Equatorial waves in the lower stratosphere. I: A novel detection method

Tindall, Julia; Thuburn, John; Highwood, Eleanor J.

doi:10.1256/qj.04.152

Cited by 27 publications

(29 citation statements)

References 38 publications

(34 reference statements)

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“…Kelvin waves are the most prominent global scale equatorially trapped wave mode in atmospheric temperatures (e.g., Tindall et al, 2006a). They are symmetric with respect to the equator, trapped at latitudes between about 20 • S and 20 • N in the stratosphere and travel eastward.…”

Section: Introductionmentioning

confidence: 99%

Wave fluxes of equatorial Kelvin waves and QBO zonal wind forcing derived from SABER and ECMWF temperature space-time spectra

Ern¹,

Preusse²

2009

Atmos. Chem. Phys.

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Abstract. The quasi-biennial oscillation (QBO) of the zonal mean zonal wind is a dynamical phenomenon of the tropical middle atmosphere. Influences of the QBO can even be found at mid and high latitudes. It is widely accepted that the phase descent of alternating tropical easterlies and westerlies is driven by atmospheric waves of both global scale (equatorial wave modes like Kelvin, equatorial Rossby, Rossbygravity, or inertia-gravity waves), as well as mesoscale gravity waves. However, the relative distribution of the different types of waves to the forcing of the QBO winds is highly uncertain. This is the case because until recently there were no high resolution long-term global measurements in the stratosphere. In our study we estimate Kelvin wave momentum flux and the contribution of zonal wind forcing by Kelvin waves based on space-time spectra determined from both Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) temperature measurements as well as temperatures from European Centre for Medium-Range Weather Forecasts (ECMWF) operational analyses. Peak values of total Kelvin wave zonal wind forcing found are about 0.2 m/s/day. There is good agreement between SABER and ECMWF results. Altitude-time cross sections are shown and the results are compared to the total wave forcing required to balance the background atmosphere. Sometimes Kelvin wave forcing is sufficient to explain almost the whole total wave forcing required for the momentum balance during the transition from QBO easterly to westerly winds. This is especially the case during the periods of strong westerly wind shear when the zonal wind is between −20 and 10 m/s at the equator in the altitude range 20 to 35 km. During other parts of the phases of strong westerly wind shear, however, the contribution of Kelvin waves can be comparably low and the missing wave forcing, which is often attributed Correspondence to: M. Ern (m.ern@fz-juelich.de) to mesoscale gravity waves or intermediate scale waves, can be the by far dominant contribution of the QBO forcing. It is also found that seasonal variations of Kelvin wave accelerations could play an important role for the maintenance of the QBO westerly wind jets in the lower stratosphere.

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Section: Introductionmentioning

confidence: 99%

Wave fluxes of equatorial Kelvin waves and QBO zonal wind forcing derived from SABER and ECMWF temperature space-time spectra

Ern¹,

Preusse²

2009

Atmos. Chem. Phys.

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“…Temperature field of Kelvin waves is in the symmetric mode (Andrews et al, 1987;Tindall et al, 2006), and according to the dispersion relation (Ern and Preusse, 2009;Matsuno, 1966), Kelvin wave components with different wave numbers and frequencies are extracted from the symmetric spectra by band pass filtering. The filtering region of Kelvin wave in the spectra is recognized by the different equivalent depth (Wheeler and Kiladis, 1999), corresponding to different phase speed of Kelvin waves (c x = √ gh e , where g is the gravitational acceleration).…”

Section: Extraction Of Kelvin Wavesmentioning

confidence: 99%

“…They are eastward propagating equatorial waves excited by tropical convection (Bergman and Salby, 1994), and are the most prominent components of the equatorially trapped wave mode of the temperature field (Tindall et al, 2006;Ern et al, 2008).…”

Section: Introductionmentioning

confidence: 99%

Variations of Kelvin waves around the TTL region during the stratospheric sudden warming events in the Northern Hemisphere winter

et al. 2016

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Abstract. Spatial and temporal variabilities of Kelvin waves during stratospheric sudden warming (SSW) events are investigated by the ERA-Interim reanalysis data, and the results are validated by the COSMIC temperature data. A case study on an exceptionally large SSW event in 2009, and a composite analysis comprising 18 events from 1980 to 2013 are presented. During SSW events, the average temperature increases by 20 K in the polar stratosphere, while the temperature in the tropical stratosphere decreases by about 4 K. Kelvin wave with wave numbers 1 and 2, and periods 10-20 days, clearly appear around the tropical tropopause layer (TTL) during SSWs. The Kelvin wave activity shows obvious coupling with the convection localized in the India Ocean and western Pacific (Indo-Pacific) region. Detailed analysis suggests that the enhanced meridional circulation driven by the extratropical planetary wave forcing during SSW events leads to tropical upwelling, which further produces temperature decrease in the tropical stratosphere. The tropical upwelling and cooling consequently result in enhancement of convection in the equatorial region, which excites the strong Kelvin wave activity. In addition, we investigated the Kelvin wave acceleration to the eastward zonal wind anomalies in the equatorial stratosphere during SSW events. The composite analysis shows that the proportion of Kelvin wave contribution ranges from 5 to 35 % during SSWs, much larger than in the non-SSW mid-winters (less than 5 % in the stratosphere). However, the Kelvin wave alone is insufficient to drive the equatorial eastward zonal wind anomalies during the SSW events, which suggests that the effects of other types of equatorial waves may not be neglected.

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“…Kelvin waves dominate sub-seasonal variability in the tropical tropopause region (Tindall et al, 2006;Kim and Son, 2012). They modulate the height and temperature of the tropical tropopause (Tsuda et al, 1994;Shimizu and Tsuda, 1997) and were found to be important for cirrus formation (Boehm and Verlinde, 2000;Immler et al, 2008;Suzuki et al, 2013) and dehydration of air entering the lower stratosphere (Fujiwara et al, 2001).…”

mentioning

confidence: 99%

“…Equatorial atmospheric waves have been investigated using satellite data from Nimbus-7 LIMS (Limb Infrared Monitor of the Stratosphere; Salby et al, 1984), the Microwave Limb Sounder (MLS; Mote et al, 2002), SABER (Sounding of the Atmosphere using Broadband Emission Radiometry; Ern et al, 2008;Ern and Preusse, 2009), and High Resolution Dynamics Limb Sounder (HIRDLS; Alexander and Ortland, 2010). Furthermore, several studies on atmospheric Kelvin waves are based on analysis or reanalysis data from numerical weather prediction (NWP) centers (Tindall et al, 2006;Suzuki and Shiotani, 2008;Suzuki et al, 2010;Fujiwara et al, 2012;Flannaghan and Fueglistaler, 2013).…”

mentioning

confidence: 99%

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

2017

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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 K 2 ). Large-scale zonal variability is dominated by transient sub-seasonal waves (2 K 2 ), and about half of subseasonal variance is explained by eastward-traveling Kelvin waves with periods of 4 to 30 days (1 K 2 ). Quasi-stationary waves associated with the annual cycle and interannual variability contribute about a third (1 K 2 ) 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.

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Equatorial waves in the lower stratosphere. I: A novel detection method

Cited by 27 publications

References 38 publications

Wave fluxes of equatorial Kelvin waves and QBO zonal wind forcing derived from SABER and ECMWF temperature space-time spectra

Wave fluxes of equatorial Kelvin waves and QBO zonal wind forcing derived from SABER and ECMWF temperature space-time spectra

Variations of Kelvin waves around the TTL region during the stratospheric sudden warming events in the Northern Hemisphere winter

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

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