Generation Of Eddy Kinetic Energy Research Articles

Investigation of ocean environmental variables and their variations associated with major Loop Current eddy-shedding events in the Gulf of Mexico

The eddy kinetic energy (EKE) variability associated with 26 major Loop Current eddies (LCEs) in the Gulf of Mexico from 1994 through 2019 was investigated. We employed 3D multivariate observation-based ARMOR3D monthly ocean analyses of salinity, temperature, and geostrophic velocity field data. In addition, we used ERA5 wind data, the fifth generation of the European Centre for Medium-Range Weather Forecasts (ECMWF) atmospheric global climate reanalysis, to analyze internal and external forcing processes affecting the evolution of these LCEs. The energy analysis was performed to understand the role of barotropic (BT) and baroclinic (BC) instabilities and their associated energy conversion mechanisms in EKE generation. Our results suggest that BT instabilities are the primary source of EKE variability in the upper water column of the LC system. Furthermore, BT was positively correlated with Yucatan Channel (YC) transport during these major LCE shedding events. YC transport plays a significant role in energy conversion from mean kinetic energy to EKE, Loop Current growth, and generation of LCEs. BC instability was inversely correlated with buoyancy frequency, and a decrease in stratification triggers the development of BC instability, which favors eddy shedding. An eddy shedding index (ESI) was developed to quantify EKE evolution. Major LCE shedding occurs when ESI ≥0.46.

Energetics of Multiscale Interactions in the Agulhas Retroflection Current System

Abstract Using the recently developed multiscale window transform and multiscale energy and vorticity analysis methods, this study diagnoses the climatological characteristics of the nonlinear mutual interactions among mesoscale eddies, low-frequency (seasonal to interannual) fluctuations, and the decadally modulating mean flow in the Agulhas Retroflection Current System (ARCS). It is found that mesoscale eddies are generated primarily in the retroflection region by mixed barotropic and baroclinic instabilities. The barotropic instability dominates the generation of eddy kinetic energy (EKE) here, contributing power roughly 10 times larger than the baroclinic one. These locally generated eddies are transported away. In the rings drift and meanders regions, the nonlocal transport serves as an important energy source for the eddy field, making a contribution comparable to that of the baroclinic instability for the EKE production. Contrarily, in the stable region, the EKE is generated mainly due to the baroclinic instability. In most of the ARCS area, the kinetic energy (KE) is further transferred inversely from mesoscale eddies to other lower-frequency motions. In particular, in the retroflection, rings drift, and stable regions, the inverse KE cascade plays a leading role in generating seasonal–interannual fluctuations, providing roughly 3–5 times as much power as the forward KE cascade from the mean flow and the advection effect. In the meanders region, however, the forward cascade contributes 4 times more KE to the low-frequency variabilities than the inverse one. All the results provide a model-based benchmark for future studies on physical processes and dynamics at different scales in the ARCS.

Intra-Annual Sea Level Fluctuations and Variability of Mesoscale Processes in the Northern Japan/East Sea From Satellite Altimetry Data

Intra-annual sea level fluctuations and variability of mesoscale processes based on eddy kinetic energy (EKE) were studied in the northern (northward of 41 N) Japan/East Sea (JES) using data from satellite altimetry for 1993–2020. Decomposition to empirical orthogonal functions (EOF) was performed of the high-pass filtered, with the cut-off period of 250 days, sea level anomalies. The leading mode accounting for the major fraction of the variance yielded sea level fluctuations which were simultaneous in the entire sea and occurred in the range from 70 to 250 days without any preferable timescale. EKE in the northern sea was also expanded to EOF and yielded the leading mode capturing mesoscale variability within the Primorye (Liman) Current and the Tsushima Warm Current. The seasonal signal was found in the simultaneous intra-annual sea level fluctuations, which matches that of EKE, and, as found in the earlier studies, of the mean currents. The sea level rises, the mean currents intensify and EKE increases in summer and fall and the opposite changes occur in winter and spring, with the seasonal extremes in October/November and March/April, respectively. This is in line with the EKE generation by instability of the mean currents. The intra-annual sea level fluctuations and EKE manifest rich variability on quasi-biennial, interannual and decadal timescales. However, in contrast with the seasonal signal, the low-frequency variability does not match, implying different kinds of forcing, probably by local wind in the northern JES and by the transport variations in the Korea – Tsushima Strait (KTS) in the southern JES. Intra-annual simultaneous SLA reveal changing relationship with Pacific Decadal Oscillation (PDO): both were in-phase in 1993–1994 and from late 2007 to 2013 and out-of-phase from 1997 to 2002, while there was no specific relationship in other times. However, the relationship of these SLA with the interannual KTS transport variation seems inconclusive.

Ocean Eddy Energetics in the Spectral Space as Revealed by High-Resolution General Circulation Models

AbstractIn this study, the global eddy kinetic energy (EKE) budget in horizontal wavenumber space is analyzed based on 1/10° ocean general circulation model simulations. In both the tropical and midlatitude regions, the barotropic energy conversion from background flow to eddies is positive throughout the wavenumber space and generally peaks at the scale (Le) where EKE reaches its maximum. The baroclinic energy conversion is more pronounced at midlatitudes. It exhibits a dipolar structure with positive and negative values at scales smaller and larger than Le, respectively. Surface wind power on geostrophic flow results in a significant EKE loss around Le but deposits energy at larger scales. The interior viscous dissipation and bottom drag inferred from the pressure flux convergence act as EKE sink terms. The latter is most efficient at Le while the former is more dominant at smaller scales. There is an evident mismatch between EKE generation and dissipation in the spectral space especially at the midlatitudes. This is reconciled by a dominant forward energy cascade on the equator and a dominant inverse energy cascade at the midlatitudes.

Energetics of Eddy–Mean Flow Interactions along the Western Boundary Currents in the North Pacific

AbstractThe energetics of eddy–mean flow interactions along two western boundary currents of the North Pacific, the Kuroshio and Ryukyu Currents, are systematically investigated using 22 years of numerical data from the Ocean General Circulation Model for the Earth Simulator (OFES). For the time-mean and time-varying flow fields, all the energy components and conversions exhibit inhomogeneous spatial distributions. In the two currents, complex cross-stream and along-stream variations are seen in the eddy–mean flow energy conversions. East of Taiwan, the kinetic energy is mainly transferred from the mean flow to the eddy field through barotropic instability, whereas the baroclinic energy conversions form a meridional dipole structure caused by the topographic constraint. In the northern area, particularly, the eddy field drains 2.25 × 108 W of kinetic energy and releases 2.82 × 108 W of available potential energy when interacting with the mean flow, indicating that mesoscale eddies impinging on the Kuroshio decay with baroclinic inverse energy cascades. In the Ryukyu Current, inverse energy conversions from the eddy field to the mean flow also dominate the power transfer in the subsurface layer. The eddy field transfers 0.16 × 108 W of kinetic energy and 1.89 × 108 W of available potential energy to the mean flow, suggesting that meososcale eddies play an important role in maintaining the velocity and hydrographic structure of the current. In other areas, both barotropic and baroclinic instabilities contribute to the generation of eddy kinetic energy with the latter one providing more than 3 times as much power as the former one.

A Lorenz/Boer energy budget for the atmosphere of Mars from a “reanalysis” of spacecraft observations

We calculate a Lorenz energy budget for the Martian atmosphere from reanalysis derived from Mars Global Surveyor data for Mars years 24–27. We present global, annual mean energy and conversion rates per unit area and per unit mass and compare these to Earth data. The directions of the energy conversion terms for Mars are similar to Earth, with the exception of the barotropic conversion between zonal and eddy kinetic energy reservoirs. Further, seasonal and hemispheric decomposition reveals a strong conversion between zonal energy reservoirs over the year, but these balance each other out in global and annual mean. On separating the diurnal timescale, the contribution to the conversion terms and eddy kinetic energy for diurnal and shorter timescales in many cases (especially during planet-encircling dust storms) exceeds the contribution of longer timescales. This suggests that thermal tides have a significant effect on the generation of eddy kinetic energy.

Impacts of enhanced CCN on the organization of convection and recent reduced counts of monsoon depressions

Monsoon depressions, that form during the Indian summer monsoon season (June to September) are known to be baroclinic disturbances (horizontal scale 2,000–3,000 km) and are driven by deep convection that carries a very large vertical slope towards cold air aloft in the upper troposphere. Deep convection is nearly always organized around the scale of these depressions. In the maintenance of the monsoon depression the generation of eddy kinetic energy on the scale of the monsoon depression is largely governed by the “in scale” covariance of heating and temperature and of vertical velocity and temperature over the region of the monsoon depression. There are normally about 6–8 monsoon depressions during a summer monsoon season. Recent years 2009, 2010 and 2011 saw very few (around 1, 0 and 1 per season respectively). The best numerical models such as those from ECMWF and US (GFS) carried many false alarms in their 3–5 day forecasts, more like 6–8 disturbances. Even in recent years with fewer observed monsoon depressions a much larger number of depressions is noted in ECMWF forecasts. These are fairly comprehensive models that carry vast data sets (surface and satellite based), detailed data assimilation, and are run at very high resolutions. The monsoon depression is well resolved by these respective horizontal resolutions in these models (at 15 and 35 km). These models carry complete and detailed physical parameterizations. The false alarms in their forecasts leads us to suggest that some additional important ingredient may be missing in these current best state of the art models. This paper addresses the effects of pollution for the enhancement of cloud condensation nuclei and the resulting disruption of the organization of convection in monsoon depressions. Our specific studies make use of a high resolution mesoscale model (WRF/CHEM) to explore the impacts of the first and second aerosol indirect effects proposed by Twomey and Albrecht. We have conducted preliminary studies including examination of the evolution of radar reflectivity (computed inversely from the model hydrometeors) for normal and enhanced CCN effects (arising from enhanced monsoon pollution). The time lapse histories show a major disruption in the organization of convection of the monsoon depressions on the time scale of a week to 10 days in these enhanced CCN scenarios.

Intraseasonal modulation of tropical cyclogenesis in the western North Pacific: a case study

The temporal clustering of the western North Pacific tropical cyclogenesis and its modulation by the Madden–Julian oscillation (MJO) during the 1991 summer were examined based on the tropical cyclone best track, outgoing longwave radiation, and NCEP/NCAR reanalysis datasets. The wavelet analysis shows that convective activities around the monsoon trough in the western North Pacific possessed a distinct MJO with a period of 20–60 days. Two or more tropical cyclones were observed to form successively during each active phase of the MJO, and tropical cyclones tended to generate around the southeastern part of the maximum vorticity of the low-frequency cyclonic circulation during the developing and peak stages of the active MJO phase. But tropical cyclogenesis scarcely occurred during inactive MJO phases. Thus the MJO was a major agent in modulating repeated development of tropical cyclones in the western North Pacific during the 1991 summer. The MJO in circulation was characterized by a huge anomalous cyclone (anticyclone) in the lower troposphere existing alternately over the western North Pacific, leading to an enhanced (weakened) monsoon trough. An examination of the meridional gradient of absolute vorticity associated with the zonal flow indicates that the zonal flow in the monsoon trough region satisfied the necessary conditions for barotropic instability, with both zonal flow and the meridional gradient of absolute vorticity varying on the similar MJO timescale. The intraseasonal oscillation of such an unstable zonal flow might thus be an important mechanism for temporal clustering of tropical cyclogenesis in the western North Pacific. The barotropic conversion could provide a major energy source for the formation and growth of tropical cyclones in the western North Pacific during active MJO phases, with the eddy kinetic energy generation being dominated by both terms of eddies interacting with zonal and meridional gradients of the basic zonal flow.

A diagnostic study of explosive development of extratropical cyclone over East Asia and West Pacific Ocean

In this paper, a diagnostic analysis is made for a kind of explosive cyclone over East Asia and the West Pacific Ocean in cold season, using the level III FGGE dataset. The cyclone started developing at 0000 UTC 30 March, 1979. Q vector analysis shows that ageostrophic wind was obvious in cyclone region. The calculation of different kinds of frontogenetical functions indicates that the development of cyclone was closely related to baroclinicity, especially, at lower levels. Isentropic analysis revealed the three-dimensional structure of cyclone development, that is, ascent of southerly warmer current and descent of northerly colder current existed around the cyclonic center during the developing process of the cyclone and is very favourable to the release of available potential energy and generation of eddy kinetic energy. Not only shear component, but also curvature component of upper level jet contributed to the explosive development of the cyclone. The computation of convergence of moisture flux demonstrated that the moisture probably came from the tropical ocean. The distribution of water vapor supply in this case was very advantageous to the deepening of cyclone, especially, during the well-developing period. Comparison between East Asia-Pacific case and North America-Atlantic case (Ogura and Juang, 1990) has been conducted. The common characteristics were that there existed strong baroclinicity in both cases. However, in the latter case, the latent heat release was of secondary importance and in our case, moisture also played very important role in certain stages of the cyclogenesis, especially, during well-developing stage when it moved over oceanic surface.

Energy transformations associated with the synoptic and planetary scales during the evolution of a blocking anticyclone and an upstream explosively-developing cyclone

Energy transformations associated with a wave system that included the development of a blocking anticyclone over the North Atlantic Ocean and the upstream explosive-development of an extratropical cyclone are studied for the period 17–21 January 1979. Included in the investigation are eddy kinetic energy (KE), release of eddy potential energy (CE), generation of eddy kinetic energy (GK), and exchange between eddy and zonal kinetic energy (CK). In addition, these quantities were partitioned into synoptic-scale, planetary-scale, and scale-interaction components. Results indicate that KE, which was about one-half of the total kinetic energy, was maintained by baroclinic conversion of potential to kinetic. Further, as released potential energy was being utilized to generate KE, a portion of the KE was barotropically converted to zonal kinetic energy. These transformations were dominated by the synoptic-scale component, in contrast to the authors' previously-reported height tendency results, which yielded significant contributions from both the synoptic and scale-interaction components. Thus, while changes in the mass field depended not only on the synoptic scale but also on the interactions between the synoptic and planetary scales, the corresponding changes in the eddy motion fields responded largely to synoptic-scale processes. DOI: 10.1034/j.1600-0870.1992.t01-2-00004.x

The subcloud-layer eddy kinetic energy budget of a microburst-producing thunderstorm determined from jaws dual-Doppler measurements

Dual-Doppler data collected from 1646 to 1648 MDT on 14 July, 1982 in Colorado were employed to study the eddy kinetic energy budget in the subcloud layer of a microburst-producing thunderstorm during its mature stage. Each term in the budget equation was computed from the Doppler-derived winds and retrieved thermodynamic fields within the 10 by 10 km horizontal domain. Results show that in the atmospheric boundary layer (ABL) where the microburst dominates, the turbulent flow extracts energy from the mean flow in order for the microburst to maintain its strong diverging outflow at low levels. The vertical transport of eddy kinetic energy is predominantly downward in the low layer due to the organized downdrafts in the microburst area. The horizontal flux convergence (divergence) of eddy kinetic energy by the mean and eddying motions is approximately balanced by that of the vertical flux divergence (convergence). Similarly, the contributions from the pressure and buoyancy production terms are nearly in balance. As a result, a net change of the eddy kinetic energy generation in the subcloud layer is relatively small in comparison with the individual term in the budget equation.

数値実験から見たコールド・サージとリー・サイクロジェネシスに及ほす山岳の影響

A 10-layer dry numerical model which includes convective adjustment, surface friction, and vertical momentum diffusion is used to identify the mechanical effects of a- mountain on transient eddies during winter. Thermal effect is simplified to the form of Newtonian cooling. Observed winter zonal mean temperature is prescribed as an equilibrium state. The mountain has a simple elliptic shape. The numerical integration was performed for 72 days, but a detailed analysis was done only for the 16-day period from day 21 to day 36.The 16-day mean fields show that the westerly jet tends to flow around, rather than over the mountain and splits into two branches in the lower troposphere. At 500 mb, winds are weakest over the mountain with a distinct splitting of the jet north and south of the mountain. Above 300 mb, the jet flows south of the mountain. These features agree well with those of the 1978-79 winter mean fields (Murakami, 1981a).At 850 mb, significant temperature perturbations originate at the northwest periphery of the mountain and extend clockwise around the mountain until reaching the southern part of the mountain. These low-level disturbances, which are trapped below 700 mb along the periphery of the mountain, are referred to as “edge” disturbances in this paper. These edge disturbances receive their eddy available potential energy via nonlinear interaction with 16- day mean temperature fields. Their eddy available potential energy is not converted into eddy kinetic energy; namely, the baroclinic conversion process contributes little to the development of edge disturbances. They acquire their kinetic energy through flux convergence of geopotential energy due to the nongeostrophic components of winds.At 500 mb, the kinetic energy of the disturbances is weakest, and baroclinic conversion is directed from eddy kinetic to the available potential energy, over the mountain. Here, the major contributing process in the generation of eddy kinetic energy is the horizontal flux convergence of eddy geopotential energy. The disturbances supply (extract) energy to (from) 16-day mean winds outside (over) the mountain.At 200 mb, a belt of large eddy kinetic energy lies south of the mountain, where the strong upper tropospheric jet stream prevails. The barotropic conversion process feeds energy to the 16-day mean westerly flows there. Again, the major generation factor for eddy kinetic energy is the flux convergence of eddy geopotential energy, while other terms, such as, baroclinic conversion are negligible.

The Dynamical Climatology of the Stratosphere in the Southern Hemisphere during Late Winter 1973

The heat, momentum and energy budgets of the region between 100 and 0.2 mb are investigated for the period 1 July to 6 September, 1973, using data derived from the Nimbus 5 meteorological satellite. The heat balance indicates that the high temperatures observed in the upper stratosphere in the south polar region are maintained against radiative cooling by intense zonal-mean subsidence. The eddy momentum flux is large in the upper stratosphere and indicates substantial driving of the mean flow by the eddies. The mean meridional circulations which were estimated independently from the heat balance and the dissipationless momentum balance for the upper stratosphere are inconsistent. The estimated heat balance requires subsidence in the polar upper stratosphere while the momentum balance suggests rising motion there. The generation of eddy kinetic energy was found to be dominated by the conversion from eddy available potential energy in the lower stratosphere and by the convergence of the vertical eddy geopotential flux in the upper stratosphere. Most of the eddy geopotential flux through the 100 mb level is absorbed in the region above 10 mb with relatively free propagation through the 100–10 mb layer during the period studied. The climatological importance of transient and stationary waves are observed to be approximately equal. Comparison of the present results with energy calculations for the 100–10 mb layer in the Northern Hemisphere during a period without a major warming indicates that the estimated zonal mean energies in the Southern Hemisphere are larger, while eddy energies are smaller than in the Northern Hemisphere. Nonetheless, the energy conversion terms are nearly the same in the two cases.

Balance of kinetic energy in the tropical circulation over the Western Pacific

AbstractThe balance of kinetic energy in the large‐scale disturbances and general flow of the tropical circulation was investigated with special Marshall Islands upper‐air network data during 1958.The cross‐isobaric generation of eddy kinetic energy has two maxima: in the lower boundary and in the upper troposphere. However, the intensity of generation is about one to two orders of magnitude smaller than that in synoptic disturbances in the middle latitudes. A major portion of the generated eddy kinetic energy is exported outside the area. The space eddies are shown to derive a significant amount of kinetic energy from the kinetic energy reservoir of the basic flow in the area. The eddy kinetic energy is mainly dissipated in the lower boundary. There is a small amount of eddy dissipation in the upper troposphere. However, as a whole the free atmosphere provides very little damping to the disturbances through eddy dissipation.The kinetic energy balance in the general flow is determined mainly by the cross‐isobaric generation of kinetic energy and the dissipation term. The vertical distribution of the cross‐isobaric generation shows there is a large internal source of kinetic energy in the tropospheric easterlies and the kinetic energy is destroyed adiabatically in the upper‐level westerlies and easterlies. The vertical profile of the dissipation closely follows that of the generation. Examination of the dissipation term obtained as the residual term of the kinetic energy equation suggests that processes of different scales of motion are significantly involved in the kinetic energy balance of the observed scale.

Kinetic Energy Sources in Large-Scale Tropical Disturbances Over the Marshall Islands Area

The maintenance of large-scale tropical disturbances has been examined with the source terms of kinetic energy generation utilizing the special 1958 upper-air observations in the Marshall Islands area. An optimized objective analysis scheme for the computation of kinematic vertical velocity as well as the method for evaluation of energy variables is presented. The time mean budgets of kinetic energy source terms are presented in terms of vertical profiles and intensity of processes represented by each term. The eddy conversion of available potential energy has its primary maximum in the layer between 400 and 200 mb, whereas the eddy kinetic energy generation shows maxima in the lower boundary and upper troposphere between 200 and 100 mb. In terms of the time mean budget only a fraction of the released energy by eddy conversion contributes to the eddy generation of kinetic energy in the area. Through examination of the time series of energy variables, it is revealed that horizontal eddy flux convergence of potential energy is the dominant term in determining the local generation of eddy kinetic energy. The migration pattern of the ITCZ further suggests that this horizontal eddy flux term is closely associated with the position of the ITCZ, with a significant divergence of eddy flux of potential energy when the ITCZ is located to the south of the area.