Solar intensity is the amount of solar energy that is converted into heat or other types of energy. The solar intensity is measured in terms of watts per square meter (W/m2).
Solar intensity changes with the seasons, with the different solstices, and over longer time periods. The term “solstice” comes from the Latin words sol, which means “sun,” and stasis, which means “standing.”
There are two solstices each year: winter and summer. These mark the times when the north or south pole is pointed most directly at or away from the sun, respectively. The length of day and night changes at these times. The northern winter solstice takes place on December 21 each year, while the southern summer solstice occurs on March 21.
This article will discuss how the amount of solar intensity changes at different times of the year due to what causes sunlight to be reflected or absorbed.
The sun is furthest from the equator on the June solstice
Because the sun moves in a circular path around the celestial north pole, its position on the sky changes with each day of the year.
On December 21, the sun appears to move southward, taking it away from the equator and toward the southern hemisphere. On June 21, the sun appears to move northward, bringing it closer to the equator.
Because of this movement, on June 21 (summer solstice) the sun appears higher in the sky than on December 21 (winter solstice). This makes noon solar intensity higher on summer solstice than on winter solstice.
Solar intensity is measured in kilowatts per square meter (kW/m²). kW/m² is similar to how metric units measure intensity: watts per square meter (W/m²). One kW/m² is equal to 1 W/m².
Latitude affects solar intensity
The latitude at which you measure the solar intensity affects the measured intensity. This is because the solar intensity depends on where the sun is in relation to the earth.
When you measure solar intensity at noon, on the summer solstice, in Northern America, where the sun is highest in the sky, it will be brighter than on the winter solstice, when it is lower in the sky.
The same applies to measuring solar intensity in other high-latitude places, such as Australia and New Zealand. On the summer solstice, when it is noon there, it will be brighter than on the winter solstice.
In places with lower latitude, such as Antarctica, there is no difference in solar intensity between the summer and winter solstices. The sun does not rise or set for weeks at a time, so there is no noon nor midnight.
Solar intensity varies by season
The solar intensity at noon varies by season due to the angle of the sun relative to the equator. The northern and southern hemispheres have opposite experiences of the intensity of the sun at noon.
During the winter solstice, the north receives less sunlight because the suns rays hit lower on the horizon. During summer solstice, the south receives more sunlight because the suns rays hit higher on the horizon.
This is because, relative to the earths axis, the earth rotates slower during winter and faster during summer. This difference in speed takes about seven days to be noticeable, which explains why there is more daylight during summer than during winter.
The average amount of light received over a day is about the same, however.
Ask an expert!
Solar intensity is the amount of energy the sun releases in a given time. This is measured in watts per meter squared (W/m²).
According to NASA, solar intensity at noon on June 21 (summer solstice) is approximately 77 watts per meter squared higher than solar intensity at noon on December 21 (winter solstice).
This increase in solar intensity may contribute to the increased number of fires and wildfires occurring during summer months. While climate change may also be a factor, this is an area of research that is still being explored.
Fire behavior experts typically use two metrics to assess fire behavior: fuel moisture content and temperature. A hotter fire with less moisture will burn more intensely, creating more smoke and leaving less residue behind.
Dr. Jennifer Balch, a fire behavior expert and professor at Harvard University, studies how vegetation burns in different seasons based on her interview with CNN.