- 1Johannes Gutenberg University Mainz, Institute for Atmospheric Physics, Germany (franziska.weyland@uni-mainz.de)
- 2Meteorological Institute, Ludwig-Maximilians-University Munich, Germany
- 3Institute for Physics of the Atmosphere, Deutsches Zentrum für Luft- und Raumfahrt, Oberpfaffenhofen, Germany
- 4Institute of Climate and Energy Systems, Stratosphere (ICE-4), Forschungszentrum Jülich, Jülich, Germany
- 5Institute for Atmospheric and Environmental Research, University of Wuppertal, Wuppertal, Germany
The mass of the lowermost stratosphere (LMS) is an important characteristic of the thermodynamic structure of the lower stratosphere. From a scientific perspective, long-term LMS mass changes illustrate the combined effect of tropopause pressure trends, tropical width trends and temperature changes in the tropical tropopause region. Further, understanding LMS mass trends can improve our knowledge of lower stratospheric ozone and water vapor trends that, despite their radiative importance, are still insufficiently understood. From a technical perspective, comparing LMS mass trends across reanalyses reveals consistencies and discrepancies between the data sets.
We examine long term trends in LMS mass using five modern reanalyses – ERA5, ERA-Interim, MERRA-2, JRA-55 and JRA3Q – for the time period 1979–2019. The focus is on changes after the year 1998, marking the anticipated beginning of stratospheric ozone recovery. The trend analysis is performed with a dynamic linear regression model (DLM).
All reanalyses consistently show decreasing tropopause pressure in the tropics and the Northern Hemisphere (NH) extratropics. This is reflected in a robust LMS mass decrease in the NH when a fixed isentrope of 380K is used as upper boundary, i.e. to approximate the tropical tropopause. However, we show that a fixed isentrope is an inadequate approximation of the upper LMS boundary for long-term studies, as the tropical tropopause also exhibits a trend. Therefore, we propose dynamically varying upper boundaries linked to the tropical tropopause potential temperature, accounting for this trend. In ERA5, ERA-Interim and MERRA-2, the dynamical upper boundaries are able to partly compensate for the tropopause rise in the NH. In contrast, the LMS mass decrease in the NH is enhanced by the dynamical upper boundaries in JRA-55 and JRA3Q. This is due to opposing absolute temperature trends in the tropical tropopause region across the reanalyses.
How to cite: Weyland, F., Hoor, P., Kunkel, D., Birner, T., Turhal, K., and Plöger, F.: Long-term Changes in the Thermodynamic Structure and the Mass of the Lowermost Stratosphere Comparing Five Modern Reanalyses, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19101, https://doi.org/10.5194/egusphere-egu25-19101, 2025.
