Perturbation Potential Energy Research Articles

Energetic connection between the South China Sea summer monsoon and Indian Ocean dipole from the perspective of perturbation potential energy

Energetic connection between the South China Sea summer monsoon and Indian Ocean dipole from the perspective of perturbation potential energy

Tropical Instability Waves in the Atlantic Ocean: Investigating the Relative Role of Sea Surface Salinity and Temperature From 2010 to 2018

AbstractWe identify and analyze tropical instability waves (TIWs) in the equatorial Atlantic Ocean during 2010–2018 using satellite derived observations of sea surface salinity (SSS), sea surface temperature (SST), sea level anomaly, and Argo profiles. In particular, the weekly 50‐km resolution SSS time series from the climate change initiative project provides an unprecedented opportunity to observe the salinity structure at a scale closer to the SST scale. We examine the relative contributions of SSS and SST to the horizontal surface density gradient on seasonal and interannual time scales and how they contribute to the TIW properties and energetics. For the central Atlantic TIWs, the maximum of the SST contribution to the density anomaly lags the SSS one by approximately one month. Argo vertical profiles indicate that temperature and salinity both significantly contribute to TIW‐related density anomalies. In May–June, salinity contributes to 50% of the perturbation potential energy in the top 60 m, and between 30% and 45% from July to September. While variations in SST appear to be related to dynamic processes, the interannual variability of SSS is also influenced by precipitations. However, the two leading modes of variability in the region (Atlantic Meridional and Zonal modes) do not well explain at 1°N these interannual variations.

Local path planning for unmanned surface vehicle with improved artificial potential field method

Aiming at the drawbacks of traditional artificial potential field method in local path planning for USV (unmanned surface vehicle), an improved artificial potential field method is proposed. By improving the gravitational potential field model and restraining the distant gravitational potential field, the problem of USV colliding with obstacles is solved. In the repulsion field model, the influence factors such as relative position and relative velocity are introduced to reduce the repulsion potential field intensity of the obstacle near the target, so as to solve the problem of goal nonreachable with obstacle nearby. The regulation mechanism of random perturbation potential energy is introduced to solve the problem that it is difficult to move at local minimum points. The rationality and superiority of the proposed improved artificial potential field method are verified by simulation and comparison experiments.

Variations in atmospheric perturbation potential energy associated with the South China Sea summer monsoon

This study investigates the energy conversion processes and their relation to convection (circulation) during the South China Sea summer monsoon (SCSSM) years from the viewpoint of atmospheric perturbation potential energy (PPE). An atmospheric PPE dipole pattern associated with the SCSSM develops over the western North Pacific (WNP) and southern Maritime Continent (SMC) in the boreal summer, serving as a link between the SCSSM and diabatic heating. Actually, the conversion between the energy variations and the convection over the WNP is distinctly different with that over the SMC. The precipitation leads the PPE over the WNP, while similar situation is reversed over the SMC. During strong SCSSM years, the higher PPE over the WNP, controlled primarily by the latent heat released from condensation related to surplus precipitation, is corresponding to the negative energy conversion ( text{C}_{k} ) over there. This indicates that more PPE is converted to perturbation kinetic energy and further intensifying ascending motion over the WNP. Consequently, the descending movement reduces the PPE and is corresponding to positive text{C}_{k} over the SMC, suggesting that the less PPE converts into the perturbation kinetic energy and in turn favors the descending movement and deficit precipitation there. The enhanced southwesterly induced by this SCSSM Hadley circulation, superimposed on the mean southwesterly wind, further favors the intensification of the SCSSM, implying that the SCSSM can maintain development through the positive convection–PPE–circulation feedback.

Atmospheric energetics over the tropical Indian Ocean during Indian Ocean dipole events

The evolution of atmospheric perturbation potential energy (PPE) over the tropical Indian Ocean is analyzed during a composite positive IOD event using reanalysis datasets for the period 1948–2015. The IOD modulates the variation in PPE, which then affects perturbation kinetic energy (PKE) through energy conversion. The PPE anomalies in the lower troposphere (1000–850 hPa) as the dominant layer of the PPE in the whole troposphere (1000–150 hPa) present a dipole pattern corresponding to the anomalous variation in SST during the IOD event. When cold SST anomalies (SSTAs) first appear in the eastern Indian Ocean (IOD-E), they reduce the atmospheric PPE in the lower troposphere rapidly. The negative PPE anomalies lead to less energy conversion to PKE, restraining the surface wind convergence over the IOD-E and weakening the climatological Walker circulation. Meanwhile, the surface easterly wind anomalies strengthen, which depresses the thermocline to the west and gives warmer SSTAs in the western Indian Ocean (IOD-W). The PPE anomalies and energy conversion (CK) over the IOD-W are opposite to those over the IOD-E, the anomalous easterly wind continues to develop, and the positive SSTAs in the IOD-W reach a peak. Thus, the response of the Walker circulation over the Indian Ocean provides a positive feedback during the IOD event and explains the delayed effect of IOD-E SSTAs on IOD-W SSTAs.

Modulation of tropical cyclone tracks over the western North Pacific by intra-seasonal Indo-western Pacific convection oscillation during the boreal extended summer

This study investigates the effect of the intra-seasonal Indo-western Pacific convection oscillation (IPCO) on tropical cyclone (TC) tracks over the western North Pacific (WNP) during the boreal extended summer (May−October). The number of west- and northwest-moving TC tracks is found to sharply increase over the WNP in the positive intra-seasonal IPCO phase. Recurving tracks have greater weight in the negative intra-seasonal IPCO phase. Possible physical mechanisms are further examined in terms of steering flow, energy conversion, and energy propagation. When the intra-seasonal IPCO phase is positive, the first-order moment term of perturbation potential energy (PPE1) converts into perturbation kinetic energy (PKE) at lower latitudes. The pressure trough spreads farther to the east. Meanwhile, Rossby waves emanating from the convective centers of the intra-seasonal IPCO over the WNP (WaveWNP) and EEIO (WaveEEIO) travel into the trough region, thereby deepening the trough. These features enhance the westward and northwestward steering flow between 20°N and about 30°N, sharply increasing the number of straight west- and northwest-moving TC tracks over the WNP. When the intra-seasonal IPCO is in a negative phase, conversion from PPE1 to PKE at lower latitudes is suppressed and the trough weakens. More PPE1 converts to PKE in the climatological western Pacific subtropical high (WPSH) region and the WPSH is intensified. Moreover, WaveEEIO intensifies the north–south ridge of the WPSH over the southern Indian Peninsula. Meanwhile, part WaveWNP propagate northeastward. These features favor northeastward motion of TCs over the WNP.

The Impact of Layer Perturbation Potential Energy on the East Asian Summer Monsoon

This paper analyzes the relationship between the 1000–850-hPa layer perturbation potential energy (LPPE) as the difference in local potential energy between the actual state and the reference state and the East Asian summer monsoon (EASM) using reanalysis and observational datasets. The EASM is closely related to the first-order moment term of LPPE (LPPE1) from the preceding March to the boreal summer over three key regions: the eastern Indian Ocean, the subtropical central Pacific, and midlatitude East Asia. The LPPE1 pattern (−, +, +), with negative values over the eastern Indian Ocean, positive values over the subtropical central Pacific, and positive values over East Asia, corresponds to negative LPPE1 anomalies over the south of the EASM region but positive LPPE1 anomalies over the north of the EASM region, which lead to an anomalous downward branch over the southern region but an upward branch over the northern region. The anomalous vertical motion affects the local meridional circulation over East Asia that leads to a southwesterly wind anomaly over East Asia (south of 30°N) at 850 hPa and anomalous downward motion over 100°–120°E (along 25°–35°N), resulting in a stronger EASM, more kinetic energy over the EASM region, and less boreal summer rainfall in the middle and lower reaches of the Yangtze River valley (24°–36°N, 90°–125°E). These LPPE1 anomalies in the eastern Indian Ocean and subtropical central Pacific appear to be connected to changes in local sea surface temperature through the release of latent heat.

Atmospheric Energetics over the Tropical Pacific during the ENSO Cycle

Abstract The atmospheric perturbation potential energy (PPE) over the tropical Pacific is calculated and analyzed in a composite ENSO cycle. The PPE over the tropical Pacific troposphere increases during El Niño and decreases during La Niña, displaying two centers symmetrical about the equator and delaying the central–eastern Pacific SST anomaly by two months. Generated from atmospheric diabatic heating, the smaller part of PPE in the lower troposphere varies synchronously with the central–eastern Pacific SST through sensible heating, while the larger part of PPE lies in the mid- and upper troposphere and lags the central–eastern Pacific SST about one season because of latent heat release. As the tropical Pacific PPE peaks during the boreal late winter in an El Niño event, two anticyclones form in the upper troposphere as a result of the Gill model response. More PPE is converted to atmospheric kinetic energy (KE) above the central–western Pacific, but less over the eastern Pacific, leading to intensified Hadley circulations over the central–western Pacific and weakened Hadley circulations over the eastern Pacific. The strengthened Hadley circulations cause surface easterly wind bursts through KE convergence in the western equatorial Pacific, which may trigger a La Niña event. The reverse situation occurs during La Niña. Thus, the response of the Hadley circulations in the central–western Pacific provides a negative feedback during the ENSO cycle.

On the Role of Perturbation Potential Energy in Variability of the East Asian Summer Monsoon: Current Status and Prospects

On the Role of Perturbation Potential Energy in Variability of the East Asian Summer Monsoon: Current Status and Prospects

The impact of extratropics‐arctic‐seesaw of perturbation potential energy on surface air temperature in boreal winters

AbstractSeesaw pattern of the perturbation potential energy in the extratropics and the Arctic (defined as PEAS) is observed. The PEAS is closely related to the Arctic Oscillation, kinetic energy and zonal wind in the middle‐ and high‐latitude. The PEAS may influence atmospheric circulation via northern migration of anomalous Ferrel cell, accompanying by suppressed subtropical jet stream and enhanced polar jet stream. Anomalous warm conditions associated with the PEAS are observed in high‐latitude of Eurasia, whereas cold anomalies are presented in Greenland, northeast Africa and southwest China, which is mainly attributed to the horizontal temperature advection.

The influence of salinity on tropical Atlantic instability waves

AbstractSea surface salinity (SSS) data derived from the Aquarius/SAC‐D satellite mission are analyzed along with other satellite and in situ data to assess Aquarius' capability to detect tropical instability waves (TIWs) and eddies in the tropical Atlantic Ocean and to investigate the influence that SSS has on the variability. Aquarius data show that the magnitude of SSS anomalies associated with the Atlantic TIWs is ±0.25 practical salinity unit, which is weaker than those in the Pacific by 50%. In the central equatorial Atlantic, SSS contribution to the mean meridional density gradient is similar to sea surface temperature (SST) contribution. Consequently, SSS is important to TIW‐related surface density anomalies and perturbation potential energy (PPE). In this region, SSS influences surface PPE significantly through the direct effect and the indirect effect associated with SSS‐SST covariability. Ignoring SSS effects would underestimate TIW‐related PPE by approximately three times in the surface layer. SSS also regulates the seasonality of the TIWs. The boreal‐spring peak of the PPE due to SSS leads that due to SST by about one month. Therefore, SSS not only affects the spatial structure, but the seasonal variability of the TIWs in the equatorial Atlantic. In the northeast Atlantic near the Amazon outflow and the North Brazil Current retroflection region and in the southeast Atlantic near the Congo River outflow, SSS accounts for 80–90% of the contribution to mean meridional density gradient. Not accounting for SSS effect would underestimate surface PPE in these regions by a factor of 10 and 4, respectively.

The oscillation of the perturbation potential energy between the extratropics and tropics in boreal winter

AbstractCorrelation analyses reveal that the perturbation potential energy (PPE) in the extratropics and tropics in boreal winters undergoes out‐of‐phase oscillations (PPE1 extratropics–tropics oscillation, PETO). PETO is closely related to both El Niño‐Southern Oscillation (ENSO) and kinetic energy, furthermore, PETO tends to dominate over the extratropics while ENSO is more important over the tropics. In the Northern (Southern) Hemisphere, positive PETO phases tend to strengthen (weaken) Hadley circulation and to weaken (strengthen) an expanded Ferrel circulation, resulting in equatorward shift of the subtropical jet streams. In addition, precipitation is enhanced in regions of ascending vertical motion, and warmer temperatures are observed in the tropics except over the western Pacific.

Zonal wavenumber three traveling waves in the northern hemisphere of Mars simulated with a general circulation model

Observations suggest a strong correlation between curvilinear shaped traveling dust storms (observed in wide angle camera images) and eastward traveling zonal wave number m=3 waves (observed in thermal data) in the northern mid and high latitudes during the fall and winter. Using the MarsWRF General Circulation Model, we have investigated the seasonality, structure and dynamics of the simulated m=3 traveling waves and tested the hypothesis that traveling dust storms may enhance m=3 traveling waves under certain conditions.Our standard simulation using a prescribed “MGS dust scenario” can capture the observed major wave modes and strong near surface temperature variations before and after the northern winter solstice. The same seasonal pattern is also shown by the simulated near surface meridional wind, but not by the normalized surface pressure. The simulated eastward traveling 1.4<T<10sol m=3 waves are confined near the surface in terms of the temperature perturbation, EP flux and eddy available potential energy, and they extend higher in terms of the eddy winds and eddy kinetic energy. The signature of the simulated m=3 traveling waves is stronger in the near surface meridional wind than in the near surface temperature field.Compared with the standard simulation, our test simulations show that the prescribed m=3 traveling dust blobs can enhance the simulated m=3 traveling waves during the pre- and post-solstice periods when traveling dust storms are frequently observed in images, and that they have negligible effect during the northern winter solstice period when traveling dust storms are absent. The enhancement is even greater in our simulation when dust is concentrated closer to the surface. Our simulations also suggest that dust within the 45–75°N band is most effective at enhancing the simulated m=3 traveling waves.There are multiple factors influencing the strength of the simulated m=3 traveling waves. Among those, our study suggests that weaker near surface static stability, larger near surface baroclinic parameter, and wave-form dust forcing for latitudinally extended dust storms are favorable. Further study is needed to fully understand the importance of these factors and others.

Relationship and Mechanism Between Perturbation Potential Energy and Atmospheric General Circulation Anomalies

AbstractBased on previous theoretical studies for local perturbation potential energy (PPE), in this study, we further focus on the relationship and mechanism between the PPE and atmospheric general circulation anomalies, and analyze coupled correlation modes between the PPE and upper, middle and lower‐level atmospheric kinetic energy (AKE) and their interannual variability. Meanwhile, we also examine the relationship between the PPE and sea surface pressure as the measure of atmospheric mass and further discuss the physical mechanisms involved in the relationships between the PPE and the AKE as well as mass. Analysis results show that the first mode in the variability of the PPE is also the leading mode in the coupled variation of the PPE and atmospheric general circulation anomalies, and the corresponding primary modes in the AKE and mass fields are also the dominant modes in their own variability, which indicates a possible interrelated physical mechanism between them. Furthermore, it is demonstrated that the formation of the prevailing mode of the extratropical atmospheric general circulation is closely associated with the feature that the PPE has both a zonal symmetry on global scale and zonal asymmetry on local scale. Moreover, there is a significant correlation between the first two orders of moments of the PPE and the southern/northern annular mode indices in the winter, but such a relationship is apparently weakened in the summer and exists in the southern hemisphere only.

Production, transformation, and dissipation of energy in internal tides near the continental shelf edge

[1] In the early 1980s, in situ observations were made of the spatial-temporal variability of the density field at three separate shelf edge sites off the Canadian east coast to improve our understanding of the dynamics of the generation, transformation, and dissipation of internal wave energy through an analysis of the potential energy budget in the water column. A description of the procedure for estimating the perturbation potential energy and its principal characteristics is given within a conceptual framework, where an internal tide is generated, propagates shoreward from the shelf edge, is transformed by nonlinear effects into shorter undulations such as solitary waves and internal bores, and eventually dissipates. On the basis of observations we find that the linear approximation of the potential energy is a major fraction of available potential energy, especially in large-amplitude internal waves. The potential energy in the generated internal tide is shown to covary with the squared current volume flux in the generating region. Turbulence and mixing are expected to occur as the short, energetic waves become unstable. From the observations, the rate of energy dissipation is smallest on the Grand Bank (0.007 W m−2 over a 30 km distance). In the Scotian Gulf the loss rate is 0.05 W m−2 over a 13 km distance. At The Gully site, where the energy concentrations are the largest, dissipation is estimated to be as large as 0.2 W m−2 over a 10 km distance.

On the calculation of the available potential energy of an isolated perturbation in a density-stratified fluid

Two methods for calculating the available potential energy (APE) of an isolated feature in a density-stratified fluid, such as an internal solitary wave or an eddy, are compared. The first formulation calculates the APE by integrating the perturbation potential energy density Ew. The second uses an available potential energy density Ea. Both formulations are based on the reference density obtained by adiabatically rearranging the density field to a state of minimum energy. It is shown, under more general conditions than used previously, that (i) the integrals of Ew and Ea over a finite domain are identical; and (ii) that for an isolated feature in an unbounded domain, the far-field density $\bar\rho(z)$ can be used as the reference density if Ea is used to find the APE. This is not the case when Ew is used, hence use of the available potential energy density formulation is simpler in this situation.

Progress in the Study of Atmospheric Energy Efficiency

The efficiency of atmospheric energy is an important component of atmospheric science research all along and has been evidently developed in the past tens of years.The present paper aims at a comprehensive review of the research progress of atmospheric energetics,especially for its efficiency problem.Focused on some problems existing in the classical theory of available potential energy,a new concept named as perturbation potential energy(PPE) has been put forward in order to extend the scale of energetic efficiency from global to local or regional atmosphere.Furthermore,some theoretical and applied problems have been preliminarily studied.Mathematical expressions have been derived and their physical senses have been discussed.In previous works,some characteristics of PPE including climatology,basal spatio-temporary features,and associations between PPE and atmospheric kinetic energy,have been diagnosed by using NCEP/NCAR reanalysis dataset,and many meaningful results have been obtained.In fact,it can be seen that the PPE is an crucial physical variable for research on variation,transform and cycle of local circulation energy,which will play an important role in investigating local or regional weather and climate change.

Instability mechanisms of a two-dimensional progressive internal gravity wave

We present a detailed investigation of the parametric subharmonic resonance mechanism that leads a plane, monochromatic, small-amplitude internal gravity wave, also referred to as the primary wave, to instability. Resonant wave interaction theory is used to derive a simple kinematic model for the parametrically forced perturbation, and direct numerical simulations of the Boussinesq equations in a vertical plane permit the nonlinear simulation of the internal gravity wave field. The processes that eventually drive the wave field to breaking are also addressed.We show that parametric instability may be viewed as an optimized scenario for drawing energy from the primary wave, that is, from a periodic flow with both oscillating shear and density gradient. Optimal energy exchange maximizing perturbation growth is realized when the perturbation has a definite spatio-temporal structure: its energy is phase-locked with the vorticity of the primary wave. This organization allows the perturbation energy to alternate between kinetic form when locally the primary wave shear is negative, then maximizing kinetic energy extraction from the primary wave, and potential form when the primary wave shear is positive, then minimizing the reverse transfer to that wave. The perturbation potential energy increases through the primary wave density gradient whether the latter is positive, that is when the medium is of reduced static stability, or negative (increased static stability). When the primary wave amplitude is small, all energy transfer terms are predicted well by the kinematic model. One important result is that the rate of potential energy transfer from the primary wave to the perturbation is always larger than the rate of kinetic energy transfer, whatever the primary wave.As the perturbation amplifies, overturned isopycnals first appear in reduced static stability regions, implying that the total field should become unstable through a buoyancy induced (or Rayleigh–Taylor) instability. Hence, a two-dimensional model is no longer valid for studying the subsequent flow development.

An incompressible stratified fluid model ofComet Shoemaker-Levy 9's collision with Jupiter

A linear model of Comet Shoemaker-Levy 9's collision with Jupiter ispresented, in which the Jovian atmosphere is taken to be a stratified, incompressible and inviscid fluid layer and the gravity wave associated with the impacts is caused by an initial impulse. Instead of adopting an initial surface deformation, we take an initial impulsive pressure P(r, z, 0) as the initial condition. It is found that this approach is more convenient for the mathematical formulation of the problem, especially for the computation of the vertical displacement of the fluid particles and the perturbation potential energy which can then be expressed by finite Fourier sine and cosine transform of P(r, z, 0). A relationship among parameters of the impact and the Jovian atmosphereand the assumed initial impulse is deduced. We also derive the wave height of the surface wave analytically for two assumed forms of P(r, z, 0).

Enhanced and Inhibited Gravity Wave Spectra

Abstract Balloon measurements were used to investigate gravity waves in the upper troposphere and lower stratosphere above the Canadian high Arctic. The amount of gravity wave activity in the stratosphere was found to be related to particular meteorological conditions that influence the generation and propagation of mountain waves. Enhanced wave activity was observed to occur when there was a small change in wind direction in the troposphere and high wind speed at the ground. These conditions correspond to strong wave generation by flow over the ground of upward-propagating waves that do not encounter critical level filtering. Inhibited wave activity was observed when the wind direction changed by more than 180° in the troposphere or when the wind speed was relatively weak at the ground. These conditions correspond to critical level filtering and weak generation of upward-propagating waves. The vertical wavenumber spectrum of perturbation potential energy was enhanced at all resolved scales when the condi...