Image caption
The polar vortex on December 4, 2023. Because the air within the polar vortex is generally much colder than the air outside of it, the polar vortex shows up on maps of atmospheric thickness ("geopotential height") as a region of low thickness. The 10-hectoPascal geopotential height is the altitude at which the pressure is 10 hectoPascals. NOAA Climate.gov image, based on Global Forecasting System (GFS) data from Laura Ciasto.