Journal cover Journal topic
Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union
Journal topic

Journal metrics

Journal metrics

  • IF value: 3.248 IF 3.248
  • IF 5-year value: 3.650 IF 5-year 3.650
  • CiteScore value: 3.37 CiteScore 3.37
  • SNIP value: 1.253 SNIP 1.253
  • SJR value: 1.869 SJR 1.869
  • IPP value: 3.29 IPP 3.29
  • h5-index value: 47 h5-index 47
  • Scimago H index value: 60 Scimago H index 60
Volume 11, issue 8 | Copyright
Atmos. Meas. Tech., 11, 4867-4882, 2018
https://doi.org/10.5194/amt-11-4867-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 24 Aug 2018

Research article | 24 Aug 2018

Comparison study of COSMIC RO dry-air climatologies based on average profile inversion

Julia Danzer1,2, Marc Schwärz1,2, Veronika Proschek1,2, Ulrich Foelsche2,1, and Hans Gleisner3 Julia Danzer et al.
  • 1Wegener Center for Climate and Global Change (WEGC), University of Graz, Graz, Austria
  • 2Institute for Geophysics, Astrophysics, and Meteorology/Institute of Physics (IGAM/IP), University of Graz, Graz, Austria
  • 3Danish Meteorological Institute (DMI), Copenhagen, Denmark

Abstract. Global Navigation Satellite System (GNSS) radio occultation (RO) data enable the retrieval of near-vertical profiles of atmospheric parameters like bending angle, refractivity, pressure, and temperature. The retrieval step from bending angle to refractivity, however, involves an Abel integral with an upper limit of infinity. RO data are practically limited to altitudes below about 80km and the observed bending angle profiles show decreasing signal-to-noise ratio with increasing altitude. Some kind of high-altitude background data are therefore needed in order to perform this retrieval step (this approach is known as high-altitude initialization). Any bias in the background data will affect all RO data products beyond bending angle. A reduction of the influence of the background is therefore desirable – in particular for climate applications.

Recently a new approach for the production of GNSS radio occultation climatologies has been proposed. The idea is to perform the averaging of individual profiles in bending angle space and then propagate the mean bending angle profiles through the Abel transform. Climatological products of refractivity, density, pressure, and temperature are directly retrieved from the mean bending angles.

The averaging of a large number of profiles suppresses noise in the data, enabling observed bending angle data to be used up to 80km without the need for a priori information. Some background information for the Abel integral is still necessary above 80km.

This work is a follow-up study, having the focus on the comparison of the average profile inversion climatologies (API) from the two processing centers WEGC and DMI, which study monthly COSMIC (Constellation Observing System for Meteorology, Ionosphere, and Climate) data from January to March 2011. The impact of different backgrounds above 80km is tested, and different implementations of the Abel integral are investigated. Results are compared for the climatological products with ECMWF analyses, MIPAS, and SABER data.

It is shown that different implementations of the Abel integral have little impact on the API climatologies. On the other hand, different extrapolations of the bending angle profile above 80km play a key role in the resulting monthly mean refractivities above 35km in altitude. Below that respective altitude the API climatologies show a good agreement between the two processing centers WEGC and DMI. Due to the downward propagation within the retrieval, effects of the high-altitude initialization lead to differences in dry-temperature climatologies down to 20km in altitude.

When applying an exponential extrapolation to the bending angles above 80km at both centers, the dry-temperature climatologies agree among WEGC, DMI, ECMWF analysis, and MIPAS up to 35km in altitude within ±0.5K and up to 40km in altitude within ±1K. We conclude that the API retrieval is a valid approach up to the lower stratosphere. It is a computationally efficient alternative method for producing dry atmospheric RO climatologies.

Publications Copernicus
Download
Short summary
Recently a new approach for the production of RO climatologies has been proposed. The idea is to propagate mean bending angle profiles through processing and retrieve directly climatological products of refractivity, density, pressure, and temperature. The averaging suppresses noise in the data, allowing the bending angles to be used up to 80 km without the need for background information. This work focuses on the comparison of the new climatologies between two processing centers.
Recently a new approach for the production of RO climatologies has been proposed. The idea is to...
Citation
Share