Construction and Uncertainty Estimation of a Satellite-Derived Total Precipitable Water Data Record Over the World's Oceans

Measurements of total precipitable water (TPW) from 11 satellite-borne microwave imaging radiometers are intercalibrated and merged into a single gridded monthly data set starting in January 1988 and continuing to the present. The resulting data set shows a global mean, ocean-only trend in TPW of 0.436 kg/m² per decade (1.49% per decade), and a trend in the deep tropics (20°S–20°N) of 0.629 kg/m² per decade (1.503% per decade). The uncertainty in the merged TPW results is analyzed on multiple time and distance scales using a Monte Carlo approach. This analysis results in an uncertainty ensemble that can be used to evaluate the effects of construction uncertainty on any subsequent application of the data set. We compare the merged data set with measurements of TPW from ground-based Global Navigation Satellite System sensors on small islands. These comparisons show no systematic long-term drifts in the differences, and the observed differences were largely explained by our uncertainty analysis. As an example of the use of the uncertainty ensemble, we evaluate the increase in TPW over the Gulf of Mexico during summer months over 1988–2017.