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Weather Master > W04 - Temp & Humidity > Flashcards

W04 - Temp & Humidity Flashcards

1
Q

Temperature

A

The temperature of a body is the condition which determines its ability to communicate heat to other bodies or to receive heat from them.

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2
Q

Dew point

A

The temperature at which the air would become saturated (with respect to water) if cooled at a constant pressure and without the addition or removal of water vapour. (expressed in degrees celsius)

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3
Q

Relative humidity

A

The ratio, expressed as a percentage, of the amount of water vapour actually present in the air to the amount of water vapour which would be present if the air were saturated with respect to water at the same temperature and pressure.

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4
Q

Stevenson screen

A

A louvred wooden box especially designed to shield thermometers from the effects of radiation, while at the same time allowing the free flow of air over the thermometer bulbs.

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5
Q

Criteria for Stevenson Screen

A

-Sides and bottom are double louvred-Door opens downward-Painted with exterior white enamel-Thermometers must be 1.25-2m above ground-Door faces true north-Is installed on a grass surface-Distance from other objects must be twice the height of the object

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6
Q

Safety precautions for mercury filled thermometers

A

-Always store upright-Never reconnect a broken mercury column-Mercury freezes at -39 degrees C (bring inside at -37)-Don’t touch thermometer when resetting and avoid obstacles-Remove thermometers one at a time -Let thaw before replacing a frozen wick

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7
Q

Characteristics of Mercury

A

-Silvery white metal-Density of 13.6-Turns to gas when exposed to air-Allowable amount of gaseous mercury in the air is 0.05mg/m cubed-When air is saturated with mercury at room temperature, the amount is 20mg/m cubed-Can be absorbed through skin, breathed in, or be ingested-If inside the body, mercury attacks the respiratory, gastro-intestinal, and central nervous systems

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8
Q

Symptoms of mercury intoxication: Nervous system

A

-headaches-dizziness-nervousness-nerve inflamation-loss of muscular control-shaking

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9
Q

Symptoms of mercury intoxication: Gastro-intenstinal system

A

-gum inflammation-nausea-vomiting-diarrhea-liver lesions

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10
Q

Symptoms of mercury intoxication: Respiratory system

A

-inflammation of nose and lungs-coughing-fever

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11
Q

Symptoms of major mercury intoxication

A

-Burning sensation in mouth and throat-laboured breathing-nausea and vomiting-abdominal pains-diarrhea and bleeding-shock-cardiac arrest

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12
Q

Procedures in case of a mercury spill

A

Clean up with a special kit, keep residues in a sealed container and dispose of at a toxic waste site. Report to the person in charge of the station and the work health and safety committee for the station.

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13
Q

When readings require 2 or more thermometers to be read, what order should they go in?

A

1-Dry bulb2-Wet bulb3-Maximum4-Minimum

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14
Q

What are the physical characteristics of a mercury filled thermometer?

A

-Filled with mercury, and above that, nitrogen.-Graduated in degrees Celsius at 0.5 degree intervals-30cm long-Marks of degrees are etched on the stern-Will be marked with manufacturer’s name and a serial number

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15
Q

What is the purpose of a correction card?

A

Correction values are to be applied to thermometer readings to obtain the true temperature. Each thermometer has its own correction card.

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16
Q

Column 34

A

Dry-bulb temperature

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17
Q

Psychrometer

A

A device for determining the moisture content of the air (used to determine dew point).Contains both a dry-bulb and a wet-bulb with a wick, muslin, or ice coating.

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18
Q

Wet-bulb temperature

A

Evaporation of water or sublimation of ice is how the wet-bulb temperature is determined. It must be the same as or lower than the dry-bulb temperature (Except below freezing). The difference between the two is called the depression of the wet bulb temperature.

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19
Q

What are the three types of psychrometer?

A

-Non-ventilated-Sling-Ventilated

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20
Q

When should the motor psychrometer be turned on?

A

At least two minutes before the thermometer reading

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21
Q

Ventilated psychrometer

A

A psychrometer that is ventilated by a motor that powers a fan

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22
Q

Non-ventilated psychrometer

A

A psychrometer that is only ventilated by the natural flow of air.

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23
Q

Sling psychrometer

A

A psychrometer that is ventilated by the physical motion of the thermometers through the air (by you).

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24
Q

What are the freezing points for mercury and alcohol thermometers?

A

Mercury: -39 degreesAlcohol: -75 degrees

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25
Q

At what temperature must a mercury thermometer be brought inside at?

A

-37 degrees Celsius

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26
Q

What type of water must be used on a wet bulb?

A

Distilled water. Clean rain water or melted snow may be used. The water container must be kept at least half full.

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27
Q

Muslin sleeve

A

A sleeve which fits over the bulb of an ordinary thermometer.-Should be replaced once a week for ventilated or non-ventilated psychrometers and once per month for sling psychrometers.

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28
Q

Rayon tubing

A

Serves as both muslin and wick. One end of a length of tubing (about 20cm) should be tied to the thermometer bulb and the remainder should stretch horizontally to the top of the water container.

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29
Q

When should rayon tubing be used as a covering for the wet-bulb?

A

0 degrees and above

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30
Q

When should muslin sleeves be used as a covering for the wet-bulb?

A

0 to -10 degrees

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31
Q

What type of wet bulb covering should be used below -10 degrees?

A

Ice coating

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32
Q

What are the guidlines for forming an ice coating on the wet bulb

A

-coating of ice 15 minutes before each reading-rotate the thermometer almost horizontally so that the bulb end is slightly lower for an even coating-watch the thermometer as the temperature will drop then rise (if it does not, it is likely supercooled, not frozen)-be sure there is only one coating of ice on the thermometer (allow the temperature to come above freezing when dipped in the water so that all of the old ice has been melted off)

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33
Q

Guidelines for using rayon tubing

A

-wick tubing is 20cm long-tied with #19 thread-entire wick must be soaked-wick should extend horizontally from container to neck of bulb so that the water does not dry up or drip.

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34
Q

Guidelines for muslin use

A

-dip muslin sleeve in water at least 15 minutes before observation-roll slowly while thermometer is held horizontally-temperature fluctuates much like when thermometer has an ice coating

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35
Q

How to use a sling psychrometer

A

-whirl at least 4 times/second-whirl as long as necessary (may be several minutes)-stand clear of obstructions-sling upwind from your body

36
Q

How fast does the motor draw air into the ventilated psychrometer?

A

8m/second

37
Q

Book 1 Form 63-2201

A

Psychrometric tables for station elevation of less than 1000ft for a ventilated thermometer

38
Q

Book 2 Form 63-2202

A

Psychometric tables for station elevation of 1000-2500ft for a ventilated thermometer

39
Q

Book 3 Form 63-2203

A

Psychometric tables for station elevation of more than 2500ft for a ventilated thermometer

40
Q

Book 4 Form 63-2204

A

Psychometric tables for station elevation of less than 1000ft for a non-ventilated psychrometer

41
Q

Book 5 Form 63-2205

A

Psychometric tables for station elevation of 1000-2500ft for a non-ventilated thermometer

42
Q

Book 6 Form 63-2206

A

Psychometric tables for station elevation of more than 2500ft for a non-ventilated thermometer

43
Q

When is a negative depression possible?

A

When the wet bulb is actually covered in ice and the humidity is very high.

44
Q

What can cause a false negative depression?

A

-A break in the liquid column of the wet-bulb thermometer-Moisture on the dry-bulb thermometer-If the fan is operated for too short a time

45
Q

Temperature increments on the psychometric tables

A

Every 0.5 degrees

46
Q

Depression increments on the psychometric tables

A

From -40 degrees to 0.4 degrees: 0.1 degree incrementsFrom 0.5 degrees and above: 0.2 degree increments

47
Q

When there is no value on the tables for a negative depression and a dry bulb temperature, what should the observer do?

A

Ensure that the reading is correct and the thermometers are working correctly, and, if so, use the nearest values listed in the tables for that dry bulb temperature

48
Q

How shall the dew point be recorded if the dew point on the tables is shown as higher than the dry-bulb temperature?

A

The dew point will be listed as the same as the dry bulb temperature.

49
Q

What should be entered in column 23 if the temperature is -37 degrees or below?

A

M

50
Q

If a ventilated psychrometer is unservicable, what shall be entered in column 23?

A

NV, followed by the reading of the thermometer

51
Q

Column 24

A

Relative humidity- only needs to be filled in if there is a regional or local need. Otherwise, it may be left blank.

52
Q

Column 35

A

Dew Point

53
Q

Maximum thermometer

A

Registers the highest temperature from the time it was last set until it is read

54
Q

Minimum thermometer

A

Records the lowest temperature reached during the period since it was last set. Filled with ethyl alcohol

55
Q

What can be used for a dry-bulb reading when the dry bulb is broken or has been brought inside due to cold?

A

Minimum thermometer.

56
Q

Explain how a maximum thermometer displays the maximum temperature from a previous time

A

When the temperature goes up, the mercury is forced up the tube past the constriction. When the temperature begins to fall, the thread of mercury breaks off at the constrictions leaving that part of mercury to indicate the maximum temperature

57
Q

Explain how a minimum thermometer displays the minimum temperature from a previous time.

A

When the air cools, the alcohol contracts, and surface tension brings the index down with the alcohol. When the air warms, the alcohol expands and flows around the index, leaving it at the coolest temperature.

58
Q

How is a maximum thermometer reset?

A

By swiftly swinging it from above your head, down to your side until the mercury travels down toward the bulb.

59
Q

How is a minimum thermometer reset?

A

By removing it from the left hook and tilting it until the index is back on the end of the alcohol column.

60
Q

Cautions to be taken when resetting a maximum thermometer

A

-Keep out of direct sunlight-Do not hold bulb end-Stay clear of obstructions

61
Q

If the alcohol column in a minimum thermometer is broken into sections, can it still be used?

A

Maybe. It may be able to be reset by holding it vertically and tapping the bulb on the palm of the hand, the interior of a large book or a soft piece of rubber. It can also be fixed in the same way a maximum thermometer is reset. If there is still a discrepancy of 0.5 degrees or more between the minimum and dry-bulb, the thermometer should be taken out of service.

62
Q

How should max and min be coded if there is a dry-bulb is higher than the max or lower than the min?

A

It should be coded using the dry-bulb temperature with the max/min in brackets.

63
Q

If a max thermometer is unserviceable, how is the value to be obtained?

A

The highest dry-bulb temperature for that period must be used.

64
Q

If a min thermometer is unserviceable, how is the value to be obtained?

A

The lowest dry-bulb temperature for that period must be used.

65
Q

RTD87

A

Also known as a dewcell, a remote temperature and dew-point system introduced in 1987 which allows the digital display of temperature. (dry, wet, min, max and sometimes soil temperatures)Once temperature and dew point are calculated, they are displayed on the RTD87 display.

66
Q

Thermistor

A

Also known as the dry-bulb, it is used for the air-temperature measurements without conversion.

67
Q

Dewcell

A

A thermistor kept within a fibre cloth saturated with a lithium-chloride solution through which two gold wires drive a current.

68
Q

Dewcell operation

A

-Lithium chloride solution within the fibre cloth absorbs moisture from the air-A current is driven through solution, warming it and the internal thermistor-Increased heat drives off some of the moisture resulting in a drying of the solution and a reduction of current flow until an equilibrium is reached with air moisture content-A measurement of the temperature is made on a scale without correction and is converted directly to dewpoint

69
Q

How is RH calculated when using the RTD87?

A

By consulting tables using the rounded values of dry-bulb and dewpoint.

70
Q

Thermistor operation

A

Thermistor is a material in which resistance (voltage/current) changes with temperature. It is installed freely in the ambient air so that its resistance varies directly with the temperature of the air.

71
Q

What should the function switch read for dry-bulb/dewpoint or max/min?

A

NORMAL-dry-bulb/dewpointMAX/MIN-max/min*to clear the max/min for the next period of data recording, the CLEAR button must be pressed when switching the function switch back to NORMAL

72
Q

When using the RTD87 system, which column on the 2322 is left blank?

A

Column 23 (wet-bulb)

73
Q

RTD87 tolerances for discrepancies for dry-bulb (compared to psychrometer)

A

0.3 degrees

74
Q

RTD87 tolerances for discrepancies for dew point (compared to psychrometer)

A

0.6 degrees when the wetbulb is greater than 0 degrees1.2 degrees when the wetbulb is less than 0 degrees

75
Q

What should be done if the tolerances for discrepancies for the dry-bulb are not met?

A

The MSC inspector should be called to replace the dry thermistor

76
Q

What should be done if the tolerances for discrepancies for the dew point are not met?

A

The dewcell shall be replaced with a clean, reactivated one.

77
Q

How often must a newly installed dewcell be compared?

A

-Hourly for the first 24 hours-4 times daily for the next two months-Once a week after that

78
Q

How often must a reactivated dewcell be compared?

A

-First four consecutive observations-Once a week after that

79
Q

Steps for replacing a dirty dewcell

A

-Apply lithium chloride to the fibre cloth of the clean dewcell to activate it-Dewcell is dried for 40mins by connecting it to the system in its clear plastic housing in the Stevenson Screen

80
Q

Steps for exchanging dewcells (dirty to clean)

A

-Turn power off-Change-Turn power on*Change must be made within 5 minutes or the new dewcell will be contaminated.

81
Q

Cleaning a dewcell

A

-Wash in Allen dewcel washer for 10 minutes in warm water and then 2 minutes in cold water.-Dry by connecting dewcel to the system in the screen for 30mins or leave it at room temp for several hours ensuring it cannot be contaminated-Store in the special storage container or in the metal or cardboard container supplied.

82
Q

Dewcel metal guard

A

Prevents the gold wires from being damaged*dewcel must never be left in the free air without the metal guard.

83
Q

How should the lamps on the RTD87 read?

A

POWER light-ONMESSAGE light-flashingERROR light-generally off, but may go on if the unit doesn’t recognize something. *continuing error messages should be reported to the MSC

84
Q

Thermograph/thermohygrograph

A

Records temperature tendency on a graph for seven or thirty one days at a site with limited hours that is not collocated with an AWOS.

85
Q

How does a thermograph operate?

A

-Porous-nib or wedge-type pens are used to record data on chart-A screw on the base of the pen arm is adjusted so the pen just touches the chart-The knurled knob above the bimetallic ring adjusts the pen and is used to make time marks-Clock speed can be adjusted if the drum turns to quickly or slowly-

86
Q

Characteristics of a thermograph

A

Chart for 7 or 31 daysTemperature goes from -35 degrees to +45 degreesTemperature tolerance must be 1.5 degrees after correctionCorrection card located on the partition plate.Above the end of the temperature trace, the dry-bulb temperature should be entered at chart change.

Weather Master (10 decks)

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