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: : Solar Shine : :

Average Duration of Sunlight

Solar Brightness

The duration in hours of sunlight, or heliophany, represents the total time of direct sunlight exposure over a location between dawn and dusk. The total amount of hours of sunlight that a place receives is one of the facts that determine the weather in this location. This meteorological aspect is important in almost every form of human activity or enterprise. Sectors such as agriculture, forestry, tourism, construction, sports and energy depend and schedule the accomplishment of their programs and future activities on the perspective of having enough hours of sunlight during the day.

An adequate knowledge of the sunlight rate also allows an estimate of the cloudiness and solar radiation in order to have an idea of the possibilities that a country has of taking advantage of the sunlight energy.

The heliographer is the instrument that allows us to measure the duration of sunlight. The one we see in this picture consists of a crystal sphere that concentrates the sun's rays and burns a belt subdivided in time intervals and as the sun inclination varies, it burns the belt. While there is a decrease in sunlight intensity, either due to cloudiness or for other reasons, the belt stops getting burned. This allows us to register how many hours of sunlight there are throughout the day.

Mapa de Brillo Solar Anual

The isohel annual map shows the spacial distribution of the average solar shine regime in the national territory. In the Pacific coast you can see the highest values, specially in the Azuero Peninsula and Cocle, and at all of the coastal line between Chiriqui and Veraguas. Over the central elevations, in Portobelo and Kuna Yala, the average solar shine duration values are below 1500 hours per year.

In February you can notice a substancial increase in the percentage of solar shine in all of the Isthmus Pacific sector, coincidentally with the existing conditions in the dry period of the region.

In May, when is the transition to the raining season, the solar shine values decreases as the nubosity increases in all the national territory. The isohel distributions show the lower varlues in the mountain areas and the high values towards the southern region with maximums towards the coastal zones in Chiriqui. October, representative month of the rainy season, presents a generalized decrease in the percentage and duration of the solar shine in the country. The presence of the Intertropical Convergence Zone, together with the cloudy developments and intense precipitations, favors the reduction of this parameter.

Historic Average of the monthly total solar shine by station
Period 1972-2008
Station Jan Feb Mar Abr May Jun Jul Aug Sep Oct Nov Dic Total Acum.
TOCUMEN 217.5 210.8 216.4 180.4 128.1 99.4 111.6 115.3 113.6 117 126.5 170.4 1807
ANTÓN 246.8 236.8 246.1 207.2 149.4 99.6 114.3 116.2 113.8 119.6 128.8 188.6 1967.2
LOS SANTOS 256.4 244.8 268.6 228 162.9 120.4 129.3 131.3 122.8 136.2 153.8 202 2156.5
SANTIAGO 237 243.8 248.4 200.1 160.9 124.2 133.9 139 127 129.6 138.5 179.5 2061.9
DAVID 275.7 261.9 269.7 215.7 164.2 129.4 141 148.4 133.8 139.8 153.8 218 2251.4
BOCAS DEL TORO 133.2 128.7 165.1 141.5 141.5 121.8 102 114.1 132.8 140.6 116 118.7 1556

The next chart shows the historic monthly behavior for the solar shine in 6 type A stations from 1972 to 2008 (36 years of analyzed data). Out of the 6 stations, one of them (Bocas del Toro) belongs to the Caribbean slope and the other five to the Pacific slope.

Bocas del Toro Graphic

To represent the solar shine behavior in the Caribbean slope, we graphed the following from the Bocas del Toro station. Note that historically March is the month with the highest sun hours average with a total of 165.1 hours, decreasing historically untill it reaches an historical monthly solar shine minimum in the month of July with 102 sun hours. This sun hours descent in July is closely related to the rainy season that manifest itself in that period of the year in the Caribbean slope.

Santiago -  Graph

In the Pacific slope, we used the Santiago station to graph the data. Notice that in the 36 years of registry, the month with a higher monthly average sun hours has been March with 248.4 hours, decreasing progressively untill it reaches its lowest in the month of June with 124.2 sun hours. At the end of December you can see an increase (179.5 sun hours) that matches the dry season start in the Pacific slope.

Historical Average of total daily solar shine by station
Period 1972-2008
Station Jan Feb Mar Abr May Jun Jul Aug Sep Oct Nov Dic Total Acum.
TOCUMEN 7 6.8 7 5.8 4.1 3.2 3.6 3.7 3.7 3.8 4.1 5.5 58.3
ANTÓN 8 7.6 7.9 6.7 4.8 3.2 3.7 3.7 3.7 3.9 4.2 6.1 63.5
LOS SANTOS 8.3 7.9 8.7 7.4 5.3 3.9 4.2 4.2 4 4.4 5 6.5 69.8
SANTIAGO 7.65 8.71 8.01 6.67 5.19 4.14 4.32 4.48 4.23 4.18 4.62 5.79 67.99
DAVID 8.89 9.35 8.7 7.19 5.3 4.31 4.55 4.79 4.46 4.51 5.13 7.03 74.21
BOCAS DEL TORO 4.3 4.6 5.33 4.72 4.56 4.06 3.29 3.68 4.43 4.53 3.87 3.83 51.2

The following chart shows the historic behavior for the daily solar shine in 6 type A stations during the 1972 to 2008 period (36 years of registers). Is important to mention that the historical data that has been used is part of the historical data bank that posseses and guards the Hydrometeorology Management.

Bocas del Toro - Graph

The daily historical sun hours for the Bocas del Toro station shows a maximum for March with 5.33 daily hours and a minimum of 3.29 hours. Both ends coincide with the average monthly behavior of this variable.

Santiago - Graph

The historic daily behavior of the sun hours for the Santiago station shows that the maximum is reached in February with 8.71 hours, and this is related with the fact that February is the month that rains the least, and the lower average is the month of June with 4.14 sun hours, wich coincide with the rainy season.

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