Improving Model Predictions of Rotor Plane Wind Speeds during Summertime Sea Breeze and LLJ Events

As development and growth of offshore wind energy continues in the region of the New York Bight (NYB; defined as the region of offshore waters south of Long Island and east of New Jersey), understanding mesoscale circulations such as the sea breeze and often accompanying low-level jet (LLJ) has become increasingly important. Offshore wind turbines continue to increase in size, and with heights extending up to 260 m above mean sea level (AMSL) there is a need for long term atmospheric measurements within the rotor plane. Aside from a temporary deployment by NYSERDA of two floating LiDAR buoys (measuring 20 – 200 m AMSL), located at Hudson South and Hudson North, and data collected from LiDAR buoys deployed by Atlantic Shores (measuring 10 – 250 m AMSL) and other offshore wind developers, the only long term wind profiles available (>5 years) are located onshore along Long Island and within NYC at New York State Mesonet (NYSM) profiler sites. Without long term hub height measurements at proposed locations for offshore wind farms, it is necessary to rely on models to fully understand the wind field.

The NYB sea breeze will play a key role in offshore wind energy in the northeastern US. The sea breeze is common in the late spring and summer months during periods of high power demand (i.e. afternoon hours) and is often accompanied by a low-level jet (LLJ). This LLJ features a wind speed maximum between 150 – 300 m AMSL, thus increasing gross capacity factors. Limited measurements of the wind profile offshore make it difficult to accurately forecast and understand the extent (both vertically and horizontally) of the sea breeze and LLJ. While models can provide a three-dimensional picture of the sea breeze circulation and extent of the LLJ, at this point, their performance in reproducing these features is underwhelming.

Using the Weather Research and Forecasting Model (WRF; Skamarock et al. 2021), the goal of this study is to perform sensitivity analysis to determine the best WRF model configuration to represent the dynamics of the New York Bight (NYB) sea breeze and LLJ. We vary planetary boundary layer (PBL) schemes, vertical levels, and land surface parameterizations to determine the effect (if any) on model performance and accuracy. The results of this sensitivity analysis will help to determine the driving forces behind LLJ development during a sea breeze by considering SST gradients, atmospheric stability, and pressure gradients.

Figure 1. Comparison of LiDAR observations to model predictions during a sea breeze and LLJ event at 2300 UTC (7 PM Local Time) on 9 June 2020. Results from one model run (using Yonsei University PBL scheme and Noah surface layer physics) at four sites, including New York State Mesonet sites Wantagh and East Hampton, and NYSERDA deployed floating LiDARs at sites Hudson North and South. The white shaded regions represent Bureau of Ocean Energy management Wind Energy Areas (BOEM WEAs).

Skamarock, W. C., & Coauthors, 2021: A Description of the Advanced Research WRF Model Version 4.3 (No. NCAR/TN-556+STR), doi:10.5065/1dfh-6p97