Parameterization-
The representation, in a dynamic model, of physical effects in terms of admittedly oversimplified parameters, rather than realistically requiring such effects to be consequences of the dynamics of the system.
Parcel-
An imaginary volume of fluid to which may be assigned various thermodynamic and kinematic quantities.
Partial pressure-
The pressure that a component of a gaseous mixture would have if it alone occupied the same volume at the same temperature as the mixture.
Particulates-
The term for solid or liquid particles found in the air.Some particles are large or dark enough to be seen as soot or smoke.
Passive cloud-
A cumulus cloud that is no longer dynamically connected with the atmospheric boundary layer via updrafts or downdrafts.
Planetary boundary layer-
The bottom layer of the troposphere that is in contact with the surface of the earth.It is often turbulent and is capped by a statically stable layer of air or temperature inversion.
Permanent echo-
A radar echo from a stationary object, such as a building, a hill, or power lines, that may interfere with the detection or measurement of other kinds of echoes.
Perturbation-
Any departure introduced into an assumed steady state of a system. The magnitude is often assumed to be small so that product terms in the dependent variables may be neglected.
Photochemical air pollution-
Type of air pollution, such as Los Angeles smog, associated with the buildup of oxidation products formed from the degradation of hydrocarbons, etc.
Photolysis-
The process by which a chemical species undergoes a chemical change as the result of the absorption of a photon of light energy.
Plow wind-
Strong straight line winds associated with nontornadic outflow from strong thunderstorms.
Plume-
Buoyant jet in which the buoyancy is supplied from a point source; the buoyant region is continuous. 2. A mostly horizontal (sometimes initially vertical) stream of air pollutant that is being blown downwind from a smokestack.
Point source-
With respect to radiation, a single point in space emitting radiation.The radiation from such a source may be expressed as flux per unit solid angle.
Point vortex-
A straight line vortex, the flow of which can be modeled in two dimensions, with a point concentration of vorticity surrounded by irrotational flow.
Pop up thunderstorm-
An airmass thunderstorm that forms rapidly in an otherwise rain free environment. This most often occurs on warm, humid days, in unstable meteorological conditions.
Potential temperature-
The temperature that an unsaturated parcel of dry air would have if brought adiabatically and reversibly from its initial state to a standard pressure, p0, typically 100 kPa.
Precipitable water-
The total atmospheric water vapor contained in a vertical column of unit cross sectional area extending between any two specified levels.
Prefrontal squall line-
A squall line less than about 100 km ahead of a cold front, in the warm sector, having an orientation more or less parallel to the cold front.
Pressure tendency-
The character and amount of atmospheric pressure change during a specified period of time, often a three hour period preceding an observation.
Pseudoadiabatic process-
A moist adiabatic process in which the liquid water that condenses is assumed to be removed as soon as it is formed, by idealized instantaneous precipitation.
