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ERA5 Momentum Flux Processing Pipeline

This collection of scripts processes ERA5 reanalysis data to compute and analyze momentum fluxes. The pipeline consists of three main steps:

1. Download ERA5 Model Level Data

download_era5_modellevel_data.py

Downloads ERA5 model level analysis fields including temperature (T), zonal wind (U), meridional wind (V), and vertical velocity (W) for specified time periods.

Usage:

python download_era5_modellevel_data.py YEAR MONTH [START_DAY END_DAY]
  • If START_DAY and END_DAY are not provided, processes entire month
  • Downloads hourly data at 0.3° resolution
  • Outputs NetCDF files to specified directory

2. Compute Momentum Fluxes

compute_momentum_flux_from_era5.py

Calculates resolved momentum fluxes using Helmholtz decomposition to separate rotational and divergent components.

Usage:

python compute_momentum_flux_from_era5.py YEAR MONTH [START_DAY END_DAY]

Key features:

  • Computes zonal (uw) and meridional (vw) momentum fluxes
  • Uses windspharm for spherical harmonic transformations
  • Applies T21 truncation for scale separation
  • Outputs hourly NetCDF files with computed fluxes

3. Coarse-grain Momentum Fluxes

coarsegrain_computed_momentum_fluxes.py

Regrids the high-resolution momentum flux data to a coarser T42 grid and combines with additional derived quantities.

Usage:

python coarsegrain_computed_momentum_fluxes.py YEAR START_MONTH END_MONTH [START_DAY END_DAY]

Key features:

  • Uses xESMF for conservative regridding
  • Computes additional fields like pressure, vertical gradients, and stratification frequency
  • Combines resolved and parameterized momentum fluxes
  • Outputs comprehensive training dataset in NetCDF format

The final output includes:

  • Input fields: u, v, w, temperature, pressure, vertical wind gradients, stratification frequency, surface geopotential
  • Output fields: resolved and parameterized momentum fluxes in both zonal and meridional directions