In
climatology
Climatology (from Greek , ''klima'', "slope"; and , '' -logia'') or climate science is the scientific study of Earth's climate, typically defined as weather conditions averaged over a period of at least 30 years. Climate concerns the atmospher ...
, the term mesothermal is used to refer to certain forms of
climate
Climate is the long-term weather pattern in a region, typically averaged over 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 meteoro ...
found typically in the
Earth
Earth is the third planet from the Sun and the only astronomical object known to Planetary habitability, harbor life. This is enabled by Earth being an ocean world, the only one in the Solar System sustaining liquid surface water. Almost all ...
's
temperate zones
In geography, the temperate climates of Earth occur in the middle latitudes (approximately 23.5° to 66.5° N/S of the Equator), which span between the tropics and the polar regions of Earth. These zones generally have wider temperature ran ...
. It has a moderate span of temperature, with winters not cold enough to sustain snow cover. Summers are warm within oceanic climate regimes, and hot within continental or subtropical climate regimes.
Origin of term
The term is derived from two
Greek
Greek may refer to:
Anything of, from, or related to Greece, a country in Southern Europe:
*Greeks, an ethnic group
*Greek language, a branch of the Indo-European language family
**Proto-Greek language, the assumed last common ancestor of all kno ...
words meaning "having a moderate amount of heat." This can be misinterpreted, however, since the term is actually intended to describe only the
temperature
Temperature is a physical quantity that quantitatively expresses the attribute of hotness or coldness. Temperature is measurement, measured with a thermometer. It reflects the average kinetic energy of the vibrating and colliding atoms making ...
conditions that prevail during the winter months, rather than those for the year as a whole.
Definition
Under the original
Köppen climate classification
The Köppen climate classification divides Earth climates into five main climate groups, with each group being divided based on patterns of seasonal precipitation and temperature. The five main groups are ''A'' (tropical), ''B'' (arid), ''C'' (te ...
, all places with an average temperature in their coldest month that is colder than , but warmer than , are said to have a mesothermal climate. The isotherm of for the coldest monthly mean temperature, was observed to be the line where the climate was likely cold enough to support a fixed period of continuous
snow
Snow consists of individual ice crystals that grow while suspended in the atmosphere—usually within clouds—and then fall, accumulating on the ground where they undergo further changes.
It consists of frozen crystalline water througho ...
cover every year.
In some climate classifications the isotherm of 0°C (32°F) for the coldest monthly mean temperature is observed as the line between mesothermal climates and microthermal climates where the coldest month has a mean temperature below .
Range
In the US, the northern boundary line between mesothermal and microthermal ranges is north of
Juneau
Juneau ( ; ), officially the City and Borough of Juneau, is the capital of the U.S. state of Alaska, located along the Gastineau Channel and the Alaskan panhandle. Juneau was named the capital of Alaska in 1906, when the government of wha ...
and
Sitka along the margins of the Pacific Ocean. It then goes southeastward around about 42N latitude across the north-central US (not including mountain regions) then eastward across the lower Midwest to the East Coast near Boston. The southern boundary line between mesothermal and megathermal (or tropical) is across south
Florida
Florida ( ; ) is a U.S. state, state in the Southeastern United States, Southeastern region of the United States. It borders the Gulf of Mexico to the west, Alabama to the northwest, Georgia (U.S. state), Georgia to the north, the Atlantic ...
just above Palm Beach.
Moisture
In addition to being subdivisible by summer temperature, mesothermal climates can also be subclassified on the basis of
precipitation
In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls from clouds due to gravitational pull. The main forms of precipitation include drizzle, rain, rain and snow mixed ("sleet" in Commonwe ...
— into
humid
Humidity is the concentration of water vapor present in the air. Water vapor, the gaseous state of water, is generally invisible to the human eye. Humidity indicates the likelihood for precipitation, dew, or fog to be present.
Humidity depe ...
,
seasonal
A season is a division of the year based on changes in weather, ecology, and the number of daylight hours in a given region. On Earth, seasons are the result of the axial parallelism of Earth's axial tilt, tilted orbit around the Sun. In temperat ...
,
semiarid
A semi-arid climate, semi-desert climate, or steppe climate is a dry climate sub-type. It is located on regions that receive precipitation below potential evapotranspiration, but not as low as a desert climate. There are different kinds of sem ...
and
arid
Aridity is the condition of geographical regions which make up approximately 43% of total global available land area, characterized by low annual precipitation, increased temperatures, and limited water availability.Perez-Aguilar, L. Y., Plata ...
subtypes.
See also
*
Megathermal
*
Microthermal
In climatology, the term microthermal is used to denote the continental climates of Eurasia and North America.
Etymology
The word ''microthermal'' is derived from two Greek words meaning "small" and "heat". This is misleading, however, since the ...
*
Temperate climates
In geography, the temperate climates of Earth occur in the middle latitudes (approximately 23.5° to 66.5° N/S of the Equator), which span between the tropics and the polar regions of Earth. These zones generally have wider temperature ra ...
References
* ''Applied Climatology'', John Griffiths (for use of 6 °C in the coldest month as poleward limit of subtropical climates
Climate and weather classification systems
{{climatology-stub