A cloud forming in maritime air containing relatively low concentrations of cloud condensation nuclei. These clouds are characterized by a broader droplet size distribution and low droplet concentrati
ons (some 100 cm-3). See continental cloud.
Air mass that forms over extensive ocean areas of the middle to high latitudes. Around North America, these air mass system form over the Atlantic and Pacific oceans at the middle latitudes. Maritime
Polar air masses are mild and humid in summer and cool and humid in winter. In the Northern Hemisphere, maritime polar air masses are normally unstable during the winter. In the summer, atmospheric stability depends on the position of the air mass relative to a continent. Around North America, Maritime Polar air masses found over the Atlantic are stable in summer, while Pacific systems tend to be unstable.
A distinctive, datable layer in ice, firn or snow; see isochrone. Ice-core stratigraphy relies on an uninterrupted series of Annual marker horizons. Volcanic eruptions and nuclear tests (see bomb hori
zon) yield marker horizons which allow the measurement of average accumulation rates. Marker horizons with relative dielectric constants that contrast strongly enough allow the mapping of accumulation with ground-penetrating radar.