TPW is measured by a variety of satellites. In this case, data from the AMSU and SSM/I microwave sensors are merged together to create a daily composite of global TPW. Values are expressed as "precipitable millimeters" or "kilograms per square meter." Both refer to an amount of water over a defined area.

Significant features that can be identified in TPW data are the atmospheric rivers that flow off the oceans and onto coastal land areas. A famous example is the Pineapple Express that forms in the Northeast Pacific and impacts the Northwest United States. Also notice how TPW values are much greater over the equator and ocean. High levels of evaporation in these areas are one of the primary drivers of atmospheric circulation.

Data Source:NOAA/NESDIS/STAR Microwave Integrated Retrieval System (MIRS) data page