Wednesday, October 25, 2017

Birdbrained Meteorology

A recent study published in the International Journal of Biometeorology by Augusta Williams and Neil Laird (unfortunately paywalled, including from campus) uses data from the National Weather Service Radar on Promontory Point (KMTX) to examine the migration of eared grebes near the Great Salt Lake.

The backstory behind the paper is an interesting one.  Neil Laird is a professor at Hobart and William Smith College in western New York who studies lake-effect snowstorms.  He and a group of students were examining radar imagery from the Great Salt Lake when they started seeing some unusual patterns that were clearly non-meteorological and desired an explanation.  As illustrated by one event presented in the paper, these patterns feature an elongated reflectivity maximum that develops near the south shore of the Great Salt Lake and grows southward, covering the Tooele Valley and Rush Valley.  At times, there is a weaker but similar feature in the Skull Valley.  

Source: Williams and Laird (2017).
It turns out the odd pattern is produced by the migration of eared grebes, a waterfowl species that find a home on the Great Salt Lake during fall and early winter to feed on brine shrimp.  Estimates suggest there are 1 to 1.5 million of these grebes on the lake during this period.  

Augusta and Neil went through 15 winters of radar data, ultimately showing that there are an average of 19 radar-detected eared-grebe migrations each winter, although there is quite a bit of variability from year to year.  Migrations typically occur under clear skies and high pressure and become detectable by the radar 30–90 minutes after sunset.  Once leaving the Great Salt Lake, the grebes go to wintering habits in Mexico and southern California.  They show an example of one event where the grebes are detectable in multiple radars from northern Utah to Yuma, Arizona.

Source: Williams and Laird (2017)
My interest in the paper was especially high because we will have a Doppler on Wheels (DOW) radar here in November as part of the Outreach and Radar Education in Orography (OREO) field campaign.

The newly unveiled OREO logo
Thus, I'm looking for uses of the radar during periods of benign weather.  Birds are effective scatterers of radar signals.  For meteorologists, they are a contaminant, but ornithologists can use radars to study bird behavior.  I know nothing about the latter, but during periods of benign weather, bird "hunting" with the radar might be fun.  We could look for eared grebes, or maybe other waterfowl species.  If it flies in flocks, we will probably be able to see it.  An advantage of the DOW is that we will be able to scan just above lake level (the lowest tilt of the National Weather Service radar is 3000–5000 feet above the lake and nearby valley floors), perhaps enabling the initial detection of the migration.  Our ability to configure the DOW scanning pattern may also allow us to better target and track some of the flocks.  

I'll call this birdbrained meteorology.  Good work if you can get it.  


  1. The folks at Cornell are all over this issue. Check out their website.

  2. Wouldn't the TWDR also show the birds with higher fidelity since it is lower in elevation? I would also be interested to if radar signal post processing algorithms used to reduce ground clutter (such as birds) can be disabled for use-cases such as these? Would be great if the raw radar signal data was archived but I would expect that just the finished (post processed) imagery is.


    1. The TDWR is usable in for some areas, but suffers from severe blockage to the west by Antelope Island and the Oquirrh Mountains.

      Ground clutter is not suppressed in the DOW data, which is not processed like an operational radar feed. Even in an operational feedI don't think that birds would be removed by most clutter algorithms.