Glossary
Aerosols: A collection of airborne or liquid particles, with a typical size between 0.01 and 10 µm that reside in the atmosphere for at least several hours. Aerosols may be of natural of anthropogenic (human) origin. Aerosols may influence climate in several ways; directly through scattering and absorbing radiation, and indirectly by acting as cloud condensation nuclei or modifying optical properties and lifetime of clouds. [Source: IPCC 4th Assessment Report, WG 1 Glossary]
AGCM: Atmospheric general circulation model. This designation, made necessary with the advent of coupled models, describes the category of GCMs that model the atmospheric and land surface components of the climate system.
AOGCM: Coupled atmosphere-ocean general circulation model. The category of GCM resulting from the coupling of an AGCM with an oceanic model. Represents the evolution of global climate of the atmosphere and oceans in four dimensions.
Attribution: Attribution is defined as the process of evaluating the relative contributions of multiple causal factors to a change or event with a formal assessment of confidence.
Climate: Synthesis of weather conditions in a given area, characterized by long-term statistics (mean values, variances, probabilities of extreme values, etc.) of the meteorological elements in that area. [Source*: International Meteorological Vocabulary. WMO - No 182]
Climate projection: A projection of the response of the climate system to emission or concentration scenarios of greenhouse gases and aerosols, or radiative forcing scenarios, often based upon simulations by climate models. Climate projections are distinguished from climate predictions in order to emphasize that climate projections depend upon the emission/concentration/radiative forcing scenario used, which are based on assumptions concerning, for example, future socioeconomic and technological developments that may or may not be realized and are therefore subject to substantial uncertainty. [Source*: IPCC 4th Assessment Report, WG 1 Glossary]
Climate system: The climate system is the highly complex system consisting of five major components: the atmosphere, the hydrosphere, the cryosphere, the land surface and the biosphere, and the interactions between them. The climate system evolves over time under the influence of its own internal dynamics and because of external forcings such as volcanic eruptions, solar variations and anthropogenic forcings such as the changing composition of the atmosphere and land use change. [Source: IPCC 4th Assessment Report, WG 1 Glossary]
Climatology: Study of the mean physical state of the atmosphere together with its statistical variations in both space and time as reflected in the weather behaviour over a period of many years. [Source*: International Meteorological Vocabulary, OMM – No. 182]
Coupled mode: Mode in which data is exchanged at the interface of at least two models during a simulation in order to influence each other (e.g. an atmospheric model coupled with an oceanic model). By contrast, in uncoupled or “offline” mode, the model outputs serve as inputs for another model without the possibility of feedbacks.
Domain of integration: Domain that is defined by the location, orientation and grid size of a climate model. In the case of GCM, the domain of integration is the entire planet, while for a RCM it can be a continent (e.g. North America) or a portion of a continent.
Driving an RCM (or the nesting of an RCM): The action of supplying a limited area regional climate model with values of variables such as winds, temperature, humidity and geopotential height at the lateral boundaries of the domain of integration in order to keep it consistent with the circulation prevailing at a broader scale outside the regional domain. These large-scale variables are taken from a global model data source such as reanalyses or a GCM simulation. The RCM is driven in a transition zone called the sponge zone that typically occupies the top ten grid points (regardless of the distance covered) on the periphery of the domain of integration. The values at the boundaries are gradually combined with those of the finer-scale RCM at each of its time steps. There are several techniques for driving (Davies relaxation, spectral nudging, etc.). When the transfer of information flows only from the global to the regional, it is referred to as unidirectional driving.
ESM: Earth system model. A third-generation GCM composed of a AOGCM coupled to a model of the carbon cycle.
GCM: Originally a general circulation model, more recently refers to a global climate model. The generic name for global climate models. Used to simulate the planetary climate in four dimensions.
Horizontal resolution: Horizontal distance between the points on the grid on which the computer code of the climate model will be run. It is usually expressed in either degrees or kilometres, depending on the model type.
Limited area model (LAM): Model with a grid that covers only a limited portion of the planet (a continent or even a smaller area). The purpose of this type of model is to significantly refine the horizontal, vertical and temporal resolution of the climate simulation. The boundaries of this type of model must be fed from another data source generally with a coarser resolution (e.g. AOGCM, reanalyses) using various techniques called nesting. Limited area models can be used for climate projections and weather forecasting.
Meteorology: Study of the atmosphere and its phenomena. [Source*: International Meteorological Vocabulary, WMO - No. 182]
Science of the atmosphere. [Source: International Glossary of Hydrology, WMO/UNESCO, 1992]
Numerical simulation: Method of studying a physical system by using a numerical model as an analogue. [Source*: International Meteorological Vocabulary, WMO
Numerical simulation of climate (or climate simulation): A method for studying a physical climate system by simulating it using a numerical climate model. A simulation produced by a climate model generates very long time series in the three spatial dimensions for over a hundred descriptive variables of the climate system. These time series contain all the information needed to construct a virtual weather description for every 3 or 6 hours. The statistics computed based on these virtual weather forecasts constitute the simulated climate.
RCM: General term for a regional climate model.
Spin up period: This is the time between the initial time of a climate simulation and the moment when the model reaches its own equilibrium. During this spin up period, the values assigned to the different variables at the model initialization gradually change under the action of the physical processes included in the climate model to reflect the values typical for the region of the Earth being simulated. This period of adjustment towards equilibrium is influenced in particular by the slowest processes in the different components of the climate model (atmosphere, hydrosphere, cryosphere, lithosphere, biosphere). The spin up period is always withdrawn from the climate simulation before proceeding to the analysis. There is no infallible method for determining whether the model has reached its equilibrium state, but once the spin up phase is complete, the statistics of the different variables in the climate simulation no longer really depend on the initial conditions. Moreover, in a simulation where greenhouse gases are kept constant, the statistics remain stationary once the spin up period is complete.
Temporal resolution: The length of the time increment, or time step, governing the progression for calculating the evolution of climate variables in a climate model. Temporal resolution is influenced by the horizontal and vertical resolutions and by the numerical method used for solving the basic equations of the physics on the grid. It is usually expressed in minutes: for example, a 30-year climate simulation with a temporal resolution of 15 minutes would take 1,036,800 time steps to complete and produce values for all variables at any point on the grid. Supercomputers can produce such a simulation in a matter of weeks.
Vertical resolution: The number of vertical levels and spacings between them that define the grid of the climate model. This is done according to altitude in the atmosphere portion of the model and of soil or ocean depth. In many climate models, the vertical layers are not equally spaced in order to more accurately reproduce various processes, especially near the Earth’s surface.
Weather: State of the atmosphere at a particular time, as defined by the various meteorological elements. [Source*: International Meteorological Vocabulary, OMM - No, 182]
Note: A meteorological element is an atmospheric variable or phenomenon that characterizes the state of the weather at a specific place at a particular time (e.g., air temperature, pressure, wind, humidity, thunderstorm, fog).
To access the definitions from the book
Go to METEOTERM and search for the term.
