"Norman" wrote:
Martin Rowley wrote:

... well, I'm probably way out of date now on all this as I know that a
lot
of work has been done in the Met Office with the DoH & individual NHS
trusts.
However, the standard algorithm we used to use to work out a
'temperature-humidity' index is as follows:-

THI = 0.4 (T + W) + 4.8 .... (for degC).

whe
THI 'Temperature/Humidity Index'
T = Dry bulb (screen) temperature
W = Wet bulb (screen) temperature

For THI 20, " increasing discomfort felt" [ for ' sedentary workers
indoors
' or outside in shade in light winds ] THI = 24 .. half sample population
will feel 'discomfort'. THI 27 .. 'all' are likely to be distressed.

From your figures, I make your THI somewhere around 23.


The one that I've used for a long time is the so-called Humisery Index
which is

Index = (((2Td) +T)/3)-12 (for deg C)

An index value of 0 is very comfortable for most people while an index of
10 is
extremely uncomfortable.

My 1500z obs gives an index of 7.9 which fits very well with how it feels.

I don't know where the Humisery Index came from. I was introduced to it by
Philip Eden many moons ago. I have half an idea that Philip actually
devised
the index but I'm not sure. No doubt he will tell us.

The story is as follows. When I first started on LBC radio in 1983, Arthur
Blackham (for readers who may not know he was my boss at Noble
Denton Weather Service at that time) persuaded me that I should
introduce a variety of novel concepts (some might unkindly call them
gimmicks; in truth they were rather more than that), including the first
regular UK outing for the Wind Chill Factor, as well as the Humisery
Index. Another, the temperature on the Noble Denton window-sill,
quickly vanished! I'm happy to admit I was reluctant, but you don't
go against your boss when you're six months into a new job.

We looked at various comfort indices in use at the time,
and discovered the term "Humisery" in a late-1970s paper in the
Bulletin of the American Met Soc, and we liked the term and
thought it was certain to catch on. (The fact that there is no
Wiki entry for it -- or even a mention -- suggests that it didn't!)

The various THI indices available then were designed for places
like Florida, or the US Gulf Coast, or Bahrain, or Singapore, so
they were not really appropriate for typical 1980s summers in
London, so it fell to me to design it. I didn't want yet another
equivalent temperature (I was already coming to the conclusion
that a windchill temperature was potentially confusing and soon
dropped it -- just as the MO were picking it up! -- in favour of
a qualitative rather than a quantitative approach. By 1985 I was
already talking of, say, a temperature of minus 5 with a large
additional chill factor, and I think this is far, far better than
throwing two different temperatures into a weather forecast).
So I came up with the idea of an index. The index had to be
simple, and what's simpler than a scale of zero to ten? So
that's what it was, and I simply used a version of the basic
THI formula that actually fitted that scale. The very rare
occasions when the index climbed above 10 were classed as
a 10, which everybody understood meant "absolutely
drippingly horrid".

The heyday of the Humisery Index on LBC was in the late-80s
and early-90s when a company selling standalone air-conditioning
units used it in their advertising campaign.

Thanks Arthur!

Philip