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. This study analyzes the characteristics of GPStropospheric estimates (zenith wet delays – ZWDs, gradients, and post-fit phaseresiduals) during the passage of mesoscale convective systems (MCSs) andevaluates their sensitivity to the research-level GPS data processingstrategy implemented. Here, we focus on MCS events observed during themonsoon season of West Africa. This region is particularly well suited for the study of these events due to the high frequency of MCS occurrences in the contrasting climaticenvironments between the Guinean coast and the Sahel. This contrast is wellsampled with data generated by six African Monsoon Multidisciplinary Analysis (AMMA) GPS stations. Tropospheric estimates for a3-year period (2006–2008), processed with both the GAMIT and GIPSY-OASISsoftware packages, were analyzed and intercompared. First, the case of aMCS that passed over Niamey, Niger, on 11 August 2006 demonstrates astrong impact of the MCS on GPS estimates and post-fit residuals when theGPS signals propagate through the convective cells as detected on reflectivity maps from the MIT C-band Doppler radar. The estimates are also capable ofdetecting changes in the structure and dynamics of the MCS. However, the sensitivityis different depending on the tropospheric modeling approach adoptedin the software. With GIPSY-OASIS, the high temporal sampling (5 min) ofZWDs and gradients is well suited for detecting thesmall-scale, short-lived, convective cells, while the post-fit residualsremain quite small. With GAMIT, the lower temporal sampling of the estimatedparameters (hourly for ZWDs and daily for gradients) is notsufficient to capture the rapid delay variations associated with the passageof the MCS, but the post-fit phase residuals clearly reflect the presence ofa strong refractivity anomaly. The results are generalized with a compositeanalysis of 414 MCS events observed over the 3-year period at the six GPSstations with the GIPSY-OASIS estimates. A systematic peak is found in theZWDs coincident with the cold pool crossing time associated with the MCSs. The tropospheric gradients reflect the path of the MCSpropagation (generally from east to west). This study concludes that ZWDs, gradients, and post-fit phase residuals provide relevant andcomplementary information on MCSs passing over or in the vicinity of a GPSstation.

Sensitivity of GPS tropospheric estimates to mesoscale convective systems in West Africa