# CAS-TECRecon30: Global Ionospheric TEC Maps, 1999–2025, 30-min Cadence

**Version:** 1.0 (2026-05-01)
**Provider:** Kun Chang & Ang Liu, Aerospace Information Research Institute,
Chinese Academy of Sciences
**License:** CC BY 4.0

## Background

Historical Global Ionospheric Map (GIM) archives are limited by 2-hour
sampling and spatial gaps in the early years. CAS-TECRecon30 provides a
complete, uniform global TEC record derived from the CAS GIM archive:
every day from 1999 to 2025 at 30-minute cadence on the standard
2.5° × 5° grid. Earlier 2-hourly days were reconstructed with the
TECRecon deep-learning framework; later days retain their native 30-min
sampling. Independent validation against ground-GNSS slant TEC
observations (2013–2015) yields a mean STEC RMS of 2.67 TECU.

For methodology and validation details, see:
*TECRecon: Reconstructing Global Ionospheric Maps for 1999–2025 at 30-Min
Cadence Using Masked Autoencoders and a Spatiotemporal Transformer*
(Chang, Liu, et al.).

## Data format

- `YYYY/trecDDD0.YYi` — IONEX 1.0, ASCII; one file per day
  (9,862 days, 1999-001 … 2025-365, no gaps)
- 49 TEC maps per file, 00:00–24:00 UT, INTERVAL 1800 s
- Grid: 71 × 73 (lat 87.5 … −87.5, step −2.5°; lon −180 … 180, step 5°)
- Values in 0.1 TECU (EXPONENT −1); single-layer shell at 450 km
- TEC maps only (no RMS section)

## Data integrity

- No invalid values: every TEC cell in the archive is a valid number.
- Daily files are continuous across midnight: each day's 24:00 map is
  identical to the next day's 00:00 map.
- Every file verified: 49 maps, 1800-s interval, full 71 × 73 grid.

## Contact

Kun Chang (changkun@aircas.ac.cn), Aerospace Information Research
Institute, Chinese Academy of Sciences.