Index: LMDZ6/trunk/libf/phylmd/atke_exchange_coeff_mod.F90
===================================================================
--- LMDZ6/trunk/libf/phylmd/atke_exchange_coeff_mod.F90	(revision 4674)
+++ LMDZ6/trunk/libf/phylmd/atke_exchange_coeff_mod.F90	(revision 4675)
@@ -240,8 +240,10 @@
         DO igrid=1,ngrid
            qq=max(sqrt(2.*tke(igrid,ilay)),1.e-10)
-           delta=1.+4.*dtime/cepsilon/l_exchange(igrid,ilay)/(2.**(3/2)) * &
-                (qq+dtime*l_exchange(igrid,ilay)/sqrt(2.)*Sm(igrid,ilay)*shear2(igrid,ilay) &
-                *(1.-Ri(igrid,ilay)/Prandtl(igrid,ilay)))
-           qq=(-1. + sqrt(delta))/dtime*cepsilon*sqrt(2.)*l_exchange(igrid,ilay)
+           delta=(2.*sqrt(2.)*cepsilon*l_exchange(igrid,ilay)/dtime)**2. &
+                 +4.*(2.*sqrt(2.)*cepsilon*l_exchange(igrid,ilay)/dtime*qq + &
+                 2.*l_exchange(igrid,ilay)*l_exchange(igrid,ilay)*cepsilon*Sm(igrid,ilay) &
+                 *shear2(igrid,ilay) * (1. - Ri(igrid,ilay) / Prandtl(igrid,ilay)))
+           qq=(-2.*sqrt(2.)*cepsilon*l_exchange(igrid,ilay)/dtime + sqrt(delta))/2.
+           qq=max(0.,qq)
            tke(igrid,ilay)=0.5*(qq**2) 
         ENDDO