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Volume 11, issue 3 | Copyright

Special issue: Observing Atmosphere and Climate with Occultation Techniques...

Atmos. Meas. Tech., 11, 1333-1346, 2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 06 Mar 2018

Research article | 06 Mar 2018

Atmospheric QBO and ENSO indices with high vertical resolution from GNSS radio occultation temperature measurements

Hallgeir Wilhelmsen1,2,3, Florian Ladstädter1,3, Barbara Scherllin-Pirscher4, and Andrea K. Steiner1,2,3 Hallgeir Wilhelmsen et al.
  • 1Wegener Center for Climate and Global Change (WEGC), University of Graz, Graz, Austria
  • 2FWF-DK Climate Change, University of Graz, Graz, Austria
  • 3Institute for Geophysics, Astrophysics, and Meteorology/Institute of Physics, University of Graz, Graz, Austria
  • 4Zentralanstalt für Meteorologie und Geodynamik (ZAMG), Vienna, Austria

Abstract. We provide atmospheric temperature variability indices for the tropical troposphere and stratosphere based on global navigation satellite system (GNSS) radio occultation (RO) temperature measurements. By exploiting the high vertical resolution and the uniform distribution of the GNSS RO temperature soundings we introduce two approaches, both based on an empirical orthogonal function (EOF) analysis. The first method utilizes the whole vertical and horizontal RO temperature field from 30°S to 30°N and from 2 to 35km altitude. The resulting indices, the leading principal components, resemble the well-known patterns of the Quasi-Biennial Oscillation (QBO) and the El Niño–Southern Oscillation (ENSO) in the tropics. They provide some information on the vertical structure; however, they are not vertically resolved. The second method applies the EOF analysis on each altitude level separately and the resulting indices contain information on the horizontal variability at each densely available altitude level. They capture more variability than the indices from the first method and present a mixture of all variability modes contributing at the respective altitude level, including the QBO and ENSO. Compared to commonly used variability indices from QBO winds or ENSO sea surface temperature, these new indices cover the vertical details of the atmospheric variability. Using them as proxies for temperature variability is also of advantage because there is no further need to account for response time lags. Atmospheric variability indices as novel products from RO are expected to be of great benefit for studies on atmospheric dynamics and variability, for climate trend analysis, as well as for climate model evaluation.

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Short summary
Tropical atmospheric variability is often described using proxy indices of the Quasi-Biennial Oscillation and the El Niño–Southern Oscillation. We introduce new proxies derived from GNSS radio occultation (RO) satellite measurements. Using the high vertical resolution of the RO temperature fields we obtain altitude-resolved indices which can improve the description of atmospheric variability patterns and can be used in climate studies where a detailed knowledge of these patterns is required.
Tropical atmospheric variability is often described using proxy indices of the Quasi-Biennial...