Climate Science Investigations South Florida - Temperature Over Time
Understanding Earth's relationships with the sun leads us directly into a discussion of how on latitude, where greater or lesser solar radiation is received on. To describe the relationship between Earth's surface temperature and the angle of insolation. To describe how time of day, and latitude, affect. The intensity of solar radiation is largely a function of the angle of incidence, the the effect the angle of incidence has on insolation intensity with the following (winter to summer) variation in day length increases with increasing latitude.
Since at latitudes far removed from the equator the sun's path through the sky is considerably lower in the winter than the summer, sun angle goes a long way towards explaining why winter is cold and summer is warm. Your local environment is warmed when solar radiation heats the surface of the earth, and the surface of the earth then radiates some of that heat back out into the air directly above it.
Lower winter sun angles mean less of the solar energy in the sky will be transferred to the ground, and this means less heat will be radiated into the air around you. Furthermore, as touched on above, winter sun angles also reduce the total solar energy in the sky by making the air mass value greater and the day length shorter. Also, many climates are cloudier in the winter than the summer.
All these factors come together to make winter so very dark and cold. Because the sun starts very low in the sky in the morning, gradually making its way to its high-point at solar noon and then heading back down until it slips away at dusk, sun angle is also clearly a big part of why mornings and evenings tend to be the cooler parts of the day. Collector Tilt and Solar Angle Of course, we can't do anything about winter except keep track of our mittens.
Look at the the picture and pretend that the red line is a tilted solar panel and that the blue line is a a horizontal solar panel.
Sun angle and insolation on a horizontal surface
The rays are hitting this panel directly and so a square mile of the sun's rays fall on a square mile of this solar panel. This means the sunlight on the tilted solar panel will be as intense as if the sun was directly overhead minus the intensity lost by the two related conditions we will discuss very soon. In contrast, the sunlight striking the horizontal solar panel is more spread-out and thus less concentrated--just like the sunlight striking the ground. The diagram gives some idea of why this is.
Since the angle of the sun is constantly changing throughout the day, the optimal tilt angle changes from moment to moment. For this reason, the only way to fully compensate for the "spreading-out" effect of lower sun angles is to constantly track the sun.
- Temperature Over Time
However, a correctly chosen permanent or seasonally adjusted tilt can greatly increase the amount of radiation falling on a solar panel. The "spreading-out" effect only applies to direct radiation and so when the sky is completely overcast and all of the solar radiation is diffuse radiation, you would actually gather more solar energy by just laying your panels out flat see types of radiation.
We have several pages devoted to tilt angles. I do not deny that much of our destiny is in the ineffable hands of the Fates but still I tell you that at our latitude, a solar collector's tilt is of great consequence! When the sun is lower in the sky, the extra atmosphere the sunlight has to pass through reduces its strength before it ever even reaches our solar panels see air mass.
The general loss of sunlight due to shorter days reduces the amount of total radiation in the sky on a given day see day length.
This causes the rays to be spread out over a larger surface area reducing the intensity of the radiation. Effect of angle on the area that intercepts an incoming beam of radiation.
6(i). Earth-Sun Relationships and Insolation
We can also model the effect the angle of incidence has on insolation intensity with the following simple equation: Let us compare this maximum value with values determined for other angles of incidence. Note the answers are expressed as a percentage of the potential maximum value. Longest days occur during the June solstice for locations north of the equator and on the December solstice for locations in the Southern Hemisphere.
The equator experiences equal day and night on every day of the year. Day and night is also of equal length for all Earth locations on the September and March equinoxes.Earth-Sun Angles - REE - GTU -
Figure 6i-2 describes the change in the length of day for locations at the equator, 10, 30, 50, 60, and 70 degrees North over a one-year period.
The illustration suggests that days are longer than nights in the Northern Hemisphere from the March equinox to the September equinox. Between the September to March equinox days are shorter than nights in the Northern Hemisphere. The opposite is true in the Southern Hemisphere.
What is the relationship between latitudes and intensity of insolation?
The graph also shows that the seasonal winter to summer variation in day length increases with increasing latitude. Figure 6i-3 below describes the potential insolation available for the equator and several locations in the Northern Hemisphere over a one-year period. The values plotted on this graph take into account the combined effects of angle of incidence and day length duration see Table 6h Locations at the equator show the least amount of variation in insolation over a one-year period.
These slight changes in insolation result only from the annual changes in the altitude of the Sun above the horizon, as the duration of daylight at the equator is always 12 hours.