J-M, Any idea why lat-lon version of HS94 would be unstable with p* coordinates? Perhaps the zonal filters? Did you ever try hs94.128x64x5 with p*? A. -- Dr Alistair Adcroft http://www.mit.edu/~adcroft MIT Climate Modeling Initiative tel: (617) 253-5938 EAPS 54-1523, 77 Massachusetts Ave, Cambridge, MA, USA