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3.5.12 Specifying Average Mixing Heights for the Long Term Model

 

     Fop the ISC Long Term model, the user must specify average values of mixing height following the AVEMIXHT keyword.  The following syntax is used:

 

Syntax:

ME AVEMIXHT  Aveper Stab Mixht1 Mixht2 Mixht3 Mixht4 Mixht5 Mixht6

Type:

Mandatory, Repeatable

 

where the Aveper parameter specifies the long term averaging period for the following inputs, and must be one of the secondary keywords used on the Long Term AVERTIME card described in Section 3.2.3.2 (i.e., JAN, WINTER, ANNUAL, etc.)  The Stab parameter specifies the stability category (A through F or 1 through 6).  The Mixht1 through Mixht6 parameters are the average mixing heights (m) for each of the six wind speed categories.  The AVEMIXHT keyword is repeated for each stability category and for each of the averaging periods being processed.  For mixing heights in rural areas, the common practice is to apply the mean afternoon mixing height given by Holzworth (1972) to stability classes B, C and D, and 1.5 times the mean afternoon mixing height to stability class A.  For mixing heights in urban areas, the common practice is to apply the mean afternoon mixing height given by Holzworth (1972) to stability classes B and C, 1.5 times the mean afternoon mixing height to stability class A, and the average of the mean early morning and afternoon mixing heights to stability class D.  The ISCLT model assumes unlimited mixing for stability classes E and F for both rural and urban conditions, and a large value such as 10,000 meters may be input for those classes.  It is also common practice to apply the average mixing height to all wind speed classes for a particular stability class, although if better information is available, separate values may be input by wind speed class.

 

     The following example illustrates the use of the AVEMIXHT keyword:

 

ME AVEMIXHT  WINTER  A  6*2250.0

ME AVEMIXHT  WINTER  B  6*2000.0

ME AVEMIXHT  WINTER  C  6*1500.0

ME AVEMIXHT  WINTER  D  6*1000.0

ME AVEMIXHT  WINTER  E  6*500.0

ME AVEMIXHT  WINTER  F  6*300.0

50

 

where repeat values have been used to apply the mixing heights to each of the wind speed categories.

 

 

 

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