Spring. Spring, also known as springtime, is one of the four temperate seasons, succeeding winter and preceding summer. There are various technical definitions of spring, but local usage of the term varies according to local climate, cultures and customs. When it is spring in the Northern Hemisphere, it is autumn in the Southern Hemisphere and vice versa. At the spring equinox, days and nights are approximately twelve hours long, with daytime length increasing and nighttime length decreasing as the season progresses until the Summer Solstice in June and December. Spring and springtime refer to the season, and also to ideas of rebirth, rejuvenation, renewal, resurrection and regrowth. Subtropical and tropical areas have climates better described in terms of other seasons, e.g. dry or wet, monsoonal or cyclonic. Meteorologists generally define four seasons in many climatic areas: spring, summer, autumn, and winter. These are determined by the values of their average temperatures on a monthly basis, with each season lasting three months. The three warmest months are by definition summer, the three coldest months are winter, and the intervening gaps are spring and autumn. Meteorological spring can therefore, start on different dates in different regions. In the US and UK, spring months are March, April, and May. In Australia and New Zealand, spring begins on 22nd or 23rd of September and ends on 21 December. In Ireland, following the Gaelic calendar, spring is often defined as February, March, and April. In Sweden, meteorologists define the beginning of spring as the first occasion on which the average 24 hours temperature exceeds zero degrees Celsius for seven consecutive days, thus the date varies with latitude and elevation. In Brazil, spring months are September, October, November. In the Northern Hemisphere, the astronomical vernal equinox can be taken to mark the first day of spring with the summer solstice marked as first day of summer. By solar reckoning, Spring is held to begin 1 February until the first day of Summer on May Day, with the summer solstice being marked as Midsummer instead of the beginning of Summer as with astronomical reckoning. In Persian culture the first day of spring is the first day of the first month which begins on 20 or 21 March. In the traditional Chinese calendar, the spring season consists of the days between Lichun, taking Chunfen as its midpoint, then ending at Lixia. Similarly, according to the Celtic tradition, which is based solely on daylight and the strength of the noon sun, spring begins in early February and continues until early May. The spring season in India is culturally in the months of March and April, with an average temperature of approx 32 °C. Some people in India especially from Karnataka state celebrate their new year in spring, Ugadi. The beginning of spring is not always determined by fixed calendar dates. The phenological or ecological definition of spring relates to biological indicators, such as the blossoming of a range of plant species, the activities of animals, and the special smell of soil that has reached the temperature for micro flora to flourish. These indicators, along with the beginning of spring, vary according to the local climate and according to the specific weather of a particular year. In England, Wales and Northern Ireland, the National Trust runs the # BlossomWatch campaign, which encourages people to share images of blossom with one another, as an early indicator of the arrival of the season. Some ecologists divide the year into six seasons. In addition to spring, ecological reckoning identifies an earlier separate prevernal season between the hibernal and vernal seasons. This is a time when only the hardiest flowers like the crocus are in bloom, sometimes while there is still some snowcover on the ground. During early spring, the axis of the Earth is increasing its tilt relative to the Sun, and the length of daylight rapidly increases for the relevant hemisphere. The hemisphere begins to warm significantly, causing new plant growth to spring forth, giving the season its name. Any snow begins to melt, swelling streams with runoff and any frosts become less severe. In climates that have no snow, and rare frosts, air and ground temperatures increase more rapidly.