[OKDXA] South Orkneys

[Kimberly Elmore]

Off-topic alert!

Good observations, Nelson! Yes, the OK mesonet site has a wealth of information 
on it, all for the asking. I may be mistaken, but I think that the temperature 
and dewpoint all come from sensors at 2 m above the ground, while the wind comes 
from sensors at 10 m, but I'll have to check with the OCS staff here.

Yep, when I rode a motorcycle I, too, noticed the changes in temperature with 
elevation, especially in the evenings and at night. If you think back, you'll 
also remember that these changes were apparent only when the wind was nearly 
calm. Great stuff!

The short-period changes you see in the night time temperatures aren't due to a 
change in the enthalpy (thermal mass, if you will) of the air, which remains 
remarkably constant despite relative humidity. If you look carefully, you will 
usually see the spikes in night time temperature are also accompanied by small 
puffs of wind. These puffs of wind represent momentum transfer from aloft, 
somewhere above the night time surface layer. Under light winds, that layer 
becomes decoupled from the flow aloft. But, occasionally turbulent mixing brings 
down some momentum from above the surface layer, and we get not only a puff of 
light winds, but also a puff of warm air.

This is why, especially in winter, if the winds stay up at night, we don't see 
the big swings from low to high temperature. Turbulent mixing in the vertical 
prevents the formation of a cold, decoupled surface layer due to radiation. 


No, this isn't DX, but it is fun stuff!

Now, back to the South Orkneys!

I still need S9DX on more bands. How long will they be there?

Kim N5OP



----- Original Message ----
From: Nelson Derks <ac5up at windstream.net>
To: Discussion of OKDXA <okdxa at mailman.qth.net>
Sent: Fri, February 11, 2011 10:43:12 AM
Subject: Re: [OKDXA] South Orkneys

Jay Eimer wrote:
> I saw the same thing on my commute yesterday morning.  My truck has a 
>thermometer display.
>
> I live on a hill - and saw 0 at my house (on top of the tallest hill in the 
>immediate vicinity).  But I saw 10 degree swings as I dropped into valleys  - 
>down to -11 at one point, -7 or -8 more typical at the bottoms, and -2 or so on 
>the crests.
>  

Speaking as an aging motor scooter pilot I can tell you that's nothing 
unusual. In the summer when it's hot it tends to be hot no matter what 
or where, but in the spring & fall when you drop down a hill to cross a 
bridge over a creek there is definitely a pocket of cooler air near the 
water. Can't miss it. It's also noticeably cooler in the shade except on 
very humid days when there is no escape from the heat anywhere...

As for the latest, if you have some spare time go up to the mesonet dot 
org site and click "weather" up top. Choose a monitoring site that 
interests you (if you park your mouse on any orange dot the name will 
pop up). Note the stat summary and abbreviated forecast, then click on 
the meteogram (green & pink graph) toward the upper right corner.

What you're looking at is time on the horizontal axis and temp displayed 
vertically in three ways by color overlay: Actual temp, dewpoint and 
wind chill. All are measured at 10 meters above ground. Park your mouse 
along any boundary line and it will pop up the time, temp, and whether 
the number is wind chill or whatever. Notice in the upper right corner 
how you can go back 1, 2 or 3 days in time. Also notice the graphs for 
wind speed, direction, yadda, yadda, yadda.

Point of all this is that you have a buttload of readings in five minute 
increments and the overnights have become very 'spikey' on the 
temperature graph. Best guess is that the air is so dry it has no 
thermal mass (thermal inertia?) which is contrary to normal conditions. 
Generally the humidity rises overnight and temp changes become more 
gradual because of the moisture. Looking at Bixby in the wee hours of 
the 10th I'm seeing two and three degree deltas within a 5-10 minute 
spread in both directions. Note also how the very coldest portions of 
the morning were relatively short lived and I think that's fortunate... 
When I saw it was around -20 at my QTH my next move was to check for a 
green puddle under the car. None found. The temp was cool enough to test 
the ol' ethylene glycol but not the exposure time. Takes a while to suck 
all the heat out of a proper engine block and Jack Frost didn't get a 
good grip on mine.

Poke around the mesonet site and you can find all sorts of groovy things 
like soil temps and month by month archived summaries from each 
measurement site. If a person has the need they can research both long 
and short term trends, and I predict the overnight temperature lines are 
going to smooth out nicely in the next day or two................

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