Davis | Weather E-news

JUNE 2009
In This Issue:

WEATHER IN ACTION
• Vantage Pro2 Helps Helicopters Land Safely on North Sea Oil Platform
• Day-in-the Life of a Busy Vantage Pro in Lawton, OK
• Way Up High Down Under

WEATHER 101
• Vintage E-News: Humbert and Humidity: Know Your Relatives!

TECH TIPS
• Setting Your Elevation: Just How High Are You?

MAILBAG
• Love and Typos
• Full Moon Fever

YOU'RE BRILLIANT!
• Quiz Question #1
• Quiz Question #2
• Quiz Question #3
• Quiz Question #4
• Quiz Question #5
• Answers to Quiz Questions

Who You Gonna Call?

Top: Climbing the tower is Martin van Gijn. ("You get used to it," says Martin.")
Above: Richard, the radioman on Platform Charly depends on his Vantage Pro2 to make sure helicopters land and take off safely.

Most Vantage Pro2s are landlubbers and enjoy watching the weather from a safe garden or rooftop. But we heard about two that lead a little more adventurous life.

They watch the weather from gas production platform P 15 Charly out in the cold North Sea, off the Netherlands. One Vantage Pro2 is on top of the microwave tower and the other is on the crane. Platform P 15 Charly is a natural gas storage facility called Peak Installation, owned by TAQA Energy BV, a global energy company. These clammy-palm photos were sent to us by Martin van Gijn, Senior Technician at TAQA Energy BV.

"We really need to know about the weather," Martin wrote, "because of the helicopters that take us to the platforms, and home again. The radio operator gives the latest weather report as they approach the platform. Wind and barometric pressure are very important."

The weather stations are so important to Platform P15 Charly's crew that they always keep a spare. If one of the stations should malfunction, they can have the backup setup and running in less than a hour.

We know many schools use Davis weather stations as part of their science education program. In the case of the 34 schools in Lawton, Oklahoma, one busy Vantage Pro, mounted on the roof of the Media Technology Center, which is right in the middle of Lawton, which is right in the middle of Tornado Alley in southwest Oklahoma, does it all. It uploads to the Lawton Public Schools web site that is accessed all day long by teachers, staff, administrators and Civil Defense volunteers. We got a glimpse into the daily life of a school Vantage Pro in the Lawton district office thanks to District Technology Coordinator Duane Del Vecchio.

Duane sent us some teacher comments and we've taken a few liberties (forgive us!) in piecing together a Day In the Life.

6:30 a.m.: Rise and Shine
A dad clicks onto the web site before waking his kids to see what the weather is looking like. He checks the forecast, the barometric pressure and the temperature before deciding just how hard to insist on jackets.

7:30 a.m.: District Office Open for Business
"Weather Freaks" (like Duane) check the console for a glimpse of the day. First stop: barometric trend. He also checks to make sure there are no weather warnings for any part of the town, making sure the weather is not threatening any of the 34 schools in Lawton.

8:45 a.m.: Greeting the Day at Pioneer Park Elementary
Teacher Shayla has her first grade students check the temperature on the LPS web site. They write it down in their weather log, then color in the classroom temperature graph based on what the temperature is. "The categories I use for my graph are cold, cool, warm, and hot," wrote Shayla. "It also has a thermometer on the page and I’ve shown this to my students so that they can see how it looks on a 'real' thermometer."

10:45 a.m.: Recess at Geronimo Road Elementary
Principal Harold clicks the web site and checks the wind chill. If it's below 30°F (-1°C), he'll order an indoor recess.

12:15 p.m.: Lunchtime at Adams Elementary
In unison, Lupe Ostruske's third graders ask, "Do I need my jacket?" Ms. Ostruske knows the answer because she just checked the web site.

2:25 p.m.: Science Class at Ridgecrest Elementary
Lori Anderson's fifth-grade class is working on their weather unit. They record barometric pressure and temperature from the web site then add their own observational data. They learn how to use both the high tech weather station and their own scientific abilities - just like all good meteorologists.

4:08 p.m.: Winding Down at the District Office
Duane takes a last look at the console before he heads home. (But as a card-carrying "Weather Freak," he knows he can check the web site again tonight before he heads off to rest up to do it all again tomorrow.)

Midnight: Vantage Pro goes to sleep - NOT! It's still sending updates, keeping all of Lawton well informed about their weather, 24/7.

Brett Vilnis of Boztek Solutions, one of our Australian distributors, really wanted to test a Vantage Pro2. What about on a power transmission tower? No problem!

"Just to show that a Davis weather station will work anywhere we installed a Davis based weather monitoring system 45 meters in the air on a power transmission tower." Brett wrote. "The unit is four meters from 330,000 volts at 1500 watts and still works! This is a trial project to monitor environmental condition and how they affect power transmission lines in NSW Australia. Data is sent back via the mobile phone network"

Even our Tech Support Team is impressed, Brett! They want to make sure we stress that mounting your weather station on a power tower is not recommended!

This article originally appeared way back in our September 2002 Weather Club E-News. We just liked it and wanted to read it again! Since many of you are new in the last six or so years, and some of you are a tad forgetful, we thought you'd like to see it again too.

Some of you are still unclear on the concept of relative humidity. You seem to get it confused with another relative, Uncle Humbert. Uncle Humbert, who gets flustered easily and tends to perspire even when the air conditioner is set at 50°F (10°C), does remind us of relative humidity, so we understand your confusion.

Just as Uncle Humbert's copious perspiration and cries of "Whoo-oo-eee, it is hot as Hades in here!" do not indicate the actual temperature in the room, relative humidity does not indicate the actual amount of water vapor in the air.

Instead, RH tells us how close the air is to being saturated. RH, which is what your weather station reports, is expressed as a percentage that indicates the amount of water vapor actually in the air compared to the amount of water vapor required for saturation at that particular pressure and temperature. Absolute humidity, on the other hand, is a measure of the actual water vapor density in a fixed volume of air - dew point is an indication of this.

Uncle Humbert, on a warm, muggy day is often heard to sigh, as he sits in the shade of his oak tree and mops his brow with a soggy handkerchief, "I don't mind the heat. I just can't take this goll-darned humidity."

He is explaining the difference, in human terms, between relative and absolute humidity. When we are warm, we perspire. The moisture evaporates into the air and cools the skin. If the RH is low, this evaporation happens very quickly and we perceive a lower air temperature. But when the RH is high and the air is approaching saturation, evaporation slows or halts and we sense higher air temperatures. Uncle Humbert is right. With his very effective perspiration system, he would be more comfortable sitting in the shade of a cactus on an even warmer day in the desert!

Relative humidity changes during the course of a day, but not because the amount of water vapor in the air changes much. It is the changing of air temperature that changes RH. As the air cools, RH increases. As it warms, RH decreases.

So when Uncle Humbert waddles over to your thermostat and thumbs it far to the left, he effectively lowers the RH! When the air conditioner cools the air, it increases its RH up to the point of saturation. The water vapor then condenses into liquid and drains out of the system. The cooled and dried air is then pumped into the house. In the winter, your heating system also dehumidifies the air. The cold arctic air outside has little water vapor. When this air is pulled into the house and heated, the vapor capacity of the air rises dramatically, and so the RH plummets. You end up with desert-dry conditions inside the house. Any perspiration evaporates very quickly, leading to the famous winter dry skin, scratchy throat, and dry mucus membranes.

So remember, while Uncle Humbert is a humid relative, he's not, we repeat, NOT, relative humidity

When you first set up your weather station console, you were asked to set your elevation so that your barometric pressure would be reported accurately. In your hurry to get your station up and running, you may have skipped over this or entered a guess.

(Quick review: Air has weight, and the combined weight of the column of air that extends from your head to the edge of the Earth's atmosphere exerts pressure on you, called atmospheric pressure. The higher you go, the less air is above you. So comparing our atmospheric pressure here at 16 feet above mean sea level to our friend Justin's in Colorado at 5,646 feet (1721 m) would be rather useless. Justin and we both have to compensate for this difference. This adjusted pressure is known as the barometric pressure. Your weather station measures atmospheric pressure and uses your elevation to translate this into barometric pressure.)

How do you know what your elevation is? You can check with a local resource, such as the library or a nearby airport, or an almanac or atlas. But what if you live on a hill quite a way from the nearest airport?

The internet has several options that can help you find a more accurate elevation. We like EarthTools. Just place the plus sign over your location and keep zooming in. You can also download Google Earth, or use Google Maps in the terrain view.

How accurate to you have to be? The rule of thumb is that the more accurate your elevation, the more accurate your barometric pressure. For the very best accuracy of your barometric pressure, you should try to be within 10 feet (3 m) of the exact elevation.

If you want to change your elevation on your Vantage Pro2, enter the Setup Mode by pressing and holding the DONE button and the - key. Press and release DONE to scroll through the screens until you get to the elevation screen. Use the +, -, <, and > keys to select each field and change it. (To change from feet to meters, or vice versa, while in the Elevation Screen, press 2ND then Units.) Press and hold DONE to return to the Current Weather Mode.

Nothing brightens our day like a love letter! Here's one we got from Bill Elkins.

"I have had my new weather station for about a month now and thought I should let you know how much I am enjoying my new station. I had [a competitor's station] and never thought I was getting what I wanted out of a $500 + weather station. I had problems with my anemometer working and receiving. Transmission distance was critical because I live in the country on a hill and the anemometer needed to be located 300 feet away to get away from the hill. I used their booster that worked somewhat but the wind speed was very slow reading. The Davis system is a JOY to work with but my wife thinks I spend to much time watching the display. I'm getting so much more information now and the distance I can receive from is actually farther than the manual says! I wish I had known about your system before I bought the other system. Thank you so much for such a great weather station that I'm really enjoying working with."

A note like Bill's softened the blow for this one from John Gould of Falmouth, Massachusetts, whose comments were seconded by Paul Reiter, amateur radio station WY71 Chromo, Colorado.

(By the way, if you click on Paul's web site, you'll see a beautiful picture of his radio tower featured on the cover of the British magazine Radcom. Look closely and you might find his Vantage Pro2 mounted on a post just to the left of the tower base.)

" I very much enjoy your Weather Club E-News," wrote John, kindly. "Thanks very much for publishing it. A small historical error made it in to the current edition, however. It states: 'Back in 1557, an American colonist named Thomas Tusser wrote: "Sweet April showers, do spring May flowers." '

"Unfortunately it was impossible for him to be an 'American colonist' in 1557. Bartholomew Gosnold did not explore the east coast until 1602, Jamestown wasn't established until 1607, and the Pilgrims did not land until 1620. Mr. Tusser was probably long dead by that time, never having left his native England. As to 'fellow colonists' - there could be none, of course. Anyway, keep up the good work! "

Okay, so we slept through high school history classes; we were saving our energy for sixth period Earth Science. Both John and Paul were paying attention (clearly, they still are!) and know there were no colonists here before 1620. Tusser never lived anywhere but his beloved England. He was a farmer and poet who gave us, "A fool and his money are soon parted," a proverb we have been known to quote liberally.

Eric Freeman and his friend Wendy Lou wanted to share this romantic shot of Eric's Vantage Pro 2.

"The shot was taken at my house in Hendersonville, North Carolina and features my Vantage Pro2 and a bright moon. It was taken around 10 p.m. on June 6. Not quite a full moon but just as bright."

What do you think of the E-Newsletter? How can we improve? How do you use your Davis weather products? Email us at news@davisnet.com..

Question 1: Could a helicopter crash out there in the North Sea be survivable?

Yes, as the 18 survivors of a helicopter accident at another oil platform in February will tell you. The chopper was ditched in the North Sea while ferrying workers to the platform; all crew and workers were quickly rescued from the cold waters. But don't count on it. The coast guards said the happy ending was "on the level of the Hudson River [crash landing] in the States." It is not clear what caused the accident but it certainly underscores the need for careful weather monitoring. Read the story in The Independent.

Question 2: In which layer of the atmosphere is that Vantage Pro2 in New South Wales? Too easy? Put the layers in order, from the bottom up.

Unless that tower is over six miles (10 kilometers) high, it's down here in the troposphere with the rest of us. Next comes the stratosphere, mesosphere, thermosphere, then exosphere.

Ha! Bet you said height! It is based on temperature. The troposphere ends at the tropopause, where the temperature stops decreasing with height. In the stratosphere, the temperature slowly increases, and then decrease again in the mesosphere. In the thermosphere, temperatures rise sharply. In the exosphere, gases are present in such small amounts temperature has to be measured in terms of each molecule's energy.

Question 3: What part of the above opening paragraph of our new thriller, The Gator Bait Murders, would most bother Bay Area meteorologist Jan Null? Why?

Jan could overlook the DEET and manure, hunting gators with a gun in Florida, and even a whining python, but he would be really irked by the "90°F (32°C) and 90%" humidity line!

Question 4: The top of Mt. Everest is undoubtedly the farthest point on earth above mean sea level. Yet there are those who make a case for it NOT to be the highest mountain on earth. Explain that!

The Earth is not a nice round ball. It actually bulges at the equator. So in order to determine the highest peak, you need to measure the distance from the center of the earth. In this case, Ecuador's inactive volcano Chimborazo takes the honors. So the argument goes.

Extra Credit: How did 19th century explorers use boiling water to determine elevation?

The Centigrade scale is based on the freezing point (0°C, 32°F) and boiling point (100°C, 212°F) of water -- at one atmosphere (generally the atmospheric pressure at sea level). A traveler could heat water, note the temperature at which it boils get a rough determination of elevation. For example, if water boiled at 208.4°F (98°C), you could guess that you were about 2,000 feet (610m) above sea level. Not terribly accurate, especially if your thermometer is also not very accurate, but there was no Google Earth in the 19th century!

Here's a calculator you can use to determine the boiling point of water at your home, using the pressure reading (inHg) from your weather station and your elevation. Now you'll have to find a very accurate thermometer and test it! (Open pot, water only, no noodles and chicken!) Click here to read an interesting article by Bob Graham about the way California explorer John Charles Frémont used meteorology in his surveys of California.

One More: True or False: The average sea level of the Atlantic is slightly lower than the Pacific.

Question 5: When the moon is full, it is at it brightest. When it's a first quarter moon, with half the disk of the moon illuminated, it is half as bright. Right?

No, not even close! It is less than 10% as bright! If the moon really were a flat disc as it appears in the sky, it would make sense that a first quarter moon would be half as bright as a full moon. But the moon is a bumpy, rocky, mountainous, pitted sphere. At first quarter, the sunlight is coming in at an angle, throwing shadows to the side of every rise and fall of the surface. When the moon is full, the sunlight is coming more directly from where we are looking (only during an eclipse is it truly direct) and we don't see any shadows. According to an article by Joe Rao on Space.com, the moon is not half as bright at as full moon until about 2.4 days from full.

Davis!
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, contact sales@davisnet.com. To request a catalog, see the links for catalog requests on our web site at www.davisnet.com/contact/catalog.asp.

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Well, that’s it for this edition. You’ll be hearing from us again next month!
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