Weather Measure
Wednesday, February 28, 2007
Weather Station Handbook
 
We recently scanned and posted our copy of the Weather Station Handbook--An Interagency Guide for Wildland Managers, published by the National Wildfire Coordinating Group in 1990. While some sections are outdated, it contains a lot of still useful information about setting up and maintaining a weather station.

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Thursday, February 22, 2007
Finding your Latitude and Altitude for Barometer Corrections
 
Online Resources

The National Map Viewer offers free access to the US Geoglogical Survey's topographic base map data. US Topo maps are available for free web download from the USGS Store.

Google Earth is free for personal use. You can find your latitude, longitude (not needed for barometer corrections), and ground elevation by entering the address or place name, then zooming in on detailed satellite photos and maps.

Paper Maps

You can get your latitude coordinate and ground elevation from many local maps of your area. The most detailed is usually the US Geological Survey 7.5 minute, 1:24,000-scale quadrangle series topo maps, available from local outfitter stores, some bookstores, your local BLM or Forest Service office, and from the USGS Online Store. Some public libraries may have topo maps available.

To find your ground elevation, look at the wavy never-ending lines on either side of your location. They are lines of constant elevation called contour lines. Find some with numbers inserted in them. The number is the elevation of that line. In the United States they are mostly in feet, the contour interval between them may be 10 feet or more, and every fifth perhaps every 50‑foot contour line may be in bold. You may interpolate your ground elevation between the elevations of the contour lines on either side of your location.

Introduction to Topographic Maps, a tutorial from the GeoSpatial Training and Analysis Cooperative, offers detailed information on understanding and using topo maps.

GPS

Commercial GPS (Global Positioning System) devices have typical latitude errors of 10–15 meters which is good enough for the relatively small gravity correction, however the GPS typical elevation errors are much too large for barometry where errors ideally should not exceed one foot.

Read more . . .

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Wednesday, February 14, 2007
Rejoining a Separated Thermometer Column
 
A separated column is one in which portions of the mercury or alcohol become separated from the main column. Column separation is common in thermometers, particularly after transit or other situations producing excessive jarring. In alcohol thermometers, column separations may appear as small bubbles. They can be caused by a distillation tendency during warm weather; alcohol vapor condenses in the upper portion of the bore. Column separation may entrap the minimum thermometer index rod.

Separated columns can usually be reunited by one of the following methods: tapping, applying centrifugal force, and heating. We explain the procedures here.

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