Abstract:

To minimize the impact of windy weather on the construction of hydropower stations and power transmission in the lower reaches of the Jinsha River, this study aims to explore the relationship between wind speed variations and barometric pressure parameters in the canyon area, and to find effective indicators about early warning of windy weather through in-depth analysis of frequent windy events in the dry season. Numerical forecasting is limited in canyon areas due to the difficulty of wind speed forecasting, thus ground-based observations are particularly important, especially for barometric pressure variations. This paper takes the north-south longitudinal canyon at the junction of Sichuan and Yunnan in the lower reaches of the Jinsha River as the research object, and uses the data from the self-built observatory in the canyon area, combining with the empirical forecasts from the hydropower station dam area, to study the relationship between wind speed and barometric pressure related parameters in the canyon area during the gale events. The results show that, before the occurrence of gale, the barometric pressure at the station usually decreases significantly, and after the decrease exceeds 7.7 hPa and lasts for 3-6 hours, the possibility of wind speed increasing increases; if wind speed increases steadily for 1-6 hours, the wind can reach the level 7 gale. The pressure variation values of the stations are very important for wind speed warning, especially the 3-hour pressure change values. When the 3-hour negative pressure change value exceeds 2.0 hPa, the surface wind speed starts to increase. The Granger causality test method reveals that there is an obvious lag in the wind speed change in the upstream and downstream of the canyon, for example, Hulukou Bridge Station usually experiences gale 1-2 hours before the downstream. The difference in barometric pressure can be used as an important early warning indicator of gales, and when the difference in barometric pressure between Huangtian and Hulukou Bridge Station reaches 18.1 hPa, the possibility of gales increases significantly.

Key words: gale forecast, pressure variation, north-south canyon, Granger causality algorithm, Jinsha River

摘要：

为减少大风天气对金沙江下游水电站建设和电力输送的影响，通过分析干季频繁发生的大风事件，探索峡谷区风速变化与气压相关参数之间的关系，寻找预警大风的有效指标。该地区因风速预报难度大，数值预报在峡谷区受到限制，因而地面观测尤为重要，尤其是气压变化。本文以金沙江下游四川和云南交界的南北纵向峡谷为研究区，利用峡谷区自建观测站数据，结合水电站坝区的经验预报，研究峡谷区大风事件中风速与气压相关参数的关系。结果表明，大风发生前，站点气压通常明显下降，下降值超过7.7 hPa并持续3~6 h后，风速增加的可能性增大；若风速稳定升高持续1~6 h，能达到7级大风。测站的变压值对风速预警极为重要，尤其是3 h变压，当3 h负变压超过2.0 hPa时，地面风速开始增加。通过格兰杰因果关系检验方法发现，峡谷上下游风速变化存在明显滞后性，葫芦口大桥站通常先于下游1~2 h出现大风。气压差可作为重要大风预警指标，当荒田与葫芦口大桥站气压差达18.1 hPa时，大风发生的可能性明显增大。

关键词: 大风预报, 气压变化, 纵向峡谷, 格兰杰算法, 金沙江