Fine-scale Characteristics of Severe Convective Cold Pools During the Warm Season in South China Based on Meteorological Gradient Tower Observations

Cold pools play a crucial role in the evolution of convective systems. However, due to the lack of observations, studies on the vertical fine-scale observational features of cold pools in South China remain scarce. Based on 1-min meteorological observations of Shenzhen Shiyan Meteorological Gradient Tower and 2-m temperature and precipitation data from the adjacent Shenzhen National Climate Observatory during the warm season (1 April to 30 September) from 2017 to 2025, cold pool events are objectively identified as episodes with 2-m temperature drop of no more than -2 ℃ within 20 min accompanied by precipitation. After excluding the impacts of cold fronts and typhoons, 284 cold pool events are selected to systematically analyze their characteristics, vertical structure, depth, and influencing factors.Cold pools mainly occur from June to September, with the highest frequency in July, averaging 8.9 events. These events mainly take place between 1100 BT and 1400 BT, while the occurrence frequency remains remarkably low at night. During the passage of cold pools, peak times of perturbations in temperature, pressure, specific humidity, equivalent potential temperature, horizontal wind speed, and vertical wind speed generally advance with increasing height. Evolution rates of these variables are significantly faster from April to June than those from July to September, and the perturbation intensity of all variables except temperature is greater in April-June.Intensities of temperature and pressure perturbation decrease with height. In contrast, intensities of specific humidity perturbation and equivalent potential temperature perturbation increase with height, indicating the intrusion of dry and cold air in the middle troposphere. Intensities of horizontal and vertical wind speed perturbation also increase with height: The horizontal wind speed perturbation tends to stabilize above 80 m, whereas the vertical wind speed perturbation at 160 m and 320 m is significantly stronger than that near the surface, suggesting enhanced upward lifting within 160-320-m layer. Based on the hydrostatic equilibrium relationship, the depth of cold pool is estimated from the vertical gradient of pressure perturbation intensity. Cold pool depth mostly ranges from 100 m to 1200 m, with a median value of 595 m, and there is little difference between April-June and July-September. Under similar evaporation potential conditions, the intensity of cold pools shows a significant positive correlation with the equivalent potential temperature perturbation, with a maximum correlation coefficient of 0.88. It demonstrates that the entrainment of dry and cold air in the middle troposphere plays a crucial role in the development and maintenance of cold pools in South China.