The authors have done a commendably thorough job of revising the paper
in response to my comments and those of the other reviewers. In
particular, the revisions to section 5 on tracer correlations are very
helpful in clarifying that material. I think the paper is now largely
suitable for publication in ACP. There are a number of minor points
remaining, and also a few clarifications (primarily to some of the new
material in section 5) that I would like to see addressed before
publication, as detailed below (there are still a number of grammatical
issues, but Iam assuming these will be addressed in the copy-editing
There are several places in the paper where the vortex (before or well
after the SSW) is referred to as "stable" (e.g., lines 276, 332, 334,
381, 402, 504). It would be helpful to clarify what this term is being
used to convey. "Stable" has a formal definition in the sense of the
necessary and sufficient conditions for various sorts of fluid dynamical
instabilities (typically baroclinic or barotropic instability in the
polar stratosphere). I don't believe that is what is meant here (and
would require a calculation of the conditions for stability if so). It
would be helpful to say what is meant (e.g., not changing rapidly,
"strong" in some defined sense, etc).
line 24, add "e.g.," before references (since EP flux is so widely used,
there are many publications that could be listed here).
line 44, insert "down" between "breaking" and "and". Also would be good
to add Randall et al. (2009, GRL, doi:10.1029/2009GL039706) to the
references listed here.
lines 54-55, please specify how long before and how long after.
lines 62-64, it would be good to also mention the Manney et al (2015)
finding of continued confinement of air in the vortex, as this was also
important to the observed behavior (and leads into the discussion of the
importance of representing mixing that follows).
lines 70-74, this is not very clear to me; I think it would help here to
define what the distinction is between "mixing" and "advection", since
"mixing" is used to describe a number of processes, some of which are
simply small-scale transport (that is, advection); is this just a matter
of scale in your usage?
line 78, I would say "one main difficulty" or "an important difficulty"
-- I think saying it is the *only* one, as implied by "the" is a bit
lines 82-87, is the material about the Riese et al (2012) paper
relevant to this paper?
lines 91-92, probably should specify "...within the extratropical surf
zone" *in winter*.
lines 99-100, should qualify that these extended lifetimes are in the
absence of chlorine-catalyzed ozone loss in the lower stratospheric
lines 112-113, why would this effect be exaggerated in models?
line 149, it is not clear to me in what way the maximum polar cap
temperature characterizes the response of the BDC to SSWs better.
line 243, might specify that 1000K is relevant since all the analysis
here is for levels well below that.
lines 250-259, I think the only Livesey et al reference that is needed
here is Livesey et al (2013, Tech Memo), which is the data quality
document that supercedes the 2011 one. The URL given is that for this
document and could be moved to the citation in the reference list as
lines 271-272, can you give any possible explanation for this small
lines 316-318, does enhanced wave forcing really necessarily drive
mixing "across the vortex edge" as is implied here? Certainly there is
more mixing in a zonal mean sense, and also more mixing in the "surf
zone" around the vortex. But in cases where the lower stratospheric
vortex remains strong after an SSW (e.g., 2013), would that necessarily
mean more mixing across the vortex edge?
lines 353-354, The subtropical barrier is only clearly apparent in
Fig. 6b for 500-700K, not at either the higher or lower layers -- is it
really limited to that layer?
lines 378-385, this isn't very clear to me, from the text or the
figure. The figure seems to indicate that mixing can be associated with
either EP flux convergence or divergence at different times. Can you be
more explicit about why this is the case?
lines 390 and 394, I think you mean "separated" rather than
line 420, and Figure 8, that the "whole correlation inclines to one
side" is hard to see here, as are some of the other changes in the lines
in the schematic. One simple thing I think might help is to put a grid
(probably in dotted lines) behind the lines on the panels (especially
those on the right) so that the read could more easily see when a line
has moved between on panel and the next.
More on Figure 8:
-Re line 425, why do you not show/discuss vertical motions before and
after the SSW? In fact, the diabatic descent is enhanced for at least a
month after the SSW, and *confined* descent is expected to be weaker
*during* the event when the vortex is compromised (I'm not aware of a
study showing this for 2009, but certainly that was the case in 2006,
e.g., Manney et al, 2008, JGR, and Manney et al, 2009, ACP). And in
fact, in the conclusions (line 573) you stated that descent is enhanced
through late March, about two months after the SSW.
-most of the lettering within the panels themselves is too small to read
-- care should be taken to make sure it is legible in the final
-when you label the y-axis "Altitude" here, does that really mean
potential temperature (this makes a big difference in what is
interpreted as vertical motion)?
-it isn't clear to me from the figure or the text what becomes of
fragments C and F.
line 476, why don't you limit MLS to the same EqLs as for CLaMs? I
think this is an important question in light of the fact (now discussed)
that limitations on the domain can result in "artificial" changes in
lines 487-489, I think you mean that it is obvious that the APs are
missing because there are APs in the box in Fig. 9a3 but not in
Fig. 9c3? The wording could be changed to clarify this.
lines 502 and 506, this is the first mention that I saw of "chaotic
advection"; this should be defined, as well as (per a comment above) how
it differs from plain "advection" and/or from "mixing".
lines 524-527, it still isn't clear to me what the "effective" vertical
resolution of CLaMS is as compared to that of MLS.
lines 529-531 and 535-543, it would be helpful to clarify the importance
of sunlight exposure in this discussion. Also, in addition to
Kuttippurath and Nikulin, Manney et al (2015, ACP; for Dec/Jan) and
Livesey et al (2015, ACPD, for the full winter) also show the amount of
lower stratospheric chemical loss in 2008/2009 compared with other
line 546, how is the "most probable location determined"?
line 546, and following, ozone here is given in ppbv, but the figures
are labeled in ppmv, please change one or the other for consistency (I'd
suggest ozone always be given in ppmv).
line 579, would be good to say how the subtropical barrier was affected,
that is, whether it was strengthened or weakened, or its location
line 584, I don't think "triggered" is the right word here -- you
haven't shown a causal connection. I would simply say something like
line 586-587, This is a bit strong. In the revised paper you have, in
fact, done a very nice job of showing how *difficult* it is to use
tracer correlations to separate dynamical and chemical effects, even if
you have additional information as you do from CLaMS and MLS.
line 590, "almost half of the vortex" -- in area, or what?
lines 593-594, would be helpful to note the altitude regions where these
loss processes are occurring.
lines 601-603, two points: first, this speculation should also apply to
final warmings after winters with significant chemical processing;
second, whether the air at lower latitudes is higher in ozone than the
vortex air depends on altitude (in much of the lower stratosphere, for
instance, in absence of chemical loss in the vortex, ozone is lowest at
lines 640-641, how did you determine that the small vertical ozone
variability and not the better resolution is the primary factor?