set carma_sulfnuc_method namelist option

	modified:   bld/build-namelist
	modified:   bld/namelist_files/namelist_definition.xml

bld/build-namelist

@@ -1268,6 +1268,7 @@ if ($carma ne 'none') {
   add_default($nl, 'carma_model',       'val'=>$carma);
   add_default($nl, 'carma_flag',        'val'=>'.true.');
   add_default($nl, 'history_carma',     'val'=>'.true.');
+  add_default($nl, 'carma_sulfnuc_method','val'=>'ZhaoTurco');
 }
 if ($carma eq 'bc_strat') {
   add_default($nl, 'carma_do_drydep',   'val'=>'.true.');
@@ -1587,7 +1588,7 @@ if (defined $nl->get_value('prescribed_strataero_3modes')) {
 
 # determine if prescribed stratospheric aerosol data is needed
 if ( ($het_chem) || ($nl->get_value('prescribed_strataero_feedback') =~ /$TRUE/io ) ){
-    if ( ($carma ne 'sulfate') && !($nl->get_value('modal_strat_sulfate') =~ /$TRUE/io) ) { # if no prognostic stratospheric aerosols
+    if ( !($nl->get_value('modal_strat_sulfate') =~ /$TRUE/io) ) { # if no prognostic stratospheric aerosols
 
         unless (defined $nl->get_value('prescribed_strataero_type')) {
             add_default($nl, 'prescribed_strataero_type','val'=>'CYCLICAL');

bld/namelist_files/namelist_definition.xml

@@ -4476,6 +4476,20 @@ is not active.
 Default: none
 </entry>
 
+<entry id="carma_sulfnuc_method" type="char*10" category="carma"
+       group="carma_nl" valid_values="ZhaoTurco,Vehkamaki" >
+ Nucleation methods:
+  ZhaoTurco
+     Zhao and Turco, JAS, V.26, No.5, 1995.
+  Vehkamaki
+     Vehkamaki, H., M. Kulmala, I. Napari, K.E.J. Lehtinen,
+     C. Timmreck, M. Noppel and A. Laaksonen, 2002,
+     An improved parameterization for sulfuric acid-water nucleation
+     rates for tropospheric and stratospheric conditions,
+     J. Geophys. Res., 107, 4622, doi:10.1029/2002jd002184
+Default: none
+</entry>
+
 <entry id="carma_conmax" type="real" category="carma"
        group="carma_nl" valid_values="" >
 A fraction that scales how tight the convergence criteria are to