scholarly journals Observed Structure of Convectively Coupled Waves as a Function of Equivalent Depth: Kelvin Waves and the Madden–Julian Oscillation

2012 ◽  
Vol 69 (7) ◽  
pp. 2097-2106 ◽  
Author(s):  
Paul E. Roundy
Keyword(s):  
Shallow Water ◽  
Deep Convection ◽  
Longwave Radiation ◽  
Kelvin Waves ◽  
Water Model ◽  
Madden Julian Oscillation ◽  
Kelvin Wave ◽  
Easterly Wind ◽  
Equivalent Depth ◽  
Westerly Winds

Abstract The view that convectively coupled Kelvin waves and the Madden–Julian oscillation (MJO) are distinct modes is tested by regressing data from the Climate Forecast System Reanalysis against satellite outgoing longwave radiation data filtered for particular zonal wavenumbers and frequencies by wavelet analysis. Results confirm that nearly dry Kelvin waves have horizontal structures consistent with their equatorial beta-plane shallow-water-theory counterparts, with westerly winds collocated with the lower-tropospheric ridge, while the MJO and signals along Kelvin wave dispersion curves at low shallow-water-model equivalent depths are characterized by geopotential troughs extending westward from the region of lower-tropospheric easterly wind anomalies through the region of lower-tropospheric westerly winds collocated with deep convection. Results show that as equivalent depth decreases from that of the dry waves (concomitant with intensification of the associated convection), the ridge in the westerlies and the trough in the easterlies shift westward. The analysis therefore demonstrates a continuous field of intermediate structures between the two extremes, suggesting that Kelvin waves and the MJO are not dynamically distinct modes. Instead, signals consistent with Kelvin waves become more consistent with the MJO as the associated convection intensifies. This result depends little on zonal scale. Further analysis also shows how activity in synoptic-scale Kelvin waves characterized by particular phase speeds evolves with the planetary-scale MJO.

scholarly journals Kelvin wave hydraulic control induced by interactions between vortices and topography

2011 ◽  
Vol 687 ◽  
pp. 194-208 ◽  
Author(s):  
Andrew McC. Hogg ◽  
William K. Dewar ◽  
Pavel Berloff ◽  
Marshall L. Ward
Keyword(s):  
Shallow Water ◽  
Analytical Solutions ◽  
Critical Condition ◽  
Numerical Models ◽  
Kelvin Waves ◽  
Water Model ◽  
Hydraulic Jumps ◽  
Hydraulic Control ◽  
Kelvin Wave ◽  
Shallow Water Model

AbstractThe interaction of a dipolar vortex with topography is examined using a combination of analytical solutions and idealized numerical models. It is shown that an anticyclonic vortex may generate along-topography flow with sufficient speeds to excite hydraulic control with respect to local Kelvin waves. A critical condition for Kelvin wave hydraulic control is found for the simplest case of a 1.5-layer shallow water model. It is proposed that in the continuously stratified case this mechanism may allow an interaction between low mode vortices and higher mode Kelvin waves, thereby generating rapidly converging isopycnals and hydraulic jumps. Thus, Kelvin wave hydraulic control may contribute to the flux of energy from mesoscale to smaller, unbalanced, scales of motion in the ocean.

scholarly journals The Spectrum of Convectively Coupled Kelvin Waves and the Madden–Julian Oscillation in Regions of Low-Level Easterly and Westerly Background Flow

2012 ◽  
Vol 69 (7) ◽  
pp. 2107-2111 ◽  
Author(s):  
Paul E. Roundy
Keyword(s):  
Longwave Radiation ◽  
Wave Dispersion ◽  
Warm Pool ◽  
Kelvin Waves ◽  
Madden Julian Oscillation ◽  
Westerly Wind ◽  
Kelvin Wave ◽  
Low Level ◽  
Geographical Regions ◽  
Zonal Wavenumber

Abstract The zonal wavenumber–frequency power spectrum of outgoing longwave radiation in the global tropics suggests that power in convectively coupled Kelvin waves and the Madden–Julian oscillation (MJO) is organized into two distinct spectral peaks with a minimum in power in between. This work demonstrates that integration of wavelet power in the wavenumber–frequency domain over geographical regions of moderate trade winds yields a similar pronounced spectral gap between these peaks. In contrast, integration over regions of background low-level westerly wind yields a continuum of power with no gap between the MJO and Kelvin bands. Results further show that signals in tropical convection are redder in frequency in these low-level westerly wind zones, confirming that Kelvin waves tend to propagate more slowly eastward over the warm pool than other parts of the world. Results are consistent with the perspective that portions of disturbances labeled as Kelvin waves and the MJO that are proximate to Kelvin wave dispersion curves exist as a continuum over warm pool regions.

scholarly journals A Reduced-Order Representation of the Madden–Julian Oscillation Based on Reanalyzed Normal Mode Coherences

2019 ◽  
Vol 76 (8) ◽  
pp. 2463-2480 ◽  
Author(s):  
Vassili Kitsios ◽  
Terence J. O’Kane ◽  
Nedjeljka Žagar
Keyword(s):  
Normal Mode ◽  
Gravity Waves ◽  
Rossby Waves ◽  
Spatial Scales ◽  
Longwave Radiation ◽  
Kelvin Waves ◽  
Madden Julian Oscillation ◽  
Kelvin Wave ◽  
Zonal Wavenumber ◽  
Vertical Scales

Abstract The Madden–Julian oscillation (MJO) is presented as a series of interacting Rossby and inertial gravity waves of varying vertical scales and meridional extents. These components are isolated by decomposing reanalysis fields into a set of normal mode functions (NMF), which are orthogonal eigenvectors of the linearized primitive equations on a sphere. The NMFs that demonstrate spatial properties compatible with the MJO are inertial gravity waves of zonal wavenumber k = 1 and the lowest meridional index n = 0, and Rossby waves with (k, n) = (1, 1). For these horizontal scales, there are multiple small vertical-scale baroclinic modes that have temporal properties indicative of the MJO. On the basis of one such eastward-propagating inertial gravity wave (i.e., a Kelvin wave), composite averages of the Japanese 55-year Reanalysis demonstrate an eastward propagation of the velocity potential, and oscillation of outgoing longwave radiation and precipitation fields over the Maritime Continent, with an MJO-appropriate temporal period. A cross-spectral analysis indicates that only the MJO time scale is coherent between this Kelvin wave and the more energetic modes. Four mode clusters are identified: Kelvin waves of correct phase period and direction, Rossby waves of correct phase period, energetic Kelvin waves of larger vertical scales and meridional extents extending into the extratropics, and energetic Rossby waves of spatial scales similar to that of the energetic Kelvin waves. We propose that within this normal mode framework, nonlinear interactions between the aforementioned mode groups are required to produce an energetic MJO propagating eastward with an intraseasonal phase period. By virtue of the selected mode groups, this theory encompasses both multiscale and tropical–extratropical interactions.

Contributions of Convectively Coupled Equatorial Rossby Waves and Kelvin Waves to the Real-Time Multivariate MJO Indices

2009 ◽  
Vol 137 (1) ◽  
pp. 469-478 ◽  
Author(s):  
Paul E. Roundy ◽  
Carl J. Schreck ◽  
Matthew A. Janiga
Keyword(s):  
Frequency Domain ◽  
Real Time ◽  
Deep Convection ◽  
Longwave Radiation ◽  
Kelvin Waves ◽  
Wind Data ◽  
Madden Julian Oscillation ◽  
The Real ◽  
The Waves ◽  
Equatorial Rossby Waves

Abstract The real-time multivariate (RMM) Madden–Julian oscillation (MJO) indices have been widely applied to diagnose and track the progression of the MJO. Although it has been well demonstrated that the MJO contributes to the leading signals in these indices, the RMM indices vary erratically from day to day. These variations are associated with noise in the outgoing longwave radiation (OLR) and wind data used to generate the indices. This note demonstrates that some of this “noise” evolves systematically and is associated with other types of propagating modes that project onto the RMM eigenmodes. OLR and zonal wind data are filtered in the wavenumber–frequency domain for the MJO, convectively coupled equatorial Rossby (ER) waves, and convectively coupled Kelvin waves. The filtered data are then projected onto the RMM modes. An example phase space associated with these projections is presented. Linear regression is then applied to isolate the wave signals from random variations in the same bands of the wavenumber–frequency domain, and the regressed data are projected onto the RMM EOFs. Results demonstrate the magnitudes of the contributions of the systematically evolving signals associated with these waves to variations in the RMM principal components, and how these contributions vary with the longitude of the active moist deep convection coupled to the waves.

scholarly journals Coastal imbalance: generation of oceanic Kelvin waves by atmospheric perturbations

2021 ◽  
Vol 926 ◽  
Author(s):  
Jacques Vanneste
Keyword(s):  
Shallow Water ◽  
Kelvin Waves ◽  
Water Model ◽  
Rossby Number ◽  
Length Scale ◽  
Kelvin Wave ◽  
Shallow Water Model ◽  
Matched Asymptotics ◽  
Geostrophic Balance ◽  
Atmospheric Perturbations

The response of a semi-infinite ocean to a slowly travelling atmospheric perturbation crossing the coast provides a simple example of the breakdown of nearly geostrophic balance induced by a boundary. We examine this response in the linear shallow-water model at small Rossby number $\varepsilon \ll 1$ . Using matched asymptotics, we show that a long Kelvin wave, with $O(\varepsilon ^{-1})$ length scale and $O(\varepsilon )$ amplitude relative to quasi-geostrophic response, is generated as the perturbation crosses the coast. Accounting for this Kelvin wave restores the conservation of mass that is violated in the quasi-geostrophic approximation.

scholarly journals Resonant excitation of coastal Kelvin waves in the two-layer rotating shallow water model

2013 ◽  
Vol 20 (6) ◽  
pp. 993-999 ◽  
Author(s):  
V. Zeitlin
Keyword(s):  
Shallow Water ◽  
Kelvin Waves ◽  
Resonant Excitation ◽  
Water Model ◽  
Coastal Current ◽  
Kelvin Wave ◽  
Baroclinic Model ◽  
Rotating Shallow Water ◽  
The One ◽  
Coastal Kelvin Waves

Abstract. Resonant excitation of coastal Kelvin waves by free inertia–gravity waves impinging on the coast is studied in the framework of the simplest baroclinic model: two-layer rotating shallow water with an idealized straight coast. It is shown that, with respect to the previous results obtained with the one-layer model, new resonances leading to a possible excitation of Kelvin waves appear. The most interesting ones, described in the paper, are resonances of a baroclinic inertia–gravity wave with either another wave of this kind, or with a coastal current, leading to generation of a barotropic Kelvin wave. A forced Hopf equation results in any case for the evolution of the Kelvin wave amplitude.

scholarly journals Tropical temperature variability and Kelvin-wave activity in the UTLS from GPS RO measurements

2017 ◽  
Vol 17 (2) ◽  
pp. 793-806 ◽  
Author(s):  
Barbara Scherllin-Pirscher ◽  
William J. Randel ◽  
Joowan Kim
Keyword(s):  
Large Scale ◽  
Deep Convection ◽  
Wave Activity ◽  
Kelvin Waves ◽  
Temperature Variability ◽  
Stationary Waves ◽  
Kelvin Wave ◽  
Quasi Biennial Oscillation ◽  
Tropical Tropopause ◽  
Tropopause Region

Abstract. Tropical temperature variability over 10–30 km and associated Kelvin-wave activity are investigated using GPS radio occultation (RO) data from January 2002 to December 2014. RO data are a powerful tool for quantifying tropical temperature oscillations with short vertical wavelengths due to their high vertical resolution and high accuracy and precision. Gridded temperatures from GPS RO show the strongest variability in the tropical tropopause region (on average 3 K2). Large-scale zonal variability is dominated by transient sub-seasonal waves (2 K2), and about half of sub-seasonal variance is explained by eastward-traveling Kelvin waves with periods of 4 to 30 days (1 K2). Quasi-stationary waves associated with the annual cycle and interannual variability contribute about a third (1 K2) to total resolved zonal variance. Sub-seasonal waves, including Kelvin waves, are highly transient in time. Above 20 km, Kelvin waves are strongly modulated by the quasi-biennial oscillation (QBO) in stratospheric zonal winds, with enhanced wave activity during the westerly shear phase of the QBO. In the tropical tropopause region, however, peaks of Kelvin-wave activity are irregularly distributed in time. Several peaks coincide with maxima of zonal variance in tropospheric deep convection, but other episodes are not evidently related. Further investigations of convective forcing and atmospheric background conditions are needed to better understand variability near the tropopause.

scholarly journals Characteristics Associated with the Madden–Julian Oscillation at Manus Island

2013 ◽  
Vol 26 (10) ◽  
pp. 3342-3356 ◽  
Author(s):  
Liping Deng ◽  
Sally A. McFarlane ◽  
Julia E. Flaherty
Keyword(s):  
Phase Structure ◽  
Deep Convection ◽  
Precipitable Water ◽  
Active Phase ◽  
Type I ◽  
Madden Julian Oscillation ◽  
Two Phase ◽  
Easterly Wind ◽  
Mature Phase ◽  
Peak Structure

Abstract Ground-based high temporal and vertical resolution datasets from observations during 2002–07 at the Atmospheric Radiation Measurement (ARM) tropical western Pacific (TWP) site on Manus Island are used to examine the characteristics of clouds and rainfall associated with the active phase of the Madden–Julian oscillation (MJO) passing over Manus. A composite MJO event at Manus is developed based on the NOAA MJO index 4 and precipitation using 13 events. The cloud characteristics associated with the active phase of the MJO at Manus show a two-phase structure as the wave passes over Manus. During the development phase, congestus plays an important role, and the enhanced convection is located between surface westerly and easterly wind anomalies (type-I structure). During the mature phase, deep convection is the dominant cloud type, and the enhanced convection is collocated with the westerly wind anomalies (type-II structure). Consistent with this two-phase structure, the heavy rainfall frequency also shows a two-peak structure during the MJO disturbance, while light rainfall does not show a clear relation to the intraseasonal disturbance associated with the MJO. In addition, a positive relationship between the precipitation rate and precipitable water vapor exists at Manus, and the atmospheric column is less moist after the passing of the MJO convection center than before.

scholarly journals Seasonality and Regionality of the Madden–Julian Oscillation, Kelvin Wave, and Equatorial Rossby Wave

2007 ◽  
Vol 64 (12) ◽  
pp. 4400-4416 ◽  
Author(s):  
Hirohiko Masunaga
Keyword(s):  
Boundary Layer ◽  
Water Solution ◽  
Austral Summer ◽  
Longwave Radiation ◽  
Boreal Summer ◽  
Dynamical Structure ◽  
Madden Julian Oscillation ◽  
Kelvin Wave ◽  
Low Level ◽  
The Impact

Abstract The Madden–Julian oscillation (MJO), Kelvin wave, and equatorial Rossby (ER) wave—collectively called intraseasonal oscillations (ISOs)—are investigated using a 25-yr record of outgoing longwave radiation (OLR) measurements as well as the associated dynamical fields. The ISO modes are detected by applying bandpass filters to the OLR data in the frequency–wavenumber space. An automated wave-tracking algorithm is applied to each ISO mode so that convection centers accompanied with the ISOs are traced in space and time in an objective fashion. The identified paths of the individual ISO modes are first examined and found strongly modulated regionally and seasonally. The dynamical structure is composited with respect to the convection centers of each ISO mode. A baroclinic mode of the combined Rossby and Kelvin structure is prominent for the MJO, consistent with existing work. The Kelvin wave exhibits a low-level wind field resembling the shallow-water solution, while a slight lead of low-level convergence over convection suggests the impact of frictional boundary layer convergence on Kelvin wave dynamics. A lagged composite analysis reveals that the MJO is accompanied with a Kelvin wave approaching from the west preceding the MJO convective maximum in austral summer. MJO activity then peaks as the Kelvin and ER waves constructively interfere to enhance off-equatorial boundary layer convergence. The MJO leaves a Kelvin wave emanating to the east once the peak phase is passed. The approaching Kelvin wave prior to the development of MJO convection is absent in boreal summer and fall. The composite ER wave, loosely concentrated around the MJO, is nearly stationary throughout. A possible scenario to physically translate the observed result is also discussed.

scholarly journals Cycles and Propagation of Deep Convection over Equatorial Africa

2011 ◽  
Vol 139 (9) ◽  
pp. 2832-2853 ◽  
Author(s):  
Arlene G. Laing ◽  
Richard E. Carbone ◽  
Vincenzo Levizzani
Keyword(s):  
Deep Convection ◽  
Active Phase ◽  
Kelvin Waves ◽  
Convective Precipitation ◽  
Atmospheric Conditions ◽  
Kelvin Wave ◽  
Mesoscale Convection ◽  
Diurnal Cycles ◽  
Continental Scale ◽  
Equatorial Africa

Long-term statistics of organized convection are vital to improved understanding of the hydrologic cycle at various scales. Satellite observations are used to understand the timing, duration, and frequency of deep convection in equatorial Africa, a region with some of the most intense thunderstorms. Yet little has been published about the propagation characteristics of mesoscale convection in that region. Diurnal, subseasonal, and seasonal cycles of cold cloud (proxy for convective precipitation) are examined on a continental scale. Organized deep convection consists of coherent structures that are characteristic of systems propagating under a broad range of atmospheric conditions. Convection is triggered by heating of elevated terrain, sea/land breezes, and lake breezes. Coherent episodes of convection result from regeneration of convection through multiple diurnal cycles while propagating westward. They have an average 17.6-h duration and 673-km span; most have zonal phase speeds of 8–16 m s−1. Propagating convection occurs in the presence of moderate low-level shear that is associated with the southwesterly monsoonal flow and midlevel easterly jets. Convection is also modulated by eastward-moving equatorially trapped Kelvin waves, which have phase speeds of 12–22 m s−1 over equatorial Africa. Westward propagation of mesoscale convection is interrupted by the dry phase of convectively coupled Kelvin waves. During the wet phase, daily initiation and westward propagation continues within the Kelvin wave and the cold cloud shields are larger. Mesoscale convection is more widespread during the active phase of the Madden–Julian oscillation (MJO) but with limited westward propagation. The study highlights multiscale interaction as a major source of variability in convective precipitation during the critical rainy seasons in equatorial Africa.

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