This section is concerned with the 6 different air mass types that affect the British Isles. These are namely, Tropical Continental (Tc), Tropical maritime (Tm), Polar continental (Pc), Polar maritime (Pm), Arctic maritime (Am) and Returning polar maritime (Rpm). There is a useful & detailed explanatory link below to the Meteorological Office website that deals with this particular subject. Also an explanation about how the ‘Polar Vortex’ works.
metoffice.gov.uk/weather/learn-about/weather/atmosphere/air-masses/types
How the Polar Vortex works: severe-weather.eu/global-weather/polar-vortex-warming-split-2022-usa-europe-forecast-fa/