[gradsusr] related Scripts for lnθe∗ -lnθ

[Faeze Shoja]

HIMy projected is focused on studyingtropical cyclone. As far as I know, I have to compute some of the parameters related to the genesis potential index (GPI)such as Vpot.   I don't know how calculate( lnθe∗ -lnθ) in GRADS? 
 "θe∗ is the saturation equivalent potential temperature at the ocean surface, and θe is the
boundary layer equivalent potential temperature" 
 Can you help me?can you send related Scripts for me?  Thank you for you consideration andyour time  
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