[wxqc] Wview pressure calculations

[Steve]

One other thing I forgot to mention is that based testing I did at the time, 
I'm confident that the item labeled "Virtual Temperature" in the Davis 
BARDATA docs is actually the mean temperature, not an actual virtual 
temperature (in the meterological usage of the term).

Steve
SoftWx

----- Original Message ----- 
From: "Phil Benchoff" <benchoff at bev.net>
To: "Discussion of weather data quality issues" 
<wxqc at lists.gladstonefamily.net>
Sent: 09/10/2008 8:09 PM
Subject: Re: [wxqc] Wview pressure calculations


> ere is some followup on my previous post on wview using the current
> outside temperature rather than the 12-hour average for converting
> SLP to station pressure:
>
>> From: Merton Campbell Crockett <m.c.crockett at roadrunner.com>
>>
>> My station, CW9691, is a Davis VP2 with wview 4.0.1 used to report
>> observations to CWOP.
>>
>> I have experienced the same problem that you report.  After upgrading
>> to wview 4.0.1, the "overshoot" has been reduced but not eliminated.
>>
>> Do your lowest and highest pressure values occur later than those on
>> the station analysis graph?
>
> Yes, I do see a lag.
>
>> From: Keith Miller <kdmiller at oldsgmail.com>
>>
>> No easy way, you could search the past days packets for wview401 here:
>> http://www.wxqa.com/activecwd/index_activecwd.html
>> I think I count 13 in the lastest day.
>
> I think that will give me a good list to start with.
>
>> From: Gerry Creager <gerry.creager at tamu.edu>
>>
>> I can help  you with a list... but not tonight.  I'll try to remember in
>> the morning but if you haven't seen something tomorrow night, please
>> ping me off-list.  Tomorrow night I should have more time to get
>> something together.
>
> I can probably get what I need from the past day packets file.  Thanks for
> the offer.
>
> -----------------
>
> I really haven't reached a conclusion, but I did hack up wview enough
> to poll the BARDATA (with the current virtual temperature and reduction 
> ratio)
> info from the console and log it and added some more logging to cwop.c.
> This ought to give enough information to see if
> there is some significant error in the way wview converts the reported
> SLP back to station pressure.  Virtual temperature is pretty close
> to outside temperature at the moment, so I'll have to wait until we get
> a good variation.
>
> Here's what the logging looks like:
>
> Sep 10 21:45:05 m-6 wviewd[7279]: <1221097505343> : getBardata(): BAR 
> 30295,ELEV
> ATION 2120,DEW POINT 55,VIRTUAL TEMP 63,C 31,R 1078,BARCAL 82,GAIN 
> 0,OFFSET -18
> Sep 10 21:46:41 m-6 wvcwopd[7290]: <1221097601340> : CWOP-test: Barometer 
> 30.296
> 000 Station Pressure 28.066000, Altimeter 30.304000 in Hg (1026.214111 
> hPa).
>
> Barometer (SLP) is what's reported from the console.  Station pressure and
> altimeter are both calculated by wview.
>
> If it turns out there is something significant here, I'll post the patches
> back to the wview list.  There is a good bit of code between the logging
> I have added and actually integrating this in wview.
>
> I assume any interested parties here are also on the wview list.
>
> Phil
> N3PB/AT008
>
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