In article ,
Adrian D. Shaw writes:
What's the difference between wet bulb and dewpoint?

Dewpoint is the temperature to which the air would have to be cooled to
become saturated, i.e. to have a relative humidity of 100%. Wet bulb
measures the degree of evaporative cooling, so that the lower the
relative humidity the greater the depression of the wet bulb reading
compared to dry bulb. At 100% RH, the dry bulb, wet bulb and dewpoint
will all be the same. For any lower RH, DB WB and, I think, WB DP.

Dewpoint can clearly
be calculated if you know temperature and humidity (well, my weather
station does it), but can wet bulb be calculated? Your description above
suggests it can be (so why would people bother measuring it?).

I think the attraction of wet bulb temperature is that it can be
measured directly, by having a thermometer whose bulb is encased in wet
muslin, or some similar device, rather than needing to be calculated.
Once you've measured dry and wet bulb temperatures, then you can use
them to calculate the relative humidity and the dewpoint. Your modern
weather station may be able to measure the humidity directly, but I
don't think that "traditional" simple met instruments could do this, so
observers would derive the humidity from the wet bulb reading rather
than vice versa.
--
John Hall
Johnson: "Well, we had a good talk."
Boswell: "Yes, Sir, you tossed and gored several persons."
Dr Samuel Johnson (1709-84); James Boswell (1740-95)

In article ,
John Hall writes:
I think the attraction of wet bulb temperature is that it can be
measured directly, by having a thermometer whose bulb is encased in wet
muslin, or some similar device, rather than needing to be calculated.
Once you've measured dry and wet bulb temperatures, then you can use
them to calculate the relative humidity and the dewpoint. Your modern
weather station may be able to measure the humidity directly, but I
don't think that "traditional" simple met instruments could do this, so
observers would derive the humidity from the wet bulb reading rather
than vice versa.

One other reason for measuring (or calculating) the wet bulb temperature
that I forget to mention. When temperatures are close to freezing, the
wet-bulb temperature becomes of interest in its own right, since whether
or not it is below zero determines whether ice or snow will melt.
--
John Hall
Johnson: "Well, we had a good talk."
Boswell: "Yes, Sir, you tossed and gored several persons."
Dr Samuel Johnson (1709-84); James Boswell (1740-95)

In article ,
John Hall writes:
I think the attraction of wet bulb temperature is that it can be
measured directly, by having a thermometer whose bulb is encased in wet
muslin, or some similar device, rather than needing to be calculated.
Once you've measured dry and wet bulb temperatures, then you can use
them to calculate the relative humidity and the dewpoint. Your modern
weather station may be able to measure the humidity directly, but I
don't think that "traditional" simple met instruments could do this, so
observers would derive the humidity from the wet bulb reading rather
than vice versa.

One other reason for measuring (or calculating) the wet bulb temperature
that I forget to mention. When temperatures are close to freezing, the
wet-bulb temperature becomes of interest in its own right, since whether
or not it is below zero determines whether ice or snow will melt.
--
John Hall
Johnson: "Well, we had a good talk."
Boswell: "Yes, Sir, you tossed and gored several persons."
Dr Samuel Johnson (1709-84); James Boswell (1740-95)

In article ,
John Hall writes:
I think the attraction of wet bulb temperature is that it can be
measured directly, by having a thermometer whose bulb is encased in wet
muslin, or some similar device, rather than needing to be calculated.
Once you've measured dry and wet bulb temperatures, then you can use
them to calculate the relative humidity and the dewpoint. Your modern
weather station may be able to measure the humidity directly, but I
don't think that "traditional" simple met instruments could do this, so
observers would derive the humidity from the wet bulb reading rather
than vice versa.

One other reason for measuring (or calculating) the wet bulb temperature
that I forget to mention. When temperatures are close to freezing, the
wet-bulb temperature becomes of interest in its own right, since whether
or not it is below zero determines whether ice or snow will melt.
--
John Hall
Johnson: "Well, we had a good talk."
Boswell: "Yes, Sir, you tossed and gored several persons."
Dr Samuel Johnson (1709-84); James Boswell (1740-95)

In article ,
John Hall writes:
I think the attraction of wet bulb temperature is that it can be
measured directly, by having a thermometer whose bulb is encased in wet
muslin, or some similar device, rather than needing to be calculated.
Once you've measured dry and wet bulb temperatures, then you can use
them to calculate the relative humidity and the dewpoint. Your modern
weather station may be able to measure the humidity directly, but I
don't think that "traditional" simple met instruments could do this, so
observers would derive the humidity from the wet bulb reading rather
than vice versa.

One other reason for measuring (or calculating) the wet bulb temperature
that I forget to mention. When temperatures are close to freezing, the
wet-bulb temperature becomes of interest in its own right, since whether
or not it is below zero determines whether ice or snow will melt.
--
John Hall
Johnson: "Well, we had a good talk."
Boswell: "Yes, Sir, you tossed and gored several persons."
Dr Samuel Johnson (1709-84); James Boswell (1740-95)

Felly sgrifennodd John Hall :
In article ,
Adrian D. Shaw writes:
What's the difference between wet bulb and dewpoint?

Dewpoint is the temperature to which the air would have to be cooled to
become saturated, i.e. to have a relative humidity of 100%. Wet bulb
measures the degree of evaporative cooling, so that the lower the
relative humidity the greater the depression of the wet bulb reading
compared to dry bulb. At 100% RH, the dry bulb, wet bulb and dewpoint
will all be the same. For any lower RH, DB WB and, I think, WB DP.

Many thanks; yes I see you're right. There's an interesting graph at:
http://ianrpubs.unl.edu/generalag/g626.htm

This graph shows that the WB temperature could equally well be calculated
from the two variables, temperature and RH. I wonder why my WS doesn't
do that too!

Adrian
--
Adrian Shaw ais@
Adran Cyfrifiadureg, Prifysgol Cymru, aber.
Aberystwyth, Ceredigion, Cymru ac.
http://users.aber.ac.uk/ais uk

Felly sgrifennodd John Hall :
In article ,
Adrian D. Shaw writes:
What's the difference between wet bulb and dewpoint?

Dewpoint is the temperature to which the air would have to be cooled to
become saturated, i.e. to have a relative humidity of 100%. Wet bulb
measures the degree of evaporative cooling, so that the lower the
relative humidity the greater the depression of the wet bulb reading
compared to dry bulb. At 100% RH, the dry bulb, wet bulb and dewpoint
will all be the same. For any lower RH, DB WB and, I think, WB DP.

Many thanks; yes I see you're right. There's an interesting graph at:
http://ianrpubs.unl.edu/generalag/g626.htm

This graph shows that the WB temperature could equally well be calculated
from the two variables, temperature and RH. I wonder why my WS doesn't
do that too!

Adrian
--
Adrian Shaw ais@
Adran Cyfrifiadureg, Prifysgol Cymru, aber.
Aberystwyth, Ceredigion, Cymru ac.
http://users.aber.ac.uk/ais uk

Felly sgrifennodd John Hall :
In article ,
Adrian D. Shaw writes:
What's the difference between wet bulb and dewpoint?

Dewpoint is the temperature to which the air would have to be cooled to
become saturated, i.e. to have a relative humidity of 100%. Wet bulb
measures the degree of evaporative cooling, so that the lower the
relative humidity the greater the depression of the wet bulb reading
compared to dry bulb. At 100% RH, the dry bulb, wet bulb and dewpoint
will all be the same. For any lower RH, DB WB and, I think, WB DP.

Many thanks; yes I see you're right. There's an interesting graph at:
http://ianrpubs.unl.edu/generalag/g626.htm

This graph shows that the WB temperature could equally well be calculated
from the two variables, temperature and RH. I wonder why my WS doesn't
do that too!

Adrian
--
Adrian Shaw ais@
Adran Cyfrifiadureg, Prifysgol Cymru, aber.
Aberystwyth, Ceredigion, Cymru ac.
http://users.aber.ac.uk/ais uk

Felly sgrifennodd John Hall :
In article ,
Adrian D. Shaw writes:
What's the difference between wet bulb and dewpoint?

Dewpoint is the temperature to which the air would have to be cooled to
become saturated, i.e. to have a relative humidity of 100%. Wet bulb
measures the degree of evaporative cooling, so that the lower the
relative humidity the greater the depression of the wet bulb reading
compared to dry bulb. At 100% RH, the dry bulb, wet bulb and dewpoint
will all be the same. For any lower RH, DB WB and, I think, WB DP.

Many thanks; yes I see you're right. There's an interesting graph at:
http://ianrpubs.unl.edu/generalag/g626.htm

This graph shows that the WB temperature could equally well be calculated
from the two variables, temperature and RH. I wonder why my WS doesn't
do that too!

Adrian
--
Adrian Shaw ais@
Adran Cyfrifiadureg, Prifysgol Cymru, aber.
Aberystwyth, Ceredigion, Cymru ac.
http://users.aber.ac.uk/ais uk

"Adrian D. Shaw" wrote in message
...
Felly sgrifennodd John Hall :
In article ,
Adrian D. Shaw writes:
What's the difference between wet bulb and dewpoint?

Dewpoint is the temperature to which the air would have to be cooled to
become saturated, i.e. to have a relative humidity of 100%. Wet bulb
measures the degree of evaporative cooling, so that the lower the
relative humidity the greater the depression of the wet bulb reading
compared to dry bulb. At 100% RH, the dry bulb, wet bulb and dewpoint
will all be the same. For any lower RH, DB WB and, I think, WB DP.

Many thanks; yes I see you're right. There's an interesting graph at:
http://ianrpubs.unl.edu/generalag/g626.htm

This graph shows that the WB temperature could equally well be calculated
from the two variables, temperature and RH. I wonder why my WS doesn't
do that too!

Adrian
--
Adrian Shaw ais@
Adran Cyfrifiadureg, Prifysgol Cymru, aber.
Aberystwyth, Ceredigion, Cymru ac.
http://users.aber.ac.uk/ais uk

Adrian, thanks for sight of a most informative graph. Interesting also to
see it applied to problems within a pig farm!

I now have to work out how to apply it to the melting ice problem, hopefully
not of concern to the pigs.

Best regards, Roger