"Bull gear" failures on the increase, taking down NEXRAD radar sites for extended periods

[Dan Robinson]

ENID, OK - Failures of a critical, hard-to-repair part of NWS radars are on the increase. The "bull gear" is part of the drivetrain that rotates the dish assembly, and at least 9 radar sites have been affected by failures of this part since October 2016.

Replacement of the bull gear requires lifting the 4,000lb dish assembly inside of the dome - a task which necessitates hoisting 15,000 pounds of equipment and tools up the tower. The Binghamton, NY office did a write-up with photos of this repair being performed on their radar in 2008, providing a glimpse of what's involved in the process:

https://www.weather.gov/bgm/eventsBullRing

The KVNX (Vance AFB, Enid) radar in northwestern Oklahoma is the latest to suffer a bull gear failure. The Norman WFO released a statement that the repair could take weeks:

https://twitter.com/NWSNorman/status/1011992697438195713

The other sites that have failed in this way within the last 20 months include:

KPUX - Pueblo, CO:
https://www.weather.gov/pub/bullgear

KDLH - Duluth, MN:
http://www.duluthnewstribune.com/ne...derway-national-weather-service-duluth-office

KPAH - Paducah, KY:
https://www.semissourian.com/story/2505611.html

KFCX - Blacksburg, VA:
https://twitter.com/NWSBlacksburg/status/900394536513482753

KILN - Wilmington, OH:
https://scottdimmich.com/2017/08/02/why-nws-wilmingtons-radar-being-down-for-2-weeks-is-a-big-deal/

KENX - Albany, NY:
https://www.timesunion.com/business/article/Work-continues-to-restore-National-Weather-12151863.php

KJAX - Jacksonville, FL:
https://www.news4jax.com/weather/na...n-jacksonvilles-radar-is-down-for-maintenance

KAKQ - Wakefield, VA
http://www.richmond.com/weather/wak...cle_578f3a74-10d4-5145-8b60-39c08a68d4be.html

Previously, bull gear failures occurred once per year on average:

https://www.roc.noaa.gov/WSR88D/PublicDocs/NEXRAD.pdf

 

[Randy Jennings]

There have been a lot of WSR-88Ds down recently. The other night I counted at least 5. Don't know how much of this was planned down time and how much was unexpected. Hopefully it was more minor than a bull gear issue. The proposed budget for GFY19 reduces the "NWS Service Life Extension Program for NEXRAD " by $16,284,000. Normally I would speculate that NEXRAD life extension is a line item congress is likely to restore, but I would never bet on congress doing anything these days. Given that the WSR-88Ds where installed between 1992 and 1997, they are starting to get old. I would bet that not too many of us use computers or drive cars from that decade still. Going to a phased array system would eliminate mechanical failures and get everyone radar data quicker, but I'm also not going to hold my breath on congress funding that anytime soon either.

 

[Jeff Duda]

The WSR-88D network has already lived out its originally intended lifespan. These kinds of repairs will almost certainly become more frequent until basically all of the radars have had this part replaced. Hopefully after that they'll be good for another 20 years.

 

[Alex Elmore]

Other than being old, there have been several other possible factors causing WSR-88Ds to go down recently. Over the last year or so, WSR-88Ds across the country, or at least in the Central Region, have been undergoing the Service Life Extension Program (SLEP). This is not official information, but it has been noticed that after the most recent phase of SLEP is performed on the WSR-88Ds, the bull gears seem to fail. Here's more about SLEP for those who are curious: https://www.roc.noaa.gov/WSR88D/SLEP/SLEP.aspx

Newer scanning strategies, such as SAILS an MRLE (www.roc.noaa.gov/WSR88D/NewRadarTechnology/NewTechDefault.aspx), might also be taxing the bull gears, but the biggest factor is age. I think SAILS can be used on WSR-88Ds nationwide, but MRLE is still experimental and only used at a few sites.

Going to a phased array system would eliminate mechanical failures and get everyone radar data quicker, but I'm also not going to hold my breath on congress funding that anytime soon either.

I'm sure there's not a single meteorologist out there that doesn't want this. But as mentioned, they are expensive and I think the WSR-88Ds are "in contract" through 2030, so any sort of major upgrade to the network would most likely not happen until then anyway.

 

[Jeff Duda]

I know this post is getting little off-topic, but I don't see phased array technology coming into operational use for a very long time, perhaps not even in my lifetime. When I took a radar signal processing course at OU I learned that, while PAR technology does substantially reduce the time between scans, there are other drawbacks that many may not consider. One of them is that the angular resolution suffers. In particular, the more off-broadside the angle, the worse the angular resolution...perhaps worse than 2 degrees once you get past 45 deg. off-broadside. That means that radar imagery would have somewhat heterogeneous spatial resolution differences and storms sampled in the "corners" (in that near-45-degree off-broadside sector) would look pretty coarse even at close ranges to the radar.

I'm thinking there is more momentum in favor of gap-filling radars and smaller dish/shorter range networks in the medium-future. Such radars are lower powered and much cheaper than the big giant S-bands that make up NEXRAD.

 

[StephenHenry]

One of them is that the angular resolution suffers. In particular, the more off-broadside the angle, the worse the angular resolution...perhaps worse than 2 degrees once you get past 45 deg. off-broadside.

That's really interesting, had never heard that about phased array setups. I'm familiar with some 3 and 4-sided phased arrays in use (for other apps, obviously). Wouldn't the answer be to just increase the number of sides? Even a pentagon would make each array responsible for at most 36 degrees off broadside. I wonder how much you can shrink each array if it is responsible for less angular sweep, or if the tradeoff even works that way.

 

[Jeff Duda]

There are other types of PAR radar designs aside from the traditional Navy surplus ones you're probably familiar with. One type is cylindrical in nature. Another, called AIR, can grab RHI scans instantly. Such a system is detailed here: https://journals.ametsoc.org/doi/pdf/10.1175/JTECH-D-12-00063.1. I'm not sure if these will reach operational usage someday, though. Cost and fragility may be issues.