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 th ...

variable that describes the state of an

air parcel In fluid dynamics, a fluid parcel, also known as a fluid element or material element, is an infinitesimal volume of fluid, identifiable throughout its dynamic history while moving with the fluid flow. As it moves, the mass of a fluid parcel remain ...

, 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 condens ...

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

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

due to an air parcel's

internal energy The internal energy of a thermodynamic system is the energy of the system as a state function, measured as the quantity of energy necessary to bring the system from its standard internal state to its present internal state of interest, accoun ...

and energy required to make room for it, its

potential energy In physics, potential energy is the energy of an object or system due to the body's position relative to other objects, or the configuration of its particles. The energy is equal to the work done against any restoring forces, such as gravity ...

due to its height above the surface, and the latent energy 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 amount of heat that must be added to one unit of mass of the substance in order to cause an increase of one unit in temperature. It is also referred to as massic heat ...

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

gravitational constant The gravitational constant is an empirical physical constant involved in the calculation of gravitational effects in Sir Isaac Newton's law of universal gravitation and in Albert Einstein's general relativity, theory of general relativity. It ...

, z is the

geopotential height Geopotential height, also known as geopotential altitude or geopotential elevation, is a vertical coordinate (with dimension of length) representing the work involved in lifting one unit of mass over one unit of length through a hypothetical spac ...

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 dep ...

. 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 cr ...

and Joanne Malkus 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 t ...

s, small cores of

convection Convection is single or Multiphase flow, multiphase fluid flow that occurs Spontaneous process, spontaneously through the combined effects of material property heterogeneity and body forces on a fluid, most commonly density and gravity (see buoy ...

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 Ea ...

to the

tropopause The tropopause is the atmospheric boundary that demarcates the lowest two layers of the atmosphere of Earth – the troposphere and stratosphere – which occurs approximately above the equatorial regions, and approximately above the polar regi ...

, 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 fields 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 a ...

, 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 ...

(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