GFDL - Geophysical Fluid Dynamics Laboratory

Reanalysis Ideas — A Strawman For Homogenization?

Some Ideas For Future Reanalysis Efforts

John Lanzante

A Strawman For Homogenization?

  • As part of the future Reanalysis effort, design a specialized system
    to produce reference series, the sole purpose of which would be to aid
    in homogenization of radiosonde temperature data. The homogenized
    temperature series would:

    1. Be of value in their own right for characterizing climate variability
    2. Would serve as input to the full Reanalysis system.
  • Inputs to the system which produces the reference series would be
    severely limited, and if possible, no radiosonde temperatures would be
    input. It would be desirable to have radiosonde winds serve as a
    backbone for the system, supplemented by surface data (homogenized
    temperature data from the Global Historical Climatology Project? and
    Sea-Level Pressure data?). The appeal of winds data is:

    1. Wind measurement is simpler with less potential for inhomogeneities
      than for temperature.

    2. Inhomogeneities in wind and temperature would not necessarily occur

    3. Given thermal wind constraints, any inhomogeneities in wind may not
      translate strongly into resulting reference temperature.

  • Simplifications:
    1. Only monthly mean outputs are needed, thus, considerable costs could
      be saved if the system were designed to ingest monthly means.
      [In most cases the time of an artificial jump can not be pinpointed
      more precisely than the nearest month or several months to a year].

    2. The reference series need not reproduce all of the details
      of the temporal variability.

  • During the developmental phase, the already homogenized LKS data could
    provide benchmarks against which to judge the progress.

  • Some validation could be provided by comparing both the reference
    series as well as the final homogenized temperatures with independent
    MSU temperature data. Although there are concerns regarding the
    homogeneity of the MSU data, two different versions are now available
    (Christy/Spencer and Wentz et al.).

  • A flowchart can be used to conceptualize the homogenization scheme.
    The input data stream would be partitioned into “Bad” data, in this case
    radiosonde temperatures containing inhomogeneities, and “Good” data,
    which are presumed less susceptible to homogeneity problems and/or
    independent of the “Bad” data. The “Good” data are transformed by some
    sort of analysis system which produces reference series (Tr).
    Homogenization is greatly facilitated by operating on the difference
    series (To-Tr) which is presumably dominated by the time-varying
    artificial systematic error of the original “Bad” data (To). After
    homogenization, the temperature time series, which now are of
    considerable value in their own right, are fed back into the reanalysis
    system to produce the “Final” Reanalysis products.

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