Precipitation Isotopes Associated with the Duration and Distance of Moisture Trajectory in a Westerly-Dominant Setting

Abstract

A Lagrangian diagnostic adjusted using specific humidity, with 6 h intervals along the trajectory and with lifting condensation level as cloud base height, was employed to identify the moisture source regions around the Tianshan Mountains, northwest China. Then, the relationship between precipitation stable isotopes and diagnosed duration–distance of moisture trajectory was analyzed. In this region, the median value of transport duration from moisture source to precipitation sampling site is approximately 3 days, and most moisture sources are closer than 1000 km. According to the Lagrangian diagnosed moisture sources, the higher precipitation summer months usually have rapid air mass movement, and remotely sourced moisture can be delivered to arid central Asia; in the dryer winter months, the moisture loading is weak, and longer transport duration and shorter source distances are observed. As trajectory duration increases, δ18O in sampled precipitation shows a positive trend, especially on the northern slope, and the short-duration events are usually significantly impacted by local recycled moisture with depleted isotopic signatures. The northern slope usually shows relatively shorter duration and longer distance, and more distant sources have more enriched isotopic values.

Seasonal Variations of Modern Precipitation Stable Isotopes over the North Tibetan Plateau and Their Influencing Factors

“…The average annual temperature remains below 0 • C, while the precipitation amount range from 115 to 440 mm, primarily concentrated from May to October. The Tianshan (TS) region stands as a "wet island" within the arid and semi-arid northwest China, receiving an average annual rainfall of over 400 mm due to westerly winds transporting moisture along the east-west Oriental mountain range [52,62]. The Muztagh (MZTG) site in the Pamir region of the northwestern TP and Qilianshan station (QLS) in the northeastern TP endure westerly winds throughout the year, featuring a cold climate with average wind speeds surpassing 4.5 m/s, however, MZTG experiences lower precipitation and relative humidity compared to Qilianshan (refer to Supplementary Materials Table S1) [51,63,64].…”

“…Research on the influence of moisture sources on precipitation isotopes in the TP areas has predominantly concentrated on the southern TP [35,48,49] and the northeastern and western TP [19,50]. However, there is also interest in the far north, such as the Tianshan Mountains [2,[51][52][53], with relatively few investigations on moisture sources in the north of the TP, where sub-cloud evaporation and continental recycling processes hold significance. Consequently, it is imperative to elucidate the impact of moisture sources, transport processes, and local environmental factors on precipitation to understand the mechanism governing regional precipitation isotopes.…”

Deuterium Excess in Precipitation Reveals Water Vapor Source in the Monsoon Margin Sites in Northwest China

“…Feng et al [29] showed a case study linking the isotopic variation to moisture sources, and found that there is a dominant effect of westerly moisture in summer and of a combined influence of westerly and polar air masses in winter. Wang et al [30,31] demonstrated that the rainfall in westerly-dominated northwest China is related to locally recycled moisture and the advected moisture via Europe and central Asia.…”