Asymmetricity of ground-based GPS slant delay data R. Eresmaa, H. Järvinen, S. Niemelä, and K. Salonen Finnish Meteorological Institute, Erik Palménin aukio 1, 00100 Helsinki, Finland
Abstract. The ground-based measurements of the Global Positioning System (GPS)
allow estimation of the tropospheric delay along the slanted signal
paths through the atmosphere. The meteorological exploitation of such
slant delay (SD) observations relies on the hypothesis of azimuthal
asymmetry of the information content. This article addresses the
validity of the hypothesis.
A new concept of asymmetricity is introduced for studying the SD
observations and their model counterparts. The asymmetricity is
defined as the ratio of the absolute asymmetric delay component to
total SD. The model
counterparts are determined from 3-h forecasts of a numerical
weather prediction (NWP) model, run with four different horizontal
resolutions. The SD observations are compared with their model
counterparts with emphasis on cases of high asymmetricity in order to
see whether the observed asymmetry is a real atmospheric signature.
The asymmetricity is found to be of the order of a few parts per
thousand. Thus, the asymmetric delay component barely exceeds the
assumed standard deviation of the SD observation error. However, the
observed asymmetric delay components show a statistically significant
meteorological signal. Benefit of the asymmetric SD observations is
therefore expected to be taken in future, when NWP systems will
explicitly represent the small-scale atmospheric features revealed by
the SD observations.
Citation: Eresmaa, R., Järvinen, H., Niemelä, S., and Salonen, K.: Asymmetricity of ground-based GPS slant delay data, Atmos. Chem. Phys., 7, 3143-3151, doi:10.5194/acp-7-3143-2007, 2007.