A comparison of ozone and thermal tropopause heights and the impact of tropopause definition on quantifying the ozone content of the troposphere

Abstract

A comparison has been conducted of the height and sharpness of the tropopause as revealed by temperature and ozone profiles. In the study, 628 ECC-type ozonesonde profiles from four stations in northern Europe were used. Two tropopauses were defined for each profile: a thermal tropopause and an ozone tropopause defined in terms of both mixing ratio and vertical gradient of mixing ratio. On average, the ozone tropopause lay 800 m below the thermal. Large differences in tropopause height were associated with indefinite thermal tropopauses which were, in turn, often associated with cyclonic conditions (some corresponding to profiles taken within the stratospheric polar vortex). On almost all profiles the thermal tropopause was the higher of the two, and of the 15 profiles that did not fit this pattern, two-thirds were associated with anticyclonic flow in the upper troposphere. It is also shown that the tropopause definition impacts greatly on the evaluation of the ozone content of the troposphere. Where the thermal tropopause is indefinite in character, on average 27% of the ozone found below the thermal tropopause lies above the ozone tropopause.

Transport in the Middle Atmosphere

“…13 also makes clear, the transition is not abrupt and occurs across a region several km deep which exhibits both tro- pospheric and stratospheric chemical characteristics. In particular, ozone does not reach characteristic tropospheric values until almost 1 km below the tropopause (lower left panel), a fact noted a decade ago by Bethan et al (1996) from ozonesonde measurements. On the other hand water vapor does not reach characteristic stratospheric values until about 2 km above the tropopause (lower right panel).…”

Stratosphere‐troposphere exchange: A review, and what we have learned from STACCATO

“…Another tropopause definition in use is based on ozone (O 3 ), which shows a sharp transition from low concentrations in the troposphere to high concentrations in the stratosphere. The O 3 tropopause is usually somewhat lower than the thermal one [Bethan et al, 1996].…”

Ozone climatologies at 9–12 km altitude as seen by the MOZAIC airborne program between September 1994 and August 1996

“…This allows localization, without ambiguity, of stratospheric and tropospheric air [Marenco et With the O3/PV estimates above, 'this corresponds to an ozone critical value ranging from 60 to 120 ppbv. Finally, a more sophisticated tropopause characterization has been elaborated by Bethan et al [ 1996] with (1) a vertical ozone gradient greater than 60 ppbv/km; (2) PV above 1.6-2 pvu; (3) ozone concentration higher than 80 ppbv; and (4) an ozone mixing ratio just above the tropopause higher than 110 ppbv. However, MOZAIC data at cruise level do not provide information on the vertical ozone gradient or tropopause altitude at the sampling position.…”

“…The rough 100 ppbv criterion, retained here, will be further improved by considering also values of th.e potential vorticity (PV), when available in the MOZAIC databank, and MOZAIC relative humidity (RH). However, the PV criterion of 2 pvu at the tropopause, used by the European Centre for Medium-Range Weather Forecasts (ECMWF) to specify the tropopause altitude, has to be reconsidered because various studies [Hoerling et al, 1991;Bethan et al, 1996] have shown seasonal variations and larger values of the PV (2.5 to 3.5 pvu) at the tropopause level. A local study of chemical, dynamic, and thermal tropopauses from 1650 MOZAIC profiles near Frankfurt (1994)(1995)(1996) thus indicates that ozone concentration at the chemical tropopause varies from 51 ppbv in winter to 75 ppbv in summer and that PV values at chemical/thermal tropopauses amount to 2.4 / 3 pvu in winter, and 3 / 3.7 pvu in summer, respectively.…”