skip to main content
US FlagAn official website of the United States government
dot gov icon
Official websites use .gov
A .gov website belongs to an official government organization in the United States.
https lock icon
Secure .gov websites use HTTPS
A lock ( lock ) or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites.

Explore Research Products in the PAR
It may take a few hours for recently added research products to appear in PAR search results.


This content will become publicly available on April 1, 2026

Title: Wave Packets and Life Cycles of Troughs in the Framework of Local Finite-Amplitude Wave Activity
Abstract Synoptic eddies embedded in a westerly flow undergo downstream developments due to their dispersive nature. This paper examines the finite-amplitude aspects of downstream development with the budget of local wave activity (LWA), including explicit contributions from diabatic heating. LWA captures well individual troughs/ridges and the wave packet, and its column budget affords simplified interpretations. In the LWA framework, (linear) downstream development demonstrated in previous analyses is represented by the LWA advection by the zonal reference flow plus LWA flux induced by the radiation of Rossby waves. In addition, convergence of nonlinear advective LWA flux, baroclinic sources at the lower boundary, meridional redistribution by eddy momentum flux, and diabatic sources and sinks complete the column budget of LWA. When applied to the life cycles of troughs within coherent wave packets in the Southern Hemisphere, the LWA budget reveals that individual troughs grow mainly through downstream development, convergence of nonlinear advective flux by eddies, and diabatic heating. Downstream development and divergence of nonlinear flux also dominate trough decay. Contributions from nonlinear advective eddy flux are large in the presence of a strong ridge either immediately upstream or downstream of the trough. Furthermore, anticyclonic components of advective LWA fluxes associated with the upstream or downstream ridge transfer LWA into or out of the trough. Diabatic contributions are significant when the heating exhibits a tilted vertical structure that gives rise to enhanced vertical gradient in heating.  more » « less
Award ID(s):
2154523
PAR ID:
10625395
Author(s) / Creator(s):
; ;
Publisher / Repository:
American Meteorological Society
Date Published:
Journal Name:
Journal of the Atmospheric Sciences
Volume:
82
Issue:
4
ISSN:
0022-4928
Page Range / eLocation ID:
789 to 808
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. ; (, Journal of Physical Oceanography)
    null (Ed.)
    Abstract Large-eddy simulations are used to investigate the influence of a horizontal frontal zone, represented by a stationary uniform background horizontal temperature gradient, on the wind- and wave-driven ocean surface boundary layers. In a frontal zone, the temperature structure, the ageostrophic mean horizontal current, and the turbulence in the ocean surface boundary layer all change with the relative angle among the wind and the front. The net heating and cooling of the boundary layer could be explained by the depth-integrated horizontal advective buoyancy flux, called the Ekman Buoyancy Flux (or the Ekman-Stokes Buoyancy Flux if wave effects are included). However, the detailed temperature profiles are also modulated by the depth-dependent advective buoyancy flux and submesoscale eddies. The surface current is deflected less (more) to the right of the wind and wave when the depth-integrated advective buoyancy flux cools (warms) the ocean surface boundary layer. Horizontal mixing is greatly enhanced by submesoscale eddies. The eddy-induced horizontal mixing is anisotropic and is stronger to the right of the wind direction. Vertical turbulent mixing depends on the superposition of the geostrophic and ageostrophic current, the depth-dependent advective buoyancy flux, and submesoscale eddies. 
    more » « less
  2. ; (, Journal of Climate)
    Abstract Given the widespread presence of clouds in the midlatitudes, one expects significant effects of condensational and radiative processes on the large-scale circulation of the atmosphere, but these diabatic effects are hard to constrain from observation. The authors propose a simple method to estimate the diabatic effects on the waviness of the jet stream based on the observed column-mean budget of Rossby wave activity. Wave activity in the midlatitudes is maintained by injection due to surface baroclinicity and/or diabatic sources, downstream transport due to advection and wave radiation, and eventual dissipation through mixing and thermal damping. Once the diabatic sources of wave activity are identified from the residual of the budget, one can suppress them and recompute the budget assuming that the transport velocity and damping rate do not change and thereby assess the impact of the diabatic sources. For the Northern Hemisphere, we found significant positive values of the residual in regions coincident with high column cloud water, suggesting that there are diabatic sources of wave activity associated with clouds. In winter, maritime diabatic sources contribute to wave activity over the Atlantic and the Pacific by about 33% and 30%, respectively, while in summer, the numbers are lower. The estimates are based on the assumptions that the perturbed wave sources do not alter the flow and that sources and sinks are geographically separated. For the Southern Hemisphere, this last assumption is questionable, and therefore, the confidence level of the estimates is low. 
    more » « less
  3. ; (, Journal of Geophysical Research: Atmospheres)
    Abstract This paper examines probability distributions oflocal wave activity(LWA), a measure of the jet stream's meander, and factors that control them. The observed column‐mean LWA distributions exhibit significant seasonal, interhemispheric, and regional variations but are always positively skewed in the extratropics, and their tail often involves disruptions of the jet stream. A previously derived one‐dimensional (1D) traffic flow model driven by observed spectra of transient eddy forcing qualitatively reproduces the shape of the observed LWA distribution. It is shown that the skewed distribution emerges from nonlinearity in the zonal advection of LWA even though the eddy forcing is symmetrically distributed. A slower jet and stronger transient and stationary eddy forcings, when introduced independently, all broaden the LWA distribution and increase the probability of spontaneous jet disruption. A quasigeostrophic two‐layer model also simulates skewed LWA distributions in the upper layer. However, in the two‐layer model both transient eddy forcing and the jet speed increase with an increasing shear (meridional temperature gradient), and their opposing influence leaves the frequency of jet disruptions insensitive to the vertical shear. When the model's nonlinearity in the zonal flux of potential vorticity is artificially suppressed, it hinders wave‐flow interaction and virtually eliminates reversal of the upper‐layer zonal wind. The study underscores the importance of nonlinearity in the zonal transmission of Rossby waves to the frequency of jet disruptions and associated weather anomalies. 
    more » « less
  4. ; ; ; (, Journal of Physical Oceanography)
    Abstract We use an interannually forced version of the Parallel Ocean Program, configured to resolve mesoscale eddies, to close the global eddy potential energy (EPE) budget associated with temperature variability. By closing the EPE budget, we are able to properly investigate the role of diabatic processes in modulating mesoscale energetics in the context of other processes driving eddy–mean flow interactions. A Helmholtz decomposition of the eddy heat flux field into divergent and rotational components is applied to estimate the baroclinic conversion from mean to eddy potential energy. In doing so, an approximate two-way balance between the “divergent” baroclinic conversion and upgradient vertical eddy heat fluxes in the ocean interior is revealed, in accordance with baroclinic instability and the relaxation of isopycnal slopes. However, in the mixed layer, the EPE budget is greatly modulated by diabatic mixing, with air–sea interactions and interior diffusion playing comparable roles. Globally, this accounts for ∼60% of EPE converted to EKE (eddy kinetic energy), with the remainder being dissipated by air–sea interactions and interior mixing. A seasonal composite of baroclinic energy conversions shows that the strongest EPE to EKE conversion occurs during the summer in both hemispheres. The seasonally varying diabatic processes in the upper ocean are further shown to be closely linked to this EPE–EKE conversion seasonality, but with a lead. The peak energy dissipation through vertical mixing occurs ahead of the minimum EKE generation by 1–2 months. 
    more » « less
  5. ; ; (, Journal of Physical Oceanography)
    Abstract Cross-frontal exchange facilitated by mesoscale eddies in the lee of major topographic features of the Southern Ocean is fundamental to the global overturning circulation. Despite the outsize importance for meridional heat flux, we lack an accurate estimation of fluxes across the Antarctic Circumpolar Current (ACC) due to the challenges of observing mesoscale eddy fluctuations on the temporal and spatial scales required. Here, 12 years of Argo data are used to observe patterns of cross-frontal exchange in the Southeast Indian Ridge system, a relatively underobserved region, known to be a hotspot of exchange. Spice variance along ACC streamlines is used as a proxy for cross-frontal exchange. Elevated exchange is observed downstream of the ridge system in nearly every streamline and is particularly prominent in the core of the ACC. Notably, exchange peaks progressively downstream at each poleward streamline suggesting a systematic north-to-south handoff across nearly the full breadth of the ACC. Employing a mixing length framework, lateral stirring is parameterized as an eddy diffusivity on the isopycnal of peak exchange. We find a highly localized pattern of diffusivity, peaking between the crest and trough of the first standing meander in the lee of the ridge system. Spatially, this diffusivity pattern correlates with an along-stream increase in eddy kinetic energy. Along-stream vertical wavenumber spectra of spice anomaly profiles indicate that the vertical scales of intrusions, which are initially large (approximately 800 m), rapidly evolve downstream to smaller wavenumbers (100–300 m) presumably in response to intense vertical shear and filamentation. 
    more » « less
  • Citation Formats
  • MLA
  • APA
  • Chicago
  • BibTeX
  • Save / Share this Record
  • Send to Email