Rupert Sheldrake is a man who believes in telepathic dogs. As one might expect from a man who believes in telepathic dogs, he finds reason to complain about the modern scientific method, and its materialistic presuppositions. In fact, he's written a book, called The Science Delusion, containing both a critique of modern science, and an exposition of his theory of 'morphic resonance'. Sheldrake proposes that we are surrounded by as-yet undetected fields, which store our memories, and provide guiding nudges to the formation of new biological organisms.
Such notions are perhaps best confined to the pages of a Terry Pratchett novel, but James Le Fanu provides further unintended amusement with an approbatory review in The Spectator.
Le Fanu states that the "law of the conservation of matter and energy...is a foundational principal of physics...However, pose it as a question 'Is the total amount of matter and energy always the same?' and the answer is clearly no in ways that transcend materialist assumptions. The compelling evidence for the creation of the universe ab initio at the moment of the Big Bang required there to be suddenly a lot more of both."
In other words, Le Fanu claims that the Big Bang violates materialism. So let's remind ourselves of what materialism, or 'physicalism' as it's now commonly dubbed, amounts to:
"Physicalism is the thesis that everything is physical, or as contemporary philosophers sometimes put it, that everything supervenes on, or is necessitated by, the physical...Of course, physicalists don't deny that the world might contain many items that at first glance don't seem physical — items of a biological, or psychological, or moral, or social nature. But they insist nevertheless that at the end of the day such items are either physical or supervene on the physical." (Physicalism, Stanford Encyclopedia of Philosophy).
So is the Big Bang, or the purported violation of the conservation of mass-energy, inconsistent with physicalism? Does either suggest that non-physical things exist? No, clearly not. Materialism is consistent with any cosmological scenario, and is not dependent upon the conservation of mass-energy, any more than it is dependent upon the conservation of angular momentum.
Big Bang cosmology proposes that the universe has existed for a finite time. Other cosmological theories propose that our universe is simply a finite bubble in a larger universe which has existed for an infinite time. There are two logical possibilities vis-a-vis materialism:
(1) Everything which exists is physical, and has existed for a finite time.
(2) Everything which exists is physical, and has existed for an infinite time.
Fred Hoyle and his colleagues proposed an alternative to Big Bang cosmology in 1948, in which our expanding universe has existed for an infinite time, but in which mass-energy is continuously created throughout space to maintain a constant energy density. Does Hoyle's scenario violate materialism any more than Big Bang cosmology? Again, clearly not.
Le Fanu, however, is capable of getting the wrong end of more than one stick, and proceeds to argue that the existence of dark matter in cosmology also undermines materialism:
"It has also emerged that the distribution of galaxies and continued expansion of the universe requires there to be vastly more of both matter and energy than can be observed...This might perhaps be relevant to similarly invisible but apparently real 'energetic' phenomena whose existence is denied by modern science — notably the 'spark of life' that so unambiguously distinguishes the animate from the inanimate."
Here, Le Fanu has misunderstood what dark matter is proposed to be. Hypothetical dark matter interacts very weakly with light, neither emitting nor absorbing it, and is therefore impossible to discern directly by means of telescopic observation. However, whilst it is, in this sense, invisible, it is not undetectable. In fact, it is the gravitational interaction of dark matter which is held to be responsible for the clumping of visible matter in the form of galaxies and galaxy clusters. Le Fanu has, quite cleverly, used an ambiguity in the term observable, to imply that invisible means undetectable, and therefore unphysical.
Le Fanu's claim that there is a 'spark of life', which "so unambiguously distinguishes the animate from the inanimate," returns us firmly to the philosophy of vitalism, and it is no surprise that he also has a problem with neuroscientific accounts of memory, asking "How do we reconcile the fixity of memory over decades with the constant turnover of the neurotransmitter chemicals in the neuronal synapses?"
Indeed, and Le Fanu might also ask how we can reconcile the fixity of the information in computer memory with the constant turnover of electrons in the semiconductor circuits. Presumably every laptop must interact with hidden magic fields to preserve the contents of its ROM-BIOS.
Sheldrake's book has also received positive reviews, on similar anti-materialistic grounds, from Mary Midgley, and Bryan Appleyard.
The fundamental problem these authors have with science is that they wish to form their beliefs first, on aesthetic or cultural grounds, and then selectively look for reasons or evidence afterwards. The scientific method rather works the other way round, and here I can only endorse the sentiments expressed by philosophers James Ladyman and Don Ross:
"What most impresses us about science is...the way in which its institutional organization selects for rationality and collective epistemic progress in the activities of a species that seems, in its more natural institutional settings, strongly disposed to superstition and fearful conservatism," (Everything Must Go, p61).
Sunday, February 26, 2012
Friday, February 24, 2012
Colin McGinn on consciousness
Philosopher Colin McGinn writes an interesting discussion of consciousness in the February 20th issue of New Statesman magazine, arguing in favour of his 'mysterian' approach to the mind-brain relationship.
McGinn begins, however, by rejecting five other common positions in the philosophy of mind: (i) eliminativism (there is no mind); (ii) reductionism (the mind reduces to the brain); (iii) dualism (the mind and the brain interact, but are fundamentally distinct modes of existence); (ii) idealism (only mental entities exist); and panpsychism (every bit of matter has a bit of mentality in it).
After rejecting these approaches, McGinn advocates his mysterian contention that "we just don't have the faculties of comprehension that would enable us to remove the sense of mystery [to the mind-brain relationship]. Ontologically, matter and consciousness are woven intelligibly together but epistemologically we are precluded from seeing how."
Whilst McGinn doesn't use the term 'unification', when he speaks of matter and mind being woven together, he's clearly advocating the notion that the mind and the brain are ontologically unified. His position, then, is to accept ontological unification, but reject epistemological unification.
Now, the distinction between ontological and epistemological unification is a useful one; more's the pity, then, that McGinn doesn't acknowledge that this distinction can be equally applied to reductionist accounts of the mind-brain relationship. Thus, whilst the mind may be ontologically reducible to the brain, it might be impossible to comprehend that reduction relationship; one might endorse ontological reductionism but reject epistemological reductionism.
In response, the question might be posed: why prefer ontological reductionism to ontological unification? The answer is that the relationship between the mind and the brain does not merely reside in correspondence, but consists of a supervenience relationship. This means that there is a many-one mapping between brain states and mental states. Multiple brain states correspond to single mental states; change a brain state slightly by changing the firing frequency of a few neurons, and the mental state remains invariant. But change a mental state, and the brain state must change.
This entails that brain states determine mental states, not vice-versa. The relationship between the mind and the brain is not bilateral or symmetrical, it is top-down. Hence, ontological reductionism is required rather than ontological unification.
McGinn is a fascinating writer, but his reasons for rejecting reductionism here are badly misconceived:
"The brain processes held to constitute conscious experience consist of physical events that can exist in the absence of consciousness. Electricity in the brain correlates with mental activity but electricity in your TV presumably does not - so how can electrical processes be the essence of conscious experience?"
This is like arguing that the information processing performed by a computer program cannot ultimately be reduced to what's going on in the electrical circuits of the computer, because a standard lamp also uses electricity, and there's no information processing going on there!
On the contrary, it's the pattern of information processing, the representation of the external world, and the partial representation of the self, which identifies humans as cognitive systems, and distinguishes them from televisions and standard lamps.
McGinn claims that "reduction is tantamount to elimination...it's like maintaining that people called 'witches' are nothing but harmless old ladies - which is tantamount to saying that there are no witches." Again, however, this is a false analogy. Imagine a comparable statement about the biological cell:
It's like maintaining that biological cells are nothing but systems of interacting molecules - which is tantamount to saying that there are no biological cells.
This clearly doesn't follow. It's perfectly coherent to argue that biological cells are nothing more than interacting systems of molecules, but still exist as objective patterns on that level of structure.
Similarly, it's perfectly coherent to argue that minds are ontologically reducible to brains, but exist as objective information processing patterns on that level of structure.
McGinn begins, however, by rejecting five other common positions in the philosophy of mind: (i) eliminativism (there is no mind); (ii) reductionism (the mind reduces to the brain); (iii) dualism (the mind and the brain interact, but are fundamentally distinct modes of existence); (ii) idealism (only mental entities exist); and panpsychism (every bit of matter has a bit of mentality in it).
After rejecting these approaches, McGinn advocates his mysterian contention that "we just don't have the faculties of comprehension that would enable us to remove the sense of mystery [to the mind-brain relationship]. Ontologically, matter and consciousness are woven intelligibly together but epistemologically we are precluded from seeing how."
Whilst McGinn doesn't use the term 'unification', when he speaks of matter and mind being woven together, he's clearly advocating the notion that the mind and the brain are ontologically unified. His position, then, is to accept ontological unification, but reject epistemological unification.
Now, the distinction between ontological and epistemological unification is a useful one; more's the pity, then, that McGinn doesn't acknowledge that this distinction can be equally applied to reductionist accounts of the mind-brain relationship. Thus, whilst the mind may be ontologically reducible to the brain, it might be impossible to comprehend that reduction relationship; one might endorse ontological reductionism but reject epistemological reductionism.
In response, the question might be posed: why prefer ontological reductionism to ontological unification? The answer is that the relationship between the mind and the brain does not merely reside in correspondence, but consists of a supervenience relationship. This means that there is a many-one mapping between brain states and mental states. Multiple brain states correspond to single mental states; change a brain state slightly by changing the firing frequency of a few neurons, and the mental state remains invariant. But change a mental state, and the brain state must change.
This entails that brain states determine mental states, not vice-versa. The relationship between the mind and the brain is not bilateral or symmetrical, it is top-down. Hence, ontological reductionism is required rather than ontological unification.
McGinn is a fascinating writer, but his reasons for rejecting reductionism here are badly misconceived:
"The brain processes held to constitute conscious experience consist of physical events that can exist in the absence of consciousness. Electricity in the brain correlates with mental activity but electricity in your TV presumably does not - so how can electrical processes be the essence of conscious experience?"
This is like arguing that the information processing performed by a computer program cannot ultimately be reduced to what's going on in the electrical circuits of the computer, because a standard lamp also uses electricity, and there's no information processing going on there!
On the contrary, it's the pattern of information processing, the representation of the external world, and the partial representation of the self, which identifies humans as cognitive systems, and distinguishes them from televisions and standard lamps.
McGinn claims that "reduction is tantamount to elimination...it's like maintaining that people called 'witches' are nothing but harmless old ladies - which is tantamount to saying that there are no witches." Again, however, this is a false analogy. Imagine a comparable statement about the biological cell:
It's like maintaining that biological cells are nothing but systems of interacting molecules - which is tantamount to saying that there are no biological cells.
This clearly doesn't follow. It's perfectly coherent to argue that biological cells are nothing more than interacting systems of molecules, but still exist as objective patterns on that level of structure.
Similarly, it's perfectly coherent to argue that minds are ontologically reducible to brains, but exist as objective information processing patterns on that level of structure.
Monday, February 20, 2012
Clarkson cleared by Ofcom
Last November, Jeremy Clarkson commented on BBC TV's The One Show, that striking public sector employees should be taken out and shot in front of their families. Clarkson's comment provoked 30,000 complaints, and he was later moved to apologise and explain that "I didn't for a moment intend these remarks to be taken seriously."
Now, the phrase, 'X should be taken out and shot', is a well-known example of rhetorical hyperbole. Unless it's uttered by either Don Corleone, a Colombian druglord, or the head of a militaristic dictatorship, it's not meant to be interpreted as a literal piece of advice. Clarkson was not issuing an instruction, he was making a political point in a caustic manner. The fact that 30,000 people still complained, should therefore be seen as the outcome of an epidemiological experiment, designed to obtain a lower bound on the number of people in the UK who suffer from ingrowing skulls.
You can disagree with Clarkson, but to be 'outraged' or 'offended' by the remark, you need to be incapable of discriminating between that which is literal, and that which is ironic or sarcastic.
It is a damning indictment of the insipid idiocracy in which we live, that Ofcom director Christopher Woolard, actually had to point out today that it was "clear to most viewers that his comments were not an expression of seriously held beliefs or views that should be literally interpreted".
The names and addresses of the cretinous 30,000 should be retained, and transferred to the National Health Service, so that precious MRI resources are not wasted on this neurologically regressive cohort.
Now, the phrase, 'X should be taken out and shot', is a well-known example of rhetorical hyperbole. Unless it's uttered by either Don Corleone, a Colombian druglord, or the head of a militaristic dictatorship, it's not meant to be interpreted as a literal piece of advice. Clarkson was not issuing an instruction, he was making a political point in a caustic manner. The fact that 30,000 people still complained, should therefore be seen as the outcome of an epidemiological experiment, designed to obtain a lower bound on the number of people in the UK who suffer from ingrowing skulls.
You can disagree with Clarkson, but to be 'outraged' or 'offended' by the remark, you need to be incapable of discriminating between that which is literal, and that which is ironic or sarcastic.
It is a damning indictment of the insipid idiocracy in which we live, that Ofcom director Christopher Woolard, actually had to point out today that it was "clear to most viewers that his comments were not an expression of seriously held beliefs or views that should be literally interpreted".
The names and addresses of the cretinous 30,000 should be retained, and transferred to the National Health Service, so that precious MRI resources are not wasted on this neurologically regressive cohort.
Saturday, February 18, 2012
Front-wing side-edge vortices
Aerodynamically speaking, a Formula 1 car is an interconnected system of vortices and vortex layers. The vorticity is created by viscous shear in thin boundary layers adjacent to the solid surfaces of the car; such boundary layers are attached vortex layers. The downforce (or lift) generated by a wing is often attributed to the presence of circulation in the airflow around the wing, but the circulation itself is nothing more than the net vorticity in the boundary layers above and below the wing.
When a vortex layer separates from a solid surface, it becomes a free vortex layer, and a separated vortex layer can roll-up into a volume of concentrated vorticity, called a vortex. These vortices possess a low pressure core, in some sort of balance with the centrifugal 'force' of the fluid elements spiralling around the vortex on helical trajectories. Oriented in a streamwise direction, such vortices can be particularly useful, both for the direct generation of downforce, and to act as air curtains, sealing off other low pressure areas.
Now, the front-wing of a car sees the air first, and therefore sets the conditions for the rest of the car, hence the vortices it generates are particularly important. Streamwise vortices are generated by lateral pressure gradients within the front-wing assembly, and these exist (i) across the endplate, (ii) at the transition between the wing-section and the neutral inner-section dictated by regulation, (iii) at the inner tips of the front-wing flaps, and (iv) at the arched sections in the front-wing.
To keep a vortex alive, one has to maintain the correct ratio between axial (streamwise) velocity, and the azimuthal velocity. If the azimuthal velocity gets too high, or the axial velocity gets too low, the vortex can breakdown.
For obvious reasons of commercial confidentiality, Formula 1 does a poor job at publishing its aerodynamic discoveries. Fortunately, however, there has been some academic research on the vortices generated by the front-wing endplates, conducted by Professor Zhang and colleagues at the University of Southampton. On the basis of wind-tunnel flow visualisation and measurement methods, such as Laser-Doppler Anemometry, Zhang et al (2006) claim that in the case of a simple front-wing, (without a rotating wheel in close proximity), the side-edge vortices possess "a low streamwise speed core...This feature is important as the vortex could break down or dissipate quickly further downstream," (p38, Ground effect aerodynamics of race cars, Applied Mechanics Reviews, Vol 59.).
Which brings us to Adrian Newey's Williams FW14/B of 1991/1992, which featured, at a time when the regulations permitted it, long extensions to the front-wing endplates. One might hypothesise that these extensions strengthened and stabilised the front-wing endplate vortices. One method of postponing vortex burst is to connect a vortex to a low-pressure area downstream, and these extensions may have been intended to join the front-wing vortices to the low pressure areas which exist behind the front-wheels. Certainly, on the current generation of Red Bulls, a similar trick is employed at the rear, the side-edge vortices on the diffuser being connected up to the low pressure regions behind the rear wheels.
One also presumes that those extensions were directing the front-wing vortices at a particular region downstream, perhaps the lower edges of the sidepods, both to seal off the low pressure region under the floor, and possibly also to feed the flow which is sucked under the floor in front of the rear wheels, thereby feeding the diffuser side-edge vortices, making one powerful, car-length vortex. One wonders how much such thinking still informs the design philosophy at Red Bull...
When a vortex layer separates from a solid surface, it becomes a free vortex layer, and a separated vortex layer can roll-up into a volume of concentrated vorticity, called a vortex. These vortices possess a low pressure core, in some sort of balance with the centrifugal 'force' of the fluid elements spiralling around the vortex on helical trajectories. Oriented in a streamwise direction, such vortices can be particularly useful, both for the direct generation of downforce, and to act as air curtains, sealing off other low pressure areas.
Now, the front-wing of a car sees the air first, and therefore sets the conditions for the rest of the car, hence the vortices it generates are particularly important. Streamwise vortices are generated by lateral pressure gradients within the front-wing assembly, and these exist (i) across the endplate, (ii) at the transition between the wing-section and the neutral inner-section dictated by regulation, (iii) at the inner tips of the front-wing flaps, and (iv) at the arched sections in the front-wing.
To keep a vortex alive, one has to maintain the correct ratio between axial (streamwise) velocity, and the azimuthal velocity. If the azimuthal velocity gets too high, or the axial velocity gets too low, the vortex can breakdown.
For obvious reasons of commercial confidentiality, Formula 1 does a poor job at publishing its aerodynamic discoveries. Fortunately, however, there has been some academic research on the vortices generated by the front-wing endplates, conducted by Professor Zhang and colleagues at the University of Southampton. On the basis of wind-tunnel flow visualisation and measurement methods, such as Laser-Doppler Anemometry, Zhang et al (2006) claim that in the case of a simple front-wing, (without a rotating wheel in close proximity), the side-edge vortices possess "a low streamwise speed core...This feature is important as the vortex could break down or dissipate quickly further downstream," (p38, Ground effect aerodynamics of race cars, Applied Mechanics Reviews, Vol 59.).
Which brings us to Adrian Newey's Williams FW14/B of 1991/1992, which featured, at a time when the regulations permitted it, long extensions to the front-wing endplates. One might hypothesise that these extensions strengthened and stabilised the front-wing endplate vortices. One method of postponing vortex burst is to connect a vortex to a low-pressure area downstream, and these extensions may have been intended to join the front-wing vortices to the low pressure areas which exist behind the front-wheels. Certainly, on the current generation of Red Bulls, a similar trick is employed at the rear, the side-edge vortices on the diffuser being connected up to the low pressure regions behind the rear wheels.
One also presumes that those extensions were directing the front-wing vortices at a particular region downstream, perhaps the lower edges of the sidepods, both to seal off the low pressure region under the floor, and possibly also to feed the flow which is sucked under the floor in front of the rear wheels, thereby feeding the diffuser side-edge vortices, making one powerful, car-length vortex. One wonders how much such thinking still informs the design philosophy at Red Bull...
Sunday, February 12, 2012
Convergence
It's been New Car Week in Formula 1, with McLaren, Ferrari, Red Bull, Williams, Force India, Toro Rosso, Sauber, and Lotus, all revealing their 2012 protagonists. There was, however, a feeling of anti-climax to the ritual this year. McLaren unveiled something which looked like their 2011 car, but with re-shaped sidepods and a pair of blisters containing the exhaust outlets. And Red Bull initially issued what appeared to be airbrushed images of the RB8 from a Scalextric box, although even the photo-shopping couldn't conceal the letterbox in the nose, through which CVs can be posted to Adrian Newey.
There continue to be detail differences between the cars and their exhaust outlets, but it finally appears as if the Formula 1 regulations are now so restrictive that there is only one optimal solution in the design landscape, and all the teams have converged towards it. As the Red Bull Technical Director put it,
"Regulation restrictions like the lost exhaust are a bit frustrating in truth, because they are exactly that, they are restrictions, they're not giving new opportunities or revenues particularly, they're just closing a door...Regulation changes I enjoy, regulation restrictions I rather lament."
Thus, whilst the technically-inclined Formula 1 fan is perhaps better-informed today than has ever been the case, with Craig Scarborough and Gary Anderson providing massively informative analysis of the new vehicles (on Autosport.com, and in the pages of Autosport, respectively), the crying shame is that there is so little innovation to write about.
Gary Anderson, of course, has joined the BBC F1 team as their technical analyst, and got off to an excellent start by using the ancient technique of pen-and-paper to explain the aerodynamics of contemporary Formula 1 to a metrosexually-scarfed Jake Humphrey. Bravo!
There continue to be detail differences between the cars and their exhaust outlets, but it finally appears as if the Formula 1 regulations are now so restrictive that there is only one optimal solution in the design landscape, and all the teams have converged towards it. As the Red Bull Technical Director put it,
"Regulation restrictions like the lost exhaust are a bit frustrating in truth, because they are exactly that, they are restrictions, they're not giving new opportunities or revenues particularly, they're just closing a door...Regulation changes I enjoy, regulation restrictions I rather lament."
Thus, whilst the technically-inclined Formula 1 fan is perhaps better-informed today than has ever been the case, with Craig Scarborough and Gary Anderson providing massively informative analysis of the new vehicles (on Autosport.com, and in the pages of Autosport, respectively), the crying shame is that there is so little innovation to write about.
Gary Anderson, of course, has joined the BBC F1 team as their technical analyst, and got off to an excellent start by using the ancient technique of pen-and-paper to explain the aerodynamics of contemporary Formula 1 to a metrosexually-scarfed Jake Humphrey. Bravo!
Whitney
So, another music industry star implodes to a singularity.
This will provoke the habitual, systematised music-industry/media response: a form of mourning which includes the re-selling of the rise-and-fall story-template, and the re-issue and marketing of Biggest-Hits albums.
It's In Memoriam, but not as Tennyson would know it.
This will provoke the habitual, systematised music-industry/media response: a form of mourning which includes the re-selling of the rise-and-fall story-template, and the re-issue and marketing of Biggest-Hits albums.
It's In Memoriam, but not as Tennyson would know it.
Wednesday, February 08, 2012
"Our genres of confidence in the world are shattering!"
Turn on to Radio 4 at a random moment during the day, and chances are that you'll alight upon one of three things: (i) a dreary, unimaginative analysis of political or economic news; (ii) a deeply earnest play; or (iii) a pompous discussion by self-important non-entities of pseudo-philosophical issues.
The last category, however, often unwittingly falls into the 'most original comedy' category, and a shining exemplar such can be found in the February 8th edition of 'Thinking Allowed' (geddit?). Here, 'cultural theorist' Lauren Berlant discharges the following array of dazzling intellectual gems:
"I think it's important not to think of the working class as having no fantasies."
"I don't think you'd want to normalise precarity so much."
"The historical present makes itself available to you when there's a crisis in the reproduction of life."
"Everyone invests in objects that organise the relation of fantasy to how they live...the working class's are in the present, the middle class's are in the future."
"In a crisis time, many people's sense of the precariousness of the present becomes present to them."
"Our genres of confidence in the world are shattering."
To criticise such meaningless, generalised drivel, to point out the lack of well-defined terms, the lack of logical reasoning, and the lack of verifiable statements based upon hard evidence, would be to potentially crush this delicate form of performance art in its nascent stage. Even in a time of such 'precarity', we must find more money to fund the lifestyle of these modern sages, and reward them with ever greater slices of publicly-funded airtime.
The last category, however, often unwittingly falls into the 'most original comedy' category, and a shining exemplar such can be found in the February 8th edition of 'Thinking Allowed' (geddit?). Here, 'cultural theorist' Lauren Berlant discharges the following array of dazzling intellectual gems:
"I think it's important not to think of the working class as having no fantasies."
"I don't think you'd want to normalise precarity so much."
"The historical present makes itself available to you when there's a crisis in the reproduction of life."
"Everyone invests in objects that organise the relation of fantasy to how they live...the working class's are in the present, the middle class's are in the future."
"In a crisis time, many people's sense of the precariousness of the present becomes present to them."
"Our genres of confidence in the world are shattering."
To criticise such meaningless, generalised drivel, to point out the lack of well-defined terms, the lack of logical reasoning, and the lack of verifiable statements based upon hard evidence, would be to potentially crush this delicate form of performance art in its nascent stage. Even in a time of such 'precarity', we must find more money to fund the lifestyle of these modern sages, and reward them with ever greater slices of publicly-funded airtime.
Saturday, February 04, 2012
Snow and horseshoe vortices
With snow blanketing much of Western Europe at the moment, here's a chance to do some aerodynamic investigation in the field.
Somewhat counter-intuitvely, it turns out that under certain conditions snow fails to accumulate on the windward side of a tree. The reason for this is that the snow at the base of the tree is scooped out by a horseshoe vortex.
A high-pressure stagnation point forms on the windward side of the tree, and this creates an adverse pressure gradient for the flow approaching the tree. The adverse pressure gradient causes the boundary layer of the flow across the ground to detach and roll-up into a vortex. (The photo and first diagram here are taken from Internal flow: concepts and applications, p117, Greitzer, Tan, and Graf, 2004). The vortex is then bent down the sides of the tree, where it also scoops out some snow.
Similar vortices can be found on cars or aircraft at the junctions between a wing-section and the endplate or fuselage.
Somewhat counter-intuitvely, it turns out that under certain conditions snow fails to accumulate on the windward side of a tree. The reason for this is that the snow at the base of the tree is scooped out by a horseshoe vortex.
A high-pressure stagnation point forms on the windward side of the tree, and this creates an adverse pressure gradient for the flow approaching the tree. The adverse pressure gradient causes the boundary layer of the flow across the ground to detach and roll-up into a vortex. (The photo and first diagram here are taken from Internal flow: concepts and applications, p117, Greitzer, Tan, and Graf, 2004). The vortex is then bent down the sides of the tree, where it also scoops out some snow.
Similar vortices can be found on cars or aircraft at the junctions between a wing-section and the endplate or fuselage.