Bill Gray was credited by Chris Landsea in his WMO and WTC presentations as the person who discovered the link between El Nino and Atlantic hurricanes. He recently suggesting a connection between Atlantic hurricanes and fluctuations in the world ocean conveyor. Judith Curry told the WSJ that Gray has “brain fossilization” and “nobody except a few groupies wants to hear what he has to say.” AT CA, she said:
I am not going to critique Gray’s paper, it is beyond rational critcism, i will save technical comments for such an unlikely event as any of this actually ever gets published. Bill Gray is not a player in the scientific debate, his ideas reflected in the paper referred to at RC are so flawed that they are unpublishable.
Gavin Schmidt had a hissy fit at realclimate – Gray and Muddy Thinking
Fast forward a few months later. The new big thing in Atlantic hurricanes is their connection with something called the Atlantic Meridional Mode (Vimont and Kossin 2007; Kossin and Vimont 2007). I’ll present some maps below comparing the Atlantic Meridional Mode to Bill Gray’s diagrams. You decide whether Judith Curry and Gavin Schmidt should be spitting and having hissy fits at Bill Gray or not.
Landsea’s recent presentations cordially acknowledge Bill Gray. See slide 33 of his WMO presentation. See Slide 25 of his WTC presentation. Perhaps these are the “groupies” that Judith Curry is referrring to.
In Landsea’s WMO presentation, after a slide (#73) showing a standard diagram of the world ocean conveyor system, there is the following diagram (slide 74) illustrating two modes for Atlantic hurricanes. On the left is one mode showing an active hurricane season (multiple arrows) associated with warm SSTs in the west Atlantic and cool SSTs in the south Atlantic, a strong meridional ocean current, low pressure offshore Africa and wet west Africa; on the right is the opposed mode showing an inactive hurricane season, cold SSTs in the west Atlantic and warm SSTs in the south Atlantic, weaker ocean currents, high pressure offshore Africa and dry west Africa.
Now here’s a related diagram from Gray’s controversial presentation previously linked to at CA here, in which you see many of the same features. The top panel shows a strong hurricane season, low pressure offshore Africa and wet west Africa – corresponding to the left panel above, while the bottom panel shows the opposing mode: fewer hurricanes, high pressure offshore Africa and dry west Africa, this time placing the Atlantic circulation modes in the context of global circulation. I have no opinion as to whether these modes are valid or invalid; I am merely observing that the modes presented by Bill Gray are the same as those presented by Chris Landsea.
The American Meridional Mode
The Atlantic Meridional Mode is discussed in a hurricane context by Vimont and Kossin, referring to Chiang and Vimont 2004, who show the following illustration (Atlantic on the right is the one of interest here) for the Atlantic Meridional Mode (their MCA Mode 1). MCA mode 1 has cool SSTs in the south Atlantic (compare to cool south Atlantic SSTs in Gray’s strong hurricane mode); low pressure offshore west Africa (again compare to Gray’s strong hurricane mode). While Gray does not refer to Chiang and Vimont nor conversely, it seems to me that the Chiang and Vimont MCA Mode 1 corresponds rather nicely to the cross-equator mode shown in the Gray and Landsea diagrams.
Chiang and Vimont 2004 FIG. 1. Spatial properties of the leading MCA mode 1 in the (left) Pacific, (right) Atlantic. (a), (b) Regression maps of the MCA leading mode SST normalized expansion coefficients on SST and 10-m wind vectors. Wind vectors are plotted where the geometric sum of their correlation coefficients exceeds 0.27 (the 95% confidence level). (c), (d) Same as (a), (b) but for precipitation (mm day21). In general, shaded regions in all panels exceed the 95% confidence level.
Kossin and Vimont
Kossin and Vimont 2007 and Vimont and Kossin 2007 are two recent articles, which associate the Atlantic Meridional Mode with changing hurricane activity. They describe the AMM as follows:
The AMM represents the leading mode of basin-wide coupled ocean-atmosphere interaction between SST and low-level winds [Chiang and Vimont, 2004] and while its amplitude is maximized in boreal spring — via a positive feedback between surface winds, evaporation, 85 and SST [Xie and Philander, 1994; Chiang et al., 1997] — there is a strong signal in the Atlantic during hurricane season, arguably due to simple persistence [Hu and Huang, 2006].
…Unlike the AMO, the AMM emerges as a true dynamical mode of variability intrinsic to the tropical coupled ocean-atmosphere system [Chiang et al., 1997; Xie, 1999], Pronounced coupled ocean-atmosphere variability in the Tropical Atlantic is generated by fluctuations in the Atlantic Meridional Mode (AMM) [Servain et al., 1999; Xie and Carton, 2004; Chiang and Vimont, 2004].
… The AMM is characterized by a meridional SST gradient near the location of the climatological inter-tropical convergence zone (ITCZ); boundary layer winds that flow toward the anomalously warmer water and veer to the right (left) in the northern (southern) hemisphere, in accord with the Coriolis force; and a meridional displacement of the ITCZ toward the warmer hemisphere.
They associate changes in the AMM with changes in hurricane activity in the Atlantic:
It is shown that a large part of the variability of overall “hurricane activity” — which depends on the number of storms in a season, their duration, and their intensity — can be explained by systematic shifts in the cyclogenesis regions. These shifts are strongly correlated with the AMM (Atlantic Meridional Mode) on interannual as well as multidecadal time-scales.
…Vimont and Kossin [2007; hereafter VK07] showed that the relationship between SST and hurricane activity could be viewed as part of a larger relationship between hurricane activity and a dynamical mode of Atlantic variability referred to here as the Atlantic Meridional Mode (AMM), but also known historically as the “gradient”, “interhemispheric”, or “Atlantic Dipole” mode [see the review by Xie and Carton, 2004].
… [The AMM] correlates significantly with hurricane activity on interannual, as well as decadal to multidecadal time scales. The interannual relationships between the AMM and a broad spectrum of local climatic factors that control hurricane activity offer a more complete and physically reconcilable link between climate and hurricanes than SST alone.Although AMM variance maximizes in boreal spring, it also exhibits variability during the Atlantic hurricane season. Variations in the AMM have been shown to be related to principal variations in hurricane tracks over the North Atlantic [Xie et al., 2005].
Their analysis was recently praised by Curry associates, Holland and Webster, as follows:
Kossin and Vitmer (2007) have shown that there is a close relationship between positive phases of the AMM and the eastward extension of the genesis region;
Of course, Holland and Webster also state that:
Mann and Emanuel (2006) have shown that the AMM is potentially increasing because of Greenhouse Warming;
Now there’s no mention in Mann and Emanuel 2006 of the Atlantic Meridional Mode whatever – but hey, this is climate science.
Let’s re-visit Gavin Schmidt’s hissy fit against Gray. Gavin:
The THC is undoubtedly important to climate, because it transports heat from one place to another. However it cannot do magical things. It cannot created energy out of thin air (or thick water), nor can it make energy mysteriously disappear.
… The fact is that neither of Gray’s story lines about the THC is sufficiently well formulated to allow any clear-cut test. Nonetheless, insofar as it can be understood at all, some aspects of Gray’s new story line about the THC are demonstrably wrong.
To the extent that the AMM is a plausible quantification of the modes identified by Gray (and they seem to be describing the same or similar phenomena on one scale), it seems inconsistent to lionize the AMM as an explanation, while not acknowledging that the AMM appears as a component of Gray’s reviled diagram.
Chiang, J. C. H., and D. J. Vimont: Analogous Pacific and Atlantic meridional modes of tropical atmosphere-ocean variability. Journal of Climate, 17, 4143-4158 (1 Nov 2004) abstract / pdf http://www.atmos.berkeley.edu/%7Ejchiang/Workpage/Paper/CV_2004.pdf Kossin, J. P., and D. J. Vimont, 2007: A more general framework for understanding Atlantic hurricane variability and trends. Bull. Amer. Meteor. Soc., accepted pending minor revision.Vimont, D. J., and J. P. Kossin, 2007: The Atlantic meridional mode and hurricane activity. Geophys. Res. Lett., in press. PDF file (1.5 Mb) http://www.ssec.wisc.edu/~kossin/articles/Vimont_Kossin_2007.pdf
Kossin, J. P., K. R. Knapp, D. J. Vimont, R. J. Murnane, and B. A. Harper, 2007: A globally consistent reanalysis of hurricane variability and trends. Geophys. Res. Lett., 34, L04815, doi:10.1029/2006GL028836. PDF file (377 Kb)