tag:blogger.com,1999:blog-7729093380675162051.post387955575915084055..comments2024-03-28T13:56:47.604+11:00Comments on moyhu: Grids, Platonic solids, and surface temperature (and GCMs)Nick Stokeshttp://www.blogger.com/profile/06377413236983002873noreply@blogger.comBlogger14125tag:blogger.com,1999:blog-7729093380675162051.post-90374256874416969752017-09-25T04:04:26.195+10:002017-09-25T04:04:26.195+10:00Read how "pretentious blog lions" are ar...Read how "pretentious blog lions" are arguing over the ENSO topic elsewhere:<br /><br />https://judithcurry.com/2017/09/16/week-in-review-science-and-policy-edition-7/#comment-858594<br /><br /><br /><br /><br />@whuthttps://www.blogger.com/profile/18297101284358849575noreply@blogger.comtag:blogger.com,1999:blog-7729093380675162051.post-88537621081225286722017-09-22T05:05:53.827+10:002017-09-22T05:05:53.827+10:00Even the "Einstein of the Oceans" thinks...Even the <a href="http://contextearth.com/2017/09/21/100-years-of-walter-munk-and-the-role-of-lunar-tides-in-ocean-circulation/" rel="nofollow">"Einstein of the Oceans"</a> thinks that lunar forcing has an impact on the pelagic zone<br /><br />@whuthttps://www.blogger.com/profile/18297101284358849575noreply@blogger.comtag:blogger.com,1999:blog-7729093380675162051.post-70054332242589456602017-09-20T09:00:05.448+10:002017-09-20T09:00:05.448+10:00This is what slight angular momentum changes can d...This is what slight angular momentum changes can do to a volume of water:<br /><br /><a href="https://twitter.com/AlexxSegura/status/910246417536602120" rel="nofollow"><br />https://twitter.com/AlexxSegura/status/910246417536602120</a><br /><br />Quake near Mexico City<br /><br /><br />@whuthttps://www.blogger.com/profile/18297101284358849575noreply@blogger.comtag:blogger.com,1999:blog-7729093380675162051.post-4313056879899020102017-09-19T22:34:43.440+10:002017-09-19T22:34:43.440+10:00I have always been describing Figure 12 in the Cla...I have always been describing Figure 12 in the Clarke paper.<br /><br />There are 3 modes in which tidal forcing can impact the ocean.<br /><br />1. Conventional ocean tides (provably forced by moon + sun, with tiny but measurable amount by wind)<br />2. Thermocline sloshing, i.e. ENSO, as per Clarke paper (believed to be forced by wind)<br />3. Deep ocean mixing described by Wunsch & Munk (forced by mix of tides and wind)<br /><br />This is what I find perplexing. For some reason tidal energy is excluded from contributing to #2 even though the periods of the ENSO cycle are precisely commensurate with the lunar fortnightly and monthly long periods.<br /><br />The analogy is like saying that both rain and hail are caused by coalescence of water in the atmosphere, but snow isn't. I know that's an extreme analogy, but trying to get wide acknowledgment or to even get this mode considered will take a huge amount of effort.<br /><br />@whuthttps://www.blogger.com/profile/18297101284358849575noreply@blogger.comtag:blogger.com,1999:blog-7729093380675162051.post-25229934067448630732017-09-19T18:00:18.390+10:002017-09-19T18:00:18.390+10:00Web
But that paper of Clarke et al is different fr...Web<br />But that paper of Clarke et al is different from what you were describing. Oscillations are an exchange between two forms of energy, with the time scale given by the rate of conversion. Your shallow water wave exchanges between potential (gravitational) energy from elevated water, vs kinetic, and has a hourish timescale as per pendulum, which has the same exchange. But Clarke et al have an exchange between depth of 20C and SSTA. That involves the timescales of heat transfer, which are very different, and possibly much slower.<br />Nick Stokeshttps://www.blogger.com/profile/06377413236983002873noreply@blogger.comtag:blogger.com,1999:blog-7729093380675162051.post-11081300952187874092017-09-19T16:44:32.101+10:002017-09-19T16:44:32.101+10:00Nick, What you are saying is at odds with the geom...Nick, What you are saying is at odds with the geometry that many of the ENSO researchers are using:<br /><br />This paper has the characteristic (resonant) period at 4.25 years<br /><br />https://i2.wp.com/imagizer.imageshack.us/a/img673/7682/m57j2Y.gif<br /><br />No damping in that wave equation, so Q is infinite in this model.<br /><br />A. J. Clarke, S. Van Gorder, and G. Colantuono, “Wind stress curl and ENSO discharge/recharge in the equatorial Pacific,” Journal of physical oceanography, vol. 37, no. 4, pp. 1077–1091, 2007<br /><br />https://yly-mac.gps.caltech.edu/AGU/AGU_2008/Zz_Others/Li_agu08/Clarke2007.pdf<br /><br />It comes down to forcing by wind or by tidal forces. And if tidal forces pace the winds, then it's essentially the tidal forces with seasonal modulation that establish the periods. Clarke talks about a curl wind force, but there is also a curl force from the nodal tidal cycle.<br /><br /><br /><br /><br /><br /><br /><br />@whuthttps://www.blogger.com/profile/18297101284358849575noreply@blogger.comtag:blogger.com,1999:blog-7729093380675162051.post-47743610720495405192017-09-19T11:49:50.049+10:002017-09-19T11:49:50.049+10:00Web,
"So the fact that Q may not be exceeding...Web,<br /><i>"So the fact that Q may not be exceedingly high gives it enough bandwidth to pass through a range of frequencies."</i><br />Well, the logical limit of that is an all-pass filter, which is just a wire (ideal). The function of Q is to allow energy storage at selected frequencies, so amplitude can be built up. The thing is, for high Q, you need to be fairly sure what the frequency is; it doesn't make sense without. Or at least the system has to know. That is why diffuse boundaries like the thermocline can't really do much with building amplitude, especially with very long horizontal wavelength. It may build up energy in one band which in a different zone is dissipative (varying thermocline depth).<br /><br />Another aspect is that if you want to maintain a resonance with a wavelength that is long relative to the cross-section geometry, there will be innumerable cross-modes into which the energy can be transferred, and you are relying on reflection at the boundaries to prevent that by interference. A diffuse boundary can't do that. You can't knit a flute.<br />Nick Stokeshttps://www.blogger.com/profile/06377413236983002873noreply@blogger.comtag:blogger.com,1999:blog-7729093380675162051.post-3937790170684663252017-09-19T11:31:26.486+10:002017-09-19T11:31:26.486+10:00I am confident that it is effectively a high-Q sys...I am confident that it is effectively a high-Q system. <br /><br />One point to consider is that for a higher Q, the narrower the bandwidth. So the fact that Q may not be exceedingly high gives it enough bandwidth to pass through a range of frequencies. That's true for a 2nd-order linear differential equation.<br /><br />But with sloshing fluid dynamics, its a nonlinear system which is often on the verge of sustaining a type of positive feedback. See e.g. the Mathieu equation. This can increase the Q while maintaining the bandwidth. So an inviscid system such as a stratified fluid with slight density differences is therefore effectively high Q.<br /><br />But I have never really thought that much about the Q factor, because the system never has shown any signs of damping -- and that, in turn, is indistinguishable from a forced response system driven by a continuous oscillation. Like conventional tides, it's really a matter of whether the energy supplied by the gravitational forcing can sustain the oscillation. And that's plausible because likely all of the ocean mixing and overturning is caused by tidal forces -- see Wunsch and Munk. It's not much of a stretch to apply that to the thermocline.<br /><br />@whuthttps://www.blogger.com/profile/18297101284358849575noreply@blogger.comtag:blogger.com,1999:blog-7729093380675162051.post-27456712169263638782017-09-19T09:18:51.402+10:002017-09-19T09:18:51.402+10:00Web,
The thing is, though, that low-Q also reduces...Web,<br />The thing is, though, that low-Q also reduces the selectivity of a pass-through filter. And the uncertainty about frequency probably means that it just isn't well characterised.Nick Stokeshttps://www.blogger.com/profile/06377413236983002873noreply@blogger.comtag:blogger.com,1999:blog-7729093380675162051.post-73085330680614431722017-09-19T05:45:11.909+10:002017-09-19T05:45:11.909+10:00I meant to imply that it is not so much that it is...I meant to imply that it is not so much that it is a resonance, but that the inertial response window provides a pass-through to the forcing. <br /><br />Same thing happens with conventional tides. The two-hour resonance window provides a pass-through for the diurnal and semidiurnal tides. The periods equal the lunisolar cycles but have the magnitude they do because they reinforce the natural resonance under gravity.<br /><br />Yet, at the reduced effective gravity of the thermocline layer, the conventional tidal response gets filtered out because the cycling is much too fast. So only the long-period tides will have an impact, and these will be on the order of time-scales of months to years, as the response gets aliases with strong seasonal impulses.<br /><br />So the exact value of the resonant frequency doesn't matter as that will never show up in the output, and it only supplies a pass-through window for potential forcings. <br /><br /><br /><br />@whuthttps://www.blogger.com/profile/18297101284358849575noreply@blogger.comtag:blogger.com,1999:blog-7729093380675162051.post-77026645320970985052017-09-19T03:26:42.764+10:002017-09-19T03:26:42.764+10:00whut,
One can point to the frequency, but the ampl...whut,<br />One can point to the frequency, but the amplitude is harder. It seems to me that it would be a very low-Q resonance. And it won't have so much effect on average monthly temperatures. It might be more interesting to try to relate it to the daily NCEP/NCAR data.Nick Stokeshttps://www.blogger.com/profile/06377413236983002873noreply@blogger.comtag:blogger.com,1999:blog-7729093380675162051.post-39796197212111247852017-09-19T00:32:26.282+10:002017-09-19T00:32:26.282+10:00The surface temperature of the Earth roughly follo...The surface temperature of the Earth roughly follows standing wave modes. Why this comes about is interesting. Consider that a natural mode of the Pacific ocean has a period of 2π(L/g)^0.5, which relates to the motion of a pendulum. This corresponds to a period of the order of 2 hours and explains why the lunar gravitational tidal pull has a strong collective effect on that time-scale. <br /><br />Now consider the pendulum of the ocean's thermocline. The effective gravity here is greatly reduced and is due to the slight difference in the density of the sea water above and below the thermocline. This difference in density could be on the order of 1/10000 or less, i.e. g'=g/10000, so period = 100*2π(L/g)^0.5. The effective resonant period now stretches from two hours to a week or longer. In turn, the standing wave mode of the ocean's thermocline is pumped by the nearly commensurate periods of the fortnightly and monthly tidal periods instead of the diurnal and semidiurnal periods for conventional tides.<br /><br />That's basic physics and the likely cause of the natural variability in temperature, as the massive thermocline oscillates toward the surface and back. I don't think a mesh is needed to estimate this effect to 1st-order. What's needed is the acknowledgment that this is a real effect.<br /><br /><br />@whuthttps://www.blogger.com/profile/18297101284358849575noreply@blogger.comtag:blogger.com,1999:blog-7729093380675162051.post-32784556781203953352017-09-18T19:04:55.475+10:002017-09-18T19:04:55.475+10:00William,
Thanks. Yes, right on both. I've fixe...William,<br />Thanks. Yes, right on both. I've fixed the text.Nick Stokeshttps://www.blogger.com/profile/06377413236983002873noreply@blogger.comtag:blogger.com,1999:blog-7729093380675162051.post-46216629857872281672017-09-18T17:58:37.692+10:002017-09-18T17:58:37.692+10:00Typos: "is that any point on the sphere can b...Typos: "is that any point on the sphere can be associated with the sphere that contains it" - "with the cell that contains it"?<br /><br />"icosahedron (3,5) has a smaller (better) defect of 90°" - 60.William M. Connolleyhttps://www.blogger.com/profile/05836299130680534926noreply@blogger.com