Ra-Rm

 

RACER

Acronym for Research on Antarctic Coastal Ecosystem Rates, a JGOFS program designed to test several hypotheses regarding the interaction of biological and physical processes in antarctic coastal regions in general, and the importance of the study area as nursery ground for antarctic krill in particular. See the RACER Web site.

 

radar

An acronym for radio detection and ranging, the use of reflected electromagnetic radiation to obtain information about distance objects. The wavelength used in normally in the radio frequency spectrum between 30 m and 3 mm.

 

radar altimeter

An instrument that uses radar to determine a vehicle's (e.g. a satellite) height above the surface and for measuring the height of small objects (e.g. waves, hills) on a planetary surface. In oceanography, the former capability is used to obtain the absolute sea surface height in relation to the geoid, and the latter to gather information about oceanic wave fields.

 

radiance

The radiation energy per unit time coming from a specific direction and passing through a unit area perpendicular to the direction.

 

radiant flux density

See irradiance.

 

radiative-dynamical-convective feedback

A positive feedback loop that links the hydrologic cycle and the ARC. It is a feedback between the radiative warming/cooling gradients associated with the high clouds produced by deep convection and the large-scale rising motion associated with convection. See also global radiative-convective feedback. See Wielicki et al. (1995).

 

radiative temperature

The temperature of a black body whose emission is equal to the actual measured emission of a given body. See Kagan (1995).

 

radiative index of dryness

An index created by M. I. Budyko in 1956 as an aid to delimiting vegetation zones. The index can be expressed as R/LP where R is the net radiation at the Earth's surface, L the latent heat of evaporation, and P the annual precipitation.

 

radical propagation factor

In atmospheric photochemistry, the probability that the free radical associated with each OH radical that enters a photochemical cycle will make it all the way through and emergy as a recreated OH radical and have the potential to start another oxidation chain. It describes the fraction of recreated OH per total OH reacting in a process. See Jeffries (1995).

 

radio altimeter

See radar altimeter.

 

radio-brightness temperature

The temperature of a black body whose emission is equal to the actual measured emission of a given body. See Kagan (1995).

 

radiocarbon

See carbon-14.

 

radiocarbon dating

See carbon dating.

 

radiolarians

Unicellular planktonic marine organisms belonging to the class of Actinopoda. The group called Polycystines have siliceous skeletons and are the only group preserved as fossils, making them valuable to micropaleontologists. Each species absorbs silica from the marine environment and builds a skeleton with a distinctive pattern which, given their enormous diversity over time, makes them of great stratigraphic interest. They range from 0.1-0.2 mm in length and can accumulate on ocean basin floors deeper than organisms with calcareous skeletons which dissolve at shallower depths. For further information, see either or both radiolarian Web pages, the rad Web page and the radiolarian home page.

 

radiolarian ooze

A deep-sea sediment composed of at least 30% of the remains of siliceous radiolarians. These sediments occur in the equatorial Pacific and Indian ocean regions where the depth exceeds the carbon compensation depth and therefore aren't overwhelmed by calcareous ooze. These form deep deposits covering 1-2% of the ocean floor, and are a type of siliceous ooze along with diatom ooze. See Tchernia (1980).

 

radiosonde

A meteorological instrument package, suspended below a balloon, consisting of instruments to sense and relay temperature, humidity and pressure (an aneroid barometer) as it ascends through the atmosphere. The ascension rate is about 5 m/s and it can gather data up to about 30,000 meters.

 

radium-228

An isotope of radium that is useful as a tracer in ocean studies. It is the 5.75 year half-life daughter of thorium-232. Thorium, a highly insoluble substance, is delivered to shelf and deep ocean sediments chiefly in detritus of continental origin. This decays into radium which dissolves off the particles and diffuses into the water column where it is mixed by diffusion and advection. This leads to a generic profile with a relative maxima at the surface and near bottom with the surface concentration decreasing with increasing distance from the shore (and the near-surface shelf sediment sources). See Sarmiento (1988) and Broecker and Peng (1982).

 

radius of deformation

See Rossby radius of deformation.

 

RAFOS

Listening floats (SOFAR spelled backwards).

 

rain band

An absorption waveband in the solar spectrum produced by water vapor in the Earth's atmosphere. It is located on the red side of the D lines.

 

random variable

A function (or mapping) from the sample space of possible outcomes of a random experiment to the real line, the complex plane, or some other such mappable entity. Basically, it's a variable denoting and containing the outcome of a random experiment, families of which comprise a stochastic process.

 

rawinsonde

A more advanced version of a radiosonde that also measures wind speed and direction.

 

RCM

In climate modeling, an abbreviation for radiative convective model.

 

RDC

See radiative-dynamical-convective feedback.

 

realization

A single instance or occurrence of a stochastic process.

 

recapitulation

See the Biogenetic Law.

 

recirculating gyres

Strong opposing flow elements adjacent to western boundary currents, e.g. the Gulf Stream in the upper ocean and the deep western boundary current in the deep water of the North Atlantic. These are a subbasin-scale component to the large-scale gyre flow, and can dominate the distribution of transport in the basin interior. See Schmitz and McCartney (1993), Hogg and Johns (1995) and McCartney (1992).

 

Redfield ratios

These represent the relatively constant proportions maintained between the elements C, N, P and O taken up during the synthesis and released by subsequent remineralization of organic matter by marine organisms. It was originally suggested that during organic matter cycling, carbon, nitrogen, phosphorous and oxygen are cycled in the ratio C:N:P:O2 = 106:16:1:138, i.e. for every phosphate ion taken up during photosynthesis, 16 nitrate ions and 106 molecules are taken up and 138 molecules of oxygen are produced. More recent studies have modified the ratios to 140:16:1:172. See Redfield et al. (1963) and Takahashi et al. (1985).

 

red noise

Noise with relatively enhanced low frequency power that results simply from serial correlation. The resulting power spectrum will have a negative slope. This is usually a good model for the noise component in a variety of climatic time series including proxy records, historical sea and air surface temperatures, and precipitation records. This type of noise can be explained in terms of the slow-response components of the climate system, such as the thermal inertia of the oceans, providing a memory that effectively integrates the forcing of such fast-reponse and more white noise-like components such as the weather. The produces a temporal persistence that leads to great noise energy at lower frequencies. Contrast with white noise.

 

red tide

More later.

 

redox discontinuity layer

A zone of rapid transition between areas of aerobic and anaerobic decomposition in oceanic sediments. Its depth within the sediment depends on the quantity of organic matter available for decomposition and the rate at which oxygen can diffuse down from the overlying water. For example, in organic muds, relatively impermeable to oxygen-carrying water, the upper aerobic layer may only be a couple of millimeters deep, while in permeable sands with a low rate of organic input aerobic conditions can extend for tens of centimeters. See Barnes and Hughes (1988).

 

Red Queen Hypothesis

An ecological view of macroevolution, codified by Van Valen (1973), asserting that it depends on the biotic development rather than a scaled-up version of microevolution, i.e. that the distinctive features of the evolution of life were produced by changes in the physical environment. His explanation of his Law of Constant Extinction, i.e. that the various species within a community maintain constant relationships relative to each other, and that these interactions are themselves evolving inspired the hypothesis, whose name comes from Lewis Caroll's Through the Looking Glass where the Red Queen tells Alice, ``Now here, you see, it takes all the running you can do, to keep in the same place.'' See also Briggs and Crowther (1990), pp. 119-124.

 

reduced gravity

In oceanography, a term that arises when the Boussinesq approximation is made where variations in density are neglected when they affect inertia but retained when they affect buoyancy, i.e. when they occur in the combination

where g' is the reduced gravity, g the normal gravitational acceleration, a density perturbation, and a standard reference density. See Turner (1973).

 

redundancy hypothesis

See functional compensation hypothesis.

 

reflectance

In radiation transfer, the fraction of incoming radiation that is reflected from a medium. The sum of this, the transmittance, and the absorptance must equal unity.

 

refractive index

The ratio of the speed of light in a vacuum to the speed of light in a given medium. It is calculated as

where is the speed of light and is the speed of light in medium i.

 

refugia

Favorable areas south of the glacier front in which species and populations survived during a glacial stage.

 

RegCM

Abbreviation for Regional Circulation Model. See regional modeling.

 

regenerated production

The uptake of ammonium by phytoplankton in the euphotic zone. It is so-called because ammonium is a product of internal processes within the euphotic zone and it is therefore recycled or regenerated nitrogen. See Najjar (1991).

 

regional modeling

In climate modeling this is defined as simulating the climate over a limited area or region rather than over the entire globe using Regional Circulation Models (RegCM). The boundary conditions needed to drive these models are supplied either from GCM output via a procedure called nested modeling or from analyses of observations. The RegCMs perform consistently better when driven by observations than by GCM output. This is largely due to the lack of regional scale geographical features (e.g. coastlines, lakes, etc.) and their concomitant climate effects in the output of GCMs, effects which are implicitly included in observations. Increased GCM resolution is found to improve RegCM simulations. This is a felicitous result since a lack of adequately dense observational data is the major limitation of using observations to drive RegCM simulations. See Houghton and Filho (1995).

 

Regional Time Scale

A local (as opposed to global, e.g. SSS) geologic time scale.

 

REINAS

Acronym for the Real-time Environmental Information Network and Analysis System, a distributed database environment supporting both real-time and retrospective regional scale environmental science. See the REINAS Web site.

 

relative humidity

The ratio of the observed mixing ratio in a sample of moist air to the saturation mixing ratio with respect to water at the same temperature.

 

relative vorticity

The vorticity imparted to a parcel or column of fluid by fluid motion. It is a characteristic of the kinematics of the fluid flow which expresses the tendency for portions of the fluid to rotate. Technically speaking, this is the curl of the fluid velocity vector, although in oceanography and meteorology it is usually only the vertical component of the curl of the horizontal velocity vector since all other components are usually negligible.

 

reshabar

A name given to a strong, very gusty, northeastly wind which blows down certain mountain ranges in southern Kurdistan. This wind, whose name means ``black wind'', is dry and comparatively hot in summer and cold in winter. This is also known by the name rrashaba.

 

resolution

In numerical modeling, the distance between contiguous points in the computational grid. This can refer to either temporal or spatial resolution, with the two being dependent in procedures using both.

 

respiration

The process by which an organism absorbs oxygen from air or water and gives out carbon dioxide. There are two types, autotrophic and heterotrophic.

 

resurgence

A general class of phenomena where, after a storm surge, the water level falls, rises, falls again, rises again, and so on for many hours after the passage of a hurricane. This has been variously explained as being due to oscillating long waves, edge waves, Kelvin waves or some combination thereof. See Wiegel (1964).

 

retroflection

In oceanography, this refers to a geographical looping of a current away from its original direction to a substantially different direction. See Schmitz and McCartney (1993).

 

Revelle, Roger

More later.

 

Revelle factor

See buffer factor.

 

Reynolds equations

An equation set for turbulent flow wherein the total dependent variables in the equations of motion are split into mean and fluctuating parts, e.g. u = U + u' where U is the mean part and u' the fluctuating part. These are substituted into the equations and an average is taken over a suitable period of time to obtain the Reynolds equations. These have the same form as the original motion equations with mean quantities replacing total quantities except for new terms involving velocity fluctuations that arise from the nonlinear terms in the original equations. These terms represent the effect of velocity fluctuations or turbulence on the mean flow, and are called Reynolds stresses since the turbulence has an effect equivalent to stress on the mean flow.

The Reynolds equations give rise to what is known as the closure problem, where the averaging procedure results in new unknowns in the form of the fluctuating quantities obtained from the nonlinear terms. Specific expressions for these fluctuating quantities can be obtained but at the price of generating yet more unknowns, ad infinitum. At some point a closure assumption must be made and the fluctuating quantities parameterized in terms of known quantities like the mean flow. The use of the eddy viscosity concept is the simplest way of obtaining closure.

This is ultimately a problem of flow resolution. If we could explicitly model the flow at a sufficiently high resolution (i.e. on a sufficiently small grid) then we wouldn't need to use an eddy viscosity since the molecular viscosity would suffice. Unfortunately, the length scale required for this is on the order of a millimeter or less, rendering it infeasible to explicitly model flow in a pipe (much less atmospheric or oceanic flow) without parameterizing the turbulent, i.e. unresolved, portion of the flow in terms of the mean, i.e. resolved, portion of the flow.

 

Reynolds stresses

Stress terms obtained by transforming the equations of motion into the Reynolds equations. They are so-called in analogy to the terms in the original motion equations involving the molecular viscosity, and to further the analogy the concept of an eddy viscosity is used to perform closure on the Reynolds equations and render them soluble.

The forces that give rise to the stresses are due to the fact that in a turbulent flow there are rapidly fluctuating as well as mean components. The fluctuating components oppose the mean motion and redistribute energy and other properties via a physical effect analogous to molecular friction, i.e. turbulent friction. This causes a more rapid distribution of momentum, heat and salt than would occur solely via molecular processes, and the analogous stresses are called Reynolds stresses.

 

Reynolds number

A dimensionless number expressing the ratio of viscous to inertial forces. It is expressed by

where is the kinematic viscosity, U an appropriate velocity scale, and L a horizontal length scale. If this is at least one order larger than unity then viscosity cannot significantly affect the motion; if it is much less than unity then molecular viscosity plays a significant role. See Kraus and Businger (1994), p. 29.

 

RH

Abbreviation for relative humidity.

 

rhizosphere

The botany, the root/soil interface. Also, the collection of microbes and fungi that surround the roots. See Collinson (1988).

 

RICE

Acronym for Regional Interactions of Climate and Ecosystems, a project designed to facilitate the integration of component models developed within IGBP into global change models. The goals of RICE are (i) to facilitate the acceptance by physical modelers of the need for interactive vegetation and soils components, (ii) to demonstrate the sensitivity to vegetation and soils components, and (iii) to examine the robustness of vegetation and soils components to climatic variables simulated by anticipated host models. See the RICE Web site for further information.

 

Richardson, Lewis Fry

More later.

 

Richardson number

A ratio of buoyancy to inertial forces which measures the stability of a fluid layer. There are several different definitions of this for various situations,including the overall, gradient, and flux Richardson numbers. See Turner (1973).

 

right ascension

One of the two coordinates (the other being declination) for specifying position on the celestial sphere in the equatorial coordinate system. It is the angular distance measured eastwards along the celestial equator from the vernal equinox to the intersection of the hour circle passing through the body. This is the celestial equivalent of longitude, with units of hours, minutes, and seconds. One hour of right ascension is 15 deg. , and the Earth's daily rotation takes the celestial sphere through one hour of right ascension in one hour of sidereal time.

 

rigid lid approximation

A filtering approximation incorporated into oceanographic models to increase their computational efficiency. This approximation filters out the fast barotropic gravity waves by setting the time variation of the surface elevation in the equations of motion equal to zero. A computational price is paid for this approximation since it requires that a prognostic Poissonlike elliptical equation be solved for the barotropic stream function (or surface pressure) at each model time step. This can be a problem as the condition number increases faster than linearly with the resolution of the computational grid, causing the equations to become increasingly difficult to solve.

This approximation also has dynamical effects that can be non-negligible. For example, although a surface elevation can be calculated from the prognostic surface pressure solution, it is strictly applicable only in the limit of a steady-state and as such the surface height cannot be accurately computed for transient and nonequilibrated flow. Additionally, this approximation effectively makes the phase speed of all barotropic Poincare waves infinite and equilibrates them at all scales. This is a reasonable approximation at mid- and high-latitudes where Poincare waves exist at high frequencies, but not so good near the equator where they evolve on a time scale equivalent to the Rossby waves. Finally, this approximation affects the phase speed of Rossby waves with wavelengths greater than the Rossby radius of deformation. See Dukowicz and Smith (1994) and Thacker and Raghunath (1994).

 

rip current

More later.

 

RIS

Acronym for Retroreflector in Space, a retroreflector for an Earth-satellite-Earth laser used in long-path absorption experiments. Measurements of ozone, CFC12, CO2, CH4 and other atmospheric constituents are carried out using infrared pulse lasers. RIS will fly on the ADEOS mission.

 

Riss

The Alpine name for the Saale glacial period.

 

RITS

Acronym for Radiatively Important Trace Species, a NOAA program for performing research concerning aerosol chemistry, air trajectories, ammonia, black carbon and radon, carbon monoxide, nitrogen oxides, ozone and peroxyacetyl nitrate. See the RITS Web site.

 

rivet hypothesis

Given the complexity of ecosystems and our lack of detailed knowledge of their functioning, especially in the long term, it is foolish to remove species randomly just as it would be foolish to pop rivets from an airplane's wing. See Heywood (1995).

 

RMS

1. Abbreviation for Royal Meteorological Society 2. Abbreviation for for root-mean-square.