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

Shengjie Wang,Liwei Wang,Mengyu Shi,Mingxia Du,Rong Jiao,Mingjun Zhang

doi:10.3390/w11122434

Shengjie Wang, Liwei Wang + Show 4 more

Open Access

https://doi.org/10.3390/w11122434

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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.

Highlights

The Tianshan Mountains are the main mountain range in arid northwest China
The stable isotope technique has been widely applied to modern precipitation to diagnose the moisture source in northwest China on a larger spatial scale [4,5,6]
A compiled database of the Tianshan Mountains [9] was revisited, as we focused on how moisture transports to the study region along the trajectory, and the duration and distance of moisture trajectory in the westerly-dominant setting is discussed

Summary

Introduction

The Tianshan Mountains are the main mountain range in arid northwest China. The variability in precipitation and water vapor provenances is currently under debate [1,2,3]. As reviewed in Zhang and Wang [13], precipitation isotopes have been observed at about 40 sites with different natural zones across the Tianshan Mountains Based on these in situ observations, the influencing regimes of below-cloud evaporation [8,14] and local moisture recycling [15,16] on stable hydrogen and oxygen isotopes in precipitation have been investigated in this arid setting. Specific humidity is used to identify a specific location where the local moisture greatly contributes, that is, the site where the specific humidity significantly increases along the backward trajectory is considered to be the most likely moisture source [21] This method is helpful to determine a suitable backward path duration for a specific climate setting [21,22,23,24]. A compiled database of the Tianshan Mountains [9] was revisited, as we focused on how moisture transports to the study region along the trajectory, and the duration and distance of moisture trajectory in the westerly-dominant setting is discussed

Data and Method

Lagrangian Diagnosed Moisture Sources

Relationship between Precipitation Isotope and Moisture Source

Conclusions