Evaluation of precipitation distribution at different altitude by the development of weight type precipitation gauge

2003 Fiscal Year Final Research Report Summary

• Project/Area Number: 14595005
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Single-year Grants
• Section: 一般
• Research Field: 水循環システム
• Research Institution: The University of Shiga Prefecture
• Principal Investigator: UENO Kenichi The University of Shiga Prefecture, Environmental Sciences, Lecturer, 環境科学部, 講師 (00260472)
• Co-Investigator(Kenkyū-buntansha): TANAKA Kenji Kumamoto University, Department of Engineer, 工学部, 助手 (30315288)
• Project Period (FY): 2002 – 2003
• Keywords: Precipitation / Weight type / Warm winter / Gauge / Snowfall / Shiga prefecture

Research Abstract

Small weight type precipitation gauge was developed trough three trial stages, to measure the winter precipitation at different altitude and to evaluate the water equivalent of snow Dover (WES) in case of temperature change in recent warm winters, At a first stage, "Trial gauge 1 (T1)" was developed to measure min and to understand the basic behavior of water level variability in the field. Transparent water tanks was used as a unique point to observe the behavior of antifreeze liquid Anti-evaporation oil and wind fence were important items to reduce the noise of water level. "Trial gauge 2 (T2)" was developed as an improved version of Ti equipped with a double wall for water tank with solar panel heating and automatic draining functions. Heat budget analysis of radiate cooling and melting of solid precipitation was done, and was verified by the experiment by using G2. The results showed that a 10W heater was enough to keep the water temperature at 0C and could be conducted only by a s olar panel with 24Wh battery in case of winter climate at Hikone. To test at colder air temperature with heavier snowfall condition, "Trial gauge 3 (T3)" was developed with fundamental reconstruction of body shape with a function of automatic supplement system of antifreeze, as a original model of "new small type weight type precipitation gauge". The T3 has a small orifice size as 5cm radiance to reduce the heating energy of antifreeze. Field campaign was conducted at Surumi observatory, northern Shiga prefecture, on January and February in 2004. The T3 was successfully measured snow and rain for two months with automatic heating and drain/supply system of antifreeze by self measurement of water level and water temperature. Hourly precipitation amount was consistent well with heating type rain gauge, except that two cases of continuous heavy snowfall and delay of melting snow on the standard gauge caud data discrepancy. One serious problem was found, such as that separated precipitation water on the antifreeze frozen in the tank due. to strong radiative cooling and caused snowcap at the next snowfall event. Separation of pressure sensor from the bottom of gauge is another issue to prevent pressure noise due to temperature change.
Unfortunately, precipitation observation at different altitude by using multiple T3 was not conducted because of the delay of gauge development and extra-ordinal warm winter in January 2004. On the other hand, seasonal change of WES was diagnosed by using simple experimental model with precipitation and temperature data measured at Surunii main and satellite station. The model was consisted with a discrimination function between solid and liquid precipitation and degree-hour wefcient to estimate melting rate as a function of temperature. Digital elevation map (DEM) was also constructed at 7m interval based on local topography map. The estimated WES well coincided with intra-seasonal variation of snow depth. In case of 2℃ temperature increase (decrease) caused anomalous increase (decrease) of WES at Surumi. Beside, temperature at satellite station, locating 200m higher than that at main station, was not always lower than that at the main station. A reason is speculated as development of inversion layer in the night due to snow cover in the small valley. Therefore, speculated WES was not increased as a function of elevation. To reveal the area averaged WES changes, we need to consider the temperature variation in the valley as well as difference of precipitation amount at different altitudes.