Aric Dunn wrote:jasons wrote:Aric Dunn wrote:Microwave suggest otherwise and its pretty clear.
Respectfully disagree. There was a very lengthy (and well-cited) writeup last night on AmericanWx about it that settled this debate.
Good to know.. lets see it ? Its also not last night anymore.
OK, I re-read this. I must apologize as I was tired last night. Apparently she was undergoing some type of ERCs but not what we typically see:
OK.. So this has been bothering me the whole night. Therefore i spent the past three hours working and researching eyewall replacement cycle s (ERC) . I will preference with this: ERC are very poorly understood and research on them is just beginning. However, I found a theory about ERC which not only makes sense, but I was likewise able to extrapolate an answer for which I believe fits why these ERC are doing nothing to weaken Irma.
Terms:
ERC : Eyewall replacement cycle. HBL : Hurricane boundary layer. NRF : Net radial force. PGF : Pressure Gradient Force.
I will also preferance with the fact that I view weather as the earth's immune system and really all weather is is an attempt for the atmosphere to find an equilibrium (much like our immune system is to bring homeostasis to the body).
So let's get to it. ERC, in this theory, are believed to take place due to a set of complicated physics. As a hurricane is born, there are three main components, physics wise, which make up the storm (at least as it pertains to ERC). The first is the HBL which extends approximately 1 km into the atmosphere, from the surface. It interacts with most of the surface friction. The second is the PGF, which essentially forces particles from areas of higher density (pressure) to areas of lower pressure. The last is known as the NRF, which is essentially the force directed towards the center of a rotating mass.
As a hurricane develops, these forces work with each other and eventually, when the storm reaches a certain intensity, an excess of NRF creates a secondary wind maximum approximately 40-60km from the center of the hurricane. This secondary wind maximum is always believed to be because the HBL cannot properly maintain a balance of angular momentum (or the acceleration of particles/mass in a circulation motion), or in other words, the HBL cannot keep the particles separated in such a way that the pressure and buildup of particles remain uniform. This, combined with a positive NRF, creates convergence. This convergence creates an up welling which then leads to a secondary maximum. This secondary maximum, in turn, creates more PGF (the force of a particle over a given area. The higher the PGF, due to more particles in a smaller area, the higher the winds). Eventually, this leads to enough of a convergence that a secondary eyewall is formed and two wind maxima are thus created. As many know, during this time, the overall windspeed of the maximum sustained winds decrease due to the maximum winds being spread out over a larger area and thus the wind speed lowers (or.. The PGF is distributed over a larger area and therefore while the mass remains the same, because force equals mass times acceleration, acceleration is lower and therfore the force or net wind speed decreases). Eventually, the PGF, combined with angular momentum, will coerce the outer eyewall to contract, thus ending the ERC. At this time, the winds will increase as will the overall size of the wind field of the storm, while allowing the hurricane to likewise strengthen.
But the question that's plagues me today is why has Irma skipped this weakening phase of the ERC and likewise why has she been constantly cycling through them and having them take place in a rapid fashion? What I propose is this. Irma has been in essentially a perfect, or lab like environment, for her lifespan. This is what is allowing her to explosively deepen and shatter records. What I likewise propose is this. Irma is showing us that hurricanes create ERC of their own accord. In other words, an ERC has nothing to do with outside influences and is strictly because of the mechanism of the hurricane itself (and the strengthening mechanisms within). Likewise, because ERC are part of the hurricanes overall structure, in theory, it should not hurt the hurricane, but rather, help it. Left to its own devices, this is what Irma is doing. It's part of a necessary strengthening cycle for well developed hurricanes. The HBL, I propose, creates the issue for ERC as within this layer, there is friction. This friction slows the contraction of the secondary eyewall and forces the storm to balance itself out to preserve itself, while it deals with the friction and the effects of it. Because Irma is in a lab like environment, the friction of the ocean is essentially non existant as it is over flat and incredibly warm water. Likewise, there is no sheer or dry air to interfere with the Core and venting mechanisms of Irma. As such, these ERC can begin and complete without any interference and then, once the outer wind maxima are mature, the PGF and angular momentum can allow the outer wind maxima to contract, replacing the old eyewall and thus completing the ERC, in time for it to build and start once again. Therefore, she can bypass any weakening state that the friction within the HBL would cause, as, essentially, there isn't any to speak of.
This, of course, is strictly a theory
Source:
https://www.americanwx.com/bb/topic/502 ... /?page=182And this analysis from LEK threw me off:
For the love of God....there has been and there is no indication of an ERC. As long as the outer eyewall attaches occasionally to the IEW (transporting angular momentum inward), you will not see the IEW contract. Concentric eyewalls can be very stable, as long as they remain far enough apart, as to not rob the IEW of surface "energy"....as a matter of fact, if the IEW remains very stout...an outer eyewall will struggle to "take over"...that's where we are at now...
You can clearly see the OEW is "connecting" occasionally to the IEW....this ENHANCES the strength of the IEW....when the connection happens, you often will see a slight deterioration of part of the IEW. I bet in a bit, you see one large eyewall....not necessarily an EWRC...more of an EW "enhancement" cycle...
Source:
https://www.americanwx.com/bb/topic/502 ... /?page=180
