Longer IPW series (up to 14 years) searched for some climatological signal sometimes reveal weak steady trend. Not only amplitudes but also phases of annual signal differ from year to year. Simple sinusoidal model has been adjusted to the IPW series (LS method) for selected stations (mainly Europe but also other continents - IGS stations), every year separately. In case of continental network (EUREF Permanent Network) reliable data we get only after reprocessing. Homogenous ZTD solution during long period is great concern in this approach (problems with GPS strategy and reference system changes). The longer and more uniform our series are the better chance to estimate the magnitude of climatological IWV changes. Long lasting changes in weather conditions: 'dry' and 'wet' years are also visible. Especially intriguing are relatively unique shape of such series in different climates. The second and most important aspect of this study concerns long series of IPW (daily averaged) which can serve as climatological information indicator (water vapour role in climate system is hard to exaggerate). This inadequacy and poor humidity data representation in NWP model extremely encourages investigating information exchange potential between Numerical Model and GPS network. Deficiency of surface humidity data to model IPW is presented for different climates. Next we analyse IPW as geophysical parameter: IPW demonstrates some physical effects evoked by station location (height and series correlation coefficient as a function of distance) and weather patterns like dominant wind directions (in case of neighbouring stations). Sunphotometer (CIMEL-318, Central Geophysical Observatory IGF PAS, Belsk, Poland) data seems the most genuine source - so we decided for direct collocation of GPS measurements and sunphotometer placing permanent GPS receiver on the roof of Belsk Observatory. We can treat operational NWP models as meteorological database within which we can calculate IWV for all GPS stations independently from network of direct measurements (COSMO-LM model maintained by Polish Institute of Meteorology and Water Management was tried). IPW values from meteorological sources we used are: radiosoundings, sun photometer and input fields of numerical weather prediction model. Nonetheless we have managed to compare IPW series derived from GPS tropospheric solutions (ZTD mostly from IGS and EPN solutions) and some independent techniques. Most thorough inter-technique comparisons of directly measured IPW are attainable only for some observatories (note modest percentage of GPS stations equipped with meteorological devices). GPS meteorology is now widely acknowledged indirect method of atmosphere sensing. Paper focuses on comprehensive investigation of the GPS derived IPW (Integrated Precipitable Water, also IWV) as a geophysical tool.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |