Interannual variation of precipitation over the Hengduan Mountains during rainy season

Abstract

The present study investigates the interannual variability of precipitation over the Hengduan Mountains (HMs) during rainy season based on daily precipitation dataset of 151 meteorological stations. More HMs precipitation is associated with an anomalous lower level cyclonic circulation over the northern South China Sea (SCS) and the upper level Silk Road pattern (SRP)‐like geopotential height anomalies. Along the north flank of the anomalous cyclonic circulation, easterly wind anomalies weaken climatology winds and prevent further movement of southwest moisture transport, leading to the enhancement of moisture convergence over HMs. Diagnosis shows that anomalous vertical motions are owing to the advection of anomalous temperature by basic zonal winds. The anomalous lower level cyclonic circulation over the northern SCS is related to La Niña‐like sea surface cooling in the equatorial central and eastern Pacific. This cooling adjusts the Walker Circulation, causing positive precipitation anomalies near the SCS, which trigger the anomalous cyclonic circulation as a warm Rossby wave response. The distribution of upper level geopotential height anomalies over the mid‐latitude Asian land resembles the SRP. Due to its barotropic structure, the SRP leads to warm and cold anomalies over the central Asia and the central China, respectively. The advection of anomalous temperature gradient by mean westerlies leads to anomalous ascending motions and more precipitation over HMs.

Interdecadal Variation of Precipitation over the Hengduan Mountains during Rainy Seasons

“…1b. Dong et al (2018), the rainy seasons in the HM are defined from May to September, when the climatological monthly mean precipitation is above the annual mean over this region (Fig. 1b).…”

“…The Hengduan Mountains (HM) lie on the southeast side of the Tibetan Plateau (TP) and west side of Sichuan basin, with the YunGui plateau and Bayan Har Mountains on the south and north sides, respectively (Li et al 2011;K. Zhang et al 2014;Fang et al 2017;Dai et al 2018;Dong et al 2018). Spanning an area of 500 000 km 2 , the HM feature the world's steepest elevation drop from about 4800 to 600 m, within a distance of 500 km from the TP to the Sichuan basin ( Fig.…”

“…The HM possess a monsoon climate with prevailing lower-level southwest winds, connecting the South Asian and East Asian summer monsoons ( Fig. 7b of Dong et al 2018), which contribute to the complex and changeable climate in this area (Zhu et al 2013;P. Zhang et al 2014).…”

“…Zhu et al (2016) indicated that the drought in the HM is mainly due to the unstable rainfall time of the South Asian monsoon. Recently, Dong et al (2018) found that the interannual variability of precipitation over the HM during rainy seasons is influenced by the combined effect of central and eastern Pacific SST anomalies and the Silk Road pattern (SRP; Lu et al 2002;Enomoto et al 2003;Kosaka et al 2009;Hong and Lu 2016;Gong et al 2018). These two factors reflect the different aspects of large-scale circulation anomalies affecting HM precipitation.…”

Analysis of Landscape Patterns of Arid Valleys in China, Based on Grain Size Effect

“…There is a distinct division between the dry and wet seasons; wet season normally occurs from May to October, with precipitation accounting for 75 to 90% of the annual total [40]. Dry season occurs from October to April; precipitation during this period is under 30 mm in most of the meteorological stations in the Hengduan Mountains [41]. Arid valleys are unique natural landscapes of the Hengduan Mountains region in southwestern China.…”