Seasonal lag
Seasonal lag is the phenomenon
A phenomenon , plural phenomena, is any observable occurrence. Phenomena are often, but not always, understood as 'appearances' or 'experiences'...

 whereby the date of maximum average air temperature at a geographical location on a planet
A planet is a celestial body orbiting a star or stellar remnant that is massive enough to be rounded by its own gravity, is not massive enough to cause thermonuclear fusion, and has cleared its neighbouring region of planetesimals.The term planet is ancient, with ties to history, science,...

 is delayed until some time after the date of maximum insolation
Insolation is a measure of solar radiation energy received on a given surface area in a given time. It is commonly expressed as average irradiance in watts per square meter or kilowatt-hours per square meter per day...

. This also applies to the minimum temperature being delayed until some time after the date of minimum insolation.

Seasonal lag 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
Latent heat is the heat released or absorbed by a chemical substance or a thermodynamic system during a process that occurs without a change in temperature. A typical example is a change of state of matter, meaning a phase transition such as the melting of ice or the boiling of water. The term was...

 of freezing and of condensation. Its length varies between different climates, with extremes ranging from as little as 15-20 days (for polar regions in summer) to as much as 2½ months (for low-latitude ocean areas). Interestingly, in many locations, it is not "seasonally symmetric", that is, the time between the winter solstice and coldest time is not the same as between the summer solstice and hottest time. In low and middle latitudes, the summer lag is longer, while in polar areas the winter lag is longer. In mid-latitude continental climates, it is approximately 20-25 days in winter and 25-35 days in summer.

San Francisco, for example, has a long seasonal lag of almost three months in the summer, with typical temperatures peaking in mid-September, and October as its second-warmest month This is unusual for a location 38° north of the equator, but 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 rapid autumn cooling.

Seasonal lag on other planets

Other planets have different seasonal lags. The gas giants Jupiter
Jupiter is the fifth planet from the Sun and the largest planet within the Solar System. It is a gas giant with mass one-thousandth that of the Sun but is two and a half times the mass of all the other planets in our Solar System combined. Jupiter is classified as a gas giant along with Saturn,...

, Saturn
Saturn is the sixth planet from the Sun and the second largest planet in the Solar System, after Jupiter. Saturn is named after the Roman god Saturn, equated to the Greek Cronus , the Babylonian Ninurta and the Hindu Shani. Saturn's astronomical symbol represents the Roman god's sickle.Saturn,...

 and Uranus
Uranus is the seventh planet from the Sun. It has the third-largest planetary radius and fourth-largest planetary mass in the Solar System. It is named after the ancient Greek deity of the sky Uranus , the father of Cronus and grandfather of Zeus...

, as well as Saturn's moon Titan
Titan (moon)
Titan , or Saturn VI, is the largest moon of Saturn, the only natural satellite known to have a dense atmosphere, and the only object other than Earth for which clear evidence of stable bodies of surface liquid has been found....

, all have substantial seasonal lags corresponding to the equivalent of between two and three months in Earth terms. Mars
Mars is the fourth planet from the Sun in the Solar System. The planet is named after the Roman god of war, Mars. It is often described as the "Red Planet", as the iron oxide prevalent on its surface gives it a reddish appearance...

, 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. And for Mercury
Mercury (planet)
Mercury is the innermost and smallest planet in the Solar System, orbiting the Sun once every 87.969 Earth days. The orbit of Mercury has the highest eccentricity of all the Solar System planets, and it has the smallest axial tilt. It completes three rotations about its axis for every two orbits...

, no seasonal lag would also be detected, even for its "anomalistical
Orbital period
The orbital period is the time taken for a given object to make one complete orbit about another object.When mentioned without further qualification in astronomy this refers to the sidereal period of an astronomical object, which is calculated with respect to the stars.There are several kinds of...

seasons" since it has no atmosphere, and its soil is very isolant.

External links

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