Insolation ( input of solar energy) as a Function of Latitude and Season
The sun's angle varies significantly depending on a particular spot's How Latitude & Altitude Affect Temperature. Relationship to Seasons. short summary of the relationship between the sun and the earth as this will affect the . below illustrates the sun angles for 56 degrees North latitude (Northern Hemisphere). The In the equatorial region, the temperature fluctuations. weather: short term (daily to yearly) changes in temperature, winds, humidity, cloud declination: latitude where the sun angle is 90o at noon.
As the solar angle gets larger, the energy received from the Sun becomes less intense.
Latitude, Angle of Sun and Solar Energy
Again, don't be confused by the terminology. We experience this effect each day.How Latitude affects the Temperature
Think of how "weak" the Sun feels at sunrise when the solar angle is largecompared to how "strong" the Sun feels at noon when the solar angle is much smaller. At any day and location Solar Noon is defined as the exact middle of the daylight period or when the sun is halfway between sunrise and sunset.
At solar noon, the Sun is aligned with true north and south.
Note that solar noon does not necessarily occur at precisely 12 PM local time, though it is usually close. No matter where you are on Earth, solar noon is the time of day when the solar angle reaches its daily minimum and the Sun's radiation is most intense.
Outside of the tropics, you know that the noon-time sun "feels stronger" in summer as compared to winter. Therefore, the solar angle must be smaller in summer as compared to winter. This seasonal change results from the geometry of Earth-Sun orientation described above.
Latitude Affects Temperature
The changes of sun angle with time of year and latitude are quantified below. The solar declination or sub-solar pointwhich is shown graphically above, is defined as the Latitude at which the sun is directly overhead at solar noon, i. The solar declination changes slowly from day to day and ranges from This latitudinal boundary defines the Tropics, which is the region between For latitudes outside of the tropics, there are zero days per year when the sun is directly overhead at solar noon.
Other notable dates include, the spring equinox, which happens around March 21 each year, and fall equinox, which happens around September On these days the noon-time sun is directly overhead at the equator.
You should know the position of the solar declination on the equinox and solstice dates as indicated in the diagram above. You should be able answer these questions: Tucson is not located in the tropics.
You should understand the following observations. In the northern hemisphere, outside of the tropics i. The more days away from the date of the summer solstice, the less intense the solar heating at noon. The reverse is true in the southern hemisphere outside of the tropics where the closer to June 21, the less intense the solar heating at noon.
The more days away from the date of the winter solstice, the more intense the solar heating at noon. The reverse is true in the southern hemisphere outside of the tropics where the closer to December 21, the more intense the solar heating at noon. It is easy to compute the solar angle at noon for any latitude and any day of the year and you may be asked to do this in exam or homework material.
At local solar noon, the sun is always located along a north-south line. The solar angle at noon is simply equal to the number of degrees of latitude between your latitude your position on Earth and the latitude of the solar declination.
If the solar declination is to the north of your location, then you will have to look toward the north to see the sun at solar noon; if the solar declination is to the south of your position, the you will have to look toward the south to see the sun at solar noon.
The seasonal variation in solar angle at noon depends upon your latitude. The yearly change in the solar angle at noon at a given latitude results in a corresponding change in the intensity of the sunlight received.
The intensity of the sunlight is reduced by the cosine of the solar angle. If you do not understand the last sentence about the cosine of an angle, don't worry, it is not something that I will test you on. You need to know the result given in bold below. The seasonal or yearly change in the intensity of the sun at solar noon at a given latitude can be determined by comparing the intensity on the day of minimum solar angle at noon largest cosine and greatest intensity to the day of maximum solar angle at noon smallest cosine and least intensity.
The result is seasonal yearly changes in the intensity of the sun and hence heating from the sun are smallest at the Equator and get larger toward the north and south poles.
This means that in the lower latitude tropics, there are only slight changes in solar heating and temperature during the year, and there are not distinct warm summers and cold winters. At higher latitudes the temperature difference between summer and winter becomes more distinct. Near the north and south poles, the change in solar intensity and temperature between summer and winter is extreme. You do not need to be able to do these calculations, but if you compute the ratio of maximum to the minimum cosine of the solar angle at noon for the three latitudes in the figures above, you can easily see that seasonal changes in the intensity of the sun and therefore in temperature are small at low latitudes and large at high latitudes.
Finally, at the Equator the ratio is 1. Length of Day The second factor which regulates seasonal changes in the amount of solar radiation energy that strikes a particular location latitude is the length of daylight or the number of hours from sunrise to sunset. I'm sure most of you know that the number of hours of daylight is longer in the summer as compared to the winter.
More hours of daylight translates to more hours of heating from the sun. As with solar angle at noon, there are mathematical formulas which one can use to calculate the number of daylight hours at any latitude for any day of the year, but the calculations for length of day are complex, and we will not use them.
It is important that you understand the this general statement the seasonal yearly changes in length of daylight hours are smallest at the Equator and get larger toward the north and south poles. In the northern hemisphere the longest day of the year is the summer solstice and the shortest day of the year is the winter solstice, while in the southern hemisphere the dates of the longest and shortest days are reversed. The figure below shows how the length of day changes at several different latitudes in the Northern Hemisphere.
At latitudes of In a sense this is like one long day per year Also note that March 21 Spring or Vernal Equinox and September 21 Fall or Autumnal Equinoxevery latitude on Earth has exactly 12 hours of sunshine and 12 hours of darkness. This only happens on these two specific dates when the axis of rotation does not point at all toward or away from the Sun.
In fact the term "equinox" means equal day and night. The figure below shows how the length of day changes during the year for several latitudes in the Northern Hemisphere. Southern latitudes are the mirror image of their Northern Hemisphere counterparts. On the summer solstice, all places north of Look at the animation below. Three lines of latitude are shown on the Earth image, the Equator, the Arctic circle in the northern hemisphere and the Antactic circle in the southern hemisphere.
Notice that on the summer solstice the entire Arctic region from the Arctic circle to the north pole is completely in sunshine, while the entire Antarctic region from the Antarctic circle to the south pole is completely in darkness even as the Earth rotates around its axis of rotation. Converselsy, on the winter solstice, all places north of This is also shown in the animation below.
Notice that on the winter solstice the entire Arctic region from the Arctic circle to the north pole is completely in darkness, while the entire Antarctic region from the Antarctic circle to the south pole is completely in sunshine even as the Earth rotates around its axis of rotation. In fact, this defines the Arctic and Antarctic regions, which are regions between For latitudes outside of the Arctic and Antarctic regions, there are never days with 24 hours of sunshine or 24 hours of darkness.
You should understand the following general observations about the length of day: The closer you are to the north and south pole, the greater the number of days with 24 hours of sunshine and 24 hours of darkness. This is why these days are called "equinoxes", or literally equal day and night everywhere on Earth. When the Earth's axis is tilted This means that the North Pole at summer solstice is effectively at But at summer solstice the North Pole is getting 24 hours per day what Stockholm, Fairbanks and Archangel get only 12 hours at the equinoxes.
It would be surprising to find open water at Stockholm or Archangel on September 21st. Using a formula developed elsewhere for the zenith angle of the Sun at each hour of the day the insolations Watts per square meter per day at the solstices and equinoxes were computed.
All refinements such as the varying path lengths and average cloud cover were ignored. The computation does take into account the fact that the Earth is closer to the Sun at the Northern Hemisphere's winter solstice December 21 than at its summer solstice June This means that the summer solstice for the Southern Hemisphere gets more intense solar radiation than the Northern Hemisphere gets for its summer solstice.
The rate of energy input varies from 1. If an area is receiving energy at a rate of 1. If its energy input falls from 1. The rate of energy input per unit area depends upon the angle of the Sun.