Sensitivity and impact of the ionospheric kappa-correction on RO cli- matologies
Presenter:
Julia Danzer
Wegener Center for Climate and Global Change (WEGC)
Wegener Center for Climate and Global Change (WEGC) and European Centre for Medium-range Weather Forecasts (ECMWF)
Talk
In the past years a new model - the so-called kappa approach - was introduced to correct for higher order ionospheric residuals in radio occultation (RO) data. The model depends on the L1 and L2 bending angle difference squared; and a factor kappa κ, which varies with time, season, solar activity, and height. The main advantage of the model is that there is no need for additional background information to correct for ionospheric residuals, except the F10.7 index.
We combine in this work the kappa correction with the average profile inversion, which averages individual profiles already in bending angle space and propagates the mean profiles through the Abel transform. The reason is that the kappa approach does not correct for errors caused by the Earth’s geomagnetic field. These errors produce noise for individual profiles, but are assumed to average out in the context of climatologies.
So far, the kappa approach has been analyzed in simulation studies. In this work it is tested on real observed RO data. First, we compute the kappa correction for each individual bending angle profile, applying also filtering and smoothing steps in the production of the residual ionospheric error. Second, we perform a thorough analysis of the kappa approach, evaluating its sensitivity during the solar cycle from the minimum year 2008 up to the maximum year 2015, for bending angle and temperature climatologies. Finally, we compare the higher order ionosphere corrected RO stratospheric climatologies to the three reference data sets ERAinterim, ERA5, and MIPAS.
Results show a clear dependence of the kappa correction on solar activity, geographic location, and altitude. For a low activity month, the correction amounts to a value of about 0.1K at 35km, increasing to about 0.8K in a high activity month. In absolute values the correction shifts RO climatologies towards warmer temperatures. However, with respect to reference data sets, it has been shown to be difficult to draw final conclusions, because the temperature shift appears to be a similar magnitude to the biases in the reference data sets.
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