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For practical purposes, a time-average of the direct insolation over the course of the year is commonly used. This averaging takes into account the absence of sunlight during the night, increased scatter in the morning and evening hours, average effects of cloud cover and smog, as well as seasonal variations of the mid-day solar elevation.
For example, with an axial tilt is 23°, and at a latitude of 45°, then the summer's peak sun angle is 68° (giving sin(68°) = 93% insolation at the surface), while winter's least sun angle is 22° (giving sin(22°) = 37% insolation at the surface). Thus, the greater the axial tilt, the stronger the seasons' variations at a given latitude.
This integrated solar irradiance is called solar irradiation, solar radiation, solar exposure, solar insolation, or insolation. Irradiance may be measured in space or at the Earth's surface after atmospheric absorption and scattering. Irradiance in space is a function of distance from the Sun, the solar cycle, and cross-cycle changes. [2]
The onset and termination of the African Humid Period both occurred when the insolation cycle reached a value of roughly 4.2% higher than today. However, shifts in the insolation cycle are too gradual to cause abrupt climate transitions like those seen at the onset and termination of the African Humid Period all on their own.
Climate modelling suggests that low solar activity may result in, for example, colder winters in the US and northern Europe and milder winters in Canada and southern Europe, with little change in global averages. [89] More broadly, links have been suggested between solar cycles, global climate and regional events such as El Niño. [90]
The intensity of albedo temperature effects depends on the amount of albedo and the level of local insolation (solar irradiance); high albedo areas in the Arctic and Antarctic regions are cold due to low insolation, whereas areas such as the Sahara Desert, which also have a relatively high albedo, will be hotter due to high insolation.
This glossary of geography terms is a list of definitions of terms and concepts used in geography and related fields, including Earth science, oceanography, cartography, and human geography, as well as those describing spatial dimension, topographical features, natural resources, and the collection, analysis, and visualization of geographic ...
The amount of Sun energy reaching a location on Earth ("insolation", shown in blue) varies through the seasons.As it takes time for the seas and lands to heat or cool, the surface temperatures will lag the primary cycle by roughly a month, although this will vary from location to location, and the lag is not necessarily symmetric between summer and winter.