Synoptic‐scale behavior of the extratropical tropopause inversion layer

Kedzierski, Robin Pilch; Matthes, Katja; Bumke, Karl

doi:10.1002/2015gl066409

Cited by 10 publications

(20 citation statements)

References 32 publications

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“…Thus, when a zonal mean N 2 profile is computed, the high N 2 max values get slightly smoothed out (Pilch Kedzierski et al, 2015). This is why the N 2 values in the first kilometer above the tropopause in Fig.…”

Section: Horizontal Structure Of Til Strengthmentioning

confidence: 88%

“…The first remarkable aspect of the tropical TIL is that the magnitude of N 2 max is much higher than in the extratropics. Values near the equator vary between 9 and 15 ×10 −4 s −2 and reach the 20 × 10 −4 s −2 mark sometimes, compared to a sTIL of 8-10 × 10 −4 s −2 generally found in polar summer or within ridges in midlatitude winter (Pilch Kedzierski et al, 2015). This can be attributed to the background temperature gradient in the lower stratosphere in the tropics, with a strong negative lapse rate and a higher background lowerstratospheric N 2 .…”

Section: Filter Settingsmentioning

confidence: 97%

“…The procedure to derive daily TIL snapshots in this study is similar to the method by Pilch Kedzierski et al (2015), but with a longitude-latitude projection.…”

Section: Mapping Of Til Snapshotsmentioning

confidence: 99%

“…TIL strength (sTIL) is calculated as the maximum static stability value (N 2 max ) above the tropopause level. This sTIL measure is commonly used Wirth and Szabo, 2007;Erler and Wirth, 2011;Pilch Kedzierski et al, 2015) because it makes sTIL independent of its distance from the tropopause and N 2 is a physically relevant quantity. Our algorithm searches for N 2 max in the first 3 km above TP z , but most often finds it in the first kilometer.…”

Section: Til Strength Calculationmentioning

confidence: 99%

“…In the extratropics, climatological studies have shown that the TIL reaches maximum strength during polar summer (Birner, 2006;Randel et al, 2007;Randel and Wu, 2010;Grise et al, 2010), whereas the TIL within anticyclones in midlatitude winter is of the same strength or even higher from a synoptic-scale point of view (Pilch Kedzierski et al, 2015). Several mechanisms for extratropical TIL formation/maintenance have been studied: water vapor radiative cooling below the tropopause (Randel et al, 2007;Hegglin et al, 2009;Kunz et al, 2009;Randel and Wu, 2010), dynamical heating above the tropopause from the downwelling branch of the stratospheric residual circulation , tropopause lifting and sharpening by baroclinic waves and their embedded cyclones-anticyclones (Wirth, 2003(Wirth, , 2004Wirth and Szabo, 2007;Son and Polvani, 2007;Randel et al, 2007;Randel and Wu, 2010;Erler and Wirth, 2011) and the presence of small-scale gravity waves (Kunkel et al, 2014).…”

Section: Introductionmentioning

confidence: 99%

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The tropical tropopause inversion layer: variability and modulation by equatorial waves

2016

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Abstract. The tropical tropopause layer (TTL) acts as a transition layer between the troposphere and the stratosphere over several kilometers, where air has both tropospheric and stratospheric properties. Within this region, a fine-scale feature is located: the tropopause inversion layer (TIL), which consists of a sharp temperature inversion at the tropopause and the corresponding high static stability values right above, which theoretically affect the dispersion relations of atmospheric waves like Rossby or inertia-gravity waves and hamper stratosphere-troposphere exchange (STE). Therefore, the TIL receives increasing attention from the scientific community, mainly in the extratropics so far. Our goal is to give a detailed picture of the properties, variability and forcings of the tropical TIL, with special emphasis on small-scale equatorial waves and the quasi-biennial oscillation (QBO).We use high-resolution temperature profiles from the COSMIC satellite mission, i.e., ∼ 2000 measurements per day globally, between 2007 and 2013, to derive TIL properties and to study the fine-scale structures of static stability in the tropics. The situation at near tropopause level is described by the 100 hPa horizontal wind divergence fields, and the vertical structure of the QBO is provided by the equatorial winds at all levels, both from the ERA-Interim reanalysis.We describe a new feature of the equatorial static stability profile: a secondary stability maximum below the zero wind line within the easterly QBO wind regime at about 20-25 km altitude, which is forced by the descending westerly QBO phase and gives a double-TIL-like structure. In the lowermost stratosphere, the TIL is stronger with westerly winds. We provide the first evidence of a relationship between the tropical TIL strength and near-tropopause divergence, with stronger (weaker) TIL with near-tropopause divergent (convergent) flow, a relationship analogous to that of TIL strength with relative vorticity in the extratropics.To elucidate possible enhancing mechanisms of the tropical TIL, we quantify the signature of the different equatorial waves on the vertical structure of static stability in the tropics. All waves show, on average, maximum cold anomalies at the thermal tropopause, warm anomalies above and a net TIL enhancement close to the tropopause. The main drivers are Kelvin, inertia-gravity and Rossby waves. We suggest that a similar wave modulation will exist at mid-and polar latitudes from the extratropical wave modes.

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Section: Horizontal Structure Of Til Strengthmentioning

confidence: 88%

Section: Filter Settingsmentioning

confidence: 97%

“…The procedure to derive daily TIL snapshots in this study is similar to the method by Pilch Kedzierski et al (2015), but with a longitude-latitude projection.…”

Section: Mapping Of Til Snapshotsmentioning

confidence: 99%

Section: Til Strength Calculationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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The tropical tropopause inversion layer: variability and modulation by equatorial waves

2016

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Tropopause sharpening by data assimilation

Kedzierski

Neef

Matthes

2016

Geophysical Research Letters

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Data assimilation was recently suggested to smooth out the sharp gradients that characterize the tropopause inversion layer (TIL) in systems that did not assimilate TIL‐resolving observations. We investigate whether this effect is present in the ERA‐Interim reanalysis and the European Centre for Medium‐Range Weather Forecasts (ECMWF) operational forecast system (which assimilate high‐resolution observations) by analyzing the 4D‐Var increments and how the TIL is represented in their data assimilation systems. For comparison, we also diagnose the TIL from high‐resolution GPS radio occultation temperature profiles from the COSMIC satellite mission, degraded to the same vertical resolution as ERA‐Interim and ECMWF operational analyses. Our results show that more recent reanalysis and forecast systems improve the representation of the TIL, updating the earlier hypothesis. However, the TIL in ERA‐Interim and ECMWF operational analyses is still weaker and farther away from the tropopause than GPS radio occultation observations of the same vertical resolution.

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