Glossary and Acronyms: P

Parallax error :

in general, it is the apparent displacement of an object caused by a change in the position from which it is viewed. Applied to tropical systems, it is the apparent discrepancy between the real centre fix and the centre viewed on the satellite imagery, when the satellite is not right above the tropical system.

Pascal:

The SI derived unit of pressure. One pascal (Pa) is equal to 1 newton m^-2. The hectoPascal (hPa) is the preferred unit for atmospheric pressure, but the more familiar millibar (mb) is the unit of pressure generally used by meteorologists, by international agreement; 1 mb = 1 hPa (hectoPascal). For a typical sea level pressure, 102.345 kPa = 1023.45 hPa = 1023.45 mb.

PDUS :

Primary Data Unit Station.

Phase diagram:

diagram with the goals of increased forecast accuracy of tropical system development (in particular from extratropical or subtropical cyclones), and the development of warm-core or hybrid structure within extratropical cyclones.
See Extratropical transition and http://moe.met.fsu.edu/cyclonephase/.

POES :

Polar Operational Environmental Satellite (USA).

Polar:

Polar air is an air mass that staid in high latitudes during several days and also became relatively cold, in the lower atmospheric layers at least.
A polar front is a quasi-permanent front of great extent, in middle latitudes, which separates polar air from tropical air.
The polar front theory (theory of the Bergen school, 1918) describes the formation and evolution of extratropical depressions in terms of the interaction between polar and tropical air masses and the characteristics of the surface of discontinuity which separates them.
A polar low is a small, shallow depression which forms mainly in winter over some high-latitude seas within a polar or arctic air mass. Its motion is approximately the same as the air stream in which it is embedded.

PPI :

Plan Position Indicator, radar product corresponding to an azimutal scanning; rain echos are projected on an horizontal surface.

Pressure gradient:

rate of change of pressure with distance (the vector is directed toward low pressure). The bigger the horizontal gradient, the stronger the wind.

PT :

Pattern T-Number. Used in the tropical cyclone intensity analysis Dvorak Technique.