Home > analysis, Modelling, solar > ERBS TSI


As part of an ongoing investigation I looked at the ERBS TSI data. This dataset is not particularly interesting and  as with all satellite data is far too short to say much. One interesting snippet did appear.

Creating a rough model posed some problems but in practice was simple.

First was the data has a Y2K corrupted date which was kindly sorted out by V.

The sampling is irregular (scattered time points) which the software can usually handle if slowly. The result is unremarkable.

I’ve shown a fore and hindcast which indicates the model is stable and sane. It will be somewhat wrong.

A surprise came when I looked at a paper associated with the dataset where the final sentence of the conclusion is “The fact that the measurements increased with time relative to the proxies  suggests the existence of a second TSI variability component with an amplitude greater than 0.04% (0.5 Wm-2), and with a period greater or equal to approximately 20 years.”
A minor model component: 20.0432969909    3.69480925972    0.124480125667

Period just over 20 years, amplitude 0.125 * 2 * sqrt(2) = 0.35W p-p

With such short data that will be way out and TSI certainly is far more complex in the long term.


I’ve shown SORCE as well. This is not really TSI, is narrowband/is in my opinion incomplete [disputed, see comments]. It does however show the wide variation is measured values. Given the extreme difficulty in making these measurements the usual rule of thumb is sensible, the instrument must be at least an order more accurate and so for absolute maybe we know +-40W sq/m

Putting that into context 40W in 1360W is +-3% of absolute, not as easy as many will imagine and for a remote instrument is an intensely hostile environment would not be a surprise. Lets hope the instrument is returned to earth for post mission calibration checks. See the point?

“Validation of spacecraft active cavity radiometer total solar irradiance  [TSI] long-term measurement trends using proxy TSI least squares analyses

“aRobert Benjamin Lee III and bRobert S. Wilson
aNASA Langley Research Center, Atmospheric Sciences, MS 420, Hampton, VA 23681-2199
Science Application International Corp. (SAIC), One Enterprise Parkway, Hampton, VA 23666 ”


A lot of interesting material on TSI  can be found here http://www.leif.org/research/

Categories: analysis, Modelling, solar
  1. April 14, 2011 at 04:07

    You say “I’ve shown SORCE as well. This is not really TSI, is narrowband”

    You are wrong on this. What SORCE calls TSI, is a real TSI: all of spectrum enters the cavity.

    • April 14, 2011 at 12:17

      Fair comment and my wording was poor.
      My understanding is SORCE is limited, all such instruments are limited at the long wavelength end, not helped by the massive dynamic range of the signal. I don’t want to mislead anyone so I’ll try and come up with something acceptable.

      • April 14, 2011 at 13:28

        TSI instruments are not limited in in wave length. They are simplicity itself: one lets oridnary, unfiltered, full sunlight fall onto a cavity. That heats up the cavity. A servo system keeps the cavity at a constant temperature [32C] by electrical heating. The amount of current needed to maintain the temperature is then a measurement of TSI.

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