higher middle latitudes experience the greatest annual change in daylight hours.
higher middle latitudes experience the greatest annual change in daylight hours.
4. which latitudes experience the greatest annual change in daylight hours?
higher middle latitudes
at middle latitudes, far from both the equator and the poles, variations in the length of daytime are moderate. in the higher middle latitudes where montreal, paris and ushuaia are located, the difference in the length of the day from summer to winter can be very noticeable: the sky may still be lit at 10 pm in summer, but may be dark at 5 pm in winter. in the lower middle latitudes where southern california, egypt and south africa are located, the seasonal difference is smaller, but still results in approximately 4 hours difference in daylight between the winter and summer solstices. the difference becomes less pronounced the closer one gets to the equator. an approximation to the monthly change can be obtained from the rule of 12ths. with 4 hours change over the six months from winter to summer the day lengthens by about 4*1/12 of an hour (20 mins) in the first month, 4*2/12 (40 mins) in the second month, 4*3/12 (1 hr) in the third month, then 1 hr, 40 mins and 20 mins in the fourth, fifth and six months.
daytime
perhaps one of the most apparent factors contributing to earth climate change is the angle at which the earth is tilted. this is the angle at which earth's axis of rotation is from the vertical, also known as earth's obliquity. earth's current tilt angle is approximately 23.5 degrees. the axial tilt angle affects climate largely by determining which parts of the earth get more sunlight during different stages of the year. this is the primary cause for the different seasons earth experiences throughout the year, as well as the intensity of the seasons for higher latitudes. for example, in the northern hemisphere, if there were no axial tilt, i.e. earth's obliquity would be zero degrees, then there would be no change in the seasons from year to year. this would be because there would be no difference in the amount of solar irradiation received, year-round, anywhere on earth. on the other hand, if earth's axial tilt angle was great (45+ degrees), the seasonality of each hemisphere, individually, would be highly exaggerated. summers would be extremely hot, with substantially more hours of daylight than night each day. winters would be extremely cold, with substantially more hours of night than daylight each day. this is because, during summer for the northern hemisphere, if the earth is tilted more (pointed towards the sun more), there would be more available hours in which the suns rays can strike any certain place, thereby increasing the number of daylight hours at any given place, with more and more daylight hours at higher latitudes. also, because the northern hemisphere would be tilted much more towards the sun, it would be physically closer to the sun, thereby increasing the intensity of the sun's rays hitting the northern hemisphere, thereby causing the northern hemisphere to become hotter. likewise, during winter for the northern hemisphere, there would be fewer hours of daylight because the northern hemisphere would essentially be pointed away from the sun. fewer daylight hours means less solar radiation hitting the northern hemisphere, especially at higher latitudes, and therefore causing the northern hemisphere to become colder. the same things can also be said about the southern hemisphere, particularly at high latitudes. in either case, the climate around the equator is not affected nearly as much as the higher latitudes, thereby creating a sizable difference in how obliquity affects different latitudes. this is all, of course, dependent on what the actual tilt angle is at any given point in time. the thing is, though, that earth does in fact change obliquity over time in a cyclic pattern. earth's obliquity does not change much, though, as obliquity has been determined to cycle between the small range of 22.2 degrees to 24.5 degrees, in a cycle that lasts approximately 41,000 years. therefore, with the small tilt variation over time, the earth has always been thought to have had a seasonal climate, at least in the high latitudes due to the solar effect of changing earth obliquity.
orbital effects on climate