Polar vortex mask based on the Nash criterion

These data provide a cumulative polar vortex mask for the Northern hemisphere between 2000-2024. The mask describes on how many potential temperature layers the polar vortex is detected on. Here the mask is based on six potential temperature levels between 395 K and 700 K. The polar vortex is a 3D structure and therefore the categorization of a point on the surface to be 'inside the vortex' is not well defined. We recommend using a threshold of 'mask>=3' to categorize a point as inside the vortex for this file.The polar vortex detection is based on the Nash criterion (DOI: 10.1029/96JD00066). This dataset is provided as a supplement to 'Reduction of airmass-dependent biases in TCCON XCH retrievals during polar vortex conditions' (DOI: 10.5194/amt-18-7105-2025), which describes the algorithm used to generate this data.