diff --git a/cost_function.py b/cost_function.py
index c87c0ffa8c78e0d338c2d57cc6348d4ab9ffd2b8..d4454b2725f25c24ed4f95e66ca07fb65a4b9b2b 100755
--- a/cost_function.py
+++ b/cost_function.py
@@ -26,6 +26,8 @@ import util_eddies
 import bisect
 import argparse
 
+Omega = 2 * math.pi / 86164.
+
 def calculate_radii_rossby(list_eddies, e_overestim, handlers, array_d_init):
     """Compute average on list_eddies of Rossby number and radius of
     maximum speed contour.
@@ -35,7 +37,6 @@ def calculate_radii_rossby(list_eddies, e_overestim, handlers, array_d_init):
     radii = 0 # in m
     rossby = 0
     n_valid_Rossby = 0
-    Omega = 2 * math.pi / 86164.
     n_eddies = len(list_eddies)
 
     for n in list_eddies: