On a low cloud phenomenon at the Breidamerkurjokull Glacier, Iceland

An impressive cloud wall has frequently been observed on the southern slope s of the Vatnajokull ice sheet, which is located in south-eastern Iceland. Its optical and dynamic features suggest a delicate balance of the atmosphe ric agents involved. This has been confirmed by a thorough analysis of a we ll documented event and by statistics covering a whole summer season. As an exemplary event, the regional development of the associated cloud has basi cally been documented with synchronous surface data along a suitable transe ct of the glacier. Data from tethered balloons, radiosoundings and routine synoptic data have also been exploited extensively. Cloud development was g enerally aided by a high moisture potential because of proximity to the ope n seas and the remnants of a frontal system. Furthermore the occurrence of the cloud phenomenon was associated with onshore (southerly) surface winds, assisting advection and lifting of the associated air masses above the slo pes of the ice sheet. Northward protrusion of the associated cloud was appa rently opposed by continuous katabatic winds and topographically induced le e effects.