The Mostly Failed Invasion of the South Shore of the St-Lawrence River by Spruce Budworm Moths on 15-16 July 2013, its Monitoring by Weather Radars, and Lessons Learned Relevant to Weather Surveillance

Every two decades, the spruce budworm population undergoes a resurgence, destroying spruces in eastern Canada and northeastern United States, and the next resurgence is overdue. To help fight this battle, the Canadian Forest Service wants to use weather radars to know where the moths of the budworms disperse to know where to preventively intervene to control their population. To that end, we developed data processing approaches to be able to better monitor insect dispersion, and evaluated them on an event where moth dispersion was particularly strong. That event saw a massive influx of budworms moving from the north shore of the estuary of the Saint-Lawrence towards the south thwarted by a sudden wind shift that brought most of those moths in the estuary or back to the north shore, saving the vulnerable south shore of Saint Lawrence and Maine from the largest dispersion in years.

More relevant to this conference than this story is actually what allowed us to be able to tell it, namely 1) what processing was done to the radar data to vividly illustrate what happened, and 2) what made the raw observations from the Canadian radar in many ways superior to that of the more sensitive WSR-88D to the south. In particular, the Canadian radar was able to observe these low flying moths over twice the area that the WSR88D could thanks to its high-perched location and its use of negative elevation angles, allowing it to detect phenomena in the boundary layer over a much broader area regardless of the radar’s weaker sensitivity. Despite the enhanced clutter that this radar experiences, we were also able to considerably clean the images by using a combination of satellite imagery, data at multiple elevation angles, and both less-sensitive clutter-filtered and more-sensitive unfiltered scans. Given the interest of the meteorological community in threatening low-level phenomena, the experience we gathered suggest that we may want to reconsider our tendency to avoid putting radar on elevated terrain and scanning at negative angles.