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

Roundy, Paul E.

doi:10.1175/jas-d-12-060.1

Cited by 47 publications

(49 citation statements)

References 18 publications

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“…During the easterly and westerly wind events (Figure (a,b)), the geopotential height and zonal wind anomalies tend to become in quadrature to each other from the western to the central Pacific basin (110°E–130°W, labelled WPAC‐CPAC), as shown by previous studies (e.g. Kiladis and Weickmann, ; Madden and Julian, ; Roundy, ). Over the eastern Pacific basin (130°W to 80°W, labelled EPAC), where the zonal wind anomalies achieve their strongest amplitude, the geopotential height anomaly is weak and can be out of phase with the zonal wind anomalies (i.e.…”

Section: Resultssupporting

confidence: 76%

The development of upper‐tropospheric geopotential height anomaly in the Western Hemisphere during MJO convective initiations

Sakaeda

Roundy

2015

Quart J Royal Meteoro Soc

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This study uses geopotential height budget and composite analysis of reanalysis data to examine the driving dynamics and structural evolution of intraseasonal upper-tropospheric circulation over the Western Hemisphere (WH) prior to and during the convective initiation of the Madden-Julian Oscillation (MJO) over the Indian basin. Previous studies by the authors showed that, during most of MJO convective initiation events over the Indian basin, upper-tropospheric equatorial easterly wind anomaly initially develops in association with subtropical and midlatitude Rossby ridges over the east Pacific basin. As the easterly wind continues to amplify and propagate farther eastward, a negative upper-tropospheric geopotential height anomaly develops over tropical South America and couples with the easterly wind anomaly, forming a structure consistent with theoretical Kelvin waves. This study shows that the development of the negative geopotential height anomaly over South America is driven by net tropospheric adiabatic cooling induced by updraughts. The convection associated with the updraughts is triggered by the intrusion of a midlatitude wave train from the Southern Hemisphere, suggesting that the interaction with midlatitude circulation is a part of the dynamics driving the formation of upper-tropospheric Kelvin wave structure over the WH.During some MJO convective initiation events, the upper-tropospheric zonal wind anomaly is positive over the east Pacific basin and the formation of Kelvin wave structure is weak or absent over South America. Those events subsequently develop weaker MJO convective envelopes over the Indian basin, apparently due to the absence of uppertropospheric divergence induced by the incoming Kelvin wave circulation that enhances convective updraughts over the region of initiating convection. The results suggest that the formation of the upper-tropospheric Kelvin wave over the WH partly determines the subsequent development of MJO convection over the Indian basin.

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Section: Resultssupporting

confidence: 76%

The development of upper‐tropospheric geopotential height anomaly in the Western Hemisphere during MJO convective initiations

Sakaeda

Roundy

2015

Quart J Royal Meteoro Soc

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“…As a result, the subdivision of the filtering boxes into two categories excluding the spectral peak region may cause overfiltering. However, Roundy (2012a) shows that based on the linear regression for signals along the Kelvin wave dispersion curves at zonal wavenumber 4, for equivalent depths of 90, 25, 12, 8, and 5 m, the wave structures continuously change with the equivalent depth. Moreover, temporal correlations of the rainfall anomaly between faster and slower components averaged over the warm pool are 0.056, 0.016, 0.011, and 0.002 for Kelvin, EIGn0, WIGn1, and WIGn2 waves, respectively.…”

Section: Resultsmentioning

confidence: 99%

“…In contrast, their statistical analyses do not significantly correlate propagation speeds and barotropic winds; that is, Doppler-shift effects from the background barotropic wind will be minimal. However, Roundy (2012b) shows that the spectra of outgoing longwave radiation (OLR) anomalies have distinctly different Kelvin wave peaks in the easterly and westerly base states; F.Kelvin wave components are more dominant in easterly base states than in the westerly base states. Therefore, we still cannot dismiss the possibility that zonal winds at specific level(s) control the propagation speed.…”

Section: Resultsmentioning

confidence: 99%

Differences between Faster versus Slower Components of Convectively Coupled Equatorial Waves

Yasunaga

Mapes

2013

Journal of the Atmospheric Sciences

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This paper describes an analysis of multiyear satellite datasets that subdivide two halves (faster and slower) of the space-time spectral signal peaks corresponding to convectively coupled equatorial waves such as Kelvin and inertia-gravity waves [n 5 0 eastward inertia-gravity wave (EIGn0 wave), and n 5 1 and n 5 2 westward inertia-gravity waves (WIGn1 and WIGn2 waves, respectively)]. The faster (slower) component of an equatorial wave is defined as that which has a spectral signal peak in the regions with deeper (shallower) equivalent depths. The data obtained from the Tropical Rainfall Measuring Mission (TRMM) precipitation radar (TRMM-PR) are composited around space-time-filtered equatorial-belt data from the TRMM-3B42 rainfall product to separately estimate the convective and stratiform rainfall modulations.Results indicate that the faster components of WIGn1 and WIGn2 waves modulate convective rain relatively more (and stratiform rain relatively less) than their slower counterparts. For Kelvin and EIGn0 waves, however, there is no significant difference in the rainfall modulation between their faster and slower components. A space-time cospectral analysis of the satellite-retrieved rainfall and moisture shows that in the spectral regions corresponding to WIGn1 and WIGn2 waves, precipitation is significantly correlated with lowlevel moisture but not with midlevel moisture. In contrast, significant coherence between rainfall and moisture at these levels is found in the spectral regions corresponding to the Kelvin and EIGn0 waves. These results may bear on different convection-wave coupling mechanisms for these ''divergent'' waves (stratiform instability versus moisture-stratiform instability).

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“…Most authors concur that convection coupled to the waves can slow their propagation (e.g. Kiladis et al ., ; Roundy, 2012a,b), thereby shifting the associated spectral signal to lower frequencies. Reduction of the cooling rate in moist ascent by condensation and precipitation would reduce the effective static stability that acts as one of the restoring forces of the waves (Neelin and Held, ; Neelin and Yu, ; Emanuel et al ., ; Frierson et al ., ; Raymond et al ., 2009).…”

Section: Introductionmentioning

confidence: 99%

A wave‐number frequency wavelet analysis of convectively coupled equatorial waves and the MJO over the Indian Ocean

Roundy

2018

Quart J Royal Meteoro Soc

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Convectively coupled equatorial waves and the Madden-Julian Oscillation (MJO) constitute the dominant coherent modes of planetary-to synoptic-scale organized convection in the Tropics. This work presents a space-time wavelet analysis of outgoing long-wave radiation (OLR) data globally at wave-numbers 0-1 and isolated more closely about the Indian Ocean at higher wave numbers. The mean power spectrum shows broad similarity to Fourier power spectra in previous works after normalization by a red background. The seasonal cycle of the power spectrum is analysed, along with its association with the phases of an index of the MJO and background-state zonal winds at a variety of pressure levels over the Indian Ocean. Results show substantial variability across the seasonal cycle and the MJO in the distribution of power above the background. Results also show that the spectral peaks associated with the MJO and Kelvin and equatorial Rossby waves lose 20-50% of their normal variance during periods of strong easterly wind in the upper troposphere over the Indian Ocean, while at the same time, fast westward-moving waves increase between wave-numbers 7 and 14 and periods of 2-6 days.

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

Cited by 47 publications

References 18 publications

The development of upper‐tropospheric geopotential height anomaly in the Western Hemisphere during MJO convective initiations

The development of upper‐tropospheric geopotential height anomaly in the Western Hemisphere during MJO convective initiations

Differences between Faster versus Slower Components of Convectively Coupled Equatorial Waves

A wave‐number frequency wavelet analysis of convectively coupled equatorial waves and the MJO over the Indian Ocean

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