A multipurpose high-rate GPS observatory for northwestern Mexico

We describe a proposed joint atmospheric and geophysical high-rate GPS observatory in northwestern Mexico complementing and extending analogous networks in the United Stated. The observatory would measure atmospheric water vapor during the North American Monsoon Experiment (NAME) as well as crustal velocities within and across the Gulf of California and the Mexican Basin and Range region for geodetic applications. The NOAA-sponsored NAME scheduled for several summers beginning in 2004 addresses the challenging issue of determining and improving the predictability of warm season precipitation in the mountainous region of the Northwestern Mexico and Southwestern US. Much of the rainfall in the region comes during the North American Monsoon each summer. Rainfall in the region is particularly difficult to model and predict because the orography and the complex land-sea geometry of the region with moisture sources in the Gulf of Mexico, Gulf of California and the eastern subtropical Pacific Ocean. The GPS provides accurate, near-continuous observations of water vapor in clear and cloudy air needed to sample the large diurnal variations in the dynamic and thermodynamic properties of the atmosphere. GPS in combination with wind and other measurements scattered in and around the region will provide much needed constraints to determine quantitatively the sources supplying moisture for precipitation within the NAME area. Tectonic applications of this continuous GPS network in Mexico include high-precision determinations of plate boundary deformation in and around the Gulf of California and possible diffuse deformation within the Mexican Basin and Range province. Because of the high sampling rate (1 Hz), the network will also provide data for seismological applications, including surface wave studies (e.g., Larson et al., SCIENCE, 2003) and potential near-field displacement records. Furthermore the network would complement the US-based Plate Boundary Observatory (PBO) facility by extending continuous GPS coverage into northern Mexico and other relatively smaller-scale continuous GPS networks in southern Mexico as well as provide important data for surveying and mapping applications. Several years of observations are required to capture the substantial year-to-year variations in the monsoon and yield accurate estimates of tectonic motion. Both objectives can be accomplished relatively inexpensively with the simple and robust GPS observations made in collaboration with investigators in Mexico.