I can't seem to get this right. :< Can't put it on the
roof with the other sensors as the deliberate exposure that
the roof affords those others interferes with the accuracy
of the temperature reported.
And, mounting it on the back porch ("up" out of the way)
shades it from direct sunlight but "keeps it warm" in the
colder weather due to heat trapped by the roof of the porch
(the same roof that *shades* it from the Sun).
So, it seems like the trick is to find shade without an
"overhead covering"? (contradiction in terms??)
I'll try the porch -- but much closer to the ground (farther
from the heat-trapping ceiling)?
I have two. One outside an east-side window
and one outside a west-side window. Except for
brief period around lunchtime there's always one
in the shade. I should acknowledge, though, that
I'm not a stickler. This morning it was low 40s.
41? 43? I don't really care. I just want an idea of
what to expect when I go out.
I'm not interested in personal comfort as much
as having "real data" for the HVAC system and
to know whether the citrus trees are in jeopardy.
E.g., Mandarins get upset at 32 (not 30 or 34)
but Navels will tolerate 28 (but not 26). The
mechanisms used to protect them usually only afford
a couple (3 or 4?) degrees of added protection -- but,
only when you *know* they need to be used.
I also can't understand why it always gets *colder*
as the Sun is rising!
All objects gain heat from outside sources and radiate it away at the
same time. When more radiant heat is lost than gained, the object cools.
When more heat is gained than lost, it warms. If they are balanced, the
temperature remains constant. Okay… that’s pretty basic. Between sunset
and sunrise, the Earth’s surface gathers no solar energy but continues
to radiate away its stored heat. During the night, the surface also
loses radiant heat faster than it steals heat from other sources, and
thus its temperature, and that of the air in contact with it, drops
steadily. At dawn, when the first light beams across the landscape, the
incoming solar radiation is very weak. It does not yet have enough
strength to counter all the heat escaping from the surface. As a result,
the surface continues to lose heat for some time following sunrise, and
the air temperature continues to fall. At some point, the solar rays
shine strongly enough to counter the heat loss. The gain-loss balance is
shifted, and the air finally begins to warm up. As a rule of thumb: the
coldest temperature is about an hour after sunrise.
But that doesn't explain why it gets *colder*.
I.e., temperature falls through the evening and STABILIZES in the wee
hours of the morning. And *stays* that way -- for HOURS! Until just as
the sun rises. *Then*, it starts downward!
Air mass also is _not_ stagnant; all of the other local and regional
effects are going on at the same time. If there's a consistent pattern
of such (and I seriously doubt it is _every_ day), there's some other
effects locally going on causing morning air currents or whatever....It
might even in a local location be owing to other non-meterological
causes such as perhaps there's a large industrial operation which starts
operation and a heat exchanger or somesuch at that time...
No way to say specifically w/o much more information.
Oh, I'm *convinced* it is a local phenomenon! We are located at the
confluence of two large washes, near the foothills of a (small) mountain
range. Our (winter) microclimate is driven by cold air cascading
down the mountain slopes and settling into the washes. Eventually,
there's "enough" that it overfills the washes and starts to
affect the properties adjoining (we're a bit uphill from the washes
but it's all a matter of degrees).
*But*, I can't see why *more* "cold air" would fall out of the
mountains as the rising Sun strikes them! Nor can I see anyplace
where "stored" cold air could be drawn in.
(We are in an entirely residential area with only "storefronts"
a mile or so away, "uphill" -- and farther from the washes -- from us.
That was my thought. There is a little river valley
just south of my house. I can feel the temperature change
if I ride my motorcycle into that little valley just a bit
after sundown. It's distinctly cooler in that little valley.
The sun would heat the upper air first as it comes up in
the morning forcing the cooler air down.
Using Opera's mail client: http://www.opera.com/mail/
Try this: the earth cools at night causing the humidity to
drop and the moisture condenses as dew. When the
sun comes up it begins to evaporate the dew and when
water changes back to vapor it absorbs a lot of heat!
That's possible if there is dew (frost) on the mountain; there's
nothing *here* at its base! That would also be more consistent
with the timing: we are often not yet in sunlight -- but the
south-facing slope of the mountains immediately to our north is!
It would also explain why the phenomenon is local to our immediate
area and not (as much) for folks several blocks further south (higher
Trees are within 10-20 feet of the house. So, there's
likely no difference in temperatures there vs here
IN THE ABSENCE OF MAN-MADE INFLUENCES.
Locating them at/in the trees would expose them to the
For example, I was outside a few minutes ago checking the
fruit. I moved a thermometer (not a wired sensor) from
it's location on the porch out into the yard -- 12 feet
away. In the time it took for me to walk to three of
the trees and back, the registered temperature had
climbed from 51F to 72F. (I'm *sure* the air temperature
hadn't changed that much! :> )
Nearby weather reporting sites range from ~47F to ~57F.
The closest to my location (unsure of its relative elevation)
reports 50F -- which is in line with my 51.
[My 51 is usually high due to its location in a "heat trap"]
I was interested in the temp difference at various roof vents once when
installing an attic fan. Went to the dollar store and picked out 12
that were reading the same in the store and set them outside of the
vents so I could read them from the ground. Then checked them with
binoculars ever couple of hours. This was on a hot summer day and all
were in the shade of the eaves. I didn't see more than a couple of
degrees difference between the sunny & shady sides of the house.
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