Seasonal and Annual Changes of the Regional Tropical Belt in GPS-RO Measurements and Reanalysis Datasets

In recent decades, the tropics have been widening. This widening is expected to impact society globally, with potentially severe impacts in some regions. However, defining the regional tropical edge is a challenge. In this study, we analyze the tropical belt using four tropopause-based metrics at a regional level, in contrast to the typical zonal mean approach. We evaluate the performance of different reanalyses and metrics in depicting regional seasonal tropical belt width from GPS-RO satellite data and four modern reanalyses (ERA-Interim, MERRA 2, JRA 55, and CFSR). We show reanalyses closely reproduce the regional tropical belt edge as depicted in GPS-RO data—but that the tropical width is moderately sensitive (within 10°) to the dataset resolution, and very sensitive (within 40°) to the choice of metric. We further find the climatological tropical tropopause break to be more representative of the subtropical jet latitude than the edge of the regional Hadley circulation.