seasonal lag
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Seasonal lag is the
phenomenon A phenomenon (; plural phenomena) is an observable In physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ''phýsis'' 'nature'), , is the natural science that studies mat ...
whereby the date of maximum average
air temperature Temperature is a physical quantity that expresses hot and cold. It is the manifestation of thermal energy, present in all matter, which is the source of the occurrence of heat, a flow of energy, when a body is in contact with another that i ...
at a
geographical Geography (from Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population is approximately 10. ...
location on a
planet A planet is an astronomical body orbiting a star or Stellar evolution#Stellar remnants, stellar remnant that is massive enough to be Hydrostatic equilibrium, rounded by its own gravity, is not massive enough to cause thermonuclear fusion, and ...

planet
is delayed until some time after the date of maximum
insolation Solar irradiance is the power (physics), power per unit area received from the Sun in the form of electromagnetic radiation as measured in the wavelength range of the measuring instrument. The solar irradiance is measured in watt per square metr ...

insolation
(i.e. the
summer solstice The summer solstice, also known as estival solstice or midsummer, occurs when one of Earth's geographical pole, poles has its maximum tilt toward the Sun. It happens twice yearly, once in each Hemispheres of Earth, hemisphere (Northern and Souther ...

summer solstice
). This also applies to the minimum temperature being delayed until some time after the date of minimum insolation. In most Northern Hemisphere regions, the month of February is usually colder than the month of November despite February having significantly later sunsets and more daylight overall. Conversely, the month of August is usually hotter than the month of May despite August having later sunrises, increasingly earlier sunsets, and less daylight overall. In all cases, the change in average air temperature lags behind the more consistent change in daylight patternsdelaying the perceived start of the next
season A season is a division of the year based on changes in weather Weather is the state of the atmosphere, describing for example the degree to which it is hot or cold, wet or dry, calm or stormy, clear or cloud cover, cloudy. On Earth, most ...

season
for a month or so. An analogous temperature lag phenomenon occurs in
diurnal temperature variation In meteorology Meteorology is a branch of the atmospheric sciences which includes atmospheric chemistry and atmospheric physics, with a major focus on weather forecasting. The study of meteorology dates back millennia, though significant progr ...
, where maximum daily temperature occurs after noon (maximum insolation).


On Earth

Earth's seasonal lag is largely caused by the presence of large amounts of water, which has a high
latent heat Latent heat (also known as latent energy or heat of transformation) is energy released or absorbed, by a body or a thermodynamic system A thermodynamic system is a body of matter In classical physics and general chemistry, matter is any sub ...
of freezing and of condensation. The length of seasonal lag varies between different
climates Climate is the long-term average of weather, typically averaged over a period of 30 years. More rigorously, it is the mean and variability of meteorological variables over a time spanning from months to millions of years. Some of the meteorologic ...

climates
, with extremes ranging from as little as 15–20 days (for polar regions in summer and continental interiors, for example
Fairbanks, Alaska Fairbanks is a home rule city and the borough seat A county seat is an administrative center, seat of government, or capital city of a county or Parish (administrative division), civil parish. The term is used in Canada, China, Romania, Hung ...

Fairbanks, Alaska
, where annual average warmest temperatures occur in early July, and August is notably cooler than June) to as much as 2½ months (for oceanic areas, whether in low latitudes, as in
Miami Miami (), officially the City of Miami, is a Coast, coastal metropolis located in southeastern Florida in the United States. It is the third most populous metropolitan area, metropolis on the East coast of the United States, and it is the sevent ...

Miami
,
Florida Florida is a U.S. state, state located in the Southeastern United States, Southeastern region of the United States. Florida is bordered to the west by the Gulf of Mexico, to the northwest by Alabama, to the north by Georgia (U.S. state), Georg ...

Florida
or higher latitudes as in the Kuril Islands, where at
Simushir Simushir (russian: Симушир, ja, 新知島, translit=Shimushiru-tō, ain, シムシㇼ, translit=Simusir), meaning ''Large Island'' in Ainu, is an uninhabited volcanic island Geologically, a high island or volcanic island is an islan ...

Simushir
annual average temperatures peak in late August), and at
Cape Sable Island Cape Sable Island, locally referred to as Cape Island, is a small Canada, Canadian island at the southernmost point of the Nova Scotia peninsula. It is sometimes confused with Sable Island. Historically, the Argyle, Nova Scotia region was known as ...
in Nova Scotia, Canada, where (by a slight margin) September is actually the year's warmest month on average. August as the narrowly warmest month can even happen in ultra-maritime areas north of the Arctic Circle, such as Røst or offshore islands like Jan Mayen and Bear Island (Norway), Bear Island in Norway. The latter is at 74th parallel north, 74°N and such high-latitude summer lag is enabled by Gulf Stream moderation tempering seasonal swings to extend the season. In many locations, seasonal lag is not "seasonally symmetric"; that is, the period between the winter solstice and thermal midwinter (coldest time) is not the same as between the summer solstice and thermal midsummer (hottest time). In much of East Asia with oceanic influences, including Korea and virtually all of Japan, January is the coldest month, but August is the warmest month. In low and mid latitudes, the ''summer'' lag is longer, while in polar areas the ''winter'' lag is longer (coreless winter in interior Antarctica and Greenland). In mid-latitude continental climates, it is approximately 20–25 days in winter and 25–35 days in summer. San Francisco, for example, has an exceptionally long seasonal lag in the summer, with average daily temperatures peaking in September, and October as its second-warmest month, but very little seasonal lag in the winter, with the lowest temperatures in December and January, around and soon after the winter solstice. This is caused by the water in the Bay Area surrounding the city on three sides. Many areas along North America's west coast have very small winter lag and are characterized by a much more gradual spring warming and relatively more rapid autumn cooling. Due to seasonal lag, in the Northern Hemisphere the autumnal equinox (around September 22) is considerably warmer than the vernal equinox (around March 20) in most regions despite the fact that both days have almost equal amounts of daylight and darkness. However even with seasonal lag the autumnal equinox is cooler than the summer solstice (around June 21) in most regions as well as the vernal equinox being warmer than the winter solstice (around Dec. 21) even in most oceanic areas. Contrary to popular belief, there is no meteorological reason for designating these dates as the first days of their respective seasons. In eastern Canada the seasonal lag is consistent both in summer and winter, resulting in February and August being the coldest and warmest months, respectively. In Western Europe the lag is lower in spite of the Atlantic coastline, usually around a month, which is also consistent with many inland areas in the North American Midwest. In Japan, Korea and nearby areas (for example, Vladivostok, Russia), seasonal lag is stronger in summer than winter; the coldest month is January, while the warmest month is August, possibly due to enhanced cloud cover and rain during June into July (for example, the "East Asian rainy season, tsuyu" rainy season in Japan over the same period).


On other planets

Other planets have different seasonal lags. The gas giants Jupiter, Saturn and Uranus, as well as Saturn's moon Titan (moon), Titan, all have substantial seasonal lags corresponding to the equivalent of between two and three months in Earth terms. Mars, on the other hand, has negligible seasonal lag of no more than a few days. For the case of Venus no seasonal lag would be detected, because the planet undergoes no seasons due to very efficient heat transport in its massive atmosphere (which would obliterate the season-causing effect of axial tilt, but its axial tilt is very small anyway) and very low orbital eccentricity (almost no changes to its distance from the Sun). This is also the case for Mercury (planet), Mercury, even for its "Orbital period, anomalistical seasons", since it has negligible atmosphere and so undergoes almost instantaneous heating and cooling.


References

{{Reflist Climatology Seasonality