[RegCNET] tmax and tmin

[Wm. J. Gutowski]

Dear Lara:
	I am not the expert on this, but I am pretty sure that 
observed Tmin and Tmax are obtained primarily from min/max 
thermometers, which record the highest and lowest temperature 
attained since the last time they were reset.  They are almost always 
reset every 24 hours, though they don't all get reset at the same 
time.  That is, different stations, even in the same country (or in 
the US, the same state) may reset their thermometers at different 
times of the day.  This can induce a small bias in one station's 
climatological averages compared to what it would get if it reset at 
another time.  This is documented in the literature somewhere, though 
I don't have the reference myself.
	Using the 3-hourly output will tend to reduce the diurnal 
temperature range you get because that is probably not sampling the 
extremes of the day, though I have not seen this reduction tabulated 
by anyone, and it probably depends on location and season.  Including 
a computation of the true daily min/max temperature would be just a 
few lines of code, and some of us RegCNETers have undoubtedly done it 
for their version of the code - we really should have it as part of 
the standard model, I think.  There would still be the question of 
what time of day to "reset the thermometer", but in model 
intercomparisons I've been part of, we typically agree to go from 00 
UTC - 00 UTC.

Bill

At 11:32 AM -0800 05.11.14, Lara Kueppers wrote:
>Hi-
>Awhile back I asked how Tmin and Tmax in the SRF output file were 
>calculated. Here is Nellie's recent reply, in case anyone else is 
>interested.:
>
>"Hi Lara,
>
>I just verified this with Bi...Tmin and Tmax are calculated from the 
>BATS output, so if you have the model output to the SRF file every 3 
>hours, then that is what the min and max are calculated from.  Bi 
>thinks this is a better way to do it since min and max temp 
>observations are generally taken from 3 or 6 hourly obs.  You can 
>increase the frequency of the srf output variables (in the regcm.in 
>file) to see how much of difference it would make in the diurnal 
>temp range. "
>
>--
>~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*
>Lara M. Kueppers, PhD
>Postgraduate Researcher
>Department of Earth Sciences
>University of California, Santa Cruz
>1156 High Street
>Santa Cruz, CA  95064
>USA
>
>831.459.3504 ph
>831.459.3074 fax
>kueppers at pmc.ucsc.edu
>
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-- 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
William J. Gutowski, Jr.
3021 Agronomy Hall
Dept. of Geological and
      Atmospheric Sciences
Iowa State University
Dept. of Agronomy
Ames, Iowa  50011-1010

gutowski at iastate.edu
Tel:1-515-294-5632
Fax:1-515-294-2619
http://www.ge-at.iastate.edu/
http://rcmlab.agron.iastate.edu/
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~