FlightAware Discussions

Weather - cold/freezing display?


#1

Does anyone knows why cold weather is displayed like this? It looks like it is centered around each of the Doppler radar sites (in US) but it’s green around the radar. See the four sites captured in my screenshoot. Almost like the radar warms up the air around each site :thinking:

List of sites: https://radar.weather.gov/
For comparation this is what the official page of Wakefield site shows (still weird):


#2

Hi Sonic,

I don’t know about the FA display, but here’s some info on the NEXRAD:

I worked for the NWS from 2007 to 2012. Our Science and Operations Officer told me that
can be caused by flying insects. (real bugs, vice the software kind) Sounds pretty bizarre, but the NEXRAD has a decent MDS level and uses DSP to enhance the target display. He said if the targets appear in the early morning or early evening hours, most of the time it’s insects, especially if the display has a “grainy” appearance.

The NEXRAD I maintain (Frederick, OK) is displaying similar targets, i.e. green near the radar changing to dark blue. then light blue as distance from the radar increases.

This is a “composite” reflectivity display:

This is a “base” reflectivity display:

The main difference is composite reflectivity shows the strongest reflected energy at all elevation scans, not just the reflected energy at a single elevation scan. Elevation is antenna elevation, i.e the angle above the horizon the antenna is positioned at.

More info on the NEXRAD at: https://www.weather.gov/iwx/wsr_88d


#3

Since this happened in the morning, at temperatures just above freezing, very close to Dew point, it was very visible to me. The effect was present in all the surrounding radars, I have posted just one, closer to me.

I am sure there where no insects :slight_smile:
Almost like the radar itself would change the reflectivity of moisture in the air just like a microwave oven affects (heats) moisture in foods.
Probably when is hotter, or colder than the Dew point, the change is less visual.


#4

The antenna has a beamwidth of ~.9° and rotates continuously at varying elevations, thus doesn’t dwell on any one radial long enough to cause appreciable heating.

The WSR-88D spends a vast amount of time “listening” for echos of the signals it transmits. When the time of all pulses transmitted each hour is totaled (the time the radar is actually transmitting), the radar is “on” for about 7 seconds each hour. The remaining 59 minutes and 53 seconds are spent listening for returned signals.

Some of the targets visible near the radar are “ground clutter.”
Ground clutter is an issue inherent to all ground based radar systems.


#5

Yeah no. You have to take in account the radar may be able to detect fog / thin clouds better at closer distances.
The signals from further away get weaker and you can’t be sure anymore you are detecting those thin clouds thus you don’t display anything farther away.

This is just a technical limitation not necessarily the detection of a difference between far away and close.

If you like looking at radar displays check out MRMS:

https://mrms.nssl.noaa.gov/

Quite sure that program is canceling out localized effects better than the scan you are looking at.

Looking at it right now all the effects you describe are not displayed except when using the non quality controlled reflectivity.


#6

Your explanation makes sense!
Also, because curvature of Earth, the farther from radar you get, the beam lower limit picks up higher and higher local elevations. If the fog is just sitting close to ground, the beam will eventually just go “above” it.

I was looking at radar.weather.gov and NEXRAD. I’ll try the MRMS too next time.


#7

Quality Control

This product is derived from the 3D Reflectivity Cube, which means non-hydrometeorological data has been removed including: Ground clutter, anomalous propagation (AP), chaff, interference spikes, and bioscatterers (e.g., angels and ghosts). However, bright band contamination (i.e., anomalously-high reflectivity caused by melting snowflakes) remains.

To see a version with non-meteorological echoes retained (to identify fronts, boundaries, etc.), refer to “Legacy Composite Reflectivity – UnQCed.”

No idea what angels and ghosts are haha :slight_smile:


#8

Also insects or birds may be the reason for the return instead of fog but they will likely only be up to a certain elevation above ground producing the same thing.

Also note that you probably don’t need many of these compared to raindrops big objects to create returns that are equivalent to fog.


#9

Radar “angels” are Bragg scattering (a type of backscatter) caused by an atmospheric boundary layer.
A radar “ghost” is simply a false target.


#10

In addition to that, the condition that causes fog, an inversion, will cause the transmitted beam to
be bent toward the ground causing a large amount of ground clutter to be displayed near the radar
site, thus obliterating most of the returns closest to the radar - the only area where the radar can detect the fog.


#11

Do you get a lot of that in the US?

You are talking about RADAR but I didn’t think you would need countermeasures for weather RADAR.

S.


#12

This night’s picture (in Midwest):