KMA Grade 9 Meteorologist key terms

The rate at which air temperature decreases with height in the atmosphere, usually expressed in degrees Celsius per kilometer; the environmental lapse rate describes the actual atmosphere, while parcel rates describe rising air.

The temperature a parcel of air would have if brought adiabatically to a standard reference pressure, usually 1000 hPa; it is conserved during dry adiabatic ascent and labels air masses.

The potential temperature a parcel would reach after all its water vapor condenses and latent heat is released; it is conserved in moist adiabatic processes and identifies air masses by heat and moisture content.

The atmosphere's resistance to vertical displacement, determined by comparing the environmental lapse rate with the dry or saturated adiabatic lapse rate; stable air resists lifting, unstable air accelerates it.

The vertically integrated buoyant energy available to a rising parcel between its level of free convection and equilibrium level; large values favor strong updrafts and severe thunderstorms.

The negative buoyant energy a parcel must overcome, usually a warm stable layer near the surface, before it can reach its level of free convection and rise freely.

The height at which a lifted parcel becomes warmer than its surroundings and therefore buoyant, marking the base of the layer where CAPE is realized in deep convection.

The thermodynamic relationship stating that the saturation vapor pressure of water increases roughly exponentially with temperature, about 7 percent per degree Celsius, which explains why warmer air holds more moisture.

The maximum partial pressure of water vapor that air can hold at a given temperature before condensation begins; it rises with temperature and sets the limit for dew point and humidity.

The ratio, expressed as a percentage, of the actual water vapor content of air to the maximum it could hold at the same temperature and pressure; it changes with temperature even if moisture is constant.

The temperature to which air must be cooled at constant pressure and moisture content for saturation to occur; its closeness to the actual temperature indicates high humidity and fog or cloud risk.

The height at which a rising parcel of air cools to its dew point and condensation begins, typically marking the base of cumuliform clouds and estimated from surface temperature and dew point.

The theoretical horizontal wind that results when the pressure gradient force is exactly balanced by the Coriolis force, blowing parallel to straight isobars aloft with low pressure to the left in the Northern Hemisphere.

An apparent force arising from Earth's rotation that deflects moving air to the right in the Northern Hemisphere and to the left in the Southern Hemisphere, growing with wind speed and latitude.

The force per unit mass that pushes air from higher toward lower pressure, directed perpendicular to isobars and proportional to how closely they are spaced on a constant-height chart.

The balanced wind along curved isobars in which pressure gradient, Coriolis, and centrifugal forces combine; it is supergeostrophic around ridges and subgeostrophic around troughs.

The vertical shear of the geostrophic wind, related to the horizontal temperature gradient; it explains why winds strengthen and veer with height in baroclinic zones such as fronts and jet streams.

A relation showing that the thickness of a layer between two pressure surfaces is proportional to its mean virtual temperature; warmer layers are thicker and appear as higher geopotential heights.

The height of a pressure surface above sea level expressed in geopotential meters, used on upper-air charts because it removes much of the variation of pressure with altitude and reveals ridges and troughs.

A measure of the local rotation of fluid parcels; positive relative vorticity indicates counterclockwise spin in the Northern Hemisphere and favors rising motion and cyclogenesis downstream.

A conserved quantity combining absolute vorticity and stratification, often on an isentropic surface; it tracks tropopause anomalies and stratospheric intrusions and helps diagnose developing cyclones.

A large-scale wave in the midlatitude westerlies driven by the variation of the Coriolis parameter with latitude; its ridges and troughs steer surface weather systems and cold-air outbreaks.

A narrow, fast-moving band of strong upper-level winds near the tropopause, located above strong horizontal temperature gradients and associated with storm tracks and clear-air turbulence.

An atmospheric state in which surfaces of constant pressure and constant density intersect, so horizontal temperature gradients exist; this configuration supplies energy for extratropical cyclones.

An idealized state in which density depends only on pressure, so isobars and isotherms are parallel and no thermal-wind shear exists; real lows tend to become more barotropic as they mature and occlude.

The process by which a temperature gradient sharpens into a front, typically through deformation, convergence, or differential diabatic heating; the opposite process is frontolysis.

The leading edge of a cooler, denser air mass advancing into warmer air; it often brings a narrow band of heavy showers or thunderstorms followed by a sharp temperature drop and wind veer.

The boundary where advancing warm air rides over cooler air, producing a broad, gently sloping cloud sequence and prolonged light precipitation ahead of the surface front.

The front that forms when a faster cold front overtakes a warm front and lifts the warm sector off the ground; it marks the late, decaying stage of a midlatitude cyclone.

The component of the wind field that stretches and squeezes air parcels without changing their area, commonly producing frontal zones and narrow precipitation bands along its axis of dilatation.

A cluster of thunderstorms organized over a scale of roughly 100 kilometers or more that produces a contiguous precipitation area, often with a leading line and trailing stratiform region.

A narrow, fast-moving line of intense thunderstorms, often along or ahead of a cold front, capable of producing damaging straight-line winds and brief heavy rainfall.

A long-lived thunderstorm with a persistent rotating updraft, or mesocyclone, sustained by strong vertical wind shear; it is the storm type most associated with large hail and tornadoes.

The change of wind speed or direction with height; moderate shear organizes thunderstorms and lengthens their life, while extreme shear supports supercells and tornado potential.

An elongated region of relatively low pressure or low geopotential height, shown as a kink in isobars or height contours; it favors convergence, ascent, and unsettled weather downstream.

An elongated area of relatively high pressure or high geopotential height; it favors subsidence, clear skies, and often heat buildup beneath it in summer.

The vertical distance between two standard pressure surfaces, such as 1000 to 500 hPa; it serves as a proxy for mean layer temperature and helps locate rain-snow lines and air-mass boundaries.

The boundary between the troposphere and stratosphere where temperature lapse rate falls below a threshold, capping most weather; its height and breaks reveal jet streams and upper-level features.

The tendency of cities to be warmer than surrounding rural areas because of heat storage in buildings, reduced evapotranspiration, and human energy release, strongest on calm clear nights.

The fraction of incoming solar radiation reflected by a surface or by the atmosphere; snow and clouds are highly reflective, while oceans and forests absorb most sunlight.

The balance between incoming shortwave solar radiation absorbed by Earth and outgoing longwave radiation emitted to space; imbalances drive global warming or cooling and shape regional climate.

The warming of the lower atmosphere because gases such as water vapor and carbon dioxide absorb outgoing infrared radiation and re-emit part of it downward toward the surface.

A radar that measures both the reflectivity and the radial velocity of precipitation particles, allowing forecasters to detect rotation, convergence, and damaging wind gusts inside storms.

An instrument package carried aloft by a weather balloon that measures temperature, humidity, and pressure and reports wind by tracking the balloon, producing a vertical sounding.

A thermodynamic chart plotting temperature and dew point against pressure, with skewed isotherms and dry and moist adiabats, used to assess stability, shear, and convective potential from a sounding.

The process of combining observations with a short numerical model forecast to produce the best estimate of the current atmospheric state, which then initializes the forecast run.

Forecasting the atmosphere by solving the governing physical equations on a three-dimensional grid from an analyzed initial state, with skill limited by resolution and chaotic error growth.

Running many slightly perturbed model simulations to sample uncertainty; the spread among members indicates forecast confidence, and agreement suggests a more reliable outcome.