Hydration and dehydration at the tropical tropopause

Abstract

Abstract. High-resolution water measurements from three tropical airborne missions in Northern Australia, Southern Brazil and West Africa in different seasons are analysed to study the transport and transformation of water in the tropical tropopause layer (TTL) and its impact on the stratosphere. The mean profiles are quite different according to the season and location of the campaigns, with lowest mixing ratios below 2 ppmv at the cold point tropopause during the Australian mission in November/December and high TTL mixing ratios during the African measurements in August. We present backward trajectory calculations considering freezedrying of the air to the minimum saturation mixing ratio and initialised with climatological satellite data. This trajectorybased reconstruction of water agrees well with the observed H 2 O average profiles and therefore demonstrates that the water vapour set point in the TTL is primarily determined by the Lagrangian saturation history. Deep convection was found to moisten the TTL, in several events even above the cold point up to 420 K potential temperatures. However, our study does not provide evidence for a larger impact of these highlylocalised events on global scales.

Comparison of Fast In situ Stratospheric Hygrometer (FISH) measurements of water vapor in the upper troposphere and lower stratosphere (UTLS) with ECMWF (re)analysis data

“…These processes include deep convection, cloud microphysics and transport. Additionally, extratropical dynamical processes like mixing, crosstropopause exchange and convective injections into the lower stratosphere (e.g., Schiller et al, 2009;Ravishankara, 2012;Ploeger et al, 2013) may affect the quality of ECMWF (re)analyses water vapor in the extratropical lower stratosphere. Dyroff et al (2014) indicated an insufficient model resolution of small-scale intrusions of air masses in the UTLS, and an influence of numerical diffusion associated with the advection scheme in the vicinity of sharp humidity gradients at the tropopause may play a role.…”

“…Polar campaigns such as RECON-CILE2010 were aimed at a better understanding of polar vortex dynamics and chemical reactions (von Hobe et al, 2013). Other campaigns, such as the eight SPURT campaigns over 2 years, were intended to observe seasonal differences of various trace gases in the midlatitude tropopause region , and tropical campaigns such as TROC-CINOX2005 investigated the impact of tropical deep convection on the distribution and the sources of trace gases, cloud and aerosol particles in the UTLS (Flentje et al, 2007;Schiller et al, 2009). …”

“…In the vicinity of the tropopause and in particular across the subtropical jet stream, large gradients of water vapor exist due to the barrier effects of the tropopause (Haynes and Shuckburgh, 2000; Pan et al, 2004;Flentje et al, 2007;Kunz et al, 2011b). In the tropics, the low temperatures at the tropopause lead to strong freeze-drying (Jensen and Pfister, 2004;Fueglistaler et al, 2009;Schiller et al, 2009).…”

Impact of a possible future global hydrogen economy on Arctic stratospheric ozone loss

“…10,11 The air enters the stratosphere through the cold tropical tropopause and is ''freeze dried'' down to a few ppmv of water. 12 After crossing the tropical tropopause, the air ascends into the upper stratosphere and finally descends at polar latitudes within a typical transit time of 4 to 6 years from the Earth's surface to the upper stratosphere (see Fig. 1).…”

Intercomparison of mid-latitude tropospheric and lower stratospheric water vapor measurements and comparison to ECMWF humidity data

“…FISH (Fast In situ Stratospheric Hygrometer) is a closed cell Lyman-α photofragment fluorescence hygrometer which has been operated on various research aircraft for more than 20 years (Meyer et al, 2015;Schiller et al, 2009). The operating principle of the instrument is described in detail by Zöger et al (1999).…”