EGU General Assembly 2022
© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.

Large-scale forcing of extreme African dust storms by double Rossby wave breaking

Jose A. G. Orza1, Saroj Dhital2, Stephanie Fiedler3,4, and Michael L. Kaplan5
Jose A. G. Orza et al.
  • 1SCOLAb, Dept. of Applied Physics, Universidad Miguel Hernandez de Elche, Elche, Spain (
  • 2USDA-ARS Jornada Experimental Range, Las Cruces, NM, USA (
  • 3University of Cologne, Institute of Geophysics and Meteorology, Cologne, Germany (
  • 4Hans-Ertel-Centre for Weather Research, Climate Monitoring and Diagnostics, Bonn/Cologne, Germany
  • 5Applied Meteorology Program, Embry-Riddle Aeronautical University, Prescott, AZ, USA (

Dust storm genesis is one of several high-impact weather phenomena that may result from Rossby wave breaking (RWB). The wave propagation into low latitudes over North Africa facilitates instability through upper-level divergence and the reduction of the static stability ahead of the cyclonic side of the wave train, and therefore modulates the low-level tropospheric conditions in dust source areas.

The analysis of three dust storm case studies that strongly impacted the Iberian Peninsula and another one impacting the Cape Verde Islands indicates that a double RWB process within the Polar Jet (PJ) stream over the eastern North Atlantic and western Europe is a common large-scale upper-level precursor to the formation of the large North African dust storms and subsequent transport of dust (Orza et al, 2020; Dhital et al, 2020).

The synoptic and larger subsynoptic scale features were analyzed using ERA-Interim reanalysis while mesoscale features were studied by high-resolution WRF-CHEM simulations. There are substantial differences between the case studies in the location and geometry of upper- and low-level features following the first break (Dhital et al, 2020; 2021). However, in all case studies (1) RWB within the PJ stream is observed; (2) there is a substantial poleward expansion of the upper-level subtropical ridge; and (3) the secondary RWB is amplified by nonlinear wave reflection from the first break.

Preliminary results from a larger number of cases study indicate the relevance of secondary RWB in the PJ stream. The dynamics may also result in cutoff lows and amplified low-PV ridging accompanying cyclogenesis and heatwaves, respectively, which emphasizes the need to improve our understanding of the involved processes.

- Dhital S, ML Kaplan, JAG Orza, S Fiedler (2020). Atmospheric dynamics of a Saharan dust outbreak over Mindelo, Cape Verde Islands, preceded by Rossby wave breaking: Multiscale observational analyses and simulations. J. Geophys. Res. Atmos. 125, e2020JD032975.

- Dhital S, ML Kaplan, JAG Orza, S Fiedler (2021). Poleward Transport of African Dust to the Iberian Peninsula Organized by a Barrier Jet and Hydraulic Jumps: Observations and High-Resolution Simulation Analyses. Atmos. Environ. 261, 118574.

- Orza JAG, S Dhital, S Fiedler, ML Kaplan (2020). Large Scale Upper-level Precursors for Dust Storm Formation over North Africa and Poleward Transport to the Iberian Peninsula. Part I: An Observational Analysis. Atmos. Environ. 237, 117688.


How to cite: G. Orza, J. A., Dhital, S., Fiedler, S., and Kaplan, M. L.: Large-scale forcing of extreme African dust storms by double Rossby wave breaking, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10592,, 2022.


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