Modeling Frontal Low-Level Jets and Associated Extreme Wind Ramps

The growing global reliance on wind energy as a clean and renewable power source brings forth significant challenges in integrating large-scale wind power into existing energy grids. Among these challenges, extreme ramp events, which are rapid and substantial fluctuations in wind power generation, pose a critical issue. These events can severely disrupt grid stability, making accurate prediction and management essential for operational efficiency. This study focuses on the modeling of frontal low-level jets (FLLJs), atmospheric phenomena that significantly influence extreme wind power ramp-down events, particularly in offshore wind farms.

Using the Weather Research and Forecasting (WRF) model, we analyzed five extreme ramp-down events, selecting two for detailed examination and three for generalization. The analysis aimed to evaluate the sensitivity of different model configurations to FLLJ and extreme ramp characteristics, including initial and boundary condition (IC/BC) datasets (ERA5 and CERRA), wind farm parameterization (WFP), planetary boundary layer (PBL) schemes, and domain configuration (single versus nested).
Our findings reveal that the choice of IC/BC data, particularly the use of CERRA datasets, significantly improves the accuracy of ramp predictions and the representation of FLLJ characteristics. CERRA’s higher resolution provides a more detailed atmospheric flow depiction, resulting in better predictions of ramp timing, intensity, and jet features compared to ERA5. Additionally, the activation of WFP in the WRF model, which simulates the interaction between wind turbines and atmospheric flow, was shown to influence wind power output by generating wake effects, leading to a slight reduction in wind speeds around wind farms.
Further analysis showed that the PBL scheme choice significantly impacts FLLJ characteristics. The scale-aware Shin and Hong (SH) scheme generated a stronger and more pronounced jet core at higher altitudes, though with slightly reduced wind speeds below 200 meters, compared to the Mellor-Yamada-Nakanishi-Niino 2.5 (MYNN 2.5) scheme. This difference in wind speed profiles is critical, as it affects the accuracy of wind power generation forecasts during ramp events. The study also highlights that a single-domain configuration can effectively simulate wind power ramps with reduced computational costs. This configuration, while producing a higher core height and more diffused jet profile, was shown to be more efficient in capturing the timing and intensity of wind power ramps.