The knowledge of how the wind works may help us understand what we see on the water and why. That knowledge may just be what gets us across the finish line ahead of that other boat.

THE Wave Generator

Besides the obvious fact that wind is the prime generator of waves, other aspects of the wind process are important to a paddler. The effect of wind on waves is explained in the section on waves.

Corner Winds

Whenever the wind encounters an obstacle, in the Northern Hemisphere, it tends to shift to the left and to strengthen. Ths is true in the case of islands, capes and points. This is due mostly due to friction of the wind with the surface, be it water or with land). The concept of these Corner Winds occurs in several places in Environment Canada marine web sites, however, it does not appear to be an otherwise widely documented phenomena.

The angular difference in wind deflection can be from 15 to 20 degrees.  Land has higher friction with air and the deflection can be an additional 15 to 20 degress to total 30 to 40 degrees.

In addition, this effect is more pronounced in stable air than in unstable air.  Stratus ceilings are indicative of stable air (the stable air resists surface wind pushing up over an island.)  Convective clouds are unstable (the wind meeting an obstacle, the island, is more likely to deflect over the island).

Deflection Rules

High above the earth's surface, the wind is not affected by friction and mostly blows freely.  Over the ocean or over land, the friction between the water or land and the water deflects it to the left in conjunction with the Coriolis Effect of the earth's rotation.

When this deflected wind is converged with the ambient wind it causes the wind speed to increase.

Convergence

When the wind is blowing parallel to the shore, it creates a narrow band in which the wind picks up speed or drops off sharple, depending on wheter the shore is on your right or your left with the wind at your back.

When the shore is on your right and less than 5 km away, the convergence effect says the wind will be approximately 25% stronger. The wind will shift slightly left due to friction, as above, and will join forces with the ambient sea wind.

Divergence

The effect is opposite with the shore on your left (with the wind at your back) as the wind is being deflected away from the ambient wind and creating a divergence, thereby lessening the wind speed by up to 25%.

 

 

 

Intersection

When winds are exiting an inlet and meet with a cross inlet ambient flow of wind, the meeting winds become convergent, will strengthen and become turbulent.

 

  

Gap Winds

Similar to funnelling, air movement can be redirected and strengthened as the wind is confronted with a land mass that has an opening, such as a river valley or valley between peaks.  The Port Alberni Valley and the Nitinat Valley on Vancouver Island are very pronounced gap effect areas.  Also Dirunal winds that rise over the land are funnelled through gaps (the Nitinat Valley) in afternoons attracting hundreds of surf sailers to the narrow lake.  This is a combination of Gap Wind and Diurnal Wind movement.

Onshore Breezes

The suns radiation produces much more heat during the day than a water mass, causing the air above the land to warm.  This warm air rises and is replaced by cooler air from the water creating an onshore flow during the daytime. 

As the sun warms the land into the afternoon, the winds freshen and veer (change direction clockwise). This can have the affect of creating an along shore current.  (See Currents in the wave section)

At night the land radiates its heat away much quicker than the water. The air above the land will subside (sink) while the air above the water will rise. The breeze will change to flow from the land towards the space left by the rising air over the sea.

Channelling

Winds are some times aligned by channels in the land such as parallel ridges or valleys, river courses, between islands, etc.  Natural topigraphical features 'channel' the wind causing it to 'appear out of nowhere' and be much stronger than any ambient wind.

 

 

 

 

Funnelling

Winds that are constricted or forced through a narrow funnel shaped gap are said to funnel.  The wind speed will be increased in accordance with the wind strength and the local topography. 

In stable air, all the above effects are more pronounced as the air mass resists vertical air movement.  In unstable air, ie after a cold front, the atmosphere does not resist vertical movement and air can rise over obstacles and terrain.

 

Fog

 

While fog may be out of place in this article on wind, it is the movement of air or lack of movement that causes the fog that affects paddlers. This may be a novel topic for some of the Queensland folks or the Hawaiins, but it is a common influence in the temperate zones of the earch.

There are several types of fog.  All fog is caused by the relative humidity of air reaching 100% either by the cooling of air to its saturation point (dewpoint) or addng moisture to the airmass raising the relative humidity to its dewpoint. The result is the same.  The saturated air cannot hold any more water vapour and it changes from a vapour to a liquid. Microscopic drops of water from the air form a cloud or fog as we call it when its at the surface.

The most persistent type of fog is known as Advection Fog and is created by warm moist air blows over cooler waters. The cold water cools the air to the dewpoint and water vapour condenses forming fog. On the coasts this phenomenon is also known as Sea Fog. This is a common phenomenon in the summer on the east and west coasts of Canada. 

Sea fog is sometimes affected by the air over coastal land being heated during the day from the sun, creating an onshore breeze.  This breeze moves the saturated cool air over some coastal communities keeping them in the fog for days at a time. The heat from the sun may raise the relative humidity and we say, the fog is being "burned off".

The next type of fog is known as Radiation Fog and forms over land when the land cools or radiates its heat away) in the absence of sunlight at night.  This cool land affects the air above it and forms condensation. This usually burns off with the sun heating the land.

When wind is forced aloft by a mountain range or otherwise rising ground, the air is forced to cool to below its dewpoint creating condensation.  This fog type is known as Upslope Fog.

Another type of fog forms on rainy days when the relative humidity reaches 100% due to rainfall, resulting in condensation of airborne water vapour forming fog.

A GPS, good eyes, good ears and a local knowledge are the best cures for fog.  So is staying ashore!