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Wang, MH, Wang JX, Bock Y, Liang H, Dong DA, Fang P.  2019.  Dynamic mapping of the movement of landfalling atmospheric rivers over Southern California with GPS data. Geophysical Research Letters. 46:3551-3559.   10.1029/2018gl081318   AbstractWebsite

Atmospheric rivers (ARs) are long, narrow, and transient corridors of strong horizontal water vapor transport that can result in heavy precipitation. Measuring the movement of these concentrated water vapor bands is important in gaining better insight into AR characteristics and forecasts of AR-caused precipitation. We describe a method to dynamically map the movement of landfalling ARs. The method utilizes high-rate GPS observations from a dense network to derive isochrones that represent the AR arrival time over specific locations. The generated isochrones show that the three ARs, during landfall over Southern California in January 2017, moved southeastward and took about 10 hr to pass over the study area. Overlaying the topography with isochrones reveals that the Peninsular Ranges slow the movement of the landfalling ARs. The large spacing between two adjacent isochrones, reflecting fast AR movement, is closely related to the increased hourly rain rate. Plain Language Summary Atmospheric rivers (ARs), "rivers in the sky," are "rivers" of water vapor rather than liquid water. The landfall of ARs can cause extreme rainfall that in turn induces disasters. We present a method with a dense high-rate GPS network to capture the movement of the landfalling ARs over Southern California. For the three landfalling AR cases in January 2017, results show that the ARs moved southeastward and the durations of AR passing over the study area were about 10 hr. The results also reveal that the landfalling AR movement is affected by local terrain and the fast AR movement is closely related to the large hourly rain rate. The use of the method provides a way to study ARs with high spatial-temporal resolution, which is important in gaining better insight into the forecasts of AR-caused rainfall.

Dong, D, Fang P, Bock Y, Cheng MK, Miyazaki S.  2002.  Anatomy of apparent seasonal variations from GPS-derived site position time series. Journal of Geophysical Research-Solid Earth. 107   10.1029/2001jb000573   AbstractWebsite

[1] Apparent seasonal site position variations are derived from 4.5 years of global continuous GPS time series and are explored through the "peering'' approach. Peering is a way to depict the contributions of the comparatively well-known seasonal sources to garner insight into the relatively poorly known contributors. Contributions from pole tide effects, ocean tide loading, atmospheric loading, nontidal oceanic mass, and groundwater loading are evaluated. Our results show that similar to40% of the power of the observed annual vertical variations in site positions can be explained by the joint contribution of these seasonal surface mass redistributions. After removing these seasonal effects from the observations the potential contributions from unmodeled wet troposphere effects, bedrock thermal expansion, errors in phase center variation models, and errors in orbital modeling are also investigated. A scaled sensitivity matrix analysis is proposed to assess the contributions from highly correlated parameters. The effects of employing different analysis strategies are investigated by comparing the solutions from different GPS data analysis centers. Comparison results indicate that current solutions of several analysis centers are able to detect the seasonal signals but that the differences among these solutions are the main cause for residual seasonal effects. Potential implications for modeling seasonal variations in global site positions are explored, in particular, as a way to improve the stability of the terrestrial reference frame on seasonal timescales.