Anticyclonic Sense Research Articles

Weather systems and extreme rainfall generation in the 2019 north Queensland floods compared with historical north Queensland record floods

Earlier papers have addressed floods from warm-air advection (WAA) in southeast Australia and around the globe, and extreme rainfall in US hurricanes and Australian tropical cyclones (TCs). This is the first paper to address the WAA phenomena in causing monsoon and TC floods and in TC-like systems which develop over the interior of northern Australia. The inland events help explain Australia’s worst tropical flooding disaster in 1916. A disastrous series of floods during late January and early February 2019 caused widespread damage in tropical north Queensland both in inland regions and along the coast. This occurred when some large-scale climate influences, including the sea surface temperatures suggested conditions would not lead to major flooding. Therefore, it is important to focus on the weather systems to understand the processes that resulted in the extreme rainfall responsible for the flooding. The structure of weather systems in most areas involved a pattern in which the winds turned in an anticyclonic sense as they ascended from the low to middle levels of the atmosphere (often referred to as WAA) which was maintained over large areas for 11 days. HYSPLIT air parcel trajectory observations were employed to confirm these ascent analyses. Examination of a period during which the heaviest rain was reported and compared with climatology showed a much stronger monsoon circulation, widespread WAA through tropical Queensland where normally its descending equivalent of cold-air advection is found, and higher mean sea level pressures along the south Queensland coast. The monsoon low was located between strong deep monsoon westerlies to the north and strong deep easterlies to the south which ensured its slow movement. This non-TC event produced heavy inland rainfall. Extreme inland rainfall is rare in this region. Dare et al. (2012), using data from 1969/70 to 2009/10, showed that over north Queensland non-TC events produced a large percentage of the total rainfall. The vertical structure associated with one of the earlier events that occurred in 2008 had sufficient data to detect strong and widespread WAA overlying an onshore moist tropical airstream. This appears to have played a crucial role in such extreme rainfall extending well inland and perhaps gives insight to the cause of a 1916 flooding disaster at Clermont which claimed around 70 lives. Several other events over the inland Tropics with strong WAA also help explain the 1916 disaster.

Statistical analyses of eddies in the Western Mediterranean Sea based on Synthetic Aperture Radar imagery

We analysed 7188 Sentinel-1A Synthetic Aperture Radar (SAR) images acquired in a 3-year period, between October 2014 and September 2017, in the Western Mediterranean Sea and found imprints of about 14,300 oceanic eddies with diameters ranging from 0.4 km to 160.1 km. Those eddies manifest on the SAR imagery either through the accumulation of surfactants or through wave-current interaction, and considering the favourable wind-speed ranges for both mechanisms we performed statistical analyses to gain insight into the eddies' spatio-temporal distribution, their typical sizes and shapes, and into the predominant mechanisms that are responsible for their formation. The vast majority of the detected eddies is elliptical, with a tendency for only large mesoscale eddies towards a circular shape. We found no general influence of the wind on the eddies' orientation, although mesoscale eddies tend to orient into the main current direction in each subregion. Submesoscale eddies do not show such tendency. Submesoscale eddies in the Western Mediterranean Sea are predominantly cyclonic (>90%), and with increasing eddy diameter there is a transition from cyclonic to anticyclonic sense of rotation. In general, we found highest densities of submesoscale eddies in autumn, when the biological activity is still high and when mean regional winds are already strong, but variable. In addition, instabilities of thermal fronts during summer and autumn and instabilities of the main and secondary currents influence the formation of submesoscale eddies. Some of our results confirm those previously obtained for other regions.

On the dynamics of current jets trapped to the flanks of mid-ocean ridges

[1] Time-mean abyssal current observations over the flanks of the East Pacific Rise (EPR) at 9–10°N and at the Juan de Fuca Ridge at 45°N document the occurrence of paired along-ridge current jets that are trapped to the ridge flanks and sheared across the ridge in an anticyclonic sense. A coincident feature, where local hydrothermal discharge effects are not in play, is the upward bowing of isopycnals over ridge crests and isopycnals plunging into ridge flanks. It would be tempting to explain the jets primarily as geostrophic responses to the doming/plunging isopycnal distribution, though that should lead to the question as to how the isopycnal perturbations originate. A numerical model of time-dependent flow on a cross-ridge (x–z) transect, forced in a way to be consistent with a yearlong, hourly sampled record of currents measured at the EPR ridge crest, is used to investigate some of the underlying physics. It will be shown that the jets can arise from oscillatory flows via eddy-momentum, eddy-heat, and eddy-salt fluxes that ultimately cause the isopycnals to dome over the ridge. As the probable offspring of velocity-velocity and velocity-density correlations that depend upon oscillatory motion, the jets are likely examples of stratified topographic flow rectification. An ancillary feature is a slight yearlong-averaged downward current O (0.1–0.5 mm/s) over the EPR ridge crest that crosses the time-mean, upward bowing isopycnals in a counter-intuitive vertical direction.

Ocean currents at Axial Volcano, a northeastern Pacific seamount

Axial Volcano is a magmatically active seamount that straddles the Juan de Fuca Ridge (JdFR). With a summit depth of ∼1400 m, the volcano intercepts deep ocean flows at a height well above that of the linear ridge adjoining it to the north and south. Multiyear, yearlong observations of currents at Axial show that mean flow circles the seamount in an anticyclonic sense, consistent with dynamical constraints, with means as large as 6.6 cm s−1. Spectra of currents indicate prominent tidal, inertial, and in some cases weather‐band period (3‐ to 7‐day) peaks, as has been seen elsewhere along the JdFR ridge. For K1, O1, and S2 tidal currents at the seamount, amplitudes are several times larger than the corresponding background amplitudes and rotation around the tidal current ellipses is anticyclonic. M2 tidal currents show none of the same properties. Energy at the inertial frequency decreases by more than an order of magnitude from 100 m above to 400 m below the volcano's summit. In contrast, weather‐band (WB) period energy increases tenfold over the same depth range, with WB energy all but unobservable at summit depth. The presence of WB oscillations makes Axial unlike other seamounts where long observations have been made. The current meter observations also provide a picture of seasonal trends. As expected, during the period Summer 1996 to Spring 1997, largest amounts of WB energy are found during autumn and winter; in contrast, WB motion at Axial Volcano during Winter 2000 was summer‐like in intensity. A linear, baroclinic model of forced damped azimuthal mode‐one oscillatory flow around an idealized axisymmetric seamount shows that amplification of diurnal flow should occur principally at the seamount summit while amplification of the WB should occur, as the observations show, on the seamount flanks. Model and measured phase relationships for temperature and current time series pairs circumscribing Axial support the view that azimuthal mode‐one oscillations are prominent. Over the 0.8‐ to 6‐day range for forcing period (TC) the model indicates that the principal topographic resonance, as indicated by kinetic energy (KE) amplification, occurs for a TC greater than 1 and less than 2 days with only mild dependence in that range on background stratification and seamount shape. Additional but weaker topographic resonances can occur at longer periods in model results, but as TC becomes slightly larger than the frictional timescale, topographic resonances no longer appear. High dissipation and thus short frictional timescales reported by others in regions of rough, sloping topography make topographic resonances at Axial at periods greater than a few days somewhat unlikely. The relatively broad WB spectral peaks at some Axial sites are consequently more likely the result of spectral peaks in forcing than of topographic resonance.

Flood–ebb disparity of tidally induced recirculation Eddies in a semi-enclosed basin: Nan Wan Bay

Nan Wan Bay is a semi-enclosed basin forming the southern tip of Taiwan. Around spring tides, a recirculating cyclonic eddy occupying a good portion of the basin develops daily during the ebb current. The eddy induces sudden temperature drops inside the Bay lasting for a few hours each. An anticyclonic recirculation eddy, if any, is much reduced in size and confined to the eastern side of the basin during the flood current. Mechanisms leading to the flood–ebb disparity of recirculation eddies are investigated below using a three-dimensional numerical tidal model. By systematically adding or removing topographic features in and around Nan Wan, the process of elimination points to two topographic features that are responsible for the flood–ebb disparity. One is a bottom ridge around the eastern cape of the Bay; the other is an elongated seamount along the mouth of the semi-enclosed basin. These topographic features deflect tidal currents in the anticyclonic sense. Bayward and seaward deflections of tidal currents weaken and strengthen recirculating eddies, respectively, producing the flood-ebb disparity. The two topographic features enhance the cyclonic eddy during ebb, especially when the prevailing tidal current off the Bay is strong. For a typical embayment with tidal currents parallel to the bay mouth, the cyclonic eddy is expected to dominate over the anticyclone if there is a prominent seamount blocking the middle reaches of the mouth region.

Convective circulation in mesoscale abyssal basins

Deep circulation in natural water basins that are smaller than the large global abyssal ocean, but bigger than a Rossby radius of deformation is both scantily documented and poorly understood. For buoyancy driving alone, angular momentum balance dictates that currents of both cyclonic and anticyclonic sense of circulation must exist, although both senses need not be of the same magnitude in the interior. Three laboratory experiments performed on a rotating turntable have been found with interior velocities that demonstrate layers with alternating cyclonic and anticyclonic azimuthal circulation. In one example an internal thermocline implies there is a set of two stacked meriodonal cells of opposite sign. Numerical results and laboratory data display qualitative agreement over a wide range of parameters. Quantitative comparison is within roughly two in the worst cases, but somewhat better for other cases. An argument based upon energetics is advanced which produces a velocity scale in rough agreement with some of the laboratory and numerical results.

Diurnal Changes in Sea-Breeze Direction

Abstract Simple mathematical theory suggests that the direction of the sea breeze must veer (move in an anticyclonic sense) during the day, until it is blowing parallel to the coast. Many observations of sea-breeze hodographs have shown that this rotation often does not occur and may sometimes be in the opposite (cyclonic) direction. Papers by Neumann and coworkers showed that either anticyclonic or cyclonic rotation could result from suitable combinations of Coriolis force and pressure gradient. Some observed examples of such cyclonic rotation are explained in the shift of direction from a “local sea breeze” to a “continental sea breeze” of a different direction; the strong pressure gradients associated with mountains can also produce cyclonic rotation. A study of the measured pressure gradient and wind velocities from southern England are shown to agree with the analysis of Neumann. It is concluded that topographical influences can often be responsible for cyclonic, rather than the expected anticyclonic...

On the branching of the Kuroshio west of Kyushu

Trajectories of satellite‐tracked surface drifters released in the continental margin area west of Kyushu indicate a separation of the inshore side of the Kuroshio that appears to form the beginning of the Tsushima Current. The trajectories also indicate an anticyclonic sense of circulation in the area between the separated branch and the eastward directed Kuroshio main stream, consistent with long‐term geomagnetic electrokinetograph measurements of surface currents, which show a broad southward flow along the west Kyushu coast. A theory is put forth that ties together these observed flow features. In the theory, the incidence is considered of an inertial current upon a step rise in topography (characterized by a step depth of H0 to simulate the west Kyushu coastal bathymetry) in an f plane, two‐layered, inviscid ocean with a quiescent lower layer. The inertial current is of a constant potential vorticity f/H, where H (>H0) is the undisturbed upper layer depth and is bounded inshore by a free streamline along which the upper layer depth is a constant hc (<H). The steady state downstream configuration of a separation branch and a deflected main stream along the step is connected to the upstream approach current through the consideration of the constancy of the Bernoulli function and the conservation of potential vorticity and mass. In the immediate neighborhood of the incidence, a complicated flow region is anticipated in which recirculation is featured and an anticyclonic gyre is expected further onto the step. The volume‐integrated balance of along‐step momentum of the constant potential‐vorticity flow allows the determination of the angle the branch current makes with the step as a function of the angle of incidence and two depth ratios, hc/H and H0/H. The bifurcation quotient, defined as the ratio of the branch current transport to that of the approach current, is found to be also such a function, except it is independent of the incidence angle. These functions yield results that are qualitatively in agreement with the observed bifurcation of the Kuroshio west of Kyushu that gives rise to the Tsushima Current.

Propagation of Low-Level Circulation Features in the Vicinity of Mountain Ranges

Abstract The local influence of mountains upon large- and synoptic-scale low-level atmospheric circulations is investigated in this study. The sea-level pressure associated with low-frequency fluctuations exhibit phase propagation of monopolar structures around mountains in an anticyclonic sense, while the corresponding 500 mb height patterns are relatively stationary and evolve in a manner consistent with the concept of Rossby wave dispersion on a sphere. The sea-level pressure patterns in the high-pass filtered data exhibit characteristics of synoptic-scale baroclinic waves and are steered around mountain ranges in an anticyclonic sense, while the corresponding 500 mb height patterns propagate nearly parallel to the time-mean flow in the middle troposphere. It is hypothesized that the phase propagation of lower tropospheric circulation patterns is a reflection of the conservation of potential vorticity in flows over variable terrain. Most of the observations presented in this study are interpreted as th...

Rossby autosoliton and stationary model of the jovian Great Red Spot

A theory proposed about 10 years ago claimed that the jovian Great Red Spot (GRS) was a solitary wave vortex (Rossby soliton) kept stationary by counter–streaming zonal winds. We have attempted to verify this soliton theory experimentally. The jovian atmosphere is modelled by a rotating thin parabolic layer of fluid (shallow water) with a free surface in which counter-streaming (zonal) flows are excited mechanically. We have found that instability of these flows can generate a Rossby autosoliton, that is, an undamped stationary solitary vortex which is alone on the perimeter of the system. This vortex rotates around its axis in the anticyclonic sense and drifts in the opposite direction to the global rotation of the system. As the observed Rossby soliton can be considered as a physical analogue (or rather as a stationary physical model) of a natural vortex such as the GRS, the results of our experiments can be considered to support the soliton theory of the GRS. We have compared the soliton model with another physical model of the GRS based on thermoconvection in rotating deep water under the action of a transverse non-monotonic temperature gradient. A new model based on a synthesis of these ideas is urgently required.

Tidal rectification and frontal circulation on the sides of Georges Bank

Using Wright and Loder's (l985a,b) depth-dependent tidal rectification model and Garrett and Loder's (1981) diagnostic frontal circulation model, predictions of the residual circulation associated with the topographic rectification of tidal currents and the summertime density field on the northwestern and open ocean sides of Georges Bank are made and compared with observations. In general, the estimates of both wintertime and summertime along-isobath currents are in qualitative agreement with observations, but the agreement between predicted and observed cross-isobath currents is poor. The circulation associated with tidal rectification is primarily along isobaths in an anticyclonic sense around the Bank at all depths. The cross-isobath circulation is much weaker and, in the Eulerian specification, is dominated by two cells with opposing current directions. However, a significant Stokes velocity is predicted such that the along-isobath Lagrangian current is generally less than its Eulerian counterpart, and the cross-isobath Lagrangian current is sometimes in the opposite direction to its Eulerian counterpart. Both the along-isobath and cross-isobath currents associated with tidal rectification are predicted to be significantly stronger in summer than in winter due to a reduction in the strength of friction as a result of reduced wind stress and increased density stratification. An additional contribution to the anticyclonic circulation around Georges Bank is associated directly with the summertime tidal front around the Bank. This flow component is predicted to form a second intense along-isobath jet on the northwestern side, slightly off-bank of that due to tidal rectification, and a broader flow on the open ocean side. The associated cross-isobath circulation is predicted to be much weaker than the along-isobath circulation, with a general on-bank bottom flowon both sides of the Bank.

Climatology of tropical cyclone genesis in the Australian region

AbstractStatistics of tropical cyclone origin in the Australian region are presented for the period July 1959‐June 1979. Cyclone genesis is found to occur in preferred areas and to have a high incidence of coastline developments, often with the precursor system forming over land. There is an average of 1.3 occurrences per year of ‘regeneration’ whereby a cyclone develops from a pre‐existing cyclone which has lost intensity after crossing on to the continent.A synoptic analysis of individual developments over five years reveals that 84 per cent of the pre‐cyclone cloud clusters first appear on the gradient level monsoon shear line, whereas 97 per cent are on the shearline at the point of development. Statistical evidence is given for the enhancement of lower and upper level vorticity fields by mid‐latitude systems prior to cyclone genesis, but on a case by case basis the role of these systems is highly variable.The structure of the pre‐cyclone systems for individual cases and composites shows the upper level warm core and large scale cyclonic surrounding circulation in the middle and lower troposphere, known to exist for similar systems in other parts of the world. At upper levels the systems are surrounded by tangential winds in the anticyclonic sense beyond 6 degrees latitude radius.

Measuring vertical vorticity in the sea

Several attempts were made to observe the vertical vorticity in the sea with a neutral buoyant float fitted with either vertical vanes or radial rods. Measurements over periods of several days were made in deep water off the New England coast, in the Gulf Stream, and southwest of Bermuda. The apparent vorticity at all locations from the float rotation, appears to fluctuate with a magnitude of several revolutions per hour in both a cyclonic and anticyclonic sense.

Sketch of the Climate of China.

China is a vast country with various topographical pecularities. As regard the climate of China however the great stretch in latitude and diversity in topo-graphy make no significant differences. The general character of the climate is, in the first place, determined by the prevalence of the monsoons. In winter cold air flows out all over the Far East from the grand anticyclonic area over south-eastern Siberia with its centre near Lake Baikal. This monsoon current bifurcates into two branches, one of them flowing around the Aleutian low in a cyclonic sense, and the other into the equatorial low area to the south of the China sea in an anticyclonic sense. Thus the winter monsoon comes from the northwest in north China and from the northeast in south China. In the cold season the monsoon blows very strongly and continues for many days together.Winter is very cold and dry in north China. The mean January temperature is -4.5°C. at Peking and -7.3°C. at Tayuan. The total fall of precipitation in January is 2.5mm at Peking and 2.1mm at Tayuan.In Summer the air flows into the Mongolian area of low pressure from the neighbouring seas and oceans. This monsoon blows from south to east in north China and southwesterly in south China. The summer monsoon is weak and intermittent. The isotherms run almost parallel to the coast line, the temperature becoming higher as we go to the interior. Thus the July temperature is 26.4°at Peking, 27.2° at Shanghai, 28.1° at Foochow and 27.9° at Hongkong. We have 30.8°C. at Hangchow, 29.9° at Kiukiang and 28.5°C. at Hankow. The rain falls copiously, the total fall in July being 200mm at Peking, 129mm at Shanghai, 180mm at Hankow, 202mm at Chengtu, and 333mm at Hongkong.The most noteworthy phenomena in the climatology of north China is dust storm in early spring and that in central China the Mai-yu or the plum-rain in early summer.China proper may be divided into four climatic regions, namely, north, central, south, and interior China climatic divisions. To these we may add the Outer Mongolia and Tibet as the remaining climatic regions.

ビンナガマグロ漁況との關係(第 1 報)

Based mainly on the latest materia's given by the local fisheries authorities in l'refs. Siduoka, Kanagawa, etc. we have investigated the catch of ‘Binnaga Maguro’ (Germo germo (Lacepede)) in relation to the hydrographical conditions. The seasonal variations of the catch of ‘Binnaga’ in every year are nearly of the same type (Fig. 1); the so-called winter season begins in October, showing its flowering season from Dec. to Feb., and ends in the middle decade of April. And the so-called summer season begins from the late April, showing its flowering season in the interval from middle May to middle June, and ends in July. Inspecting Fig. 2 we notice the remarkable decline of the summer catch (landed mainly at the harbours in Siduoka Pref.) in the adjacent waters of Japan. On the other hand, the winter off-shore fishing grounds were extended year by year to the east with the increase of the landings, and now cover the waters distant about 2, 000 sea-miles from our coast. The former fishing ground moves north-easterly from spring to summer with the advance of Kur03iWO, while the latter (in winter) accumulates in the regions along the line of subtropical convergence. Apparently we can see the fishing grounds during the whole year rotating in the anti-cyclonic sense with the run of Kurosiwo and its back current of salty water-masses. The optimum water temperature of the catch lies at 17°-19°C (max. at about 18°C) in Nov. -Feb., but lying at 18°-21°C (max. at about 20°C) in May and June. The catch represents 2 maxima in winter, one at the salinity of 34•6-14•9% and the other above 35•5%, while in summer only one at 34•8 %. The shoals distributed in the region comparatively near the land lack the large-sized fishes and contain more small-sized ones than off-shore shoals. In conclusion, summarizing the above mentioned facts, the writer (M. UDA) proposes the following hypothetical theory on the migration of Binnaga Maguro, following the instructions kindly given him by Dr. M. TAUTI: There are two partially inter-related stocks, one in the waters near the land (I) and the other in the offing (II). The former consists of the native stock A0 and the incoming stock from (II) B' (of small and partially of middle-sized fish), while the latter (II) consists of the native stock BO and the incoming stock from (I) A' (of medium and partially of small sizes). The recent overfishing of (I), particularly of A, , caused the decline of the yield of `Binnaga Maguro' in summer.

颱風の高さと上層雲の雲行き

In the inner zone of a typhoon, centering at 20°_??_30°N latitude even at the altitude of high clouds, the spirally inflowing currents in cyclonic sense are often observed. The neutral plane must then lie higher than the level of high clouds. Also the outflowing currents in anticyclonic sense at the level of high clouds are also observed. Thus the observational material of high clouds in the inner zone of a typhoon, gives a good evidence in favor of the view that a tropical cyclone have about the same height as the cyclone of middle latitudes, and that the height of the neutral plane is estimated to be about 10 km.