What is Eckman's Effect?

Question

As far as I know it's to do with rainfall over tea plantations, can anyone shed any more light on it

Thanks to everyone who answered.

1OFSELBYS - Excellent answer as always, have learned much from your wealth of experience, hope you get chance to answer more meteorology questions. I was aware of the effect you described although didn't know what it was called.

I'd heard mention of the Eckman Effect in respect of trees and tea plantations although this is perhaps not quite the correct term for it.

BELLADONNA - This was the type of info I was looking for - thanks for that.

Answer 1

There are different names for patterns in different materials. Eckman Spirals are the patterns found in wind. Because you can not see wind it is difficult to appreciate Eckman Spirals but a very similar effect is evident in water, these are known as Von Karman trials. To demonstrate these in water place a upright stick in a fast flowing stream, the patterns which are created are very similar to Eckman Spirals in wind.

Vagn Ekman 1874-1954 was an oceanography, who gave a theoretical description of the consequence of the Corriollis effect on ocean currents. He stated that surface currents are deflected to the right of the wind direction.

An understanding of Ekman's theories can be for useful in Permaculture. Either using it positively or avoiding its negative effects. Eckman's Effects are usually associated with stands of trees, or shelter belts. Wind approaching trees is compressed as it climbs above them, then the consequential drop in pressure on the lee of the trees creates a downward Ekman's spiral. This is a negative effect in terms of wind on crops because the wind is speeded up which results in crop damage. This is typically twenty times the height of the obstruction away.

A positive effect on a larger scale such as forests on mountainous regions is the increase in rainfall which we know is one of the major limiting factors in vegation growth.

Studies in Holland and Sweden reveal that forty percent of rainfall measured down wind of trees of more than forty feet tall is caused by the above effect.

A far more modest effect can be created by planting condensing trees such as lombard poplars. Moist morning air
condenses freely on cool branches.

In some desert regions it has been found that even hanging nets above collection gutters will collect enough moisture from the air to allow a modest amount of vegetation to flourish. Which in turn collects more moisture so you have more and more moisture. Plants are then facilitated in growing large enough to produce shade, thus reducing evaporation and making the whole area more moist.

Cloud seeding is a form of weather modification. In order for water droplets to form they require something to form a nucleus. This usually consists of dust particles blown into the air. It has also now been found that air pollutants make excellent nuclei.

I argue that Ekman spirals actually spiral down, therefore to seed the clouds you would need to use thermals. Thermals are warm air rising from a well illuminated area such as cliffs and bare rock. Imagine the red indian stood on the cliff top doing his rain dance, thermals rising and large amounts of dust from the fire being carried by the thermals upwards into the air creating the required nuclei. It has also been noted that fine dust particles from tea plantations have a similar effect.

Answer 2

A lot of your readers are terribly confused on what the Ekman (not Eckman) spiral is. Very simply put, as you go up from the earth's surface the effect of friction decreases and the net forces on the wind direction change such that the wind vector spirals towards a more geostrophic balance. Mathematically, it is a trivial problem to develop. It also describes the change in ocean currents with depth.

Answer 3

Ekman spiral effect
In oceanography, theoretical description of a consequence of the Coriolis effect on ocean currents, whereby currents flow at an angle to the winds that drive them. It derives its name from the Swedish oceanographer Vagn Ekman (1874–1954).

In the northern hemisphere, surface currents are deflected to the right of the wind direction. The surface current then drives the subsurface layer at an angle to its original deflection. Consequent subsurface layers are similarly affected, so that the effect decreases with increasing depth. The result is that most water is transported at about right-angles to the wind direction. Directions are reversed in the southern hemisphere.

Answer 4

It refers to a structure of currents or winds near a horizontal boundary in which the flow direction rotates as one moves away from the boundary. For everything you need to know go here: http://en.wikipedia.org/wiki/Ekman_spiral.

Answer 5

"American in a foreign country"-against Me! "All-American woman"-Carrie Underwood "Breakfast in u.s."-Supertramp "Cupid's Chokehold/Breakfast in u.s."-fitness center type Heroes "TRANSAMERICA"-MATT AND ISOM "lost in u.s."-Alice Cooper

Answer 6

http://www.eckmanfineart.com/learn.html