From 159a90db03bbb604aa6450727b05243bc1928f67 Mon Sep 17 00:00:00 2001
From: David Dowell <David.Dowell@noaa.gov>
Date: Wed, 1 Nov 2023 15:22:10 +0000
Subject: [PATCH] Changes for reducing the influence of reflectivity
 observations in precipitation.

---
 src/gsi/obsmod.F90      |  3 ++-
 src/gsi/read_dbz_nc.f90 | 12 +++++++++---
 src/gsi/setupdbz.f90    |  5 ++++-
 3 files changed, 15 insertions(+), 5 deletions(-)

diff --git a/src/gsi/obsmod.F90 b/src/gsi/obsmod.F90
index c43a23c1e6..3cdb3f4ec1 100644
--- a/src/gsi/obsmod.F90
+++ b/src/gsi/obsmod.F90
@@ -769,7 +769,8 @@ subroutine init_obsmod_dflts
     if_model_dbz=.false.
     if_model_fed=.false.
     innov_use_model_fed=.false.
-    inflate_obserr=.false.
+!   increase error for reflectivity observation when |O-F| exceeds gross error magnitude
+    inflate_obserr=.true.
     whichradar="KKKK"
 
     oneobradid="KKKK"
diff --git a/src/gsi/read_dbz_nc.f90 b/src/gsi/read_dbz_nc.f90
index 7f8604b9d2..f4bf288c9a 100644
--- a/src/gsi/read_dbz_nc.f90
+++ b/src/gsi/read_dbz_nc.f90
@@ -412,9 +412,15 @@ subroutine read_dbz_nc(nread,ndata,nodata,infile,lunout,obstype,sis,hgtl_full,no
 ! changed to hard-coded value for now; dbznoise used for two different purposes in this subroutine:
 !                   (1) threshold for lowest reflectivity value considered to be an observation and 
 !                   (2) ob error
-        thiserr = 5.0_r_kind
-                 
- 
+
+!       Specify a larger error standard deviation for reflectivity observations in precipitation
+!       than for reflectivity observations that indicate a lack of preciptation.
+        if( dbzQC(i,j,k) < 5.0_r_kind ) then
+          thiserr = 5.0_r_kind
+        else
+          thiserr = 10.0_r_kind
+        end if
+
         nread = nread + 1
  
  !####################       Data thinning       ###################
diff --git a/src/gsi/setupdbz.f90 b/src/gsi/setupdbz.f90
index 453c4a5f8d..a1951ef95b 100644
--- a/src/gsi/setupdbz.f90
+++ b/src/gsi/setupdbz.f90
@@ -1260,7 +1260,10 @@ subroutine setupdbz(obsLL,odiagLL,lunin,mype,bwork,awork,nele,nobs,is,radardbz_d
          end if
 
      else
-        if (ratio > cgross(ikx) .or. ratio_errors < tiny_r_kind) then
+
+!       Apply gross error check only to reflectivity observations in precipitation (>= 5 dBZ).
+        if ( ( (data(idbzob,i) >= 5_r_kind) .and. (ratio > cgross(ikx)) ) .or. (ratio_errors < tiny_r_kind) ) then
+
            if ( inflate_obserr .and. (ratio-cgross(ikx)) <= cgross(ikx) .and. ratio_errors >= tiny_r_kind) then 
            ! Since radar reflectivity can be very different from the model background
            ! good observations may be rejected during this QC step.  However, if these observations