Home > Research Papers, satellites > ZGG09: Error and Atmos Temp Trends in Obs from the MSU

ZGG09: Error and Atmos Temp Trends in Obs from the MSU

2010 August 15

Error Structure and Atmospheric Temperature Trends in Observations from the Microwave Sounding Unit


The Microwave Sounding Unit (MSU) onboard the National Oceanic and Atmospheric Administration polar-orbiting satellites measures the atmospheric temperature from the surface to the lower stratosphere under all weather conditions, excluding precipitation. Although designed primarily for monitoring weather processes, the MSU observations have been extensively used for detecting climate trends, and calibration errors are a major source of uncertainty. To reduce this uncertainty, an intercalibration method based on the simultaneous nadir overpass (SNO) matchups for the MSU instruments on satellites NOAA-10, -11, -12, and -14 was developed. Due to orbital geometry, the SNO matchups are confined to the polar regions, where the brightness temperature range is slightly smaller than the global range. Nevertheless, the resulting calibration coefficients are applied globally to the entire life cycle of an MSU satellite. Such intercalibration reduces intersatellite biases by an order of magnitude compared to prelaunch calibration and, thus, results in well-merged time series for the MSU channels 2, 3, and 4, which respectively represent the deep layer temperature of the midtroposphere (T2), tropopause (T3), and lower stratosphere (T4).

Focusing on the global atmosphere over ocean surfaces, trends for the SNO-calibrated T2, T3, and T4 are, respectively, 0.21 +/- 0.07, 0.08 +/- 0.08, and 20.38 +/- 0.27 K decade21 from 1987 to 2006. These trends are independent of the number of limb-corrected footprints used in the dataset, and trend differences are marginal for varying bias correction techniques for merging the overlapping satellites on top of the SNO calibration.

The spatial pattern of the trends reveals the tropical midtroposphere to have warmed at a rate of 0.28 +/- 0.19 K decade21, while the Arctic atmosphere warmed 2 to 3 times faster than the global average. The troposphere and lower stratosphere, however, cooled across the southern Indian and Atlantic Oceans adjacent to the Antarctic continent. To remove the stratospheric cooling effect in T2, channel trends from T2 and T3 (T23) and T2 and T4 (T24) were combined. The trend patterns for T23 and T24 are in close agreement, suggesting internal consistencies for the trend patterns of the three channels.



We have intercalibrated the Microwave Sounding Units on the NOAA-10, -11, -12, and -14 satellites using the simultaneous nadir overpass (SNO) method. In this method the radiance differences between pairs of satellite measurements are analyzed when both satellites are viewing the same area on the earth at the same time. Such SNO matchups occur in polar regions; nevertheless, the calibration coefficients obtained from the matchups are applied globally for the entire life cycle of each satellite. After the recalibration, intersatellite radiance biases at the SNO matchups are exactly zero. Mean biases in the global oceanic atmosphere of the gridded dataset generated from the recalibrated, limb-corrected radiances are generally O(0.05–0.1 K). This is an improvement of nearly an order of magnitude over use of the prelaunch calibration. Orbital-drift-related warm target contamination has been reduced to a minimum (nearly zero for channels 2 and 4) by the SNO calibration. This leads to stable intersatellite difference time series with an averaged standard deviation of 0.04 ;0.05 K for means of the global oceanic atmosphere.

Trend differences for two independent techniques for merging the data of overlapping satellite records—the SNO 1 constant bias and SNO 1 Christy methods—are minimal: only 0.015 K decade21 for the midtroposphere (T2) and tropopause layer (T3) and 0.04 K decade for the lower stratosphere (T4). Mean trends of global oceanic atmosphere for T2, T3, and T4 during 1987–2006 are respectively 0.207 +/- 0.068, 0.083 +/- 0.081, and 20.379 +/- 0.267 K decade21 for the average of the two merging techniques.

By removing inter-satellite biases for each grid cell, regional trends have been derived from the MSU observations. Large warming trends are found for most regions of the troposphere. The tropical mid-troposphere (T24 or T23) is found to be warming at a rate of 0.28 +/- 0.19 to 0.32 +/- 0.21 K decade21 from 1987 to 2006. The Arctic troposphere is warming at 0.6 +/- 0.2 to 0.8 +/- 0.3 K decade21 for the same period, which is two to three times faster than the global average. The upper troposphere is warming much faster than estimated by previous studies. Meanwhile, a cooling area is found throughout the atmosphere across the southern Indian and Atlantic Oceans adjacent to the Antarctic continent. However, because statistical uncertainty is high for the T3 and T4 trends over the polar region, one should expect the values to be highly variable for different statistical periods.

With the characteristics shown in this study, the MSU observations for the different NOAA satellites appear to be inter-calibrated quite well, and they are expected to benefit future reanalysis in reducing spurious climate jumps and variability related to satellite transitions.

Jeff Id jokingly stated that it was time to fix the thermometers. It won’t be the first time the models were right and the satellite analysis wrong.

For context, the T2 (MSU channel 2) is a broad tropospheric channel with contributions from the surface and the stratosphere. It is used in the construction of both the LT and MT. MSU channel 2 is now defunct. AMSU channel 5 is the rough equivalent for LT and MT and replaces or augments MSU T2 when available. I don’t believe that any of the MSU satellites are still operational, having been replaced by NOAA-15 with AMSU and AQUA.


Magicjava has some good posts on this stuff.
Spencer wrote in 2006 that the near nader overlap was insufficient to justify the correction. Zou published his first SNO paper in the same year.

I saw no mention of Zou on Dr Roy Spencer’s site (google search).

IPCC AR4 WG1 discussion

h/t to Gavin's Pussycat

  1. cce
    2010 August 15 at 9:24 am

    Another good quote from this paper:
    “In an Intergovernmental Panel on Climate Change (IPCC) project on model comparisons, Santer et al. (2005) found that the tropical atmospheric temperature trend was increasing vertically from the surface to about 300 mb for all 19
    models used in the study, which was consistent with those predicted by the moist adiabatic lapse rate theory suggested by Stone and Carlson (1979). The T23 and T24trend results from this study and RSS dataset support these model results, although the magnitude of the amplification is different. For the global ocean means, the tropospheric amplification also occurs for temperature trends of this study, but is not obvious for the RSS and UAH datasets.”

    These studies (both mentioned) of MSU/AMSU measurements also find much higher rates of warming than either UAH or RSS.


    I’m not exactly sure how observations are supposed to prove that the models are wrong, when observations themselves are wildly different.

  2. Steven Mosher
    2010 August 16 at 1:10 pm


    You cant read Annan and put any belief whatsoever in the approach that Santer ( or MMH) used in comparing models to ‘data’.

    and just a philosophical note. There is no such thing as raw observation. all observation ( data) is the result of a ‘modeling’ process. we are always choosing between one set of models ( in this case GCMs) and another set of models ( processed bit streams from an instrument) neither one has logical priority. its always a give and take. The decision is always practical, and at worse political.

  3. Steven Mosher
    2010 August 16 at 1:13 pm

    Ps nice find Ron, Itw as funny the other day somebody was asking me about the latest fight over Santer/McIntyre and models and data and I said, ‘the observations will change’. Not a conspiracy thing, just the recognition that looking at old “observations” is a constant option, in my expereince there are always good things to be found by trudging through the old “accepted” observations. especially by third parties who have fresh eyes.

  4. PolyisTCOandbanned
    2010 August 16 at 2:17 pm

    Head for the ice! Oh wait…

  5. Warm
    2010 August 16 at 2:56 pm

    (sorry for my poor english)

    I carefully read the recent papers of Zou et al.


    They worked “step-by-step” by publishing first a new calibration method (SNO), and then they used MSU on a subset of satellites (because the mixing with NOAA-9 and 10 is problematic) on ocean only (for minimizing diurnal drift): this is the paper you present)

    In this paper: http://www.star.nesdis.noaa.gov/smcd/emb/mscat/mscat_files/SPIE_paper_7456-16_Zou-1-color-1.pdf , they addressed the diurnal drift problem and extend the esimation over land.

    In the last paper (http://www.star.nesdis.noaa.gov/smcd/emb/mscat/mscat_files/Zou.2009.JTech.Stability.pdf ) they presented the 1.2 version of their reconstruction: a MSU only product from 1979 to 2006 for ocean and land. The note about this version is here: ftp://ftp.orbit.nesdis.noaa.gov/pub/smcd/emb/mscat/data/

    I did not found new publications about the last version of their reconstruction (2.0) . The patch note indicate a full MSU/AMSU merging from 1979 to 2010 (including NOAA-15 to NOAA-18) (however only gridded data are available until june 2010, global estimates are only to december 2009). The trend of this new version is lower than the “MSU – ocean only – 1987 -2006” they published in april 09, but it is significantly higher than RSS or UAH (0.131K/decade). This is a mid-troposhere estimates (T2, MSU channel 2 AMSU channel 5), not a near-surface estimates such as classical UAH – RSS temp.

  6. cce
    2010 August 16 at 8:21 pm


    At every moment of every day, a “skeptic” is declaring that the models have been disproven by “observations.” i.e. Global warming has stopped, and if it is warming, it isn’t warming fast enough, and, besides, the “hot spot” doesn’t exist. This voyage into ensemble means, intra-model comparisons, standard deviations and the like is interesting, but I think all people really need to do is look at the spread of model results, and look at the spread of observations and make the obvious conclusion that nobody is going to prove or disprove any of this stuff until something better comes along.

  7. 2010 August 16 at 8:30 pm

    Warm, your English is very good.
    Thank you for the link to Zou’s satellite analysis.

  1. 2010 August 16 at 8:28 pm
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