Aura (OMI + MLS)

NASA’s flagship atmospheric chemistry mission — the third platform in the A-Train constellation. OMI’s tropospheric NO₂ + total ozone records are foundational for air-quality science and the Antarctic ozone hole monitoring. MLS measures stratospheric chemistry profiles critical for ozone-layer assessment.

What it sees

• OMI (Ozone Monitoring Instrument): UV-Visible spectrometer 270-500 nm. Same band class as Sentinel-5P TROPOMI (which is OMI’s spiritual successor). 13×24 km nadir pixel.
• MLS (Microwave Limb Sounder): limb-emission microwave; profiles stratospheric O₃, H₂O, ClO, BrO, HCl, HNO₃, N₂O, CO from ~10-100 km altitude. The only operational limb sounder for many chemistry species.
• Aura was the platform for HIRDLS (failed within months) and TES (decommissioned 2018) — both no longer producing data.

Why it matters

• Total ozone trend since 2004 — extends the multi-decadal record from Nimbus-7 TOMS (1978-1993) + EP-TOMS through OMI to TROPOMI (2018+). Continuous monitoring of the Antarctic ozone hole.
• OMI NO₂ is the canonical long-term tropospheric pollution record; pre-TEMPO and pre-TROPOMI it was the only daily global product.
• Volcanic SO₂ detection — OMI catches major eruption plumes globally.
• MLS stratospheric chemistry — critical for WMO ozone assessments and Montreal Protocol verification.

Where to get the data

• earthaccess Python: short names with OMI_*, OMI_L2*, OMI_L3*, ML2* prefixes
• GES DISC: disc.gsfc.nasa.gov (Aura data)
• Giovanni: giovanni.gsfc.nasa.gov — interactive Aura analyses for non-programmers
• NASA Worldview: imagery layers for OMI products

What it enables

• Tropospheric NO₂ trend studies (2004-present) — comparison with current TEMPO + TROPOMI
• Antarctic + Arctic ozone hole monitoring
• Volcanic SO₂ + ash tracking (e.g., Hunga Tonga 2022)
• Stratospheric chlorine + bromine inventories (Montreal Protocol verification)
• Tropospheric formaldehyde for VOC + wildfire smoke
• Long-term solar cycle effects on stratospheric chemistry (via MLS)

Gotchas

• OMI row anomaly since 2007. A persistent fault has degraded OMI’s swath coverage. Some across-track positions have been unusable since 2007; the affected rows expanded over time. Use only “good rows” for science-quality work; check the QA flag carefully.
• OMI is 2x degraded vs spec (pixel size, signal-to-noise) due to aging. For modern air-quality, prefer TROPOMI (10 km, 2018+) or TEMPO (hourly, 2024+, North America).
• MLS data products require version awareness — recent MLS V5 has improvements over V4; older versions still distributed.
• Aura is in the “old” A-Train orbit which has been progressively losing satellites as missions end (Aqua close, CloudSat orbit-decay, Aura ending ~2026-27). Don’t assume A-Train cross-mission alignments anymore.
• No NRT products — Aura is research-cadence, not operational.

Related missions

• TROPOMI on Sentinel-5P (ESA): OMI’s modern successor; 7 km × 3.5 km, daily global, 2018+.
• TEMPO (s07 →): geostationary OMI-class over North America, hourly, 2023+.
• GEMS (KARI/NIER): geostationary atmospheric chemistry over Asia.
• Sentinel-4 (ESA): geostationary over Europe, launching 2026.
• MLS has no direct planned successor — its end-of-mission will leave a stratospheric-chemistry observation gap.

Related datasets