OCR Text |
Show and causing an undesirable amount " pumping" of the recording pen arm. Furthermore, this type does not seem to provide uniform snow collection. The collector pictured in the accompanying sketch and photo circumvents these difficulties by providing an exhaust orifice for the wind. By increasing the wind channel diameter between inlet and exhaust, at the same time directing the air flow upward, a chance is afforded the wind- borne snow to fall into the recording gauge in a relatively undisturbed fashion. The collector is fabricated from standard galvanized sheet metal heating duct elements, and can easily be duplicated by a sheet metal shop. The support frame must be rigid, but offer minimum interference to snow collection. The pipe frame illustrated is recommended as sturdy and simple to assemble from standard pipe parts. With the full eight- inch diameter of the inlet exposed, this collector gathers into the gauge over twice as much as snow as accumulates on an adjacent snow stake platform on the ground. It, therefore, has been necessary to mask the inlet with a diaphragm until the inlet cross- section has an area of about 28 square inches. This value was achieved empirically by adjusting the inlet area until a consistent match was obtained with snowfall on the ground. A good correlation was found in the collected snow in the gauge and that deposited on the ground over ranges of wind speed from 5 to 25 mph. Too few reliable data are available for determining the correlation at higher wind speeds. At very low wind speeds the collector, of course, gathers very little snow into the gauge, but these conditions are of lesser interest to avalanche forecasting. During a heavy snowstorm, sufficient snow collects in the gauge to swamp it if not melted. This can be countered to some extent by charging the gauge bucket with calcium chloride or other anti- freeze, but this is not adequate to melt all the snow if precipitation is heavy. An artificial supply of heat must be furnished - 6 - |