Climate: Sun and Clouds
Sun/Solar Radiation
Mean Hourly radiation by month at three elevations in The Luquillo Experimental Forest over the course of a day. (Average hourly data from 2000 - 2002)
Solar radiation gets lower as elevation and cloud cover increase
Solar radiation is greater during the midday hours. (Three points labeled S, B, and E are at 3 different elevations: S (Sabana Station) is at 153 meters; B (Bisley Watersheds) are 265 to 456 meters; and E (Pico del Este East Peak) is 1056 meters.
- Line graph shows more radiation late morning though mid afternoon at all elevations, with the most radiation during the midday.
- Line graph shows no radiation until approximately 8 a.m. and then radiation peaks at noon, declining to no radiation again at approximately 7 p.m. Watts per meter squared peak at 400 for a location at 1,000 meters and 800 for a location at 153 meters.
- Line graph suggests 11 hours of sunlight, but this is an average of all months.
- Cloud cover is responsible for lower solar radiation at the higher elevations.
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Solar Insolation does not vary with the Season
Dry Season (e.g., March) Wet Season (e.g., October)
- Seasonality does not impact radiation; it is the same in the the wet and dry seasons of approximately 8 – 16 megajoules per meter squared per day.
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Clouds
Cloud cover increases with elevation and when solar radiation declines.
rainfall at higher levels when the cooler air condenses
- Trade winds from the Atlantic Ocean bring moist air, which cools and condenses as it rises up the steep mountains in the forest.
rainfall at higher levels when the cooler air condenses
- Reduces solar radiation to the Forest surface and results in lower photosynthesis and transpiration
- Dry season (e.g., March): probability of cloud cover is lower
- Wet season (e.g., October): probability of cloud cover is higher
- Less cloud cover when sunlight is strongest midday.
- When sunlight is less, cloud cover increases (later in day) as condensation level rises when solar radiation declines.