Detailed Analysis of HOMEDIR in the Weather Forecast System

The HOMEDIR: '/scratch1/NCEPDEV/global/${USER}' setting defines a critical path in the global weather forecast modeling system. This directory serves multiple specialized functions:

Core Usage Purposes

1. Experiment Root Directory

   • Serves as the base location for experiment directories (EXPDIR)
   • Each forecast experiment (identified by PSLOT) typically creates a subdirectory here
   • Contains the workflow configuration files (XML definitions for Rocoto)

2. Persistent Model Output Storage

   • Houses COM directories that store model outputs needing to persist between cycles
   • Stores post-processed GRIB2 files and other forecast products
   • Maintains ensemble member outputs for statistical processing

3. Restart File Repository

   • Contains model restart files required for cycling data assimilation
   • Stores initial condition files modified by the user
   • Holds atmospheric and oceanic state information between forecast cycles

4. Configuration Management

   • Stores custom namelists and parameter files
   • Contains user modifications to model physics options
   • Houses experiment-specific variable settings

5. Log Collection

   • Central repository for job logs that need persistence
   • Maintains error reports across multiple cycles
   • Stores performance metrics and timing information

Technical Characteristics

1. File System Properties

   • Located on scratch1 filesystem, optimized for high I/O performance
   • Not backed up but more persistent than temporary directories
   • Higher quota allocation than standard home directories

2. Workflow Integration

   • Referenced by the Rocoto workflow manager for job dependencies
   • Used as a base path for experiment directory structures
   • Linked to NOSCRUB variable for long-term data retention

3. User Management Responsibilities

   • User is responsible for managing quota usage
   • Requires periodic cleanup of old experiments
   • Not automatically purged like STMP and PTMP directories

4. Path Relationships

   • Distinguished from STMP and PTMP which handle transient data
   • More persistent than job-specific temporary directories
   • Less permanent than archive storage (HPSS) defined in ATARDIR

This directory is fundamental to the workflow's data management strategy, providing the balance between performance, persistence, and user-specific isolation needed for operational meteorological modeling.