[1] Dual frequency GPS observables only allow the elimination of the 1st -order ionospheric term. Although higher -order ionospheric terms may cause a range bias of several centimeters, accounting for such effects is not yet a common strategy for GPS data analysis. In comparison to previous investigations a rigorous application of 2nd and 3rd -order ionospheric corrections is examined for the estimation not only of receiver positions but of all included parameters. The results reveal a linear dependence of the frame's origin on the integrated electron density. Furthermore, satellite positions are affected at the centimeter level when applying the above -mentioned corrections. Since the ionospheric correction terms show a significant impact on various GPS estimates, their consideration becomes necessary for scientific applications. Hence, the modeling of 2nd and 3rd -order ionospheric correction terms is part of the optimized strategy in an ongoing reprocessing project dealing with a global GPS network and spanning the time period from 1994 up to present time. Citation: Fritsche, M., R.

Land glacier extent and volume at the northern and southern margins of the Drake Passage have been in a state of dramatic demise since the early 1990s. Here time‐varying space gravity observations from the Gravity Recovery and Climate Experiment (GRACE) are combined with Global Positioning System (GPS) bedrock uplift data to simultaneously solve for ice loss and for solid Earth glacial isostatic adjustment (GIA) to Little Ice Age (LIA) cryospheric loading. The present‐day ice loss rates are determined to be −26 ± 6 Gt/yr and −41.5 ± 9 Gt/yr in the Southern and Northern Patagonia Ice Fields (NPI+SPI) and Antarctic Peninsula (AP), respectively. These are consistent with estimates based upon thickness and flux changes. Bounds are recovered for elastic lithosphere thicknesses of 35 ≤ h ≤ 70 km and 20 ≤ h ≤ 45 km and for upper mantle viscosities of 4–8 × 1018 Pa s and 3–10 × 1019 Pa s (using a half‐space approximation) for NPI+SPI and AP, respectively, using an iterative forward model strategy. Antarctic Peninsula ice models with a prolonged LIA, extending to A.D. 1930, are favored in all χ2 fits to the GPS uplift data. This result is largely decoupled from Earth structure assumptions. The GIA corrections account for roughly 20–60% of the space‐determined secular gravity change. Collectively, the on‐land ice losses correspond to volume increases of the oceans equivalent to 0.19 ± 0.045 mm/yr of sea level rise for the last 15 years.

[1] During the 10 years since the official start of the International GNSS Service (IGS) in 1994 considerable improvements in the processing strategies and modeling of global GPS solutions were achieved. Owing to changes at the individual IGS Analysis Centers during these years the resulting time series of global geodetic parameters are very inhomogeneous and inconsistent. A geophysical interpretation of these long series and the realization of a high-accuracy global reference frame are therefore difficult and questionable. In view of these deficiencies, the Technical Universities of Munich and Dresden decided to perform a reprocessing of a global GPS network over the last decade in a joint effort. First results of the reprocessing of 11 years of data show significant improvements in the quality and homogeneity of the estimated parameters and will allow for new geodynamic and geophysical interpretations. In the early years an improvement of the coordinate repeatability by a factor of more than 2 could be achieved. The formal errors of subdaily Earth rotation parameters could be reduced by 30%. Advanced modeling approaches like a mapping function based on numerical weather models, consideration of second-and third-order ionospheric corrections and absolute antenna phase center corrections for receivers and satellites were tested to achieve further improvements.

S U M M A R YA GPS network, consisting of 10 sites, was established in the ice-free area of West Greenland and was observed for the first time in 1995. In 2002 a complete re-observation was carried out. These repeated GPS observations served as a basis for the determination of vertical crustal deformations. The data analysis was performed using the Bernese Software version 5.0. For the central site Kangerlussuaq a negative uplift rate (subsidence) of (−3.1 ± 1.1) mm yr −1 was obtained, related to the reference frame IGb00. The regional pattern is characterized by an east-west gradient of up to 4 mm yr −1 between the outer coast and the subsiding area along the present ice margin, which can be explained to a great extent as a result of the late Holocene re-advance of the Greenland ice sheet. Relative sea-level changes could be calculated taking the present eustatic sea-level rise into account. The present-day sea level rises at the outer coast between Maniitsoq and Paamiut, and in the large fjords with increasing rates of more than 4 mm yr −1 in their innermost parts. These findings are in agreement with the general picture obtained from geomorphological and archaeological research. For Sisimiut and the Disko Bay area the present sea-level change is almost zero, whereas the crustal uplift rate for Ilulissat was observed to be 1.6 mm yr −1 . We conclude that this present vertical uplift rate in Ilulissat is affected by the retreat of the ice margin during the last 150 yr and the present negative mass balance of the Jakobshavn Isbrae and its drainage basin.

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[1] Observations of the Global Positioning System (GPS) were reanalyzed over the period from 1994 to 2004 in a joint project of the technical universities in Dresden and Munich. The estimated tropospheric parameters were converted into precipitable water (PW) using surface pressure observations from the World Meteorological Organization and atmospheric mean temperature fields from the European Centre for Medium-Range Weather Forecasts. For the first time a systematic study of the homogeneity of global GPSderived precipitable water time series was carried out regarding the influence of changes in the GPS antennas and radomes as well as changes in the number of recorded observations. The focus of this study is on interannual changes in precipitable water. Over Europe, large parts of North America, and Iceland and in the region south of 30°S, these changes are very small. The range of the PW variations on interannual time scales is less than 2 mm in these areas. However, in the southeastern part of North America and north Australia, these anomalies in precipitable water show a range of up to 6 mm. In the tropics, PW anomalies with a range of up to 10 mm were found. GPS PW was compared with a modeled PW assuming water vapor saturation. This shows that GPS PW of stations located in the middle and high northern and southern latitudes is consistent with the temperature-related saturation values of water vapor. In the tropics and subtropics the annual temperature variations are low. In these regions the variations in the PW can be dominated by other factors, including water vapor transport. At seasonal time scales the water vapor transport can be associated with atmospheric circulation such as monsoonal flow.Citation: Vey, S., R. Dietrich, M. Fritsche, A. Rülke, P. Steigenberger, and M. Rothacher (2009), On the homogeneity and interpretation of precipitable water time series derived from global GPS observations,

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In contrast to previous studies validating numerical weather prediction (NWP) models using observations from the global positioning system (GPS), this paper focuses on the validation of seasonal and interannual variations in the water vapor. The main advantage of the performed validation is the independence of the GPS water vapor estimates compared to studies using water vapor datasets from radiosondes or satellite microwave radiometers that are already assimilated into the NWP models. Tropospheric parameters from a GPS reanalysis carried out in a common project of the Technical Universities in Munich and Dresden were converted into precipitable water (PW) using surface pressure observations from the WMO and mean atmospheric temperature data from ECMWF. PW time series were generated for 141 globally distributed GPS sites covering the time period from the beginning of 1994 to the end of 2004. The GPS-derived PW time series were carefully examined for their homogeneity. The validation of the NWP model from NCEP shows that the differences between the modeled and observed PW values are time dependent. In addition to establishing a long-term mean, this study also validates the seasonal cycle and interannual variations in the PW. Over Europe and large parts of North America the seasonal cycle and the interannual variations in the PW from GPS and NCEP agree very well. The results reveal a submillimeter accuracy of the GPS-derived PW anomalies. In the regions mentioned above, NCEP provides a highly accurate database for studies of longterm changes in the atmospheric water vapor. However, in the Southern Hemisphere large differences in the seasonal signals and in the PW anomalies were found between GPS and NCEP. The seasonal signal of the PW is underestimated by NCEP in the tropics and in Antarctica by up to 40% and 25%, respectively. Climate change studies based on water vapor data from NCEP should consider the large uncertainties in the analysis when interpreting these data, especially in the tropics.