Hydraulic responses of groundwater-level in deep wells to the passage of a squall line: A case study from North China

Squall lines occur with a high frequency in North China, but it is still unclear that how
this kind of meso-scale severe weather disturbs the groundwater levels in deep wells. Inasmuch as the current situation, a targeted research is needed in order to uncover the features of hydraulic responses. On 21 September 2017, a squall line passed across the central North China, and significantly disturbed the groundwater levels in four wells deeper than 1 km for Wuji, Xinji, Yongqing, Ningjin. Here we mainly adopt the spectrogram and linear regression methods to systematically examine the unique signals excited by this squall line. The results show that: ① From a macro perspective, the barometric pressures recorded at the deep wells can abruptly jump induced by the passage of squall line; instantly, the strong pulse-like disturbances were observed on groundwater graphs associated with pressure jumps; ② The duration of disturbance could last as long as about 127 minutes for this case; ③ In the high-frequency band, the barometric waves induced by squall line have a period between 15 and 25 cpd (cycles per day). Correspondingly, the cross-correlation coefficients of barometric waves to groundwater changes can be lower than -0.95 for the four deep wells in this special frequency band. Furthermore, the barometric pressure response coefficients vary from about -4.9 to -6.9 mm/hPa for the four wells, determined as the linear regression coefficient between groundwater level and barometric pressure data band-passed to the 15-25 cpd band. Our analysis shows that this work can extend our understating of the signatures which caused by squall line in the field of groundwater research. Additionally, owing to the large amplitude of barometric waves, the squall line can help quantifying the precise responses of groundwater levels in deep wells to barometric pressures in the high frequency band.