[RegCNET] tmax and tmin

[Lara Kueppers]

Bill-
As another non-expert, but someone who has used weather station data in 
Colorado, I agree that what is recorded is Tmin and Tmax using min-max 
thermometers. Daily averages are typically calculated as the mid-point 
between min and max for any given day. This suggests that the observed 
daily average T is probably slightly biased as well.

I endorse your call for true Tmin and Tmax to be included as output from 
RegCM! It would certainly facilitate comparisons with observations. The 
reset time you suggest makes the most sense from many points of view I 
think.

Lara



Wm. J. Gutowski wrote:

> 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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>
>
>

-- 
~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*
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