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tybeedave

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Re: Tides
« Reply #50 on: April 07, 2020, 04:39:10 AM »
 hi yall,

I'm not going to cite anything, but the idea of any liquid pulling anything in any way, shape, or form is misleading.  the only forces of nature that i'm aware of only push. point in case, using a straw to drink with.  one doesn't actually suck the drink up against gravity, one lowers the pressure and atmospheric pressure pushes it up thru the straw to your mouth.

the same forces are at work in Fram export.  Higher pressure from physical forces caused and transferred by collisions between floes does create pressure in a particular direction, add to this tide and local wind and there is a perfect storm for export.    a significant amount, imho, of the CAB just got spit out via the Fram and to a lesser, but not insignificant, volume of older ice into the Barents Sea.

Until one recognizes the actual causality to an event, understanding is unlikely

Sometimes events are hidden because of the fear of being the one called out with chants of "prove it"

Sometimes events aren't recognized because of the chatter drowns out the data. 

Sometimes one can be wrong, but i fail to see such incorrect examples except in my bell-ringing, uncited, wake-up approach and what i feel is a more detrimental approach as that displayed by binntho which celebrates misdirection and denial.

peace and excuse the lack of capitalization, but today, the 7th, is my birthday and i've been celebrating all day.  don't worry, i quit drinking a long time back when i began to have children.  so, what i type is thought out, even if possibly incorrect.  in other words, for at least the next 24 hrs, i will listen to anyone but care less :P

td
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Hopen Times

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Re: Tides
« Reply #51 on: April 07, 2020, 09:07:08 AM »
I am trying to understand how tides are supposed to give changes in how much ice that moves thru Fram Strait over time, but it is hard for me to understand it. I have no problem seeing that the tides moves the ice back and forth, but in my head the back and forth movement ends in zero movement caused by the tide. How can it be anything else than a back and forth movement ending in zero movement?

Here is video I made, showing how tides move ice back and forth. Sorry for the repost of it, but I think it gives a nice example of how the tides moves ice back and forth. It is made here: https://norgeskart.no/#!?project=norgeskart&layers=1011&zoom=7&lat=8519505.88&lon=777966.88
There is a current moving south in this area.
In the clip starting at 2:18 the wind is acting as well.
I know this is not the Fram Strait.




oren

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Re: Tides
« Reply #52 on: April 07, 2020, 09:22:49 AM »
HT, it depends on  the location but it's not necessarily a net zero. Suppose the tide pushes the ice beyond a headland where the currents are different and they carry the ice away. Some kind of ratcheting is possible, depending on the geometry and the bathymetry.

Hopen Times

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Re: Tides
« Reply #53 on: April 07, 2020, 10:24:40 AM »
Thanks oren. I think I can see that. Then I wonder, is the geometry and bathymetry in the Fram Strait like this? Further, can it have any big effect on the export numbers in the Fram Strait? Asked in a silly way, can we say, here comes a big tidal wave an it is going to move a lot more ice than normal thru the Fram Strait?

johnm33

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Re: Tides
« Reply #54 on: April 07, 2020, 10:45:05 AM »
"If the question is" My suggestion is that tidal forces, which have always operated, are now pushing more A.W. deeper into the Arctic via the Barentz shelf and these surges/pulses are beginning to become detectable. The surges create turbulence and I'm guessing some internal waves as they reach the basins, they force temporary currents some of which persist a while and may become permanent. These temporary currents themselves ease the influx of more A.W. and since the Arctic sea level remains self similar there has to be an increased outflow and it seems to me that this is below the shear level of the water held steady by the chaotic underside of the ice. The surges happen at speed the actual water trails far behind probably best judged by late +temp. anomolies in Kara/Laptev.
The full moon is upon us, and the biggest tides of the year so either the flow will be contained in the Norwegian/Greenland seas and thus halt the outflow or it will penetrate into Barents accelerating outflow. A possible proxy is the anomoly by Svalbard, here the flow of A.W. has moved directly north gaining about 16mph pero relative to its position and moving towards the rotational axis has also gained/lost[?] +/-angular momentum such that if it builds up both forms of kinetic energy will be expressed there as heat, both here and Barentz by the white sea anomolies are rising at the moment. Todays mslp suggests more contained tomorrows suggests not.

oren

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Re: Tides
« Reply #55 on: April 07, 2020, 10:49:20 AM »
To be honest, I think the effect of tides is cumulative and not necessarily driven by a specific tide. But perhaps a period of higher tides (king tides, spring tides) could have some non-negligible effect, as sometimes happens with iceberg calving.
I don't pretend to know if the effect is strong or very weak, but I am sure it is not zero, which for me was the original debate about tides and ice.

Andreas Muenchow

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Re: Tides
« Reply #56 on: April 08, 2020, 01:39:30 AM »
Tidal currents in the Arctic Ocean are small (< 5 cm/s) and this applies to Fram Strait as well. Furthermore, these tidal currents are largely linear which means that the water going into the Arctic during the "flood" is the same that comes out of the Arctic on the ebb. For linear wave motions the average velocity over a wave period is zero. Sinusoidal (linear) waves do not transport mass or matter such as ice or water, they transport energy. (A tsunami is a very good analogy for this.)

Only if the wave amplitude is similar to the water depth does a wave transport matter and energy. This (nonlinear) process closely relates to wave breaking.

Tides have a negligible effect on the flux of sea ice into or out of Fram Strait.

P.S.: Tidal currents are strong in Nares Strait (~ 1 m/s), but as in Fram Strait the tidal currents move ice back and forth only with a net displacement (during an entire tidal cycle for the tidal current) is close to zero.
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Jim Hunt

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Re: Tides
« Reply #57 on: April 08, 2020, 03:01:24 PM »
See also this from Copernicus:

https://twitter.com/CMEMS_EU/status/1247808183436894215

Quote
New Arctic Ocean tidal current forecast model is now available using a high-res. numerical model. Such tidal current information is used across a wide range of applications including: coastal management, marine renewable energy, navigation & more!
Reality is merely an illusion, albeit a very persistent one - Albert Einstein

tybeedave

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Re: Tides
« Reply #58 on: April 08, 2020, 11:48:49 PM »
It pains me when one can't see the forest for the trees.

Nowhere did anyone say that tides were the driving force behind Fram export.  The wind is the driving force, and while the synergetic addition of the tide is a relatively minor, yet significant contributor to export volume, the tide goes up and down, except when windblown. then things go sideways in more than one respect.

I thought this wind event was subsiding, but it continues melting much older ice than the 'normal' sloshing in Fram.  Tide or no tide, it is a major event, imho.

Lets stop arguing about trivial differences in definition.  as richard feynman said, ' you can know the all the names of all the birds, but that doesn't help you understand birds.

td
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uniquorn

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Re: Tides
« Reply #59 on: April 10, 2020, 05:07:21 PM »
Internal Waves and Mixing in the Marginal Ice Zone near the Yermak Plateau
https://journals.ametsoc.org/doi/full/10.1175/2010JPO4371.1
Quote
The aim of this study is to investigate the role of tides, internal waves and topography in mixing near the Yermak Plateau. To this extent, we use day-long time series of finescale and microstructure measurements at stations near the ice edge over the southern YP. The present work has implications beyond the study site, for the Arctic Ocean in general. Although peripheral regions such as the YP are home to anomalously large tidal velocities (30–40 cm s−1; Padman et al. 1992; Padman and Erofeeva 2004), the maximum tidal velocities over most of the central Arctic Ocean are sufficient (5–10 cm s−1; Kowalik and Proshutinsky 1993) to generate internal waves over suitable topography such as midbasin ridges and the continental shelf break. Including a simple representation of tidal mixing in a coupled ocean–ice model for the Arctic Ocean, Holloway and Proshutinsky (2007) show that tides enhance loss of heat from AW and have profound implications for Arctic hydrography and circulation. Furthermore, studies in the marginal ice zone (MIZ) can aid understanding how the decreasing trend in Arctic ice cover (Giles et al. 2008) will affect the vertical mixing. Currently, the deep Arctic Ocean away from coasts and submarine topographic features is a remarkably quiescent environment (Rainville and Winsor 2008; Fer 2009). Maintenance of this weak turbulent mixing in the interior Arctic Ocean is crucial for the cold halocline layer (Fer 2009), hence the ice cover, and the AW layer circulation (Zhang and Steele 2007). However, recent finding shows that large inertial waves, enhanced shear, and mixing are tightly related to the absence of sea ice (Rainville and Woodgate 2009). In a seasonally ice-free Arctic, vertical mixing can be comparable to the levels in the MIZ with potential impacts on the heat content in the upper-layer circulation, nutrients, and the ecosystem.

johnm33

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Re: Tides
« Reply #60 on: April 10, 2020, 10:12:51 PM »
Whilst i'm not suggesting that the tidal forcings are localised to Fram [more Barents and deeper penetration] there are tidal forces local to Fram. The tidal 'pressure' builds for about 6hrs. and since the water arriving has some additional inertia once through Fram much of it moves too far away to be drawn back as the pressure reverses. Also the A.W. is more saline/denser and moves through at a deep level, some fraction of it is drawn towards Nares by tidal forces there and has formed a permanent deep southbound current, another fraction is drawn along the face of the shelf north of Barentz, this too has become an established current. So even here as water flows in at depth a separate higher layer of water moves out in it's stead.
" Abstract

An upward‐looking Acoustic Doppler Current Profiler deployed from July 2007 to September 2008 in the Yermak Pass, north of Svalbard, gathered velocity data from 570 m up to 90 m at a location covered by sea ice 10 months out of 12. Barotropic diurnal and semidiurnal tides are the dominant signals in the velocity (more than 70% of the velocity variance). In winter, baroclinic eddies at periods between 5 and 15 days and pulses of 1–2 month periodicity are observed in the Atlantic Water layer and are associated with a shoaling of the pycnocline. Mercator‐Ocean global operational model with daily and 1/12° spatial resolution is shown to have skills in representing low‐frequency velocity variations (>1 month) in the West Spitsbergen Current and in the Yermak Pass. Model outputs suggest that the Yermak Pass Branch has had a robust winter pattern over the last 10 years, carrying on average 31% of the Atlantic Water volume transport of the West Spitsbergen Current (36% in autumn/winter). However, those figures have to be considered with caution as the model neither simulates tides nor fully resolves eddies and ignores residual mean currents that could be significant.
https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2017JC013271

uniquorn

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Re: Tides
« Reply #61 on: April 11, 2020, 02:06:03 PM »
Here showing an animation of 3 mosaic Pbuoys that report location and drift speed every 30mins. It runs at 24 frames/sec so 12hrs/sec. I think I can see lurches in speed roughly every second so I subtracted the drift speed from 6hrs before in each row to show the difference.

6hr difference = driftspeed(t)-driftspeed(t-6hr)

P201 is the top one. Is the method meaningful?
edit:I made a mistake and the p201 chart is for 5hr difference. I looked at P204 and calculated 4 to 6.5hr differences to see what they look like. The curve shifts along the time axis as anticipated but drift speed difference was more variable than I expected over time. (Converted to km/hr.)
click for full resolution.
Some clean peaks and troughs for calculating frequency.
« Last Edit: April 11, 2020, 09:59:30 PM by uniquorn »

johnm33

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Re: Tides
« Reply #62 on: April 12, 2020, 01:14:12 AM »
'meaningful' not yet but there are some indications, for instance the mslp and full moon tides [which i see as a seven day event balanced around the actual] seemed to indicate a slowdown before the 8th and then an acceleration of forcing by both diversion of A.W. onto Barentz shelf and consequentially more  'suction' by low tides  seems to be present [though there may be other explanations]. So another tool[complication] in the box. Thanks. When the actual 'surge' from deeper penetration of A.W. comes remains to be seen, IF. But this is best guess territory and the more tools the better.


uniquorn

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Re: Tides
« Reply #63 on: April 20, 2020, 12:54:46 AM »
Following up on using buoy data to show tidal movement, here are a selection of Mosaic Pbuoys that calculate drift speed every 30minutes. The 6hr difference in drift speed is shown by colour and size.
Just over 17 days in 815 frames, 24 frames/day running at 12 frames/sec
edit: reposting with negative drift speed
No graticule as processing takes too long
« Last Edit: April 20, 2020, 01:09:50 AM by uniquorn »

johnm33

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Re: Tides
« Reply #64 on: April 20, 2020, 10:36:27 AM »
This doesn't specifically refer to tides but it's implicit that if the Atlantic front can move with the seasons then it can also move with the tides. Thus on the surface at least it's probable that the same water moves into and out of the Arctic as the tidal pressure waxes and wanes. Not sure the buoys are close enough to feel this yet but another signal to look for.
 Evidence for where any Atlantic waters entered in the last tidal cycle are ambiguous at best but glbhycomsss shows increase both towards Banks is. and above Lomonosov opposite St. Anna with subtle changes to Laptev.

uniquorn

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Re: Tides
« Reply #65 on: April 20, 2020, 11:19:33 AM »
I struggle to reconcile the connection between ocean currents (and possibly tides) with the Lomonosov ridge because the peaks are ~1500m deep but the Mercator model implies a connection.

A max drift speed difference of ~0.5km/hr in deep waters is not much and the movement is likely to be 'smoother' than a wind shear, for example. However, the effects may be becoming more apparent as the ASI thickness decreases.

I took a closer look at P157 in the Laptev last october.
« Last Edit: April 20, 2020, 11:55:16 AM by uniquorn »

johnm33

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Re: Tides
« Reply #66 on: April 20, 2020, 02:51:22 PM »
St. Anna bottoms out close to 700m so in your graphic within the Atlantic Water layer, i'm thinking that the largest fraction of tidal driven A.W. leaves Barentz here. Dropping into the basin it causes waves in the Arctic Deep Water layer which radiate out, as ripples in a pond except for the complications of being at the interface of two dense mediums, so these internal waves travel directly towards Lomonosov but also reflections of them arrive in interference patterns [that remain opaque] and it's the turbulence generated as these pass the ridge that causes vertical mixing. The actual water probably turns right[east] and adds to the complex of waves traversing the deep layer, it may even be that it's energy is showing up in ESS causing the movment there apparent in Aluminiums gif.  [I think]
 The gifs motion does tie in with the number of tides.

uniquorn

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Re: Tides
« Reply #67 on: April 20, 2020, 05:25:18 PM »
Mercator (model) salinity at 300m shows turbulence beyond the Nansen/Gakkel ridge but not much. A daily image wouldn't show tides and I doubt that it models internal waves but took a look anyway. Ani runs at 61fps (~6sec/year).
gmrt bathy for reference.

https://polarresearch.net/index.php/polar/article/download/3094/html?inline=1
Quote
Abstract

The Barents Sea throughflow accounts for approximately half of the Atlantic Water advection to the Arctic Ocean, while the other half flows through Fram Strait. Within the Barents Sea, the Atlantic Water undergoes considerable modifications before entering the Arctic Ocean through the St. Anna Trough. While the inflow area in the south-western Barents Sea is regularly monitored, oceanographic data from the outflow area to the north-east are very scarce. Here, we use conductivity, temperature and depth data from August/September 2008 to describe in detail the water masses present in the downstream area of the Barents Sea, their spatial distribution and transformations. Both Cold Deep Water, formed locally through winter convection and ice-freezing processes, and Atlantic Water, modified mainly through atmospheric cooling, contribute directly to the Barents Sea Branch Water. As a consequence, it consists of a dense core characterized by a temperature and salinity maximum associated with the Atlantic Water, in addition to the colder, less saline and less dense core commonly referred to as the Barents Sea Branch Water core. The denser core likely constitutes a substantial part of the total flow, and it is more saline and considerably denser than the Fram Strait branch as observed within the St. Anna Trough. Despite the recent warming of the Barents Sea, the Barents Sea Branch Water is denser than observed in the 1990s, and the bottom water observed in the St. Anna Trough matches the potential density at 2000 m depth in the Arctic Ocean.
Correspondence
Vidar S. Lien, Department of Oceanography, Institute of Marine Research, P.O. Box 1870, NO-5817 Bergen, Norway. E-mail: vidar.lien@imr.no
(Published: 20 September 2013)

If this is too far off topic I'll move it to the AO salinity thread
« Last Edit: April 20, 2020, 09:29:01 PM by uniquorn »

oren

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Re: Tides
« Reply #68 on: April 20, 2020, 05:42:03 PM »
Good post which contributes to the discussion at hand. I suggest to cross post it to the other thread as well, as it contains useful stuff.

johnm33

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Re: Tides
« Reply #69 on: May 01, 2020, 11:28:18 AM »
A cut and slowed version of the current Hycom animation 0804-0705

I'm thinking the openings in the upper left quarter are caused by internal waves generated by tidally driven waters falling into Nansen from St. Anna. Some hint of them are present on the salinity gif but anything i try to enhance it destroys detail so best looked at as is, looking [zoomed in] at the 150E-pole line, and whilst it's open noting the increasing salinity across the CAAs Arctic coastline.
+
Plus a close up from 28:04
« Last Edit: May 01, 2020, 12:33:49 PM by johnm33 »

uniquorn

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Re: Tides
« Reply #70 on: May 27, 2020, 12:02:58 AM »
https://follow.mosaic-expedition.org/ mentions tides again today with no accompanying data or detail. Mosaic buoy P128 is, I think, the southernmost Pbuoy yesterday at
2020-05-25T22:00:00   81.2715   7.8702
further south than Polarstern according to Fomo.

The 6hr drift speed doesn't show a large increase in tidal drift since April1. Maybe the effects are more noticeable when attempting ice-breaking.

johnm33

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Re: Tides
« Reply #71 on: May 28, 2020, 12:07:42 AM »
Figured out how to expand the hycomsss without ruining all detail. This could go in 'waves' too but I'm looking at the tidal 'effects' here the interference waves generated by deep water movements washing up against Lomonosov [imho]

 short read for anyone interested https://syrte.obspm.fr/jsr/journees2014/pdf/Sidorenkov.pdf

johnm33

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Re: Tides
« Reply #72 on: June 02, 2020, 09:03:11 AM »
I've been looking at worldview, here and here to try to figure out tidal movements. What I think I'm seeing is that according to atmospherics, mslp gradients and winds, differing amounts of Atl. water pass through Iceland/Scotland gap, it's temp. varies, some is short circuited and rounds Iceland joining Irminger current and eventually flowing up the west coast of Greenland, some heads north. It's progress north is again affected by atmospherics so can be somewhat erratic but the tides and currents slowly deliver it to either Fram or Barents by N.Z. . The fraction delivered deeper into Barents also divides some going into Kara and some sinking into St. Anna trough this is delivered into Nansen and pushes onwards across Gakel into Amundsen basin. This delivery sets up deep disturbences, internal waves, eddies and pulsed currents. The waves wash against Lomonosov and their reflections rebound causing turbulence that reaches the surface weakening the ice. The eddies get caught up in the trough by Gakel and turn east towards Laptev. It looks like a recent pulse was exceptional and caused a large series of radiated waves from somewhere near the center of the Siberian side of Amundsen.
Bremen AMSR2

johnm33

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Re: Tides
« Reply #73 on: June 14, 2020, 10:30:55 AM »
This is the same view as above but from amsr2 on polarview[010620], it's more subtle, hard to see the waves unless you know they're there.

with that in mind a gif that starts on the 5th pauses/repeats where i see wave forms with the last image from yesterday [13020]

What i suspect is happening is that the current dropping down St. Anna enhanced by tidal surges, and possibly river discharge, is causing resonant wave forms to set up in the depths of the Eurasian basin both across it and along it and at some point these 'spout out' ''  followed by a quieter period as that energy dissipates, probably starting tomorrow.

johnm33

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Re: Tides
« Reply #74 on: June 14, 2020, 10:40:13 AM »

johnm33

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Re: Tides
« Reply #75 on: June 18, 2020, 01:05:46 PM »
This animation runs from  11:06 til' 17:06 it looks to me that another spouting out event happened in the deeper layers, so somewhat subdued compared to a surface event, but then the waves spread and have now subsided. Just in time for the build up of the next tidal acceleration of currents, that is if there's any 'reality' to my hypothesis.

There's a possibility that the wave action had some impact on the thinning showing up on Hycoms thickness

if that's the case then the ice will be slaughtered by the next event, if indeed there is one, so perhaps around  25:06 we see a 'peak' of losses on the eurasian side.

johnm33

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Re: Tides
« Reply #76 on: June 20, 2020, 12:11:26 PM »
Parallel waves showed up on the 19:06 amsr2 just north of FJ suggesting the surge was on a much broader front than the above post implies, and todays sees that quashed possibly by outflow between FJ and SvBd, with the ice either side smashed by interacting waves. So tying that to the [uniquorns] bathymetry

If i find time i'll try to improve the gif.
« Last Edit: June 20, 2020, 12:32:50 PM by johnm33 »

uniquorn

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Re: Tides
« Reply #77 on: June 25, 2020, 12:12:42 AM »
https://os.copernicus.org/articles/14/225/2018/
North sea, not the arctic but perhaps still relevant
Quote
Tides are of fundamental importance for understanding shelf sea dynamics and ecosystems. Not only are tidal currents frequently the dominant flows in these regions (Otto et al., 1990), but the turbulence, bottom-mixing, and circulation patterns to which they give rise also have a profound effect on the physics, biogeochemistry, and ecology of shelf seas (Holt and Umlauf, 2008; Lenhart et al., 1995; Simpson and Hunter, 1974). In shallow regions with fast tidal currents, full-depth mixing is maintained throughout the year. In deeper regions or where tidal currents are slower, tidal mixing cannot overcome buoyancy forcing in summer and the water column stratifies seasonally. The boundaries between mixed and stratified areas are sharp (Hill et al., 2008) and are known as tidal mixing fronts. These fronts separate water masses with markedly different physical and biogeochemical properties, and the density-driven jets to which they give rise are important transport pathways (Hill et al., 2008). Consequently, understanding the processes that control the formation and location of tidal mixing fronts, alongside an accurate knowledge of the tidal currents themselves, is necessary for effective management of economically important shelf sea ecosystems and for modelling the dispersion of tracers, contaminants, and organisms.
Quote
2.2 Tidal ellipses

Tidal ellipses of the glider-derived tide show a decrease in the amplitude of zonal and meridional tidal velocity with distance offshore (Fig. 3a). Semi-major axes are consistently larger than semi-minor axes, and the offshore decrease in the magnitude of the semi-major axes is greater than the offshore decrease in semi-minor axes. The smaller rate of change in the eastern part of the section is because bathymetry gradients are smaller than in the west. Velocity amplitudes were multiplied by the mean water depth in each bin to derive ellipses of tidal transport per unit width (Fig. 3b). Compared with velocity amplitude, transport amplitude changes less markedly with distance offshore, suggesting that the greater tidal velocities observed in shallow water than in deep water are primarily a result of volume continuity rather than the exponential offshore decay of the tidal Kelvin wave.

uniquorn

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Re: Tides
« Reply #78 on: July 01, 2020, 04:10:11 PM »
Reposting here as this gif is showing Laptev ocean surface movement using infrared.
2 day loop, Lena delta in lower left, requires a click.  Shortwave infrared. Contrasted boosted for detail.

2m winds relatively constant from SE during the two days.
nullschool wind

johnm33

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Re: Tides
« Reply #79 on: July 03, 2020, 11:55:09 PM »
The present and forecast mslp promises an increased inflow of Atl. waters, so both St. Anna and Franz Victoria troughs will see some action possibly as soon as 04:07 [07:04US] increased turbulence and forcing both along the Barents shelf and towards the pole, so maybe a [near] pole hole tues 07:07. Nares won't last that long, may have gone already, big tides will dislodge fast coastal ice and even if the wind changes the high slp should force enough water through to almost clear it next week.
I'm trying to make the case that the recent internal wave action in Beaufort was the resonant remains of the last full moons tides, if there's anything to that then we should see a repeat sometime around 23-25:07 trashing a much weaker Beaufort.

johnm33

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Re: Tides
« Reply #80 on: July 09, 2020, 09:47:53 AM »
Looking at https://www.polarview.aq/arctic AMSR2 the damage by the tidal forcing of currents shows up well. This last full moon combined with high mslp has forced flow mainly towards St. Anna and the surges and vortices fed by that have damaged bottom ice, failed to open a pole hole but close, and now arguably the waves passing over/bouncing off Lomonosov are passing through and dissipating in the ocean to both sides. These may lead to secondary internal waves which will more likely show up as upwellings either by the coast or deeper shelves, how long these take to form and show remains opaque.

uniquorn

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Re: Tides
« Reply #81 on: July 09, 2020, 09:41:13 PM »
Not sure how much credence to give to the follow mosaic site but maybe this statement about tides will be confirmed by a paper at some point.
click to run
added P201 july drift.
« Last Edit: July 09, 2020, 10:19:21 PM by uniquorn »

blumenkraft

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Re: Tides
« Reply #82 on: July 09, 2020, 09:54:25 PM »
Uniquorn, i was wondering the same. I think this picture is shifted in perspective. No idea why they would do such a thing though.
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uniquorn

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Re: Tides
« Reply #83 on: July 09, 2020, 10:26:37 PM »
Off topic, but that perspective makes PS look a lot further from the Fram Strait.

uniquorn

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Re: Tides
« Reply #84 on: July 10, 2020, 10:18:21 AM »
Might be applicable to wind driven drift..

What makes ships mysteriously slow down or even stop as they travel, even though their engines are working properly?

https://www.sciencedaily.com/releases/2020/07/200706152701.htm
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This was first observed in 1893 and was described experimentally in 1904 without all the secrets of this "dead water" being understood. An interdisciplinary team from the CNRS and the University of Poitiers has explained this phenomenon for the first time: the speed changes in ships trapped in dead water are due to waves that act like an undulating conveyor belt on which the boats move back and forth. This work was published in PNAS on July 6, 2020.

In 1893, the Norwegian explorer Fridtjof Nansen experienced a strange phenomenon when he was travelling north of Siberia: his ship was slowed by a mysterious force and he could barely manoeuvre, let alone pick up normal speed. In 1904, the Swedish physicist and oceanographer Vagn Walfrid Ekman showed in a laboratory that waves formed under the surface at the interface between the salt water and freshwater layers that form the upper portion of this area of the Arctic Ocean interact with the ship, generating drag.

This phenomenon, called dead water, is seen in all seas and oceans where waters of different densities (because of salinity or temperature) mix. It denotes two drag phenomena observed by scientists. The first, Nansen wave-making drag, causes a constant, abnormally low speed. The second, Ekman wave-making drag, is characterized by speed oscillations in the trapped boat. The cause of this was unknown. Physicists, fluid mechanics experts, and mathematicians at the CNRS' Institut Pprime and the Laboratoire de Mathématiques et Applications (CNRS/Université de Poitiers) have attempted to solve this mystery. They used a mathematical classification of different internal waves and analysis of experimental images at the sub-pixel scale, a first.

This work showed that these speed variations are due to the generation of specific waves that act as an undulating conveyor belt on which the ship moves back and forth. The scientists have also reconciled the observations of both Nansen and Ekman. They have shown that the Ekman oscillating regime is only temporary: the ship ends up escaping and reaches the constant Nansen speed.

This work is part of a major project investigating why, during the Battle of Actium (31 BC), Cleopatra's large ships lost when they faced Octavian's weaker vessels. Might the Bay of Actium, which has all the characteristics of a fjord, have trapped the Queen of Egypt's fleet in dead water? So now we have another hypothesis to explain this resounding defeat, that in antiquity was attributed to remoras, 'suckerfish' attached to their hulls, as the legend goes.

The dual nature of the dead-water phenomenology: Nansen versus Ekman wave-making drags.
Johan Fourdrinoy, Julien Dambrine, Madalina Petcu, Morgan Pierre, and Germain Rousseaux.
PNAS, 2020 DOI: 10.1073/pnas.1922584117
Quote
A ship evolving in a stratified fluid is sometimes slowed down in comparison to a homogeneous case. This dead-water phenomenon was reported by the Norwegian explorer Fridtjöf Nansen during his North polar expedition in 1893. The physicist and oceanographer Vagn Walfrid Ekman was the first to study in the laboratory the physical origin of dead-water phenomenon in 1904: at the interface between saline water and freshwater, internal gravity waves appear, propagate, and generate a wave-making drag. Here we show that the velocity oscillations of pulled ships models à la Ekman caught in dead water are due to a transient internal dispersive undulating depression produced during the initial acceleration of the ship that we predict with a linear analytical model.

Abstract

A ship encounters a higher drag in a stratified fluid compared to a homogeneous one. Grouped under the same “dead-water” vocabulary, two wave-making resistance phenomena have been historically reported. The first, the Nansen wave-making drag, generates a stationary internal wake which produces a kinematic drag with a noticeable hysteresis. The second, the Ekman wave-making drag, is characterized by velocity oscillations caused by a dynamical resistance whose origin is still unclear. The latter has been justified previously by a periodic emission of nonlinear internal waves. Here we show that these speed variations are due to the generation of an internal dispersive undulating depression produced during the initial acceleration of the ship within a linear regime. The dispersive undulating depression front and its subsequent whelps act as a bumpy treadmill on which the ship would move back and forth. We provide an analytical description of the coupled dynamics of the ship and the wave, which demonstrates the unsteady motion of the ship. Thanks to dynamic calculations substantiated by laboratory experiments, we prove that this oscillating regime is only temporary: the ship will escape the transient Ekman regime while maintaining its propulsion force, reaching the asymptotic Nansen limit. In addition, we show that the lateral confinement, often imposed by experimental setups or in harbors and locks, exacerbates oscillations and modifies the asymptotic speed.

johnm33

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Re: Tides
« Reply #85 on: July 10, 2020, 11:22:20 PM »
Gif covers first to tenth, what are the odds that the spread of secondary waves wash up against Greenland/Ellesmere making the following days somewhat like the first?