diff --git a/parameters.jl b/parameters.jl
index 474573a..32c4938 100644
--- a/parameters.jl
+++ b/parameters.jl
@@ -8,7 +8,7 @@ const Numtype = Float32
 # DOMAIN RESOLUTION AND RATIO
 const nx = 100                  # number of grid cells in x-direction
 const Lx = 2000e3               # length of the domain in x-direction
-const L_ratio = 2               # Domain aspect ratio of Lx/Ly
+const L_ratio = 1               # Domain aspect ratio of Lx/Ly
 
 # PHYSICAL CONSTANTS
 const gravity = 10.             # gravitational acceleration
@@ -19,11 +19,11 @@ const ω = 2π/(24*3600)          # Earth's angular frequency [s^-1]
 const R = 6.371e6               # Earth's radius [m]
 
 # WIND FORCING OPTIONS
-const wind_forcing = "channel"  # "channel", "double_gyre", "shear" or "none"
+const wind_forcing = "double_gyre"  # "channel", "double_gyre", "shear" or "none"
 const Fx0 = 0.12                # wind stress strength [Pa], default 0.12
 
 # BOTTOM TOPOGRAPHY OPTIONS
-const topography_feature = "ridges" # "ridge", "seamount", "flat"
+const topography_feature = "flat" # "ridge", "seamount", "flat"
 const topofeat_height = 80.      # height of seamount
 const topofeat_width = 200e3    # horizontal scale [m] of the seamount
 
@@ -36,10 +36,12 @@ const η_refw = 100e3             # width [m] of the tangent used for the interf
 # TIME STEPPING OPTIONS
 const RKo = 4                   # Order of the RK time stepping scheme (3 or 4)
 const cfl = 1.0                 # CFL number (1.0 recommended for RK4, 0.6 for RK3)
-const Ndays = 100            # number of days to integrate for
+const Ndays = 50                # number of days to integrate for
+const nstep_diff = 20           # diffusive part every nstep_diff time steps.
+const nstep_advcor = 10          # advection and coriolis every nstep_advcor time steps.
 
 # BOUNDARY CONDITION OPTIONS
-const bc_x = "nonperiodic"         # "periodic" or anything else for nonperiodic
+const bc_x = "nonperiodic"      # "periodic" or anything else for nonperiodic
 const lbc = 1.                  # lateral boundary condition parameter
                                 # 0 free-slip, 0<lbc<2 partial-slip, 2 no-slip
 
@@ -57,7 +59,7 @@ const ν_const = 500             # [m^2/s] scaling constant for Constant biharmo
 const c_smag = 0.15             # Smagorinsky coefficient [dimensionless]
 
 # TRACER ADVECTION
-const tracer_advection = true   # "true" or "false"
+const tracer_advection = false   # "true" or "false"
 const tracer_relaxation = false  # "true" or "false"
 const injection_region = "rect"  # "west", "south" or "rect"
 const sstrestart = false        # start from previous sst file
@@ -71,9 +73,9 @@ const SSTϕ = 0.5                # latitude/longitude ∈ [0,1] of sst edge
 # OUTPUT OPTIONS
 const output = true                # for nc output
 const output_vars = ["u","sst"]
-const output_dt = 12             # output time step in hours
+const output_dt = 6             # output time step in hours
 #const outpath = "/network/aopp/chaos/pred/kloewer/julsdata/ssthr/"
-const outpath = "/Users/milan/phd/"
+const outpath = "/local/kloewer/julsdata/timest/"
 
 # INITIAL CONDITIONS
 const initial_cond = "rest"   # "rest" or "ncfile"
diff --git a/src/PV_adv.jl b/src/PV_adv.jl
index 78fb5be..8539c3c 100644
--- a/src/PV_adv.jl
+++ b/src/PV_adv.jl
@@ -46,10 +46,10 @@ end
 Energy and enstrophy conserving (in the limit of non-divergent mass flux) scheme with τ = 0."""
 function PV_adv_ArakawaHsu!(qhv,qhu,q,qα,qβ,qγ,qδ,q_u,q_v,U,V,V_u,U_v)
     # Linear combinations α,β,γ,δ of potential vorticity q
-    AHα!(qα,q)
-    AHβ!(qβ,q)
-    AHγ!(qγ,q)
-    AHδ!(qδ,q)
+    #AHα!(qα,q)
+    #AHβ!(qβ,q)
+    #AHγ!(qγ,q)
+    #AHδ!(qδ,q)
 
     # Linear combinations of q and V=hv to yield qhv
     m,n = size(qhv)
diff --git a/src/diffusion.jl b/src/diffusion.jl
index e616308..728e577 100644
--- a/src/diffusion.jl
+++ b/src/diffusion.jl
@@ -177,7 +177,7 @@ function add_drag_diff_tendencies!(u,v,Bu,Bv,LLu1,LLu2,LLv1,LLv2)
 
     @inbounds for j ∈ 1:n
         for i ∈ 1:m
-            u[i+2,j+2] += Δt*(Bu[i+1-ep,j+1] + LLu1[i,j+1] + LLu2[i+1-ep,j])
+            u[i+2,j+2] += nΔt_diff*(Bu[i+1-ep,j+1] + LLu1[i,j+1] + LLu2[i+1-ep,j])
         end
     end
 
@@ -188,7 +188,7 @@ function add_drag_diff_tendencies!(u,v,Bu,Bv,LLu1,LLu2,LLv1,LLv2)
 
     @inbounds for j ∈ 1:n
         for i ∈ 1:m
-             v[i+2,j+2] += Δt*(Bv[i+1,j+1] + LLv1[i,j+1] + LLv2[i+1,j])
+             v[i+2,j+2] += nΔt_diff*(Bv[i+1,j+1] + LLv1[i,j+1] + LLv2[i+1,j])
         end
     end
 end
diff --git a/src/grid.jl b/src/grid.jl
index 6f4e638..d22095c 100644
--- a/src/grid.jl
+++ b/src/grid.jl
@@ -38,7 +38,8 @@ function timestep()
     nt = Int(ceil(Ndays*3600*24/dtint))    # number of time steps to integrate
     dt = Numtype(dtint)                    # convert to Numtype for multiplication of the RHS
     Δt = Numtype(dtint/Δ)                  # timestep combined with grid spacing Δ
-    return dt,Δt,dtint,nt
+    nΔt_diff = Numtype(nstep_diff)*Δt      # timestep for diffusive terms
+    return dt,Δt,nΔt_diff,dtint,nt
 end
 
 """ Returns the tracer advection time step dtadv and the number of timesteps nadvstep after which
@@ -82,8 +83,8 @@ const y_v = Δ*Array(1:ny-1)
 const x_q = if bc_x == "periodic" x_u else Δ*Array(1:nx+1) .- Δ end
 const y_q = Δ*Array(1:ny+1) .- Δ
 
-# halo of ghost points (because of the biharmonic operator) - don't change.
-const halo = 2
+# halo of ghost points - don't change.
+const halo = 2          # 2 because of biharmonic diffusion operator (wider stencil)
 const haloη = 1
 const halosstx = 1      #TODO change for domain decomposition
 const halossty = 0
@@ -107,16 +108,13 @@ const y_v_halo = Δ*Array(-1:ny+1)
 const x_q_halo = if bc_x == "periodic" x_u_halo else Δ*Array(-1:nx+3) .- Δ end
 const y_q_halo = Δ*Array(-1:ny+3) .- Δ
 
-# matrices of x and y positions with halo (dimensionless - actually indices!)
-#TODO think about a grid that works well with nx/ny large and 16bit
-#TODO delete for relative grid - redundant
-const xxT,yyT = meshgrid(Numtype.(Array(1:nx)),Numtype.(Array(1:ny)))
-
 # time and output
-const dt,Δt,dtint,nt = timestep()
+const dt,Δt,nΔt_diff,dtint,nt = timestep()
 const nout = Int(floor(output_dt*3600/dtint))   # output every nout time steps
 const nout_total = (nt ÷ nout)+1                # total number of time steps for output
 const t_vec = Array(0:nout_total-1)*dtint       # time vector for output
 
 # advection time step
 const dtadvu,dtadvv,dtadvint,nadvstep,nadvstep_half = adv_timestep()
+
+println((dtint,dtint*nstep_diff,dtint*nstep_advcor,dtadvint,output_dt*3600))
diff --git a/src/rhs.jl b/src/rhs.jl
index 52b2ba7..b222aa6 100644
--- a/src/rhs.jl
+++ b/src/rhs.jl
@@ -10,28 +10,28 @@ function rhs!(du,dv,dη,u,v,η,Fx,f_q,H,η_ref,
     thickness!(h,η,H)
     Ix!(h_u,h)
     Iy!(h_v,h)
-    Ixy!(h_q,h)
+    #Ixy!(h_q,h)
 
     # mass or volume flux U,V = uh,vh
     Uflux!(U,u,h_u)
     Vflux!(V,v,h_v)
 
     # off-diagonals of stress tensor ∇(u,v), ∇(U,V)
-    ∂x!(dvdx,v)
-    ∂y!(dudy,u)
+    #∂x!(dvdx,v)
+    #∂y!(dudy,u)
     ∂x!(dUdx,U)
     ∂y!(dVdy,V)
 
     # Bernoulli potential
-    speed!(u²,v²,u,v)
-    Ix!(KEu,u²)
-    Iy!(KEv,v²)
+    #speed!(u²,v²,u,v)
+    #Ix!(KEu,u²)
+    #Iy!(KEv,v²)
     Bernoulli!(p,KEu,KEv,η)
     ∂x!(dpdx,p)
     ∂y!(dpdy,p)
 
     # Potential vorticity and advection thereof
-    PV!(q,f_q,dvdx,dudy,h_q)
+    #PV!(q,f_q,dvdx,dudy,h_q)
     PV_adv!(qhv,qhu,q,qα,qβ,qγ,qδ,q_u,q_v,U,V,V_u,U_v)
 
     # adding the terms
@@ -40,6 +40,55 @@ function rhs!(du,dv,dη,u,v,η,Fx,f_q,H,η_ref,
     continuity!(dη,dUdx,dVdy,η,η_ref)
 end
 
+# """Tendencies du,dv,dη of the right-hand side with pressure gradient and wind forcing."""
+# function rhs_pressure!(du,dv,dη,u,v,η,Fx,H,h,h_u,h_v,U,V,dUdx,dVdy,dpdx,dpdy,η_ref)
+#
+#     # layer thickness
+#     thickness!(h,η,H)
+#     Ix!(h_u,h)
+#     Iy!(h_v,h)
+#
+#     # mass or volume flux U,V = uh,vh
+#     Uflux!(U,u,h_u)
+#     Vflux!(V,v,h_v)
+#     ∂x!(dUdx,U)
+#     ∂y!(dVdy,V)
+#
+#     # Pressure gradient
+#     ∂x!(dpdx,η)
+#     ∂y!(dpdy,η)
+#
+#     # adding the terms
+#     momentum_u_pressure!(du,dpdx,Fx)
+#     momentum_v_pressure!(dv,dpdy)
+#     continuity!(dη,dUdx,dVdy,η,η_ref)
+# end
+#
+
+""" Update advective and Coriolis tendencies."""
+function rhs_advcor!(u,v,η,H,h,h_u,h_v,h_q,U,V,dvdx,dudy,u²,v²,KEu,KEv,
+                    q,f_q,qhv,qhu,qα,qβ,qγ,qδ,q_u,q_v,V_u,U_v)
+
+    thickness!(h,η,H)
+    #Ix!(h_u,h)
+    #Iy!(h_v,h)
+    Ixy!(h_q,h)
+
+    # mass or volume flux U,V = uh,vh
+    #Uflux!(U,u,h_u)
+    #Vflux!(V,v,h_v)
+
+    ∂x!(dvdx,v)
+    ∂y!(dudy,u)
+
+    speed!(u²,v²,u,v)
+    Ix!(KEu,u²)
+    Iy!(KEv,v²)
+
+    PV!(q,f_q,dvdx,dudy,h_q)
+    #PV_adv!(qhv,qhu,q,qα,qβ,qγ,qδ,q_u,q_v,U,V,V_u,U_v)
+end
+
 """Layer thickness h obtained by adding sea surface height η to bottom height H."""
 function thickness!(h,η,H)
     m,n = size(h)
@@ -143,6 +192,31 @@ function momentum_v!(dv,qhu,dpdy)
     end
 end
 
+# """Sum up the tendencies of the non-diffusive right-hand side for the u-component."""
+# function momentum_u_pressure!(du,dpdx,Fx)
+#     m,n = size(du) .- (2*halo,2*halo) # cut off the halo
+#     @boundscheck (m+2-ep,n+2) == size(dpdx) || throw(BoundsError())
+#     @boundscheck (m,n) == size(Fx) || throw(BoundsError())
+#
+#     @inbounds for j ∈ 1:n
+#         for i ∈ 1:m
+#             du[i+2,j+2] = -g*dpdx[i+1-ep,j+1] + Fx[i,j]
+#         end
+#     end
+# end
+#
+# """Sum up the tendencies of the non-diffusive right-hand side for the v-component."""
+# function momentum_v_pressure!(dv,qhu,dpdy)
+#     m,n = size(dv) .- (2*halo,2*halo) # cut off the halo
+#     @boundscheck (m+2,n+2) == size(dpdy) || throw(BoundsError())
+#
+#     @inbounds for j ∈ 1:n
+#         for i ∈ 1:m
+#              dv[i+2,j+2] = -g*dpdy[i+1,j+1]
+#         end
+#     end
+# end
+
 """Continuity equation's right-hand side with surface relaxation
 -∂x(uh) - ∂y(vh) + γ*(η_ref - η)."""
 function continuity_surf_forc!(dη,dUdx,dVdy,η,η_ref)
diff --git a/src/time_integration.jl b/src/time_integration.jl
index e3efdd4..2f389d6 100644
--- a/src/time_integration.jl
+++ b/src/time_integration.jl
@@ -55,6 +55,8 @@ function time_integration(u,v,η,sst)
                 qhv,qhu,q,q_u,q_v,
                 qα,qβ,qγ,qδ)
 
+            #rhs_pressure!(du,dv,dη,u1,v1,η1,Fx,H,h,h_u,h_v,U,V,dUdx,dVdy,dpdx,dpdy,η_ref)
+
             if rki < RKo
                 u1 .= u .+ RKb[rki]*Δt*du
                 v1 .= v .+ RKb[rki]*Δt*dv
@@ -67,15 +69,36 @@ function time_integration(u,v,η,sst)
             η0 .+= RKa[rki]*Δt*dη
         end
 
-        # DIFFUSIVE PART - SEMI-IMPLICIT EULER
-        # use u0 = u^(n+1) to evaluate tendencies, add to u0 = u^n + rhs
         ghost_points!(u0,v0,η0)
-        bottom_drag!(Bu,Bv,KEu,KEv,sqrtKE,sqrtKE_u,sqrtKE_v,u0,v0,η0,
+
+        # ADVECTION and CORIOLIS TERMS
+        # although included in the tendency of every RK substep,
+        # only update every nstep_advcor steps!
+        if (i % nstep_advcor) == 0
+            rhs_advcor!(u0,v0,η0,H,h,h_u,h_v,h_q,U,V,dvdx,dudy,u²,v²,KEu,KEv,
+                        q,f_q,qhv,qhu,qα,qβ,qγ,qδ,q_u,q_v,V_u,U_v)
+
+            if adv_scheme == "Sadourny"
+                Iy!(q_u,q)
+                Ix!(q_v,q)
+            elseif adv_scheme == "ArakawaHsu"
+                AHα!(qα,q)
+                AHβ!(qβ,q)
+                AHγ!(qγ,q)
+                AHδ!(qδ,q)
+            end
+        end
+
+        # DIFFUSIVE TERMS - SEMI-IMPLICIT EULER
+        # use u0 = u^(n+1) to evaluate tendencies, add to u0 = u^n + rhs
+        if (i % nstep_diff) == 0    # evaluate only every nstep_diff time steps
+            bottom_drag!(Bu,Bv,KEu,KEv,sqrtKE,sqrtKE_u,sqrtKE_v,u0,v0,η0,
                 H,h,u²,v²,h_u,h_v)
-        diffusive!(dudx,dudy,dvdx,dvdy,DS,DS_q,DT,νSmag,νSmag_q,Lu,Lv,
+            diffusive!(dudx,dudy,dvdx,dvdy,DS,DS_q,DT,νSmag,νSmag_q,Lu,Lv,
                 dLudx,dLudy,dLvdx,dLvdy,S11,S12,S21,S22,
                 LLu1,LLu2,LLv1,LLv2,u0,v0)
-        add_drag_diff_tendencies!(u0,v0,Bu,Bv,LLu1,LLu2,LLv1,LLv2)
+            add_drag_diff_tendencies!(u0,v0,Bu,Bv,LLu1,LLu2,LLv1,LLv2)
+        end
 
         # RK3/4 copy back from substeps
         u .= u0
@@ -86,19 +109,11 @@ function time_integration(u,v,η,sst)
         # TRACER ADVECTION
         # mid point (in time) velocity for the advective time step
         if tracer_advection && ((i+nadvstep_half) % nadvstep) == 0
-            # um .= zero(u)#.+Numtype(0.5)
-            # um[:,end-2] .-= Numtype(0.5)
-            # um[:,3] .-= Numtype(0.5)
-            #
-            # vm .= zero(v)
-            # vm[3,:] .+= Numtype(0.5)
-            # vm[end-2,:] .+= Numtype(0.5)
             um .= u
             vm .= v
         end
 
         if tracer_advection && (i % nadvstep) == 0
-            #departure!(um,vm,u_T,v_T,um,vm,um_T,vm_T,uinterp,vinterp,xd,yd)
             departure!(u,v,u_T,v_T,um,vm,um_T,vm_T,uinterp,vinterp,xd,yd)
             adv_sst!(ssti,sst,xd,yd)
             if tracer_relaxation
diff --git a/src/tracer_adv.jl b/src/tracer_adv.jl
index d01c97e..0e410a6 100644
--- a/src/tracer_adv.jl
+++ b/src/tracer_adv.jl
@@ -13,25 +13,25 @@ function departure!(u,v,u_T,v_T,um,vm,um_T,vm_T,uinterp,vinterp,xd,yd)
     Iy!(vm_T,vm)
 
     # simple mid-point in time advection
-    #backtraj!(xd,xxT,dtadvu,um_T)
-    #backtraj!(yd,yyT,dtadvv,vm_T)
+    #backtraj!(xd,dtadvu,um_T)
+    #backtraj!(yd,dtadvv,vm_T)
 
     # fixed-point iteration for departure point
     # initial guess for departure point - mid point
-    backtraj!(xd,xxT,one_half*dtadvu,u_T)
-    backtraj!(yd,yyT,one_half*dtadvv,v_T)
+    backtraj!(xd,one_half*dtadvu,u_T)
+    backtraj!(yd,one_half*dtadvv,v_T)
 
     # interpolate um,vm onto mid-point
     interp_uv!(uinterp,um_T,xd,yd)
     interp_uv!(vinterp,vm_T,xd,yd)
 
     # update departure point
-    backtraj!(xd,xxT,dtadvu,uinterp)
-    backtraj!(yd,yyT,dtadvv,vinterp)
+    backtraj!(xd,dtadvu,uinterp)
+    backtraj!(yd,dtadvv,vinterp)
 end
 
-""" Solves the trajectory equation for a given arrival point ra (this can be either x or y),
-a time step dt and the velocity uv (this can be u or v). One function for three cases
+""" Solves the trajectory equation for a given time step dt and the velocity uv (this can be u or v).
+One function for three cases
 
 (i) u is interpolated from u-grid with halo onto T-grid
 (ii) v is interpolated from v-grid with halo onto T-grid
@@ -39,9 +39,8 @@ a time step dt and the velocity uv (this can be u or v). One function for three
 
 Uses relative grid nodes in the departure points rd, such that actually solved is rd = 0 - dt*uv.
 The indices i,j of rd determine the arrival grid point."""
-function backtraj!(rd::AbstractMatrix,ra::AbstractMatrix,dt::Real,uv::AbstractMatrix)
+function backtraj!(rd::AbstractMatrix,dt::Real,uv::AbstractMatrix)
     m,n = size(rd)
-    @boundscheck (m,n) == size(ra) || throw(BoundsError())
 
     if (m,n) == size(uv)            # update departue point case, matrices have same size
         ishift = 0