AIRS V7¶

Aqua Atmospheric Infrared Sounder (AIRS) Version 7 Level 2 and Level 3 Standard Physical Retrieval

Available

At a glance¶

Note on period: AIRS-only L2 (AIRS2RET) starts on 2002-08-30, daily L3 (AIRS3STD) on 2002-08-31 and monthly L3 (AIRS3STM) in September 2002. As checked on 2026-10-13, L2 runs through 2026-10-09, daily L3 through 2026-10-06 and monthly L3 through September 2026. AIRS+AMSU (AIRX*) ended on 2016-09-25 and AIRS+AMSU+HSB on 2003-02-05. No L2 or L3 products were generated for 19–28 January 2026 because of an AIRS detector anomaly.

Overview¶

Temperature and water vapour profiles, surface air temperature, clouds, and ozone, carbon monoxide and methane retrieved since 2002 from AIRS, the 2,378-channel hyperspectral infrared sounder on NASA's Aqua satellite, using cloud clearing to work in partly cloudy scenes. It comes as 6-minute L2 swath granules along the orbit and as L3 daily and monthly 1° grids kept separate for the ascending (day) and descending (night) passes. Since parts of the AMSU microwave instrument failed, the infrared-only AIRS-only stream is the baseline; its 20-plus-year record is widely used for tropospheric temperature and humidity change and for evaluating reanalyses and models.

What changes with the successor¶

AIRS+AMSU (AIRX2RET·AIRX3STD·AIRX3STM) → AIRS-only (AIRS2RET·AIRS3STD·AIRS3STM)¶

Transition: 2016-09

The combined infrared plus microwave retrieval ended when AMSU-A2 lost power on 24 September 2016; the only continuing record since then is the infrared-only AIRS-only stream, which has been processed consistently for the whole mission from 2002.

Sources: AIRS/AMSU/HSB Version 7 Level 2 Product User Guide (V1.1, 2021-07-14) · CMR — AIRX2RET V7.0 (ended with AMSU-A2 power loss) · AIRS outages and anomalies (AIRS Project)

AIRS Version 6 → AIRS Version 7¶

Transition: 2019-12

Version 7, released at the end of 2019, is the current full-mission reprocessing. At Level 3 the monthly averaging method changed, and the 8-day products and some total-column trace-gas fields were dropped.

Sources: AIRS Version 7 Level 3 Product User Guide · AIRS documentation index (including V7 Changes from V6)

Available variables¶

L3 names are the field names in the AIRS V7 L3 user guide; each carries an _A (ascending) or _D (descending) suffix and comes with _ct and _sdev companions (for example Temperature_A). L2 field names follow the V7 L2 standard pressure levels and QC and error estimation documents; error estimates append Err and quality flags append _QC to the name (QC 0 best, 1 good, 2 do not use). The fill value is -9999.

instantaneous mean accumulated maximum minimum static — instantaneous: value at the time stamp · mean/accumulated/maximum/minimum: over the indicated interval · static: does not change with time

L3 temperature and water vapour (AIRS3STD daily / AIRS3STM monthly)¶

L3 clouds, radiation and trace gases¶

L2 swath (AIRS2RET)¶

The full variable list is in the official documentation.

How to get the data¶

• NASA GES DISC — AIRS3STM V7.0 (monthly) — Web, HTTPS, OPeNDAP and subsetting (HDF-EOS2)
  • Daily data are on the AIRS3STD_7.0 page and L2 on AIRS2RET_7.0. A free NASA Earthdata Login is required.
• GES DISC HTTPS data directory (L3 monthly) — HTTPS (wget, curl with Earthdata Login)
• NASA Earthdata Search — AIRS2RET V7.0 (L2) — Earthdata Search / earthaccess
• CLIMCAPS-Aqua V2 (the same AIRS observations processed with a different algorithm, netCDF) — Earthdata Search / earthaccess (SNDRAQIL2CCPRET and others)
  • CLIMCAPS uses MERRA-2 as its first guess, so it has no NRT version; the same algorithm is applied to CrIS (Suomi NPP, NOAA-20) to carry the record beyond AIRS.

Example code¶

Run earthaccess.login() once with a NASA Earthdata account first. AIRS L2 and L3 files are HDF-EOS2 (HDF4), so read them with pyhdf.

# pip install earthaccess pyhdf numpy
import earthaccess
import numpy as np
from pyhdf.SD import SD, SDC

earthaccess.login()
results = earthaccess.search_data(
    short_name="AIRS3STM", version="7.0",          # AIRS-only L3 monthly
    temporal=("2025-01-01", "2025-12-31"),
)
files = earthaccess.download(results[:1], "./airs")

f = SD(files[0], SDC.READ)
t = f.select("Temperature_A")[:].astype(float)   # (24 levels, 180 lat, 360 lon), ascending (day) orbit
t[t == -9999] = np.nan                            # fill value
print(t.shape, np.nanmean(t[0]))                  # mean 1000 hPa temperature (not area-weighted)

Practical tips¶

• Use only AIRS-only (AIRS2RET, AIRS3STD, AIRS3STM) for long-term trends. AIRX (AIRS+AMSU) ended on 2016-09-25, and the two streams differ in retrieval sampling and quality control.
• The L3 user guide notes unrealistic relative humidity values above 200% (sometimes up to 500%); screen them out.
• L3 grid values average only retrievals that pass QC (0 or 1), so heavily cloudy or rainy regions are biased toward clearer scenes. Treat cells with low counts (_ct) as less representative, but do not use the grid-box cloud fraction for extra QC (per the guide).
• L3 grid edges fall on the dateline (180°), so longitudes run -180 to 180. Reorder the longitude bins to draw a map centred on 0°.
• Aqua has been drifting since December 2021, with later equator crossing times and lower altitude. Recent trends in variables with a strong diurnal cycle (surface air temperature, skin temperature, low-level humidity) can be affected by the change in observation time.
• No L2 or L3 products exist for 19–28 January 2026, and the January 2026 monthly mean is missing that period.
• V7 has no 8-day product. To combine several days, weight the daily files by _ct.

Notices and change history¶

References for your paper¶

Dataset citation¶

L3 monthly (AIRS-only) V7.0 — DOI 10.5067/UBENJB9D3T2H

@misc{airs3stm_v7,
  author    = {{AIRS project}},
  title     = {Aqua/{AIRS} {L3} Monthly Standard Physical Retrieval ({AIRS}-only) 1 degree x 1 degree {V7.0}},
  year      = {2019},
  publisher = {Goddard Earth Sciences Data and Information Services Center (GES DISC)},
  address   = {Greenbelt, MD, USA},
  doi       = {10.5067/UBENJB9D3T2H}
}

L3 daily (AIRS-only) V7.0 — DOI 10.5067/UO3Q64CTTS1U

@misc{airs3std_v7,
  author    = {{AIRS project}},
  title     = {Aqua/{AIRS} {L3} Daily Standard Physical Retrieval ({AIRS}-only) 1 degree x 1 degree {V7.0}},
  year      = {2019},
  publisher = {Goddard Earth Sciences Data and Information Services Center (GES DISC)},
  address   = {Greenbelt, MD, USA},
  doi       = {10.5067/UO3Q64CTTS1U}
}

L2 swath (AIRS-only) V7.0 — DOI 10.5067/VP1M6OG1X7M1

@misc{airs2ret_v7,
  author    = {{AIRS project}},
  title     = {Aqua/{AIRS} {L2} Standard Physical Retrieval ({AIRS}-only) {V7.0}},
  year      = {2019},
  publisher = {Goddard Earth Sciences Data and Information Services Center (GES DISC)},
  address   = {Greenbelt, MD, USA},
  doi       = {10.5067/VP1M6OG1X7M1}
}

L2 swath (AIRS+AMSU) V7.0, 2002-08 to 2016-09 — DOI 10.5067/URTYDAGTM548

@misc{airx2ret_v7,
  author    = {{AIRS project}},
  title     = {Aqua/{AIRS} {L2} Standard Physical Retrieval ({AIRS}+{AMSU}) {V7.0}},
  year      = {2019},
  publisher = {Goddard Earth Sciences Data and Information Services Center (GES DISC)},
  address   = {Greenbelt, MD, USA},
  doi       = {10.5067/URTYDAGTM548}
}

Reference papers¶

AIRS mission overview — DOI 10.1175/BAMS-87-7-911

@article{chahine2006airs,
  author  = {Chahine, Moustafa T. and Pagano, Thomas S. and Aumann, Hartmut H. and Atlas, Robert and Barnet, Christopher and Blaisdell, John and others},
  title   = {{AIRS}: Improving Weather Forecasting and Providing New Data on Greenhouse Gases},
  journal = {Bulletin of the American Meteorological Society},
  volume  = {87},
  number  = {7},
  pages   = {911--926},
  year    = {2006},
  doi     = {10.1175/BAMS-87-7-911}
}

Acknowledgements¶

GES DISC asks that each collection used be cited in the form above (author, year, title, version, distributor, access date, DOI). It is good practice to cite the V7 L2/L3 user guides (see the AIRS documentation index) for the algorithm and quality description as well.

Information on the datasets used in this study was compiled with the help of the Korean Climate Data Navigator (KCDN) (Sim, 2026; https://doi.org/10.5281/zenodo.23300923).

Links¶

• AIRS Project (NASA JPL)
• AIRS Version 7 L2/L3 products
• AIRS V7 L3 Product User Guide
• AIRS V7 L2 Product User Guide
• Overview of the AIRS Mission (2nd ed., 2021, includes CLIMCAPS)
• Aqua mission home page (orbit drift, instrument status)