--- manual/s_phys_pkgs/text/gchem.tex	2004/10/12 18:16:03	1.2
+++ manual/s_phys_pkgs/text/gchem.tex	2004/11/29 00:47:04	1.3
@@ -30,7 +30,7 @@
 {\it GCHEM\_OPTIONS.h} includes the compiler options to be used
 in any experiment. For instance \#define ALLOW\_CFC allows
 the CFC code to be run. An important compiler option is
- \#define PTRACERS\_SEPARATE\_FORCING which determined 
+ \#define GCHEM\_SEPARATE\_FORCING which determined 
 how and when the tracer forcing is applied (see discussion
 on Forcing below).
  There are further runtime parameters
@@ -65,7 +65,7 @@
 
 There are two routine used to initialize parameters and fields
 needed by the experiment packages. These are
-{\it gchem\_init\_fixed.F} which is called from packages\_init\_fixed.F, and
+{\it gchem\_init\_fixed.F} which is called from \textit{packages\_init\_fixed.F}, and
 {\it gchem\_init\_vari.F} called from 
 packages\_init\_variable.F. The first should
 be used to call a subroutine specific to the tracer experiment
@@ -80,7 +80,7 @@
 {{\bf LOADING FIELDS}}\\
 External forcing fields used by the tracer experiment are read
 in by a subroutine (specific to the tracer experiment) called from
-{\it gchem\_fields\_load.F}. This latter is called from forward\_step.F.
+{\it gchem\_fields\_load.F}. This latter is called from \textit{forward\_step.F}.
 
 \vspace{.5cm}
 
@@ -93,35 +93,41 @@
 interface. For tracers that are essentially passive (e.g. CFC's)
 but may have some surface boundary conditions
 this can easily be done within the regular tracer timestep. In this case
-{\it gchem\_forcing\_int.F} is called from ptracers\_integrate.F.
+{\it gchem\_calc\_tendency.F} is called from {\it forward\_step.F}, where the 
+reactive (as opposed to the advective diffusive) tendencies are computed.
+These tendencies, stored on the 3D field \textbf{gchemTendency}, are added to
+the passive tracer tendencies \textbf{gPtr} in {\it gchem\_add\_tendency.F}, 
+which is called from {\it ptracers\_forcing.F}.
 For tracers with more complicated dependencies on each other,
 and especially tracers which require a smaller timestep than
 deltaTtracer, it will be easier to use {\it gchem\_forcing\_sep.F}
 which is called from forward\_step.F. There is a 
 compiler option set in {\it GCHEM\_OPTIONS.h} that determines
-which method is used: \#define PTRACERS\_SEPARATE\_FORCING
+which method is used: \#define GCHEM\_SEPARATE\_FORCING
 does the latter where tracers are forced separately from the
-advection-diffusion code, and \#undef PTRACERS\_SEPARATE\_FORCING
+advection-diffusion code, and \#undef GCHEM\_SEPARATE\_FORCING
 includes the forcing in the regular timestepping.
 
 \vspace{.5cm}
 
 \noindent
 {{\bf DIAGNOSTICS}}\\
-This package also includes routines {\it gchem\_monitor.F} and 
-{\it gchem\_mon\_print.F} which print out tracer statistics
-as often as the model dynamic statistic diagnostics (dynsys) are written.
+This package also also used the passive tracer routine {\it ptracers\_monitor.F}
+which prints out tracer statistics 
+as often as the model dynamic statistic diagnostics (dynsys) are written (or
+as prescribed by the runtime flag \textbf{PTRACERS\_monitorFreq}, set in {\it data.ptracers}).
 There is also a placeholder for any tracer experiment
 specific diagnostics to be calculated and printed to files.
 This is done in {\it gchem\_diags.F}. For instance the time average CO2
 air-sea fluxes, and sea surface pH (among others) are written
-out by dic\_biotic\_diags.F which is called from gchem\_diags.F.
+out by {\it dic\_biotic\_diags.F} which is called from {\it gchem\_diags.F}.
 
 \subsection{Do's and Don'ts}
 
-The pkg ptracer is required with use with this pkg.
-By itself, gchem pkg will read in {\bf data.gchem} and will
-write out ptracer diagnostics. It requires tracer experiment
+The pkg ptracer is required with use with this pkg. Also, as usual, the
+runtime flag \textbf{useGCHEM} must be set to \textbf{.TRUE.} in \textbf{data.pkg}.
+By itself, gchem pkg will read in \textbf{data.gchem} and will
+write out gchem diagnostics. It requires tracer experiment
 specific calls to do anything else (for instance the calls
 to dic and cfc pkgs).