next message in archive
no next message in thread
previous message in archive
Index of Subjects
This is a multi-part message in MIME format.
------=_NextPart_000_016B_01D1058F.58FF17B0
Content-Type: text/plain;
charset="iso-8859-1"
Content-Transfer-Encoding: quoted-printable
Hi Paul, Andrew & All Oct 13, 2015
This didn't get posted the first time; perhaps because it had become =
too large so I have pasted the original with several earlier exchanges =
clipped.
START OF PASTE\\\\\\\\\\
Hi Paul, Andrew & All, Oct 11, 2015
Having thought this over again, I suspect I overlooked the key =
factor which bears on both the value of air movement and the timing of =
greatest risk.=20
All bodies will radiate heat at rates (as I recall) which depend =
only on their temperature and at temperatures under consideration there =
will always be some heat lost by out radiation. Consequently thin or =
small organs (with consequently low heat content), such as leaves and =
flowers will continue to cool relatively rapidly by out radiation, and =
cool the adjacent air by conduction unless this heat loss is offset by =
heat gain. One possible way to replenish this heat loss, on a cloudless =
night, is in radiation from haze or nearby warm objects. But I suspect =
that air flow, provided the air is warmer than the sheath of cold air in =
the vicinity of the leaf or flower, is far more effective in general. =
Thus the value of air flow down a slope, wind machines and low aircraft. =
Probably for much of NS the concepts of land breeze and sea breeze =
apply: land breeze at night, when land is cooling off faster than the =
sea, and sea breeze in the daytime, when land is warming rapidly =
relative to the sea.=20
If the overall flow or air, when winds do not confuse matters, is =
downhill at night and uphill in the daytime then there must be a period =
of slack flow when downhill flow slows to zero and uphill flow is still =
also zero. This turnaround period should start shortly after there has =
been appreciable warming of high ground but not enough warming to =
initiate a reverse of flow from low ground to high. Which roughly would =
be shortly before sunrise at low elevation to an hour or so after =
sunrise (a guess). As I recall this fits experience with frost quite =
well.=20
When in doubt consult the manual; so I dug out my old Met. book last =
evening and to my surprise found nothing on frost but a fair amount on =
condensation and sublimation. And found that I had misremembered the =
role of various particles and humidity in air.=20
Condensation nuclei are usually salt crystals or droplets of =
sulfuric acid or smoke particles and sublimation nuclei are usually =
particles of soil (according to this 1954 text).
Condensation nuclei are hygroscopic and start to collect water at =
about 80% RH but grow much faster at 96% RH or above. Sublimation starts =
only after RH exceeds saturation by several percent.
DW comment: Sublimation is the process which would be involved in =
frost formation.
Yours truly, DW
My final answer. I promise; sort of.
----- Original Message -----=20
From: rita.paul@ns.sympatico.ca=20
To: naturens@chebucto.ns.ca=20
Sent: Sunday, October 11, 2015 9:02 AM
Subject: RE: Long: Re: [NatureNS] Frost in the morning
Very interesting Dave and Andrew.=20
Up and out before the sun and not coming in til after dark
was very interesting at this time of year. even if harvesting potatoes =
was
hard work!=20
One evening after the sun went down and we were finishing up one
member of the crew pointed out a bright light going across the sky.
More like the sun reflecting of metal rather than a light. It wasn't =
very high
higher than an airplane but not as high as satellites nowadays. From =
the newspapers=20
of the day we deduced it was an early Russian satellite - an memorable =
sighting.=20
Enjoy the day=20
Paul =20
> On October 10, 2015 at 8:21 PM "Hebda, Andrew J" =
<Andrew.Hebda@novascotia.ca> wrote:=20
>=20
>=20
>=20
> Thanks David=20
>=20
> That makes sense.=20
>=20
> Now with a low tide (here at about 06:40 - Noel), that pretty well =
guarantees the cold dense air will win tonight.=20
>=20
> A=20
END OF PASTE\\\\\\\\\\
------=_NextPart_000_016B_01D1058F.58FF17B0
Content-Type: text/html;
charset="iso-8859-1"
Content-Transfer-Encoding: quoted-printable
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<HTML><HEAD>
<META content=3D"text/html; charset=3Diso-8859-1" =
http-equiv=3DContent-Type>
<META name=3DGENERATOR content=3D"MSHTML 8.00.6001.23588">
<STYLE></STYLE>
</HEAD>
<BODY>
<DIV>Hi Paul, Andrew & All =20
=
=20
Oct 13, 2015</DIV>
<DIV> This didn't get posted the first time; perhaps =
because=20
it had become too large so I have pasted the original with several =
earlier=20
exchanges clipped.</DIV>
<DIV> </DIV>
<DIV>START OF PASTE\\\\\\\\\\</DIV>
<DIV>
<DIV>Hi Paul, Andrew &=20
All, &nb=
sp; &nbs=
p; =20
Oct 11, 2015</DIV>
<DIV> Having thought this over again, I suspect I=20
overlooked the key factor which bears on both the value of air =
movement and=20
the timing of greatest risk. </DIV>
<DIV> </DIV>
<DIV> All bodies will radiate heat at rates (as I =
recall)=20
which depend only on their temperature and at temperatures under=20
consideration there will always be some heat lost by out radiation. =
Consequently=20
thin or small organs (with consequently low heat content), such as =
leaves and=20
flowers will continue to cool relatively rapidly by out radiation, and =
cool the=20
adjacent air by conduction unless this heat loss is offset by heat =
gain.=20
One possible way to replenish this heat loss, on a cloudless night, is =
in=20
radiation from haze or nearby warm objects. But I suspect that air flow, =
provided the air is warmer than the sheath of cold air in the vicinity =
of the=20
leaf or flower, is far more effective in general. Thus the value of air =
flow=20
down a slope, wind machines and low aircraft. </DIV>
<DIV> </DIV>
<DIV> Probably for much of NS the concepts of land =
breeze and=20
sea breeze apply: land breeze at night, when land is cooling off =
faster=20
than the sea, and sea breeze in the daytime, when land is warming =
rapidly=20
relative to the sea. </DIV>
<DIV> </DIV>
<DIV> If the overall flow or air, when winds do not=20
confuse matters, is downhill at night and uphill in the daytime =
then there=20
must be a period of slack flow when downhill flow slows to zero and =
uphill flow=20
is still also zero. This turnaround period should start shortly after =
there has=20
been appreciable warming of high ground but not enough warming to =
initiate a=20
reverse of flow from low ground to high. Which roughly would be=20
shortly before sunrise at low elevation to an hour or so after =
sunrise (a=20
guess). As I recall this fits experience with frost quite well. </DIV>
<DIV> </DIV>
<DIV> When in doubt consult the manual; so I dug out =
my old=20
Met. book last evening and to my surprise found nothing on frost but a =
fair=20
amount on condensation and sublimation. And found that I had =
misremembered=20
the role of various particles and humidity in air.=20
<DIV> </DIV>
<DIV> Condensation nuclei are usually salt crystals or =
droplets of sulfuric acid or smoke particles and sublimation nuclei are =
usually=20
particles of soil (according to this 1954 text).</DIV>
<DIV> </DIV>
<DIV> Condensation nuclei are hygroscopic and start to =
collect=20
water at about 80% RH but grow much faster at 96% RH or above. =
Sublimation=20
starts only after RH exceeds saturation by several percent.</DIV>
<DIV> </DIV>
<DIV> DW comment: Sublimation is the process which =
would be=20
involved in frost formation.</DIV>
<DIV> </DIV>
<DIV>Yours truly, DW</DIV>
<DIV>My final answer. I promise; sort of.</DIV>
<DIV> </DIV></DIV>
<BLOCKQUOTE=20
style=3D"BORDER-LEFT: #000000 2px solid; PADDING-LEFT: 5px; =
PADDING-RIGHT: 0px; MARGIN-LEFT: 5px; MARGIN-RIGHT: 0px"=20
dir=3Dltr>
<DIV style=3D"FONT: 10pt arial">----- Original Message ----- </DIV>
<DIV style=3D"FONT: 10pt arial; BACKGROUND: #e4e4e4; font-color: =
black">From: <A=20
title=3Drita.paul@ns.sympatico.ca =
href=3D"">rita.paul@ns.sympatico.ca</A> </DIV>
<DIV style=3D"FONT: 10pt arial">To: <A title=3Dnaturens@chebucto.ns.ca =
href=3D"">naturens@chebucto.ns.ca</A> </DIV>
<DIV style=3D"FONT: 10pt arial">Sent: Sunday, October 11, 2015 9:02 =
AM</DIV>
<DIV style=3D"FONT: 10pt arial">Subject: RE: Long: Re: [NatureNS] =
Frost in the=20
morning</DIV>
<DIV><BR></DIV>
<DIV><SPAN style=3D"FONT-SIZE: 12pt">Very interesting Dave and =
Andrew.</SPAN>=20
</DIV>
<DIV><SPAN style=3D"FONT-SIZE: 12pt">Up and out before the sun and not =
coming in=20
til after dark<BR></SPAN></DIV>
<DIV><SPAN style=3D"FONT-SIZE: 12pt">was very interesting at this time =
of year.=20
even if harvesting potatoes was<BR></SPAN></DIV>
<DIV><SPAN style=3D"FONT-SIZE: 12pt">hard work! <BR></SPAN></DIV>
<DIV><SPAN style=3D"FONT-SIZE: 12pt">One evening after the sun went =
down and we=20
were finishing up one<BR></SPAN></DIV>
<DIV><SPAN style=3D"FONT-SIZE: 12pt">member of the crew pointed out a =
bright=20
light going across the sky.<BR></SPAN></DIV>
<DIV><SPAN style=3D"FONT-SIZE: 12pt">More like the sun reflecting of =
metal=20
rather than a light. It wasn't very high<BR></SPAN></DIV>
<DIV><SPAN style=3D"FONT-SIZE: 12pt">higher than an airplane but not =
as high as=20
satellites nowadays. From the newspapers</SPAN> </DIV>
<DIV><SPAN style=3D"FONT-SIZE: 12pt">of the day we deduced it =
was an early=20
Russian satellite - an memorable sighting.</SPAN> </DIV>
<DIV><SPAN style=3D"FONT-SIZE: 12pt">Enjoy the day</SPAN> </DIV>
<DIV><SPAN style=3D"FONT-SIZE: 12pt">Paul <BR></SPAN></DIV>
<DIV></DIV>
<DIV></DIV>
<DIV><BR>> On October 10, 2015 at 8:21 PM "Hebda, Andrew J"=20
<Andrew.Hebda@novascotia.ca> wrote: <BR>> <BR>> <BR>> =
<BR>>=20
Thanks David <BR>> <BR>> That makes sense. <BR>> <BR>> Now =
with a=20
low tide (here at about 06:40 - Noel), that pretty well guarantees the =
cold=20
dense air will win tonight. <BR>> <BR>> A =
<BR></DIV></BLOCKQUOTE></DIV>
<DIV>END OF PASTE\\\\\\\\\\</DIV></BODY></HTML>
------=_NextPart_000_016B_01D1058F.58FF17B0--
next message in archive
no next message in thread
previous message in archive
Index of Subjects