Glossary#

Terms are written for scientific software engineers rather than meteorologists. Each entry states the concept plainly, then how it appears in tephpy. See Documentation Style for the entry and cross-reference rules. Where a definition is the discipline’s rather than this package’s, the American Meteorological Society’s Glossary of Meteorology [AmericanMSociety24] is the authority.

tephigram#: A thermodynamic diagram that plots temperature against entropy on a rotated coordinate system, so that isotherms and dry adiabats form an exactly perpendicular straight-line grid. tephpy renders it as a Matplotlib projection named "tephigram".
projection#: Matplotlib’s name for a custom Axes class registered under a string, selected with plt.subplots(subplot_kw={"projection": ...}) — nothing to do with a map projection. Importing tephpy registers TephigramAxes under "tephigram", which is why every example imports the package even where it names nothing from it.
sounding#: A vertical profile of atmospheric measurements (pressure, temperature, dewpoint, wind) from a single ascent. In tephpy a sounding is carried by the Sounding dataclass — pressure and temperature arrays (plus optional dewpoint and wind) held as pint quantities with station/time metadata — and drawn with ax.plot_sounding(...) as red temperature and green dewpoint profiles.
dewpoint#: The temperature air must cool to, at constant pressure and moisture content, to become saturated; it is never above the air temperature (equality means saturation). In tephpy it is the optional dewpoint field of a Sounding (°C internally, any pint temperature unit accepted), plotted green alongside the red temperature line.
profile#: One curve of a temperature-like quantity against pressure — a sounding’s temperature or dewpoint trace, or a computed parcel path (the calc.Profile dataclass). ax.plot_profile(...) draws it through the tephigram transform machinery.
entropy#: The thermodynamic quantity whose defining property, for reading a chart, is that area on a temperature–entropy diagram is energy. For dry air the specific entropy is \(c_p \ln \theta\) plus a constant, so potential temperature carries it: tephpy plots \(\ln \theta\) and never computes entropy itself, which is why the diagram is called T–ln θ rather than T–s.
potential temperature#: The temperature an air parcel would have if moved dry-adiabatically to the 1000 hPa reference pressure; written θ (theta). In tephpy it is the second native coordinate of the tephigram plane — transforms.theta_from_pressure_temperature computes it (°C) from pressure (hPa) and temperature (°C).
dry adiabat#: A line of constant potential temperature — the path an unsaturated parcel follows when lifted. On a tephigram, dry adiabats are straight lines exactly perpendicular to the isotherms.
isotherm#: A line of constant temperature. On a tephigram, isotherms are straight parallel lines; their exact perpendicularity to the dry adiabats is the diagram’s defining property and is asserted directly in the test suite.
isopleth#: A line along which one quantity is constant. The tephigram background is five isopleth families — isotherms, isobars, dry adiabats, moist adiabats, and lines of constant humidity mixing ratio — each drawn by one zoom-aware Matplotlib artist (IsoplethFamily) that selects the members appropriate to the current view.
isobar#: A line of constant pressure. Pressure is not an axis of the tephigram, so each isobar is a gentle curve across the temperature/potential temperature grid; tephpy labels isobars in hPa and reconfigures them via ax.isobars(...).
moist adiabat#
saturation adiabat#
saturated adiabat#
wet adiabat#: The path a saturated air parcel follows when lifted: heat released by condensation makes it cool more slowly than a dry adiabat. Each curve is labelled by its wet-bulb potential temperature — the temperature where it crosses 1000 hPa. tephpy computes moist adiabats with metpy.calc.moist_lapse() and truncates them at low temperature where they converge onto the dry adiabats; “moist adiabat” is the canonical name, matching the AMS Glossary headword and MetPy’s vocabulary.
lapse rate#
dry adiabatic lapse rate#
DALR#
moist adiabatic lapse rate#
saturated adiabatic lapse rate#
SALR#: The rate at which temperature falls with height. Two of them matter on a tephigram, and they are the rates the two adiabat families draw: the dry adiabatic lapse rate (DALR), which an unsaturated parcel cools at, and the moist adiabatic lapse rate (SALR, for saturated), which a saturated one cools at — more slowly, because condensation releases heat into the parcel as it rises. Which of the two a lifted parcel is following, and where it changes over, is the whole content of a parcel ascent. “Moist” leads here for the same reason it leads in moist adiabat: one canonical spelling per concept, and that entry chose it. tephpy has no lapse-rate API of its own. The dry rate is implicit in every dry adiabat the diagram draws, and the saturated rate is MetPy’s — metpy.calc.moist_lapse() is what a moist adiabat is integrated from, and what it integrates is strictly the pseudoadiabatic rate, which differs from the reversible saturated rate by an amount no tephigram resolves.
wet-bulb potential temperature#: The temperature a parcel would have if brought saturated along a moist adiabat to the 1000 hPa reference pressure; written θw (theta-w). It is conserved along a moist adiabat, which is why tephpy uses it (°C) as the member value labelling each moist adiabat.
humidity mixing ratio#
mixing ratio#
isohume#: The mass of water vapour per mass of dry air, in g/kg. On a tephigram, a line of constant saturation mixing ratio (an isohume) marks where air of a given moisture content saturates; tephpy computes these lines with MetPy and labels them in g/kg via ax.mixing_ratios(...).
parcel#
air parcel#: An imagined small mass of air lifted through the surrounding environment without mixing with it — the tephigram’s basic tool for reasoning about stability. Its parcel ascent is what the diagram plots; in tephpy the parcel= option of calc.parcel_path chooses where that ascent begins: "surface" or "mixed-layer" (the lowest 100 hPa averaged).
parcel ascent#
parcel path#: The path a lifted parcel traces on the diagram: dry-adiabatically from its start level to the LCL, then along a moist adiabat above it. Comparing that path against the environment sounding is what yields CAPE, CIN, and the LFC and EL levels — the ascent is the construction, they are its readings. calc.parcel_path(...) computes it as a calc.Profile.
lifting condensation level#
LCL#
Normand’s point#: The level where a lifted, unsaturated parcel first saturates — on a tephigram it is Normand’s construction: the dry adiabat through the parcel’s temperature meets the humidity mixing ratio line through its dewpoint. calc.normand_point(...) returns it as scalar (pressure, temperature) pint quantities, calc.parcel_path splices it into the ascent exactly, and the operational -25 mb cloud-base correction is applied only when requested via cloud_base_correction=.
level of free convection#
LFC#: The level above which a lifted parcel becomes warmer than its environment and rises freely. In tephpy it is the lfc_pressure/lfc_temperature fields of calc.SoundingIndices — NaN quantities when the parcel never becomes positively buoyant (“does not exist” is an answer, not an error).
equilibrium level#
EL#: The level above the LFC where a rising parcel cools back to the environment temperature — roughly the anvil top of a thunderstorm. The el_pressure/el_temperature fields of calc.SoundingIndices; NaN when the parcel is still buoyant at the profile top (CAPE can be positive with no EL).
CAPE#
convective available potential energy#: The energy per unit mass (J/kg) available to a parcel between the LFC and the EL, where it is warmer than the environment — the fuel gauge for deep convection. calc.indices(...) reports it (0 J/kg — never NaN — when there is none) and ax.shade_cape(snd, parcel) shades the region.
CIN#
convective inhibition#: The energy per unit mass (J/kg, non-positive) a parcel must be given to reach its LFC through the layers where it is cooler than the environment — the cap that must break before CAPE is released. Reported by calc.indices(...) and shaded by ax.shade_cin(snd, parcel).
cap#
capping inversion#: The warm, stable layer above the surface that holds a lifted parcel down until something breaks it — the physical thing CIN measures, which is why forecasters quote a cap in J/kg and speak of it eroding through the day. tephpy reports the number as the cin field of calc.SoundingIndices.
lifted index#: The environment-minus-parcel temperature difference at 500 hPa (°C); large negative values mean instability. The lifted_index field of calc.SoundingIndices; NaN when the profile tops out below 500 hPa.
radiosonde#: The instrument package a weather balloon carries aloft, transmitting pressure, temperature, humidity, and wind as it rises — the source of most real soundings. tephpy ingests radiosonde archives through the tephpy.io readers.
special sounding#
special#: A radiosonde release outside a station’s scheduled times — 00Z and 12Z, where the Z is UTC — made when the weather warrants an extra look. The 17Z ascent that tephpy.samples ships is one, sent up about three hours before the Moore tornado of 2013-05-20.
IGRA#
Integrated Global Radiosonde Archive#: NCEI’s quality-controlled archive of the global radiosonde record, distributed as one fixed-width file per station (version 2). igra.read(...) reads one ascent from such a file into a Sounding.
wind barb#: A glyph giving the wind at one level: the shaft points toward the direction the wind comes from, and its feathers sum to the speed — half barb 5 kt, full barb 10 kt, flag 50 kt, rounded to 5 kt bins; a bare circle is calm. ax.plot_barbs(snd) draws a sounding’s barbs on a staff in the right-hand gutter, each level at the height where its isobar meets the diagram’s edge.
hodograph#: A plot of a sounding’s winds as vectors from a common origin, joined in height order, so that the shape of the curve is how the wind turns and strengthens with height. It answers what a tephigram cannot: the diagram carries the thermodynamics, and its wind barbs give one level at a time. tephpy draws no hodograph — MetPy’s metpy.plots.Hodograph composes onto the same figure, and the Examples Gallery insets one over a tephigram.