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

Flannaghan, T. J.; Fueglistaler, S.

doi:10.1002/jgrd.50418

Cited by 26 publications

(41 citation statements)

References 45 publications

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“…7a shows amplitude variations that are strongly modulated by the QBO, with enhanced wave activity in periods of transition from easterly to westerly stratospheric wind (westerly shear zones). Similar results have been found by Randel and Wu (2005); Ern et al (2008); Alexander and Ortland (2010); Flannaghan and Fueglistaler (2013). These peaks in Kelvinwave activity are expected since Kelvin-wave energy is accumulated below the critical level, which is located near the zero-wind line.…”

Section: Temporal Variations In Kelvin-wave Activitysupporting

confidence: 85%

“…This was also found by Ryu et al (2008), who showed that background zonal wind plays an important role in modulating Kelvin waves close to the tropical tropopause. More recently, Flannaghan and Fueglistaler (2013) showed that seasonal and interannual variability of Kelvin-wave propagation is dominated by the variability in the background wind field. However, we have explored this behavior and do not find any evident relationships between Kelvin-wave amplitudes and changes in winds near the tropopause (based on Singapore winds).…”

Section: Temporal Variations In Kelvin-wave Activitymentioning

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%

“…Due to their characteristics of high vertical resolution, accuracy, and global coverage (see Sect. 2.1 for more details) these data have been extensively used to analyze temperature variability and Kelvin-wave activity in the upper troposphere and lower stratosphere (UTLS) region (Tsai et al, 2004;Randel and Wu, 2005;Ratnam et al, 2006;Gettelman and Birner, 2007;Alexander et al, 2008;Steiner et al, 2011;Kim and Son, 2012;Scherllin-Pirscher et al, 2012;Das and Pan, 2013;Flannaghan and Fueglistaler, 2013;Randel and Wu, 2015).…”

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confidence: 99%

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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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Section: Temporal Variations In Kelvin-wave Activitysupporting

confidence: 85%

Section: Temporal Variations In Kelvin-wave Activitymentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

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

2017

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“…With finer vertical resolution (W_L103) the model produces a stronger upwelling in the tropics (and a consistent cooling) up to the tropopause region, with westerly wind anomalies above. This strengthened tropical upwelling cannot continue further up because of the westerly wind anomalies which block the transport into the subtropics (Simpson et al, 2009;Flannaghan and Fueglistaler, 2013). Above the tropical tropopause there is less upwelling and in particular more transport from the subtropics into the tropical TTL, leading to a stronger warming around 19 km in the W_L103 experiment.…”

Section: Changes In the Brewer-dobson Circulationmentioning

confidence: 97%

Quantifying contributions to the recent temperature variability in the tropical tropopause layer

2015

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Abstract. The recently observed variability in the tropical tropopause layer (TTL), which features a warming of 0.9 K over the past decade (2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010)(2011), is investigated with a number of sensitivity experiments from simulations with NCAR's CESM-WACCM chemistry-climate model. The experiments have been designed to specifically quantify the contributions from natural as well as anthropogenic factors, such as solar variability (Solar), sea surface temperatures (SSTs), the quasi-biennial oscillation (QBO), stratospheric aerosols (Aerosol), greenhouse gases (GHGs) and the dependence on the vertical resolution in the model. The results show that, in the TTL from 2001 through 2011, a cooling in tropical SSTs leads to a weakening of tropical upwelling around the tropical tropopause and hence relative downwelling and adiabatic warming of 0.3 K decade −1 ; stronger QBO westerlies result in a 0.2 K decade −1 warming; increasing aerosols in the lower stratosphere lead to a 0.2 K decade −1 warming; a prolonged solar minimum contributes about 0.2 K decade −1 to a cooling; and increased GHGs have no significant influence. Considering all the factors mentioned above, we compute a net 0.5 K decade −1 warming, which is less than the observed 0.9 K decade −1 warming over the past decade in the TTL. Two simulations with different vertical resolution show that, with higher vertical resolution, an extra 0.8 K decade −1 warming can be simulated through the last decade compared with results from the "standard" low vertical resolution simulation. Model results indicate that the recent warming in the TTL is partly caused by stratospheric aerosols and mainly due to internal variability, i.e. the QBO and tropical SSTs. The vertical resolution can also strongly influence the TTL temperature response in addition to variability in the QBO and SSTs.

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Kelvin and Rossby‐gravity wave packets in the lower stratosphere of some high‐top CMIP5 models

et al. 2014

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We analyze the stratospheric Kelvin and Rossby‐gravity wave packets with periods of a few days in nine high‐top (i.e., with stratosphere) models of the fifth Coupled Model Intercomparison Project (CMIP5). These models simulate realistic aspects of these waves and represent them better than the tropospheric convectively coupled waves analyzed in previous studies. There is nevertheless a large spread among the models, and those with a quasi‐biennial oscillation (QBO) produce larger amplitude waves than the models without a QBO. For the Rossby‐gravity waves this is explained by the fact that models without a QBO never have positive zonal mean zonal winds in the lower stratosphere, a situation that is favorable to the propagation of Rossby‐gravity waves. For the Kelvin waves, larger amplitudes in the presence of a QBO is counter intuitive because Kelvin waves are expected to have larger amplitude when the zonal mean zonal wind is negative, and this is always satisfied in models without a QBO. We attribute the larger amplitude to the fact that models tuned to have a QBO require finer vertical resolution in the stratosphere. We also find that models with large precipitation variability tend to produce larger amplitude waves. However, the effect is not as pronounced as was found in previous studies. In fact, even models with weak precipitation variability still have quite realistic stratospheric waves, indicating either that (i) other sources can be significant or that (ii) the dynamical filtering mitigates the differences in the sources between models.

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

Cited by 26 publications

References 45 publications

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

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

Quantifying contributions to the recent temperature variability in the tropical tropopause layer

Kelvin and Rossby‐gravity wave packets in the lower stratosphere of some high‐top CMIP5 models

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