Temperature (and humidity) measurement: Difference between revisions

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Temperature (and humidity) measurement (view source)

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This is the same cooling effect as you experience by going into a thick fog, or when you perspire a lot on exposed skin.
This is the same cooling effect as you experience by going into a thick fog, or when you perspire a lot on exposed skin.
==Diurnal variation measurements==
== James Six and Diurnal Variation measurements ==
A thermometer can be modified to hold a register of an extreme temperature (i.e. allows that extreme to be read at a time that suits the observer). It is called a Six's thermometer after the Briton,James Six, who invented the maximum and minimum registering thermometer still used today.  
A thermometer can be modified to hold a register of an extreme temperature (i.e. allows that extreme to be read at a time that suits the observer). It is called a Six's thermometer after the Briton, James Six, who invented the maximum and minimum registering thermometer still used today.  


Colourless Alcohol on the lowest measuring side of a U-shaped glass tube expands and contracts with temperature. A liquid (which traditionally was mercury, but now is a coloured liquid that does not mix with the alcohol) pushes a slider along as the alcohol contracts for lower temperatures, but when the alcohol expands as it warms again, it passes beside the slider, therefore allowing the smallest temperature to be registered. Gravity, shaking, or a magnet are used to move the slider back against the coloured liquid to reset the Six's Thermometer.  
Colourless Alcohol on the lowest measuring side of a U-shaped glass tube expands and contracts with temperature. A liquid (which traditionally was mercury, but now is a coloured liquid that does not mix with the alcohol) pushes a slider along as the alcohol contracts for lower temperatures, but when the alcohol expands as it warms again, it passes beside the slider, therefore allowing the smallest temperature to be registered. Gravity, shaking, or a magnet are used to move the slider back against the coloured liquid to reset the Six's Thermometer.


On the highest side of the u-tube, there is a vacuum between the coloured liquid and the end of the tube and the slider in there registers the highest temperature and is reset the same way as the lowest register. Resetting once a day at a standard time stores the diurnal temperature observations.
On the highest side of the u-tube, there is a vacuum between the coloured liquid and the end of the tube and the slider in there registers the highest temperature and is reset the same way as the lowest register. Resetting once a day at a standard time stores the diurnal temperature observations. Whilst mercury was very good at pushing the sliders on its two ends, replacement liquids are unreliable, so the ban on use of mercury has effectively ended the use of the James Six design in meteorology.
 
An alternative way of achieving registration (preserving the value) is to have a narrow bore tube (minimum volume to be affected by expansion/contraction) with a capilary constriction separating off the bulb (that does contract but becomes isolated from the narrow bore tube permitting it to continue displaying the highest temperature).  This design was used for the traditional clinical body temperature measurement, also largely abandoned following the mercury ban.


An alternative way of achieving registration (preserving the value) is to have a narrow bore tube (minimum volume to be affected by expansion/contraction) with a capilary constriction separating off the bulb (that does contract but becomes isolated from the narrow bore tube permitting it to continue displaying the highest temperature).  This design was used for the traditional clinical body temperature measurement.
=Temperature Scales=
=Temperature Scales=
Temperature scales use a unit called degrees apparently because some early thermonmeter designs were based on circular tubes containing liquid and had 360 equally spaced markings on them as a rough way of reporting relative 'temperatures' before any formal scales based on calibrated points was introduced.
==Fahrenheit==
==Fahrenheit==
Daniel Gabriel Fahrenheit (24 May 1686 to 16 September 1736) visited Ole Remer in 1708. In 1709 Fahrenheit originated the alcohol-in-glass thermometer, and in1724 Fahrenheit developed the scale named after him based on 3 fixed points (a slightly modified version of this scale still called Fahrenheit is still used by some people and is the official scale in a few countries such as the USA).
 
This remains the official scale to use in just one nation - the USA.
 
Daniel Gabriel Fahrenheit (24 May 1686 to 16 September 1736) visited Ole Remer in 1708. In 1709 Fahrenheit originated the alcohol-in-glass thermometer, and in1724 Fahrenheit developed the scale named after him based on 3 fixed points (a slightly modified version of this scale still called Fahrenheit is still used by some people in UK and it is this modified scale that is the official scale in United States).
 
== Rankine ==
 
Rankine is the name given to a scale starting at absolute zero (similar to Kelvin, but based on scale divisions that match Fahrenheit ones).
 
==Celsius==
==Celsius==
The history of Celsius is confusing.
The history of Celsius is confusing.


INTERNATIONAL STANDARD:  The international standard scale for temperature measurements in the weather context is Celsius (after the Swedish person Anders Celsius 1701 to 1744) and defined internationally by two points - absolute zero (-273.15 degrees Celsius - the start of the Kelvin temperature scale) and the triple point of purified water (0.01 degrees Celsius).
INTERNATIONAL STANDARD:  The international standard scale for temperature measurements in the weather context is Celsius (after the Swedish person Anders Celsius 1701 to 1744) and defined internationally by two points - absolute zero (-273.15 degrees Celsius - the start of the Kelvin temperature scale whose scale divisions match Celsius) and the triple point of purified water (0.01 degrees Celsius).


ANDERS CELSIUS SCALE:  Anders defined 0 on his Celsius scale as the boiling point of water and 100 on his scale as the freezing point of water. Carolus Linnaeus (1707 to 1778) in 1744 (after the death of Anders Celsius) reversed that Celsius scale, to the order we know now. Various other people are also credited with developing what was known under various names and became known in the 19th Century as the Centigrade scale.
ANDERS CELSIUS SCALE:  Anders defined 0 on his Celsius scale as the boiling point of water and 100 on his scale as the freezing point of water. Carolus Linnaeus (1707 to 1778) in 1744 (after the death of Anders Celsius) reversed that Celsius scale, to the order we know now. Various other people are also credited with developing what was known under various names and became known in the 19th Century as the Centigrade scale.


CENTIGRADE:  Zero Centigrade is the freezing point of water and 100 units from there is water's boiling point at a pressure of one standard atmosphere. Jean-Pierre Christin in 1743 independently developed a temperature scale with zero for water's freezing point and 100 for water's boiling point and in May of that year he published the design of a thermometer by a craftsman in Lyon using this scale. The temperature scale 'in 100 steps' or in Latin 'centum gradus' (anglicised as Centigrade) officially ceased to exist in 1948, when the unit became degrees Celsius. Older people still use the term Centigrade sometimes in the temperature measuring context, outside the Spanish- and French-speaking world where grad applies to angular measurement (and centigrade is equivalent to 0.009 angular degrees - angular degrees is the unit where 360 is one rotation).
CENTIGRADE:  Zero Centigrade is the freezing point of water and 100 units from there is water's boiling point at a pressure of one standard atmosphere. Jean-Pierre Christin in 1743 independently developed a temperature scale with zero for water's freezing point and 100 for water's boiling point and in May of that year he published the design of a thermometer by a craftsman in Lyon using this scale.  
*The temperature scale 'in 100 steps' or in Latin 'centum gradus' (anglicised as Centigrade) officially ceased to exist in 1948, when the unit became degrees Celsius.
*This terminology is not used in the Spanish- and French-speaking world where grad applies to angular measurement (and centigrade is equivalent to 0.009 angular degrees - angular degrees is the unit where 360 is one rotation).
*Older people still use the term Centigrade sometimes in the temperature measuring context.
*Centigrade is often quoted by TV journalists, in the UK anyway, despite them being born after 1948!
 
=Instruments=
=Instruments=
==Liquid-in-glass==
==Liquid-in-glass==
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In practice, any temperature sensor mounted at a height of one and a half times the height of roughness objects (buildings, trees etc) is expected to be largely unaffected by those objects, so putting a tall pole above your house is deemed okay.
In practice, any temperature sensor mounted at a height of one and a half times the height of roughness objects (buildings, trees etc) is expected to be largely unaffected by those objects, so putting a tall pole above your house is deemed okay.
A more advanced model considers the density of the roughness, and for lots of tightly packed buildings (or trees), uses a bigger clearance (height or horizontal separation). (See [http://www.rmets.org/weather-and-climate/observing/guidelines-observing-0 Royal Meteorological Society website] in UK, or the equivalent of a Meteorological Bureau for your country).
A more advanced model considers the density of the roughness, and for lots of tightly packed buildings (or trees), uses a bigger clearance (height or horizontal separation). (See [http://www.rmets.org/weather-and-climate/observing/guidelines-observing-0 Royal Meteorological Society website] in UK, [http://www.bom.gov.au/climate/how/observations/airtemp-measure.shtml BOM temperature measurement advice] in Austrailia, or the equivalent of a Meteorological Bureau for your country).
 
=How Cumulus software handles Temperature and Humidity=
Cumulus expects all stations to report a minimum number of parameters including outside temperature and relative humidity.  Some weather station types also report wind chill, dew-point temperature, and other derivatives related to temperature and/or relative humidity.  Cumulus is able to calculate wind chill, dew-point, and other derivatives (and if any of these are available from your station, you can choose whether to use the value from station or the value Cumulus calculates).
 
If Cumulus (1 or MX) is using "outside temperature" in a calculation of parameters like dew-point, or apparent temperature, then for most stations it will apply any calibration settings to the temperature read from the station before using it in that calculation. In Cumulus 1, uncalibrated temperature values are used from Instromet, see support forum for more details.
 
Similarly if humidity is read from the station, the calibrated value is used in subsequent calculations. See the support forum for further information e.g. '''for Instromet stations''', Cumulus 1 ''calculates the relative humidity from the reported wet bulb, and dry bulb'', temperatures, the uncalibrated values of temperature and (calculated) humidity are then used to calculate dew-point.
 
== Logged values ==
At the logging interval you set, Cumulus logs outdoor temperature, dew-point, and relative humidity; plus a whole host of values derived from them (and from wind speed), in [[Standard_log_files]], with separate files for each month.
 
Optionally, measurements from extra sensors can be logged in [[Extra_Sensor_Files| extra monthly files]]. For Oregon Scientific stations, temperature readings from one extra sensor can optionally replace the main sensor for "outdoor temperature", see [[Webtags#Web_tags_mentioning_.28outside.29_temperature|here]]for details.
 
Optionally, but only in Cumulus 1, indoor measurements can be logged in [[speciallog.txt|a special ongoing log]].
 
From release 3.12.0, MX maintains a [[Cumulusmx.db|database table]] that can hold temperatures at one (assuming MX has been left running) minute intervals for the last 7 days.
 
==Cumulus Calculated Parameters==
 
See external Wiki or other sections of this Wiki for specific information on the values that Cumulus calculates:
 
[http://en.wikipedia.org/wiki/Wet_bulb Wet bulb]
 
and [[#How_does_Cumulus_know_the_height_of_the_cloud_base.3F]]


=Cumulus Calculated Parameters=
*The dew point calculation for Cumulus 1 uses a third party library which uses the Davis dew point calculation '''dewpoint := tempinC + ((0.13 * tempinC) + 13.6) * Ln(humidity / 100)'''
See other sections of this Wiki for specific information on the values that Cumulus calculates:
* The dew point calculation for MX follows the standard [https://en.wikipedia.org/wiki/Dew_point calculation in wikipedia]
<pre>public static double DewPoint(double tempC, double humidity)
        {
            double lnVapor = Math.Log(ActualVapourPressure(tempC, (int) humidity));
            return ((243.12 * lnVapor) - 440.1) / (19.43 - lnVapor);
        }</pre>


[[Wet bulb]]  and   [[Dew point]] and [http://wiki.sandaysoft.com/a/FAQ#How_does_Cumulus_know_the_height_of_the_cloud_base.3F FAQ: height of the cloud base]
Note this means that Cumulus 1 and MX log files have a continuity break in dew point values when you migrate from one flavour to another.


[[Humidex]] and [[Wind chill]] and  [[Heat index]] and [http://wiki.sandaysoft.com/a/FAQ#My_heat_index.2Fhumidex.2Fwind_chill_is_the_same_as_my_temperature FAQ: criteria for calculating]


[[Apparent temperature]] and [http://wiki.sandaysoft.com/a/FAQ#What_formula_does_Cumulus_use_for_Apparent_Temperature.3F FAQ: what formula does Cumulus use]


[[Heat/cold degree days]]
Look up [[Humidex]], [[Wind chill]], [[Heat index]], [[Apparent temperature]], [[Feels Like|Feels Like temperature]], [[Heat/cold degree days and Chill hours]], [[Average temperature]],
[[Extra_Sensor_Files|Extra temperatures]] for details about the various derivatives.


[[Average temperature]]


[[Extra temperature]]




[[Category:Terminology]]
[[Category:Terminology]]
<br>
History:
[[User:Sfws|Sfws]] 00:34, 29 November 2012 (UTC)
* Created: [[User:Sfws|Sfws]] 00:34, 29 November 2012 (UTC) for legacy Cumulus
* Amended: [[User:Sfws|Sfws]] ([[User talk:Sfws|talk]]) 19:49, 31 July 2021 (UTC) to also cover MX as at 3.12.0
Sfws
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