The North American Monsoon GPS TRANSECT Experiment 2013

The need for meteorology observations in Northwest Mexico strongly motivated the North American Monsoon GPS TRANSECT Experiment 2013; however, the goals of this experiment are much broader. The GNSS/GPS technique for providing water vapor measurements has now been used for almost two decades, particularly for validation, observational studies and forecasting.  These studies suggest the technique provides total column water vapor with high accuracy and with a high degree of stability over time making it very useful for many research applications over a variety of time scales. The Experiment has two principal scientific aims: (1) to address basic science questions regarding the role of water vapor fluxes in the SMO in initiating deep convection and growth into MCSs by utilizing a novel measurement technique. (2) to improve NAM operational forecasts through PWV data assimilation

Broader impacts of the experiment also include strengthening the international long-term collaborative efforts between Mexico and the US focusing on the climate and meteorology of Northwest Mexico and the Southwest US.

10 GPS meteorological stations in addition to 7 existing Suominet sites (http://www.suominet.ucar.edu/) . were arranged in 3 specific transects, each with a particular observational goal. To cover the highest reaches of the SMO, a transect from Bahía de Kino to Chihuahua City was constructed providing the opportunity to evaluate convective initiation and the diurnal cycle of precipitable water vapor fields over complex terrain. The second transect along the Gulf of California (GoC) coastal plains was motivated by the need to capture of low-level moisture “gulf surges” propagating up the GoC in addition to other tropical disturbances. The third transect, Los Mochis to Badiraguato, captures the strong precipitation gradient between the GoC and the foothills of Sinaloa.

We present initial results on the diurnal cycle of precipitable water vapor as a function of elevation for both convective and non-convective days. In addition, we introduce typical deep convective timescales derived from GPS precipitable water vapor for convective development across the SMO and along the GoC. We conclude with future work on data assimilation into regional forecast models.