From 46b37ba7f953f7ec48f91c7d450b45a5279dc8e6 Mon Sep 17 00:00:00 2001
From: Anna Shlyaeva <annash@ucar.edu>
Date: Fri, 21 Feb 2025 05:52:50 -0700
Subject: [PATCH] Add options to inflate the ensemble while recentering (#1501)

# Description

Adds code to the ensemble recentering to optionally inflate/deflate the
ensemble variance by either a scalar (same for all variables) or a field
from the file (has to be specified for all variables).

This is not exercised yet, since we don't know the parameters of
inflation/deflation yet, but I tested with both options to check whether
it behaves as expected.

Note: in the future refactoring we should switch to oops::Inflation that
provides several different inflation options.

# Issues

Related to #1496 (doesn't fix yet since we need to decide what
parameters to use this with)

# Automated CI tests to run in Global Workflow
<!-- Which Global Workflow CI tests are required to adequately test this
PR? -->
- [ ] atm_jjob <!-- JEDI atm single cycle DA !-->
- [ ] C96C48_ufs_hybatmDA <!-- JEDI atm cycled DA !-->
- [ ] C96C48_hybatmaerosnowDA  <!-- JEDI aero/snow cycled DA !-->
- [ ] C48mx500_3DVarAOWCDA <!-- JEDI low-res marine 3DVar cycled DA !-->
- [x] C48mx500_hybAOWCDA <!-- JEDI marine hybrid envar cycled DA !-->
- [ ] C96C48_hybatmDA <!-- GSI atm cycled DA !-->

---------

Co-authored-by: Anna Shlyaeva <anna.v.shlyaeva@noaa.gov>
Co-authored-by: Guillaume Vernieres <guillaume.vernieres@noaa.gov>
---
 utils/soca/gdas_ens_handler.h | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/utils/soca/gdas_ens_handler.h b/utils/soca/gdas_ens_handler.h
index d3f22d15f..4674c392d 100644
--- a/utils/soca/gdas_ens_handler.h
+++ b/utils/soca/gdas_ens_handler.h
@@ -170,6 +170,22 @@ namespace gdasapp {
           // Set variables to zero if specified in the configuration
           postProcIncr.setToZero(incr);
 
+          // Optionally apply inflation
+          if (fullConfig.has("ensemble inflation.value")) {
+            const double inflation = fullConfig.getDouble("ensemble inflation.value");
+            mom6_incr *= inflation;
+            oops::Log::info() << "incr after scalar inflation " << i << ":"
+                              << mom6_incr << std::endl;
+          }
+          if (fullConfig.has("ensemble inflation.field")) {
+            soca::Increment weight(geomOut, mom6_incr.variables(), mom6_incr.validTime());
+            const eckit::LocalConfiguration weightConf(fullConfig, "ensemble inflation.field");
+            weight.read(weightConf);
+            mom6_incr.schur_product_with(weight);
+            oops::Log::info() << "incr after field inflation " << i << ":"
+                              << mom6_incr << std::endl;
+          }
+
           // Save the increments used to initialize the ensemble forecast
           result = postProcIncr.save(mom6_incr, i+1);