Preprints
https://doi.org/10.5194/egusphere-2024-2402
https://doi.org/10.5194/egusphere-2024-2402
23 Aug 2024
 | 23 Aug 2024

The role of ascent timescale for WCB moisture transport into the UTLS

Cornelis Schwenk and Annette Miltenberger

Abstract. Warm conveyor belts (WCBs) are coherent ascending airstreams in extratropical cyclones. They are a major source of moisture for the extratropical upper troposphere and lower stratosphere (UTLS), where moisture acts as a potent greenhouse gas and WCB-associated cirrus contribute to cloud radiative forcing. However, the processes controlling WCB moisture transport and cloud properties are poorly characterised. Furthermore, recent studies have revealed (embedded) convection as a ubiquitous feature of WCBs, highlighting the importance of understanding their updraft and microphysical structure. We present a Lagrangian investigation of WCB moisture transport for a case from the WISE (Wave-driven ISentropic Exchange) campaign based on a convection-permitting simulation. Lagrangian non-dimensional metrics of the moisture budget suggest that the ascent timescale (τ600) strongly controls the end-of-ascent total moisture content, which is largest for slowly ascending trajectories (τ600 > 20 h, ~30 % of all WCB trajectories). This is due to relatively warm end-of-ascent temperatures and the strong temperature control on transported water vapor. Deviations from equilibrium water vapor – condensate partitioning are largest for slow trajectories due to faster glaciation and lower ice crystal numbers. A local moisture transport minimum at intermediate tau600 results from a shift towards a riming dominated precipitation formation pathway and decreasing outflow temperatures with decreasing τ600. The fastest trajectories (τ600 < 5 h, ~5 % of all WCB trajectories) transport the largest condensate mass to the UTLS due to less efficient condensate loss, and produce the longest-lived outflow cirrus. Models that parameterise convection may under-represent these processes, potentially impacting weather forecasts and climate predictions.

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Cornelis Schwenk and Annette Miltenberger

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2024-2402', Anonymous Referee #1, 13 Sep 2024
    • AC2: 'Reply on RC1', Cornelis Schwenk, 14 Oct 2024
  • RC2: 'Comment on egusphere-2024-2402', Anonymous Referee #2, 04 Oct 2024
    • AC1: 'Reply on RC2', Cornelis Schwenk, 14 Oct 2024

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2024-2402', Anonymous Referee #1, 13 Sep 2024
    • AC2: 'Reply on RC1', Cornelis Schwenk, 14 Oct 2024
  • RC2: 'Comment on egusphere-2024-2402', Anonymous Referee #2, 04 Oct 2024
    • AC1: 'Reply on RC2', Cornelis Schwenk, 14 Oct 2024
Cornelis Schwenk and Annette Miltenberger
Cornelis Schwenk and Annette Miltenberger

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Short summary
Warm conveyor belts (WCBs) transport moisture into the upper atmosphere, where it acts as a greenhouse gas. This transport is not well understood, and the role of rapidly rising air is unclear. We simulate a WCB and look at fast and slow rising air to see how moisture is (differently) transported. We find that for fast ascending air more ice particles reach higher into the atmosphere, and that frozen cloud particles are removed differently than during slow ascent, which has more water vapour.