COOL RADAR STUFF: What Is Ducting?

Interesting radar images thanks to humidity.....


NEXRAD weather radar is one of the most important tools in a meteorologist's arsenal This tool of course allows us to survey storms and even the smoke plumes from wildfires. Every now and then radar can create some pretty interesting artifacts or anomalies. Some of these anomalies are caused by software while others are from what the radar thinks it's trying to see.


The most common anomaly that we see all the time is the giant "radar ring/blob" or what is commonly referred to as ground clutter. Ground clutter shows up best near the radar site since the radar beam's trajectory takes it from close to the surface at the physical radar site to higher elevations moving away from the radar site. This entail creates the ring or blob especially before sunrise and after sunset. 

The other two common anomalies that we see when it comes to radar are "Ducting" and "Superrefraction". These two terms represent how the radar beam essentially computes an image over a curved surface.

In the case of "Ducting" the radar beam bends so much that it hits the surface, causing extremely high dBZ returns (The colors you see on radar that represent precipitation). The reason that the beam creates the high returns is because the ground below is way thicker than the average rain drop that the beam usually slices through. 

A good example of this actually occurred this Monday morning (August 6, 2018) in our area. Increased humidity allows for a weighted atmosphere which of course helps create ducting. As a result the radar beam was hitting the surface throughout Central Maryland and even on the Eastern Shore creating very high dBz returns which to the untrained eye would look like thunderstorms. Instead of thunderstorms the radar was tricking us with high anomalous propagation which is a real problem this time of year when things get super muggy. 


Superrefraction on the other hand is the complete opposite. This is when the beam bends low to the ground but instead of running into the ground it goes beyond it's range. Since the beam is close to the ground it keeps running into multiple insects, dust particles, and other pollutants as it moves further and further away from the radar. The farther the beam goes of course the worse superrefraction will be causing the clutter area to grow. This process usually occurs under darkness and decreases as the morning rolls on. 

Either way the beam travels with respect to the Earth's curvature as is determined by a complex equation that can vary greatly over small distances. With that said happy hunting on multiple types of refraction that are likely to occur at the same time. 

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