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: : Wind : :

What is Wind?

Direction and speed of current wind

Anemometer

Image N°1
Anemómetro, sensor de velocidad y dirección del viento

The wind is the movement of the air that's present in the atmosphere, specially in the troposphere, produced naturally.

In the Earth, the variations in pressure and temperature are due, mostly by the uneven distribution of the solar warming, with the different properties of the surfaces of the planet and the oceans. When the adjacent region's temperature differ, the cold air, because is more dense and it tends to go down towards the hot air mass, and the hot air, and this because is less dense it goes up. That's why the air masses circulate, and that phenomenon is called "wind". The generated winds are highly disturbed by the earth's rotation.

In summary, the wind is a product of:

1. The earth's movement of rotation and revolution that origin considerable in solar radiation

2. The uneven air warmth, that produces the pressure diferences.

The winds can be clasiffied in four main classes: dominant, stational, local and last, cyclonic and antyciclonic.

Wind speed

The oldest instrument to know the wind direction is the weather vane, that with the help of the compass rose, defines the wind origin, that is, the direction from where they blow.

The speed and direction of the winds is measured with the anemometer (image N° 1), but nowadays we're incorporating the digital sensors (ultrasonic sensor). They both register the speed and direction through time, also, we use balloons or radiosonde, this last instrument helps to graphic the temperature and humidity profiles in the different levels of the Troposphere, making about 15 Km height.

The wind intensity is ordered according to its speed, using the Beaufort scale. This scale is divided in several stretches according to its effects ir caused danages, from calm air to category 5 hurricanes and tornadoes.
The marines and the meteorologists use the Beaufort scale to indicate the wind speed. It was designed in 1805 by the Irish hydrographer Francis Beaufort. It's original denominations were modified later.

The dangerous stated notices for small vessels are usually emmited for winds of scale 6.

Beaufort Scale

Wind
Speed
(KmPH)

Wind
Speed
(MPH)
Indicators
Used Terms in the NWS Predictions (National Meteorological Service)
0
0-2
0-1
Calm; Smoke rises vertically.
Calm
1
2-5
1-3
The direction can be noticed by the direction of the smoke, but not by the weather vanes.
Light air
2
6-12
4-7
Wind felt on exposed skin. Leaves rustle, vanes begin to move.
Light breeze
3
13-20
8-12
Leaves and small twigs constantly moving, light flags extended.
Gentle breeze
4
21-29
13-18
Dust and loose paper raised. Small branches begin to move.
Moderate breeze
5
30-39
19-24
Branches of a moderate size move. Small trees in leaf begin to sway.
Fresh breeze
6
40-50
25-31
Large branches in motion. Whistling heard in overhead wires. Umbrella use becomes difficult. Empty plastic garbage cans tip over.
Strong breeze
7
51-61
32-38
Whole trees in motion. Effort needed to walk against the wind.
High wind,
Moderate gale,
Near gale
8
62-74
39-46
Some twigs broken from trees. Cars veer on road. Progress on foot is seriously impeded.
Gale,
Fresh gale
9
75-87
47-54
Some branches break off trees, and some small trees blow over. Construction/temporary signs and barricades blow over.
Strong gale
10
88-101
55-63
Trees are broken off or uprooted, saplings bent and deformed. Poorly attached asphalt shingles and shingles in poor condition peel off roofs.
Storm,
Whole gale
11
102-116
64-72
Widespread damage to vegetation. Many roofing surfaces are damaged; asphalt tiles that have curled up and/or fractured due to age may break away completely.
Violent storm
12
117 o ms
73 ms
Very widespread damage to vegetation. Some windows may break; mobile homes and poorly constructed sheds and barns are damaged. Debris may be hurled about.
Hurricane-force

General Circularion of winds

General Circularion of winds

Image N°2
Atmosphere general circulation

Our atmosphere is heated by the direct effect of sun exposition.

In the equatorial region is where most of the heat is received because they come perpendicularlly, distinctively from the polar regions.

The uneven of the warming in the different regions produces atmospheric movements in a planetary scale. Due to the elevated temperatures of the equatorial zones a system known as Hadley cells (image #2) is produced, that's started by the ascendant movement of the air masses, these are accumulated in the higher atmospheric levels, and from there they diverge to the high latitudes, descending in the 30° of latitude, approximatelly, that originates a potent anticyclone called Subtropical High Pressure. This system presents itself in the northern hemisphere as well as the southern.

Another process that affects the wind circulation, very similar to the previous, is produced in the poles, forming the Ferrel an polar cells. By the effect of rotation of the Earth its produced the Coriolis Force, the winds that blow in the Northern hemisphere are deviated to the right and in the southern hemisphere to the left, creating different types of circulation, like the trade winds of the NE and the SE and the winds of the W. This effect is bigger int he poles and smaller in the equator.

Types of winds: We have 3 types of winds: The planetary winds, the regional winds and the local winds.

  1. The planetary winds, global or constants are generated mainly as a consequence of the earth's rotation movement, that originates an uneven warming in the atmosphere by insolation and proceed from action centers arranged in latitudinal stripes of high and low pressure, that is, of anticyclones and depresions. These belts are arranged approximatelly in the equatorial latitudes, the subtropical and the polar.
    1. Intertropical Convergence Zone (ZCIT), is a belt of low pressures in equatorial latitudes, and is determined by the Earth's rotation, that generates what is known as equatorial terrestial swelling, better noticed, by its density, in the oceans than in the continents, and even more noticeable in the atmosphere.
    2. Subtropical Divergence Zones, are cold air zones, they proceed from the great heights of the intertropical convergence zone, that is, the equatorial stripe, and they originate, at the same time, the trade winds, that return to the equator in low heights, and to the western winds, that increase their speed as they increase their latitude.
    3. Polar Convergence Zones, are low pressure zones that attract the winds coming from the subtropical latitudes. These winds bring warmer and moister air masses that loose condensation (rains, dew and frost) as they find colder air with the increase of latitude.

    These winds known as trade winds in the intertropical latitudes and the west winds in the temperate zones.

      Marine Breezes

      Image N°3
      The marine breezes:
      A) Day marine breeze
      B) Night land breeze

 

  1. Regional winds, are determined by the land and sea distribution, as well as for the high continental relieves.
  2. Local winds, present a movement from zones of high pressure to low pressure zones, determining the dominant winds and the reigning winds of a more or less wide area.
    These types of winds are the following:

Wind direction

Compass Rose

Compass Rose with 16 courses. A compass rose is a circle with the divisions of the courses marked from the horizon circumference

The direction of the wind depends on the pressure distribution, for it tends to blow from the region of high pressure to the regions with lower pressures.

Its called wind direction to the point of the horizon where it comes or blows. To distinguish them we use the main courses names of the compass, using the well known compass rose. As we can see on picture #4, the four main points belong to the cardinal points: North (N), South (S), East (E) y West (W). There are 32 intermediate, although the main and mostly used are the following with their equivalence in azimuth grades.

Panama Wind

The high pressures or the semipermanent Northern Atlantic anticyclone affects sensitively the climate conditions for the country, because from this system are generated the trade winds from the northeast that in the lower layers of the atmosphere come to Panama.

The confluence zone for both hemisphere's trade winds (north and south) affects the weather in the places that fall under its influence, specifically in the tropical regions. For our country, it's got special importance the Intertropical Convergence Zone (ZCIT), because its north-south migration produces the rainy and dry seasons, main characteristic of the panamanian climate.

In the next table we observe the monthly historic average for the 10 m wind speed for the period of 1974-2005 in the Bocas del Toro, David, Santiago, Anton, Los Santos and Tocumen stations.

Monthly Historic 10m Wind Average (m/s) Period 1974-2005
Station
Jan
Feb
Mar
Apr
May
Jun
Jul
Ago
Sep
Oct
Nov
Dic
Accumulative Total
Bocas del Toro
2.1
2.1
1.9
1.9
1.7
1.7
1.8
1.8
1.6
1.7
2.1
2.1
1.9
David
2.5
2.9
2.8
2.2
1.7
1.6
1.6
1.7
1.7
1.7
1.6
1.8
1.9
Santiago
2.5
3.0
2.9
2.5
1.8
1.6
1.5
1.6
1.7
1.9
1.6
1.8
2.0
Antón
3.9
4.4
4.4
3.7
2.2
1.7
2.2
1.9
1.4
1.4
1.9
2.8
1.8
Tocumen
2.1
2.4
2.3
2.2
1.6
1.5
1.5
1.5
1.5
1.6
1.6
1.8
2.0

Behavior of the wind in the different slopes (Atlantic & Pacific), for the period 1974-2005.

Pacific Slope

In the Pacific slope, were used the average wind speed data from the David station. The analysis of the graphic indicates us that February and March are the months that historically present the higher monthly average speed at 10 m, decreasing by the months of May through November.

Caribbean Slope

In the caribbean slope, we used the Bocas del Toro station for the graphic, maintaining the higher 10 m winds historic average in the months of November, December, January and February, decreasing from March through October, having as a minimum the month of September.

 

 

 

 

 

 

 

Annual 10 m Wind Map

We present an annual map for the 10 m winds, that indicates the different frequencies for direction (%) and speed (m/s) of the Bocad del Toro, Santiago, Tocumen, Anton, David and Los Santos stations for the period of 1973-2002.

Annual 10 m Wind Map

References:
http://es.wikipedia.org/wiki/Brisa
http://es.wikipedia.org/wiki/Viento

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