A part explanation on Gravesend-Broadness, calm at tide turn

Posted: November 5, 2014 by tchannon in Surfacestation, Tides

I may be boring folks yet detail is what breaks to understanding. This is rather fun, things fit. 

 

UK extremes

 

Parameter Location Value
Highest maximum temperature Gravesend 14.1 °C
Lowest maximum temperature Pennerley 5.7 °C
Lowest minimum temperature South Newington -2.0 °C
Highest rainfall Redesdale Camp 19.8 mm
Sunniest Leconfield 6.0 hours

Issued at: 2303 on Tue 04 Nov 2014

 

Hourly data, a peak temperature which elsewhere seems to coincide with a short period of high visibility, probably sunshine. But look at the green wind data trace, falling west wind, calm, east wind then resume west. Humidity drops low.  The station is on a tidal estuary.

The estimate tide from various web sites at Gravesend-Broadness was low tide at 16 hours but the PLA chart for Tilbury which is 2km downstream is  0.76 m @  17:10 hrs

Assuming I have my timing spot on, actually not sure about this, a bit tricky with daylight saving. I’ve just spotted a mistake on the plot, software bug, date is wrong is actually 2014-11-04. Data collect was after zulu 30 (readings are centred on hour and produced after the following half hour).  (swearword, I hate date and time programming)

This is not proof but is a clue that part of the reason for extremes is local sea tidal effects producing air movement. Tide effects can cancel out wind.

I’ve wondered about this from my time when I have been near the sea. I recall odd effects, you tend to know tide turn.
A web trawl awhile ago produced nothing.

Trying again, yay, anecdotal, wind at high tide, and reversal is mentioned.
http://www.ybw.com/forums/archive/index.php/t-261318.html

Includes

In my opinion the main effect is down to temperature. I’ve not come across any sceintific papers on this, and one day when I have more time on my hands (yeah!) I’d like to look into it further.

You see, there are a couple of scenarios. A change in tide can bring a change in water temperature as eddies within the water bring warmer/colder water to the surface. This must have an impact on the air above the surface, changing the temperature and increasing the temperature gradient, hence leading to an increase in wind.

In this case goodness knows how the water is temperature stratified given the power station cooling etc. etc. I’d go though more with simply wind change including cooling what was in the lee hence plumes of warm.

Over the last few months I’ve spotted a trend when I’ve been out kitesurfing – the wind weakens noticeably at the turn of the tide. Often on marginal days it dies out completely but even on some of the more hectic days it drops quite markedly.

And in the Thames estuary

I’ve also noticed at Southend that at the turn of the tides the winds drop and pick up half an hour later. it also happened on Sunday at Uncle Tom’s in Southend. Marginal wind and it died right off at tide turn.

http://www.kiteboarder.co.uk/kitesurfing/viewtopic.php?f=1&t=5279

Microclimate is unlikely to explain everything and yet this almost always involved with extremes.

In this case  the station is  in a hollow formed by bunds, sea defences. Also in the hollow is a radar station.

Given more data I expect some correlations.

What the river looks like at low tide, Queen Elizabeth Bridge so this is looking west (towards London).
https://www.flickr.com/photos/29342184@N06/11584117586/

[update: plot updated with corrected timestamp]

Post by Tim

(If I am blogging excessively give me a hint)

Comments
  1. Scute says:

    Tim

    It’s not boring. I’ve been following this with interest. I remember that in the 2012 Gravesend article comments you were interested in the tides and did a bit of research to try and correlate them with the temps. But we didn’t talk about wind drop, just river flow and eddies. You said something like “who knows what result the different tidal effects would have on temperature”.

    I think it could be a combination of the two effects, water flow drop and wind drop. It would make sense if the warm water from the power station started backing up as the tide turned from low to high because instead of being hurried out to sea, there’s an inflow blocking its outward flow. Then, it sits there in the horseshoe surrounding the station bathing the whole area with heat. Then the wind drops as you say and the lack of convection means that air temperatures soar.

    Both effects are due to a lack of convection, firstly of the river water out to sea, secondly of the surface winds.

  2. Paul Vaughan says:

    “A change in tide can bring a change in water temperature as eddies within the water bring warmer/colder water to the surface. This must have an impact on the air above the surface, changing the temperature and increasing the temperature gradient, hence leading to an increase in wind.”

    Where I sea kayak freezing cold water wells up where water races over sills, particularly in one particular narrows where one day when it was overcast and the temperature was near the dewpoint it was raining heavily over the cold narrows while not raining elsewhere where the surface water was much warmer. There was vertical circulatory coupling with the local mountainous topography such that there was a moderate downdraft and the strong water temperature gradient correlated with a noticeable mild-to-moderate air temperature gradient on a scale of only tens of meters.

  3. craigm350 says:

    Thanks Tim. It’s not boring by any means and imo quite educational.

    Btw – have you been watching Nuri as it is due to recurve and become a bit of a monster?

    I’ve covered some of the output here:

    http://weatheraction.wordpress.com/2014/11/05/planetary-wave-due-to-wobble-as-cyclone-crashes-into-jetstream/

    US in for brutal early cold again.

  4. tchannon says:

    Good, there is some interest. I’ll fix the timestamp problem and probably complete reverse engineering some tidal data from min/max, party trick of the analyser software here.

    Maybe then add some comments.

  5. tchannon says:

    Nuri, no. Initially it affects the other side of the world, what then? Historically I assume we have a good idea of what comes next.

    Sustained blocking over the US would be bad news for us given this leaves the North Atlantic open for a flow aiming water at the UK but also a mild winter.

  6. Brett Keane says:

    I often wondered at this phenomenon during years working at sea, in the mid-latitude southern hemisphere. Guessing at changing boundary effects, friction and T?, on lightish wind strengths. Reminds me of day/night boundary effects. Brett Keane, NZ

  7. tchannon says:

    Updated the article plot, timestamp is corrected. Stamp now says “local”. Moved text slightly, was misaligned.

  8. tchannon says:

    Brett,

    I am very interested in these effects which seem to be anecdotal yet I’d be amazed if there is a dearth of papers. Maybe it is out of fashion.

    Dawn dusk effects are very clear in near coastal regions, how far inland this stretches I don’t know. Many of these stations plots exhibit dawn effect, still at dawn then wind rises through the day, tending to fall again at dusk. I could probably show hundreds.

    Related to this is why I bang on about planet rotation, day and night, not handled well by weather GCM..

    Same thing with the nocturnal jets

    Click to access s10546-011-9639-8.pdf


    http://adsabs.harvard.edu/abs/2013EGUGA..15.3050T

    Click to access J142.pdf

    And so on

    Polar regions, oh yes.

    Convection fails when the ground cools.

  9. Brett Keane says:

    @tchannon says:
    November 6, 2014 at 4:01 am: thanks for the jet papers. The land/sea breeze effect is maybe different – but might relate to Gravesend – differential heating on an otherwise fairly even energy field.

    @Ren: there did seem to be quite a drop in the above 80N temps, made me sit up. Glad to be10,000miles away, got enough rubbish weather here. Brett NZ

  10. tchannon says:

    Yesterday the Met Office Datapoint hourly data blew a gasket tripping my software refusing to process the 24 hours yet reporting three new stations, one on the Thames estuary.

    Bugs in my stuff is to be expected, there is no specification nor sane documentation for Datapoint, all guesswork on what the Met Office mean or even the formats.

    On investigating…
    The entire day of data has a hole in it, looks like their system was down, nothing was recorded on their server.

    The three new stations, all with single digit ID, itself a huh? had one (1) datapoint at zulu. Those data values were not for zulu… such as 10C off.

    That’s sorted but what of the stations? Not there in the data for the following day.

    All airports /. fields

    Site ID=5 Name=London City Airport 51.5048,0.058 2.0m
    Site ID=6 Name=Lydd 50.9561,0.9392 3.0m
    Site ID=3 Name=Southampton Airport 50.9503,-1.3567 11.0m

    London City, a very hairy place to fly

    This one is not far from Gravesend-Broadness.

    Best guess after a good look around is this
    51.504304° 0.067508°

    Lydd use to be well known, would be good as south of the hot part of Kent.

    Not at all sure if this is the met stuff. Old fashioned place, private flying but next to probably the control tower is a possibility
    50.957107° 0.936389°

    Eastleigh Airport (Southampton Airport)

    Can’t see a met enclosure, usual lots of “objects”

    Instead here is I think a brown pants device 50.942419° -1.361174° you never want to see up close. Stupidly a motorway was built too close to the end of the runway, worse, the land falls away, been a dire overrun there, so this is probably a Lytag or somesuch arrester bed.
    http://www.lytag.com/case-studies

    An accident 1993, Cessna Citation charter plane landed on a wet runway with a tailwind beyond the aircraft specification, came off the end of the runway and onto the motorway, collided with two cars. By some miracle no-one was killed.
    http://www.aaib.gov.uk/publications/formal_reports/5_1994_g_jetb.cfm

  11. tchannon says:

    And again

    UK extremes

    Parameter Location Value
    Highest maximum temperature Gravesend 15.1 °C
    Lowest maximum temperature Killylane 5.5 °C
    Lowest minimum temperature Aboyne -1.9 °C
    Highest rainfall Middle Wallop 22.2 mm
    Sunniest Kinloss 6.2 hours

    Issued at: 2302 on Sat 08 Nov 2014

    Only thing notable is due south wind and gusting to 30mph, strong for off land.

    Tide 8th Saturday at Tilbury
    0121 6.69
    0753 0.54
    1332 6.67 < == high tide
    2017 0.64

  12. craigm350 says:

    I think the thing with Nuri is it will amplify the jetstream disrupting the vortex as wave activity increases. In the short term it does mean a fair bit of rain to come but hemispheric background is not like last year and the stratosphere looks promising (if you like cold). I actually think we could be in for a snow good dumping instead of a long deep freeze. Upper profile similar to 2009/10 but not quite. Time as ever will tell.

    Nuri being reported as lowest but current 924mb is an estimate, previous was directly measured so no record as yet and historic coverage is poor for long term comparison.

    The most powerful storm, at least in terms of depth of pressure, to affect Alaska in modern history was that of October 25-26, 1977. Dutch Harbor, on the Aleutian Island of Unalaska, recorded a minimum pressure of 925 mb (27.31”) on the evening of October 25th. Winds gusted to 130 mph at Adak, also in the Aleutian Islands. Adak reported a continuous 12-hour period with wind gusts of 110mph+ between 1800Z Oct. 25 and 0600Z Oct. 26. Enhanced infrared radar imagery indicated a closed ‘eye wall’ with this storm. Wave heights of 35 feet on top of swell heights of 60 feet produced significant wave heights of 72 feet according to NWS analysis and ship reports. The analysis speculated that there was the potential for waves as high as 120 feet, although nothing of this magnitude was actually observed. The cyclone had its origins, as is often the case with powerful Alaskan storms, as a West Pacific typhoon.

    http://www.wunderground.com/blog/weatherhistorian/comment.html?entrynum=49

    1977/8 an interesting winter both sides of Atlantic.