# Presentation: 528058

## High Level Overview of GSI System

- John C. Derber
- NOAA/NWS/NCEP/EMC

## Orientation Meeting general comments

- This orientation meeting was set up because there were several external regional GSI users (or potential users) visiting EMC in Jan. and wanted instruction.
- Meeting is intended to be a description of current system not a scientific discussion.
- We acknowledge that not everything is done in “best” way –
- suggestions welcomed
- but not all suggestions will be adopted

## Orientation Meeting general comments

- GSI analysis code is an evolving system.
- Scientific advances – e.g.,
- situation dependent background errors
- new satellite data
- new analysis variables
- Improved coding – e.g.,
- Bug fixes
- Removal of unnecessary computations, arrays, etc.
- More efficient algorithms
- Generalizations of code to allow use on different compute platforms
- Improved documentation

## Orientation Meeting general comments

- New versions released approximately every month
- Old versions are not supported
- Developers are expected to keep up with current version
- Code is intended to become Operational
- must satisfy NCEP coding requirements
- must fit into NCEP infrastructure
- EMC does not have resources to provide high level of support.

## History

- The GSI system was initially developed as the next generation global analysis system
- Wan-Shu Wu, R. James Purser, David Parrish
*Three-Dimensional Variational Analysis with spatially Inhomogeneous Covariances. Mon. Wea. Rev., 130, 2905-2916.*
- Based on SSI analysis system
- Replace spectral definition for background errors with grid point version based on recursive filters

## History

- After development of initial GSI analysis system, desire for single global/regional analysis system expressed by EMC management
- realization that GSI fairly straightforward to modify for both applications
- GMAO collaboration
- Modification to fit into WRF and NCEP infrastructure
- Evolution to ESMF

## Basic analysis problem

**J = J****b**** + J****o**** + J****c**
**J = (x-x****b****)****T****B****-1****(x-x****b****) + (H(x)-y****0****)****T****(E+F)****-1****(H(x)-y****0****) + J****C**
**J = Fit to background + Fit to observations + constraints**
**x****	****= Analysis**
**x****b****	****= Background**
**B****	****= Background error covariance**
**H****	****= Forward model**
**y****0****	****= Observations**
**E+F****	****= R = Instrument error + Representativeness error**
**J****C****    ****	****= Constraint term**

## Overview of presentations

- Data usage
- Input data (Keyser)
- Observation error and basic QC (Wu)
- Satellite radiances (Derber)
- Radar and surface data (under development -Marshall/Pondeca)
- Nonlinear QC (under development – Parrish)

## Overview of presentations

- Background error
- Recursive filters (Purser)
- Background errors and their estimation (Wu)
- Anisotropic capabilities (under development – Parrish/Pondeca)
- Solution of minimization problem
- Overview of code (Treadon)
- Minimization technique (Derber)

## Overview of presentations

- Running the system
- Connections to WRF (Parrish)
- Analysis Input/Output files (Treadon)
- Cycling issues (Wu)
- Coding issues (Treadon)

## GSI Code - General Flow

- User input &
- initializations

- Read in &
- distribute
- observations

- Additional
- initializations

- Outer loop
- (Read/distribute) guess & derived fields
- (Read/distribute) background error
- Set up right hand side of analysis equation
- Call inner loop
- Compute gradient information
- Apply background error
- Compute search direction
- Compute step size
- Update analysis increment

- Write analysis & related output

## Expected Scientific advancements

- Inclusion of new types of data
- COSMIC GPS – radio-occultation
- Radiance data
- SSM/I and SSM/IS radiances
- NASA instruments from AQUA, TERRA, CHEM
- NPOESS and METOP
- Next Generation Geostationary satellite
- Doppler radial velocities and reflectivies
- Precipitation observations
- Cloud observations
- Ozone observations

## Expected Scientific advancements

- Improved specification of observational errors
- Situation dependent representativeness errors
- Increased granularity in specification of obs errors.
- Advanced DA techniques
- Situation dependent background errors
- 4-D var.
- Improved balance constraints

## Expected Scientific advancements

- New analysis variables
- SST
- Clouds
- Aerosols
- Precipitation
- Constituents
- Others