24 Jul 2023
 | 24 Jul 2023
Status: a revised version of this preprint is currently under review for the journal AMT.

Assessing the Ducting Phenomenon and its Impact on GNSS Radio Occultation Refractivity Retrievals over the Northeast Pacific Ocean using Radiosondes and Global Reanalysis

Thomas E. Winning, Feiqin Xie, and Kevin J. Nelson

Abstract. In this study, high-resolution radiosondes from the MAGIC field campaign and ERA5 global reanalysis data are used to assess the elevated ducting layer characteristics along the transect over the northeastern Pacific Ocean from Los Angeles, California to Honolulu, Hawaii. The height of the planetary boundary layer (PBLH) increases as the strength of the refractivity gradient and resultant ducting decrease from east to west across the analysis transect. The thickness of the ducting layer remains remarkably consistent (∼110 m) in the radiosonde data. On the other hand, the ERA5 generally resolves the ducting features well but underestimates the ducting height and strength especially over the trade cumulus region near Hawaii. A simple two-step end-to-end simulation is used to evaluate the impact of the elevated ducting layer on RO refractivity retrievals. A systematic negative refractivity bias (N-bias) below the ducting layer is observed throughout the transect, peaking approximately 70 meters below the PBL height (−5.42 %), and gradually decreasing towards the surface (−0.5 %). Further, the underestimation of the N-bias in the ERA5 data increases in magnitude westward and while the correlation of the N-bias with the minimum gradient and sharpness are all strong; there is no evidence of zonal dependence.

Thomas E. Winning et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on amt-2023-150', Anonymous Referee #1, 12 Sep 2023
    • AC1: 'Response to Reviewer 1 Comments', Thomas Winning, 12 Nov 2023
  • RC2: 'Review of amt-2023-150', Anonymous Referee #2, 14 Sep 2023
    • AC2: 'Response to Reviewer 2 Comments', Thomas Winning, 12 Nov 2023

Thomas E. Winning et al.

Thomas E. Winning et al.


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Short summary
The effect of ducting due to the presence of the planetary boundary layer (PBL) is prevalent over the northeastern Pacific Ocean from Los Angeles to Honolulu. The ducting induced refractivity bias in the radiosonde climatology and global reanalysis data is highly correlated with the height of the PBL. The magnitude of bias is linearly dependent on the strength of ducting but not the location and the overall reanalysis data systematically underestimates the height of the PBL by as much as 120 m.