Penitentes are a snow formation found at high altitudes. They take the form of tall thin blades of hardened snow or ice closely spaced with the blades oriented towards the general direction of the sun. Penitentes can be as tall as a person.
Penitentes were first described in the literature by Darwin in 1839. On March 22, 1835, he had to squeeze his way through snowfields covered in penitentes near the Piuquenes Pass, on the way from Santiago de Chile to the Argentinian city of Mendoza, and reported the local belief (continuing to the present day) that they were formed by the strong winds of the Andes. These pinnacles of snow or ice grow over all glaciated and snow covered areas in the Dry Andes above 4,000 m (Lliboutry 1954a, Lliboutry 1954b, Lliboutry 1965). They range in size from a few cm to over five metres. (Lliboutry 1965, Naruse and Leiva 1997).
Lliboutry noted that the key climatic condition for the differential ablation that leads to the formation of penitentes is that dew point is always below freezing. Thus, snow will sublimate, which requires higher energy input than melting. Once the process of differential ablation starts, the surface geometry of the evolving penitente produces a positive feedback mechanism, and radiation is trapped by multiple reflections between the walls. The hollows become almost a black body for radiation, while decreased wind leads to air saturation, increasing dew point temperature and the onset of melting. In this way peaks, where mass loss is only due to sublimation, will remain, as well as the steep walls, which intercept only a minimum of solar radiation. In the troughs ablation is enhanced, leading to a downward growth of penitentes. A mathematical model of the process has been developed by Betterton (2001), although the physical processes at the initial stage of penitente growth, from granular snow to micropenitentes, still remain unclear. The effect of penitentes on the energy balance of the snow surface, and therefore their effect on snow melt and water resources have been described by Corripio (2003) and Corripio and Purves (2005).
Penitentes were first described in the literature by Darwin in 1839. On March 22, 1835, he had to squeeze his way through snowfields covered in penitentes near the Piuquenes Pass, on the way from Santiago de Chile to the Argentinian city of Mendoza, and reported the local belief (continuing to the present day) that they were formed by the strong winds of the Andes. These pinnacles of snow or ice grow over all glaciated and snow covered areas in the Dry Andes above 4,000 m (Lliboutry 1954a, Lliboutry 1954b, Lliboutry 1965). They range in size from a few cm to over five metres. (Lliboutry 1965, Naruse and Leiva 1997).
Lliboutry noted that the key climatic condition for the differential ablation that leads to the formation of penitentes is that dew point is always below freezing. Thus, snow will sublimate, which requires higher energy input than melting. Once the process of differential ablation starts, the surface geometry of the evolving penitente produces a positive feedback mechanism, and radiation is trapped by multiple reflections between the walls. The hollows become almost a black body for radiation, while decreased wind leads to air saturation, increasing dew point temperature and the onset of melting. In this way peaks, where mass loss is only due to sublimation, will remain, as well as the steep walls, which intercept only a minimum of solar radiation. In the troughs ablation is enhanced, leading to a downward growth of penitentes. A mathematical model of the process has been developed by Betterton (2001), although the physical processes at the initial stage of penitente growth, from granular snow to micropenitentes, still remain unclear. The effect of penitentes on the energy balance of the snow surface, and therefore their effect on snow melt and water resources have been described by Corripio (2003) and Corripio and Purves (2005).
1 comments:
nadaa ! meni pake nhs inggris hehe, btw follow aku juga ya !
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