20 Jun 2022
20 Jun 2022
Status: this preprint is open for discussion.

Equatorial waves resolved by balloon-borne Global Navigation Satellite System Radio Occultation in the Strateole-2 Campaign

Bing Cao1, Jennifer S. Haase1, Michael J. Murphy1, M. Joan Alexander2, Martina Bramberger2, and Albert Hertzog3 Bing Cao et al.
  • 1Scripps Institution Oceanography, University of California San Diego, La Jolla, CA, USA
  • 2Northwest Research Association, Boulder, CO, USA
  • 3Laboratoire de Météorologie Dynamique, Sorbonne Université, École Polytechnique, CNRS, Palaiseau, France

Abstract. Current climate models have difficulty representing realistic wave-mean flow interactions, partly because the contribution from waves with fine-vertical scales is poorly known. There are few direct observations of these waves and most models have difficulty resolving them. This observational challenge cannot be addressed by satellite or sparse ground-based methods. The Strateole-2 long-duration stratospheric superpressure balloons that drift with the horizontal wind on constant density surfaces provide a unique platform for wave observations across a broad range of spatial and temporal scales. For the first time, balloon-borne Global Navigation Satellite System (GNSS) radio occultation (RO) is used to provide high vertical resolution equatorial wave observations. By tracking navigation signal refractive delays from GPS satellites near the horizon, 40–50 temperature profiles were retrieved daily, from balloon flight altitude (∼20 km) down to 6–8 km altitude, forming an orthogonal pattern of observations over a broad area (±400–500 km) surrounding the flight track. The refractivity profiles show an excellent agreement of better than 0.2 % with co-located radiosonde, spaceborne COSMIC-2 RO and reanalysis products. The 200–500 m vertical resolution and consecutive sampling in time and space make it possible to extract properties of Kelvin waves to shorter period gravity waves with vertical wavelengths as short as 2–3 km. A short dataset from the extra Galileo and GLONASS constellations demonstrates the feasibility to nearly double the sampling density in planned follow-on campaigns. The results will contribute to improved estimates of momentum forces for wave driving of the Quasi-biennial Oscillation (QBO) and improved QBO representation in models, and illustrate the importance of measuring intrinsic period in the Lagrangian reference frame.

Bing Cao et al.

Status: open (until 01 Aug 2022)

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Bing Cao et al.

Bing Cao et al.


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Short summary
Atmospheric waves that carry momentum from the tropospheric weather systems into the equatorial stratosphere modify the winds there. The 2019 Strateole-2 campaign launched long-duration stratospheric superpressure balloons to measure these equatorial waves. We deployed a GPS receiver on one of the balloons to measure atmospheric temperature profiles beneath the balloon. Temperature variations in the retrieved profiles show planetary-scale waves with a 20 day period and 3–4 day period waves.