Wave modulation of the extratropical tropopause inversion layer

Abstract

Abstract. This study aims to quantify how much of the observed strength and variability in the zonal-mean extratropical tropopause inversion layer (TIL) comes from the modulation of the temperature field and its gradients around the tropopause by planetary-and synoptic-scale waves. By analyzing high-resolution observations, it also puts other TIL enhancing mechanisms into context.Using gridded Global Positioning System radio occultation (GPS-RO) temperature profiles from the COSMIC mission (2007-2013), we are able to extract the extratropical wave signal by a simplified wavenumber-frequency domain filtering method and quantify the resulting TIL enhancement. By subtracting the extratropical wave signal, we show how much of the TIL is associated with other processes, at midand high latitudes, for both hemispheres and all seasons.The transient and reversible modulation by planetary-and synoptic-scale waves is almost entirely responsible for the TIL in midlatitudes. This means that wave-mean flow interactions, inertia-gravity waves and the residual circulation are of minor importance for the strength and variability in the midlatitude TIL.At polar regions, the extratropical wave modulation is dominant for the TIL strength as well, but there is also a clear fingerprint from sudden stratospheric warmings (SSWs) and final warmings in both hemispheres. Therefore, polar vortex breakups are partially responsible for the observed polar TIL strength in winter (if SSWs occur) and spring. Also, part of the polar summer TIL strength cannot be explained by extratropical wave modulation.We suggest that our wave modulation mechanism integrates several TIL enhancing mechanisms proposed in previous literature while robustly disclosing the overall outcome of the different processes involved. By analyzing observations only, our study identifies which mechanisms dominate the extratropical TIL strength and their relative contribution. It remains to be determined, however, which roles the different planetary-and synoptic-scale wave types play within the total extratropical wave modulation of the TIL, as well as what causes the observed amplification of extratropical waves near the tropopause.

Composite analysis of the tropopause inversion layer in extratropical baroclinic waves

“…The presence of high clouds supports the hypothesised importance of moist dynamical and radiative processes during the formation of the TIL (e.g. Randel et al, 2007;Kunkel et al, 2016). The composites further reveal a maximum in vertical shear of the horizontal wind S 2 within the region of strongest enhancement of static stability above the tropopause.…”

“…Aside from adiabatic dynamics, diabatic processes have been shown to be of importance for the TIL. Randel et al (2007) showed that the radiative forcing of ozone and water vapour in the UTLS leads to a sharpening of the tropopause due to heating above and cooling below. Kunkel et al (2016) extended the adiabatic simulations of baroclinic waves by including the contributions from different diabatic forcings.…”

The Tropopause Inversion Layer Interaction With the Inertial Gravity Wave Activities and Its Latitudinal Variability

“…The tropopause inversion layer (TIL) was first discovered by Birner et al (2002) in the analysis of high vertical resolution radiosonde observations at two midlatitude stations and then proven to be a global phenomenon (Birner, 2006;Gettelman & Wang, 2015;Grise et al, 2010;Pilch Kedzierski et al, 2015Son et al, 2011). Several studies have pointed out that the TIL has close relationship with atmospheric waves (Birner, 2006;Grise et al, 2010;Kunkel et al, 2014;Miyazaki et al, 2010;Pilch Kedzierski et al, 2016, 2017Sjoberg & Birner, 2014;Wang et al, 2016;Zhang et al, 2015) and even has impacts on the vertical wave propagation (Birner, 2006;Sjoberg & Birner, 2014;Zhang et al, 2015).…”

New insights into Rossby wave packet properties in the extratropical UTLS using GNSS radio occultations

“…Williams and Colucci (2010) showed that RWP properties in the upper troposphere depended on lower-stratospheric conditions, namely the strength of the polar vortex. New case studies about extreme cyclones are pointing to a significant role of stratospheric conditions in their development (Odell et al, 2013;Tao et al, 2017a, b), and a more general study about severe European windstorms found that in 20 of 60 cases the stratospheric contribution during their deepening phases was over 10 % (Pirret et al, 2017). Nevertheless, despite their interaction with the stratosphere, it is generally assumed that RWPs cannot propagate upward due to the typical wind regimes in the stratosphere (Charney and Drazin, 1961).…”