Atmospheric and Earth System Research with HALO

(High Altitude and Long Range Research Aircraft)



          Wave-driven ISentropic Exchange

Mission Time Period: September - October 2017, Mission completed                                  News

Principle Investigators  

Lead Institutions

Partner Institutions

Scientific Background

Changes in the distributions of trace gases, like water vapor and ozone, and thin cirrus clouds in the upper troposphere and lower stratosphere (UTLS) strongly impact radiative forcing of the Earth's climate and surface temperatures (e .g. Riese et al., 2012), and are of key importance for understanding climate change (e. g. Solomon et al., 2010). Mixing processes at the tropopause cover a scale range from the micro scale to planetary scales and have to be parameterized in global models. Uncertainties in the description of mixing, however, introduce large errors to the estimates of the radiative forcing and are thus of key importance for understanding climate change (Riese et al., 2012).

It is therefore of great importance to quantify the physical and chemical processes (e.g. exchange of air masses, cirrus formation) that govern the composition of the UTLS. The so-called overworld above θ ≥ 380 K influences directly the composition of the extra-tropical stratosphere with significant contributions of air originating from the Asian monsoon circulation (Vogel et al., 2014; Ploeger et al., 2013). Below, the extra-tropical transition layer (ExTL) is strongly affected by bidirectional (quasi-isentropic) mixing across the tropopause (Hoor et al., 2010). The upper bound of the ExTL roughly coincides with the tropopause inversion layer (TIL), which constitutes a region of enhanced stability above the tropopause. The impact of radiatively active species like water vapour and ozone on the temperature structure makes the TIL a sensitive indicator for changes of ozone chemistry or changes of tropopause temperatures which directly affect water vapour which in turn feeds back into the static stability.

WISE will address the relation between composition and dynamical structure of the UTLS by focusing on the following three main research topics:

ST1) Interrelation of the tropopause inversion layer (TIL) and trace gas distribution

ST2) Role of Planetary wave breaking for water vapor transport into the extra-tropical lower stratosphere

ST3) Role of halogenated substances for ozone and radiative forcing in the UTLS region

ST4) Occurrence and effects of sub-visual cirrus (SVC) in the lowermost stratosphere

Figure 1: Schematic of the UTLS. Major UTLS features are the extra-tropical transition layer (ExTL) and the Tropopause Inversion Layer (TIL). The lowermost stratosphere (LMS) is the region in the extra-tropical stratosphere that is directly connected with the troposphere by isentropic surfaces. Wind contours (solid black lines 10ms − 1 interval), potential temperature surfaces (dashed black lines), thermal tropopause (red dots) and potential vorticity surface (2PVU: light blue solid line) represent data from a cross section along 60 ◦ longitude on February 15, 2006 (adapted from Gettelman et al., 2011)

Specific scientific questions are:

  • What is the impact of wave-driven large scale eddy mixing on the composition of the mid- to high-latitude LMS?
  • What is the role of the Asian Monsoon in moistening the extra-tropical UTLS in summer?
  • What are typical time scales for mixing and how are these related to the underlying dynamical processes and source regions
  • Does the TIL affect transport and mixing into the lower stratosphere and within the lower stratosphere?
  • Which factors determine the formation of the TIL and how do these in turn affect transport?
  • What is the link between Rossby wave breaking events and associated transport of water vapor and cirrus formation at mid latitudes?



Addressing the WISE objectives requires a unique set of 3D measurements of temperature and static stability, various trace gases (e. g. water vapor, ozone, tracers), and cirrus clouds obtained from remote sensing instruments of unprecedented resolution and data coverage, in combination with high precision in-situ observations. The 3D measurement capabilities of the new GLORIA infrared limb imager play an important role for the quantification of dynamical structures (e.g. static stability) and trace gas structures associated with cross-tropopause exchange. A unique combination of limb and nadir remote sensing instruments (IR limb imaging/ lidar / uv-vis) will be used for innovative studies of optically and vertically thin cirrus clouds in the UTLS region. High-precision in-situ observations provide detailed information on mixing processes and tracer structure with high spatial resolution, which is essential to perform tracer-tracer analyses (e.g. CO-O3 correlations).

Further Information