A numerical investigation of supercells in landfalling tropical cyclones

Hi all,

On Thursday October 28th, I will be presenting some of my research on TC supercells.

This study aims to understand the environmental and physical mechanisms that lead up to tornadogenesis in a TC supercell. To address certain gaps in the knowledge base, our study uses idealized numerical simulations to run a series of sensitivity tests where TC supercells evolve in different environments. Our working hypotheses are as follows.

  • The sea-to-land transition is a crucial factor in TC supercell intensification due to the impacts of a larger diurnal temperature variation and increased surface friction over land.
  • The storm-scale processes that lead to updraft rotation are enhanced in supercells that develop in and near dry air intrusions due to (1) localized midlevel evaporational cooling in the typically moist TC environment, and (2) cloud erosion, which leads to increased surface insolation during the day.

As part of our ongoing research, the net effects of these processes are investigated in both maritime and landfalling TCs.

Last week I presented this work in the form of a poster at the Severe Local Storms conference in Denver, CO. Below are the links to my extended abstract and poster.

http://www4.ncsu.edu/~nwsfo/storage/resupdates/Morin_SLS_extended_abstract_FINAL.pdf

http://www4.ncsu.edu/~nwsfo/storage/resupdates/Morin_SLS_Poster_FINAL.pdf

I welcome any feedback you have.

Cheers,

Matt Morin

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6 Responses to A numerical investigation of supercells in landfalling tropical cyclones

  1. Jonathan Blaes says:

    Matt,

    Thanks for the update. I wanted to pass along some comments/questions that Barrett Smith shared with me last week when he took a peek at your preprint and poster.

    A) Very nice poster, both in content and visual appeal

    B) Regarding the sensitivity to supercell intensification and landfall, does Matt suppose there would be any similar sensitivity to the TC interacting with the Gulf Stream, given that region should be a little more instability-rich and also act as a natural baroclinic zone (though not nearly to the extent as during the cool season). It appears the sensitivity tests were done with a uniform SST field? Of course, the frictional effects would be negligible here.

  2. Barrett Smith says:

    Matt, a comment and a question….

    A) Very nice poster, both in content and visual appeal

    B) Regarding the sensitivity to supercell intensification and landfall, do you suppose there would be any similar sensitivity to the TC interacting with the Gulf Stream, given that region should be a little more instability-rich and also act as a natural baroclinic zone (though not nearly to the extent as during the cool season). It appears the sensitivity tests were done with a uniform SST field?

  3. Matt Morin says:

    Hi Barret, thanks for the nice comment. Yes, my SSTs are all the same (26°C). I imagine there would be favorable impacts on TC supercells if the parent rainband were to interact with the Gulf Stream, though that particular sensitivity hasn’t been tested in my study. The importance of low-level baroclinic boundaries on TC tornadogenesis has been noted often in the literature.

  4. jhudgins says:

    Matt…

    Poster looks great with a lot of good info! Just a quick question about the landfall simulation results regarding landfall time of day and TC supercell formation. From the TC tors that I looked at near the coast it seemed that most of them that were with a more organized TC did occur during the daytime but systems that were remnants or disorganized seemed to favor the nocturnal hours for tors especially those that interacted with a residual coastal front/trof etc. This would be systems that were along or east of the coastal plains while everthing west of there was heating induced. Just seems to be a difference regarding the strength/organization of the landfalling TCs and timing of the tors?

  5. Matt Morin says:

    Hi James, and thanks for your comment. That’s an interesting observation about those nocturnal TC tornadoes. I noticed that in my night landfall simulation, there was a local peak in TC supercell formation overnight a day after landfall. In my idealized landfall simulations I do not have preexisting heterogeneities such as fronts or troughs, though I imagine those would be beneficial to TC supercells and tornadoes as a means to overcome low-level CIN. So far, I have run my finest-mesh domain from just before landfall to two days after. I do have a 2 km grid that has been run through four days after landfall. Loops of simulated radar reflectivity show periodic peaks in supercellular-like convection throughout that time and even overnight (from the disorganized remnants of the landfalling TC).

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