Short-term alteration of climate, usually as a response to external impact (e.g. rapid warming within some decades).

Moisture content of unit volume of air (g/m³).

Part of solar radiation absorbed on aerosol particles.

The process when sulphur-dioxide released into the atmosphere, to the effect of water vapour, turns into sulphuric acid and nitrogen-oxides into nitric acid and then through dry or wet deposition (with precipitation) causing damage by reducing the pH of soils and surface waters.

Process with neither heat gain or release of the atmospheric system; changes in the properties of an ascending moist air mass according to the moist adiabatic gradient on the windward side and according to the dry adiabatic gradient on the leeward side of a mountain.

Mostly horizontal motion of major air masses, conveying heat, vapour and/or salts.

Precipitation event due to the rapid motion of moist air, accompanied by friction-originated electric discharges (thunder and lightning).

Solid or fluid particles of typically 0.01 to 10 micrometres floating in the air (dust, soot, or acidic water droplets).

Body of air with distinct properties typical of the area of formation although modifed as they move (an example is a polar maritime cold and moist air mass).

Percentage of solar insolation reflected from a surface (for instance, for a fresh snow surface: around 90%).

Medium high heaped cloud, disrupted stratus cloud; it form after entensive rainfall due to downward air motion.

High-pressure atmospheric phenomenon with clockwise air swirling near the ground on the Northern Hemisphere and bright skies.

Layer of the ionosphere at 200-400 km elevation, named after Sir Edward V. Appleton, a British physicist; it reflects short-length radio waves even at night.

The air layer around the Earth or other planets; subdivided into the troposphere, stratosphere, mesosphere, thermosphere and exosphere.

Near-surface layer of the atmosphere with friction and most efficient heat transfer.

Atmospheric low pressure.

Polar light caused by the interactions between the electrically charged solar particles reaching the Earth’s magnetic field and the atmospheric gases in the ionosphere at high latitudes (called aurora borealis in the north and aurora australis in the south).

12-grade wind strength classification named after Sir Francis Beaufort, British rear admiral; its highest grade is the hurricane (wind speeds above 120 km per hour).

Group of aerosols with particular light absorbing properties and chemical reactions (mainly soot, charcoal and other organic substances).

Snow storm formed below freezing point, involving intense snowfall and wind ( above 50 km per hour) with visibility drastically reduced.

Typical cold and dry stormy wind in the Adriatic Sea region.

Wind province of 6-49 km per hour velocity on the Beaufort scale.

Natural law discovered by Christophorus Henricus Diedericus Buys Ballot: standing on the Northern Hemisphere with back to the wind, low pressure is to the left in front and high pressure is to the right in the back; the opposite is true for the Southern Hemisphere.

Variable atmospheric gas of natural origin, produced by the burning of fossil fuels and the biomass; the most important greenhouse gas of enthropogenic origin.

Enhancing the photosynthesis of crops by raising CO₂ concentrations.

Graphitic carbon particle of microscopic size, deriving from the burning of the biomass; belongs to aerosols.

Warm and dry descending (”snow-devouring”) wind in the Rocky Mountains.

Overcooled, quasi frozen water which usually encircles a methane molecule.

High-level cloud type of clusters arranged in rows; descending air indicating enduring sunny weather.

High-level, thin, white, heaped and rippled cloud layer.

High-level cloud type, indicates approaching warm front.

Statistical characterization of the physical state of the atmospheric system over a longer period (for minimum 30 years) expressed by mean values and variability of climate elements.

Modification of mean values and variability determining climate over time (minimum several decades).

Interaction between the processes of the climate system; positive if one process intensifies the other and negative if it weakens.

Numerical description of the climate system based on the physical, chemical and biological properties and interactions (feedbacks) of its elements (e.g. Atmosphere-Ocean General Circulation Models, AOGCM).

Probability estimation concerning climate in the future.

Estimation of the response of the climate system to emissions and concentration changes of greenhouse gases; involves greater uncertainty than climate predictions.

Description of imaginary future climates (often in strongly simplified form) in order to present the consequences of human modification of climate, often projecting trends; input for climate modelling.

It shows how the Earth’s climate changes to the effect of climate forcings (e.g. mean temperature change to the doubling of CO₂ concentration).

Intricate system of five main subsystems (the atmosphere, hydrosphere, cryosphere, land surfaces and biosphere) and their interactions under the influence of climate forcings.

Variation of mean climate parameter values and other statistical indicators (standard deviation, probability of extreme values) at any spatial and temporal scale; natural processes induce internal, while human activities external variability.

The difference between precipitation amount on the ground and evapotranspiration.

Scientific discipline concerned with the climate of the Earth, the distribution of climate types, and changes of the climate system.

Atmospheric formations at various levels, originated from the precipitation of water vapour from the air, composed of ice crystals and/or water droplets.

Aerosol particles on which water wapour precipitates during cloud formation and water droplets are produced.

Proportion of the sky obscured by clouds (traditionally expressed in eighths or oktas); occurrence of various types of cloud.

The process when the moisture content of the air precipitates on condensation nuclei and condenses into water droplets.

Climate forcing caused by various greenhouse gases compared to carbon-dioxide as a unit.

Frontal zone between warm air masses in an area and the cold air masses arriving there; cold air squeezes out warm air.

Components of the atmosphere the percentages of which remain unchanged for a long period (like nitrogen, oxygen and noble gases).

Ascending air current generally due to the heating of the ground surface.

Deflecting effect on air masses caused by the Earth’s rotation, a fictitious force; first described by Gaspard-Gustave de Coriolis, French mathematician and engineer; on the Northern Hemisphere wind and water currents are deflected to the right, while on the Southern Hemisphere to the left.

Stream of high-velocity particles (atoms, electrons) partly arriving from the Sun but mostly from our Galaxy; their impact on the atmospheric processes on the Earth is largely unknown.

The geosphere which includes all water in a frozen state (snow, continental and sea ice, frozen ground).

Heaped cloud type of great vertical extension, associated with cold fronts and high-intensity precipitation.

Heaped cloud type of great vertical extension, composed of water droplets and ice crystals and indicating ascending air motion ("fairweather-cumuli").

Low-pressure atmospheric phenomenon with anticlockwise air swirling near the surface on the Northern Hemisphere; accompanied by extensive cloud formation and weather fronts.

Short warm spells (several centuries) of the Quaternary climate followed by gradual cooling; events reconstructed from ice core analyses.

Local air currents on the leeward side of mountains with gradually rising air temperature and dropping relative humidity.

Land degradation of arid regions as a result of climate variability and human activities.

Micro-precipitation from vapour saturated air of above-freezing temperatures at clear calm nights, formed at the dew point.

Saturation temperature at which relative humidity is 100% and water vapour precipitates from the air.

Scattering of part of the incoming radiation on aerosol particles; its consequences: daylight, blue sky, red dawn, red sky at sunset.

The difference between the maximum and minimum temperature within 24 hours.

Measure of total ozone amount: the height of a compacted ozone column at normal atmospheric pressure (1013 hPa) and 0 ºC temperature (10-5 m); its average value is 300 DU.

Hot and moist zone between trade winds over the equatorial oceans, along the ITCZ.

Obtaining information valid for a place or region from global models.

Low intensity rainfall of raindrops below 0.5 mm diameter.

The extent of the influence of some natural or anthropogenic mechanism on climate, compared to the effect of carbon-dioxide.

Irregular distribution of temperature conditions over the Pacific Ocean (El Niño), combined with alternating patterns of air pressure distribution (Southern Oscillation); although it influences the climate of several continents, its explanation is still unknown.

Input of some substance (generally causing pollution) into the atmosphere.

Difference between total incoming radiation to and total outgoing radiation from the Earth’s surface.

Evaporation from the ground surface plus transpiration of the vegetation (in mm).

The outermost atmospheric layer above 500 km altitude; with polar light (aurorae) phenomena.

Impact on climate coming from outside the climate system (e.g. volcanic eruption, change of the solar constant and man-induced effects).

Weather record only very seldom occurring at a given location (e.g. precipitation event once in 100 years; maximum or minimum temperature or wind speed).

Air circulation model named after William Ferrel, American meteorologist, for the mid-latitudes of the Earth; now replaced by the model of jet streams.

Drying effect on the leeward side of mountains caused by the gradual warming of air in the descending air current with no change in vapour content and, consequently, with reducing relative humidity.

Micro-precipitation, a cloud type formed close to the ground surface; advection fog results from warm and moist air mixing with cooler air; radiation fog occurs in clear weather over cold ground surface.

Precipitation event resulting from the encounter of a moist and warm air mass and a cold air mass, accompanied by electric discharges (lightning and thunder♫) induced by friction.

Figure 3.1. The intensity of rainfall in the Carpathian Basin during the passage of a cold front [source: Hungarian Meteorological Survey]

Large-scale system of atmospheric currents around the rotating Earth, driven by differential warming of the surface.

Air current generated by the horizontal distribution of air pressure and influenced by the Coriolis force, independent from friction with the ground.

Rain frozen onto a surface below freezing point; solid and transparent icing.

Reduction in incoming solar radiation between 1960-1990, evidenced in decreased evaporation.

Solid precipitation type of ice grains smaller than hail (2-5 mm diameter).

Heat storing capacity of the atmosphere; greenhouse gases and clouds absorb and re-radiate the radiation of the ground surface at longer wavelengths (infrared or thermal radiation) resulting in the warming of the ground and the troposphere.

Atmospheric components of natural or anthropogenic origin which absorb the infrared radiation of the ground and re-radiate it to the surface (water vapour, carbon-dioxide (CO₂), nitrous oxides (N_xO), methane (CH₄), ozone (O₃) and the halocarbons (CFCs).

Temperature value measured at 1.5 m above the ground in a well-ventillated place.

Air current system driven by temperature differences in the tropical belt (rising air near the Equator, upper tropospheric currents towards the Poles, descending air at the latitudes of the tropics and trade winds near the surface returning air to the Equator; adjusted to the seasonal shift of the Intertropical Convergence Zone (ITCZ).

Formation of ever growing ice crystals in clouds during thunderstorms, caused by intense upward air motion; then ice grains of larger than 5 mm diameter fall to the ground; the most destructive form of precipitation.

Short-lived optical phenomenon in the atmosphere, annular random refraction of light on ice particles floating in the air; it appears at angles of 22 and 46 degrees around the Sun or the Moon.

Synthetically produced organic compounds, which contain elements (mainly chlorine) damaging the ozone layer, including the HFC compounds (with hydrogen replacing chlorine) intended to substitute them.

Cool and dry southern wind in the Sahara, often with sand storms.

Reduction in the transparency of the atmosphere due to its dust and other pollutant concentration.

Exceptionally hot weather associated with anticyclones in the temperate regions of the Northern Hemisphere; temperatures are above 30°C during the day and above 25°C at night for several days coupled with high humidity contributing to high mortality .

Layer of the ionosphere at 90-120 km altitude, named after Oliver Heaviside British and Arthur E. Kennelly American atmospheric physicists; reflecting radio waves, this layer allows long-distance broadcasting; weakened significantly at night.

Atmospheric gases with considerably changing proportions (over some days or weeks) at a certain location (water vapour, carbon-monoxide, nitrogen-dioxide and others).

Microprecipitation falling from vapour saturated air below freezing at the dew point in bright calm weather.

Tropical cyclone formed in the Caribbean region if sea surface temperature reaches 26.5°C; maximum wind speed in the vortex is above 120 km per hour.

Subsystem of the climate system, including liquid water on the surface and underground (oceans, seas, rivers, lakes, groundwater).

Deposition of pollutants from the air.

Solar radiation arriving at the upper boundary of the atmosphere; dependent on geographical latitude and season.

low-pressure zones near the Equator, where northeastern trade winds meet the southwestern trade winds and ascending air motion develops; also called thermal equator.

Atmospheric province (between 50 and 2000 km altitude), where solar radiation ionizes air molecules (also observed as polar light or aurorae).

Line connecting points of the same air pressure.

Line connecting points of the same air temperature.

High-velocity (180-500 km per hour) westerly air current system between latitudes 30 and 60 degrees in the middle and upper troposphere, encircling the globe.

Descending air current, particularly the gentle mountain breeze from hillslopes at night driven by the radiation of the Earth surface.

Corollary of the United Nations Framework Agreement of Climate Change in 1992, negotiated in Kyoto (Japan) in order to reduce the release of greenhouse gases originating from human activities (by at least 5% between1990 and 2008/2012); in force since 16 February 2005.

The state of the tropical ENSO system when the sea surface is cold and air pressure is high along the coasts of South America.

Temperature change with elevation above sea level; in the case of thermal inversion it has negative values.

Heat transfer from the ground to the atmosphere at evaporation; a component of the energy budget of the ground surface.

The period (about 1400-1900 AD), when temperatures on the Northern Hemisphere (and particularly in Europe) were generally somewhat lower than today.

Daily, monthly or yearly average of air temperature values.

The period (about 1000-1300 AD), when the climate was much warmer on the Northern Hemisphere than during the ensuing Little Ice Age.

Atmospheric province above the stratosphere up to about 80 km altitude, to the mesopause; in the mesosphere air temperature decreases again.

Arid environmental conditions due to prolonged lack of precipitation or reduced precipitation amount.

One of the earth sciences specialized on the study of atmospheric processes (dynamic meteorology) and weather forcasting (synoptic meteorology) (atmospheric science); in a broader sense includes climatology.

Climatic conditions extending over a small area of the boundary layer, formed in an anticyclonal situation when local (topographic, soil, vegetation) variations are more effective.

Refraction phenomenon in the air layer immediately above the ground on hot days; caused by great contrasts in temperature (and consequently in air density) and thermal inversion on coasts, in deserts and over asphalt and water surfaces.

Cold and dry descending wind in the French Mediterranean .

Air circulation system of seasonally changing direction (the angle between winter and summer wind directions is minimum 120°), generated by the difference in thermal capacity between land and sea; the summer monsoon brings large amounts of rain to land.

International agreement, negotiated in 1987, aimed at the reduction of the emission of substances damaging the ozone layer (chlorfluorocarbons, CFCc; hydrocarbons, methilchloroform, carbon-tetrachloride etc.).

Low-level cloud type of apparently dark shade, associated with warm fronts and bringing prolonged rainfall.

Atmospheric dynamics driven by the air pressure gradient between Iceland and the Azores Islands, influencing westerly winds and cyclone tracks.

The more rapidly advancing cold front catches up with the warm cold in the cyclone and occludes the warm air, i.e. forces it to rise, and the cyclone dissolves.

Increasing heat storage in oceans proportional to global warming (measured in W/m²/ºC), one of the indicators of climate system sensitivity.

Particles of organic compounds (carbon, hydrogen, oxygen and some other elements) floating in the air.

Precipitation due to topographic obstacle forcing air masses to rise.

A form of oxygen composed of three atoms, a highly unstable variable atmospheric gas, formed from diatomic oxygen, in the troposphere partly by human influence and photochemical reactions, while in the stratosphere by the action of ultraviolet light.

A layer of the stratosphere, at ca 12-40 km above ground, where the ozone reaches maximum concentration; it is threatened by the emission of chlorine and bromine-containing gases.

Figure 3.2. Changes in the thickness of the ozone layer over Antarctica, 1979-2010 [source: Earth Observatory]

Climate in former geological or even historical ages which cannot be described by measured data, only by proxy data.

A zone of about 100-200 km between the latitudes 40° and 60°, where polar and tropical air masses come into contact.

Easterly wind current system within the polar circles.

Water vapour precipitated in different liquid and solid forms falling to the ground.

Substances which can evolve into or influence the formation of greenhouse gases or aerosols.

Substituting data series on the paleoenvironment, suitable to supply indirect evidence – based on the physical and biophysical rules – on previous climates (e.g. pollen, tree rings, corals, ice cores etc.).

Balance of incoming and outgoing radiation in the tropopause (measured in W/m²) to the effect of some external driving force (e.g. change in the solar constant or in the CO₂ concentration).

Liquid precipitation; its forms with growing intensity are drizzle, light rain, shower, extensive rain or cloudburst.

Atmospheric light phenomenon due to the double refraction and reflection of sunlight on raindrops; its arc forms in an angle of 42°; the order of colours (red, orange, yellow, green, blue, indigo and violet) reverses in the secondary bow generated by double reflection (arc angle: 50°).

Phenomenon on the leeward side of mountains where regions (e.g. orographic deserts) receive lower amounts of precipitation.

Part of solar radiation is reflected from aerosol particles and water droplets in clouds.

Absolute vapour content expressed in percentage of the vapour content corresponding to the dew point (100%).

Subsystem of the climate system (except the atmosphere) which is capable of uptake, storage and release of carbon, greenhouse gases or their precursors (e.g. oceans, soils, forest etc.).

The period necessary for the restoration of the equilibrium of the climate system after and external or internal influence (feedback); its length is variable for the different elements of the system.

Crystalline icing on overcooled surface objects; vapour precipitates from moving moist air at the dew point; it can be a damaging load on transmission wires and tree branches.

Zone of strong westerly winds around Antarctica throughout the year, at the southern latitudes of 40-50°, where no continent weakens winds.

Large swings of the jet stream which became unstable because of its high velocity named after Carl-Gustav Arvid Rossby, a Swedish meteorologist; along the polar circles the waves generate cyclones due to the Coriolis force.

Diagram which shows how much water water a unit volume of air of a certain temperature can store (100% relative humidity).

Hot and dry southern wind on North African coasts.

Periods of the year due to the tilting of the Earth’s axis and its motion around the Sun, resulting in variations in the inclination and (consequently the amount) of incoming solar radiation, primarily in the temperate belt.

High-intensity precipitation, in which raindrops can reach 5 mm diameter.

Any process, activity or mechanism that is capable to remove greenhouse gases, aerosols or their precursors from the atmosphere.

Precipitation type, a mixture of raindrops and snowflakes.

Air veneer of variable composition in urban areas caused by industrial and/or traffic emissions; sulphuric smog derives from the burning of fossil fuels, while photochemical smog is generated by photochemical reactions in the lower troposphere through photochemical reactions from nitrogen-oxides and evaporated hydrocarbons.

Solid precipitation type of hexagonally crystallized snowflakes.

Variability of the number of sunspots, the radiation capacity and magnetic field of the Sun as well as in its release of high-energy particles, observed at several time scales.

Theoretical climatic belts along geographical latitudes distinguished according to the angle of incidence of solar radiation.

More or less regular cycle of solar activity with a 9-13-year periodicity.

Short-wave electromagnetic radiation from the Sun, the primary source of energy for atmospheric processes.

Products of burning, mostly composed of carbon and partly of oxygen and hydrogen in the atmosphere.

Any process, activity or mechanism which release greenhouse gases, aerosols or their precursors into the atmosphere.

Paths of tropical cyclones (hurricanes, typhoons, tropical storms) and the regions affected by them.

Developing stratiform heaped cloud; high level strips of clouds indicating change of weather.

Atmospheric layer above the troposphere beginning at 9 km altitude at high latitudes and at 16 km the tropics and reaching up to ca 50 km altitude; temperature rises because the ozone layer absorbs heat.

Cloud type of variable altitude: high-level cirrostratus, extensive altostratus covering the whole sky or nimbostratus bringing prolonged rainfall.

The duration of direct solar radiation, annual sum of hours when the sun shines.

Positive or negative deviation of actual mean temperature at a certain location from the long-term mean value calculated for its geographical latitude on the basis of the solar radiation received.

Narrow upward current of air heated and made unstable by solar radiation during the day, exploited by hang and blanket gliders to rise in the air.

Radiation from the ground surface, the atmosphere and the clouds at greater wavelengths than near infrared radiation.

Irregular rise of temperature with elevation in some (inversion) layer of the troposphere.

Atmospheric layer above the mesosphere (at 80-500 km altitude) with thin but hot air; incorporates the ionosphere.

Phenomenon accompanying lightning during thunderstorms; the interference of sound waves arriving from sites remote from and closer to the observer produce the characteristic deep tone.

Shower accompanied by atmospheric electric phenomena (lightning and thunder) and intensive rainfall.

Figure 3.3. Lightning flash related to a cold front above Transdanubia [source: Hungarian Meteorological Survey]

Threshold value above which Earth climate changes fundamentally and irreversibly.

Low-pressure whirlwind formed where warm and cold air masses encounter; extremely low pressures are typical inside the funnel of only 50-500 m diameter and strong sucking effect.

All the radiation from the Sun measurable at right angles of its direction, at the outer boundary of the Earth atmosphere, at medium Earth-Sun distance; its average value is 1368 Wm^-2.

The zonal wind system of the tropical belt; on the Northern Hemisphere northwestern, while on the Southern Hemisphere northeastern trade winds blow, but they are deflected by the Coriolis force when crossing the geographical Equator, to the left on the Southern Hemisphere (becomes northwestern), and to the right on the Northern (becomes southwestern).

Transport of some pollutant by wind in the atmosphere.

Boundary between the troposphere and the stratosphere.

The lowermost atmospheric layer, where ca 80% of air is concentrated and where weather processes take place.

International agreement signed at the Earth Summit in Rio de Janeiro which was aimed at stabilizing the atmospheric concentrations of greenhouse gases at a level not threatening the climate system of the Earth.

In the centres of cities air temperature is usually higher than in the neighbouring rural areas; it is explained by changes in hydrological conditions, surface sealing, alterations of albedo, growing amounts of aerosols, air pollution etc.

Atmospheric gases which change their proportion over short time (within years or decades) (carbon-dioxide, methane, hydrogen, ozone).

The distance from which an object of the terrain can still be seen clearly; it depends on the amount of aerosols and water droplets in the atmosphere.

Atmospheric precipitation of water droplets on aerosol particles of volcanic origin.

Boundary of a warm air mass arriving over an area with a cold air mass; the warm air glides over the cold along the warm front.

Whirlwind originating above or shifting over water surfaces lifting water.

The totality of physical states and processes in the troposphere driven by solar energy; change of the state of the atmosphere over a shorter period.

The momentary physical state of the atmosphere at a given location.

Physical variables characterizing the state of the atmosphere (solar radiation, air temperature and pressure, wind, humidity, cloud cover and precipitation).

Air current system between latitudes 30° and 60° on both hemispheres.

Air current parallel with the ground surface caused by air pressure variation; characterized by its strength and direction.