Understanding Katabatic Winds

[Caprelous 217]

Some of us have experienced a situation when wind blowing in our face whilst stalking an animal and suddenly it spooks getting wind of us ,which is hard to explain ,how can a deer sense you when wind is coming towards us. even in light wind conditions,

 

The following may go a little way in understanding what happens when faced with Katabatic Winds. and Anabatic winds

 

 

Katabatic winds

Katabatic wind (from the Greek: katabaino - to go down) is the generic term for downslope winds flowing from high elevations of mountains, plateaus, and hills down their slopes to the valleys or planes below. Katabatic winds exist in many parts of the World and there are many different names for katabatic winds depending where they are located and how they are formed.

 

Warm, dry katabatic winds occur on the lee side of a mountain range situated in the path of a depression. Examples for these descending, adiabatically warmedkatabatic winds are the Foehn winds.

 

Cold and usually dry katabatic winds, like the Bora, result from the downslope gravity flow of cold, dense air. Katabatic flows slumping down from uplands or mountains may be funneled and strengthened by the landscape and are then known asmountain gap wind such as the Santa Ana, mountain breeze or drainage wind. The gentler katabatic flows of hill slopes produce frost hollows. Mountain breezes are part of a local wind system. When the mountainside is heated by the Sun the mountain breeze will break down, reverse and blowing upslope. These winds are known as valley wind or anabatic wind.

 

However, katabatic winds might also reach gale force as an outblowing wind over ice-covered surfaces in Antarctica and Greenland, where the wind may be extremely strong and gusty near the coasts and less severe in mountain regions.

 

Most katabatic winds (except the Foehn) are more or less the result of air in contact with upper level ground is cooled by radiation, increases in density, and flows downhill and along the valley bottom. For example radiation cooling during nighttime can cause a katabatic flow in the early morning when a pool of cold, high elevation air begins to descend beneath warmer, less dense air. This effect is enhanced during winter over snow covered surfaces and after dry, clear nights. These types of winds can reach velocities of up to 4 meters per second. The rush of cold air down the slopes rapidly decreases the surrounding air temperature as it speeds down the topography to the valleys and planes below it.

 

Many strong katabatic winds are synoptically triggered or are activated by large scale weather features such as a high pressure system over high elevations, as in Greenland, in California or, for example, the fjords of Norway.

 

An anabatic wind, from the Greek anabatos, verbal of anabainein meaning moving upward, is a wind which blows up a steep slope ormountain side, driven by heating of the slope through insolation.^[1][2] It is also known as an upslope flow. These winds typically occur during the daytime in calm sunny weather. A hill or mountain top will be radiatively warmed by the Sun which in turn heats the air just above it. Air at a similar altitude over an adjacent valley or plain does not get warmed so much because of the greater distance to the ground below it. The effect may be enhanced if the lower lying ground is shaded by the mountain and so receives less heat.

The air over the hill top is now warmer than the air at a similar altitude around it and will rise through convection. This creates a lower pressure region into which the air at the bottom of the slope flows, causing the wind. It is common for the air rising from the tops of large mountains to reach a height where it cools adiabatically to below its dew point and forms cumulus clouds. These can then produce rainor even thunderstorms.^[2]

Anabatic winds are particularly useful to soaring glider pilots who can use them to increase the aircraft's altitude (this necessitates flying through cloud which in some countries such as Australia is illegal).^[3] Anabatic winds can be detrimental to the maximum downhill speed of cyclists.

Conversely, Katabatic winds are down-slope winds, frequently produced at night by the opposite effect, the air near to the ground losing heat to it faster than air at a similar altitude over adjacent low-lying land.

Edited December 5, 2011 by Caprelous

[Malt 379]

Not sure if it's applicable in this context, but the opposite is an anabatic wind is it not? ie: in which the air flows up a slope creating a breeze?

[Caprelous 217]

Not sure if it's applicable in this context, but the opposite is an anabatic wind is it not? ie: in which the air flows up a slope creating a breeze?

 

Correct its where the wind flows upwards taking your scent with it then flows back down behind the deer thats spooked

[martin 332]

This happens a lot in the sort of land I stalk which consists of a lot of small valleys,the winds are never going one way,so sometimes it seems best to forget about the wind altogether.

 

M

[tegater 789]

Another interesting thread Stuart.

 

When I first started stalking, and studying wildlife genrally, these were simply called diurnal winds, and it was explained how these winds would fall downhill at night and early morning, and travel uphill, as the ground warms up.

 

Yours is a more in depth explanation.

[skycat 6,174]

Very interesting indeed Thanks for posting.

[Squirrel_Basher 17,100]

Good topic mate ,glad you stayed .

[MrBarnDoor 1]

Just joined this forum, and am being educated already! Very informative and gives one explanation of what happened to me earlier this year... or rather as my mates will no doubt say... another excuse in my armoury!

 

Cheers

[seprim 32]

Another nice post Caprelous

[matt_hooks 188]

The info on katabatic and anabatic flow is interesting, but not entirely sure how you would use it to explain an upwind beast scenting you.

 

There are some places I know where the wind at the bottom of the valley can be the exact opposite of the wind half way up. That's often due to an influx of air from a hanging valley or some other funneling effect. That can seriously b####r up your stalk. You're happily trotting along towards a herd of bambi, wind in your face, then suddenly you feel the wind swing round to your back and herd of bambi disappears into the sunset.

 

For the "wind in your face but they still spot you" moment, I'd say it's more likely they spot movement, or hear a noise, rather than actually scenting you.

Edited January 17, 2012 by matt_hooks