However, most of the remaining return is from birds flying north, so the velocity data indicates motion toward the north, except for the showers and outflow boundaries to the north that are moving southeast, consistent with prevailing mid-level winds.
In the below example from Topeka, KS, the prevailing winds are from the west or northwest, consistent with the direction the rain showers are moving. One key thing that can distinguish migrating birds from insects is that the radar velocity may be different from the prevailing wind. In general, the pattern is similar to the “bloom” pattern above, in that reflectivity ramps up shortly after sunset in a large circle or ring surrounding the radar. Reflectivity loop showing a rapid increase of reflectivity after sunset commonly referred to as “bloom.” This likely contains both insects and migrating birds.ĭid you know that some researchers use radar to study the migration patterns of some bird species? It’s true, here are some links: The increase in size covered by these echoes from daytime to nighttime is mostly related to changes in the vertical temperature and moisture profile that cause the radar beam to stay closer to the ground at night (more about this in part 3 of this series). Bloom may also be enhanced by migratory birds in the spring and fall, as several migratory species fly at night. Reflectivity loop showing multiple bat colonies leaving their roosts near sunsetĮver notice that green blob that pops up around virtually every radar in the spring and summer about the time the sun goes down? This imagery is commonly referred to as “bloom” and is mostly due to radar return from all the insects that are flying around in the evening. The best way to tell if it is birds or bats is the time of day (birds will be seen near sunrise and bats near sunset). The radar signature of bats and birds taking off in large numbers from a roosting area are very similar (expanding ring of reflectivity, high differential reflectivity, low correlation coefficient) to each other. However, because bats are nocturnal, they take off around sunset. Reflectivity loop showing several flocks of birds taking off near sunrise (circled areas)īats also sleep in large numbers in a single spot, usually in a cave, then take off all at once to find food. Common dual-polarization signatures of birds are high differential reflectivity and low correlation coefficient. This motion frequently shows up as an expanding ring of reflectivity for a few scans around sunrise.
Part 2 - Biological Scatter Birds in the MorningĬertain types of birds (purple martins are one of the most common) spend the night roosting in large flocks, and then they all take off in the morning to search for food. The following can help identify what kind of creatures are responsible for specific common patterns of biological echoes in radar data at certain times of the day or year. These types of echoes generally have low a correlation coefficient and high differential reflectivity. Dual-polarization data is usually the best way to distinguish biological echoes from precipitation, especially in a static image.
#TOPEKA RADAR IN MOTION SERIES#
In this second part of the series looking at common non-precipitation radar echoes, we will look at several examples of biological scatter, including birds, bats, and insects.
0 kommentar(er)
