TSC ninst mods

tsc.py

index 330677383..4a22ab908 100644
--- a/CIME/SystemTests/tsc.py
+++ b/CIME/SystemTests/tsc.py
@@ -105,8 +105,12 @@ class TSC(SystemTestsCommon):
 
         nstep_output = OUT_FREQ // dtime
         for iinst in range(1, NINST + 1):
+
+            cmd = '\cp -f ' +  f'user_nl_{self.atmmod} ' +  f'user_nl_{self.atmmod}_'+str(iinst).zfill(4) + '\n'
+            os.system(cmd)
+
             with open(
-                f"user_nl_{self.atmmod}_" + str(iinst).zfill(4), "w"
+                f"user_nl_{self.atmmod}_" + str(iinst).zfill(4), "a"
             ) as atmnlfile, open(
                 f"user_nl_{self.lndmod}_" + str(iinst).zfill(4), "w"
             ) as lndnlfile: