Bi‐Hourly Changes in Land‐Atmosphere Coupling Metrics and Convective Environments During GRAINEX

Abstract

Land use land cover change and irrigation plays an important role in modulating weather and climate. This research uses data from a field campaign, named, the Great Plains Irrigation Experiment (GRAINEX), conducted over southeastern Nebraska, and quantifies the impacts of irrigation on bi‐hourly evolution of the convective environment. The study used the Convective Triggering Potential (CTP) and Low‐Level Humidity Index (HI _low ), and the Lifting Condensation Level (LCL) Deficit for this purpose. The data were analyzed by Intensive Observation Period (IOP; IOP1 vs. IOP2), by cloud cover (clear vs. non‐clear days), and by both IOP and cloud cover. The study found that daytime evolution started with high CTP in the morning, lower CTP at midday, and higher CTP in the late afternoon and evening hours. During IOP2, regardless of time‐of‐day compared to non‐irrigated land use, CTP was higher over irrigated land use and it coincided with widespread irrigation. CTP was much higher during early morning (0700 LST), late afternoon (1700 LST) and early evenings (1900 LST). Irrigation's influence on CTP is even more apparent for all times during the clear days of IOP2. In addition, regardless of cloudy or non‐cloudy conditions, HI _low values over irrigated areas were lower at all hours during IOP2. Average LCL deficit declined for most hours over irrigated land use during IOP2. In combination with higher CTP, lower HI _low and a lower LCL deficit, it is clear that regardless of background conditions irrigation provides a favorable environment for convection development and precipitation.