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Tropical Cyclones workshop

Filed under: — gavin @ 8 April 2006

One of the nice things about a being a scientist is that you can sometimes go to workshops and meetings and actually hear something new now and again. At the well-timed Tropical Cyclones and Climate Workshop at Columbia a week or so ago, I got a chance to sit in and listen to Emanuel, Landsea, Knutson and Bell talking about their recent work, but I also got to hear some new voices (and issues) in the discussion. It was all pretty enlightening even if it didn’t end up in complete reconciliation of the different views.

I won’t bother recapping the main points of contention (you can read about them here and here), but instead I’ll just mention a few salient points that struck me as interesting.

Data quality: No-one was happy with the current state of the historical Tropical Cyclone (TC) databases, and some questions were even raised (by Landsea) about the quality of the satellite-era record (though no evidence was presented that demonstrated a real problem). However, no-one questioned the recent rise in hurricane activity in the Atlantic.

Modelling: Though it often seems as if the Knutson and Tuleya paper is the only relevant modelling study, there were quite a few new studies talked about that will be interesting – a new Japanese study that actually has high enough resolution to simulate (reasonable?) TCs, season-by-season studies of hurricanes using the GFDL hurricane model and boundary conditions from the reanalyses. Though it seems like a good idea, no-one has yet started using the IPCC AR4 model runs (with all the relevant 20th C forcings) to see if there is any support for a forced signal over the instrumental period…

Potential Intensity theory: This is the theoretical framework that most of this discussion falls into and a number of relevant points were made by Emanuel and others. I should point out that these points were simply new to me (because this isn’t my field) but are worth highlighting for the other interested amateurs out there.

  • PI theory relates the maximum potential intensity that a hurricane could reach given the temperature gradient from surface to tropopause (the outflow) and the surface heat flux.
  • The key ‘outflow’ temperature is not in the ‘mid-tropopshere’ but at the tropopause, and so the surface to mid-troposphere moist static stability (the lower tropospheric lapse rate) is not actually part of the theory and (apparently) hasn’t been shown to be a particularly important variable for intensity in observations.
  • tropopause temperatures can be influenced by more than just greenhouse temperatures – volcanic eruptions and ozone depletion came up as additional factors
  • the surface heat flux term is where the link to SST comes in, but depending on what is actually changing, there could be very different correlation between the heat flux and SST. For instance a change in radiative effects would produce a different SST-heatflux correlation than changes due to ocean circulation. Thus there is no unique theoretical relationship between SST and hurricane intensity, you really need to know what the real underlying change is. So looking at the results from imposed SST changes in an atmospheric model is not necessarily a useful analog for the intensity/SST link seen in the late 20th Century.

Ocean interactions: Claudia Pasquero, following on from some of the comments that Emanuel made, showed the difference in modelled hurricanes as a function of including an interactive ocean component. One effect is to reduce the intensity over a case with fixed SST (because the hurricane cools the surface through enhanced vertical mixing), but a more interesting effect is that if you change the heat content of the mixed layer (and hence the intial SST), the change in intensity is much greater than if you simply change the SST. This was a good demonstration of Emanuel’s point – it matters why SST changes.

Atlantic Multi-decadal Oscillation: The AMO, as an alternative reason to global warming for the changes in Atlantic SST, didn’t get much support here. Emanuel pointed out the evidence does not support the existence of a multidecadal pattern in the North Atlantic that is distinct from global SST trends. Bell, whose talk was heavily based on the notion that the Atlantic multi-decadal patterns are coherent and linked to SST variability didn’t particularly insist on the AMO link and appeared to concede that it could be a forced pattern.

NOAA’s ‘official’ position: This was highly criticised by many speakers, mainly on the grounds that it isn’t up to an agency to have an ‘official’ position on the science at all, let alone one that is not a consensus even within the agency. Thus the modified NOAA statement was welcomed. A number of NOAA employees were present, and Chris Landsea specifically criticised the agency’s previous position.

All in all, one ends up being just as confused as ever, but to paraphrase someone famous, I ended up being confused about maybe more fundamental questions than I was before the meeting. It’s not a reconcilliation, but it is progress of a sort…

As an aside, the three bloggers there (myself, RP Jr. and Chris Mooney) managed to find time for a pleasant glass of wine together – nice to finally meet them!


46 Responses to “Tropical Cyclones workshop”

  1. 1
    Eric Swanson says:

    After last summer’s rather warm SST’s in the Gulf of Mexico, it’s been interesting to watch the return of warm water to the Gulf.

    http://www.ssd.noaa.gov/PS/TROP/DATA/RT/SST/PAC/20.jpg

    The current from the Caribbean flows between Cuba and the Yucatan, then loops around and exits the Florida Strait on it’s way north to become the Gulf Stream. The rest of the Gulf is somewhat cutoff from this flow, but is still warming, as seen in the southwestern section. The anomaly picture shows only slight warming underway at present.

    http://weather.unisys.com/surface/sst_anom.html

    Stay tuned, hurricane season is just around the corner!

  2. 2
    Steve Bloom says:

    Just to note that there are sufficient SSTs in the Caribbean for TC formation now, but formation is impossible because of high seasonal shear winds.

    Regarding the modified NOAA position, I’ll believe the NOAA powers that be have reformed when they do something more than put a teeny-weeny footnote at the end of the long statement claiming a “natural cycle” consensus within NOAA. The question is whether Landsea, Bell and Mayfield, the three NHC folks who were allowed to speak to the media during the 2005 season, will again be the only ones speaking during the 2006 season, and if so what they’ll say. It’s interesting that Bell too now seems to have backed off the natural cycle claim, but my suspicion is that they’ll fall back on a natural variability argument (a subtle distinction from the POV of the media and public) rather than face up to the GW connection.

  3. 3
    Ian K says:

    I presume the Japanese are interested in cyclones in the Pacific. Any trends there? Cyclone Larry has been the first economically significant cyclone to hit Australia in quite a while, but AGW issues have not been prominent. Are the Chinese engaging in climate research or are they no more than a forcing ;)?

  4. 4
    Harold Brooks says:

    Re 2: A point of organizational clarification. During the 2005 season, Max Mayfield was the only one of the 3 people you mention who worked for NHC (technically Tropical Prediction Center, but they still use the old name for some purposes.) As the director, he’s the primary spokesman for TPC. Gerry Bell works for the Climate Prediction Center, in charge of NOAA’s seasonal hurricane forecasts. Chris Landsea didn’t go to TPC until 1 October, IIRC (it might have been 1 September). During most of the 2005 season, Landsea was at the Atlantic Oceanographic and Meteorological Laboratory, leading the work to look at historical hurricanes.

  5. 5
    Eli Rabett says:

    Again, everyone makes the mistake of insisting on OR (natural cycles OR anthropic climate change) as the issue wrt the upcoming hurricane season. AND (natural cycles AND anthropic climate change)is what is really worrying for this year. Finally, we have the AND of an impending El Nino which may overcome both of the drivers to another disasterous season in the Carribean.

  6. 6
    Steve Bloom says:

    Re #4: Thanks for the clarification, Harold. In any case they all work for NOAA head Conrad Lautenbacher (a Bush political appointee), who I forgot to mention was the other NOAA spokesperson last fall. I’ve mentioned it before, but should underline the point that the “natural cycle” argument remains extremely convenient for the Bush administration as it dodges a major pressure point relative to the need for action on global warming. It will be very interesting to see what they say this season since the Bell and Chelliah work is no longer available to buttress the natural cycle position. The Bush administration must be praying for a mild season without major U.S. land strikes.

  7. 7
    cwmagee says:

    “The Bush administration must be praying for a mild season without major U.S. land strikes.”

    Aren’t we all?

  8. 8
    Ender says:

    “”The Bush administration must be praying for a mild season without major U.S. land strikes.”

    Aren’t we all? ”

    Absolutely – Our recent cyclone season was bad enough. Fortunately here in Western Australia we have a LOT of sparsely populated country for cyclones to hit. The same cannot be said of the GOM coast.

    Which higlights one of the other point of the TRS debate. The storms are more destructive now even if they are not more intense because of the development of coastal areas and the destruction of natural defenses. The Kimberly coast north of where I live is very unlikely to be developed however in regions where significant development has taken place there are more targets to hit now.

  9. 9

    Eli makes a very good point when he says that hurricanes depend on both natural cycles and global warming. During El Nino North Atlantic hurricanes seem to be less active. Moerove, the solar cycle must also have an effect, not to mention the quasi biennial oscillation (QBO. )

    So, if there are fewer hurricanes this year than last it will be because of natural cycles. OTOH if there are more hurricanes this year than last it will be due to global warming!

    Cheers, Alastair.

  10. 10
    pat neuman says:

    re 4. Max Mayfield was on NBC nightly news this evening along with Dr. W. Gray. Nothing said by either (or asked by NBC) about global warming.

    Your question about whether Landsea, Bell and Mayfield … seems like more of the same to me. NHC and TPC are under NWS. NWS became part of NOAA when NOAA was created in the 1970s. NWS didn’t follow a chain of command under NOAA until G.W. Bush made that happen a year or two after he first became president. NWS began as the Weather Bureau during the 1800s and still makes up about half of the total staff in NOAA. NWS has about 130 offices serving the public with operational forecasts of weather and flood, and providing public education dealing with weather and climate. However, NWS has avoided it’s responsibility in educating the public on climate that is changing … regional climate change and global climate warming. The important question to me is whether or not NWS will continue to avoid it’s responsibility to serve the public in education on climate change, and whether or not NWS will continue to threaten those who try to do anything related to climate change with formal suspensions and removal from government service for what they determine to be a misconduct. A misconduct label hits hard in that a person and family cannot even qualify for state unemployment benefits due to a misconduct claim, nor can realistically dispute it since global warming is too political and controversial according to NWS and NOAA headquarters. All one need to do to get a misconduct label is be concerned enough about how climate change might be having an effect on ones responsibility at work in hydrologic modeling and flood prediction, or other duties called for in truly serving in the public service.

  11. 11
    Eli Rabett says:

    No Alister, Bill Gray and co, predict that without any anthropic forcing the hurricane season for the next decade and a bit more will be worse than average. I take him seriously. I also take Emmanuel seriously who points out that warming SST from anthropic forcing will make hurricanes more damaging.

    The only thing on the horizon that would help in the short term on the Atlantic side would be an El Nino and one may be coming. That leaves the Eastern Pacific at the mercy of two rising trends.

  12. 12
    C McCown says:

    Re. Number 3

    The Japanese government has the Himawari (Sunflower) series of weather satellites and are working towards greater independence in ground-based tracking stations. You can visit the Japan Meteorological Agency website at

    http://www.jma.go.jp/en/typh/

    It is my one-stop shopping page in English.

  13. 13

    Re #11 Eli, one point that Gavin makes is that the stratosphere plays an important part when it comes to hurricanes. The period of the cycle, when hurricanes were less, was from 1945 – 1978, the same time as when nuclear weapon testing was injecting aerosols, or just damp tropospheric air, into the stratosphere. In other words the ‘natural’ cycle that Gray et al. have discovered was not natural – it was anthropogenic!

    Putting it another way, just as causes can be natural AND anthropogenic, so natural causes can be from solar cycles AND El Ninos, and anthropogenic causes can be from greenhouse gases AND ozone depletions AND from atomic bomb testing.

    It may be correct that the current effects from greenhouse gases are only a minor cause of the current increase in hurricanes. However, if we continue with business as usual policies, then the effects from more CO2 will only get worse until they totally dominate all the other effects. We dare not wait until we are in that state, before we take action. By waiting to see if Gray and Landsea are correct, we would be doing just that!

    Alternatively, if GWB does nuke Iran, perhaps that will give us the breathing space on the hurricane front we need :-)

  14. 14
    Urs Neu says:

    El Nino upcoming?
    Attribution of recent SST increase to global warming

    I haven’t seen any indications of an upcoming El Nino for this year. Actually we have a weak La Nina which probably will persist for the next few months. Model forecasts point to more or less neutral conditions until the end of the year. That’s at least the opinion of the CPC, see http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory/
    This would mean that ENSO conditions at the moment tend to favour an enhancement of hurricane occurance compared to last year (at least at the beginning)…
    I’m not aware of differing predictions. Are there any?

    At EGU, Gillett (from CRU) and Stott (from Hadley Centre) presented the results of a detection and attribution study with the HadCM3 coupled model for the SSTs in the main hurricane development region (MDR). They compared the SSTs in a run with only natural forcing to the SSTs in a run with natural and anthropogenic forcing. They and up with the conclusion:
    “After verifying the model’s internal variability, we go on to find that the warming in the latter half of the twentieth century is largely attributable to anthropogenic influence, and inconsistent with simulated internal variability.”
    Abstract see http://www.cosis.net/abstracts/EGU06/03698/EGU06-J-03698.pdf
    Due to natural forcings, SSTs wouldn’t have risen in the second half of the 20th century, at least in the HC model.

    I haven’t seen any evidence until now, that decadal or multidecadal variability of SSTs in the Atlantic hurricane region shows any other pattern than northern hemisphere or global patterns of temperature variability.

  15. 15
  16. 16
    Jan Rooth says:

    Re #15:

    The argument that GW would lead to an increase in “super el Ninos” seems reasonable.

    But I’d note that one of the features thi paper cites as suggestive of an impending el Nino this year (the warm anomaly off the SA coast in February) has already disappeared. So it still seems likely the dice won’t come up “el Nino” this time.

  17. 17
    Stephen Berg says:

    Re: 15,

    Thanks, Eli, for the link! It looks to be of good use for my honours thesis. It has a more clear Nino region SST graph than I had previously.

  18. 18
    pat neuman says:

    re 15.

    The parts of the pdf by Hansen which relate to Michael Crichton and UHI will not be amusing from my perspective, but I will be interested in discussions about ENSO. From the pdf (Spotlight on Global Temperatures by James Hansen, et.al. March 29, 2006, draft),

    Excerpt:

    “In a popular novel, Michael Crichton (2004) suggests that observed global warming inferred from weather station measurements is dubious especially because of urban warming effects, and he asserts that, even if measured warming is accepted, climate model predictions made by James Hansen in congressional testimony in 1988 (based on Hansen et. al. 1988) proved to be wrong by 300 percent”. …

    That will not be amusing to me because while I was a National Weather Service (NWS) employee, I wrote (2004):

    “Today I have two proposals. 1. A summary of my October, 2003 article (including figures), which I used at the NWS CPC Workshop. 2. A new article that I would like to do on how urban heat island (UHI) influences temperature measurements in urban-suburban airport stations. I would use monthly and annual station averages of daily max and min temperatures for both urban-suburban airport stations and non urban NWS cooperative climate stations… within or near the NCRFC area. My first choice of the two proposals indicated above is to do an article on UHI. I think knowing more about the magnitude of UHI would help in NCRFC calibrations and operational forecasting.”

    My NWS supervisor* replied: “As I promised from our previous discussion in the conference room. Do not do any research on government time concerning, … how urban heat island (UHI) influences temperature measurements in urban-suburban airport stations. … Do not submit your paper and results from Nevada … to the NCRFC Newsletter. That subject is too sensitive at this point in time for yourself, NCRFC, and the NWS. As far as the GODE at the Mall of America. Do not present the results from your paper at the GODE. The WFO wants to get the word out to the public as to what we do and who we are, not to present scientific research of any type. … research concerning climate change or “global warming” is more conducive to the meteorology side of our agency. Let’s focus on tasks that need to be done in support of the NCRFC AOP and our mission, which is forecasting and calibration of basins. ..

    *Hydrologist in Charge, NWS North Central River Forecast Center (NCRFC), Chanhassen MN.

    Climate Prediction Center (CPC)

    Government on Display Exhibition (GODE)

    WFO NWS Weather Forecast Office

    Annual Operating Plan (AOP)

    *Oct 2003 paper: Earlier in the Year Snowmelt Runoff and Increasing Dewpoints for Rivers in Minnesota, Wisconsin and North Dakota, Patrick J. Neuman, Snow Hydrologist, September 11, 2003
    http://www.mnforsustain.org/climate_snowmelt_dewpoints_minnesota_neuman.htm

    None the less, I have done research some research on urban warming effects after I was removed from government service by NWS. My work involved comparisons of near station temperature data from NOAA NWS cooperative climate station data versus airport station data for similar time periods. My analysis and results have not been peer reviewed.

    Another reason THAT will not be amusing to me is because the novel by Michael Crichton (2004) was kept at the NWS NCRFC office for reading by a coworker (who claimed to be learning quite a bit about climate in reading the novel at work).

  19. 19
    alisa brooks says:

    What are the acronyms NWS and GOM meant to abbreviate please?

  20. 20
    Jan Rooth says:

    #18:

    NWS = National Weather Service

    GOM = Gulf of Mexico

  21. 21
    alisa brooks says:

    Thanks! I see that Pat had already answered my question of NWS before I asked! But thanks Jan! Some of these abbreviations are beyone me!

  22. 22
    C. W. Magee says:

    Re 13: “The period of the cycle, when hurricanes were less, was from 1945 – 1978, the same time as when nuclear weapon testing was injecting aerosols”

    Actually, Gray’s “low intensity” period is 1970-1993. The partial test ban treaty was signed in 1963, not 1978. If anything, the period of high 14C (a measure of irradiation of the atmosphere) corresponds more closely with the previous high in hurricane intensity (1950-1964), not the post-1970 lull.

    Except, of course, that the 14C deviation doesn’t begin until 1955.

  23. 23
    Brian Green says:

    i hope hurricanes hit all the oil and gas industrial areas because usa politicians are too weak to handle the oil and gas problem

  24. 24
    Steve Bloom says:

    Re #16: Could you post a link to that information, Jan? Thanks.

  25. 25
    Hank Roberts says:

    France and China continued atmospheric testing, China most recently in 1980.
    The average over time is — gasp!

    Quoted from: http://archive.greenpeace.org/comms/nukes/ctbt/read9.html

    “…. total yield of all the atmospheric nuclear weapons tests conducted is 438 megatons.
    … equivalent to 29,200 Hiroshima size bombs.

    “In the 36 years between 1945 and 1980 … equivalent to exploding
    a Hiroshima size bomb in the atmosphere every 11 hours.”

  26. 26
    Hank Roberts says:

    re #14-16 — daily SST anomalies here.
    http://www.osdpd.noaa.gov/PSB/EPS/SST/climo.html

    I don’t know over what period a change has to persist so the day to day changes are just pretty pictures for me for now.

    Re that, note the last 3 pictures for the Gulf of Mexico, is that the loop current surrounding a little donut hole of cool water inside a ring of warm?

  27. 27
    C. W. Magee says:

    Re: 25
    When people talk about alarmist pseudoscience, this is exactly what they have in mind.
    A cursory glance at any of the nuclear proxies will show that the testing that occured in the 20th century was NOT equivalent to one Hiroshima every 11 hours. Only if the various particulate and gas species produced had an infinite atmospheric residence time would a continuous low-grade effect be the same as a concentrated mid-centry pulse. If you look at the atmospheric 14C record,
    http://en.wikipedia.org/wiki/Radiocarbon_dating
    …you will see that the Indian and French tests don’t even register. Neither does Chernobyl. The vast majority of atmospheric irradiation, which is roughly proportional to energy release, came in the decade following the discovery of the H bomb, as the US and Russia tested increasingly powerful versions of this weapon. Since then, 14C has been decaying towards the natural background, as the isotope is removed from the atmospheric system. I don’t see how your hypothesis is supported by any available historical data.

    Of course, you could propose an experimental test to your hypothesis, instead of relying on archived data. If atmospheric nuclear tests inhibited hurricanes then, they should still do so today. I’m sure that if you asked the hawkish federal politicians to “Resume nuclear testing to stop the next Katrina”, they would jump all over the idea, evidence or no. Heck, why not go one step further: “Nuke Iran to stop the next Katrina.”

    It’s us or them. God bless America.

  28. 28

    The paper describing the behavior of tropical cyclones in warmer climate in the high-resolution atmospheric GCM of the Meteorological Research Institute of Japan is

    Oouchi K., Yoshimura J., Yoshimura H., Mizuta R., Kusunoki S., and Noda A., 2006:
    Tropical cyclone climatology in a global-warming climate as simulated in a 20-km mesh global atmospheric model: Frequency and wind intensity analyses.
    Journal of the Meteorological Society of Japan, Vol. 84 (No. 2), in press.

    Its PDF version will be available hopefully by the end of April from a page linked from the home page of the Meteorolgical Society of Japan (http://wwwsoc.nii.ac.jp/msj/). Its final draft is available from the page of the simulation project (http://kyousei.aesto.or.jp/~k041open/ipcc_ar4/) .

    [Response: Thanks for the reference. -gavin]

  29. 29
    Hank Roberts says:

    <25
    It’s not “my” hypothesis, Magee, it came out of Russia, he’s argued that water clouds changed things. I’m just checking references and dates.

    I’ve assumed — haven’t yet found the numbers — that tropical circulation continuously puts far more water into the stratosphere than a few hundred various-sized mushroom clouds that momentarily rose to from 18km (Nagasaki) to 64km (Tsar Bomba).

  30. 30

    Re #27 Hey Mr Magee you have nicked my idea :-(. I suggested nuking Iran to stop global warming. See #13. And I was the one who said that nuclear testing affected the climate, not Hank. Although, as Hank wrote, the idea that the climate was altered by damp air from the troposphere being injected into stratosphere came from Shaidurov. See; http://www.math.le.ac.uk/RESEARCH/APPLIED/VISITORS/MA-05-15–shaidurov.pdf

    The idea that atomic weapon testing prevented global warming during the 40s – 70s is not new. See this web page for confirmation of the cooling then. http://en.wikipedia.org/wiki/Image:Instrumental_Temperature_Record.png The first thought was that the atomic weapons could not be causing the cooling because the energy they released was so much less than a hurricane. I don’t think that the radioactivity was ever considered as a climate altering feature. However, a nuclear winter was considered a threat, and I am saying we did suffer a nuclear fall (autumn.)

    Experiments to test if it is water which links atomic testing to climate have already been performed. In 1946 the US Navy exploded a bomb in the Pacific Ocean, and the Russians exploded a bomb in the Arctic in 1962. Both resulted in the following winters producing low temperatures and high snowfalls the following winters in Britain. The chart above seems to suggest that there was global cooling at that time.

    However, I claimed that the hurricanes were affected by atom bombs, and that was obviously wrong if the low in their cycles was in the 90s. I have been looking for a chart of their frequency but still not found one, but I have found this: http://hurricane.atmos.colostate.edu/forecasts/2006/april2006/ which does have a list for the last six years. It also describes Gray’s techniques for estimating future hurricanes. Interestingly for me he uses the QBO which I mentioned. This is the quasi biennial osciliation of stratospheric winds. Quasi biennial means ‘sort of every second year’. From Gray’s tables the sequence of hurricanes is 8,9,4,7,9,15. That is: up from 8 to 9, down to 4, up to 7, up to 9, and up to 15. So we get a biennial oscillation as far as 7. A new series may be starting at 9 with the next number being less than 15 viz. 2006 will have less hurricanes than the 15 of 2005. That is what Gray thinks. He predicts 13. However, it may be that global warming is over-riding the effects of the QBO, and the number of hurricanes in 2006 will exceed those of 2005.

    Well that’s my 2 cents worth.

  31. 31
    C. W. Magee says:

    Chris Landsea’s graph of # of intense hurricanes per year is here:
    http://www.aoml.noaa.gov/hrd/Landsea/atlantic/fig3.html
    And hurricane days:
    http://www.aoml.noaa.gov/hrd/Landsea/atlantic/fig5.html
    from:
    http://www.aoml.noaa.gov/hrd/Landsea/atlantic/
    Data ends in 1996, but you should be able to find recent stuff around.

  32. 32
    Hurricane! says:

    Tropical Cyclones Workshop
    Very good post on a Cyclone workshop….

  33. 33
    Ike Solem says:

    California is currently having a very wet late season, running about 140% of normal through most of the state (‘normal’ being defined, for some reason, as the average rainfall from 1971-2000). This is from the NWS climatology page. They use the same logic in calculating ‘normal’ temperatures (a 1971-2000 avg.) The main problem with the NWS climatology pages is the poor manner in which the data is presented. The temperature and rainfall record levels data, on the other hand, stretches from 1927-2006. Why isn’t this NWS data presented in a more clear and graphical manner? The fact that this heavy rainfall is occurring in a non-El Nino year is unusual, but relating it to the larger climate picture is difficult.

    Here is the current SST anomaly: SST anomaly and NOAA ENSO discussion.

    The article also says that the heat content of the mixed layer is more important the SST’s alone in predicting hurricane intensity. Thanks also for the notion of the potential intensity measure of a hurricane.

    Regarding this statement:
    “The key ‘outflow’ temperature is not in the ‘mid-tropopshere’ but at the tropopause, and so the surface to mid-troposphere moist static stability (the lower tropospheric lapse rate) is not actually part of the theory and (apparently) hasn’t been shown to be a particularly important variable for intensity in observations.”

    -> So if we have a dry lapse rate or a saturated lapse rate the difference will be minimal in terms of promoting vigorous convection? The rate at which air containing water vapor cools is slower then that of dry air, so it would seem that their would be slower adiabatic cooling of rising warm air and more intense convection in the saturated case, due to the latent heat of water condensation overcoming the adiabatic cooling? Isn’t this what drives the hurricane, or are they saying you are always dealing with a saturated lapse rate once a hurricane has developed? In which case the initiation of a hurricane might be sensitive to the lapse rate?

    Consider this also, directly from C. Landsea’s NOAA FAQ pages on hurricanes, regarding easterly waves generated over North Africa:

    “The waves move generally toward the west in the lower tropospheric tradewind flow across the Atlantic Ocean. They are first seen usually in April or May and continue until October or November. The waves have a period of about 3 or 4 days and a wavelength of 2000 to 2500 km, typically. These “waves” are actually convectively-active troughs along an extended wave train. On average, about 60 waves are generated over North Africa each year, but it appears that the number that are formed has no relationship to how much tropical cyclone activity there is over the Atlantic each year….
    ….It is currently completely unknown how easterly waves change from year to year in both intensity and location and how these might relate to the activity in the Atlantic (and East Pacific).”

    It seems there are many unknowns in the hurricane intensity and frequency picture. If easterly waves (poorly understood, but influenced by warm air over N. Africa) encounter persistently warm deep mixed layers (linked to SST’s but not directly) they might generate hurricanes of paticular severity. The other factors are then wind shear and the initial lapse rate, or not?

    Would Landsea, Grey and Pielke state that global warming will clearly lead to more intense hurricanes, with the frequency issue being undecided? Haven’t we seen this already, or is the notion still that ‘there isn’t enough data’ ? It seems the burden of proof is by far on those claiming ‘natural variability’ at this point.

  34. 34
    Mats A says:

    I follow the Realclimate posts regulary, and find this site extremely informative. However, I find it often difficult to understand some of the acronyms. SST for instance, in this post. I am sure that not only I would find a list of acronyms most helpful. As far as i can see, SST is not in the glossary.

    [Response: I'm sympathetic. When I first entered the field, I heard a lot of people talking about the "LGM," which to me meant "Little Green Men," rather than "Last Glacial Maximum." Similarly, many people think of "Supersonic Transport" when they hear "SST," whereas for us it means "Sea Surface Temperature." --raypierre]

  35. 35
    jack says:

    Atleast somebody thought about cyclone workshop. Good site, really informative. Unique topic. Keep the good work going!!!!!

  36. 36
    G. Sotir says:

    I am not sure where to place this question but this forum seems appropriate.

    In terms of precipitation and general storminess are the East coast of continents (in the Northern Hemisphere?) more active than the Western coasts? Why is this? Is it the Earth’s roation, and denser water filled atmospheres moving with that rotation, or the Coriolis effect? Or something else?)

    What implications are there for these coastal regions from climate change and warmer sea surface temperatures? And, does that mean that Western sides of continents will be less stormy than the Eastern coasts?

    Hope this question isn’t too simplistic.

    [Response: A quite good question, really. Classic example of regional/synoptic climatology. The west coasts of the mid-latitude continents (take e.g. San Francisco or the Canary Islands)) tend to have (in the Northern Hemisphere case) cold Northerly ocean currents and cold coastal upwelling in addition to that. By contrast, the east coasts have warm southerly currents and little upwelling. This means that the air coming in off the oceans is saturated at a low temperature (and therefore relatively depleted of moisture) when it encounters the west coast, giving the arid conditions of e.g. the California coast or the Mediterannean. By contrast, the oceans off the east coasts (e.g. Japan or the Gulf/southeastern U.S. Coast) are relatively warm, and the the winds that spiral into the eastern U.S. off these warm ocean surfaces are saturated at a high temperature (and therefore quite humid). Thus, when they encounter the Gulf and southeastern U.S. land regions, these winds deliver the humid conditions characteristic of the southeastern U.S. or Japan/southern China. These wind patterns are, in turn, due to the activity of the prevailing mid-latitude westerly winds and the tropical trade winds on the large-scale ocean circulation, and the impact of northerly winds along the west coasts (which leads to the cold upwelling). These atmospheric features are part of the large-scale circulation about the sub-polar low pressure and subtropical high pressure regions, and they have a fairly complicated influence on the ocean circulation (which depends not just on Coriolis effect, but more importantly the so-called "beta" effect, the change in the so-called "Coriolis parameter" with latitude, first emphasized in this context by the famous oceanographer Henry Stommel more than 50 years ago). Of course, this itself is a fairly simplistic description, since all of these features vary due to other factors as well (e.g. mountain ranges) and change with the seasons. You can probably turn up quite a bit more discussion of this on the web by googling some of these key words. --mike]

  37. 37
    C. W. Magee says:

    Another question about el nino and hurricanes:

    When Darwin is hit by a tropical cyclone, like this week, do the people who measure the Southern Oscillation Index correct the Darwin surface pressure for the effects of the storm? It seems like if they don’t do this, some modeller dude in the northern hemisphere might be inclined to predict a huge la nina every time Darwin gets nailed.

  38. 38
    Mauri Pelto says:

    I am interested to gain some perspective on the causes of the two unusually strong cyclones Larry and Monica. Australia has also endured an unusual one-two punch in the last 12 months.

  39. 39
    llewelly says:

    In my previous comment, #39, I got the link to the paper about forecasting El Nino wrong. Try this link instead.

  40. 40
    llewelly says:

    C. W. Magee , the Southern Oscillation Index is always smoothed or averaged over some period of time. For example, NOAA uses a 3-month running mean. A single tropical cyclone is unlikely to affect pressures at Darwin for more than two days, and it is unlikely for Darwin to be struck by two or more TCs in the same 3-month period. (Same effect applies to Tahiti, which can also be struck by tropical cyclones. ) So TCs affect the SOI, but the effect is small due to their short presence over a single point.

    The theory behind the SOI is that it is a measurement of the Hadley-Walker circulation, in which air rises in the western tropical Pacific, and descends in the eastern tropical Pacific. A TC dramatically increases the rate of air rising, but only for a short time. So it seems to me that averaging in the small number of extreme pressures reached when a TC hits Darwin, is more likely desirable than not.

    I’m neither a climatologist nor a meteorologist, but I’ve yet to find a climate index that is not measured over a medium to long period of time. The indices which measure the Arctic Oscillation, the North Atlantic Oscillation, are also smoothed or averaged over some number of months.

    I know less about the forecasting methods, but I get the impression that few if any rely on only one ENSO index. NOAA’s CPC ENSO page has links to the indices used by NOAA. If you read this presentation, you’ll see that quite a lot of data goes into their forecasting methods. This paper has some general information about forecasting El Nino. Both statistical and physics based dynamical models are used, both of which use much more data than just the SOI. Dynamical models in particular are initialized with large numbers of temperature, pressure, and wind measurements from many different locations. No forecaster would make a prediction consisting solely of raw model output; not only are multiple models used, but they are judged by expert forecasters that know the strengths and weaknesses of the models.

  41. 41
    Hank Roberts says:

    This is modeling, not field work unless there’s more in the full article, but still interesting:

    GEOPHYSICAL RESEARCH LETTERS, VOL. 33, L07713, doi:10.1029/2005GL025558, 2006

    Coupled ocean-atmosphere response to Indian Ocean warmth
    Shuanglin Li et al.
    NOAA-CIRES Climate Diagnostics Center

    …Coupled model experiments show that this NAO response forces a local air-sea feedback over the North Atlantic Ocean, which intensifies the NAO response … through a positive feedback between the NAO atmospheric circulation anomaly and a tripolar North Atlantic SST pattern…”

    Is the Indian Ocean a relatively more efficient solar energy collector such that it can ‘pump’ other cycles, accumulating more heat locally rather than quickly spreading around the heat collected there?

    I can’t tell from the abstract what the “tripolar” pattern is — three factors? three locations?

    Also from AGU just now, this apparently started from satellite data and has been modeled successfully:

    GEOPHYSICAL RESEARCH LETTERS, VOL. 33, L08601, doi:10.1029/2005GL024524, 2006

    Summertime subtropical sea surface temperature variability

    A. M. Chiodi, D. E. Harrison
    “… a new class of summertime subtropical sea surface temperature (SST) anomalies that have basin scale, amplitudes up to 3°C and duration of up to 2 weeks. These have been discovered in the Microwave Imager (TMI) SST analyses. One-dimensional physics and numerical weather prediction operational air-sea fluxes are able to reproduce many aspects of the observations. The mechanism of creation of these summertime anomalies depends on the formation of shallow ocean mixed layer depths. Their persistence is controlled primarily by the duration of appropriate atmospheric conditions. Model studies also suggest that near synoptic scale surface flux variations, of the type considered here, cause significant warming of SST over monthly to seasonal timescales.

  42. 42
    Paul Stockton says:

    Here’s a first hand fact, not another “I think” scenario.
    Now retired, I’ve spent 35 years primarily designing environmental sensors. While working a NOAA in Boulder, CO. in 1988 I did a freebee programming job for the High Altitude Observatory (HAO, not NOAA). They had atmospheric data from 1948 stored on punched cards, cassette tapes, 9″ tapes and floppy disks. Amazingly, no one every put it all together, too much of a daunting task. So I took on the job (unpaid) just because I could and considered it a fun thing to do. I put all the data in a B-Tree (for those who know a little about databases) database and provided selective data extraction and graphing of any combination of data desired. Just for laughs I averaged the temperature data from 5 independent high altitude (above 9000 feet in the Rocky Mountains) monitoring sites. I then did a linear regression through all the 43 years of average air temperature. The slope was constant even for shorter periods.

    It amazed me that over 43 years the average air temperature (this is very clean air by the way) increased 1.25 degrees F. Which, ironically seemed to agree with just about every global warming documentary I’ve seen.

    I don’t just think global warming is true, I know it’s true! And I knew it in 1988.

    Think about this; Where do you think all those exhaust gases go? They are gasses, just like air itself. Air does not easily fall to the ground or there would be no air hanging around. There seems to be a tendency for people to only consider how much greenhouse gas is being produced per year. This is a rate value and it may seem (with very little thought) that this is not that much compared to the entire atmosphere. But the accumulation is substantial! Like a dripping faucet into a bucket. Really doesn’t seem like a problem but its amazing how fast that bucket will fill up when youâ??re not watching it. I truly believe everyone who has had a dripping bucket experience has said; I would never have guessed that much water would accumulate from that drip in that short of a period of time.

    Think about it! Also, donâ??t blame scientists! They gain nothing by the results they are reporting but definitely stand to loose everything if they are wrong. Their careers are in the balance. And believe me; scientists are really critical of each other. This is why there is never a completed thought at scientific conferences. Theyâ??re afraid for their careers. So, a summary of results is only available through documentaries where their true thoughts get exposed behind closed doors. None the less, itâ??s insane to believe that all these well educated people from such a variety of scientific disciplines from all over the world are making all this up.

  43. 43
    Bill Nicholls says:

    Re: Comment 33

    Just FYI, Washington State where I live had a terrible winter for snow and rain in 2004-2005 (about 40% normal) and the third wettest winter on record in 2005-2006. Exactly what this means in the larger picture I am unsure. However I find that the variability of weather in this region appears to have reached wider swings recently, as illustrated by the two recent winters snowpack and total precip.

  44. 44
    joe says:

    I m a regular visitor of the Realclimate blog. Find this blog to be really informative. Your site is unique because of the topic in discussion is always different. Site is enlightening putting light on cyclones and climate.

  45. 45
    stu says:

    Regarding the question in #36, why is it that there is typically less upwelling on eastern coasts? Is it because there is an abundance of warm water being pushed over to those costs, and therefore it is not displaced enough by Ekman transport for the nutrient rich cold water to come to the surface?

  46. 46
    Dean Myerson says:

    Any response to the Klotzbach (out of CSU, so publicized on W Gray’s website) paper in Geophysical Research Letters challenging the conclusions of Emanuel and Webster?

    [Response: I think there was some discussion of this in the article "Gray and Muddy Thinking." It's not quite accurate to describe the paper as a "challenge" to the conclusions of the others, though it's sometimes been touted that way. --raypierre]


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