Bottom Ice in the Freshwater Thames!
One of the great scientific facts of my childhood was the understanding that whilst most liquids become denser as they get colder this only applies to water down to a point, and that point is at about 4ºc. Water is at its densest at this temperature and then as it cools further it actually gets less dense.
This strange quirk of nature is probably responsible for the survival of life on earth and certainly for life on land. Together with the fact that ice is less dense than water and therefore floats – it means that even relatively small bodies of water never freeze through to the bottom – and therefore life could survive.
The convection currents caused by water cooling at the surface, becoming denser and falling, cease at 4ºc and even reverse (colder water being forced to the surface where it freezes and insulates the rest). I write this because I have recently discovered the following:
It is in “Oxfordshire of One Hundred Years Ago” by Eleanor Chance. W E Sherwood writes –
There is another thing which I suspect the Conservancy, by their dredging, may have stopped, but I am not certain, as it is so long since we have had a severe winter, and that is the formation of ‘ground ice’, ice that is that forms on the bottom of the river. When I spoke to my science master about it he talked about the maximum density of water, and told me that the thing was impossible, but I took him down to the river, and showed him, opposite the barges [i.e. the College Barges along the left bank at Christchurch Meadow], the bottom all covered in ice.
I think he was annoyed, but at the river for behaving so unaccountably – indecently even, he seemed to think – and not at me. He was so far right that in a lake or in a river of uniform depth the ice cannot so form, but in the Thames in those days there were deep reaches followed by banks of gravel over which the water was shallow.
In times of frost the heavier warmer [ie 4ºc] water sank and remained in the deep parts, and what flowed on was the lighter water at or close to freezing point, and when the crystals formed in this they attached themselves, as forming crystals will, to any solid they could find; in this case to the gravel at the bottom.
This ice rose from time to time in spongy masses, bringing with it some of the gravel, and floated on until it reached the lock. Here it packed, and if the frost continued, formed a thick mass of rough ice which, as more came down extended further and further upstream; and it was on this ice, far more than surface ice, that on three occasions I remember a coach and four was driven from Folly Bridge to Iffley.”
I think that the assertion that improving local drainage can significantly affect local temperatures. Dredging = No more Bottom Ice may well be valid.
And the dates? And the historic references to Binsey/Thorney which go back to pagan times or close thereto.
All at nearly the same Thames river heights for the last 2000 years or so!
You would think that that change would show up in http://www.gtc.ox.ac.uk/about-gtc/history-and-architecture/the-radcliffe-observatory.html as it is less than a mile away from Port Meadow! (See Google maps or similar).
So it is my assertion that UHI http://www.smithsonianmag.com/science-nature/city-hotter-countryside-urban-heat-island-science-180951985/?no-ist started back as far as 600AD or so in Oxford!
Two bites. One when the river was diverted from the ‘old’ Thames to the ‘Isis’. And another when it was dredged and run-through was improved.
And a world class, reference, thermometer just yards away in the Radcliffe!
https://en.wikipedia.org/wiki/Urban_climate Rural areas have more wet surfaces (in towns, rivers are often covered and water runs off into drains). Evaporation from these wet surfaces produces cooling because heat is absorbed by the process of evaporation. Buildings are heated, and vehicles and air conditioning systems generate heat.
Heat islands exist because the land surface in towns and cities, which is made of materials like Tarmac and stone, absorbs and stores heat. That, coupled with concentrated energy use and less ventilation than in rural areas, creates a heating effect.
Evaporative cooling and evapotranspiration. Though it is termed ‘evaporative cooling’ it is not cooling as such, rather ‘warming less’ (Gill, 2006). Through evaporation, incoming energy is used to convert water into water vapour. Energy is being used to drive the evaporation process rather than being transferred to the sensible heat that we feel, thus air temperatures are lower (Oke, 1987). Where the water is within a plant, on its surfaces or in the soil, the process is termed evapotranspiration. Vegetation is sparser in cities than in the countryside, reducing cooling through evapotranspiration and much of the surface is sealed, reducing cooling through evaporation. This is a primary contributor to the UHI.
I would also have thought that the weir at Wytham or close to would provide a very good sampling point for the land area to the West, almost to the Severn, for both rainfall and water temperature. This before it gets polluted by urban heat later on down the river
I wonder if this area might be a possible area of interest to
as a potential case study?
As the actual area itself goes back to medieval days or before almost untouched except for farming. It sits just slightly below the city to its East so UHI will have a draft effect rather than heating for most wind directions.
Its local climate is driven almost totally by evaporation requirements. It floods every year. And has done so down recorded history.
How far down history?
““the quiet little hamlet of Woolvercot; the only living creatures visible being some white geese on the green,” wrote William Black of it as he knew it. It was here, according to Holinshed, that King Memphric, who about a thousand years before Christ originally founded Oxford, calling it Caer Memphric, was seized and devoured by wolves in a solitary dingle; hence the name.””
I suppose that this other 3000 year old site may be able to provide as much insight into aspects of Climate on the other side on England.
That makes two 3000 year old sites in the UK!
The Binsey site for the West of England, the Radcliffe and CET. The Whittlesey site to the East for habitation, food, diet, estimated sea level, etc.
That’s not bad for a crowded, small island at the edge of the North East Atlantic. Mind you, one who at its core understands about relative and absolute and where bearings cross at night and an absolute is something you would pay a lot of money for. Before GPS that is.
As a reference to the boundary layer problems with temperature sampling and local drainage and humidity, turbulence, etc.
“The lowest layer of the atmosphere is called the troposphere. The troposphere can be divided into two parts: a planetary boundary layer, PBL, extending upward from the surface to a height that ranges anywhere from 100 to 3000 m, and above it, the free atmosphere. The boundary layer is directly influenced by the presence of the Earth’s surface, responding to such forcings as frictional drag, solar heating, and evapotranspiration. Each of these forcings generates turbulence of various-sized eddies, which can be as deep as the boundary layer itself, lying on top of each other. Consider the case of solar heating: solar heating of the ground on a sunny day creates thermals of warmer air that rise over colder air causing vertical mixing and turbulence. Therefore, in any weather prediction model, the PBL must be parameterized as a mechanism for turbulence (Stull, 1988).
A good surface forecast is often critically dependent on accurate estimates of surface fluxes, and in turn, on reasonably accurate soil moisture and temperature estimates.”
“This movie is a combined visualization of the PBL and wind dynamics over the LA basin for a one-month period. Vertical motion of the PBL is represented by the gray “blanket”. The height of the PBL is largely driven by convection associated with the changing surface temperature of the Earth (for example, rising during the day and sinking at night). The colored arrows represent the strength and direction of winds at different altitudes”
Please note, what you see above will be reduce to a few numbers when dealing with Climate data analysis.
““Physical laws and equations of motions, which govern the planetary boundary layer dynamics and microphysics, are strongly non-linear and considerably influenced by properties of the Earth’s surface and evolution of the processes in the free atmosphere. To deal with this complicity, the whole array of turbulence modelling has been proposed. However, they are often not accurate enough to meet practical requests. Significant improvements are expected from application of a large eddy simulation technique to problems related to the PBL.
Perhaps the most important processes, which are critically dependent on the correct representation of the PBL in the atmospheric models (Atmospheric Model Intercomparison Project), are turbulent transport of moisture (evapotranspiration) and pollutants (air pollutants). Clouds in the boundary layer influence trade winds, the hydrological cycle, and energy exchange.”
I seem to remember the Roman’s had fountains to provide a similar, local, cooling effect. Perhaps Port Meadow has kept Oxford cool? Natural air conditioning.
And in defense of my assertion that the two instrument sets, thermometer and satellite see different views. They do. One lives in the PBL and tries to measure that. The other probably sees the layers above 3000m better.
And if I may quietly observe, in the days before radio and satellites, our weather predictions were pretty poor. Am I being asked to believe that we do any better with Global Temperature? The two temperature series need to be bought into cross-calibration to do what the other can’t IMHO.
Warm is easy to measure. Cold less so It can leak back in over the next few days.