The moist static energy is a

thermodynamic Thermodynamics is a branch of physics that deals with heat, work, and temperature, and their relation to energy, entropy, and the physical properties of matter and radiation. The behavior of these quantities is governed by the four laws of ther ...

variable that describes the state of an

air parcel In fluid dynamics, within the framework of continuum mechanics, a fluid parcel is a very small amount of fluid, identifiable throughout its dynamic history while moving with the fluid flow. As it moves, the mass of a fluid parcel remains constan ...

, and is similar to the

equivalent potential temperature Equivalent potential temperature, commonly referred to as theta-e \left( \theta_e \right), is a quantity that is conserved during changes to an air parcel's pressure (that is, during vertical motions in the atmosphere), even if water vapor condense ...

. The moist static energy is a combination of a parcel's

enthalpy Enthalpy , a property of a thermodynamic system, is the sum of the system's internal energy and the product of its pressure and volume. It is a state function used in many measurements in chemical, biological, and physical systems at a constant ...

due to an air parcel's

internal energy The internal energy of a thermodynamic system is the total energy contained within it. It is the energy necessary to create or prepare the system in its given internal state, and includes the contributions of potential energy and internal kinet ...

and energy required to make room for it, its

potential energy In physics, potential energy is the energy held by an object because of its position relative to other objects, stresses within itself, its electric charge, or other factors. Common types of potential energy include the gravitational potentia ...

due to its height above the surface, and the

latent energy Latent heat (also known as latent energy or heat of transformation) is energy released or absorbed, by a body or a thermodynamic system, during a constant-temperature process — usually a Phase transition#Modern classifications, first-order phase ...

due to water vapor present in the air parcel. It is a useful variable for researching the atmosphere because, like several other similar variables, it is approximately conserved during adiabatic ascent and descent. The moist static energy, S, can be described mathematically as: ::

S=C_p \cdot T + g \cdot z + L_v \cdot q

where C_p is the

specific heat In thermodynamics, the specific heat capacity (symbol ) of a substance is the heat capacity of a sample of the substance divided by the mass of the sample, also sometimes referred to as massic heat capacity. Informally, it is the amount of heat t ...

at constant pressure, T is the absolute air temperature, g is the

gravitational constant The gravitational constant (also known as the universal gravitational constant, the Newtonian constant of gravitation, or the Cavendish gravitational constant), denoted by the capital letter , is an empirical physical constant involved in ...

, z is the

geopotential height Geopotential height or geopotential altitude is a vertical coordinate referenced to Earth's mean sea level, an adjustment to geometric height (altitude above mean sea level) that accounts for the variation of gravity with latitude and altitude. Thu ...

above sea level, L_v is the latent heat of vaporization, and q is water vapor

specific humidity 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 depen ...

. Note that many texts use mixing ratio r in place of specific humidity q because these values tend to be close (within a few percent) under normal atmospheric conditions, but this is an approximation and not strictly correct. Through the study of moist static energy profiles,

Herbert Riehl Herbert Riehl (March 30, 1915 – June 1, 1997) was a German-born American meteorologist who is widely regarded as the father of tropical meteorology. He is well known for his work with Joanne Simpson on the importance of hot towers, and their crit ...

and

Joanne Malkus Joanne Simpson (formerly Joanne Malkus, born Joanne Gerould; March 23, 1923 – March 4, 2010) was the first woman in the United States to receive a Ph.D. in meteorology, which she received in 1949 from the University of Chicago.Atlas D and Lemone ...

determined in 1958 that

hot tower A hot tower is a tropical cumulonimbus cloud that reaches out of the lowest layer of the atmosphere, the troposphere, and into the stratosphere. These formations are called "hot" because of the large amount of latent heat released as water vapor co ...

s, small cores of

convection Convection is single or multiphase fluid flow that occurs spontaneously due to the combined effects of material property heterogeneity and body forces on a fluid, most commonly density and gravity (see buoyancy). When the cause of the convec ...

approximately wide that extend from the

planetary boundary layer In meteorology, the planetary boundary layer (PBL), also known as the atmospheric boundary layer (ABL) or peplosphere, is the lowest part of the atmosphere and its behaviour is directly influenced by its contact with a planetary surface. On Ear ...

to the

tropopause The tropopause is the atmospheric boundary that demarcates the troposphere from the stratosphere; which are two of the five layers of the atmosphere of Earth. The tropopause is a thermodynamic gradient-stratification layer, that marks the end of ...

, were the primary mechanism that transported energy out of the tropics to the middle latitudes. More recently, idealized model simulations of the tropics indicate that the moist static energy budget is dominated by

advection In the field of physics, engineering, and earth sciences, advection is the transport of a substance or quantity by bulk motion of a fluid. The properties of that substance are carried with it. Generally the majority of the advected substance is al ...

, with shallow inflow in the lowest of the atmosphere with outflow concentrated about above the surface. Moist static energy has also been used to study the

Madden–Julian oscillation The Madden–Julian oscillation (MJO) is the largest element of the intraseasonal (30- to 90-day) variability in the tropical atmosphere. It was discovered in 1971 by Roland Madden and Paul Julian of the American National Center for Atmospheric R ...

(MJO). As with the tropics as a whole, the budget of moist static energy in the MJO is dominated by advection, but also is influenced by the wind-driven component of the surface latent heat flux. The relationship between the advection component and the latent heat component influence the timing of the MJO.

References

{{Reflist Atmospheric thermodynamics

See also

References