Pentru discutiile din aceste zile legate de masurarea cantitatii de precipitatii pe viscol si - legat de asta - a unui strat "reprezentativ" sau "mediu" de zapada, recomand articolul (publicat in iun. 2012):
http://journals.ametsoc.org/doi/full/10 ... 11-00052.1din care citez:
"There are many challenges for the measurement of solid precipitation regardless of gauge type or mechanism of measurement. The most significant challenge is the measurement of snowfall in a windy environment. Nearly all precipitation gauges experience a reduction in the catch efficiency (CE) of snowfall with increasing wind speed. A precipitation gauge installed above the surface of the ground presents a barrier to air flowing around it, causing a deformation of the wind field above the gauge orifice (Sevruk and Klemm 1989). As air flows around and over a precipitation gauge, falling snow hydrometeors are deflected by the flow and do not enter the gauge. The degree of deflection, which increases with wind speed, is dependent on the profile of the gauge (Sevruk et al. 1991) and the type of wind shield (if any) employed around the gauge (Goodison et al. 1998). Wind bias in the gauge measurement of a snowfall event can vary substantially depending on the wind speed, temperature, precipitation characteristics, and gauge configuration, but can be as high as 100% (Goodison and Yang 1996). At some sites, the existing vegetation can be used to shield a precipitation gauge from the wind. The wind bias can also be reduced by the choice of wind shield and by shield type, ranging from a large octagonal double fence, as used with the DFIR (Golubev 1989; Yang et al. 1993) to a single Alter wind shield (Alter 1937). Generally, the more extensive double structures are more effective at reducing the wind bias, but the trade-off is the increased size (footprint) of the structure as well as increased installation and maintenance costs."
Articolul mentioneaza o subestimare a acumularii de pana la 64% pe ninsoare la un vant de numai 5 mps, putand ajunge la 75% la viteze mai mari. Asadar, nu pare deloc exagerata ideea unei multiplicari cu 4 a valorilor masurate pe viscol - urmand ca stratul mediu de zapada sa fie obtinut dupa conversia acestei cantitati corectate...