Recent Ground Based GPS Meteorology Developments for SuomiNet

Over the past 10 years significant progress has been made in atmospheric sensing with GPS. Both spacebased atmospheric sounding and ground-based measurements of integrated delay due to the troposphere have shown promise for meteorological applications. Now the focus is shifting from developing and validating the sensing technology towards applying it to weather forecasting. This paper will focus on ground-based GPS meteorology applications. New GPS networks are now under development in several countries. For many of these networks the use of the GPS data for meteorology is of increasing importance. In this paper we will introduce a new network, called SuomiNet (Ware et al., 2000). This network is presently established in the USA and it also has several international sites. We will describe near real-time data analysis for SuomiNet. One novel aspect of the analysis of the SuomiNet data is that it utilizes gridded weather fields for computing site and time specific mapping functions. This paper shows that the use of this so-called direct mapping technique (Rocken et al. 2001) significantly reduces the dependence of the GPS results on the observation elevation cutoff angle. Improving the mapping function is especially important for low elevation observations. Low elevation observations are in turn important for the meteorological impact of GPS. Simulation studies by McDonald et al. (2001) have shown that low elevation GPS slant observations can be used to reconstruct three-dimensional water vapor fields. In the last part of this paper we provide results from the assimilation of simulated GPS data into the MM5 numerical weather model.