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National radar weather use optical instruments, which have problems like other optical tools. When light passes through an instrument, it will reflect and refract, resulting in inaccurate readings. Reflection and refraction are minimized by using multiple lenses and mirrors on the instrument.
Fiber-optics, for instance, work by sending light down a glass duct. Because of the sharp changes in density, index of refraction, and curvature at the boundary, none of the energy gets out. As a result, we have a very efficient medium.
Sometimes, though, light escapes where we don't want it to and efficiency suffers. False signals can be caused by stray light entering or reentering the system. Radar imagery can be messed up by a lot of limitations and artifacts.
Why do we want to know more about weather radar problems?
Understanding weather radar technical problems can help you make better decisions about how to prepare for upcoming weather conditions by interpreting the data provided by the radar. It can also help you troubleshoot any potential problems with weather radar if you know the technical stuff.
The same principles can affect the national radar weather data in the first three examples. Anomaly propagation, AP, results from them.
Here are brief explanations of each of these weather radar problems shown in the diagram below:
- When mountains or tall buildings block the radar signal, the radar can't see what's behind them. Thus we have shielding by solid objects.
- In blocking, precipitation or other objects in the atmosphere block the radar signal, making it hard for the radar to detect what's beyond them.
- Radar beam filling happens when the radar beam is too wide to measure precipitation particles accurately, making interpretation tricky.
- It's when radar waves reflect off melting snowflakes, creating a bright band in the radar image.
- Overshooting: When a thunderstorm pushes upward so strongly that the top of the storm rises above the radar's scan altitude, causing the image to be distorted.
- When air is forced up over mountains, it cools and condenses into clouds and precipitation. Rainfall amounts can be higher near mountains because of this orographic enhancement.
- There's something called drizzle. It's light rain that falls in very small droplets that are hard to detect with radar, because they don't reflect the signal very well.
- Ducting is when layers of air with different temperatures and moisture levels bend the radar signal, causing it to travel farther than it would normally, creating false radar echoes.
- Radar anomalous propagation: When the radar signal interacts with layers of air with different densities, it bends and creates false echoes.
- A second trip echo (shown above) happens when radar beam reflects off an object, like a building or mountain, and then reflects off the ground or another object before returning to the radar antenna. It can make a second radar echo appear behind the original object.
When a radar beam hits a tall building and then reflects off the ground, it may create a second trip echo behind the building on the radar display. Radar operators can get confused by this because it looks like there's precipitation behind the building when it's actually just radar artifacts.
It's also possible to get second trip echoes when a radar beam reflects off other things in the environment, like trees or hillsides, before reflecting off the ground and returning to the radar antenna. Radar operators are trained to spot and account for these types of artifacts.
On an animated radar weather display, these show up as bright areas that sometimes dance around. Weather pictures can sometimes be seen from a long way away. Why? Reflecting boundaries are caused by:
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What Imperfections Might You See on National Radar Weather?
Be sure to check your local weather radar carefully. There are technical problems with the radar pictures on the national radar weather service. These unusual distortions may affect the images.
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