temperature & humidity
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EMPERA URE
& HUMIDI Y
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EMPERA URE
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Temperature is a degree of
hotness or coldness measuredon a definite scale
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TERMINOLOGIES
• Mean Daily Temperature – the average
of the daily maximum and minimum
temperature
• Normal Daily Temperature – the average
daily mean temperature for a given date
computed for a specific 30-year period.
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• Daily Range Temperature – the
difference between the highest and the
lowest temperatures recorded on a
particular day
• Mean Monthly Temperature – the
average of the mean monthly maximum
and minimum temperatures
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• Mean Annual Temperature – the average
of the monthly means for the year
• Degree-day – a departure of one degree
for one day in the mean daily temperature
from a specified base temperature
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MEASUREMENT OF
TEMERATURE
• In order to measure air temperature
properly, T!ERMOMETER must be
placed where air circulation is
relatively unobstructed and yet
protected from the direct rays of thesun and from precipitation.
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"a#i$ Type# o% Thermometer#
&' Traditional Thermometer
- designed for at home use for measuring the
temperature of the air or water in both F or . !hese
should not re"uire much maintenance, but they may
have a varied accuracy, range and resolution.
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(' Re#i#tan$e Thermometer
- designed to measure temperatures between
-#$0 and %00 degrees elsius by noting the
resistance change of a li"uid by a currant flowingthrough the platinum wire inside.
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*' Dual Sen#or Thermometer - designed for professional use as they
provide dual readings of environments that can
remain steady for long periods of time. !he main
reader of this thermometer can be mounted to ades) or wall and the probes can be inserted into
a variety of environments for readings.
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+' Fi,ed and ired ro.e Thermometer
*robe thermometers are designed to provide
accurate readings of temperatures in foods,
li"uids or semi-solids in retail or laboratory
settings. !hese are mainly designed for hygienetesting, and they will vary in si+e and focus on
providing solid, accurate readings to ensure user
safety.
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/' 0-type Thermometer
- designed to measure extreme temperatures in
the air, li"uids or surfaces within a professional
environment. !he specific temperature range willvary by brand but they wor) to provide a non-slip
grip that is manoeuvrable for use in a variety of
environments without compromising accuracy.
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1' Data Logging Thermometer
!hese provide temperature results in real time that
can be downloaded to a computer to note the
temperature history of an environment to chec) forvariances. !his can be used to provide graphical data
and accurate readings that are suitable for
professional use.
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2' In%rared Thermometer !hese can measure very high or low surface
temperatures without the need to ma)e contact with
the item in "uestion, which is ideal for spot chec)ing
temperature settings within an environment.owever, there can be up to a 30 percent error
reading due to this lac) of contact, but this can be
corrected with a traceable accuracy setting.
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3' "imetal Thermometer - designed to note temperature changes as the
metal in the base expands and contracts. !hese
are typically used on thermostats or dial
thermometers to note the temperature at aspecific time by allowing the dial in the face to
rotate as necessary.
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&4' Li5uid-$ry#tal Thermometer
!hese thermometers will change colors due to the
li"uid crystals in the face to reflect the temperature on
the forehead or other substance where this is placed.
!he designated temperature will become dar)er on theface to designate a reading that also provides a digital
reading.
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&&' Ga# Thermometer
!hese are a very common type of industrial
thermometer that are used to )eep the
temperature of stored gas constant within aconfined area. !he pressure of this gas will be
measured to determine the temperature inside.
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Ma,imum Thermometer –
has a constriction near the bulb
which prevents the mercuryfrom returning to the bulb as
the temperature falls and thus
registers the highest
temperature since its last
setting
Minimum Thermometer –
of alcohol in glass-type
has an index which
remains at the lowest
temperature occurringsince its last setting
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Thermograph – with either a
bimetallic strip or a metal tube
filled with alcohol or mercury forits thermometric element, ma)es
an autographic record on a chart
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/orlds 1argest
!hermometer is
in alifornia
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LASE RATES
Lap#e Rate vertical temperature gradient
– the rate of change of temperature with
height in the free atmosphere.
Temperature Inversion – an increase of
temperature with altitude in the surface
layer
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• Dry-adia.ati$ Lap#e Rate ' degree
elsius per '00 m – the rate of
temperature change of unsaturated air
resulting from expansion or compressionas the air rises lowering pressure or
descends increasing pressure without
heat being added or removed
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• Super-adia.ati$ Lap#e Rate exceeding
' degree elsius per '00 m – an
unstable condition since any parcel of air
lifted dry-adiabatically remains warmerand higher than the surrounding air and
thus has a tendency to continue rising.
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• Saturated-adia.ati$ Lap#e Rate – if any parcel
of saturated air is lifted adiabatically, the
temperature decreases and its water vapor
condenses, releasing latent heat of ofvapori+ation
• #eudo-adia.ati$ Lap#e Rate – if the moisture
in the rising air is precipitated as it is condensed,
the temperature of the air will decrease
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Neutral Equilibrium – condition when a
layer of saturated air having a saturated or
pseudo-adiabatic lapse rate
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Land and 7ater ma##e#
In the interior of the large islands and
continents, temperatures are higher in
summer and lower in winter than on
coasts at corresponding latitudes.
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Topography
!emperatures at high elevations are
colder than at low levels and southern
slopes have warmer temperatures than
northern slopes.
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8egetation
Forested areas have higher daily
minimum and lower daily maximum
temperatures than barren areas
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TIME 8ARIATIONS OF
TEMERATURE
• In continental regions, the warmest and
coldest points of the annual temperature
cycle lag behind the solstices by about '
month. In 45, 6anuary is usually thecoldest month and 6uly the warmest.
•
7t oceanic stations, the lag is nearer #months and the temperature difference
between the warmest and coldest months
is much less.
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• !he daily variation of temperature lags
slightly behind the daily variation of solar
radiation.
• !he daily range of temperature is affected
by the state of the s)y. 8n cloudy days, the
maximum temperature is lower because ofreduced insolation and the minimum is
higher because of reduced outgoing
radiation.
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HUMIDI Y
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Type#
• A.#olute humidity
It is the total amount of water vapor present in a given volume
of air. It does not ta)e temperature into consideration. 7bsolute
humidity in the atmosphere ranges from near +ero to roughly
30 grams per cubic meter when the air is saturated at 30 9. 7bsolute humidity is the mass of the water vapor mw divided
by the volume of the air and water vapor mixture Pnet , which
can be expressed as2
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• Relati9e humidity
!he relative humidity : of an air-water mixture is defined
as the ratio of the partial pressure of water vapor #8
ew
in the mixture to the saturated vapor pressure ofwater e;w at a given temperature. !hus the relativehumidity of air is a function of both water content and
temperature.
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ropertie# o% ater 8apor
• 8apori:ation or e9aporation – the
process whereby a solid is transformed
directly to the vapor state
• Su.limation meteorology – direct
transformation from ice to vapor and vice
versa
• 6onden#ation – process by which vaporchanges to the li"uid or solid state
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• 8apor re##ure – the partial pressure
exerted by water vapor
• Saturation 8apor re##ure – the
pressure exerted by the vapor in saturated
space which is the maximum vapor
pressure possible at a given time
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8apori:ation removes heat from
the li"uid being vapori+ed while$onden#ation adds heat.
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• Latent !eat o% 8apori:ation – the amount of
heat absorbed by unit mass of a substance
without change in temperature while passing
from the li"uid to the vapor state
v ? #.$0 – 0.00#3(!
where T is the temperature in degree Celcius and
Hv is in kilooules per gram
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• Latent !eat o% Fu#ion for water, 0.33% )6@g
at 0 A – is the amount of heat re"uired to
convert ' g of ice to li"uid water at the same
temperature
• Latent !eat o% Su.limation - for water,
#.B3 )6@g at 0 A – is the amount of heatre"uired to convert ' g of ice into vapor at the
same temperature without passing through
the intermediate li"uid state
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• !he #pe$i%i$ gra9ity of water vapor is 0.(##
times that of dry air at the same temperature
and pressure
• !he density of water vapor in g@cm3
Cv ? (.## e
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• !he density of dry air in grams per cubic
meter g@m3 is2
Cd ? '0 Cd
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• !he density of moist air is e"ual to the
mass of water vapor plus the mass of dry
air in a unit volume of the mixture.
Ca ? '0 Ca x ' – 0.3%B e
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• 8apor re##ure – the basic element in
practically al expressions of air density and
vapor content
• De7point – the temperature at which space
becomes saturated when air is cooled under
constant pressure and with constant water
vapor content. It is the temperature having a
saturation vapor pressure es e"uals to the
existing vapor pressure e.
TERMINOLOGIES
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• Relati9e !umidity – is the percentage
ratio of the actual to the saturation vapor
pressure and is threfore a ratio of the
amount of moisture in a given space to theamount the space could contain if
saturated, f ? '00 x e@es
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• Spe$i%i$ !umidity – is the mass of water
vapor per unit mass of moist air expressed
in grams per )ilogram
"h ? (## e (## e
*a – 0.3%B e * a
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• Mi,ing Ratio – the mass of water vapor
per unit mass of perfectly dry air in a
humid mixture
wr ? (## e
*a - e
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S;6!ROMETER uses the difference in
readings between two thermometers, one
having a wet bulb and the other having a drybulb, to measure the moisture content or
relative humidity of air.
MEASUREMENT OF
!UMIDIT;
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• !air !ygrometer – ma)es use of
the fact that the length of a hair
varies with relative humidity
•
!air !ygrograph – a hairhygrometer operating a pen
mar)ing a trace on a chart
• !ygrothermograph – combining
the features of both the hairhygrograph and thermograph that
records both relative humidity and
temperature on one chart
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• De7point !ygrometer – measures dewpoint
directly and is used mostly for aboratory
purposes
• De7-$ell !ygrometer – measures the
dewpoint by regulating the temperature of a
saturated a"ueous lithium chloride solution sothat the water vapor pressure of the solution
is e"ual to that of the surrounding atmosphere
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• Spe$tral !ygrometer – measures
selective absorption of light in certain
bands of the spectrum by water vapor.
Deasurement of humidity is one of the
least accurate instrumental procedures in
meteorology
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GEOGRA!I6 DISTRI"UTION OF
!UMIDIT;
• 7tmospheric moisture tends to decrease
with increasing latitude but relative
humidity, being an inverse function of
temperature, tends to increase.• It is greatest over oceans and decreases
with distance inland.
• It also decreases with elevation and isgreater over vegetation than over barren
soil.
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• In actual water vapor content,
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END OF
DIS6USSION
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*repared by2
DAR;L GRA6E 6' ADUA
E55-$7
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