02 Aug 2023
 | 02 Aug 2023

Observability of Moisture Transport Divergence in Arctic Atmospheric Rivers by Dropsondes

Henning Dorff, Heike Konow, Vera Schemann, and Felix Ament

Abstract. This study emulates dropsondes to elucidate how adequately sporadic airborne sondes represent divergence (convergence) of moisture transport in arctic Atmospheric Rivers. The convergence of vertically integrated moisture transport (IVT) plays a crucial role as it favours precipitation that significantly affects arctic sea ice properties. Long range research aircraft can transect ARs and dropsondes determine their IVT divergence. However, a limited number of sondes may deteriorate the representation of IVT variability and divergence. We disentangle errors arising from undersampling by discrete soundings and from the flight duration in order to assess the representativeness of future sonde-based IVT divergence in arctic ARs.

Our synthetic study uses CARRA reanalyses to set up an idealised scenario for airborne AR observations.For nine arctic spring ARs, we mimic flights transecting each AR in CARRA and emulate sonde-based IVT representation by picking single vertical profiles. The emulation quantifies IVT divergence observability by two approaches. First, sonde-based IVT and its divergence are compared to the continuous IVT interpolated onto the flight cross-section. The comparison specifies uncertainties of discrete sonde-based IVT variability and divergence. Second, we determine how temporal AR evolution affects IVT divergence values by contrasting time-propagating sonde-based values with the divergence based on instantaneous snapshots.

For our arctic AR cross-sections, we find that moisture transport variability contributes less than 10 % to its lateral mean, while wind and moisture variability individually are higher. Both quantities can be uncorrelated and do not consistently exhibit a coherent pattern. Moisture turns out as the more varying quantity. We show that sounding spacing greater than 100 km results in errors greater than 10 % of the total IVT along AR cross-sections. For IVT divergence, the arctic ARs exhibit similar gradients in moisture advection and mass convergence across the embedded front as mid-latitude ARs, but we identify moisture advection being dominant. We overall confirm their observability with an uncertainty lower than 25 % by a sequence of at least seven sondes per cross-section. Rather than sonde undersampling, it is the temporal AR evolution over the flight duration that leads to higher deviations in divergence components. Dedicated planning of sonde-based IVT divergence purposes should not only involve sonde positioning but rather pursue optimizing the flight duration. Our benchmarks quantify sonde-based uncertainties as a prerequisite to be used for future airborne moisture budget closure in arctic ARs.

Henning Dorff, Heike Konow, Vera Schemann, and Felix Ament

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2023-1570', Anonymous Referee #1, 10 Oct 2023
    • AC1: 'Reply on RC1', Henning Dorff, 02 Dec 2023
  • RC2: 'Comment on egusphere-2023-1570', Anonymous Referee #2, 11 Oct 2023
    • AC2: 'Reply on RC2', Henning Dorff, 02 Dec 2023
Henning Dorff, Heike Konow, Vera Schemann, and Felix Ament

Data sets

Arctic regional reanalysis on pressure levels from 1991 to present. H. Schyberg, X. Yang, M. A. Ø. Køltzow, B. Amstrup, Å. Bakketun, E. Bazile, J. Bojarova, J. Boxx, P. Dahlgren, S. Hagelin, M. Homleid, A. Horányi, J. Høyer, Å. Johansson, M. A. Killie, H. Körnich, P. Le Moigne, M. Lindskog, T. Manninen, P. Nielsen Englyst, K. P. Nielsen, E. Olsson, B. Palmason, C. Peralta Aros, R. Randriamampianina, P. Samuelsson, R. Stappers, E. Støylen, S. Thorsteinsson, T. Valkonen, and Z. Q. Wang

ERA5 hourly data on pressure levels from 1940 to present. H. Hersbach, B. Bell, P. Berrisford, G. Biavati, A. Horányi, J. Muñoz Sabater, J. Nicolas, C. Peubey, R. Radu, I. Rozum, D. Schepers, A. Simmons, C. Soci, D. Dee, and J.-N. Thépaut

Model code and software

ARcatalog (UCLA) Bin Guan

Henning Dorff, Heike Konow, Vera Schemann, and Felix Ament


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Short summary
Using synthetic dropsondes, we assess how discrete spatial sampling and temporal evolution during flight affect the accuracy of real sonde-based moisture transport divergence in arctic Atmospheric Rivers (ARs). Non-instantaneous sampling during temporal AR evolution deteriorates the divergence values more than spatial undersampling. Moisture advection is the dominating factor but most sensitive to the sampling method. We suggest a minimum of seven sondes to resolve the AR divergence components.