Tracking Kelvin waves from the equatorial troposphere into the stratosphere

Flannaghan, T. J.; Fueglistaler, S.

doi:10.1029/2012jd017448

Cited by 12 publications

(30 citation statements)

References 32 publications

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“…The resolution in the TTL is approximately 1 km (levels at approximately 132 hPa, 113 hPa, 95 hPa, 80 hPa, and 67 hPa) and is therefore sufficient to resolve Kelvin waves. In this paper, temperature and wind averages over the ±10° latitude band are considered, in line with previous studies [see Flannaghan and Fueglistaler , , and references therein].…”

Section: Methodsmentioning

confidence: 80%

“…Suzuki and Shiotani [] give a detailed climatology of Kelvin wave activity in the TTL using the European Centre for Medium‐Range Weather Forecasts (ECMWF) ERA‐40 reanalysis data set and also find that this is not closely related to wave activity in tropospheric convection, and suggest that zonal wind is modulating the waves. Suzuki et al [] present another interesting analysis of the longitudinal structure of Kelvin waves in the TTL and provide the basis for some of the filtering techniques used here (see Flannaghan and Fueglistaler [] for a more detailed discussion of the relation of this work to ours). Ryu et al [] find that zonal wind plays an important role in modulating waves in the TTL and use an approximation to the ray tracing equations to argue that there is a direct link between zonal winds and Kelvin wave amplitude in the TTL.…”

Section: Introductionmentioning

confidence: 99%

“…Here we analyze the climatology of Kelvin waves and, in particular, the zonal distribution of waves, using a novel method of wave tracking described in Flannaghan and Fueglistaler []. Section 2 presents the data and methods used in this study.…”

Section: Introductionmentioning

confidence: 99%

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The importance of the tropical tropopause layer for equatorial Kelvin wave propagation

Flannaghan

Fueglistaler

2013

JGR Atmospheres

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[1] We analyze the propagation of equatorial Kelvin waves from the troposphere to the stratosphere using a new filtering technique applied to ERA-Interim data (very similar results for Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) temperatures) that allows separation of wave activity into number of waves and wave amplitude. The phase speed of Kelvin waves (order 20 m/s) is similar to the magnitude of zonal wind in the tropical tropopause layer (TTL), and correspondingly, we find that the seasonal and interannual variability of Kelvin wave propagation is dominated by the variability in the wind field and less by tropospheric convectively coupled wave activity. We show that local relations between wave activity and zonal wind are ambiguous, and only full ray tracing calculations can explain the observed patterns of wave activity. Easterlies amplify and deflect the eastward traveling waves upward. Westerlies have the opposite effect. During boreal winter, the strong dipole of zonal winds in the TTL centered at the dateline confines wave propagation into the stratosphere to a window over the Atlantic-Indian Ocean sector (30°W to 90°E), which casts a lasting "shadow" into the lower stratosphere that explains the remarkable zonal asymmetry in wave activity there. During boreal summer, the upper level monsoon circulation leads to maximum easterlies, and wave amplitude (but not number of waves) maximizes over the Indian Ocean sector (30°E to 90°E). Interannual variability in wave propagation due to El-Niño/Southern Oscillation, for example, is well explained by its modification of the zonal wind field.

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Section: Methodsmentioning

confidence: 80%

Section: Introductionmentioning

confidence: 99%

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The importance of the tropical tropopause layer for equatorial Kelvin wave propagation

Flannaghan

Fueglistaler

2013

JGR Atmospheres

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“…While Gan Island is located in a region of the Indian Ocean that is relatively far removed from other land surfaces, Manus island is located just to the east of the Maritime Continent. The Maritime Continent is known to diminish both Kelvin waves (Flannaghan and Fueglistaler, 2012) and convective signals -such as the MJO (Zhang, 2005) -that force these waves.…”

Section: Time Series Resultsmentioning

confidence: 99%

Intraseasonal to interannual variability of Kelvin wave momentum fluxes as derived from high-resolution radiosonde data

2017

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Abstract. Observational estimates of Kelvin wave momentum fluxes in the tropical lower stratosphere remain challenging. Here we extend a method based on linear wave theory to estimate daily time series of these momentum fluxes from high-resolution radiosonde data. Daily time series are produced for sounding sites operated by the US Department of Energy (DOE) and from the recent Dynamics of the MaddenJulian Oscillation (DYNAMO) field campaign. Our momentum flux estimates are found to be robust to different data sources and processing and in quantitative agreement with estimates from prior studies. Testing the sensitivity to vertical resolution, our estimated momentum fluxes are found to be most sensitive to vertical resolution greater than 1 km, largely due to overestimation of the vertical wavelength. Climatological analysis is performed over a selected 11-year span of data from DOE Atmospheric Radiation Measurement (ARM) radiosonde sites. Analyses of this 11-year span of data reveal the expected seasonal cycle of momentum flux maxima in boreal winter and minima in boreal summer, and variability associated with the quasi-biennial oscillation of maxima during easterly phase and minima during westerly phase. Comparison between periods with active convection that is either strongly or weakly associated with the MaddenJulian Oscillation (MJO) suggests that the MJO provides a nontrivial increase in the lowermost stratospheric momentum fluxes.

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“…Power spectra in the zonal wave‐number frequency domain generated from satellite outgoing long‐wave radiation (OLR) data illustrate peaks that are consistent with the dispersion properties of Kelvin waves, equatorial Rossby (ER) waves, mixed Rossby gravity (MRG) waves, and inertia gravity (IG) waves (Wheeler and Kiladis, ; Roundy and Frank, ). The spectra indicate that convectively coupled equatorial waves propagate at phase speeds substantially lower than their dry counterparts previously detected in the stratosphere (Wallace and Kousky, ; Wheeler and Kiladis, ; Flannaghan and Fueglistaler, ). These spectra also support the view that an eastward‐moving intraseasonal oscillation, consistent in temporal and spatial scales with the pattern previously reported by Madden and Julian (), hereafter the Madden–Julian Oscillation (MJO), is associated with the strongest subseasonal variations in rainfall in the Tropics.…”

Section: Introductionmentioning

confidence: 62%

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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Tracking Kelvin waves from the equatorial troposphere into the stratosphere

Cited by 12 publications

References 32 publications

The importance of the tropical tropopause layer for equatorial Kelvin wave propagation

The importance of the tropical tropopause layer for equatorial Kelvin wave propagation

Intraseasonal to interannual variability of Kelvin wave momentum fluxes as derived from high-resolution radiosonde data

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

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