Interannual variability of thunderstorm days over the Tibetan Plateau: Synergistic effects of the Indian Ocean basin-wide mode modulation and CAPE forcing

This study investigates the interannual and decadal variability of dominant summer thunderstorm day anomaly modes over the Tibetan Plateau (TP) using observational data from 39 stations during 1979–2013, focusing on their linkages to TP thermodynamics and ocean–atmosphere interactions. Empirical orthogonal function and wavelet analyses reveal two primary spatiotemporal modes: The first mode exhibits a northeast–southwest meridionally inclining dipole pattern with widespread positive anomalies over the northeastern TP, showing significant interannual variability of 3–5 years and 8 years. The second mode presents a southwest–northeast zonally inclining dipole pattern with prominent positive anomalies over the southwestern TP, displaying 3-year and 5-year interannual oscillations. The TP exhibits significant interannual variability in thunderstorm days, with an evident amplification after 2000. Convective available potential energy (CAPE), as a key indicator of the lightning and severe thunderstorm environment, dominates the interannual variability of TP thunderstorm days. The Indian Ocean Basin-Wide mode (IOBW) modulates thunderstorm days by influencing the large-scale divergence–convergence dynamics and moisture environment. Specifically, the IOBW strengthens the Bay of Bengal anticyclone, enhancing moisture transport to the southeastern TP, and amplifies upper-tropospheric divergence. Combined with enhanced CAPE, these processes collectively lead to an increase in thunderstorm days. Multiple-variable regression analyses indicate that IOBW and CAPE collectively explain 52.1% of the interannual thunderstorm day variability. These findings advance the understanding of the mechanisms underlying TP interannual thunderstorm activity and provide crucial insights for improving regional climate projections. 本研究基于青藏高原39个台站1979–2013年雷暴日观测资料, 研究了夏季雷暴日数异常主模态的年际和年代际变化特征, 并探讨了其与高原热动力,大气环流和海气相互作用的关系.通过EOF分析和小波分析, 揭示青藏高原夏季雷暴日数时空变化存在两种主模态:第1主模态呈现以东北区域大范围正信号为主的东北-西南偏经向“+−”偶极子型, 具有3–5年和8年左右周期振荡的显著年际变化特征;第2主模态表现为以西南区域大范围正信号为主西南-东北偏纬向“+−”偶极子型, 显示出3年和5年周期振荡.高原雷暴日数存在显著年际变率特征并且年际变率在2000年之后显著增强.CAPE作为闪电和强雷暴环境的重要指标, 主导着青藏高原雷暴日的年际变化.热带印度洋海温海盆一致模 (IOBW) 通过影响大尺度辐合-辐散动力学和水汽环境来调节雷暴日年际变化.具体来说, IOBW 加强了孟加拉湾反气旋, 增强了向青藏高原东南部的水汽输送, 并扩大了上对流层辐散;这些过程与 CAPE 的增强相结合, 共同导致了雷暴日的增加.多元回归分析表明, IOBW和CAPE共同解释了52.1%的雷暴日数年际变率, 其中CAPE (标准化回归系数为0.68) 对雷暴日年际变率的作用相对大于IOBW (标准化回归系数0.31) .这些发现加深了人们对青藏高原年际雷暴活动机制的理解, 为改进区域气候预测提供了重要启示.