EGU2020-762
https://doi.org/10.5194/egusphere-egu2020-762
EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

The impact of southward propagation of the upper-tropospheric Rossby wave activity on the Red Sea trough

Zakieh Alizadeh1, Alireza Mohebalhojeh1, Farhang Ahmadi-Givi1, Mohammad Mirzaei1, and Sakineh Khansalari2
Zakieh Alizadeh et al.
  • 1University of Tehran, Institute of Geophysics, Department of Space physics, Iran, Iran, Islamic Republic of (zaki_alizadeh@ut.ac.ir)
  • 2Atmospheric Science and Meteorological Research Center, Tehran, Iran

The Red Sea Trough (RST) is an inverted trough of low-pressure system at lower tropospheric levels over the northeast Africa and the Red Sea. The previous research conducted on the RST suggests that when this system is activated, heavy rainfall occurs in large parts of the eastern Mediterranean and southwest Asia. The main aim of this article is to investigate the way Rossby wave activity at the upper level troposphere and its interaction with the lower tropospheric circulation activate the RST.

This study was carried out in three stages: first, the climatological behavior of RST in winter (December to February) was studied and then, cyclones were identified and tracked in the northeast Africa and the Red Sea using a cyclone tracking scheme. In the second stage, the Rossby wave activity flux at the 300 hPa level was considered in the region. Finally, the interaction between the wave activity flux and the RST was investigated. Two critical phases for the wave flux entering the region were considered. The critical positive (negative) phase corresponds to the month when on average the highest (lowest) values of the wave activity flux enter the northeast Africa and Red Sea regions. The results show that, during the critical positive phase, the RST strengthens and extends to the northeast of the Mediterranean Sea and cyclogenesis is increased in the northeast of Africa and especially in the northeast of the Red Sea.

With regard to the divergence of wave activity flux with an associated southward flux, the source of activity needed for cyclogenesis and reinforcement of the RST is provided by the North Atlantic storm track and the divergence core over the Mediterranean Sea. The results of the wave activity time series show that part of the activity from the northeast is integrated with the convergence core of the Mediterranean storm track, leading to enhancement of the cyclones in the northeast of the Red Sea and the extension of the RST to the northeast. But most of the activity joins the flux divergence core of the Mediterranean storm track in the west of the region and results in amplification of Sudan’s cyclones and activation of the RST along both the meridional and zonal directions; the important point to consider is that the wave activity flux entering the region is greater in the zonal direction. In addition to the southward propagation of the wave activity, the packets of flux convergence and divergence in the central North Atlantic are tilted in the southwest–northeast direction, indicating the dominance of anticyclonic Rossby wave breaking. Associated with the upper-level wave activity fluxes entering the region, there is jet enhancement and low-level cold advection from higher latitudes to the tropical and subtropical regions. The difference of RST between the critical positive and negative phases is turned out to be statistically significant with confidence levels of greater than 90%.

Keywords: Red Sea Trough, Northeast Africa and Red Sea cyclones, wave activity flux, critical positive and negative phases, Mediterranean storm track, North Atlantic storm track

How to cite: Alizadeh, Z., Mohebalhojeh, A., Ahmadi-Givi, F., Mirzaei, M., and Khansalari, S.: The impact of southward propagation of the upper-tropospheric Rossby wave activity on the Red Sea trough, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-762, https://doi.org/10.5194/egusphere-egu2020-762, 2019

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Presentation version 2 – uploaded on 20 Apr 2020
I have added explanations to each slide
  • CC1: Comment on EGU2020-762, Olivia Romppainen-Martius, 27 Apr 2020

    Dear Zakieh

    Very interesting analysis. Do you know if these cyclones are anomalously stationary and persistent? 

    cheers

    Olivia

    • AC1: Reply to CC1, Zakieh Alizadeh, 28 Apr 2020

      Dear Olivia

      Thank you very much for your encouraging remark. Our focus has been on the surface cyclones with longevity of more than one day. We have not yet analysed the distribution of cyclones in terms of their persistence, but from slide 10 the impression one can get is that the cyclones are largely travelling features.   

       

       

    • AC2: Reply to CC1, Zakieh Alizadeh, 08 May 2020

      Dear Olivia

      Yes, these cyclones (the Sudan low) are strong semi-permanent and qusi-stationary character and the RST is persistent stationary wave (de Vries et. al, 2013). But I didn't understant your question, did I make a mistake in my work? Thank you for pointing me to my mistake to make my article better.

      Thanks

Presentation version 1 – uploaded on 04 Apr 2020 , no comments