Precipitation characteristics in a mountainous region of the Tuul river basin, Mongolia

The Tuul river basin, Mongolia, is located in the southern limit of seasonal snow cover area. The diurnal variation and altitude dependence of precipitation have been analyzed using ground-based precipitation gauges installed in the basin and the weather radar near the Ulaanbaatar airport covered the basin. The following conclusions were derived from the results and discussion. (1) The main pronounced phase of diurnal variations in the Tuul river basin is found to be around noon in June and around evening in September. The main phase of diurnal variation of the highest altitude gauge appears earlier than that of other gauges. These features were associated with the local circulation. In addition, precipitation intensity is weaker at night due to the soil conditions. (2) Although hourly ground-based precipitation does not depend on altitude, total ground-based precipitation depends on altitude. Because, even thought the precipitation intensity of high altitudes equals to that of low altitudes, the precipitation duration of high altitudes is longer. (3) Systematic error of wind-induced loss for half-hourly ground-based precipitation was corrected. Wind-induced loss increases monthly measured precipitation by about 10 %. The bias correction is not influential in seasonal changes of precipitation. (4) Radar precipitation using the Z-R relationship was corrected, and correction increases radar precipitation using the Z-R relationship by 3 times. (5) The radar at 5 km AGL does not detect winter precipitation well due to less precipitation and the precipitation activity below 5 km AGL. (6) Corrected radar precipitation increases with altitude in summer. On the other hand, an opposite negative dependence is found from spring to summer and from summer to autumn. Seasonal changes of the altitude dependence were confirmed. These features were also associated with the convective activity.