A thought: Convection during cumulus cloud formation induces convergence toward that location. The history of the "air volume" may reveal a source region of vorticity that remains in the air volume ("air mass" has association with weather fronts and may be misleading here). Convergence yields enhanced rotation of the thermally driven volume. Thermal forces drive the system locally, but the spin may have come from afar.

Think: an air volume must have time to acquire the earth's rotation for vorticity convergence to produce tropical storm rotation. Strong winds and strong wind shear have other Coriolis and vorticity influences.

Well, just a thought. Len

Dear Leonard Hall, At the equator, the Coreolis force does not lead to twisting. In this zone, the Coreolis force causes the horizontal wind flow to rise or fall. In the intratropical convergence zone, convective structures never twist and they never form cyclones with a storm eye. At the equator, only cyclones are formed typical for temperate latitudes, where atmospheric pressure is also low. If an equatorial cyclone enters a high pressure zone, into the tropics, it becomes a cyclone with an "eye" of the storm. Sincerely, Boris.

Dear Borys Kapochkin, I agree with the information in your reply, however your original point is that cyclones do form at the equator. How? Whence the rotation?

I suggested for your consideration that the "air volume" that converges to a convection center, or a low-pressure center, has come from a higher latitude source. It acquired vorticity in that source region and convergence to a tropical convection center revealed the vorticity by rotation, even proving it had come from the northern hemisphere by the cyclonic circulation in the Boffa event.

The vortex in water at a reservoir drain is a similar event in which the diffused vorticity of the water that has rotated with the earth is concentrated at the outlet. The vortex is essential to drain the vorticity along with the water.

Well, as noted earlier, just a thought, Len

Dear Leonard Hall. Now I understand. Thank you. We need to see what Typhoon Boffа formed from. Sincerely, Borуs

Dear Borys, Yes, history may be very important when the present is hard to explain. Happy Trails, Len

Dear Borys Kapochkin

The partial answer to this question is presented in the recent paper published in the QJRMS: Tropical cyclogenesis at and near the Equator.

https://rmets.onlinelibrary.wiley.com/doi/abs/10.1002/qj.3529

The mechanism discussed in the above paper involves advection of the vorticity and stretching of the vortex patches by convection. We can explain the entire phenomenon using a concepts of supercritical process driven by stretching and folding of the material surfaces.

It is possible to propose an analytical model for this type of cyclogenesis in addition to the existing modelling studies.

Dear Colleagues, Borys Kapochkin, Janusz Pudykiewicz, Natalia Kucherenko (included from another of Borys Kapochkin's questions), greetings from Idaho, North America, USA. This is a very fine experience - discussion.

The paper cited by Janusz Pudykiewicz clarifies in several model runs and four real systems that the origin of the vorticity which is concentrated by convection to form a cyclone in equatorial areas is often present in the shear in regional winds. This is quite different from my mental image of an "air volume" advected from some source region. Borys Kapochkin's acknowledgement that diffuse vorticity was concentrated by convection was correct but the cited paper clarifies the source region in several cases as local. Fortunately, I prefer learning to having been right. Thank you, Janusz Pudykiewicz, for that citation.

Natalia Kucherenko emphasized in her reply to Borys' question of the relative damage due to the hurricanes Katrina and Rita in 2005 in Louisiana, that all too often there are "more things in Heaven and Earth" than enter our scientific efforts. I have included this observation here because the philosophy of science and the limits of education are important. The most deadly phrase in education is "It is known that . . .." No! Something like "So far we have shown to our satisfaction that . . .," would be far better! Many of the things I have learned in 82 years have been corrections to "it is known that," although those "in the know" have as often corrected my "mistake." For example, the critical papers cited in the paper, QJRMS: Tropical cyclogenesis at and near the Equator, were published since I retired and they modify the previous "knowledge" significantly. Another example, solar tides amount to less than 2 hPa and pressure departures in hurricanes are much larger but can the tides act as triggers timing processes of much greater energy? Is that question worth study? Upper atmosphere events used to be considered irrelevant to the dense air down here, but we have learned. For engineering and manufacturing one cannot be bothered with such ideas if "what is known" works well enough, and many scientists are governed by what works - incrementing the known for career security. I am exploiting this opportunity to express my appreciation that some of us are still explorers, and any explorer worth his salt will end up in a box canyon someday because "it is known" is unsafe when it is in control.

Please pardon this excursion into philosophy, but I wanted to acknowledge the exploration of Borys Kapochkin's questions, and the sense of that among us. I have found discussion to be rare, Len

Oops, I need colleagues to proof because I never do everything right, apologies: It should be "Idaho, USA, North America," sigh. (I used to be more formal, but not necessarily more accurate.) Sorry, Len

Dear Leonard Hall. You were absolutely right when you said: "Another example, solar tides amount to less than 2 hPa and pressure departures in hurricanes are much larger but can the tides act as triggers timing processes of much greater energy?". We also doubted and carried out calculations to verify. We studied the development dynamics of Cyclone Nadine (Atlantic September 2012).

According to the satellite digital map of atmospheric precipitation, area indicators - average value, dispersion, entropy and others - were calculated every three hours. We recognize that changes in the amount of condensed water in the atmosphere are proportional to the energy received by the cyclone due to condensation and vacuumization (a dynamic component of the condensation process). I have attached the results of calculations in the form of time series.

According to the satellite digital map of atmospheric precipitation, area indicators - average value, dispersion, entropy and others - were calculated every three hours. We recognize that changes in the amount of condensed water in the atmosphere are proportional to the energy received by the cyclone due to condensation and vacuumization (a dynamic component of the condensation process).

The graphs show a high amplitude of water condensation fluctuations during the day.

I have attached the results of calculations in the form of time series.These are periodograms of time series: from the top - by indicators of the average value of the cloudiness indicator field (red), estimates of the standard deviation of cloudiness on a fixed area (green); below – entropy estimates. It is important to take into account that the period of 12 hours is a component of the period of 24 hours (this is how statistics work).

I want to draw your attention to the period of 12 hours for entropy (changes in the degree of ordering of condensation over the area). This means that every 12 hours a drop in atmospheric pressure provokes an increase in water condensation, uniform over the area. If you are interested, I can show how these processes revive the weakened cyclone. Sincerely, Borуs.

Dear Borys Kapochkin, thank you for the more detailed information on your approach to hurricane evolution and the offer for further involvement on my part. If you have glanced at my research efforts presented in a project on my ResearchGate pages you will recognize that I better spend my time there instead. I have enjoyed this interaction and wish you well in its pursuit and acceptance. Happy Trails, Len

Dear Leonard Hall, I am an oceanologist by profession. My scientific achievements are maximum in the field of geodynamics and seismology. My favorite pastime is to organize and conduct expeditions to study coral reefs. But I do not limit myself and deal with incomprehensible problems with students and graduate students. I am very grateful to you for your time. Your ideas are very helpful for me and my friends. Sincerely, Boris.

We investigated the conditions of formation and development of a cyclone in the Indian Ocean, the diameter of which was more than 2,000 km. It was formed in the third decade of November 2011 (slide attached). It reached the Persian Gulf, where it turned into a tropical cyclone and caused destruction. Data Jaxa

This is quite interesting. It appears to be similar to the storms treated in the paper cited by Janusz Pudykiewicz. One can see shear in the satellite view as marked in the attached image.

It is quite interesting that this storm intensified at the beginning of the winter monsoon and one wonders if warm ocean currents were involved. A look into the literature shows many articles here on ResearchGate that treat that subject, and I hopefully await knowing discussion to the forcing processes of this tropical cyclone development. Len

Convectively coupled Kelvin waves are considered by many researchers to be a plausible cause of tropical cyclogenesis. This fascinating subject is discussed in the paper: Kelvin Waves and Tropical Cyclogenesis: A Global Survey by CARL J. SCHRECK III.

https://www.atmos.albany.edu/daes/atmclasses/atm527/Journal_Discussion_files/Schreck_2015.pdf

I am adding a map of wave heights in the cyclone area south of Sri Lanka. This is objective satellite altimetry data from their website.

We have studied the influence of monsoon winds on tropical cyclogenesis. The surface temperature of the tropical zone in the northern part of the Indian Ocean is higher than in the Pacific and Atlantic oceans at all times of the year. Conditions for tropical cyclogenesis in the northern part of the Indian Ocean are favorable in May - December. But in the tropical zone of monsoon circulation, during the favorable warm season, winds are formed that do not allow the formation of convection as the initial stage in the formation of a tropical cyclone. For our analysis, we chose 2018 as one of the warmest and potentially favorable years for the formation of tropical cyclones. In 2018, the planet had 98 tropical cyclones that exceeded the norm by 18%, and in the Northern Hemisphere, the norm was exceeded by 28%. Data on the number of tropical cyclones in 2018 in the northern and southern hemispheres of the Indian Ocean were analyzed (cyclones with wind speeds up to 85 km/h were studied). In the northern hemisphere of the Indian Ocean, where there is no negative effect of monsoons on tropical cyclogenesis, the cyclone season began in November and continued until April inclusive.

In the northern hemisphere of the Indian Ocean in 2018, the tropical cyclone season began on 05/21/18 (wind speed 175 km/h, atmospheric pressure 960 hPa), and was interrupted by a monsoon wind. The recovery of tropical cyclogenesis took place in October and lasted until December (6.10.18 (wind speed 140 km/hour, atmospheric pressure 976 hPa), 8.10.18 (wind speed 150 km/hour, atmospheric pressure 970 hPa); 10.11 18 (wind speed 140 km/hour, atmospheric pressure 992 hPa), 13.12. 18 (wind speed 100 km/hour, atmospheric pressure 993 hPa)).

Howdy, Borys,

Excellent! Your data and discussion cover the character of the region well and clear my curiosity about the cyclone energy forcing process there. It fills out the original image and note. The wave heights image even indicates a cyclonic circulation south of Sri Lanka.

I've learned a great deal about tropical cyclones from you and from both articles cited by Janusz Pudykiewicz (and a dozen articles cited therein needed to follow them). Thank you both.

Happy Trails,

Len