diff --git a/R/sysdata.rda b/R/sysdata.rda
index a4292f4c..d96b2bc7 100644
Binary files a/R/sysdata.rda and b/R/sysdata.rda differ
diff --git a/data-raw/1_Input/treatments/tr_siteparamin/siteparam.in b/data-raw/1_Input/treatments/tr_siteparamin/siteparam.in
index 624028f6..28b936e9 100644
--- a/data-raw/1_Input/treatments/tr_siteparamin/siteparam.in
+++ b/data-raw/1_Input/treatments/tr_siteparamin/siteparam.in
@@ -53,12 +53,13 @@
 1.1		# range
 
 #---- Site location and topography
--105.58	# longitude of the site in degrees (W < 0; E > 0)
+-105.58	# longitude (degrees; W < 0; E > 0)
 				# (currently not used by simulation, but useful for site documentation)
-39.59		# latitude of the site in degrees (N > 0; S < 0)
-1000		# elevation of site (m a.s.l.)
-0		# slope at site (degrees): no slope = 0, vertical = 90
-999		# aspect at site (degrees): S=0, E=-90, N=±180, W=90; ignored if slope = 0 or aspect = 999
+39.59		# latitude (degrees; N > 0; S < 0)
+1000		# elevation (m a.s.l.)
+0				# slope (degrees): no slope = 0, vertical surface = 90
+NAN			# aspect = surface azimuth angle (degrees): S=0, E=-90, N=±180, W=90;
+				# ignored if slope = 0 or aspect takes a missing value, i.e., NAN or 999
 
 #---- Soil temperature
 # from Parton 1978, ch. 2.2.2 Temperature-profile Submodel