Aura MLS¶

EOS Aura Microwave Limb Sounder (MLS) Level 2 and Level 3 Version 6

Available

At a glance¶

Note on period: Standard L2 products start on 2004-08-02, one file per day. As checked on 2026-10-13, both L2 v6 (ML2T 006) and v5 (ML2T 005) run through 2026-10-11. L3 v6 (netCDF4) is still being populated at GES DISC (as of September 2026 only the 2005 file was present for the monthly binned temperature), while L3 v5 remains available. Since May 2024, water vapour, N2O, HCN and upper-stratospheric HNO3 exist only on the days the 190 GHz radiometer is on (a few days a month).

Overview¶

Vertical profiles of temperature, geopotential height, water vapour, ozone and some 20 other species (ClO, HCl, HNO3, N2O, CO and more) from the upper troposphere to the mesosphere, retrieved since 2004 from thermal emission measured by the Microwave Limb Sounder on NASA's Aura satellite as it views the edge of the atmosphere. Because it is little affected by clouds and aerosols and observes day and night, it is a core record for stratospheric ozone chemistry, the polar vortex, stratospheric water vapour change and the effects of volcanic eruptions.

What changes with the successor¶

MLS v5.0x → MLS v6.0x¶

Transition: 2026-03

v6 corrects the calibration drift of the 190 GHz radiometer and revises the 118 GHz temperature channel shapes, and reprocesses the whole record. N2O and temperature change the most; v5 forward processing continues for the time being.

Sources: Aura MLS v6.0x Level 2 and 3 data quality and description document (v6.0-1.0, 2026-03-26) · Aura MLS home page (v6 release and 190 GHz operations)

Available variables¶

L2 comes as one file per product (species), for example ML2T temperature, ML2H2O water vapour and ML2O3 ozone; the values sit at HDFEOS/SWATHS/<swath>/Data Fields/L2gpValue. The standard swath has the same name as the product (Temperature, H2O, O3, GPH, RHI and so on), so the variable column below reads swath/L2gpValue. Each file also holds an a priori swath ending in -APriori, and the temperature file holds the WMO tropopause pressure swath WMOTPPressure, so always name the swath when reading. The precision and quality fields sit under the same swath's Data Fields. Units and useful ranges below follow the GES DISC V006 collection descriptions. Always apply the v6 quality document screening (precision > 0, even Status, Quality and Convergence thresholds, useful pressure range). L3 (netCDF4) has one group per species and grid (for example O3 PressureGrid, O3 PressureZM), each holding statistics variables with the same names.

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

L2 profiles (HDF-EOS5 file per species, variables as swath/L2gpValue)¶

L2 quality fields (common to all species)¶

L3 (netCDF4, averages after screening)¶

The full variable list is in the official documentation.

How to get the data¶

• NASA GES DISC — ML2T V006 (L2 temperature) — Web, HTTPS, OPeNDAP (HDF-EOS5)
  • Each species has its own collection, such as ML2H2O_006 for water vapour and ML2O3_006 for ozone. A free NASA Earthdata Login is required.
• GES DISC HTTPS data directory (Aura MLS L2) — HTTPS (wget, curl with Earthdata Login)
• NASA Earthdata Search — ML2T V006 — Earthdata Search / earthaccess
• Zenodo Aura MLS community (selected products) — Web download
  • Secondary distribution point named in the v6 quality document.

Example code¶

Run earthaccess.login() once with a NASA Earthdata account first. The screening thresholds are examples; take the actual values for each species and pressure range from the v6 quality document tables.

# pip install earthaccess h5py numpy
import earthaccess
import h5py
import numpy as np

earthaccess.login()
results = earthaccess.search_data(
    short_name="ML2T", version="006",               # MLS L2 temperature v6
    temporal=("2025-01-15", "2025-01-15"),
)
files = earthaccess.download(results[:1], "./mls")

with h5py.File(files[0], "r") as f:
    print(list(f["HDFEOS/SWATHS"]))                  # 'Temperature', 'Temperature-APriori', ...
    g = f["HDFEOS/SWATHS/Temperature"]
    val = g["Data Fields/L2gpValue"][:]              # (profiles, levels), K
    prec = g["Data Fields/L2gpPrecision"][:]
    status = g["Data Fields/Status"][:]
    quality = g["Data Fields/Quality"][:]
    conv = g["Data Fields/Convergence"][:]

good = (status % 2 == 0) & (quality > 0.9) & (conv < 1.03)   # example thresholds — check the quality document
val = np.where(good[:, None] & (prec > 0), val, np.nan)
print(val.shape, np.nanmean(val, axis=0)[:5])

Practical tips¶

• Do not remove negative values. The quality document warns that masking negatives biases averages of low-abundance species high (v6 water vapour is interpolated in log space and has no negatives).
• Screening has four steps: use only the useful pressure range, discard points with L2gpPrecision ≤ 0, discard profiles with odd Status, and apply the Quality and Convergence thresholds. Thresholds differ by species and pressure range.
• Since May 2024, monthly water vapour and N2O means are built from only a few days of observations. Do not treat them as the same sampling as earlier years, and report the number of observing days per month.
• The team says cloud ice (IWC, IWP) should not be used on days when the 190 GHz radiometer is off, but L2 files do not yet flag those days. Filter them by date yourself.
• A limb profile averages over a long stretch along the line of sight. When comparing with models or reanalyses, apply the averaging kernels that the MLS team archives separately.
• v4 data are no longer available from GES DISC (per the MLS team). Re-check older v4-based results with v5 or v6.

Notices and change history¶

References for your paper¶

Dataset citation¶

L2 temperature V006 — DOI 10.5067/Aura/MLS/DATA2620

@misc{ml2t_v006,
  author    = {Schwartz, M. and Livesey, N. and Read, W.},
  title     = {{MLS/Aura} Level 2 Temperature {V006}},
  year      = {2026},
  publisher = {Goddard Earth Sciences Data and Information Services Center (GES DISC)},
  address   = {Greenbelt, MD, USA},
  doi       = {10.5067/Aura/MLS/DATA2620}
}

L2 water vapour V006 — DOI 10.5067/Aura/MLS/DATA2608

@misc{ml2h2o_v006,
  author    = {Lambert, A. and Read, W. and Livesey, N.},
  title     = {{MLS/Aura} Level 2 Water Vapor ({H2O}) Mixing Ratio {V006}},
  year      = {2026},
  publisher = {Goddard Earth Sciences Data and Information Services Center (GES DISC)},
  address   = {Greenbelt, MD, USA},
  doi       = {10.5067/Aura/MLS/DATA2608}
}

L2 ozone V006 — DOI 10.5067/Aura/MLS/DATA2616

@misc{ml2o3_v006,
  author    = {Schwartz, M. and Froidevaux, L. and Livesey, N. and Read, W.},
  title     = {{MLS/Aura} Level 2 Ozone ({O3}) Mixing Ratio {V006}},
  year      = {2026},
  publisher = {Goddard Earth Sciences Data and Information Services Center (GES DISC)},
  address   = {Greenbelt, MD, USA},
  doi       = {10.5067/Aura/MLS/DATA2616}
}

L2 temperature V005 (if you stay on v5) — DOI 10.5067/Aura/MLS/DATA2520

@misc{ml2t_v005,
  author    = {Schwartz, M. and Livesey, N. and Read, W.},
  title     = {{MLS/Aura} Level 2 Temperature {V005}},
  year      = {2020},
  publisher = {Goddard Earth Sciences Data and Information Services Center (GES DISC)},
  address   = {Greenbelt, MD, USA},
  doi       = {10.5067/Aura/MLS/DATA2520}
}

Reference papers¶

v6 data quality and description document (recommended alongside the data) — DOI 10.5067/AURA/MLS/DOC/v6_dataqualitydocument

@techreport{mls_v6_dqd,
  author      = {Livesey, N. J. and others},
  title       = {Aura Microwave Limb Sounder ({MLS}) Version 6.0x Level 2 and 3 data quality and description document, Version 6.0-1.0},
  institution = {Jet Propulsion Laboratory},
  year        = {2026},
  doi         = {10.5067/AURA/MLS/DOC/v6_dataqualitydocument}
}

Acknowledgements¶

GES DISC asks that each species collection used be cited in the form above (author, year, title, version, distributor, access date, DOI). The MLS team asks users to read the quality document and follow its screening rules; questions go to mls-data@jpl.nasa.gov.

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¶

• Aura MLS home page (NASA JPL)
• Aura MLS v6.0x data quality and description document (2026-03-26)
• Aura MLS v5.0x data quality and description document
• Aura MLS NRT user guide (v5)
• NASA Aura mission page