DanieleItalyRm wrote: Vince_and_Grace_fan wrote:
I am a meteorology student in Hungary, and I interested in tropical cyclones, particulary that occur near Europe, and also the tropical-like systems over the Mediteranean Sea.
I wrote a brief summary from this cyclone on my Wunderground blog: https://www.wunderground.com/blog/Zivip ... ranean-sea
This is of course not official, just my opinion. But I think, this cyclone became a real tropical storm for a short time, and also was subtropical before it.
I agree with your analysis. I'm glad we scored the same path of 90M.
90M has developed over more warm water than TCAlex developed in January 2016 . Advice this study for who still believes in old meteorological concepts:" Revisiting the 26.5°C Sea Surface Temperature Threshold for Tropical Cyclone Development, 2014".
A high sea surface temperature is generally accepted to be one of the necessary ingredients for tropical cyclone development, indicative of the potential for surface heat and moisture fluxes capable of fueling a self-sustaining circulation. Although the minimum 26.5°C threshold for tropical cyclogenesis has become a mainstay in research and education, the fact that a nonnegligible fraction of storm formation events (about 5%) occur over cooler waters casts some doubt on the robustness of this estimate. Tropical cyclogenesis over subthreshold sea surface temperatures is associated with low tropopause heights, indicative of the presence of a cold trough aloft. To focus on this type of development environment, the applicability of the 26.5°C threshold is investigated for tropical transitions from baroclinic precursor disturbances in all basins between 1989 and 2013. Although the threshold performs well in the majority of cases without appreciable environmental baroclinicity, the potential for development is underestimated by up to 27% for systems undergoing tropical transition. An alternative criterion of a maximum 22.5°C difference between the tropopause-level and 850-hPa equivalent potential temperatures (defined as the coupling index) is proposed for this class of development.
When combined with the standard 26.5°C sea surface temperature threshold for precursor-free environments, error rates are reduced to 3%–6% for all development types. The addition of this physically relevant representation of the deep-tropospheric state to the ingredients-based conceptual model for tropical cyclogenesis improves the representation of the important tropical transition-based subset of development events.
Daniele, my friend...
As always, it is good to see your posts on this subject. You and I have had this same conversation before in the "Xandra" (2014) thread.viewtopic.php?f=31&t=116987
It's now apparent (or at least it should be apparent) to those who study such things that the 26C threshold only works in a standard or seasonal "MDR-type" barotropic environment. My thoughts there are similarly relevant here, so I will repeat them...
"The traditional low end SST threshold of 26-27C (79-81F) assumes a barotropic atmosphere typical of the deep tropics. Generally, in absence of cold core TUTT cells or troughs that show some reflection down into the mid levels, this type of atmosphere features 500MB temperatures of -4C to -6C. Since instability is a function of temperatures both at the surface and aloft, obviously traditional SST thresholds for TC formation will rarely apply to "medcanes", given their formation north in the range between 30-37N.
I think a decent rule of thumb here might be to look for a temperature difference of no less than 30C between SST/near surface air mass and 500MB when looking at true TC processes (i.e latent heat feedback from convection). In other words, when your SSTs drop to, say...20C, as long as 500MB temps have cooled to at least -10C or lower, and in absence of a significant intrusion of a dry and/or cool (polar) air mass at the time, the local atmosphere, would still support TC formation, at least thermodynamically
Since your proposal looks at 850MB-tropopause and mine looks at near surface-500MB, I think it would be interesting to compare the two alternative thresholds (or similarly less stringent alternatives) for this subset of developments.
This is a FANTASTIC opportunity for a comprehensive M.S. thesis just waiting to be written!