[NLRS] 2m enhancement from EN24

Tue Jul 11 21:50:54 EDT 2017

Weather fronts like we have had the last couple days are often very 
effective at enhancing VHF and microwave propagation. Often there is 
warm air over running cold air and that reverses the normal temperature 
gradient and causes a great deal more refraction. And can trap signals 
to propagate in the front as if in a waveguide.

I saw a strong example of that one Sunday I think about 1976. My TV in 
the kitchen was seeing a Milwaukee WI UHF TV station with just a single 
telecoping rod antenna. That was from a mile south of Gilbert Iowa, 
probably a distance of 300 miles. A strong front that in a short while 
created a super cell and a tornado on the ground a mile in diameter 
located south of Ogden Iowa about 20 miles from Gilbert but visible from 
my back porch. That tornado dissipated and another formed near the tiny 
town of Jordon. The Jordon tornado was also a mile wide and rotating 
reversed to normal tornadoes. Jordon was about 5 miles south and 8 miles 
west of my house. The tornado passed about two miles west of me, 
dropping a side funnel that broke up after draining the Gilbert sewage 
lagoon. It dropped debris about 200 yards from my house. There was 
another side funnel that I didn't see that went past my house about 3/8 
mile east that did damage. The main funnel sometimes lifted over houses 
but in fields it looked like the field had been graded with a mile wide 
grader blade. It went on NNE and lifted up at Story City, damaging the 
tall enclosed tower at the fire department where they dried hoses.

The radio noise from that thunderhead was so great that the county 
deputies couldn't hear their dispatcher in Nevade about 12 miles SE of 
Gilbert. After the funnels had moved on I went into Gilbert to WB0BQV's 
house where he had his generator running and had been supplied a county 
sheriff's radio for such emergencies by the local civil defense 
director. We relayed for the dispatcher for a while, then as the storm 
moved on we learned that the mutual aid radio at the hospital in Story 
City wasn't working so we went to see what was wrong. We climbed up to 
the roof and found 18" of water on the flat roof. The tornado had 
dropped a bunch of tree leaves that blocked the drains. And it had blown 
over the antenna. While Dave fixed the antenna I took off my shoes and 
rolled up my pant legs and waded to the drain and cleaned off the 
leaves. That was a lot of weight on that roof.

The amazing thing for the afternoon that there was only one injury in 
the miles the big funnels were on or close to the ground, an arm broken 
by a falling limb in Story City.

Lots of effects along that front. Contents from some of the damaged farm 
house like books and checks were found 80 or 90 miles NE in a day or 
two.The little town of Jordon is mostly a memory now, most of it was 
blown down by the tornado.

Another very good creator of long VHF and up propagation can be a 
stationary high pressure dome. I've worked 1296 from Gilbert to Dallas 
Texas with 2.35 watts and to Houston on 432 with 100 watts while under 
such a stationary high pressure dome. It also causes a wide area 
temperature inversion preserved by calm winds.

A calm cloudless morning without any other weather features often shows 
enhanced propagation due to a temperture inversion. The inversion is 
cured by breezes mixing the lower atmosphere. The inversion is caused by 
radiant cooling (on a clear night) of the earth's surface often 
significantlly cooler than the air at the NWS standard elevation of 6 
feet. I have software running for decades now at weather.net that 
compares cloud temperature to surface temperature to tell clouds from 
cooled ground and uses the clouds as a mask for radar to mask out odd 
propagation (Anomalous Propagation) echoes. In use its been found that 
the satellite temperature data threshold has to be set as much as 15 
degrees fahrenheit below the official observation dew point sometimes to 
keep from judging the radiant cooled earth surface as a cloud. 
Especially on a calm clear night.

73, Jerry, K0CQ

On 7/10/2017 8:26 PM, Mary Brown wrote:
>
>
> WD9BGA/b(EN53, 144.296ish) is 5x6  and N0LL/b(EM09, 144.294ish) is 5x2 into
> EN24, as the sun sets conditions may improve with this still air.
>
>
>
> Mary
>
> W0AAT
>
>
>
> ---
> This email has been checked for viruses by Avast antivirus software.
> https://www.avast.com/antivirus
> ______________________________________________________________
> NLRS mailing list
> Home: http://mailman.qth.net/mailman/listinfo/nlrs
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:NLRS at mailman.qth.net
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html