12 Jun 2023
 | 12 Jun 2023

jsmetrics v0.1.1: a Python package for metrics and algorithms used to identify or characterise atmospheric jet-streams

Tom Keel, Chris Brierley, and Tamsin Edwards

Abstract. The underlying dynamics controlling this planet’s jet streams are complex, but it is expected that they will have an observable response to changes in the larger climatic system. A growing divergence in regional surface warming trends across the planet, which has been both observed and projected since the start of the 20th century, has likely altered the thermodynamic relationships responsible for jet stream formation and control. Despite this, the exact movements and trends in the changes to the jet streams generally remain unclear and without consensus in the literature. The latest IPCC report highlighted that trends both within and between a variety of observational and modelling studies were inconsistent (Gulev et al., 2021; Lee et al., 2021). Trends in the jet streams were associated with low to medium confidence, especially in the Northern Hemisphere.

However, what is often overlooked in evaluating these trends is the confused message in the literature around how to first identify, and then characterise, the jet streams themselves. For characterisation, approaches have included isolating the latitude of the maximum wind speed, using sinuosity metrics to distinguish jet ‘waviness’, and using algorithms to identify jet cores or jet centres. Each of these highlights or reduces certain aspects of jet streams, exist within given time windows, and characterise the jet within a given (Eulerian or Lagrangian) context. While each approach can capture particular characteristics and changes, they are subject to the spatial and temporal specifications of their definition. There is therefore value in using them in combination, to assess parametric and structural uncertainty, and to carry out sensitivity analysis.

Here, we describe jsmetrics v0.1.1, a new open-source Python 3 module with standardised versions of 16 metrics that have been used for jet stream characterisation. We demonstrate the application of this library with two case studies derived from ERA-5 climate reanalysis data.

Tom Keel 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 egusphere-2023-661', Anonymous Referee #1, 17 Jul 2023
    • AC2: 'Reply on RC1', Tom Keel, 18 Sep 2023
  • RC2: 'Comment on egusphere-2023-661', Gloria Manney, 04 Aug 2023
    • AC1: 'Reply on RC2', Tom Keel, 16 Aug 2023
    • AC3: 'Reply on RC2', Tom Keel, 18 Sep 2023

Tom Keel et al.

Tom Keel et al.


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Short summary
Jet streams are an important control on surface weather as their speed and shape can modify the properties of weather systems. Establishing trends in the operation of jet streams may provide some indication of the future of weather in a warming world. Despite this, it has not been easy to establish trends, as many methods have been used to characterise them in data. We introduce a tool containing various implementations of jet stream statistics and algorithms which work in a standardized manner.