09 May 2022
09 May 2022
Status: this preprint is currently under review for the journal AMT.

Estimation of refractivity uncertainties and vertical error correlations in collocated radio occultations, radiosondes and model forecasts

Johannes K. Nielsen, Hans Gleisner, Stig Syndergaard, and Kent B. Lauritsen Johannes K. Nielsen et al.
  • Danish Meteorological Institute, Lyngbyvej 100, DK 2100, Copenhagen, Denmark

Abstract. Random uncertainties and vertical error correlations are estimated for three independent data sets. The three collocated data sets are: 1) Refractivity profiles of radio occultation measurements retrieved from the Metop-A and B and COSMIC-1 missions, 2) refractivity derived from GRUAN processed RS92 sondes and 3) refractivity profiles derived from ERA5 forecast fields. The analysis is performed using a generalization of the so-called Three-Cornered Hat method to include off-diagonal elements such that full error covariance matrices can be calculated. The impacts from various sources of representativeness error on the uncertainty estimates are analyzed. The estimated refractivity uncertainties of radio occultations, radiosondes and model data are stated with reference to the vertical representation of refractivity in these data sets. The existing theoretical estimates of radio occultation uncertainty are confirmed in the middle and upper troposphere and lower stratosphere, and only little dependence on latitude is found in that region. In the lower troposphere refractivity uncertainty decreases with latitude. These findings have implications for both retrieval of tropospheric humidity from radio occultations and for assimilation of radio occultation data in NWP models and reanalyses.

Johannes K. Nielsen et al.

Status: open (until 15 Jun 2022)

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Johannes K. Nielsen et al.

Johannes K. Nielsen et al.


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Short summary
This paper provides a new way to estimate uncertainties. The method is a generalization of a know method called the Three Cornered Hat: Instead of calculating uncertainties from assumed knowledge about the observation method, uncertainties are estimated statistically from tree independent observation series, measuring the same variable. The results are useful for future estimation of atmospheric specific humidity from the bending of radio waves.