A Meteorological Cosmology

How the Atmosphere Works, In Brief

Energy and Mass; Processes and Scales

Like any physical system, Earth’s atmosphere is composed of energy and mass. This energy takes many forms, such as the internal energy of the molecules, the latent energy stored within water vapor, and the radiative energy absorbed and emitted by the surface and the air. The atmosphere’s mass consists of gases and suspended particles that respond to gravity and pressure gradients as they move through space.

Both energy and mass evolve according to physical processes of four types that act continuously, although each process operates on its own characteristic scale and interacts with the others in specific ways.

Thermodynamic processes govern how temperature, density, and pressure adjust as air expands or compresses. Microphysical processes regulate how water changes phase and how droplets and ice crystals form and dissipate. Radiative processes determine how ultraviolet, visible, and infrared radiation flows through the atmosphere. Kinematic processes determine how momentum is transferred through wind and turbulence.

None of these processes act in isolation, since the atmosphere remains a coupled system in which a change in one variable alters the environment in which the others evolve. The structure and behavior of the atmosphere therefore emerge from the way these processes interact across the full range of spatial and temporal scales.

These scales span from the microscopic motions of water molecules to the global circulation that redistributes energy across the planet. Each scale contains its own family of processes, and each process contributes to the overall evolution of the atmosphere. The result is a system that appears complex in its details yet remains coherent in its organization, because every motion, cloud, and pattern we observe can be traced back to the underlying interactions among energy, mass, and the processes that link them.

Four Types of Atmospheric Processes: A Summary

• Thermodynamic (orange for heat): adjustments between the energy of the system and the energy of the system’s surroundings
• Microphysics (blue for water): conversions between active and potential energy through droplet and ice crystal growth
• Radiative (yellow for sun): electromagnetic energy from the sun, the earth, and the atmosphere
• Kinematic (green means go): atmospheric motion

A Process-Based Framework for the Atmosphere

The graphic above shows the four types of processes in the atmosphere, more specifically in the troposphere, its lowest layer. The troposphere extends from the surface to a height of about 11 kilometers, on average. Tropo- is the Greek root for “changing”.

At the largest scales in the troposphere, the dominant interactions arise from the coupling between thermodynamic and kinematic processes. Temperature gradients across continents and oceans establish pressure gradients. Air is drawn from high toward low pressure, creating broad accelerations of air. These accelerations organize into the jet stream when the horizontal temperature contrasts in the midlatitudes become sharp enough to support a strong pressure gradient. Thus, thermodynamic structure and kinematic response reinforce one another over thousands of kilometers, producing a directed flow that persists for days or weeks.

At the atmosphere’s smallest scales, the balance shifts because thermodynamic and kinematic couplings no longer act alone. Near the surface, moisture, aerosol particles, and radiative processes structure the background temperature and humidity patterns, and this structure determines when small parcels of air become buoyant enough to rise. Radiative heating by the sun sets the vertical temperature gradient, while aerosols and moisture establish the temperature threshold at which condensation begins, releasing microphysical energy in the form of latent heat. Once rising motion forms, vertical currents known as convection become the primary pathway by which energy and moisture are carried upward from the surface.

Thus, convection is the mechanism that re-distributes the sun’s energy throughout the depth of the troposphere and mediates the exchange of energy between small and large scales. The pattern in which buoyant plumes of rising air release their energy influences how the atmosphere couples across scales and how the entire troposphere reorganizes itself from the surface to its upper boundary, since each release alters the pathways through which energy and mass circulate through the system.

The Four Types of Atmospheric Processes

Thermodynamic

Thermodynamic Processes in General

Thermodynamic processes govern how temperature, density, and pressure evolve under expansion, compression, and phase changes of water as air moves up and down in the atmosphere. They determine how fast the molecules are moving (temperature), how close together they are (density), and how much force they exert on their surroundings (pressure). Mathematically, these three variables are related by the ideal gas law.

In the atmosphere, pressure and density generally maintain vertical gradients in the form of a smooth, exponential decay (see purple and yellow lines in the photo below). Pressure and density are strongly coupled in the atmosphere, and they depend on altitude.

When the air near the earth’s surface becomes sufficiently warmer than the air above, thermodynamic processes create a linear vertical gradient in temperature. We refer to the slope of this line as the lapse rate. Averaged over a long time, a constant lapse rate (red line below) extends throughout the entire depth of the troposphere (the lowest layer of the atmosphere; red box below).

Adiabatic Processes, Latent Heating, and Moist Convection

On a sunny day, solar radiation warms the earth’s surface. Warm air parcels (blobs of air) freely rise from near the surface, cooling and expanding as they ascend. The warm, rising current that results from surface heating – illustrated in Figure 3 below – is known as a thermal. In response, sinking air forms outside the of the thermal. These sinking air parcels warm and compress. The responses of temperature, density, and pressure as the air parcels move vertically in this convection cell are called adiabatic.

As air parcels rise, they naturally expand adiabatically (without outside heat) because the pressure in the surrounding environment decreases. As rising air cools to its saturation point and continues upward, water vapor in the rising parcel condenses, producing liquid droplets. This phase change warms the air parcel a bit, partially offsetting the parcel’s expansional cooling as it rises. If enough cloud droplets form and remain held together, a cumulus cloud forms. The cross-domain process that lifts that air to produce such cumulus clouds is known as moist convection. Dry convection, which does not result in cloud production, is possible in dry climates.

Let’s visualize these relationships on a diagram. As an air parcel rises, we consider it to be a closed system whose state is governed by two thermodynamic processes: adiabatic processes (top) and latent heating (bottom). Dry adiabatic processes (left left) involve the three-way interaction among temperature, pressure, and density. Pressure and density are coupled, because they display the same exponential decay throughout the atmosphere. When we need to account for the effect of the phase changes of water in the air parcel, the process becomes moist adiabatic.

While we assume that no outside heat is entering the parcel as it rises, the internal thermodynamic change produced by condensation is communicated outward because the added heat affects the surrounding environment. This creates a cross-scale coupling between microscale phase changes and macroscale temperature tendencies. The diagram captures this in the lower panel by placing microphysical processes on the small-scale side of the system and by showing how latent heating links them directly to the larger thermodynamic structure that shapes the atmosphere’s behavior.

Weather Balloon Soundings

Tying It Together

The ratio of latent heating processes to adiabatic (closed-system) processes in the atmosphere tends to remain around 0.33, reflecting the dominance of adiabatic cooling in the overall thermodynamic balance. The value of this ratio is determined by the nesting among the processes of which it is composed, as is illustrated in Figure 4 above. Pressure-density couples with temperature in adiabatic processes, while latent heating is a separate process that is purely microphysical, giving an overall ratio of 1:2. Thus, this ratio reflects the structure of the process network itself.

Observations show that the ratio of latent heating to adiabatic cooling varies between roughly 0.3 to 0.4, depending on the extent to which other processes are coupled with the rising air. For example, kinematic processes can modify this ratio when wind shear or turbulent mixing alters the rate at which a parcel entrains or detrains surrounding air, since these exchanges change the parcel’s temperature and moisture content before condensation occurs. As a result, the observed ratio reflects not only the internal structure of dry and moist adiabatic processes but also the influence of the surrounding environment and the pathways through which energy is exchanged with it.

Kinematic

Kinematic processes describe the how air moves under the influence of forces (pressure gradients, Coriolis acceleration, and friction). Kinematic processes serve as the atmosphere’s transport mechanism, and they are ultimately derived from Newton’s second law (Force = Mass times Acceleration). They move thermodynamic energy and mass, including water in the form of ice, liquid, and vapor. If we view thermodynamic processes as the compression and expansion that power a steam engine, then kinematic processes are the train coming down the tracks.

When kinematic movements are coupled with thermodynamic processes, they produce organized vertical currents, such as thermals. As we have seen, thermodynamic processes also couple with microphysical processes to create moist convection. These resulting cross-domain interactions determine how convective structure and organization evolves to form thunderstorms and other precipitation systems.

Wind and Turbulence

Wind can be understood as the organized motion of air that arises when pressure gradients establish a preferred direction of flow. These gradients form when temperature and density fields evolve through adiabatic and latent-heating processes, which means that wind an expression of the thermodynamic structure beneath it. As the atmosphere adjusts toward equilibrium, air accelerates from regions of higher pressure toward lower pressure, and the resulting motion carries with it the imprint of every process that shaped the underlying temperature and moisture distribution.

Turbulence forms when this organized motion becomes unstable at smaller scales. Any parcel that accelerates through a non-uniform environment encounters gradients in temperature, moisture, and momentum that disrupt its trajectory. These disruptions break the flow into eddies of many sizes, although the smallest eddies are governed by the same thermodynamic constraints that shape the dry and moist adiabatic pathways. Turbulence therefore represents a loss of coherence in the flow, since the parcel can no longer maintain a single relationship among pressure, density, temperature, and microphysical activity.

Wind and turbulence often coexist because the atmosphere rarely evolves under perfectly uniform conditions. As a result, the same vertical structures that promote rising motion and phase changes also establish regions where the flow becomes uneven or even chaotic. Turbulence influences how efficiently rising air entrains or detrains surrounding air, while wind defines the larger environment in which these smaller-scale adjustments occur. In this framework, both wind and turbulence are expressions of how the atmosphere reconciles the coupling among its thermodynamic, kinematic, and microphysical processes at different scales.

Rotation

When thermodynamic and microphysical couplings adjust the vertical structure of the atmosphere, they also change the environment in which rotation organizes itself. Rotation is always present in the atmosphere in weak, disorganized form, but it rarely produces concentrated vortices.

Rotation becomes more organized when coupling between kinematic and other processes establishes a vertical gradient in wind speed or direction, known as wind shear. This shear creates layers of air that move past one another at different velocities, and the difference in motion produces small amounts of horizontal rotation, or vorticity.

Under normal conditions, this vorticity remains diffuse and has no pathway to intensify, although it is always present as a background property of the flow. Turbulence then acts on this sheared environment by breaking the flow into eddies, each carrying fragments of this horizontal rotation. Most of these eddies remain short-lived, since the surrounding atmosphere dissipates them quickly, although they still reveal the underlying structure of the shear field.

When rising motion becomes established, the situation changes because a sustained updraft can lift and stretch the vorticity that shear and turbulence have already generated. Stretching preserves angular momentum and increases the rotation rate, although this increase will only persist when the updraft remains coherent over depth.

Thermodynamic and microphysical processes maintain that coherence by controlling buoyancy, lapse rates, and the location where phase changes occur. As the updraft deepens and cools more slowly in response to latent heating, it gains the ability to draw in and vertically align the scattered patches of rotation produced by shear and turbulence. This alignment allows rotation to shift from a diffuse background property to an organized, vertically oriented circulation.

Tornadoes: A Process-Based Framework

A tornado requires a set of conditions in which the evolving temperature and moisture structure lowers the strength of the density gradient in a rising current while preserving the ambient wind shear that supplies horizontal vorticity. When a rising parcel approaches saturation, latent heating reduces its lapse rate, slows its rate of cooling, and allows the updraft to maintain buoyancy for a greater depth. This deeper buoyant column can then lift and stretch the background vorticity that already exists in the environment.

The stretching increases the rotation rate through angular momentum conservation, in much the same way that a skater spins faster by lifting her arms. Stretching requires that the amplification only occurs when the thermodynamic environment supports a sustained vertical current.

Tornadoes therefore emerge when the coupling among adiabatic processes, latent heating, and the ambient shear field creates a vertically continuous pathway for rising air that is capable of concentrating rotation into a narrow core.

Microphysical

Microphysical processes provide the physical fuel for the atmosphere’s kinematic engine. An engine only moves if something else makes it move. The fuel is water, and the “combustion” of that fuel occurs through water’s phase changes: solid, liquid, gas. Microphysics involves not only the phase changes of water, but also the interactions between water and aerosols (small solid and liquid particles). Aerosols provide the sites on which water vapor condenses to form liquid droplets.

Of the phases of water, liquid droplets are especially important because they are most equipped to efficiently recycle thermodynamic energy at a bulk scale through the exchange of latent heat with the surroundings. Although microphysical processes occur at micrometer scales, wider kinematic and thermodynamic processes organize droplet production, creating concentrated regions of phase changes that power storms.

The Subcritical Aerosol-Moisture Feedback

Microphysical processes are involved in the three-way Subcritical Moisture-Aerosol Feedback (SAMF) among moisture, aerosols, and radiation. My recent, peer-reviewed study from last April’s solar eclipse provides evidence for SAMF and briefly explains how it operates.

When radiative forcing changes, such as during the morning as the sun angle becomes more direct, the surface layer begins to reorganize its temperature and moisture structure. The increase in shortwave radiation warms the ground and accelerates evaporation, which raises the humidity of the air immediately above the surface. Aerosol particles absorb this moisture according to their composition and size, and they determine how quickly the vapor field approaches saturation.

As the radiative input continues to rise, the boundary layer experiences repeated cycles of slight warming and slight moistening, and these cycles alter the balance between adiabatic cooling in rising parcels and the latent heating that accompanies condensation. The atmosphere therefore enters a period in which moisture, aerosols, and radiation repeatedly adjust each other, and the small changes in their coupling begin to accumulate.

This pattern of adjustment lies at the core of the Subcritical Aerosol–Moisture Feedback. In SAMF, the earth’s boundary layer remains below the threshold for deep convection, yet the interactions among moisture, aerosols, and radiative forcing allow the system to store energy in a manner that is not immediately expressed as buoyant ascent. Each increment of radiative warming modifies the humidity field; each change in humidity alters the propensity of aerosols to take up water; and each microphysical adjustment influences how quickly rising parcels can convert latent heating into buoyancy. The feedback can either suppress or accelerate the onset of convection depending on the responses within the system.

The feedback arises because these changes reinforce one another, allowing the boundary layer to retain moisture and energy more effectively than traditional parcel theory would suggest. As the morning progresses, the system becomes increasingly primed for release, even though no single process is strong enough to initiate deep convection on its own.

Microphysical Control of Lapse Rates and Convective Readiness

As SAMF strengthens, the microphysical adjustments it produces begin to influence the lapse rate itself. Moisture retained in the boundary layer raises the dewpoint, which reduces the temperature at which rising parcels reach saturation. Earlier saturation increases the contribution of latent heating, which slows the rate of cooling with height and steepens the contrast between the environmental lapse rate and the parcel’s effective lapse rate.

Even though convection has not yet initiated, the boundary layer becomes more vertically structured because the moisture field and the aerosol population now dictate how buoyancy will develop once rising motion begins. In this way, SAMF allows microphysical processes to modulate the thermodynamic profile long before any clouds form, creating the conditions under which a later release can occur rapidly and with greater depth.

These relationships depend strongly upon aerosol composition, in particular the relative abundance of hydrophilic and hydrophobic aerosol particles. When hydrophilic aerosols dominate, heat and moisture are distributed more evenly, which tends to dampen the impact of the onset of convection. When hydrophobic aerosols dominate, the opposite scenario unfolds: gradients of heat and moisture are larger, and the onset of convection is more delayed but more explosive. The evolution of the aerosol population over time through chemical reactions can determine the organization of the convective storms that are produced. This causal chain is detailed in this blog post.

Radiative

Radiative processes involve the electromagnetic radiation that is produced by all objects. Right now, radiative processes are most important at the climate scale, because we’ve poured lots of greenhouse gases into the atmosphere. In an atmosphere where greenhouse gas concentrations rise rapidly, the rate at which longwave radiation escapes to space decreases, and the system becomes slower to shed the thermal anomalies produced by surface heating through radiative cooling. The atmosphere therefore spends more time in a state of elevated energy before the next episode of ventilation restores part of the vertical temperature structure.

The vertical redistribution of radiative energy by greenhouse gases has resulted in the build-up of heat in cold regions, especially at the surface, which we call Arctic amplification, and the cooling of the upper troposphere and lower stratosphere in the tropics.

Radiative processes also play a critical role within convective storms, especially near their tops and along their edges, where the atmosphere transitions from dense, particle-rich clouds to the surrounding clear air. Longwave radiation escapes efficiently from cloud tops into the cold upper troposphere. This loss of radiative energy cools the cloud top and strengthens the density contrast that sustains rising motion from below.

Along cloud edges, both longwave and shortwave exchanges alter the heating and cooling of droplets and ice particles, which affects how they grow, evaporate, or sublimate. These radiative adjustments feed directly into the thermodynamic and microphysical processes that govern buoyancy, latent heating, and entrainment, and they determine the depth and intensity of the updrafts that form. In this way, radiative processes help regulate the vertical pathway through which energy and moisture are transported from the surface into the upper troposphere.

At the shorter timescales that govern weather, radiative processes are primarily paired with microphysical processes because coupling among moisture, aerosols, and radiation regulates how convective potential builds and is released near the earth’s surface.

Toward a Process-Based Forecasting Approach

A process-based forecasting approach begins by identifying which families of processes are active at a given time and how they are coupling across scales. Instead of focusing on predetermined storm types or predefined regimes, the forecaster examines the balance among thermodynamic, kinematic, microphysical, and radiative processes and determines how these balances evolve.

This requires attention to where the atmosphere is gaining or losing energy, where moisture and aerosols are creating buoyancy, and where vertical or horizontal gradients are building pathways for organized motion. When seen in this way, the atmosphere becomes a continuously adjusting system in which each change in structure reflects a change in the strength or configuration of the underlying processes.

This perspective improves forecasting because it treats the relevant interactions directly rather than relying on surface-level analogies. A forecaster who can identify when the boundary layer is primed for deep coupling, when radiative cooling at cloud top will strengthen ascent, or when microphysical activity will alter lapse rates is better positioned to anticipate how the atmosphere will reorganize itself. This approach also sharpens the diagnosis of severe weather potential, because it reveals when the atmosphere is assembling the specific combinations of buoyancy, shear, and microphysical activity that allow rotation to organize and storms to intensify.

A process-based approach therefore offers a pathway to more consistent and physically grounded forecasts, because it connects the behavior of the atmosphere at small scales to the patterns that emerge across the troposphere and ultimately give rise to the weather we observe.

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Author’s Note: This summary is freely available for educational use. Please cite “Jessup, S. (2025). How the Atmosphere Works: A Process-Based Framework” in scholarly work.

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