Acronym for Radiation, Aerosol and Cloud Experiment, a measurement
program that took place from Aug. to Oct. 1995 in Nova Scotia and
Ottawa, Canada. The objectives were to determine the effect of
cloud microphysics on the albedo of low stratus clouds, to
determine the impact of aerosol particles on cloud microphysics,
to examine satellite retrieval methods for determining cloud
properties, and to determine the interaction of chemical
constituents with clouds. See the
RACE Web page.
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.
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.
An earth observation satellite developed by Canada to provide
information for researchers in such fields as agriculture,
cartography, hydrology, forestry, oceanography, ice studies, and
coastal monitoring. The satellite, launched on Nov. 4, 1995,
carries a C-band SAR capable of imaging
a ground swath 500 km wide at 100 meter resolution. The
expected lifetime of RADARSAT is five years.
RADARSAT Web site.
- 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.
The radiation energy per unit time coming from a specific direction
and passing through a unit area perpendicular to the direction.
- radiant flux density
- radiation stress
A mechanism whereby waves can exert a stress on the fluid in which
they propagate. This stress tensor was discovered and named by
Longuet-Higgins and Stewart (1964) and defined as the excess flux
of momentum due to the presence of waves. Gradients in this
quantity therefore correspond to a net addition of loss of
momentum to a water column, i.e. a net force, arising from
the processes of wave shoaling and breaking. The theoretical
work was prompted by laboratory experiments with breaking waves
that showed a mild depression or set-down in sea level in the vicinity
of the wave breaking point and a larger elevation or set-up
throughout the rest of the surf zone.
If longshore uniformity is assumed, then the
flux of x-directed momentum
is given (correct to second
where k is the wavenumber, L the wavelength, h the
depth below still water, and E the wave energy density
where is the fluid density, g the acceleration due
to gravity, and H the wave height. This will given, for
equilibrium conditions, a momentum balance of the form
where is the adjustment of the sea level away
from still water level, i.e. the sea level will adjust
until the radiation stress gradients are everywhere balanced by the
sloping sea level.
See Holman (1990),
- 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 dating
See carbon dating.
- radioisotopic dating methods
Dating methods that take advantage of the fact that
unstable atoms called radioactive isotopes
undergo spontaneous radioactive decay by the loss
of nuclear particles and may transmute into a new element.
If the decay rate is invariable a given amount
of a radioactive isotope will decay to its daughter product
in a known interval of time, creating a geological clock
by which large time intervals can be measured.
Measuring the present isotope concentration indicates the
amount of time that has passed since the sample was emplaced
and the clock, i.e. the decay process, started. An important
factor is the time it takes for the material to decay to half its
original amount, i.e. its half-life, an indicator of the
length of the time interval over which it can be used.
A radioisotope's usefulness for dating is dependent
on whether it or its daughter products occur in
measurable quantities and can be distinguished from
other isotopes or have a measureable decay rate.
It must also have a half-life appropriate to the period
being dated, a known initial concentration, and some connection
between the event being dated and the start of the radioactive
Radioisotopic dating methods can be divided into three major
groups: (1) those that entail the direct measurement of
radioisotopes or decay products, e.g.
carbon-14 dating and
(2) those that measure the degree to which members of a chain
of radioactive decay are restored to equilibrium following
some initial external perturbation, e.g.
uranium-series dating; and
(3) those that measure the effect of some local radioactive
process on the sample materials compared to the
environmental flux, e.g.
fission-track dating and
See Bradley (1985).
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
See Tchernia (1980).
A device that uses a photocell to measure the power of a
specific light field.
The use of a radiometer to
quantitatively describe the power from a specific light
field. The description can be made in terms of several
properties including magnitude, geometrical distribution
(or direction), spectral distribution, state of polarization,
and time variability.
Before the advent of satellite oceanography, the primary use of radiometry
was to sample the radiant power in
the vicinity of an organism to obtain quantitative information
about how it reacts to light.
Now the use of radiometers in instruments aboard
satellites to measure various properties of incident,
reflected and emitted radiation
is nearly ubiquitous, with new types of radiometers
seemingly developed for each new mission.
See Tyler (1973) for a discussion of the physics of
radiometry and its appliation to studying the responses of
organisms to light.
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.
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
See Sarmiento (1988) and
Broecker and Peng (1982).
- radius of deformation
Rossby radius of
A subsurface float introduced by Thomas Rossby in 1985 that listens
to acoustic signals instead of transmitting (like the
earlier SOFAR float). At the end of its
mission it surfaces by dropping a weight and uploads to the
Argos satellite all the information it collected at depth,
including the Times of Arrovals (TOAs) of pulses sent by sources
at known geographical positions.
See Rossby and et al. (1986).
- 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.
Acronym for Regional Atmospheric Monitoring and Analytical
Network, a program of NOAA's ATDD.
The purpose of the study is to study the effects of complex
terrain on atmospheric properties.
RAMAN Web site.
- 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
Abbreviation for Real Aperture Radar.
Acronnym for Regional Association for Research on the Gulf of
Maine, an association of institutions which have active research
interests in the Gulf of Maine and its watershed. It was founded
in 1991 and is housed at Dartmouth College. The missions of
the association are to advocate and facilitate a coherent program
of regional research, to promote scientific quality, and to provide
a communication vehicle among scientists and the public.
RARGOM Web site.
Acronym for Research on Antarctic Shallow and Littoral Systems.
Acronym for radar wind sounding, the determination of winds by
radar observation of a balloon.
A more advanced version of a radiosonde
that also measures wind speed and direction.
- Rayleigh scattering
The dominant wave scattering mechanism when the dimension of
the region or object causing the scattering is much less than
the wavelength of the wave being scattered.
In climate modeling, an abbreviation for radiative convective model.
See radiative-dynamical-convective feedback.
A single instance or occurrence of a
See the Biogenetic Law.
- recirculating current
See recirculating gyre.
- recirculating gyre
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
- 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 Sea
A long, narrow marginal sea centered at about
38 E and 22 N which separates the African
and Asian continents.
Its total length is 1932 km and the average width 280 km, with
a maximum width of 306 km and a minimum width of 26 km.
The area is about 450,000 km and the volume around 50,000 km .
The average depth is about 491 m with the greatest depths over
2500 m in the trough between 19 and 22 N.
The Sinai peninsula divides the northern part into the shallow
Gulf of Suez to the west and the deep Gulf of Aquaba to the east.
The southern limit, which separates it from the Gulf of Aden,
is a line joining Husn Murad and Ras Siyan.
See Morcos (1970), Cember (1988)
and Tomczak and Godfrey (1994).
- red tide
- 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
See also Briggs and Crowther (1990), pp. 119-124.
- reduced gravity
In oceanography, a term that arises when the
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
a density perturbation, and a standard reference
See Turner (1973).
- redundancy hypothesis
See functional compensation hypothesis.
See coral reef.
A global database on coral reefs and their resources.
This is available on CD-ROM from
ReefBase Web site.
- reference level
A depth, pressure or density level at which the horizontal
current field is either known from direct measurements or
indirectly estimated. This may be zero velocity surface
or one with non-zero horizontal velocities.
This reference level is combined with the relative velocity
fields obtained via the
to obtain fields of absolute
The techniques of
satellite altimetry have
provided another possibility for a reference level, i.e. the
ocean surface. If the vertical departure of the ocean surface
from the local geoid can be measured
with sufficiently accuracy then it can be used as a reference
This is also known variously as the level of no motion, the
level of known motion, the zero velocity surface, etc.
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.
Favorable areas south of the glacier front in which species and
populations survived during a glacial stage.
Abbreviation for Regional Circulation Model.
See regional modeling.
- regenerated production
The uptake of ammonium by phytoplankton in the
It is so-called because ammonium is a product of internal processes
within the euphotic zone and it is therefore recycled or
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
See Houghton and Filho (1995).
- Regional Time Scale
A local (as opposed to global, e.g. SSS) geologic
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. It is given by
where q is the specific humidity
and the saturation specific humidity.
- 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.
- Rennell, James (1742-1830)
See Peterson et al. (1996), p. 47.
A class of the subphylum Vertebrata of
the phylum Chordata that contains
those reptiles that dwell in the sea, i.e. snakes and
- Research Vessel Technical Enhancement Committee (RVTEC)
An organization of technical support personnel associated with
the university oceanographic Research Vessel fleet of the U.S.
RVTEC is charted by UNOLS and
publishes a newsletter called ``INTERFACE.''
RVTEC Web site.
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
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.
The process by which an organism absorbs oxygen from air or water
and gives out carbon dioxide. There are
two types, autotrophic and
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).
In oceanography, this refers to a geographical looping of a current
away from its original direction to a substantially different
See Schmitz and McCartney (1993).
- Revelle, Roger
- 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
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.
Royal Greenwich Observatory.
Acronym for RADARSAT Geophysical
Processor System, a computer system that takes RADARSAT SAR
images of Arctic sea ice for input and creates geophysical
data products for output. These include sea ice motion,
the thickness distribution of new ice, and the backscatter
history of the ice.
RGPS Web site.
Abbreviation for relative humidity.
The botany, the root/soil interface. Also, the collection of
microbes and fungi that surround the roots.
See Collinson (1988).
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
- 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
and flux Richardson numbers.
See Turner (1973).
Acronym for Ridge Inter-Disciplinary Global Environments
Initiative, a coordinated program aimed at understanding the
geology, physics, chemistry and biology of processes occurring
along the global mid-ocean ridge system.
RIDGE Web site.
Acronym for Ross Ice Drainage System.
- right ascension
One of the two coordinates (the other being
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 degrees, 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
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
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
A narrow seaward return flow caused by waves breaking in the
surf zone and piling up water against the coast. This establishes
a hydraulic head which, combined with bathymetric irregularities
along the coast, causes the narrow seaward flow.
See Komar (1976).
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.
Abbreviation for Ross Ice Shelf Program or Project, a New
The Alpine name for the Saale
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.
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
See Heywood (1995).
1. Abbreviation for
Royal Meteorological Society
2. Abbreviation for for root-mean-square.