基于高分辨率资料同化数据对青藏高原强对流天气的评估

Evaluation of Severe Convective Weather over the Tibetan Plateau Based on High-Resolution Assimilation Data

利用美国环境预报中心(NCEP)的Final Operational Global Analysis data-ds083.2资料生成WRF模式的初始场信息,用GrADS格式输出地面气象要素的彩色图像,分析了青藏高原发生对流时的环境特征和2015~2020年高原强对流的年代变化特征,得到以下结论:1) 青藏高原东北部青海湖附近湟水河谷地和祁连地区2016年8月17~18日发生极端天气事件,从南海输送而来的暖湿气流与南下的冷空气交汇诱发了此次强对流天气。17日下午14时温度开始升高,湿度增大,气压异常。夜间19时~22时发生冰雹,受灾中心区域向下长波辐射通量380~400W m−2,平均风速超过5 m/s,风向为东南风。18日07时~08时部分地区发生短时强降水,水汽在青海湖东南部积聚,随后影响其周边地区,最大站点雨量超过50 mm。2) 2015~2020年青藏高原强对流年代变化特征为2015、2017、2018和2019年温度和湿度条件更好,向下长波辐射通量数值也更大,反应了对流强度和频率较高,而2016和2020年则强度较低。青藏高原强对流的月变化特征与东亚季风的活动密切相关。5月份高原的对流活动受西风带影响较大,水汽开始在高原东南部汇聚;6月份随着亚洲夏季风的爆发,西南季风的加强,对流开始活跃起来,最强的对流仍集中在高原东南侧;7、8月份是高原对流活动最旺盛的时期,孟加拉湾和南海等地气旋活动也达到高潮,强劲的西南季风引导水汽从高原南麓缺口爬坡,逐渐影响中部和东北部,形成多个强对流带和强对流活动中心;随后对流能量向高原西北部频散,对流活动逐渐减弱。

The initial field information of the WRF model is generated by using the Final Operational Global Analysis data-ds083.2 data of the US Environmental Forecasting Center (NCEP), and the color images of ground meteorological elements were output in GrADS format, and the environmental characteristics of convection occurred on the Qinghai-Tibet Plateau and the chronological char-acteristics of strong convection on the plateau from 2015 to 2020 were analyzed, and the following conclusions were obtained: 1) Extreme weather events occurred in the Huangshui River Valley and Qilian area near Qinghai Lake in the northeast of the Qinghai Plateau on August 17~18, 2016, and the warm and humid air flow from the South China Sea and the cold air from the south induced this strong convective weather. At 14:00 on the afternoon of the 17th, the temperature began to rise, the humidity increased, and the air pressure was abnormal. Hail oc-curred at night from 19:00 to 22:00, and the downward long-wave radiation flux in the affected central area was 380~400 W m−2, the average wind speed exceeded 5 m/s, and the wind direction was southeasterly. From 07:00 to 08:00 on the 18th, short-term heavy precipitation occurred in some areas, and water vapor accumulated in the southeast of Qinghai Lake, which subsequently affected its surrounding areas, and the maximum station rainfall exceeded 50 mm. 2) The strong convective chronology of the Qinghai-Tibet Plateau from 2015 to 2020 is characterized by better temperature and humidity conditions in 2015, 2017, 2018 and 2019, and the downward long-wave radiation flux values are also larger, reflecting the higher convection intensity and frequency, while the intensity in 2016 and 2020 is lower. The lunar variation characteristics of strong convection on the Tibetan Plateau are closely related to the activity of the East Asian monsoon. In May, the convective activity of the plateau was greatly affected by the westerly wind belt, and water vapor began to converge in the southeast of the plateau;in June, with the outbreak of the Asian summer wind, the southwest monsoon strengthened, convection began to be active, and the strongest convection was still concentrated in the southeast side of the plateau;July and August were the most vigorous periods of convective activity in the plateau, and cyclonic activity in the Bay of Bengal and the South China Sea also reached a climax, and the strong southwest monsoon guided the water vapor to climb from the gap in the southern foothills of the plateau, gradually affecting the central and northeastern regions, forming a number of strong convective zones and strong convective activity centers. Convective energy is then dispersed to the northwest of the plateau, and convective activity gradually weakens.