Observational characteristics of the tropopause inversion layer derived from CHAMP/GRACE radio occultations and MOZAIC aircraft data

Abstract

[1] In this study we discuss characteristics of the Northern Hemisphere (NH) midlatitude (40°N-60°N) tropopause inversion layer (TIL) based on two data sets. First, temperature measurements from GPS radio occultation data (CHAMP and GRACE) for the time interval 2001-2009 are used to exhibit seasonal properties of the TIL bottom height defined here as the height of the squared buoyancy frequency minimum N 2 below the thermal tropopause, the TIL maximum height as the height of the N 2 maximum above the tropopause, and the TIL top height as the height of the temperature maximum above the tropopause. Mean values of the TIL bottom, TIL maximum, and TIL top heights relative to the thermal tropopause for the NH midlatitudes are (−2.08 ± 0.35) km, (0.52 ± 0.10) km and (2.10 ± 0.23) km, respectively. A seasonal cycle of the TIL bottom and TIL top height is observed with values closer to the thermal tropopause during summer. Secondly, high-resolution temperature and trace gas profile measurements on board commercial aircrafts (Measurement of Ozone and Water Vapor by Airbus In-Service Aircraft (MOZAIC) program) from 2001-2008 for the NH midlatitude (40°N-60°N) region are used to characterize the TIL as a mixing layer around the tropopause. Mean TIL bottom, TIL maximum, and TIL top heights based on the MOZAIC temperature (N 2 ) measurements confirm the results from the GPS data, even though most of the MOZAIC profiles used here are available under cyclonic situations. Further, we demonstrate that the mixing ratio gradients of ozone (O 3 ) and carbon monoxide (CO) are suitable parameters for characterizing the TIL structure.

In situ temperature measurements in the upper troposphere and lowermost stratosphere from 2 decades of IAGOS long-term routine observation

“…The median ozone mixing ratio in the UT is 60 ppb, median CO mixing ratio is 90 ppb, and median PV is 0.5 PVU. Within the LMS, the median values for O 3 (310 ppb), for CO (40 ppb), and for PV (7 PVU) are consistent with previous studies (Pan et al, 2004;Kunz et al, 2008;Brioude et al, 2009;Schmidt et al, 2010). …”

“…Since 2001, GPSRO data have been assimilated in numerical weather prediction models and reanalysis products. Schmidt et al (2010) characterized the tropopause inversion layer in the Northern Hemisphere with temperature profiles from in situ measurements and from the model for the period from 2001 to 2009 and concluded that the cold point at the tropopause agreed well.…”

“…A wellsuited data source for temperature profiles is the relatively new Global Positioning System radio occultation (GPSRO) technique (Kursinski et al, 1997;Wickert et al, 2001). The reliability of these measurements within the UTLS region has been demonstrated with trend analyses of GPSRO temperature (Steiner et al, 2009) or GPSRO-derived trends in the thermal tropopause temperature and tropopause height (Schmidt et al, 2010;Rieckh et al, 2014;Khandu et al, 2016). Ho et al (2017) demonstrated the usefulness of the GPSRO measurements to correct the temperature bias of radiosondes with different sensor types in the lowermost stratosphere (LMS), which is an important task to reduce the temperature uncertainties.…”

Wave modulation of the extratropical tropopause inversion layer

“…The study by Zhang et al (2015) supports this hypothesis by showing inhibited upward propagation of inertia-gravity waves (IGWs) due to the TIL, with data from a single US radiosonde station. Also, the TIL is likely to inhibit the cross-tropopause exchange of chemical compounds: high static stability suppresses vertical motion and is corre-lated with strong trace gas gradients (Hegglin et al, 2009;Kunz et al, 2009;Schmidt et al, 2010). In the next paragraphs we briefly review what is known so far about the observed variability in the extratropical TIL and the mechanisms proposed for its formation/enhancement.…”

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

“…Also, static stability suppresses vertical motion and correlates with sharper trace gas gradients, inhibiting the cross-tropopause exchange of chemical compounds (Hegglin et al, 2009;Kunz et al, 2009;Schmidt et al, 2010). For these reasons, the TIL attracts increasing interest from the scientific community.…”