Quasi-stationary Jet Research Articles

Concurrent extremes in mid-latitude Asia triggered by resonance of multi-scale zonal wind

Abstract Climatic changes worsen concurrent extreme climate events. In July and August of 2022 and 2020, respectively, unexpected concurrent extreme events occurred in mid-latitude Asia. The sudden and severe consequences highlight the importance of a thorough understanding of the drivers of such extreme events, which is crucial for improving predictions and implementing preventive measures to mitigate future risks. By applying multi-scale window transform methodology, a unique mechanism of multi-scale zonal wind resonance is identified, which manifests as a quasi-stationary co-coupling with low-frequency zonal winds. This resonance leads to barotropic instability, triggering abnormal low-frequency Rossby wave behavior in the entrance and exit regions of the quasi-stationary jet stream. Simultaneously, the intensified meridional wind, coupled with adiabatic atmospheric warming, amplifies baroclinic instability, resulting in an enhanced wave pattern and the high concurrence events of 2022. Under long term future global warming levels of 4 °C, the concurrence, strengthened by multi-scale zonal wind resonance, is expected to persist. The mechanism evident in 2022 plays a broader and more significant role in concurrent events compared to the mechanism in 2020. Under the process of warming, resonance phenomena, as observed in 2022, are projected to become more frequent.

Steady nutrient upwelling around a biological hotspot of the confluence between the quasi-stationary jet and the Oyashio in the western North Pacific

The quasi-stationary jet, a branch of the Kuroshio Extension, transports warm saline water in the mixed water region of the western North Pacific. Around the subarctic front between the quasi-stationary jet and Oyashio and its downstream area is a biologically productive area including small pelagic fishes. However, how nutrient is supplied to the euphotic zone in this region remains elusive, especially into the quasi-stationary jet. Using high-resolution hydrography sections across the jet, we showed that Oyashio water isopycnally intrudes under the jet around 26.5–26.8 σθ and forms nutrient-rich intermediate water. Upwelling associated with ageostrophic secondary circulation across the front, caused by confluence, uplifts the intermediate water. A local nitrate maximum was also identified inside the jet by the hydrographic observation. Upwelling has been suggested as a precondition for nutrient supply from nutrient-rich intermediate water to the jet through water mixing which potentially sustains high biological production in the downstream.

A Hydrodynamic Model of a Magnetized Jet Flow in the Magnetosphere

Abstract—A new hydrodynamic model of a quasi-stationary jet is presented. Approximation of the idealhydrodynamics of an incompressible fluid is found using an analytical solution, corresponding to a jet limitedin space, under conditions of compensation for the nonlinear effects of velocity and magnetic field in theequation of motion. An axially symmetric low-parameter model of a stationary jet was created for the boundaryconditions typical for jets in astrophysics and in laboratory modeling experiments, which makes it possibleto describe the structure of the velocity field and magnetic field.

MOMO. IV. The Complete Swift X-Ray and UV/Optical Light Curve and Characteristic Variability of the Blazar OJ 287 during the Last Two Decades

Abstract We have been carrying out a dense monitoring of the blazar OJ 287 with Swift since late 2015 as part of our project MOMO (Multiwavelength Observations and Modeling of OJ 287). This is the densest existing monitoring of OJ 287 involving X-ray/UV data. In this latest publication of a sequence, we characterize the multiwavelength variability of OJ 287 based on >4000 Swift single-wave-band data sets including archival data since 2005. A structure function analysis reveals a characteristic timescale of ∼5 days in the optical–UV at epochs of low-level activity and larger during outbursts. The discrete correlation function shows zero lag between optical and UV, with τ = 0 ± 1 day at the epoch of densest cadence. During outbursts (in 2016/17 and 2020) the X-rays follow the UV with near-zero lags. However, during quiescence, the delay is 7–18 days with X-rays leading or lagging, interpreted as due to a different X-ray component dominated by inverse Compton emission. Scaling relations are used to derive the characteristic length scales of the broad-line region and torus in OJ 287. A remarkable, symmetric UV–optical deep fade is identified in late 2017, lasting 2 months. We rule out occultation from the passage of a dusty cloud and a model where the secondary black hole deflects the jet between the primary and observer. We speculate about a temporary dispersion or jet swing event in the core or in a bright quasi-stationary jet feature. The deep fade reveals an additional, spatially distinct X-ray component. The epoch 2020.9–2021.1 was searched for precursor flare activity predicted by the binary black hole model of OJ 287.

Surface water pathways in the subtropical–subarctic frontal zone of the western North Pacific

A peculiar water mass forms as a result of stirring and mixing between water originating from the Kuroshio and Oyashio currents in the Transition Domain, which is a boundary region between the subtropical and subarctic gyres extending zonally at approximately 40°N in the western North Pacific west of the dateline. The domain is important not only for oceanographic processes such as the inter-gyre exchange of water masses but also for mid-latitude climate and biological processes. We investigated how water from the Kuroshio and Oyashio currents is transported to the Transition Domain and then mixed, especially in relation to the geostrophic velocity fields, bottom topographic features, and the local eddy activity in the upstream region of the domain. We have clarified the pathways of the water from the Kuroshio and Oyashio currents from a Lagrangian point of view by conducting drifting buoy observations in 2015 and 2017, as well as by particle tracking using geostrophic surface flow fields. Herein, we visualize how the water pathways within and around the Transition Domain are closely tied to low-rise bottom topographic features. Time-variation of the geostrophic field in the upstream region of the Transition Domain also likely plays an important role in supplying water from the Kuroshio region to the Transition Domain; if a steady climatological flow field is used, the Transition Domain will be occupied solely by water from the Oyashio current. Once the water from the Kuroshio region enters a quasi-stationary jet in the western North Pacific (the so-called western Isoguchi Jet; J1) due to the eddies at the Oyashio Second Branch in addition to eddies at another region of the J1′s meander, it is further transported northeastward in the subarctic gyre via the Transition Domain. The subtropical–subarctic exchange through the Transition Domain could essentially be driven by the eddies in these local regions.

Large-scale distribution and composition of floating plastic debris in the transition region of the North Pacific

Floating plastic debris was investigated in the transition region in the North Pacific between 141°E and 165°W to understand its transportation process from Asian coast to central subtropical Pacific. Distribution was influenced primarily by the current system and the generation process of the high concentration area differed between the western and eastern areas. West of 180°, debris largely accumulated around nearshore convergent area and was transported by eddies and quasi-stationary jet from south to the subarctic region. The average was 15% higher than that previously reported in 1989, suggesting an increase in plastic debris in 30 years. East of 180°, debris concentrated in the calm water downstream of the Kuroshio Extension Bifurcation with considerably high concentration (505,032 ± 991,989 pieces km−2), due to the accumulation of small transparent film caused by calm weather conditions, suggesting a further investigation on small plastic (<1 mm) in the subsurface depth in the subtropical North Pacific.

Flow structure of a quasi-stationary jet in the western subarctic Pacific (the Western Isoguchi Jet)

The Western Isoguchi Jet, a quasi-stationary baroclinic jet that separates from the Kuroshio Extension, has been detected for a decade. Here we report the first observations of the vertical structure and temporal variations of the jet via moored current meters (September 2011–September 2012) and intensive hydrographic measurements (September 2010, 2011, and 2012). The jet flows northeastward and supplies subtropical water (northeastward velocity was ∼0.16ms−1 and temperature was ∼4.4°C at 300m depth, and they were ∼0.05ms−1 and ∼2.9°C at 1000m depth). We newly estimated the volume, heat, and salt transports of the jet to be 13.6–26.5Sv, 0.0745–0.173PW (reference potential temperature of 4.0°C), and 5.58–9.91×106kgs−1 (reference salinity of 33.5), respectively. Year-to-year changes of the jet axis complicated its horizontal distribution. The jet flowed stably northeastward throughout the year with weak seasonal variability. The vertical structure of the jet is quite different from that of the surrounding flow. These observations are consistent with the mechanism proposed by Mitsudera et al. (2018) and Miyama et al. (2018) to be responsible for the formation and maintenance of the jet.

A Recollimation Shock in a Stationary Jet Feature with Limb-brightening in the Gamma-Ray-emitting Narrow-line Seyfert 1 Galaxy 1H 0323+342

Abstract We report the discovery of a local convergence of a jet cross section in the quasi-stationary jet feature in the γ-ray-emitting narrow-line Seyfert 1 galaxy (NLS1) 1H 0323+342. The convergence site is located at ∼7 mas (corresponding to the order of 100 pc in deprojection) from the central engine. We also found limb-brightened jet structures at both the upstream and downstream of the convergence site. We propose that the quasi-stationary feature showing the jet convergence and limb-brightening occurs as a consequence of recollimation shock in the relativistic jets. The quasi-stationary feature is one of the possible γ-ray-emitting sites in this NLS1, in analogy with the HST-1 complex in the M87 jet. Monitoring observations have revealed that superluminal components passed through the convergence site and the peak intensity of the quasi-stationary feature, which showed apparent coincidences with the timing of observed γ-ray activities.

Dynamics of a Quasi-Stationary Jet along the Subarctic Front in the North Pacific Ocean (the Western Isoguchi Jet): An Ideal Two-Layer Model

ABSTRACTThe dynamics of a quasi-stationary jet along the Subarctic Front in the North Pacific Ocean (the Western Isoguchi Jet) were investigated using an idealized two-layer model. The experiments suggested that a seafloor topography, which is 500 m high, produces a jet along its eastern flank. The formation mechanism of the jet can be explained via baroclinic Rossby wave characteristics. Baroclinic Rossby waves propagate along characteristic curves, which are significantly distorted by anticyclonic barotropic flow on the seafloor topography. A baroclinic surface jet is formed where a characteristic curve originating in the subtropical gyre and one originating in the subpolar gyre meet because the pycnocline depth varies discontinuously at this location. The barotropic flow on the seafloor topography is induced by eddies.

Long-term mean and seasonal variation of altimetry-derived Oyashio transport across the A-line off the southeastern coast of Hokkaido, Japan

To understand long-term mean and seasonal variations of the Oyashio transport off the southeastern coast of Hokkaido, time series of estimated transports were generated by combining satellite altimetry and CTD data from the period 1993–2014 along a monitoring transect referred to as the “A-line”. Linear regressions between CTD-derived geostrophic transport and altimetry-derived sea level anomaly differences were calculated by minimizing a cost function newly proposed in this study. The horizontal structure of 21-year mean transport was characterized by a southwestward flow on the continental slope (SW-1) associated with the First Oyashio Intrusion, a northeastward flow (NE-2) likely trapped against the Kuril-Kamchatka trench, a southwestward flow (SW-3) related to the Second Oyashio Intrusion, and a very stable northeastward flow (NE-4) corresponding to a combination of the Oyashio Return Flow and quasi-stationary Jet. Analysis of long-term mean monthly transports revealed four alternating flows that were present throughout all seasons of the year. The boundaries between adjacent pairs of the four flows on the A-line did not change on a seasonal timescale as much as the southernmost latitude of the First Oyashio Intrusion. At a 0-month (1-month) time lag, the sum of the SW-1, NE-2, and SW-3 (SW-1 and NE-2) transports, which corresponds to net Oyashio transport (partial net Oyashio transport related to the southernmost latitude of the First Oyashio Intrusion), was correlated with Sverdrup transport more robustly than was each of the four alternating flows. This result suggests that as the Oyashio crossed the A-line, it responded barotropically to basin-scale wind stress by adjusting transports composed of both southwestward and northeastward flows.

The influence of the Gulf Stream on wintertime European blocking

Wintertime blocking is responsible for extended periods of anomalously cold and dry weather over Europe. In this study, the influence of the Gulf Stream sea surface temperature (SST) front on wintertime European blocking is investigated using a reanalysis dataset and a pair of atmospheric general circulation model (AGCM) simulations. The AGCM is forced with realistic and smoothed Gulf Stream SST, and blocking frequency over Europe is found to depend crucially on the Gulf Stream SST front. In the absence of the sharp SST gradient European blocking is significantly reduced and occurs further downstream. The Gulf Stream is found to significantly influence the surface temperature anomalies during blocking periods and the occurrence of associated cold spells. In particular the cold spell peak, located in central Europe, disappears in the absence of the Gulf Stream SST front. The nature of the Gulf Stream influence on European blocking development is then investigated using composite analysis. The presence of the Gulf Stream SST front is important in capturing the observed quasi-stationary development of European blocking. The development is characterised by increased lower-tropospheric meridional eddy heat transport in the Gulf Stream region and increased eddy kinetic energy at upper-levels, which acts to reinforce the quasi-stationary jet. When the Gulf Stream SST is smoothed the storm track activity is weaker, the development is less consistent and European blocking occurs less frequently.

Currents Associated with the Quasi-Stationary Jet Separated from the Kuroshio Extension

Abstract The hydrographic structure of a quasi-stationary jet separated from the Kuroshio Extension, a phenomenon that possibly leads to deepening of the winter mixed layer, is revealed via intensive observations using a conductivity–temperature–depth profiler and a ship-mounted acoustic Doppler current profiler (ADCP) carried out in September 2009. Data collected from profiling floats set to drift isopycnal layers and time series of sea surface buoys and satellite altimeters were also analyzed to understand the continuity, water characteristics, and time variation of the jet. Although the flow field was complex due to disturbances such as energetic eddies, the jet transported subtropical water to the downstream (northeastern) observation region in a layer shallower than 400 dbar and its highest velocity was concentrated in the mid- and deep layers (≤0.30 m s−1 at the sea surface and ≥0.05 m s−1 at 800-m depth). The velocity axes of the jet detected from the satellite data corresponded to those detected through analysis of the ADCP data, and the intensity of the jet at the sea surface varies over interannual-to-decadal time scales. Part of the interannual-to-decadal variation in the velocity field of the jet is controlled by the dynamic state of the Kuroshio Extension and is correlated with that of the Kuroshio Extension latitude (linear correlation coefficient r ~ 0.67). The relationship between these variations can be interpreted qualitatively as being responsible for the inertial streamers that separate from the crests of meanders of the Kuroshio Extension to the jet region due to the large steering effect.

Interannual variability of high potential vorticity in South Atlantic

In this study, we examined intrusions of the high potential vorticity (HIGH-PV) at the 350 K isentropic level over the South Atlantic during the period December–January–February (DJF) 1979–2001. These events have a large interannual variability and are negatively correlated with the Southern Oscillation Index. Many events occur during the El Nino years except in 1997/1998, while there are none or few cases in La Nina years except in 1988/1989. The intrusion events which show interactions between the tropics and extratropics are associated with the ‘westerly ducts’ in the tropics and also with the amplitude of quasi-stationary waves and subtropical jet intensity. Copyright © 2011 Royal Meteorological Society

A possible jet precession in the periodic quasar B0605–085

The quasar B0605-085 (OH 010) shows a hint for probable periodical variability in the radio total flux-density light curves. We study the possible periodicity of B0605-085 in the total flux-density, spectra and opacity changes in order to compare it with jet kinematics on parsec scales. We have analyzed archival total flux-density variability at ten frequencies (408 MHz, 4.8 GHz, 6.7 GHz, 8 GHz, 10.7 GHz, 14.5 GHz, 22 GHz, 37 GHz, 90 GHz, and 230 GHz) together with the archival high-resolution very long baseline interferometry data at 15 GHz from the MOJAVE monitoring campaign. Using the Fourier transform and discrete autocorrelation methods we have searched for periods in the total flux-density light curves. In addition, spectral evolution and changes of the opacity have been analyzed. We found a period in multi-frequency total flux-density light curves of 7.9+-0.5 yrs. Moreover, a quasi-stationary jet component C1 follows a prominent helical path on a similar time scale of 8 years. We have also found that the average instantaneous speeds of the jet components show a clear helical pattern along the jet with a characteristic scale of 3 mas. Taking into account average speeds of jet components, this scale corresponds to a time scale of about 7.7 years. Jet precession can explain the helical path of the quasi-stationary jet component C1 and the periodical modulation of the total flux-density light curves. We have fitted a precession model to the trajectory of the jet component C1, with a viewing angle phi=2.6+-2.2 degrees, aperture angle of the precession cone Omega=23.9+-1.9 degrees and fixed precession period (in the observers frame) P = 7.9 yrs.

An ensemble of dynamically identical thermals and vertical profiles of turbulent moments in the convective surface layer of atmosphere

An ensemble of convective thermals is distinguished from the surface layer of penetrative turbulent convection over a heated horizontally uniform surface. For an isolated convective element, an integral model of a quasi-stationary spontaneous jet is proposed which admits an exact analytical solution. A simple statistical model is constructed for an ensemble of dynamically identical thermals. In this model, convective thermals ascend in a static environment, their dynamic parameters are described by the equations of an isolated quasi-stationary jet, and their diameters are stochastic. It is shown that the ensemble of thermals rising in a horizontally homogeneous environment forms surface-layer turbulent moments. The analytical relationships for higher turbulent moments of vertical velocity and temperature are compared with experimental data from the second to the forth order inclusive.

On the Mechanism of Cyclonic Circulation in Lake Kinneret in Summer

In summer, the circulation of water in Lake Kinneret stratified in the vertical direction is characterized by the presence of a quasistationary jet coastal cyclonic current [S. Serruya, Ver. Int. Verein. Limnol., 19, 73 (1975) and S. Serruya (ed.), Lake Kinneret, Junk, Hague (1978)]. This circulation cannot be described by a fairly complete three-dimensional baroclinic model [V. A. Ivanov, S. P. Lyubartseva, et al., Morsk. Gidrofiz. Zh., No. 6, 26 (2001)] if the motion is induced by the action of monthly average external factors. Within the framework of a two-layer model of round lake with parabolic bottom, it was shown [H. W. Ou and J. R. Bennett, J. Phys. Oceanogr., No. 6, 1112 (1979)] that cyclonic currents may appear under the action of daily variations of spatially homogeneous winds caused by the influence of nonlinearity and friction on the forced Kelvin internal waves. Daily variations of the wind in the investigated region are connected with the consecutive transformations of the local land breeze (i.e., a relatively weak wind blowing from the land to the lake and characterized by the presence of wind convergence) into the large-scale sea breeze (i.e., a practically uniform strong wind blowing from the Mediterranean Sea) and vice versa. However, the numerical experiments performed by using the three-dimensional model of Lake Kinneret [V. A. Ivanov, S. P. Lyubartseva, et al., Morsk. Gidrofiz. Zh., No. 6, 26 (2001)] show that, for the correct description of the circulation of waters in the lake, it is necessary to take into account not only the time variability of the wind [see H. W. Ou and J. R. Bennett, J. Phys. Oceanogr., No. 6, 1112 (1979)] but also its horizontal inhomogeneity, i.e., the cyclonic vorticity of the wind, predominant in its daily variation. The indicated cyclonic vorticity is formed during the period of land breeze as a result of the wind convergence caused by the rotation of the Earth.

On the Nature of Variability of Extragalactic Radio Sources: Fundamental Ideas by I.S. Shklovsky

The majority (maybe all) of proposed relativistic and non-relativistic models for variable extragalactic radio sources are based on the same general ideas proposed in the early model by Shklovsky (1960, 1965) – in particular, that the variability is caused by the synchrotron emission of magnetized clouds during their expansion. This model was a "standard" or "canonical" model for more than 20 years. One of the models that uses its ideas and approach is the "hedgehog" model, in which clouds or jets emit and expand in the strong external radial magnetic field of the nucleus of the source. This model has been suggested for a long time, but recent new results comparing it's predictions with observations of multifrequency spectra – especially, instantaneous spectra of many variable sources – and with the typical VLBI structure of compact objects have given strong new arguments in it's favour. The nature of the variability can be satisfactory explained by the hedgehog jet model for many variable and compact extragalactic radio sources. Thus, following up the ideas of I.S. Shklovsky, we conclude that the observed spectra and structure of compact sources can be caused by the synchrotron emission of a quasi-stationary jet in a longitudinal magnetic field, and the nature of variability can be explained by the variable ejection of the continious jet from the nucleus.

Formation of a quasistationary jet within a nozzle during its shock start-up

Formation of a quasistationary jet within a nozzle during its shock start-up