Interesting and readable paper about shear and TPW

[Ed Lizard]

With a little effort, even a non-met can understand most of this, and understand all the relevant points. Now, if some of the red tags disagree with the conclusions, feel free to add input.

Note Dr. Landsea is an advisor on this master's thesis...

http://orca.rsmas.miami.edu/~derek/thesis/dec_07_final/DOrttF07.pdf

Interesting conclusion, while dry air external to the TC isn't good for it once it is well established, it takes some shear to get the dry air to the core and really weaken a well developed storm.

Also suggests storms embedded in a high TPW environment are less prone to eyewall replacement cycles.

[LocoAko]

Isn't Derek Ort that got all over S2K?

[am19psu]

Also suggests storms embedded in a high TPW environment are less prone to eyewall replacement cycles.

This is a little misleading. High TPW is a necessary but not sufficient condition for an ERC. The hypothesis of the paper is that a dry exterior AND moist interior promotes an eyewall replacement cycle due to the constraints on the size of the rainbands and their distance from the center.

There still have not been any studies (that I am aware of, at least) showing the difference in environmental conditions between those cases that undergo an ERC and those cases that undergo RI. They both require low shear, high TPW in the interior of the eyewall, and are more likely to occur over warm SSTs than cool.

P.S. for more on the interaction between shear and dry air, look at some of Jason Dunion's latest stuff.

[k***]

Isn't Derek Ort that got all over S2K?

I like to call his legion of sycophants the ortt cloud

[CUmet]

The interaction between shear and dry air in the TC environment is quite an interesting one. It has become quite well-established in both the operational and research community that the combination of shear and dry air is even more detrimental to TC intensity than shear alone. It is also thought that it is extremely difficult for dry air to penetrate into the TC core without the presence of significant wind shear. Exactly how these evolve together is still an area of much research.

One interesting topic that comes up in Jason Dunion's work (large ppt here) and in other papers as well is the relationship between the shear direction and the location of the dry environmental air. Indeed, the total precipitable water in the quadrant centered upshear of the TC is a new SHIPS RI predictor. One might infer that the shear vector "advects" dry air into the TC core, but it's not quite as simple as that. Significant shear imparted on the TC generally results in stronger radial inflow downshear, and radial outflow upshear of the center. Keeping in mind that air doesn't simply flow directly into the TC core, but gets rotated counterclockwise around the center for some distance, the preferred source region of dry air that gets entrained into the TC core may actually be downshear to right-of-shear. Model simulations of a TC in significant easterly shear done in a paper by Riemer & Montgomery show this (Figs. 6 and 11) .

The asymmetry of the convection is also thought to contribute to dry air entrainment into the TC core for several reasons. The first, mentioned by Ortt, is that convection in a TC modifies the dry air as it approaches the core, minimizing its effect. If convection is missing from part of the storm, though, dry air remains unmodified as it gets into the core. The second reason, as suggested by Riemer and Montgomery and also Tang and Emanuel 2010 is that the persistent downdrafts associated with the asymmetric convection transport low theta-e air into the boundary layer, choking off the TC's main energy source.