# Changelog

## Data version 1.0 — 2026-05-01

Initial release of CAS-TECRecon30: 9,862 daily global ionospheric TEC maps
covering 1999-001 through 2025-365 at 30-minute cadence, with no missing days.

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# Distribution history

Entries below record changes to how version 1.0 is packaged and served. They do
not change any TEC value.

## 2026-07-27 — distribution layout reorganised

The release originally consisted of 27 yearly ZIP archives at the top level.
Partners asked for the per-day layout that IGS-style IONEX archives conventionally
use, so the data is now offered in three equivalent forms under `v1.0/`:

- **Added `v1.0/daily/`** — one gzip-compressed IONEX file per day under per-year
  folders (`v1.0/daily/2018/trec0010.18i.gz`). This is now the canonical tree.
  Every file is byte-identical to the corresponding member of the yearly ZIP; this
  was verified by decompressing and comparing against the ZIP members directly.
- **Added `v1.0/netcdf/`** — one CF-1.8 netCDF-4 file per year, TEC packed as
  int16 in units of 0.1 TECU with `scale_factor = 0.1`. Because the IONEX source
  already stores integers with `EXPONENT -1`, this packing is bit-exact rather
  than lossy. Intended for array and machine-learning workflows that should not
  have to parse 9,862 ASCII files.
- **Moved the yearly ZIPs to `v1.0/bulk/`** — unchanged bytes, and still the
  fastest way to fetch a whole year. Their SHA-256 sums are the same as those
  published on 2026-07-18.
- **Added per-file SHA-256 sums** — `SHA256SUMS.txt` inside every `daily/<year>/`
  folder and alongside `bulk/` and `netcdf/`. Previously only the yearly ZIPs
  were covered.
- **Added `v1.0/filelist.txt`** — a complete relative-path manifest for scripted
  bulk download.
- **Added `LICENSE`** (full CC BY 4.0 legal code), **`CITATION.cff`**, and this
  changelog. The licence was previously stated only in prose in the README.
- **Added a `latest` symlink** pointing at `v1.0/`, so scripts can either pin a
  version or always follow the newest one.

The version number is now part of the path. Any future release that changes TEC
values will appear as a sibling `v1.1/` rather than overwriting `v1.0/`, so a URL
cited in a paper keeps returning the bytes it returned on the day it was cited.

Note for anyone who bookmarked a URL before this date: the yearly ZIPs moved from
the top level into `v1.0/bulk/`. The file names and their contents are unchanged.