Characteristics of Observed Surface Pressure Waves (Gravity Waves) in the Contexts of Storm Structure and Reflectivity Features

We utilize two networks of high sensitivity and temporal resolution pressure sensors in the Toronto, ON, Canada, and New York, NY, areas to detect surface pressure signals which could be associated with gravity waves. The pressure sensors have 0.8-Pa precision and 1-Hz recording frequency. Time series of pressure data were collected and analyzed from 2020 to 2023. We use WSR-88D radar data to examine horizontal radar features, such as enhanced reflectivity or waves in Doppler velocity, when wave events occur in the pressure sensor time series. Wavelet analysis was used to objectively identify and extract the strongest wave signals in the pressure time traces within a wave period range from 1 minute to 120 minutes. Cross-correlations between the extracted wave signals from each pressure sensor were used to determine when a coherent signal could be tracked across multiple sensors and to estimate the time lag between wave passages at each pair of sensors. The wave phase velocities were then estimated using a least-squares fit from the estimated time lags. Wave events which were detected in at least 4 pressure sensors where the fitting error in the time lags was sufficiently small (RMSE below 90 s, and normalized RMSE below 0.1) were considered robust and trackable.

Twenty-seven robust and trackable pressure wave events were found between January 2020 and January 2023. Two-thirds of these wave events occurred between the months of December and March, and no events occurred between June and August. All but one of the wave events had an eastward component to its phase velocity, and most wave events had phase speeds between 15 and 35 m s^-1. Most trackable wave events had an amplitude above 1 hPa, and the strongest event amplitude found was 5.5 hPa. Several examples of surface front or outflow boundary passages resulted in trackable wave events, but most pressure sensor wave events were not associated with either fronts or outflows. Sixteen pressure wave events occurred during the cool season and with precipitation in the area. Pressure wave events were more common in the southwest and southeast quadrants of cyclones.