong inverse KE cascade from the mesoscale window to the mean flow window to build up the KE reservoir for the meander. Synoptic frontal eddies are episodically intensified due to the baroclinic instability of the meander, but they immediately feed back to the mean flow window through inverse KE cascade. These results highlight the important role played by inverse KE cascades in generating and maintaining the Kuroshio large meander.

Causes and underlying dynamic processes of the mid-winter suppression in the North Pacific storm track

Baroclinic wave activity in the North Pacific exhibit peaks in late fall and early spring, and a local minimum in midwinter, when by linear baroclinic instability theory it should attain its maximum. This counterintuitive phenomenon, or “midwinter suppression” (MWM) as called, is investigated with a functional analysis apparatus, multiscale window transform (MWT), and the MWT-based theory of canonical transfer and localized multi-scale energetics analysis, together with a feature tracking technique, using the data from the European Centre for Medium-Range Weather Forecasts ReAnalysis (ERA-40). It is found that the MWM results from a variety of different physical processes, including baroclinic canonical transfer, diabatic effect, energy flux divergence, and frictional dissipation. On one hand, baroclinic canonical transfer and diabatic effect achieve their respective maxima in late fall. More transient available potential energy is produced and then converted to transient kinetic energy, resulting in a stronger storm track in late fall than in midwinter. On the other hand, in early spring, although baroclinic instability and buoyancy conversion are weak, energy flux convergences are substantially strengthened, leading to a net energy inflow into the storm track. Meanwhile, frictional dissipation is greatly reduced in spring; as a result, less transient energy is dissipated in early spring than in midwinter. It is further found that the weakening of baroclinic canonical transfer in midwinter (compared to late fall) is due to the far distance between the storm and the jet stream (located at its southernmost point), which suppresses the interaction between them. Regarding the increase in energy flux convergence in early spring, it appears to originate from the increase (enhancement) in the number (strength) of storms from the upstream into the Pacific.

Canonical transfer function of band‐pass NGD circuit

This study introduces the generalised canonical transfer function (TF) of the band-pass negative group delay (NGD) circuit. The principle to identify the unfamiliar band-pass NGD circuits is suggested. Similar to the filter theory, the band-pass NGD TF can be established from low-pass to band-pass frequency transform. The fundamental characteristics of the NGD topology are described. The canonical TF feasibility is concretised with the second-order equivalent impedance constituted by passive elements. The synthesis formulas in function of the desired NGD level and bandwidth are analytically established. Application examples of band-pass NGD impedance synthesis, designed and fabricated are proposed as a proof of concept. Prototypes of band-pass NGD circuits with centre frequencies 1 and 1.5 MHz for the targeted group delay optimal values, respectively, −1 and −1.5 µs are designed and fabricated. As expected, band-pass NGD results in good agreement with the theoretical prediction were obtained with simple lumped circuits. In the future, thanks to theory simplicity, the NGD band-pass cell can be potentially useful for the signal delay correction.

The intrinsic nonlinear multiscale interactions among the mean flow, low frequency variability and mesoscale eddies in the Kuroshio region

Using a new functional analysis tool, multiscale window transform (MWT), and the MWT-based localized multiscale energetics analysis and canonical transfer theory, this study reconstructs the Kuroshio system on three scale windows, namely, the mean flow window, the interannual-scale (low-frequency) window, and the transient eddy window, and investigates the climatological characteristics of the intricate nonlinear interactions among these windows. Significant upscale energy transfer is observed east of Taiwan, where the mean Kuroshio current extracts kinetic energy from both the interannual and eddy windows. It is found that the canonical transfer from the interannual variability is an intrinsic source that drives the eddy activities in this region. The multiscale variabilities of the Kuroshio in the East China Sea (ECS) are mainly controlled by the interaction between the mean flow and the eddies.The mean flow undergoes mixed instabilities (i.e., both barotropic and baroclinic instabilities) in the southern ECS, while it is barotropically stable but baroclinically unstable to the north. The multiscale interactions are found to be most intense south of Japan, where strong mixed instabilities occur; both the canonical transfers from the mean flow and the interannual scale are important mechanisms to fuel the eddies. It is also found that the interannual-scale energy mainly comes from the barotropically unstable jet, rather than the upscale energy transfer from the high frequency eddies.

The asymmetric eddy–background flow interaction in the North Pacific storm track

Using a recently developed methodology, namely the multiscale window transform (MWT) and the MWT‐based theory of canonical transfer and localized multiscale energetics analysis, we investigate in an eddy‐following way the nonlinear eddy–background flow interaction in the North Pacific storm track, based on the ERA‐40 reanalysis data from the European Centre for Medium‐Range Weather Forecasts. It is found that more than 50% of the storms occur on the northern flank of the jet stream, about 40% are around the jet centre, and very few (less than 5%) happen on the southern flank. For storms near or to the north of the jet centre, their interaction with the background flow is asymmetric in latitude. In higher latitudes, strong downscale canonical available potential energy transfer happens, especially in the mid‐troposphere, which reduces the background baroclinicity and decelerates the jet; in lower latitudes, upscale canonical kinetic energy transfer intensifies at the jet centre, accelerating the jet and enhancing the middle‐level baroclinicity. The resultant effect is that the jet strengthens but narrows, leading to an anomalous dipolar pattern in the fields of background wind and baroclinicity. For the storms on the southern side of the jet, the baroclinic canonical transfer is rather weak. On average, the local interaction begins about 3 days before a storm arrives at the site of observation, achieves its maximum as the storm arrives, and then weakens.