青藏高原东南部色季拉山地区夏季小时降水特征分析

Characteristics of summertime hourly precipitation over the Sygera Mountains on the southeastern Tibetan Plateau

摘要

青藏高原东南部的色季拉山是雅鲁藏布大峡谷水汽通道西北侧的重要地形屏障，该地区夏季降水频率远高于周边山脉。因此，开展对色季拉山夏季小时降水事件特征的研究，对揭示雅鲁藏布大峡谷水汽通道影响下复杂地形区的降水精细化分布规律、提升该地区气象次生灾害的预报预警能力具有重要意义。利用 2016—2021 年 6—8 月青藏高原东南部色季拉山 9 个气象观测站小时降水资料，以及 ERA5 和 ERA5-Land 逐小时再分析资料，分析了色季拉山夏季小时降水和小时强降水事件的时空分布特征，对比了不同海拔高度和山谷走向影响下小时降水空间分布特征，并揭示了地形对小时降水特征的影响。结果表明：(1) 色季拉山夏季以持续时间为 1~3 h 的短历时降水事件最为频发，降水主要发生在夜间和午后，降水量在 03 时 (当地时，下同) 达到峰值，午后至傍晚为另一个高值时段。(2) 小时强降水时次对总降水量的贡献率达 52.6%，且以持续时间超过 6 h 的长历时降水事件为主，具有降水强度强、持续时间长、发生频率低的特征。小时强降水事件同样主要发生在午后到傍晚时段，夜间次之，其降水量在午后和夜间相当。(3) 受海拔高度和山谷走向的影响，色季拉山夏季不同区域的小时降水事件存在显著空间差异。山顶站的降水量、频率和强度均高于山谷站；准南北向山谷以高频、长历时事件为主，准东西向山谷则以低频、高强度的事件为主。对于小时强降水事件，准东西向山谷以高强度、低频事件为主，准南北向山谷则以低强度、高频、长历时事件为主。(4) 色季拉山地区夏季降水空间分布受地形热力与动力作用的协同影响，二者在准南北向山谷造成的降水量均高于准东西向山谷，地面饱和比湿和经向风的日变化主导了两种山谷站降水的日变化特征。

Abstract

Located on the southeastern margin of the Tibetan Plateau (TP), the Sygera Mountains represent a key topographic barrier on the northwestern flank of the water vapor channel of the Yarlung Zangbo Grand Canyon, where summer precipitation frequency is significantly higher than that in the surrounding mountainous areas. Therefore, investigating the characteristics of summertime hourly precipitation events over the Sygera Mountains is of great significance for revealing the fine-scale precipitation distribution patterns over complex terrain influenced by the water vapor channel of the Yarlung Zangbo Grand Canyon, and for improving the forecasting and early warning capabilities for meteorological secondary disasters in this region. Using hourly precipitation data from 9 meteorological stations in the Sygera Mountains and hourly ERA5 and ERA5-Land reanalysis data during June–August from 2016 to 2021, this study analyzes the spatiotemporal distribution characteristics of summer hourly precipitation events and hourly heavy precipitation events, compares the spatial distribution of hourly precipitation under the influence of altitude and valley orientation, and reveals the topographic effects on hourly precipitation characteristics. The results are as follows. (1) In summer, short-duration precipitation events lasting 1–3 h are the most frequent over the Sygera Mountains. Precipitation mainly occurs at night and in the afternoon, with a peak at 03:00 (local time, i.e., Beijing Time minus 2 h; hereinafter the same) and another high-value period from afternoon to evening, during which relatively higher values appear around 14:00 and 18:00. (2) Hourly heavy precipitation events contribute 52.6% of the total summer precipitation and are dominated by long-duration events exceeding 6 h, characterized by high intensity, long duration, and low frequency. These heavy events also mainly occur from afternoon to evening, with a secondary peak in the early morning, and their precipitation amounts are comparable between afternoon and early morning, differing from the diurnal variation characteristics of hourly precipitation events. (3) Influenced by altitude and valley orientation, significant spatial differences exist in summer hourly precipitation events across different regions of the Sygera Mountains. The precipitation amount, frequency, and intensity at the summit station are higher than those at valley stations. The quasi-north-south oriented valley is dominated by high-frequency, long-duration events, whereas the quasi-east–west oriented valley features lower-frequency events with slightly higher intensity. For hourly heavy precipitation events, valley stations exhibit longer durations than the summit station. The quasi-east–west oriented valley is characterized by high-intensity, low-frequency events, while the quasi-north–south oriented valley is dominated by low-intensity, high-frequency, and long-duration events. (4) The summer precipitation distribution over the Sygera Mountains is jointly influenced by the thermal and dynamic effects of topography, with both effects producing higher precipitation amounts in the quasi-north–south oriented valley than in the quasi-east–west oriented valley. The diurnal variations of surface saturated specific humidity and meridional wind dominate the diurnal variation characteristics of precipitation at stations in both valley orientations.

关键词

青藏高原 / 色季拉山 / 夏季 / 小时降水

Key words

Tibetan Plateau / Sygera Mountains / summer / hourly precipitation

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基金资助

国家自然科学基金项目(42030611)

国家重点研发计划项目(2023YFC3007502)

西藏自治区重大科技专项(XZ202402ZD0006-06)