DISCUSSION: When observing the radar at night, large circles of reflectivity usually surround the radar scan area. It is likely that this reflected feedback from the radar is ground clutter, although in other cases you might see something else. When there isn’t any active weather within a radar coverage area, the local radar is set to a slower antenna rotation which causes the radar to have a finer resolution and heightened sensitivity. This setting is called “clear air mode”. During this mode of operation, the radar will pick up reflected ground clutter from mountains, buildings and tall objects as well as clear air echoes such as dust particles, light drizzle, air mass boundaries and fronts. Clear air mode is also used by scientists to pick up on certain echoes that many wouldn’t think of being a possibility. These specific clear air echoes are birds and insects. This has been beneficial to scientists who have used clear air mode to study bird and insect migrations for years.
When the radar is in clear air mode, it has an advantage of picking up on small objects such as insects and birds. This is because of its increased sensitivity and resolution. When birds or insects cluster together in larger groups, they become increasingly visible by the radar. The more birds and insects in one area, a higher reflectivity is shown in the radar image. Scientists can determine the difference between bird and insect reflectivity in a multitude of ways. For birds, it depends on the time of day. Most species of migrating birds continue their travel at sunset and fly through most of the night before landing at sunrise. Using radar velocity imagery, scientists can also decipher between birds or insects by comparing their movement to the prevailing winds. If the reflectivity moves against or faster than the wind, it could be birds. It is challenging to determine if the reflectivity is caused by insects because they fly with the wind rather than against it. For insects, it depends on the time of year and location more so than the time of day and speed. Many insects in the spring and summer tend to swarm near rivers, lakes, fields and ocean shores where they hatch, use up resources and gather to reproduce.
In the image above, a radar signature posted by NWS Norman, Oklahoma shows grasshoppers and beetles as they move over agricultural fields in Quanah, Texas on July of 2015. The radar shows the movement of these insects to be northeast in the direction of Oklahoma. It is typical for grasshoppers and beetles to migrate from one area to another using up resources and then moving on to find more food elsewhere. Grasshoppers are especially one of the most burdensome migratory insects to agriculture. They eat most of the grain, cereal, tomato and onion crops until there is nothing left.
Radar is used in detecting density, location, direction, and speed of birds and insects. A study done by Dr. Sid Gauthreaux and Carroll Belser was able to quantify bird migration using radar reflectivity by interpreting magnitude of bird migration in terms of radar values measured in dBZ (decibels of Z, where Z represents the energy reflected back to the radar). Their findings are used today as a guide to scientists who record and predict migrating bird patterns. The guide is established as follows:
Radar has been very beneficial to the science of studying bird and insect migration just as much as it has been for meteorologists who study and forecast the weather. One would not expect, aside from the normal radar imagery of precipitation in large and small storms, that they would have the ability to see insects and birds as well. Clear air mode allows for this and is a very useful tool in furthering scientific discoveries.
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©2018 Meteorologist Alexandria Maynard
DISCUSSION: There is no debate that the first "true round" of severe weather has now arrived across the Central United States over the past 24 to 48 hours. This multi-day severe weather event has been predominantly characterized by impressive storm structure, impressive lightning displays, and very heavy rainfall bursts anywhere in the path of the more intense convective storms. However, a very important aspect of severe weather which is quite often overlooked is the impact of how modern satellite imager observations have revolutionized the ways in which scientists study, analyze, and forecast both current and past severe weather events.
There is no debate across the atmospheric science forecasting and research communities that GOES-East satellite imagery has completely "changed the game" in terms of how meteorological forecasters and/or researchers analyze and study the atmosphere. More specifically, the GOES-East Advanced Baseline Imager (ABI) 16-channel platform facilitates incredibly high-resolution analyses of storms on very small scales. One such example can be found with the GOES-East 1-minute visible satellite imagery on 2 May 2018 as storms fired up across many parts of Kansas and also across northwest Oklahoma. In the aforementioned 1-minute visible satellite imagery attached above, you can see how there appears to be a "bubbling" phenomena occurring near the center of the cloud deck associated with the blossoming convective storm complex.
This "bubbling" effect is a visual manifestation of what are known as "overshooting tops." Overshooting tops are an indication of the fact that there is a particularly intense region of a given thunderstorm wherein the updraft is so strong that it breaks through the upper-most part of the thunderstorm. This point at which the updraft breaks through the top of the given cloud deck is what is visually observed as the "overshooting top" part of the thunderstorm. Therefore, it goes without saying that when severe thunderstorms develop these "overshooting tops" features, that is not a time that you want to be under or in the path of such a storm since it would have that much of a greater potential to develop heavier rainfall and even hail at times.
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© 2018 Meteorologist Jordan Rabinowitz