part of adjacent to composed primarily of atmospheric boundary layer planetary surface snow area of perennial ice or snow NLCD:12 nlcd2011 An area of a planet's surface which is primarily composed of snow or water ice, present throughout multiple years, in contact with an atmospheric column extending from the planetary boundary layer to the planet's exosphere with little to no physical obstruction. According to the NLCD 2011, these areas are characterised by ice and/or snow cover generally greater than 25% of total cover. The definition of perennial needs clarification. perennial ice/snow envoPolar astronomical body part ice fiat part of an astronomical object