Instruments

Instruments
This page describes how to use, where to find and how to maintain the various operational instruments at the Observatory. A large selection of inactive, historical instruments (not described here) are on display in the history room on the ground floor of the Observatory tower.

Temperature	Wind	Precipitation	Pressure	Sunshine, etc.
Psychrometer	Wind Gust Chart Recorder	Standard Eight-Inch Rain Gage	Mercury Barometer	Sunshine Recorder
Maximum & Minimum Thermometers	Wind Speed Chart Recorder	Weighing Eight-Inch Rain Gage	Microbarograph	Visibility
Hygrothermograph	Aerovane Wind Recorder	Ombroscope	Four-day Barograph	ASOS
Digital Thermometer (Nimbus)	Maximum, Inc. Wind Recorder (Merlin)	Digital Rain Gage Display (Nimbus)	Digital Barometer (Nimbus)
	Maximum, Inc. Gust Recorder (Max #1)	Snow Board	NWS Aneroid Barometer
	Young Wind Display

Charts, etc.

Temperature	Wind	Precipitation	Pressure	Sunshine, etc.
Hygrothermograph Chart	Wind Gust Chart	Weighing Gage Chart	Microbarograph Chart	Sun Card
	Wind Speed Chart	Ombroscope Chart	Four-Day Barograph Chart	Dew Point Calculator
	Aerovane Chart

Psychrometer

Use:
Dry and wet bulb temperature measurement; used to derive calculated dew point, relative humidity, and vapor pressure.

Location:
Enclosure Hazen shelter, hand-held, or sling psychrometer. Enclosure shelter must be kept closed at all times except for a few minutes during readings. Hand-held psychrometer can be placed in a shaded area on the iron fence around the Observatory or on the exterior of the shelter and left for several minutes to equilibrate. A sling psychrometer (if available) can also be used in a shaded area near the enclosure shelter.

Procedure:
1) Completely saturate wick with clean water, turn on fan for ventilation, and allow wet bulb to reach a stable temperature. This will take from one to ten minutes depending on conditions, but the shortest possible time should be allowed, as the wet bulb reading will be invalid if wick begins to dry. In below freezing temperatures, note whether wick is wet or frozen. If freezing occurs, wet bulb will require at least five minutes to stabilize.

2) Read the dry and wet bulb temperatures to the nearest tenth of a degree F from scale on glass, while viewing thermometer with eye at the level of the mercury. Readings to be recorded are the lowest temperatures noted during the observing period. Turn off fan and close shelter.

3) In the office, use the round psychrometric calculator to convert dry and wet bulb temperatures to dew point temperature and relative humidity.

4) Vapor pressure is obtained from the calculated dew point temperature with a table in the office.

Maintenance:
Replace cotton wick around wet bulb twice each year. Wick must fit tightly around entire bulb and be attached at top and bottom with thread. Replace wick carefully, as the narrow section of the mercury thermometer is fragile. Occasionally clean the glass surfaces as necessary.

Maximum & Minimum Thermometers

Use:
Record official maximum and minimum temperatures for previous 24 hour period.

Location:
Enclosure Hazen shelter

Procedure:
1) Maximum thermometer (mercury) is held in horizontal position by metal latch at all times except when reading.

2) Read maximum thermometer by releasing latch and turning to a vertical position with the bulb at the bottom. Read temperature to nearest tenth of a degree F from scale on glass, while viewing thermometer with eye at the level of the mercury.

3) Reset maximum thermometer by spinning rapidly several times. Check that mercury level has been reset to the current temperature.

4) Shrinkage of the mercury column is accounted for by adding a correction to the maximum temperature. The correction (in deg F) is the product of the total drop in temperature from the maximum to the morning minimum multiplied by 0.0138 (representing the amount of column shrinkage per degree F of temperature change). The corrected maximum temperature is derived with this formula:

Tmax(corrected) = Tmax(obs) + 0.0138 * [Tmax(obs) – Tmin(obs)].

If the maximum temperature was observed shortly after it occurred, this observation is used instead of the corrected maximum.

5) Minimum thermometer (alcohol) is read in its latched horizontal position before turning on the ventilation fan (to avoid any vibration from the fan affecting the reading). Read minimum temperature at the right-most end of the floating blue index inside the thermometer to the nearest tenth of a degree F from the scale on the glass.

6) Reset minimum thermometer by releasing its latch and turning it upside down until the blue index drops to the top of the alcohol column. Restore thermometer to a horizontal position and replace latch so that the bulb end is slightly higher than the top end.

Maintenance:
Little is required other than an occasional cleaning of the glass surfaces.

Hygrothermograph

Use:
Continuous chart recording of temperature and relative humidity for 24-hour period ending at 8 AM EST to derive hourly temperature and six-hourly relative humidity.

Location:
Enclosure Hazen shelter

Procedure:
1) To replace the chart, raise cover, lift pens from chart with lever, and remove drum from clock mechanism. Replace chart and elastic bands, making sure elastic bands will not interfere with chart recording and that chart is properly positioned on drum (with paper touching the bottom of the cylinder).

2) Wind clock when necessary (every few days), turning winding mechanism no more than seven or eight times. Stop when spring begins to feel tight.

3) Replace drum on clock mechanism and make sure pens make contact with paper at the current time. Adjust pens up or down as necessary, using dials at right to keep recorded values close to observed values. Close cover.

4) Hourly temperatures are obtained from the chart as follows. Write observed hourly temperatures from previous day and current day on chart. Note the time of the highest temperature on the chart. Mark the chart with the previous day’s observed maximum temperature and the difference between the observed maximum and the chart maximum to the nearest tenth of a deg F. Mark the morning minimum temperature and the difference from the chart minimum temperature. At each hour for which no observations were taken derive a smoothly-varying correction between the previous day’s maximum and the morning minimum (to the nearest tenth of a deg F). Add this correction to the chart temperature at each hour (to the nearest tenth deg F), and write the resulting temperature for each hour on the chart (rounded to the nearest deg F).

5) Six hourly relative humidity is obtained from the chart as follows. Write the observed relative humidity from the previous day (usually 10 AM and 1 PM) and the current day (7 AM). Calculate corrections between the observed RH and the chart RH to the nearest percent. Apply a smoothly-varying correction for the intervening six-hourly intervals (7 PM and 1 AM). Add the correction to the chart RH and write value on the chart to the nearest percent.

Maintenance:
This instrument requires periodic cleaning to remove dirt or pollen that collects on the surfaces. The hair element is very sensitive and should never be over-tightened or touched with fingers. Relative humidity readings will be inaccurate if hairs begin to separate from the hair element, which should be replaced if such damage occurs.

Digital Thermometer (Nimbus)
Use:
Continuous digital readout of unofficial current temperature as observed by Nimbus temperature sensor. This unit replaced the Maximum/Minimum Temperature System (MMTS) that was in use at BHO from 1987-2001.

Location:
Digital display in second floor tower office, on top of desk shelf; sensor in enclosure Hazen shelter.

Procedure:
1) Display provides readout of current temperature. In dry weather conditions, discharge static electricity from your hand by touching something metal before touching the Nimbus display, since this can adversely affect this unit's memory.

2) Press ‘Read’ to alternately display maximum and minimum temperature since last reset

3) Press and hold ‘Clear’ for several seconds to reset maximum and minimum temperature memory.

Maintenance:
Little maintenance is required if unit remains in good working order. The long underground wire from the tower to the enclosure makes this unit vulnerable to lightning. Display unit should be grounded (by flipping toggle switch on wind console near Aerovane recorder) during any threat of thunderstorms to prevent electrical damage to the display.

Mercury Barometer

Use:
Observation of station pressure at 7 AM EST and occasionally at other times. This is also used to obtain the corrections for the microbarograph and four-day barograph.

Location:
Second floor tower office in the wooden and glass case. The largest (second from left) Hicks barometer (No. 872) remains in daily use since first being installed in December 1887 and first being used operationally on January 1, 1888. The other mercury barometers (No. 818, second from right, dating from October 1885; and No. 1019, at left, dating from November 1892) are no longer actively used. A modern mercury barometer (at right) is also on display in this case.

Procedure:
1) Read and record temperature on mercury thermometer mounted at the front of the barometer.

2) At the base of the instrument, set the mercury level in the cistern to the reference level to ensure that the station pressure is measured at the identical height above sea level each day. Turn on the light near the bottom of the case. Looking through the magnifying glass and using the metal knob at the bottom of the barometer, raise or lower the cistern as necessary so that the horizontal surface of the mercury meets the bottom of the suspended ivory index inside the cistern at right. Eye level must be at the same level as the mercury surface in the cistern. Adjust the cistern until the mercury and ivory index meet. When properly set, reflected light from the white surface on the back of the case will show through a small space between the mercury surface and the ivory index as shown on the drawing mounted on the back of the barometer case. Turn off the lower light to avoid heating the mercury.

3) With the mercury column set to its reference level, read the barometric pressure at the top of the mercury column to the nearest tenth of a millibar. First, turn the dial at right to raise or lower the movable central scale so that the bottom horizontal level of the scale just meets the top of the meniscus of the mercury column.

4) Read the station pressure to the nearest millibar on the fixed scale at right as the point that is at or below the zero line of the movable central scale. This central scale has 11 etched lines that correspond to the numbers 0 through 10. Without moving the central scale, find which of these etched lines exactly meets an etched line on the fixed scale at right and note the number of that line on the left scale. This number, divided by ten, is the tenths digit for the station pressure instrument reading.

5) Obtain the final station pressure by applying two corrections to this measured pressure. First, subtract a constant instrument correction of 0.2 mb. This correction accounts for the difference between reading the pressure at the top of the meniscus and the desired pressure reading, which is the value averaged across the meniscus.

6) Second, use the instrument-corrected pressure and the temperature of the mercury observed earlier to obtain the correction for temperature and gravity from the chart in the office desk. A straight edge is placed across this chart from the observed pressure on the left scale to the temperature on the right scale. The correction is found on the chart where the straight edge crosses the center scale on the chart. Subtract the combined temperature and gravity correction from the instrument-corrected pressure to obtain the final station pressure to the nearest tenth of a millibar. Convert to inches by multiplying by 0.02953, and record pressure to the nearest thousandth of an inch. The instrument is accurate to 0.003 in. The temperature corrections in the chart were derived from published Smithsonian tables.

7) Convert the station pressure to sea-level pressure by adding the value found on chart in the office desk for sea-level correction. This adjustment (in mb) will always be positive and is determined from the station pressure and the 12-hour mean outdoor temperature (average of 7 PM the previous day and 7 AM on the present day), which is taken to represent the average temperature for the layer between the surface and sea-level at the time of observation.

Maintenance:
Historically, dirt and dust that collects on the surface of the mercury in the cistern over time would be carefully removed to facilitate reading the instrument. Also, on at least one occasion, this instrument (No. 872) has been calibrated to ensure proper operation at the Smithsonian Institution. Neither procedure has been performed in many years.

Microbarograph

Use:
Continuous daily chart recording of station pressure (in inches Hg), used to obtain daily 1900 EST station pressure and monthly maximum and minimum pressures.

Location:
Second floor tower office on shelf above the desk.

Procedure:
1) Replace chart by lifting cover, raising pen with lever, and removing cylinder. Place new chart so that paper sits on the bottom of the cylinder and replace elastic bands.

2) Replace cylinder on clock mechanism and make sure pen makes contact with the chart at the current time. Adjust pen as necessary to keep pressure close to observed values. Close cover.

3) Wind clock when necessary (every few days), turning winding mechanism no more than seven or eight times. Stop when spring begins to feel tight. Add a small amount of purple ink to pen as necessary.

4) Mark the used chart with observed 0700 EST station pressures for the previous day and current day (on and off times for the chart. Determine pressure corrections at these times (to the nearest 0.001 inch) as the difference between the observed and the chart pressure. The chart correction for 1900 EST is found by averaging the two 0700 EST corrections. Read the chart pressure at 1900 EST (to the nearest 0.001 inch), add the correction for that time, and write corrected 1900 EST pressure on the chart.

Maintenance:
Little maintenance required as long as clock remains in working order.

Four-day Barograph
Four Day Barograph

Use:
Continuous four-day chart recording of station pressure (in mb).

Location:
Second floor tower office on top of the wind console.

Procedure:
1) Before changing the chart, read the mercury barometer to obtain the current station pressure for correcting the barograph.

2) Replace chart every four days at 10 AM or 11 AM by raising pen with lever, and removing cylinder. Place new chart so that paper sits on the bottom of the cylinder and replace elastic bands.

3) Replace cylinder on clock mechanism and make sure pen makes contact with the chart at the current time. Adjust pen as necessary to keep pressure close to observed values. Cover for this barograph remains open.

4) Wind clock whenever chart is changed, turning winding mechanism eight to ten times. Stop when spring begins to feel tight. Add a small amount of purple ink to pen when chart is changed.

5) Mark chart with observed pressures (to the nearest 0.1 mb) for 0700E and 1900E and chart corrections (the difference between the observed pressure and what is read on the chart).

Maintenance:
Little maintenance required as long as clock remains in working order.

Digital Barometer (Nimbus)
Nimbus boxes

Use:
Electronically-stored hourly recording of station pressure and extremes. This is also used to obtain 3-hour pressure trends.

Location:
Second floor tower office on shelf above main desk.

Procedure:
1) In normal mode, unit displays current station pressure to 0.01 inch.

2) Switch unit to “Memory”, then press the “Read” button multiple times to display pressure for previous hours.

3) Press button at left to view high and low extremes since last reset.

Maintenance:
Replace batteries when unit indicates low power level with an “L” in the display.

Digital Rain Gage Display (Nimbus)
Use:
Electronically-stored unofficial recording of hourly precipitation and storm total.

Location:
Display is located in second floor tower office on main desk and is connected to the small, plastic Rainwise tipping rain gage in northeast corner of the outdoor enclosure.

Procedure:
1) In normal mode, unit displays total precipitation to 0.01 inch since last reset. When precipitation has occurred, the 24-hour total should be recorded and display is reset to 0.00 at 0700 EST.

2) Switch unit to “Memory”, then press the “Read” button multiple times to display precipitation for previous hours.

3) Simultaneously press and hold “Read” and “Clear” buttons at left for several seconds to reset display of 24-hour total.

Maintenance:
Replace batteries when unit indicates lower power level with an “L” in the display.

NWS Aneroid Barometer

Use:
Observation of current station pressure (in mb).

Location:
Second floor tower office mounted within wind console below 420C chart recorder.

Procedure:
1) Before reading aneroid barometer, lightly tap the glass or metal frame and allow needle to settle.

2) Read pressure from numbers on dial directly below needle, interpolating between the lines to the nearest 0.1 mb.

3) Ignore tha paper label taped to the metal frame to the right of the barometer that reads 'Add 1.4 mb for sea level pressure'. This instrument was formerly in use at a station close to sea-level and this adjustment is not appropriate for the Blue Hill summit location.

Maintenance:
Little maintenance required as long as the instrument remains in working order.

Standard Eight-Inch Rain Gage
8-inch Rain Gage

Use:
Official 24-hour daily precipitation measurement.

Location:
Southeast corner of outdoor enclosure. It is surrounded by a metal Nipher wind shield, with top of gage and shield always at a uniform height of 3.5 feet above the ground.

Procedure:
1) During warm season operation (generally May to November), the outer eight-inch can, the 1.25 inch inner metal tube, and the metal funnel are used. During cold season operation (generally December to April) the eight-inch can is used alone with a round wooden block under the can to keep the top of the can at the same level as it is during summer when the funnel is used.

2) In the warm months, replace small inner tube only and bring indoors for measurement. Place spare funnel over the small tube and insert measurement stick into tube with zero end at bottom. Allow stick to sit for one or two minutes before removing stick to read precipitation to the nearest 0.01 of an inch.

3) In cold months, replace entire 8-inch can and bring indoors for measurement. If wet snow has accumulated on top of the can, drop approximately half of this snow into the can and discard the rest. If necessary, melt all snow and ice in the can before measuring. Pour liquid into one of the dry, 1.25 inch inner metal tubes covered with a funnel and measure with the stick as above.

4) If more than two inches of precipitation has fallen when the inner tube is in use, the excess will have spilled over from the top of the inner tube into the larger outer can and both must be replaced and brought inside for measurement.

Maintenance:
Little maintenance is required except for occasionally ensuring that none of the metal cans or tubes is leaking.

Weighing Eight-Inch Rain Gage
Use:
Continuous chart recording of precipitation for obtaining rainfall amounts hourly and for other time periods. Chart records the weight of water collected in a bucket suspended on spring mechanism, which is calibrated to indicate rainfall amount in inches. Note that this instrument is currently out of calibration.

Location:
Northeast corner of outdoor enclosure mounted on concrete pedestal. Top of gage is at a height of five feet above the ground.

Procedure:
1) The chart is designed to accommodate up to six inches of precipitation, so chart typically remains in use for several weeks. Generally the pen ascends the chart as precipitation is collected. The instrument is designed for the pen to reverse direction and descend the chart when the top is reached, though this capability is used only rarely during extreme rainfall events.

2) Replace chart as needed or usually at the end of the month so that data can be used to prepare hourly and other interval rainfall amounts. Wind clock and add ink to pen as necessary. When the chart is changed, the casing is opened and the contents of the bucket are emptied.

3) In warm months, if the gage contains precipitation for a single event, the bucket can be brought indoors and the precipitation measured as for the standard rain gage by pouring the water into one of the 1.25 inch metal tubes. This is unofficial, but provides a comparison for the standard gage.

4) In winter months, precipitation is generally left in the bucket until the chart is changed. Antifreeze is added to the water in the inner bucket to prevent freezing. Clearly this can not be recorded manually as precipitation with a stick measurement. If snow does collect on the opening of the gage, drop half into the gage and discard the other half.

5) Since the required data are the relative changes in rainfall over time, the placement of the pen at the start of a precipitation event is arbitrary. Thus, a small stone is typically placed in the inner bucket to artificially raise the pen above previous records of precipitation on the chart to prevent overwriting.

Maintenance:
The housing for this instrument has traditionally been heated in winter to prevent snow buildup on the opening, though this is not done at present. This instrument must be kept calibrated so that the chart records the same amount of precipitation that collects in the bucket. At present, this gage is out of calibration, and this must be considered when using these recordings until proper operation is restored.

Snow Board
Snow Boards

Use:
Manual measurement of snow accumulation on the ground.

Location:
East end of outdoor enclosure next to fence. Secondary board is located in northeast corner of enclosure.

Procedure:
1) Standard modern practice is to measure snow depth on the board (with one of the black precipitation sticks) and to clear the board of snow every six hours from 0700 EST. Generally this is only done once per day at 0700E, though a six-hour measurement can be taken at 1300 EST, 1900 EST, and 0100 EST if an observer is present.

2) Snow accumulation (to the nearest 0.1 inch) is taken as the average of several measurements over the board.

3) Snow depth on the ground is observed (to the nearest inch) daily at 0700 EST. This is generally obtained from a yard stick kept in an undisturbed location inside the enclosure. Under very windy conditions, or when snow has melted unevenly, snow depth is determined from an average of measurements in the enclosure, from the clearing northeast of the enclosure, and even from the nearby surrounding woods. The recorded snow depth should represent an average for the entire summit area except around the Observatory itself, where the wind typically prevents significant accumulation.

Maintenance:
None other than shoveling board free of all snow at 0700E as necessary.

Ombroscope

Use:
Chart recording for time-of-occurrence of precipitation (beginning and ending times), and determination of precipitation types. In continuous use since approximately 1905.

Location:
Small, silver-colored metallic housing close to ground at east end of outdoor enclosure between standard and weighing rain gages.

Procedure:
1) If precipitation has occurred in the past 24 hours, the chart must be changed whether precipitation is falling or not before a previous record of rainfall is obscured.

2) To replace the chart when no precipitation is occurring, open the cover and loosen the bolt at one end of the cylinder. Bring cylinder indoors to replace chart. Before replacing cylinder in housing, reset metal frame and gear mechanism to starting position. Place cylinder into the frame so that midnight on the chart lines up with the metal bar adjacent to the cylinder. Turn cylinder so that the current time on the chart lines up with the metal bar adjacent to the cylinder. Tighten the bolt sufficiently so that it will not loosen, but not so tight that the cylinder is unable to turn. Close cover, and mark chart through the small opening with a pen to indicate time of chart change.

3) To replace the chart while precipitation is occurring, the paper-covered cylinder must be wrapped in plastic at the same time the cover is opened to prevent any stray precipitation marks on the chart. Bring cylinder indoors and replace chart. Cover cylinder with dry plastic sheet to prevent paper from being stained by water during installation. Place cylinder in frame starting at midnight, turn cylinder to current time and tighten bolt. Carefully remove plastic covering as the cover is closed to ensure that paper is stained only by precipitation entering through the mall opening at the top of the housing. Mark chart with a pen through the opening to indicate time of chart change.

4) Charts are prepared for use by coating the printed (light green) ombroscope charts with dark blue magic marker. The original green printed ink is not water sensitive, but the magic marker ink coating is sufficient to leave a permanent stain when wet with water.

5) Wind the ombroscope with considerable care due to the age of the clock mechanism. Insert the long metal key into one of the winding holes until the end of the key is properly set around a bolt at the bottom of the winding hole. Turn the key clockwise once to test the tightness of the spring. If loose, turn several more times, but no more than four or five times. DO NOT OVERWIND THE SPRING. Repeat for the other winding hole. Always restore the sliding metal covers after winding to prevent stray material or insects from entering the cylinder and disrupting the clock mechanism.

Maintenance:
The ombroscope base must be kept level for proper operation and incorporates a small bubble level to facilitate this. The housing is currently mounted on several bricks to maintain the unit in a level position. Unit must remain close to the ground for continuity of the recording and to minimize wind effects. An electric wire is presently used to warm the housing during winter months in order to prevent snow from accumulating and blocking the small opening. The clock mechanism should be considered fragile and should never be over-wound (no more than four or five turns of the key in each opening). The gears that turn the paper-covered cylinder are also rather fragile and continual monitoring is required to ensure proper operation. The sliding metal covers for the winding holes should always be positioned to cover the openings at all times except when winding to prevent material from entering the cylinder and disrupting the clock mechanism.

Wind Gust Chart Recorder

Use:
Continuous chart recording of instantaneous wind gusts (in knots) for determination of daily peak gust. Also known as the NWS 420C recorder. This and the wind speed recorder are 1950s era instruments that have been in service at BHO since May 3, 1960. The gust recorder was replaced with a similar unit in 2002.

Location:
The chart recorder is located in the wind console in the second floor tower office. This record and the 420C dial readout on the console display wind information from the same three-cup (black-colored) anemometer mounted on one of the cross-arms on the main wind mast on the tower roof. This instrument was first put in service during the late 1950s.

Procedure:
1) Prepare wind gust information for the previous calendar day by cutting off that portion of the chart (at midnight along the curved line) and place chart on bench. Stamp chart with station ID and date.

2) Mark chart with the highest gust (or gusts) in knots and mph, direction of the gust (from Aerovane chart) and the time of occurrence. If a peak gust that was visually observed on the 420C dial exceeds the corresponding gust on the chart, the observed dial reading can be used as the official peak gust.

3) Install a new chart in the recorder when the end-of-roll mark (wide red line on right side of chart) appears. If chart is near the end of the roll be certain that sufficient paper remains to ensure uninterrupted recording until at least 0800 EST the following morning. When installing a new chart be certain that the end of the chart exiting the recorder hangs down far enough (about one foot) to allow the chart to fall away from the recorder. If the paper exiting the recorder is too short, the curved paper may get pulled back into the upper roller mechanism and jam the recorder.

4) As necessary (once or twice per month), remove the pen and the ink reservoir and add a small amount of red ink to the reservoir and replace.

Maintenance:
At present, no regular corrections are applied to the gusts recorded on the chart. The recorder has had a history of occasional problems with dried ink adversely impacting the mechanism and causing erroneously low gusts. Care must be taken to avoid spilling ink from the reservoir into the mechanism of the recorder. Dried ink clogging the pen has been known to suppress the flow of ink to the chart. The pen can be cleared by removing it from the recorder and either soaking it in hot water or, if necessary, blowing air through the pen.

Wind Speed Chart Recorder

Use:
Continuous chart recording of wind speed (in mph) for measurement of hourly and daily mean wind speeds and the fastest mile. This and the wind gust recorder are 1950s era instruments that have been in service at BHO since May 3, 1960.

Location:
The chart recorder is located in the wind console in the second floor tower office. It is connected to the NWS contacting anemometer (the highest three-cup instrument) mounted at the center of the main wind mast on the tower roof.

Procedure:
1) Prepare wind speed information for the previous calendar day by cutting off that portion of the chart (at midnight along the straight dark gray line) and place chart on bench. Stamp chart with station ID and date. It has become common practice to save chart paper by setting the pen at a time marked on the chart that is different from the actual time. Make sure the chart is cut off at the proper time (end of the calendar day in EST). If the actual chart time is different from the times on the chart, then hand write the correct times at each hour for clarity.

2) Determine hourly wind speeds by counting the intervals between the marks on the chart (each of which represents a fixed number (approximately 500) of anemometer rotations and one mile of wind moving past the station) for each hour on the chart. The last interval for each hour is counted in the hour in which most of the interval occurs. If a one-mile interval is evenly divided at the end of an hour, it is counted in the preceding hour. Write the total for each hour on the chart directly below the wind speed marks.

3) On the wind speed chart, write the hourly prevailing wind direction (obtained from the Aerovane) at the top of the chart in each hour.

4) Determine the fastest mile, which is the shortest interval between any two marks on the chart, by using the clear plastic ruler located on the bench. The numbered intervals on the ruler represent wind speeds, with the smallest intervals indicating the highest wind speeds. Locate the shortest one-mile interval on the chart by laying the ruler over the wind speed marks. The fastest mile is the interval with the highest speed for which the black lines on the ruler can be made to lie exactly over the center of the red lines on the chart. Fastest miles of 27 mph or greater are adjusted with a negative correction found in the table over the main desk, which ensures consistency with earlier wind measuring equipment.

5) Mark the chart with the total of the 24 hourly wind speeds, the average, and the prevailing wind direction for the day. The prevailing wind is the direction that occurs for the greatest number of hours. In the event of a tie between two directions, use the total number of hours for each direction including its adjacent directions (e.g. for a tie between WNW and NE count the hours for W-WNW-NW and NNE-NE-ENE).

6) Install a new chart in the recorder when the end-of-roll mark (wide red diagonal line ) appears. If chart is near the end of the roll be certain that sufficient paper remains to ensure uninterrupted recording until at least 0800 EST the following morning. When installing a new chart be certain that the end of the chart exiting the recorder hangs down far enough (about one foot) to allow the chart to fall away from the recorder. If the paper exiting the recorder is too short, the curved paper may get pulled back into the upper roller mechanism and jam the recorder.

7) As necessary (once or twice per month), remove the pens and the ink reservoir and add a small amount of red ink to the reservoir and replace.

Maintenance:
At present this recorder works very reliably with minimal maintenance. The pen should be cleaned from time to time to free it of dried ink at the writing end. A reservoir for anemometer oil at the top of the wind mast should be checked at three month intervals and oil added as necessary.

Aerovane Wind Recorder
Aerovane Wind Chart Recorder

Use:
Continuous chart recording of wind direction (in mph) and secondary, unofficial measurement of instantaneous wind gusts. Used primarily for determination of hourly and daily prevailing wind direction. A similar instrument and recorder were used for a short time to obtain wind gusts at BHO from December 1955 to June 1959. The present unit was installed in the late 1980s and has been in continuous use since then.

Location:
The chart recorder is located in the wind console in the second floor tower office and simultaneously records continuous wind direction and wind gust. It is connected to the Aerovane sensor at the top of the secondary wind mast on the tower roof.

Procedure:
1) Cut off the portion of the chart containing winds for the previous calendar day (at midnight along the curved line) and place chart on bench. Since the hours are hand numbered, and the actual chart time is different from the times marked on the chart, be certain the chart is cut off at the correct time. Stamp chart with station ID and date.

2) Mark hours on chart. The Aerovane recorder is currently used in “2x” mode, so that two hours of data are recorded on one printed hour on the chart.

3) Determine the hourly prevailing wind direction by visual inspection as one of the 16 primary or intermediate wind directions. For each hour interval, draw an imaginary line (parallel to the printed direction lines on the chart) that evenly divides the red wind direction recording on the chart. The prevailing wind is the direction that is closest to the imaginary line (Note that each of the 16 wind directions covers 22.5 degrees out of 360 degrees, so for example West extends from 258.75 to 281.25 degrees). Write the hourly prevailing wind direction on the wind speed chart recording.

4) Determine the speed and direction of the peak gust. Units may be in mph or knots depending on the chart used in the recorder. If the highest printed speed on the chart is 120, then mph are used; if the highest printed speed is 100, then knots are used.

5) Install a new chart in the recorder when the distance to the end of the roll (shown in feet on the right side of the chart) approaches 3 feet (about one day’s worth). If chart is near the end of the roll be certain that sufficient paper remains and that the paper is free to enter the recorder in order to ensure uninterrupted recording until at least 0800 EST the following morning.

6) As necessary (once or twice per month), remove the pens and the ink reservoirs and add a small amount of red ink to the reservoirs and replace. Do not over-ink.

Maintenance:
The wind direction pen will occasionally fail to automatically reset to the center of the chart when the movement of the wind has forced the pen to either side of the chart. This can be alleviated manually by momentarily turning off the chart recorder (move switch at lower right to the center position), raising the pen from the chart (to protect the glass tip), slowly pushing the pen to the center of the chart and restoring it to the paper. Restarting the recorder (move switch to the bottom position) usually allows the pen to re-center automatically.

Maximum, Inc. Wind Recorder (Merlin)
Use:
Digital readout of current wind speed, peak gust and average wind since last reset, and ten-minute trend. Unofficial data collected for comparison only.

Location:
The display is located in the wind console in the second floor tower office. It is connected to a small plastic anemometer on the secondary wind mast on the tower roof.

Procedure:
1) Toggle display among current wind speed, peak gust and average wind speed since last reset, and 10-minute trend by pushing the switch at bottom to the right.

2) Reset peak gust and average wind speed by holding the switch at bottom to the left for a few seconds while displaying the quantity to reset.

Maintenance:
None

Maximum, Inc. Gust Recorder (Max #1)
Use:
Analog readout of instantaneous gust and highest gust since last reset. Unofficial data collected for comparison only.

Location:
Location: The display is located in the wind console in the second floor tower office. It is connected to a small plastic anemometer on the secondary wind mast on the tower roof.

Procedure:
1) Read highest gust on dial at point adjacent to the moveable gold indicator.

2) Reset peak wind indicator by rotating center knob counterclockwise to push indicator down to current wind gust, or not lower than about 20 mph. Replace reset index to normal down position.

Maintenance:
Wind needle has been known to stick to the peak wind indicator if indicator is set too low. Thus, high wind indicator should be set no lower than about 20 mph.

Young Wind Display

Use:
Display of current wind speed and peak gust (since last reset) from the Young wind sensor component of the Davis Vantage Weather Pro system.

Location:
Location: The display is located on the shelf above the desk in the second floor tower office

Procedure:
1) Read current wind speed from the display at upper left and read the peak gust from the display at upper right.

2) Reset peak wind indicator by pressing the 'Reset Select' button at lower right.

Maintenance:
Little maintenance is required.

Campbell-Stokes Sunshine Recorder

Use:
Continuous record of bright sunshine sufficient to burn heavy paper card by sunlight focused through a solid glass sphere. Used to determine hourly minutes of bright sunshine each day. The Campbell-Stokes sunshine recorder was first put in service in January 1886 and was replaced with a modern, identical instrument in 1993. This is the most continuous of all records maintained at the Observatory. Knowing the possible number of minutes from sunrise to sunset, the observed sunshine is converted to a percent of possible bright sunshine for the day. Currently two different values are recorded. The first, called the uncorrected sunshine, considers only the minutes of sunshine on the card and the total possible minutes with 30 minutes subtracted to exclude the 15 minutes after sunrise and 15 minutes before sunset when the sun is insufficiently bright to burn the card even when visible. This uncorrected sunshine is recorded to maintain continuity with historical sunshine measurements. The second value, known as the astronomical sunshine is among the data reported to the NWS each month. This includes the 30 total minutes at the beginning and ending of the day in the total possible, then this is multiplied by the uncorrected sunshine percentage to obtain the "observed" astronomical or corrected minutes of sunshine for the day.

Location:
South end of parapet on tower roof.

Procedure:
1) A single sun card is intended for one-day use when sunshine occurs. Care must be taken to ensure that the card is replaced before the sun over-burns a previous record of sunshine. The sun card should be replaced as late in the observing shift as possible. An unburned card can be left out indefinitely as long as sunshine is not expected.

2) The sun card records on solar time, which varies from one to more than 30 minutes later than EST depending on the time of the year. This daily time adjustment from EST to solar time is listed on a chart in the office. Before replacing the sun card, the new card should be marked with the date, the time correction, and the solar time (e.g. “1430S”) at which the card is being changed.

3) Three types of sun cards are used depending on the time of the year, and each is placed in a different slot in the metal frame beneath the glass sphere. Winter cards are the shortest, curve downward, and are placed between the highest notches in the frame, since the sun is lowest in the sky at this time of year. Equinoctal cards are used for several weeks before and after the Vernal and Autumnal equinoxes, are uncurved, and are placed between the center notches in the frame. Summer cards are longest, curve upward, and are placed between the lowest notches in the frame. All cards are slightly longer than necessary, and a small triangular section is removed from both ends before use.

4) To replace a sun card while the sun is out, cover the glass sphere with a hand to momentarily prevent the sun from burning while the card is moved. Remove the pin holding the card in place, slide out the old card, and insert the new card into the frame. Position the card so that the noon time mark is aligned with the small notches in the center of the frame. Re-insert the pin to hold the card in place, and remove hand from the glass sphere. Keep hands clear of the focused sunlight below the glass as this point of light is extremely hot. There is no need to cover the glass during the change, if the sunlight is insufficient to burn the card.

5) Burned cards are used to determine the number of minutes of bright sunshine in each hour to the nearest six minutes. A graded ruler (with lines representing 6(?) minute intervals) is used as a guide and the total number of minutes of sunshine for the day is determined. Measure burns at sunrise/sunset from the tip of the back burn, and beginnings of lines in the middle of the day in the missle of the initial burn hole. The possible number of minutes is the total time between sunrise and sunset with 30 minutes subtracted to account for the sunlight being insufficiently strong to burn the card for 15 minutes after sunrise and before sunset. The percent of possible bright sunshine is the ratio of the observed minutes to the adjusted possible minutes.

6) For continuity, only the chief observer determines the uncorrected and astronomical sunshine minutes from the sun cards each day. However, all observers should be familiar with the procedure.

Maintenance:
Recorder is mounted in a frame oriented north-south and is set for latitude. Under normal operation this will not change, though this orientation should be checked occasionally to ensure consistency. In winter, the card and glass sphere can become covered with ice. Warm water can be used to remove the card when it is frozen into the frame and to remove obscuring ice from the glass.

ASOS

Use:
National Weather Service Automated Surface Observing System. Automatically collects data from various outdoor sensors, encodes the data, and transmits it hourly to the NWS for wider distribution. The station ID for the Blue Hill Observatory ASOS is KMQE.

Location:
Main ASOS processor (shown) is located on the south side of the third floor tower. ASOS instruments are located on the tower roof and outdoor enclosure. The computer, keyboard and monitor to access ASOS data is located in the second floor tower ofice.

Procedure:
1) ASOS works automatically without input from the manual observers.

2) Instructions for using the ASOS display will be added here in the future.

3) Apparent problems with any components of ASOS should be reported to the NWS.

Maintenance:
All maintenance is currently performed by trained NWS technicians only.

Visibility
BHO North View

Use:
Estimated horizontal mean prevailing visibility based on appearance of fixed-distance natural features and other markers. Prevailing visibility is the greatest distance that can be seen in one-half or more of the full horizon circle.

Location:
Obtained from the tower roof for unobstructed 360-degree view of the horizon.

Procedure:
1) Determine (with the naked eye although binoculars can be used) the average horizontal prevailing visibility (in miles) relative to the appearance of the following known markers (others can be found on the hand-drawn charts in the office). Among the established markers are:

Kite shed: 1/16 mile, E
NWS Weather Radio/State Police radio mast: 1/16 mile, SW
MDC fire tower: 1/8 mile, NNE
Hemenway Hill: 3/4 mile, E
Houghton’s Pond: 1 mile (near shore), 1 1/3 miles (far shore), ESE
Hancock Hill: 1 mile, ENE
Ponkapoag Pond: 1 1/2 miles (near shore), 2 miles (far shore), SSE
Buck Hill: 2 miles, E
Chickatawbut Hill: 3 miles, ENE
Reservoir Pond, Canton: 3 miles (far shore visible only), S
Norwood airport: 3 1/4 miles, SW
Great Pond, Braintree: 4 miles (only eastern shoreline visible), ESE
Dedham Courthouse: 4 miles, NW
Norwood High School: 5 miles, SW
Franklin Park: 5 miles, N
Quincy Harbor: 7 miles, NE
Dorchester gas tank: 7 1/8 miles, NNE
Dexter Southfield School Observatory, Brookline: 8 miles, NNW
Moose Hill, Sharon: 8 miles, SSW
Downtown Boston: 10 miles, N
Boston Light, Little Brewster Island: 14 miles, ENE
Prospect Hill, Waltham: 14 miles, NW
Mormon Temple, Arlington: 19 miles, NNW
Nobscot Hill, Framingham: 20 miles, WNW          (Mountain No. 1)
Miles Standish Monument, Duxbury: 26 miles, SE
Providence, RI: 31 miles (skyscraper above horizon), SSW
Ocean horizon from tower roof: 33 miles, NE
Manomet Hill, Plymouth: 33 miles, SE
Copicut Hill, Fall River: 34 miles, S
Wachusett Mountain, Princeton, MA: 44 miles, WNW          (Mountain No. 2)
North and South Pack Monadnock, Peterboro, NH: 60 miles, NW
Grand Monadnock, Jaffery, NH: 68 miles, NW          (Mountain No. 3)

2) Visiblity is observed in statute miles in intervals of:
Sixteenths of a mile up to 1/4 mile,
Eighths of a mile from 1/4 through 3/4 mile,
Quarter miles from 3/4 through 2 1/2 miles,
Half miles from 2 1/2 through 3 miles,
Whole miles from 3 through 15 miles,
Five miles from 15 through 50 miles,
Ten miles from 50 through 90 miles.

3) Record which of mountains 1, 2, or 3 are visible and its condition (coded with an integer from 0 to 3). Intermediate conditions are allowable (e.g. Mtn 2 @ 1-2 or Mtn 3 @ 1.5)
Condition 0: Faintly visible
Condition 1: Visible but hazy
Condition 2: Clearly visible
Condition 3: Reserved for the clearest possible

4) At present, the highest visibility recorded is 90 miles during the clearest possible conditions. Zero visibility is reserved for the unusual circumstance of the WGBH-FM radio mast being not visible from the observatory. Under conditions of total obscuration, vertical visibility is estimated (to the nearest 100 feet) based on the 235-foot-high radio mast.

Hygrothermograph Chart
Use:
Continuous chart recording of temperature and relative humidity for determining hourly temperatures and six-hourly relative humidities. Two types of chart are used with different ranges of temperature, depending on the season. Replace chart at 8 AM each day.

Form ID: NWS 5-207-D (check for summer and winter chart ID)

Location:
Blank and used charts are kept in the large wooden cabinet and workbench in the tower office.

Interpretation:
Details will be added in the future.

Ombroscope Chart

Use:
In Ombroscope to measure beginning and ending times of precipitation. Prepare the charts for use by uniformly coating the printed (light green) chart with water soluble ink (blue magic marker is presently used). The printed green ink is not water soluble. Cut off one-inch white section on right end of chart before using.

Location:
Blank and used charts are kept in the large wooden cabinet and workbench in the tower office.

Interpretation:
Precipitation will stain the water soluble ink on contact. Beginning and ending times of precipitation are determined from the printed time lines on the chart and the water stains, which will vary in appearance based on the intensity and type of precipitation. Spreading of the stain from soaking must be considered when estimating the times of precipitation. Also, stains that appear as long or short streaks are likely splash marks and are generally disregarded. True precipitation stains will be circular if isolated or in small amounts. Heavier rainfall will stain larger areas of the chart.

Weighing Rain Gage Chart

Use:
Continuous chart recording of precipitation for determining hourly precipitation amounts. Replace chart on the 1st of the month, or change the chart after 3-4 rainstorms or when total precipitation reaches 3-4 inches.

Form ID: NWS 1028C:

Location:
Blank and used charts are kept in the large wooden cabinet and workbench in the tower office.

Interpretation:
Details will be added in the future. At present, only the chief observer uses this chart to determine hourly precipitation values, and amounts for other time periods.

Microbarograph Chart
Use:
Continuous 24 hour chart recording of station pressure for determining the 7 PM value from the 7 AM measurements. Cut off narrow white strip at right end of chart before use. Replace chart at 7 AM each day after reading the mercury barometer.

Form ID: NWS 455-18

Location:
Blank and used charts are kept in the large wooden cabinet and workbench in the tower office.

Interpretation:
Details will be added in the future.

Four-Day Barograph Chart
Use:
Continuous four day chart recording of station pressure used as a backup for determining the 7 PM value from the 7 AM measurements. Cut off narrow white strip at right end of chart before use. Replace chart every fourth day at 10 AM or 11 AM as necessary, after reading the mercury barometer.

Form ID: NWS 455-12

Location:
Blank and used charts are kept in the large wooden cabinet and workbench in the tower office.

Interpretation:
Details will be added in the future.

Sun Card

Use:
Continuous recording of bright sunshine for determining the daily possible bright sunshine in hours and percent. Cut off a small triangular piece from each end of the sun card to prevent loss of data near sunrise or sunset. Be sure to change the sun card before it overburns any previous record. There are three types of sun cards: summer, equinoctal and winter. There are three slots in the sunshine recorder, one for each type of card. This is to accomodate the sun angle at different times of year.

Form ID:

Location:
Blank sun cards are kept in the large wooden cabinet and workbench in the tower office. Used cards are stored in the upper desk drawer until the data have been extracted.

Interpretation:
Details will be added in the future.

Psychrometric (Dew Point) Calculator

Use:
To calculate the dew point temperature from dry and wet bulb temperature measurements, and to determine relative humidity from dry bulb and dew point temperatures. Instructions for use are printed on each side of the calculator. The two sides function identically except they are valid for different temperature ranges (one for summer with a range from -10F to 120F and the other for winter with a range of -60F to 50F).

Location:
Typically kept on desk in second floor tower office.

Procedure:
First, take a reading of dry and wet bulb temperatures from the psychrometer. Use one side of the calulator for temperatures above freezing and the other for below freezing temperatures.

To find Dew Point:
1.) Rotate the top wheel so that the 0 degree (heavy arrows) are aligned with the wet bulb temperature on the outer ring.
2.) Move the bar slider so that it is aligned with the temperature difference between the wet and dry bulbs. NOTE: you will need to use the proper color ring. The rings are associated with different pressures, typically the yellow bar (29 inches) will be appropriate.
3.) Read the temperature on the outer ring. This temperature is the dew point.

To find Relative Humidity:
1.) Find the dew point.
2.) Rotate the top wheel so that 100% is aligned with the dry bulb temperature on the inner temperature scale.
3.) The relative humidity will be the % on the inner wheel aligned with the dew point on the inner temperature scale.