Non-hydrostatic GPS Corrections on Jungfraujoch in the Swiss Alps Using Theoretical and Numerical Modeling and Meteorological Observations

Francesca Scire Scappuzzo, Beat Buerki, Hans-Gert Kahle, and Bruce T. Anderson

Abstract:	The Global Positioning System can be effectively used in weather and climate research due to its ability to provide estimates of the Integrated Precipitable Water Vapor (PWV) with 1-2 mm accuracy. In GPS Meteorology, PWV is derived from a model based on known atmospheric variables, GPS measurements of the Zenith delay, and Dry Zenith Delay (DZD) estimates. The DZD is conventionally computed from a hydrostatic model that includes surface pressure measurements at the site. In this study we show that on narrow ridges (mountains of half-width L~1-10 km) affected by high winds (in excess of approximately U=15m/s) non-hydrostatic equilibrium conditions might often take place. We have demonstrated that, because the surface pressure measured during severe weather on mountains is lower than it would be in hydrostatic conditions, it is necessary to introduce a nonhydrostatic correction to the classic GPS estimation of the Dry Zenith Delay for high accuracy purposes. In particular, from our research it emerges that on Jungfraujoch, in the Swiss Alps, the pressure deviation from hydrostatic equilibrium is about –3.4 mbar for wind speeds of 20 m/s, which occur about 15%-20% of the time during winter months. This error translates in an under estimation of the Dry Zenith Delay of about 7.8 mm. In turn, this causes a positive bias in the PWV estimate of 1.4 mm. Therefore, for GPS Meteorology, a non-hydrostatic correction is necessary at this site for surface wind speeds of 20 m/s or above. Even high accuracy non-hydrostatic numerical weather models cannot capture this small-scale phenomenon (orographic uplifting). Therefore, until new more accurate numerical models are available we need to rely on approximate theoretical models (such as the one proposed in this paper) for the non-hydrostatic correction of the DZD and PWV.
Published in:	Proceedings of the 63rd Annual Meeting of The Institute of Navigation (2007) April 23 - 25, 2007 Royal Sonesta Hotel Cambridge, MA
Pages:	181 - 188
Cite this article:	Scappuzzo, Francesca Scire, Buerki, Beat, Kahle, Hans-Gert, Anderson, Bruce T., "Non-hydrostatic GPS Corrections on Jungfraujoch in the Swiss Alps Using Theoretical and Numerical Modeling and Meteorological Observations," Proceedings of the 63rd Annual Meeting of The Institute of Navigation (2007), Cambridge, MA, April 2007, pp. 181-188.
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