Geography · Ch 14 — Solar Radiation, Heat Balance and Temperature
Inversion of Temperature
Inversion of Temperature
The map is a world map, drawn with contour-like bands that connect places sharing the same annual range of temperature. The annual range is the difference between the mean temperature of the warmest month (July in the Northern Hemisphere) and the coldest month (January). Each band is labelled with a number in degrees Celsius: 3, 10, 20, 30, 40, 50 and 60. These are not temperatures themselves, but differences — how much the climate swings between the two extremes of the year.
The most striking feature is the bullseye of 50–60°C sitting over the north-eastern part of the Eurasian interior, deep in Siberia. This is the heart of the world's greatest temperature contrast: bitterly cold January averages and warm July averages produce a swing that no other landmass matches. The bands radiate outward from this core, with values falling as you move away — 40, 30, 20, 10 — until you reach the 3°C band. That narrow band hugs the Equator, running through both the oceans and the equatorial landmasses. Near the Equator, the sun's height and day length barely change through the year, so January and July temperatures are nearly identical; the range collapses to almost nothing. …
Normally, temperature decreases as elevation increases. That steady drop is the normal lapse rate. But sometimes the situation flips: temperature increases with height instead of decreasing. That reversal is called inversion of temperature.
Inversions are usually short-lived, yet they are quite common. The ideal conditions for one are a long winter night, clear skies, and still air. During the night, the heat absorbed by the earth during the day radiates back into space. By early morning, the ground has cooled down more than the air just above it, so the air near the surface becomes colder than the air higher up — the normal lapse rate is inverted.
Over polar areas, this inversion is not an occasional event; it is normal throughout the year. The surface stays so cold for so long that the air above it is almost always warmer.
A surface inversion promotes stability in the lower layers of the atmosphere. Because the cold, dense air sits at the bottom and warm air sits above it, there is little vertical mixing. Smoke and dust particles get trapped beneath the inversion layer and spread horizontally, filling the lower strata of the atmosphere. This is why dense fogs are common in the mornings, especially during winter. The fog and the inversion itself typically last only a few hours — until the sun rises and begins to warm the earth, breaking the stable layer. …
The highest range of temperature is more than 60 degree C, over the north-eastern part of the Eurasian continent -- this is due to continentality. The least range of temperature, 3 degree …