Download Section 1 - Inland Seas Education Association

VII. WEATHER STATION
INTRODUCTION
Weather is all around us, and yet few of us really
understand the weather and its changes. For sailors, a
“weather eye” is not only prudent, but also incredibly
interesting. Observations of wind direction, wind
speed, visibility, barometric pressure, cloud type and
cloud cover, wave height, and air temperature can be
combined to form a picture of the present weather and
how it might be changing.
Wind direction influences what course can be sailed and
it may also affect water temperature by pushing warm
surface water on or off shore. Wind speed influences
wave height and air temperature. The trend in the
barometer may affect the percent cloud cover. Major changes in barometric pressure, along with strong
winds, can lead to the development of a seiche (lake wide wave) and the rising and falling of lake levels.
Throughout the day, the types of clouds observed may follow a pattern that indicates a warm front
moving in, or a cold front.
At this station, instructors will help students make and record weather observations.
LEARNING OBJECTIVES
Students will be able to:
1. Determine the visibility, cloud types, percent cloud cover, precipitation, wind direction, and wave
height.
2. Measure the wind speed, air temperature, surface water temperature, and water clarity, and
identify the devices used to make these measurements.
3. Recognize the impact invasive zebra and quagga mussels have on water clarity.
4. Define a watershed as the land that water flows across or under that drains into a common water
body.
TOOLS
Cloud diagram
Cloud pictures
Secchi disk
Thermometer
Visibility chart
Wind gauge
TEACHING THE STATION
Most instruments needed for the Weather Station are kept in one-gallon plastic “weather buckets.” Some
observations should be taken while underway (visibility, cloud types, percent cloud cover, precipitation,
wave height, and air temperature), while others require the vessel to be stopped (wind direction, wind
speed, surface water temperature, and water clarity). Lead instructors will inform instructors when to
begin their Weather Station. Before taking any measurements, discuss the importance of recording
weather (to describe conditions that exist when samples are taken and to predict weather to help the
captain decide if and where to sail). Do not lower any equipment over the side of the vessel until the lead
instructor rings the ship’s bell or makes an announcement. This means the ship is anchored securely and
it is safe to lower equipment. Instructions for each observation are listed below in an order that is often
followed on the ship (consistent with the order in the student log books).
Visibility
The visibility charts show the distance in statute miles to several locations that may be visible from the
ship during the Schoolship Program. Have the students identify each location that is visible from the ship,
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starting with the closest. Locate the furthest point of visible land and note the distance on the navigation
chart. Have students record this distance in their log books as the visibility in statute miles. Visibility
charts can be found on pages 76 and 77 of this manual.
Cloud Type(s) & Percent Cloud Cover
Use the cloud charts to help the students determine the cloud type(s). Start by a general distinction
between “flat” or stratus clouds and “puffy” or cumulus clouds. Then have the students further identify
the cloud type using the charts. Record the cloud type(s) present and the percent of the total sky that is
covered by clouds. Note the changing nature of clouds. The cloud chart can be found on pages 78-80 of
this manual.
Precipitation
Note any precipitation at the time of observation (rain, snow, mixed, hail, or none).
Wind Direction & Wind Speed
Have the students determine the direction of the wind. This can be obtained using the flag and the ship’s
compass (or visibility chart) to determine what direction the wind is coming FROM. Then quickly show
the students how to hold the wind gauge, and allow them to make the final wind speed measurements.
1. Hold instrument near the bottom, facing into the wind so the scale is visible to the user (make sure
there are no obstructions in front of the student that might block the wind).
2. If the wind is less than 10 mph, students read the wind speed on the low scale (left side).
3. If the wind is over 10 mph, hold wind gauge in left hand with index finger over the top opening.
Read wind speed on the high scale (right side).
4. If reading is erratic, try holding the wind gauge higher, out over the side of the ship, or move students
up to the foredeck or away from masts, shrouds, or other sources of turbulence.
5. Record wind speed in mph.
Wave Height
This measurement is an estimate of wave height from crest to trough (see diagram below). The weather
service uses wave height increments of 0-1 ft., 1-2 ft., etc. Have the students discuss what factors can
influence wave height (wind speed, wind direction, depth, and substrate).
CREST
TROUGH
Air Temperature & Surface Water Temperature
Instruct students on the proper use and reading of the thermometer:
1. Hold the thermometer near the top, not at the bulb (otherwise, they are taking their own temperature).
2. Keep out of the sun and away from radiating surfaces.
3. Read with the eye at a right angle (90 ) to the top of the alcohol column.
4. Record air temperature first, and then water temperature.
5. Sample surface water with the bucket (when vessel is anchored). Place the thermometer in the water
for a minute or two before reading the temperature. Keep the thermometer bulb immersed in water
when reading the water temperature.
Temperature Conversion Formula:
ºC = (ºF - 32)/1.8
ºF = (ºC x 1.8) + 32
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A shorthand way to convert from degrees Fahrenheit to degrees Celsius is to use the formula shown
above, but round off the two conversion values to 2 and 30 for ease of calculation. For example, if
the water temperature is 50º F, the temperature in degrees Celsius is: ºC = (50º F -30)/2 =10ºC. To
convert from Celsius to Fahrenheit, go the other way: ºF = (10ºC x 2) + 30 = 50º F.
Water Clarity
Instruct students on the proper use and reading of the Secchi disk depth:
1. Have a student unwind the line around the Secchi disk. Another student should hold the bitter end of
the line.
2. Have a student lower the disk into the water, with all students keeping track of the calibrations along
the line (each mark is a meter) until the disk disappears. Note this depth.
3. Raise the disk until it is visible again. Average the two depths to obtain the Secchi disk depth.
4. Use the shady side of the boat when possible.
5. Discuss what causes turbidity (plankton, dissolved and suspended materials) during this activity and
the role that zebra mussels have played in increasing water clarity in the Great Lakes. The photic zone
(the upper region of the lake where there is enough light for photosynthesis) is 2-3 times the depth of
the Secchi disk measurement. Phytoplankton (plant plankton that rely on this available light) are the
primary producers responsible for much of the dissolved oxygen in the lake. This provides a
connection between the Secchi disk depth, the plankton sample, and the water chemistry analysis.
Stewardship Component
It is important for students to be introduced to the concept of a watershed in order to understand their role
as stewards within the Great Lakes watershed. A watershed should be explained as an area that water
flows over and into a common water body, i.e. Suttons Bay or Grand Traverse Bay.
1. Point out the high points that can be seen from the deck of the boat and ask students to decide how
rain will run down the hill; which side?
2. Reinforce that all bodies of water have a watershed and the size of the watershed depends on the size
of the body of water.
3. In much the same way that rain within the watershed makes its way into the bay, so does all the
human activities on-land within the watershed.
4. Pull out the lake Michigan/Great Lakes watershed diagram to show them a watershed boundary.
Teaching Tip:
It is very important to allow students to use all of the weather instruments while gathering data. This
interaction with the equipment will enhance their experience and keep them better engaged. Try to
get the students to think in terms of making predictions about the weather for the next day.
DATA COLLECTION
The weather page of the student log book (shown below) has blank spaces for all the observations
described above. Encourage students to complete this portion of the log book while in the weather station,
including the temperature conversions. The surface water temperature and Secchi disk depth are also
listed on the Weather Station page of the student log book, although they will be discussed again during
the Water Chemistry Station.
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VOCABULARY
Anemometer: instrument used for measuring wind speed.
Barometer: instrument used to measure air pressure.
Secchi disk: instrument used to measure water clarity.
BACKGROUND INFORMATION
Wind Gauge
Our wind gauges work by a vacuum created by the wind moving over a hole at the top of the gauge. This
vacuum causes the little ball inside the instrument to be drawn upward. Our wind gauges read in mph.
Inland Seas' anemometer (on top of fore topmast) reads in knots.
Anemometer
This instrument is used for measuring wind speed. A common type of anemometer consists of three or
four cups on spokes that are turned by the force of the wind. The instrument is used to calculate wind
speed by the number of times the cups turn in a fixed time. On Inland Seas, the wind speed can be read
off a small box on the port side of the pilothouse. Note the direction on the anemometer display in the
pilot house is the direction relative to the direction of the ship – do not simply read the direction off the
display.
Barometer
Although a barometer is not used during the weather station, it is an important instrument and should be
mentioned (time permitting). A barometer is an instrument used to measure air pressure. We then refer to
this pressure reading as the barometric pressure. The barometric pressure is used by weather observers as
a guide to weather changes. High pressure is generally associated with warmer, sunny conditions and low
pressure is generally associated with cooler, rainy conditions. If the barometric pressure is rising, we can
expect a change for better weather, whereas if it is falling, we can expect a change for the worse.
There are two types of barometers: mercury barometers and aneroid barometers. The mercury barometer
is simply a column of mercury enclosed in a glass tube and reservoir. A decrease in air pressure causes
the mercury to fall within the tube. An increase in air pressure causes the column of mercury to rise. The
movement of this column is read as inches of mercury. The standard for this scale is 29.92 inches of
mercury – this means air will support a column of mercury 29.92 inches tall.
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The aneroid barometer is much more common. These are the types of barometers used during the
Schoolship Program. They have an airtight container in which there is a partial vacuum. Changes in the
air pressure cause the box to expand or contract. A pointer attached to the box moves over a dial and
indicates this change in pressure. Although the aneroid barometers do not rely on mercury for their
reading of barometric pressure, the gauge is standardized to read the pressure in traditional inches of
mercury. There is a marine aneroid barometer on Inland Seas, located just below the ship's clock in the
pilot house. On Manitou, the aneroid barometer is located in the main cabin on the wall facing the
companionway ladder.
Secchi Disk
A secchi disk is a weighted disk that is divided into black and white quadrants. It is used to measure the
transparency of the water. This method was first used by Father Pietro Angelo Secchi, an Italian
astronomer in the spring of 1865 on the Mediterranean Sea.
REFERENCES
Donn, W. L. 1975. Meteorology. McGraw-Hill, New York.
Eichenlaub V. 1979. Weather and Climate of the Great Lakes Region. University of Notre Dame Press,
South Bend, IN.
Lehr, P.E., R.W. Burnett, and S.Z. Herbert. Weather (Golden Guide). Golden Press, New York, NY.
Leszek Bledzki (Lead Author);Nidhi Nagabhatla (Topic Editor) "Secchi disk". In: Encyclopedia of Earth. Eds.
Cutler J. Cleveland (Washington, D.C.: Environmental Information Coalition, National Council for Science and the
Environment). [First published in the Encyclopedia of Earth October 15, 2009; Last revised Date October 5, 2010;
Retrieved December 21, 2011 <http://www.eoearth.org/article/Secchi_disk>
Schaefer, B.J. and J.A. Day. 1981. A Field Guide to the Atmosphere. Houghton Mifflin Co, Boston, MA.
Williams, J. 1992. The Weather Book. Vintage Books, New York, NY.
Internet Sites of Interest
http://www.ndbc.noaa.gov/station_page.php?station=45002 (access to real time wind and wave data from
the weather buoy in northern Lake Michigan)
http://www.wxdude.com
http://www.intellicast.com (forecast maps, radar summaries of cities and regions across the US)
DIAGRAMS & RELEVANT DATA
Suttons Bay Visibility Chart (page 76)
Grand Traverse Bay Visibility Chart (page 77)
Cloud Charts (page 78-80)
Secchi Disk Depth 1989-2012 (page 81)
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