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[IDV #IXS-684583]: Dewpoint depression formula mixing units

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  • Subject: [IDV #IXS-684583]: Dewpoint depression formula mixing units
  • Date: Wed, 21 Apr 2010 13:05:58 -0600
Hi Simon-

> Full Name: Simon Metcalf
> Email Address: address@hidden
> Organization: NSW Rural Fire Service
> Package Version: 2.7u2 build date:2009-08-26 16:33 UTC
> Operating System: Windows XP
> Hardware: Java: home: C:\Program Files\IDV_2.7u2\jre version: 1.6.0_13 
> j3d:1.5.2 fcs (build4)
> Description of problem: Hi,
> 
> IDV is not handling the units for its dewpoint depression function.  The 
> function relies upon calculating dewpoint from temp and relhum in my data.  
> The unit for temp in my data is Kelvin, but IDV outputs dewpoint in degrees 
> Celsius, so when it attempts to calculate dewpoint depression, it uses temp 
> in Kelvin from the file and dewpoint in celsius from its calculation.  It may 
> well be accounting for this in the calculation, but the resultant dewpoint 
> depression calculation thinks it's in Celcius when the data looks more like 
> Kelvin, leading to display and further calculation problems.  It may well be 
> getting the function for dewpoint depression wrong because of the mixup in 
> units.

The problem is that the IDV does not have a notion of "delta" units.  So, it 
sees K and thinks it's absolute degrees so when it converts to Celsius, it adds 
~273.15.

> Is there a possible solution to this problem as intend to use dewpoint 
> depression in further calculations.

The only suggestion I have is to use the noUnit procedure I sent yesterday to 
strip off the units once you've calculated the dewpoint depression.

Don Murray

Ticket Details
===================
Ticket ID: IXS-684583
Department: Support IDV
Priority: Critical
Status: Open