Vertical characteristics of temperature and relative humidity during the spring continuous warming processes in Altay, Xinjiang of China

Abstract

To understand the triggering conditions of snowmelt floods in northern Xinjiang, China, the diurnal evolution and altitude dependence characteristics of spring temperature and relative humidity (RH) are investigated, particularly placing emphasis on continuous warming process, mainly based on the data collected from the densely sounding experiment at Altay Station in spring 2021. The results show that the mean maximum and minimum temperature respectively occur at nightfall and sunrise, the mean RH below 2,000 m is the highest at sunrise and the lowest at nightfall, and the mean RH above 5,000 m is the highest at sunrise and the lowest at midday. The mean RH value climbs up first but goes down later, and the largest mean RH is within the height range of 2,500–5,000 m. The radiation inversion with the depth of 660 m tends to occur frequently at midnight and around sunrise, and it does not exist when the continuous warming process sets out but gradually develops with the advancing process. During the continuous warming processes, there exists an unsynchronized warming from the ground to the upper air. The upper-air warming lags behind that on the ground for 2–5 d, and then it continues the trend. Below 2,000 m, accompany with the advance of the warming processes, the RH keeps at relatively low level and changes small along height after the first 2–3 days, when the max RH drop swiftly from 80%–98% to less than 25% and tend to be consistent at the four observation times. The trough and ridge systems responsible for the continuous warming processes in early and middle spring are mainly the deep long-wave system, but in the middle and late spring, the adjustment speed of the trough and ridge systems are accelerated and more short-wave activities fuel the continuous warming.