An Automatic Detector for Observing Bay Breezes in the Atmosphere of Baltimore, Maryland via Doppler LiDAR Remote Sensing

Bay breezes are a type of sea breeze that occur over bays and they play a crucial role in shaping local weather patterns in coastal regions. This phenomenon occurs when there is a difference in the temperature of the atmosphere above an ocean and land causing a pressure gradient force (PGF) from the water to the land near the surface (Stull 1988). Bay breezes impact the temperature, formation of clouds, and the distribution of aerosols in an area, ultimately impacting the heat stress and air quality of inhabitants. We used wind direction, wind speed, and aerosol backscatter data from a Doppler LiDAR deployed in Baltimore, Maryland. When bay breezes occur in this area, the wind generally shifts from northwesterly to southeasterly. The goal of this study was to create an automated bay breeze detector that would accurately identify bay breeze days. In order to be classified as a bay breeze day, we tested for three conditions: 1) both offshore and onshore wind directions within the day, 2) wind shift of at least 45 degrees within an hour, and 3) wind shift occurring during the late afternoon. We studied 161 days (November 2023 - May 2024), and found bay breezes on 11 of those days based on the given criteria, accounting for 6.83% of the days. We suspect nine false negatives occurred based on the Doppler lidar wind data; however, accurately verifying bay breeze days generally requires additional data such as routine observations of relative humidity, which were not present at the lidar location. The eventual goal is to be able to study temporal variability in bay breeze occurrence with implications for human health.