Local Winds

LOCAL WINDS: Local winds are small scale phenomena produced purely by local factors due to topographical peculiarities and local temperature differences. These winds are put in the category of tertiary circulation (under primary circulation planetary wind comes i.e. trade winds, Westerlies and Easterlies and under secondary circulation tropical and extra-tropical cyclones come). Characteristics: (i)

Since, it is locally generated so, its zone of influence is quite limited.

(ii)

Its vertical extent is limited to only a few thousand meters.

(iii)

These local winds have very individualistic characters; hence they are given

different names in different localities. (iv)

Though, these local wind systems have little climatological importance,

nevertheless, it play very significant role in the weather and climate of a particular locality. There are two categories of local winds viz…. (1) Hot winds and

(2) Cold winds.

Land and Sea Breeze Land and Sea Breeze local winds are found in coastal regions, caused by diurnal heating (causes sea breeze) and nocturnal cooling (causes land breeze). These winds also some time called as monsoon because of reversal characteristics.

Land Land

Land

Ocean

Ocean

Fig. A (Sea breeze)

Fig. B (Land breeze)

The land mass has the property of heating faster than the adjacent water mass, hence, during the day time when both surfaces (land & water) get exposure, land mass gets heated faster than water body, consequently, the warm land surface also heats overlying air, thereby, lowering air density. And the air, above the water surface in relatively cooler (because water surface itself comparatively cooler), resultantly horizontal air pressure gradient develops between land and

water and isobaric surfaces bend upward which allow the cooler air to move across the coast line from sea to land. And this on shore wind is popularly known as sea breeze (as shown in fig A). Unlike day in the night winds reverse its direction because due to faster radiation land mass cools faster than water mass. Thus the land become cooler and hence overlying air also cooled. On the contrary, the water mass is relatively warmer (and air over it is also warmer) hence, this time pressure gradient is directed from land to sea, therefore there is a gentle flow of air from land to sea. This off-shore wind is called the land breeze (as shown in fig B). This phenomenon is largely controlled by latitude and time of the year. Mountain and valley breeze: During the day time the valley surface heated and this heated surface heats overlying air, consequently, this heated air starts to rising along the valley. This upslope breeze is called as valley breeze (and also anabatic wind). Some times these valley wind also give birth to cumulus cloud near mountain peaks or over escarpments, therefore some times these regions also experience afternoon rainfall.

Fig. A (Valley breeze)

Fig. B (Mountain Breeze)

On the contrary, in the night the mountain slops cool more rapidly as result of which the cool air drains into the valley below. This down slope air is known as mountain breeze or katabatic wind. This mountain breeze also engender radiation fogs in the valleys specifically during the winter Important hot local winds of the world Foehn: It is a general term given to a warm and dry wind on the lee site of a mountain range. As soon it descends along the mountain slope, it heats adiabatically; this ultimately raised

the temperature of adjacent areas. This rise of temperature some times conducive, but some times disastrous. Therefore, these winds play a great role in changing local weather.

Foehn wind Foehn wind has different name in different parts of the world as for example: 1.

Chinook: Popularly known as snow-eater. Specifically during the winter season on the

eastern slope of Rocky mountain in Wyoming and Montana the Chinook winds increase temperature (around 200C) in short span of time which reduced the severity of winter in this region 2.

Yamo-Japan:

3.

Tramontane-Central Europe

4.

Norwester-New Zealand

5.

Berg – South Africa

6.

Santha Ana – California (USA)

7.

Zonda – Argentina

Depression winds: These depressions are the topographical features and the winds associated with are known as depression winds. These depression winds originate in tropical region and move towards polar region are warm winds and another one which originate in polar region and move towards tropical region are called cold depression winds. Warm depression winds Sirocco: It is hot, dry and dusty wind blowing from Sahara Desert over central Mediterranean and southern Italy in the form of an advancing depression. The sirocco which extends to southern France and Italy is warm and humming, inasmuch; it picks up moisture from over the Mediterranean Sea and popularly known leveech in Spain and lesty in Madeira and

Morocco. The same wind in Victoria (Australia) is known brickfielder, khamsin in Egypt and gibli in Tunisia. Simoon has also same characteristic blowing in Iran. But these winds are very dusty hence, very suffocating too, causing breathing problem. Shamal is a similar north east wind blowing in Mesopotamia and the Persian Gulf. Harmattan wind originating in Sahara desert and blowing towards west cost of Africa has unique characteristic. Since it contains some amount of moisture procure rainfall in West African region and provide relief to the inhabitants of the concerning areas. Therefore it is also known as doctor wind. Convection winds: Due to intense heating of the grounds engender uprising dusty winds, which commonly known as dust devil. This is the special characteristic of deserts and semi-arid areas where the grounds are dry and high surface temperature foment strong updrafts. It is just like miniature tornados. Since, it is very intense therefore, when it rises it carries colossal quantity of dust, hence, it is called dust devil. Cold local winds: 1.

Mistral: This is cold and dry wind blown into the western Mediterranean basin from high

elevation to north and channeled down along Rhone valley, during winter months 2.

Bora: Along the eastern shore of Adriatic Sea a cold and dry north-easterly wind blowing

from the mountains is called bora. 3.

Blizzards: This term is widely used for a very strong cold wind accompanied with mass

of dry powdery snow and ice-crystals in higher latitudes (Antarctica). 4.

Buran: Extremely cold north-easterly or easterly wind blowing in eastern Russia and

central Siberia are called Buran. Some other local cold winds are viz….. i)

Norther: Occurs in winter and blown from Texas towards gulf of Mexico

ii)

Tehuantepecer: Blowing in southern Mexico and north central America

iii)

Purga: Russian Tundra region:

iv)

Bisa: France

v)

Levanter: Span

vi)

Friagem: Amazon Valley

vii)

Haboob: Sudan

viii)

Papmpero: Argentina and Uruguay.

ix)

Surazo: Brazil

x)

Takuwind: Alaska (USA) Although, these local winds (either cold or hot) have very little climatological importance,

nevertheless the play important role in local weather phenomena. Abreast, they exert a great stress on flora and fauna of concerning regions. Some winds have negative influence, while, few of them have salutary effect on local weather system. Apart from this these local winds are also transport atmospheric pollutions from one region to another region. Hence, we can say that these local winds have distinguished role to play for local weather systems.

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Map showing local winds: Cold wind Warm wind

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1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12.

Chinook Norther Pampero Berg Harmattan Sirocco Levech Mistral Bora Purga Buran Brickfielders