Davis
Instruments Weather Club
February 2003
In This Issue:
So,
You Saw TWO Suns Setting Last Night… What Medications Are You Taking?
Remember that
time we were stranded in the desert, reduced to crawling across
the hot white sands, gasping, "water… water…" and we looked up and
saw, shimmering in the near distance, a cool blue lake of crystal
clear, cool water? We were delusional and what we saw was a mirage,
a product of dehydration and dangerously high body temperature.
Well, maybe that wasn't us, but some guys in a movie we saw once,
but the point is that seeing a mirage means you're out of your mind,
right? But in a more reality-based childhood memory, we were once
mesmerized by the shimmering blue pool of water floating on the
hot asphalt of the road ahead of us, zipping along at the same speed
as our car and remaining in the near distance. Were we out of our
minds then? We were in serious want of a chocolate-dipped Frosty,
but that was pretty far from hallucination-inspiring suffering.
So, which is it? Are mirages something we see only under mental
duress? Are they like an optical illusion in which a straight line
appears to waver or one dot looks larger than another the same size?
And what, oh what, does this have to do with the weather!?
Well, plenty.
Much of what we see and enjoy in weather phenomena is all mixed
up with the amazing properties of light and how it interacts with
our atmosphere, our retinas, and our brains. Mirages, from the desert
oasis to the upside down sailing ships and vast mid-sea phantom
cities reported by olden-day sailors to "double sunsets" and the
mysterious green flashes one can sometimes see just after the sun
sets, are not delusions, nor are they optical illusions. Andrew
T. Young, writing on his website,
tells us that mirages are "real phenomena of atmospheric optics,
caused by strong ray-bending layers in steep thermal gradients."
Optical illusions come from the human mind's efforts to interpret
visual clues, and mirages can often lead to optical illusions, but
they are not at all the same thing.
Atmospheric
mirages happen as a result of light hitting the boundary between
layers of air of different densities, especially if the light comes
in at an extreme angle. The air's density, which is strongly affected
by temperature, affects how the light is refracted. Adding to the
fun, the boundary may be curved, creating a sort of lens that further
distorts or magnifies the mirage. A mirage is a real phenomenon
that can be photographed - just try taking a picture of a delusion!
Mirages can
even be classified. An inferior mirage is one in which we see an
inverted image below the object. The most common are caused when
the air just above the ground is heated by the ground and less dense
than the cold layer above it. The image of the sky ("water") just
above the asphalt and the double-sunset, in which a second sun is
seen just below the setting one, are inferior mirages. A superior
mirage shows up as an inverted image above the object. But superior
mirages caused by the dramatic vertical changes of air temperature,
can be very strange. There may be several images above the object,
and parts of the mirage may be stretched or otherwise distorted.
Then there are the 3-image mirage, in which an inverted image is
seen between two objects, and "Fata Morgana," named after King Arthur's
much-maligned sister, in which the sea surface seems to rise up
like castles that disintegrate moments later.
On Lee
Krystek's website, you can read about a mirage that led Admiral
Peary on a long and pointless hike to explore the "Crocker Lands"
he could see in the north arctic back in 1909. (The Inuit guides
who accompanied Peary must have been shaking their heads the whole
way, muttering, "These Europeans are not too smart - they don't
even know an arctic mirage when they see one!")
Atmospheric
optics from mirages, to refraction and reflection make watching
weather all the more fun - and a basic understanding of the subject
will arm you to answer the next four-year old who looks up at you
and says, "Why is the sky blue, Daddy?" (But you'll need an advanced
understanding of child development to make your explanation of the
fact that air particles scatter light of different wavelengths more
or less, and that it scatters blue light the most effectively before
the little one gives up and wanders off to watch "Barney"…) For
those of you who are deep-thinking analytical types and want to
get more immersed in the science can start off with a couple of
cool websites, including Andrew
T. Young's, and
Spectrum Educational Enterprises'.
But all you
really need to enjoy the show is to put yourself outside where it
all happens and to be on the lookout for mirages, brilliant red
sunset, halos and sundogs and coronas, crepuscular rays and iridescent
clouds. Never mind the physics - but do bring the camera!
P.S. You really
should visit the great website of Pekka
Parvainen, of the University of Turku, Finland. His photos of
ships sailing in the sky, among others, are way cool! Photos of
many lovely weather light shows can be enjoyed on Les
Crowley's website. Our personal favorite, is of iridescent
clouds over Northern California.
Weather
Check Quiz Question 1: Most of us started including the weather
phenomena of crepuscular rays in our early Crayola artwork: yellow
lines converging on our smiley-faced sun -- so we are all familiar
with those. But do you know what kind of rays you might see if you
turn your back on those crepuscular rays and look at the horizon
opposite the setting or rising sun?
Dew
Point: The Amazing Weather Predictor
Here's an amazing
magic trick you can do with your Vantage
Pro to amaze and astound your friends! You can, at sunset, accurately
predict the overnight low! You won't be 100% accurate every time,
but pretty darned close. What you do is look at the dew point at
sunset. If it's 43ºF, tell your pals, "It won't go below 43ºF tonight."
Next morning, use your VP's 24-hour outside temperature history
to prove your prediction.
Dew point is
the temperature to which the air must be cooled for saturation to
occur. As the temperature drops overnight, condensation slows the
rate at which the temperature declines. Once the dew point is reached,
a sort of balance is achieved because the formation of dew releases
a bit of heat into the air, and the air is unlikely to get much
colder. Of course, if a hunk of cold air moves into your backyard
overnight, this won't work. So don't perform this trick without
a little checking up on any expected cold fronts. (It's also is
most likely to work if the daytime relative humidity stays above
50%.)
Weather
Check Quiz Question 2: Say you've got your buddies all lined
up ready to spring your trick on them. But, you forgot to tune in
to the Weather Channel, or to look at the weather page in your newspapers.
You don't want to risk a cold front ruining your whole game. What
weather conditions might indicate that a cold front is approaching
and that this is not a good time to try your magic?
Temperature
Requirement Kicked Out of Freezing Fog Definition
Precision-weather-thinker
and newspaper weather columnist, Jan Null, was not completely satisfied
with our "technically correct" definition of freezing fog in last
month's E-news quiz. We said it was what you get when fog is present
and air temperature is below 32ºF.
He just happened
to have recently researched the very same topic and found several
definitions, with the most universal being the American Meteorological
Society's: "A fog the droplets of which freeze upon contact with
exposed objects and form a coating of rime and/or glaze."
Jan wanted to
point out that temperature is not included in that definition.
"Just like it
is possible to have frost when the air temperature is above 32ºF,"
he wrote, "because objects can cool to less than 32ºF by radiative
cooling, it would also be possible to have fog droplets freeze upon
contact with sub-freezing objects. The difference from frost is
that the process is sublimation, that is, water vapor to frozen,
while with freezing fog it is simply freezing, that is, liquid to
frozen."
By the way,
Jan really does know all the answers to our quiz questions and just
about any weather question you can come up with. You can ask your
question through his website --
and he might answer it in his column in the San Jose Mercury News.
You might want to check his archive
first, as it is just loaded with interesting weather information.
Weather
Check Quiz Question 3: This is a question that appears in Jan's
most recent column. It came from Myron Gananian of Menlo Park. "I
have heard two explanations for the contrails behind high-flying
airplanes. One is that the water in the exhaust turns into ice crystals.
The other is that the particulates in the exhaust are a nidus for
moisture to condense. Which is, or are both, correct?"
Our
Readers Know Best
Mike Friese gave
us this interesting little tidbit, after reading in our last issue
that Lord Kelvin, in designing his scale, avoided negative temperatures.
"Temperatures
in the Kelvin scale," says Mike, "are never written with a degree
symbol. It appears Lord Kelvin didn't like minus signs or degree
symbols!" (Mike, how'd you know that?)
Steve Eustis,
who has an excellent memory when it comes to extreme weather, wrote
to say that he remembered a challenge to Mount Washington Observatory's
fastest wind ever recorded (231 mph). He thought he remembered reading
that a higher wind had been recorded somewhere in the Pacific. What
he was recalling was a wind recording that caused another little
storm within the world of weather professionals.
In December
of 1997, Anderson Air Force Base in Guam, reported a gust of 236
mph - a new world record for a surface gust. But in the weeks following
the report, it was decided by the National Climate Extremes Committee
that the claim could not be substantiated. There is an interesting
play-by-play of the event on the Mount
Washington Observatory website. So Steve's memory was right,
but the end of the story is that Mount Washington Observatory remains
the reigning King of High Winds. Thanks, Steve. You're pretty good
for a guy who's memory cells are being frozen as we speak by a brutal
northern Vermont winter!
R. Heilman,
also of cold Vermont, had his memory jogged by our story about the
Mount Washington Observatory. He took his first and only trip up
to the summit about 30 years ago, and was stunned to step off the
cog railroad to temperatures in the mid 70's! He joined the Observatory
that day, and read in the first newsletter he received that the
Observatory had recorded an all-time high temperature for the very
day the Heilman family visited. "What are the chances of such a
coincidence," he muses. Maybe he ought to go up there again and
see if he can warm up the east coast a bit…
Finally, Larry
Dapolito, (Dapa@worldnet.att.net),
who lives in Brookline, New Hampshire would like to compare local
weather data with other Davis Vantage Pro owners in his neck of
the woods (Southern New Hampshire) via email.
Weather
Check Quiz Question 4: In honor of our Vermont correspondents,
here are two snow questions. First, why is snow white, Daddy?
Extra
Credit: Water is the only substance that we encounter near its
triple point everyday. What is the definition of triple point, and
what is the triple point of water?
Are
Aliens Making Canadian Town Super-Intelligent?
This story is
not for the timid. It concerns a mystery so confounding and thrilling,
we are gearing up to handle the calls from Hollywood moguls who
will want to make a movie out of it. The facts come from Linda Neil
of Farmtronics, which sells Davis products.
A few months
ago, Linda met a woman from La Crete, a small town in Northern Alberta,
who bought a Vantage
Pro for her husband. Since then, according to Linda, the whole
town of La Crete seems to be buying Vantage Pros! In fact, some
people are inquiring about buying three or four at a time! Linda
has not been able to find out just why La Crete-ians are going mad
for Vantage Pros.
La Crete bills
itself as a close-knit, agricultural community, which also enjoys
some pretty extreme weather, but it is clear that there is something
else going on here. It is obvious, from the number of VPs owned
per capita, that he citizens of La Crete are way more intelligent
than average.
Here's what
we, as wanna-be screenwriters think: Maybe an alien race, seeking
a colonization point, has chosen La Crete for its natural beauty
and smart residents, and has been doing something to the water supply
to turn La Crete into a town of mental giants. Their evil conspiracy
includes plans to take over the human race and use the folks of
La Crete as a sort of enslaved think tank. But, they've underestimated
the very brilliance and toughness of human beings in general, and
Northern Albertans in particular. Those La Crete-ians have a few
surprises for their uninvited guests, and it won't be pretty! Are
you scared yet?
(Coming soon
to a theater near you: "They Came With the Wind;" opening scene:
a lone Davis anemometer spinning over silent, snowy farm; a storm
cellar door cracks opens and a very long, greenish finger extends.
Camera pans to widen shot, including a small girl, completely immersed
in reading War and Peace. Without looking up from her book, she
extends a tiny booted foot and lowers it with a resounding smack
on the alien digit…)
Weather
Check Quiz Question 5: Who should play the pivotal role of
the Davis E-Newsletter editor? A. Julia Roberts, B. Gwyneth Paltrow,
C. Jennifer Aniston, D. Yogi Berra
Dog
Owners: Who Needs a Weather Station?
"To determine
the weather, go to your back door and look for the dog. If the dog
is at the door and he is wet, it's probably raining. But if the
dog is standing there really soaking wet, it is probably raining
really hard. If the dog's fur looks like it has been rubbed the
wrong way, it's probably windy. If the dog has snow on his back,
it's probably snowing. Of course to be able to tell the weather
like this, you have to leave the dog outside all the time, especially
if you expect bad weather. Sincerely, The Cat." (Anonymously
posted on an online weather message board.)
Vantage
Pro Riding a Subaru Is a Crowd Pleaser
Brian Yeaton,
of Mount Washington Observatory's Weather Notebook has had a grand
time cruising across the United States in his very fancy Subaru
(with the Vantage Pro
on top) on The Weather Notebook National Tour from New Hampshire
to Long Beach, California and back again. Along the way he's stopping
to talk to weather enthusiasts everywhere, and finds that the VP
really draws the crowds.
In his online
journal entry of January 30, from Mobile, Louisiana, Brian wrote,
"Of course, everyone came out to see the buggy: the Davis-decked
out Weathermobile. . . . With the Davis Vantage Pro weather station
dominating the port side, I am always asked if I will use the car
to chase tornadoes. Hmmmmmm. Hey-I'm game. I'll have to hook up
with the folks from the National Severe Storms Lab again. Wouldn't
that be cool!" You can check in with Brian's and the "Weathermobile's"
trek via his journal
and website.
Vantage
Pro Informs Surfers, Emergency Personnel, the World About City's
Dreamy Weather
Our readers on
the East Coast may want to go out and shovel some snow instead of
reading this story. It could be too painful. You see, it's about
a town in California where, on the coldest of cold winter days,
the temperature hovers around 50ºF. The average temperature in winter
is only about 10ºF cooler than in the summer.
The pretty little
beach town is San Clemente, and none of the 51,000 residents, a
great many of whom surf, swim, kayak, bodysurf, and/or stroll on
the beach, would think of venturing down to the sea without checking
the city's weather web page.
A temperature sensor in a conduit running down a piling on the San
Clemente pier reports to the Vantage Pro on the pier and allows
surfers and swimmers to check the water temperature from their computers.
(Photo credit: Jerry Cox, www.jerry.cox.org)
Not long ago,
Mike Morgan of San Clemente's Beach, Parks, and Recreation Department
told us, his department installed a Davis Vantage
Pro on the pier. Since many of the city's residents are as concerned
about the temperature of the water as that of the air, the department
also purchased a wireless temperature station. The sensor was run
down a conduit from the pier to about a foot above the ocean floor.
At this depth (about eight feet), the waves do a good job of mixing
the water, which, according to Mike, can be as much as five degrees
warmer in the first foot. The sensor gives swimmers a very good
idea of just how cold the water will feel. The rest of the station
is also out on the pier and beach strollers can watch the wind cups
spin. The department did encounter one problem in uploading the
information to the Internet: a pier is not normally well-served
with telephone lines, and those that were present are dedicated
to marine services. But instead of trenching a new line from the
pier, the department used a wireless Ethernet connection to a router
to a T1 line - and thence to the whole Internet-using world.
While the station
is very popular with beach-goers, it is much more useful to city
officials than just a perk for citizens. Because San Clemente has
a nuclear power plant for a neighbor, it is mandated to have a very
well-prepared emergency preparedness plan. The VP plays an important
role in the plan, and city officials are well versed on the importance
of real-time weather information in case of an emergency. The weather
station has been such a success, that Mike had no trouble convincing
the City that a second, inland station is needed.
"The ocean,"
Mike told us, "is like a big insulating blanket. If you go even
five miles inland, the temperature can be as much as 30ºF different."
The new station will offer a clear demonstration of this effect,
as well as providing additional support for emergency services and
residents.
The City is
planning on using the weather stations to help manage more than
100 irrigation controllers (using the Vantage
Pro Plus' ET calculations), which may save thousands of dollars
annually on their water bill.
You really should
visit the San
Clemente Weather website. It's full of good, enviable information,
presented in a clear and accessible format. Mike, who set up the
weather page, said he got "lots of good ideas from the other sites
on Davis's Weather World 'Round page."
"The page has
served as something of keynote," Mike said. "We've been tracking
hits to the City's site and have found that the weather page gets
the most hits. From there, people click onto other city pages. It's
more effective at bringing people into our site than the entry page!"
So, maybe you
can't take the afternoon off and go surfing in San Clemente. But
you can, with just a click here, know just how pleasant it would
be if you could!
Weather
Check Quiz Question 6: Why is the sky often hazy near the ocean?
You're
Brilliant! Answers to Quiz Questions
Question
1:
You might be lucky enough to see anti-crepuscular rays, which converge
on the anti-solar point. It's a rare treat, but even rarer is the
occasion to see the ray arcing all the way across the sky from solar
to anti-solar point. To understand what you're seeing, imagine a
railroad track running across the sky from horizon to horizon. In
perspective, an arced parallel track would appear to converge at
both ends.
Question
2: Let's assume you live in the continental U.S., and not in
a coastal region. Before a cold front, the winds will probably be
from the SSW. The barometer will be steadily falling, and the dew
point will remain high and steady. There might be showers, but the
temperature will be relatively warm. If these conditions prevail,
your trick may fail!
Question
3: Jan's answer: "It is actually a combination of both.
Water vapor that is exhausted from jet engines is sometimes just
substantial enough to make the air saturated and for condensation
to occur. Additionally, the exhaust contains tiny particles that
can act as condensation nuclei that aid in the formation of contrails,
which are nothing more than a skinny man-made cirrus cloud. The
time that they linger in the upper atmosphere is dependent on the
humidity of the surrounding air and the direction and strength of
winds that will dissipate the contrail."
Question
4: Well, honey, snow is white because snow crystals have many
surfaces from which light is reflected. Because of all the planes,
the light reflects in all directions, bouncing around within the
snow bank or clump, and finally back out to our eye. Since the surfaces
reflect all wavelengths, or colors, of light equally, we see the
light as white.
Extra Credit:
The triple point is that temperature at which a substance can
coexist as a solid, a liquid, and a gas. At 0.01ºC, water can
be ice, liquid water, or water vapor.
Source: Caltech's
Kenneth G. Libbrecht's "Snowflake"
website. Be sure to check out this celebration of snow and snow
flakes, from a scientific, artistic, and cultural point of view.
The photographs are really wonderful!
Question
5: We have ways of knowing which answer you chose.
Question
6: Water, in perfectly clean air conditions, doesn't really
like to stick together. In order for a droplet to form, there must
be a tiny particle of some kind, called condensation nuclei, of
which there are plenty in even clean air. The ocean puts lots of
salt particles into the air. These salt particles are hydroscopic
("water seeking") and are very good at clumping water
molecules together. The combination of condensation nuclei and humidity
make for lots of water droplets in the air near the ocean and creates
the thin white haze ubiquitous to seaside communities.
Who You Gonna Call?
Each month after the E-News goes out, we receive messages back. Sometimes
the messages are in response to a story we shared; other times they
are a request for help of some kind. We read all the emails, answer
those we can, and pass the rest on to the appropriate departments.
We think you
should know, though, that if you're interested in the fastest possible
reply, news@davisnet.com
may not be the best place to send your message. Questions about
how things work should be addressed to tech support directly at
support@davisnet.com.
For general information about the products, such as how much cable
comes with a station contact sales@davisnet.com.
To request a catalog, you’ll find links for catalog requests
on our web site at http://www.davisnet.com/contact/catalog.asp
Please continue
to send your comments, weather URLs, and story suggestions to news@davisnet.com.
We look forward to getting your comments and any responses you have
to the E-News. Member participation is what keeps the E-News alive
and kicking.
Well, that’s
it for this edition. You’ll be hearing from us again next month!
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Weather Monitor, Weather Wizard, WeatherLink, Weather Envoy, Weather
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