EGU2020-5411
https://doi.org/10.5194/egusphere-egu2020-5411
EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Local diagnostics of Rossby wave packet properties – Seasonal variability and their role in temperature extremes

Georgios Fragkoulidis and Volkmar Wirth
Georgios Fragkoulidis and Volkmar Wirth
  • Johannes Gutenberg University, Mainz, Institute for Atmospheric Physics, Physics, Mainz, Germany (gfragkou@uni-mainz.de)

Transient Rossby wave packets (RWPs) are a prominent feature of the synoptic to planetary upper-tropospheric flow at the mid-latitudes. This prompts the development of diagnostic methods to identify and investigate the spatiotemporal evolution of key RWP properties. Such properties include the RWP phase speed and group velocity, the diagnosis of which has so far remained non-local in space and/or time. To this end, a novel diagnostic approach is presented here, which is based on the analytic signal of upper-tropospheric meridional wind velocity and thus allows the evaluation of RWP properties locally in space and time. The detailed insight into these properties can be utilized toward a better understanding of the upper-tropospheric circulation, its interplay with local weather features, and its model representation. In particular, climatologies of RWP amplitude, wavenumber, phase speed, and group velocity are investigated using reanalysis data for the time period 1979 – 2018. Pronounced features of seasonal and interregional variability are highlighted. Moreover, the role of RWP amplitude and phase speed in the occurrence and duration of temperature extremes in Europe is explored. Finally, indications of systematic biases in medium-range forecasts of these fields suggest that a correct representation of the RWP evolution is crucial for the predictability of temperature extreme events.

How to cite: Fragkoulidis, G. and Wirth, V.: Local diagnostics of Rossby wave packet properties – Seasonal variability and their role in temperature extremes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5411, https://doi.org/10.5194/egusphere-egu2020-5411, 2020

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Presentation version 1 – uploaded on 04 May 2020
  • CC1: Comment on EGU2020-5411, Tim Woollings, 05 May 2020

    Nice presentation and results! I don't quite follow the setup though - how exactly do you define A_v from the v field? 

    • AC1: Reply to CC1, Georgios Fragkoulidis, 05 May 2020

      Thank you for the comment Tim! The analytic signal of a 1-dimensional signal (in this case, 300hPa meridional wind along a latitude circle) is computed as follows. We first discard the negative frequencies of the Fourier transform of the signal and then we compute the inverse Fourier transform. Given that we zeroed-out the negative frequencies, the result is not the original signal itself, but a complex representation of it that is called the "analytic signal". The modulus of this complex signal has been used in the past to diagnose the local amplitude of RWPs (e.g. https://doi.org/10.1175/1520-0493(2003)131<1011:EEORWP>2.0.CO;2). Here, we also compute the argument of this signal (i.e., atan2[Imaginary part, Real part]) in order to get the local phase. The local phase is then "exploited" to compute the local phase speed as shown in the slide. I am happy to provide further input in case this was not helpful enough

      • CC2: Reply to AC1, Tim Woollings, 06 May 2020

        Thanks Georgios, that's very helpful. I should try that method, it seems to be working very well. Best wishes, Tim

        • AC2: Reply to CC2, Georgios Fragkoulidis, 07 May 2020

          You're welcome!