Task: Class Definition Understanding (ontology: Earth_Environment/SWEET)

Which of the following definitions best describes 'squall'?

A. A strong wind characterized by a sudden onset, a duration of the order of minutes, and then a rather sudden decrease in speed.
B. A strong, low-level wind through either a relatively level channel between two mountain ranges or a gap in a mountain barrier; originally applied to strong (10?20 m s-1) easterly winds through the Strait of Juan de Fuca between the Olympic Mountains of western Washington State and the mountains of Vancouver Island, British Columbia, Canada. There they have been defined as ?a flow of air in a sea level channel that accelerates under the influence of a pressure gradient parallel to the axis of the channel.? As in the case of mountain- gap winds, this term has also been applied to pressure-gradient winds accelerating through a gap in a mountain barrier. The pressure gradient often results from a stable, post-cold-frontal anticyclone approaching the barrier and being partially blocked (see blocking) as it ascends the barrier, except for the flow through the gap or channel. The tehuantepecer of Central America is a well- known gap wind by this definition. These flows have sometimes been referred to as jet-effect wind and canyon wind.
C. The diurnal cycle of local winds in a mountain valley during clear or mostly clear periods of weak synoptic flow.
D. The humid east wind that crosses the divide of the Andes east of Lake Titicaca and descends on the west in violent squalls; probably the same as puelche.

Answer: A strong wind characterized by a sudden onset, a duration of the order of minutes, and then a rather sudden decrease in speed.