Winter is the coldest of the four seasons in the world’s subtropical, temperate, subpolar and arctic climates. Depending on whether it currently prevails in the northern or southern hemisphere, one speaks of northern winter or southern winter. The northern winter takes place simultaneously with the southern summer.
The seasons occur because the earth’s rotation is not in the plane of the orbit around the sun, but inclined by 23.4 °. As a result, the south and north poles are alternately half a year in grazing sunlight, and the zenith of the sun alternates between the southern and northern tropics in the annual cycle.
Beginning of winter and duration
Astronomically or calendar-wise, winter begins with the winter solstice – the time at which the sun is perpendicular to the tropic of the other half of the earth and the days are shortest:
in the Northern Hemisphere on December 21st or 22nd and
in the southern hemisphere on June 21.
Then the days get longer and the nights get shorter. Winter ends at the same day as spring on
March 20 or the night of March 21 in the northern hemisphere and
September 22 or 23 for the southern hemisphere.
Winter therefore lasts 89 days in the northern hemisphere and 93 days in the southern hemisphere.
In the East Asian culture, which is shaped by the Chinese calendar, winter begins when the sun is 45 ° before the solstice (November 7th or 8th) and ends when the sun is 45 ° behind (3rd, 4th or February 5th). The solstice is in the middle of winter.
Since the orbit of the earth around the sun is slightly elliptical, i. H. deviates from an exact circular path by 1.7%, the four seasons are not exactly the same length. The northern winters are a little shorter and milder than the southern winters due to the proximity of the sun (Perihel on January 3).
In meteorology, the beginning of the (north) winter is scheduled on December 1st. It therefore covers the months of December, January and February.
The beginning of winter can vary considerably from the astronomical point of view and, in addition to the land-sea distribution (maritime vs. continental climate), is often marked by the beginning of a permanent blanket of snow. The increase or decrease in glaciers depends less on the winter snow than on the first fresh snow in autumn, which inhibits ablation.
Approximately, the months of December, January and February are assigned to winter in the northern hemisphere and June, July and August in the southern hemisphere. The “polar night” prevails at the geographical poles for six months; near the polar circles, it lasts from a few days to weeks.
In the energy industry, the winter is defined as the winter half-year from October 1 to March 31 because of the then higher energy requirements, deviating from the seasonal definitions.
Weather conditions and their influence on winter weather
The winter weather is determined by various weather conditions, which result from the interaction of high and low-pressure areas. The weather conditions can last from one day to several weeks. Your existence or change can only be determined a few days in advance. Depending on the altitude, it can snow or rain. Storms coming from the west are possible.
Winter and climate change
Winters have globally been wetter and milder for over two decades. This trend continues after previous climate forecasts. However, according to recent studies, the melting of the ice at the North Pole caused by global warming paradoxically favors the formation of high-pressure areas over Eurasia, so that more severe winters are expected in parts of the northern hemisphere.