- Mach number
- More later.
- Acronym for Mediterranean Assistance and Data Management in
Oceanography, an initiative to set up and run an infrastructure
to provide assistance in the field of oceanographic data
management to the MTP, including the
different subprojects and associated
The general objective of MADAM is to compile and produce an
up-to-date dataset, the MTP Data Set, comprising data from
the MTP as well as a set of basic tools for the scientific
use of the data. Secondary objectives include managing and
making available the data set during the course of MTP,
set up and running a network to provide links between associated
scientists, and providing support for subprojects for specific
data handling problems.
- Madeira Mode Water
- A type of Mode Water formed north of
Madeira in the North Atlantic Ocean. It is characterized by
a summer thermostad at 70-150 m
depth and provides a major contribution to the formation of
North Atlantic Central Water (NACW).
See Siedler et al. (1987).
- Mad Sea
- An instance of the
phenomenon in the Strait of Sicily.
See Candela et al. (1999).
- A northwesterly wind in the Adriatic, most frequent on the western
shore and in summer. This is also applied to northwesterly winds
in other parts of the Mediterranean.
- Acronym for Marine Aerosol and Gas Exchange, an IGAC activity beginning
in 1990 to study the major sources and sinks of trace species that affect
the radiative balance of the earth either directory or indirectly by
altering the photochemistry of the marine atmosphere.
The scientific goals of MAGE were:
- to understand the chemical, biological and physical mechanisms that
control the exchange of trace gases and particulate material between the
atmosphere and ocean surface;
- to develop formulations of ocean exchange processes for inclusion
in global-scale climate and air chemistry models; and
- to extend the experimental knowledge of air-sea interchange to
conditions with strong winds, rough seas and spray.
- Acronym for Middle and High Latitude Ocean Variability Study, an
investigation whose aim is to study and characterize bio-physical
interactions and variability in the atmosphere-ocean-biology system.
- Maine Bottom Water (MBW)
- See Bisagni et al. (1996).
- Maine Coastal Current
- See Bisagni et al. (1996).
- Maine Intermediate Water (MIW)
- See Bisagni et al. (1996).
- Maine Surface Water (MSW)
- See Bisagni et al. (1996).
- Makaroff Deep
- See Guiana Basin.
- Malabiss Expedition
- See Rice (1986b).
- Maluku Sea
- See Molucca Sea.
- Malvinas Current
- A jet-like northward looping extension of the
Antarctic Circumpolar Current located in the southwest Atlantic
Ocean. The cold waters of this current form an intense front
with the warm waters of the
Brazil Current as it separates
from the continental shelf at around 35 S.
This is also called the Falkland Current.
See Tomczak and Godfrey (1994) and
Vivier and Provost (1999).
- Acronym for Mediterranean Association of Marine Biological
Oceanography, an ICSU project.
- map projections
- Any of an extremely large number of methods for mapping, or projecting,
the spherical (well, almost) Earth onto a two-dimensional surface.
An overview of map projections
is available on the Web.
- marginal ice zone (MIZ)
- The interface between seasonal sea ice and open water.
This is not a clear-cut boundary but a complex belt with
The MIZ may be up to 100-200 km wide, with the poleward
parat comprising broken ice in the early stages of melting.
The geographic location of the outer edge can vary over relatively
short time scales due to compaction and release caused by
variations in wind stress.
- Acronym for Margin Experiment, an
large-scale hydrographic experiment along
the continental shelf and slope region of Antarctica from
80 to 165 E whose objectives include:
- estimating the rate of formation of surface and
Antarctic Bottom Water (AABW) masses;
- defining the evolution and
modification of Antarctic
water masses along the shelf and
slope in this region;
- estimating the relative importance
of air-sea interaction and advection of surface and deep
waters on property changes in the major water masses; and
- constructing numerical models of the formation and dynamics of
water masses south of the
Antarctic Convergence over the full
The MARGINEX experiment consisted of two components. The first was
carried out from March through April 1995 in the eastern region
from 150 to 165 E. The Nathaniel B. Palmer was
used for CTD and tracer
work on a 45 day cruise from March 16 to April 30.
The second component was carried out in early January 1996 on the
Aurora Australis on a cruise to study both the hydrography and
the krill population. The experiment was timed to coincide with the
minimum sea-ice extent for the region, and was the optimum period for
the sampling of the summer water masses and krill abundance on the
The hydrographic measurements covered the region from 80 to 150 E with
eight north-south transects connected by sparse zonal sections in the
deep water. This CTD network created a total of seven closed volumes against
the Antarctic coast. The transects were spaced at approximately every
10 of latitude and were designed to extend from the coast to the
- Margules' equation
- In physical oceanography, an equation that allows the estimation of
the slope of the surface density discontinuity associated with
in the sea and of fronts in the atmosphere
from a knowledge of the component speeds of geostrophic motion along
the interface and the density difference across the interface. The
equation is given by
where is a finite increment of vertical distance,
a finite increment of horizontal distance along the dip
of the interfacial slope, the
the gravitational acceleration,
the density, and the geostrophic velocity parallel with one
side of the interface, and the primed variables the values of
corresponding properties on the other side.
This equation is helpful in clarifying the sometimes confusing
problem of estimating the change of frontal slope as a function of
latitude or a change in density contrast across the front at the
same latitude but with different velocities of flow.
See Von Arx (1962).
- marine biogeography
- See Hedgpeth (1957a).
- marine bioluminescence
- See Tett and Kelly (1973).
- marine palynology
- The study of pollen deposits in marine sediment records.
See Stanley (1969).
- marine pollution
- See Duursma and Marchand (1974).
- marine snow
- Oceanic particles which are amorphous, heterogeneous aggregates
greater than 500 m and composed of detrital material,
living organisms and inorganic matter.
See Fowler and Knauer (1986) and
Alldredge and Silver (1988).
- Marine XML
- A project to create a universal marine data standard within the XML or
Extensible Markup Language environment.
- Acronym for the MARine Information Service, a project in the
Netherlands to improve the overview of and access to marine
expertise, information, and data related to the sea and its
uses. See the
MARIS Web site.
- Maritime Province Current
- See Mid-Japan Sea Current.
- Marmara Sea
- A marginal sea centered near 28.5 E and 40.5 N
whose primary significance is to serve as part of the connection between
the Black Sea and the
It reaches 75 km in width, 250 km in length, has a surface area
of about 11,500 km, and a maximum depth of 1390 m.
It is located between the
Bosporus Strait to the northeast
(which connects to the Black Sea) and the
Dardanelles to the west (which connects
to the Aegean Sea).
The northern part of the Marmara comprises three topographic
depressions. The eastern (1240 m), central (1389 m) and
western (1097 m) basins are connected by sills about 750 m
and widths (from west to east) of 20 km and 40 km.
The southern continental shelf is shallow (100 m) and
wide (30 km), while the northern shelf is much narrower
( 10 km).
The mean upper layer circulation is a basin scale anticyclonic
gyre driven mainly by the sea level differences between the
Black Sea and the
Aegean Sea. This gyre is modified
by the Bosphorous jet during high outflow conditions in spring
and early summer and by the wind stress during the winter.
See Besiktepe et al. (1994).
- See Mad Sea.
- Acronym for the Maritime Remote Sensing Experiment, an experiment to
measure ocean surface waves with a high frequency radar that took
place from Sept. 10, 1979 to Oct. 15, 1979.
MARSEN was originally a ground truth campaign to provide and calibration
and validation of SEASAT's microwave instruments, although that focus
was somewhat relaxed when SEASAT failed after gathering data for only
MARSEN included a collection of studies on wave dynamics, air-sea fluxes,
and remote sensing via aircraft and ground-based systems, and was
carried out in the North Sea.
Key results included that drag coefficients depended on sea state and
wave age, and that shallow water waves produce higher drag than deep
See Hasselmann and Shemdin (1982) and
- Count Marsigli (1658-1730)
- See Peterson et al. (1996), p. 32.
- Abbreviation for Marvor float, a multicycle
RAFOS type float developed by
IFREMER and TEKELEC (now MARTEC).
A MARVOR float cycles several times between the surface and its
planned depth during its mission. When it surfaces it sends the
data collected to the ARGOS satellite
which relays it to land-based stations.
It is equipped with a hydraulic system that controls its depth
by transferring oil from an internal reservoir to the external
See Ollitrault and et al. (1994).
- Abbreviation for Mesoscale Air-Sea Interaction Group.
- Abbreviation for meters above sea level.
- mass spectrometry
- A method for making isotope abundance measurements
on gases in geochemical work. The instrument separates and detects
ions on the basis of the motions of charged particles with different
masses in magnetic or electrical fields.
- Acronym for the Midocean Acoustic Transmission Experiment, a
project of the APL of the
University of Washington Department of Oceanography.
It was conducted
near Cobb Seamount in the Northeast Pacific Ocean about 450 km
off the coast of Washington during June-July 1977.
In this experiment simultaneous measurements of temperature
and velocity time series, vertical and horizontal temperature
profiles, and acoustic transmissions were performed to
attempt to ascertain the effects of internal waves on
See Ewart and Reynolds (1984).
- Maury, Matthew Fontaine (1806-1873)
- See Peterson et al. (1996), p. 79.
- Abbreviation for
Modified Atlantic Water.
- 1. Abbreviation for Marine Biology Laboratory, located at
2. Abbreviation for marine boundary layer.
- Abbreviation for
Modified Circumpolar Deep Water.
- Abbreviation for mechanical current meter.
- Abbreviation for multichannel sea surface temperature, a satellite
SST data set derived from the TIROS-N/NOAA series satellite
SST estimates are obtained from AVHRR radiances by first using radiative
transfer theory to correct for the effects of the atmosphere on the
observations. This is done in so-called windows of the spectrum
where little or no atmospheric absorption occurs. Channel radiances
are transformed (through the use of the Planck function) to units of
temperature, and then compared to a prior temperatures measured at
the sruface. This yields coefficient which, when applied to AVHRR
data, provide SST estimates with a nominal accuracy of 0.3C.
See Wick et al. (1992).
- Abbreviation for the Maritime Continent Thunderstorm Experiment,
conducted from Nov. 13 to Dec. 10, 1995 over the Bathurst and Melville
Islands located approximately 50 km off the coast of Australia's
The basic objective was to improve knowledge of the dynamics and interaction
of the physical processes involved in the organization and life cycle
of tropical island convection over the Maritime Continent and the role
of this convection in the atmosphere energy and moisture balance.
- mean meridional circulation
- An average circulation feature or cell defined to consist of the zonal-mean
meridional and vertical velocities. In the tropics and subtropics this
mean meridional circulation cell is known as the
Hadley cell and in midlatitudes as
the Ferrel cell.
- mean sea level (MSL)
- A concept defined differently in the fields of tidal analysis and
In tidal analysis, MSL means the
still water level averaged over a period
of time such as a month or year so periodic changes in sea level
due to, e.g. the tides, are also averaged out.
MSL values are measured with respect to the level of
benchmarks on land, and as such a change in an MSL can result from
either a real change in sea level or a change in the height of
the land on which the tide gauge is located (e.g. from
In geodesy, MSL usually means the local height of the global
Mean Sea Surface (MSS) above a level reference surface called
See Lisitzin (1963).
- Acronym for Marine Environment Changes and Basin Evolution in the
East Sea of Korea, a KORDI project.
- Acronym for Model for Estuarine and Coastal Circulation
- A project to create a hydroraphic data bank for the Mediterranean
Sea. The objectives are to create a data project which includes
an update of currently available data sets, a quality control of
the data set in conformance with IOC and MAST recommendations,
revised climatological statistics for the Mediterreanean Sea, and
making the final product available electronically.
- A coherent, clockwise-rotating lens of warm salty Mediterranean
outflow water. Meddies are typically 40-150 km in diamter and
contain maximum salinities of around 36.5 psu and maximum temperatures
of around 13.0C in the depth range 800-1400 m.
As they translate westward from the eastern boundary of the Atlantic
into cooler and fresher water, their core waters become apparent
as large anomalies that can reach 1 psu and 4C.
The anomalously warm and salty meddy core water extends vertically
from around 600 to 1700 m, and density sections show the lens shape
frequently extending from the surface down to at least 2000 m, with
the dynamical structure extending beyond the layers occuped by
temperature and salinity anomalies.
They are often found in the vicinity of the
Azores Current which flows eastward
near 34N, its cut-off rings, and other eddies.
Meddies are generated along the southwestern boundary of the Iberian
Peninsula, usually where the downstream topography takes a sharp
bend to the right and the Mediterranean Undercurrent separates
from the coast. They typically translate northwestward near the boundary,
then more westward, and finally southwestward with a typical speed
of 2 cm/s. About 70% are inferred to collide with the Horseshoe
Seamounts, either disintegrating or being greatly weakened, with
the remaining 30% passing northward around the
seamounts and into the Canary Basin. Many of the meddies that make
it into the Basin end up colliding with the Great Meteor Seamounts.
The central core region of a meddy rotates with nearly solid body
rotation at each depth between about 500 and 1500 m.
Maximum rotation rate and swirl velocity 30 cm/s are found near
the central depth of the core, i.e. 1000 m, although the central
depth varies from 700 to 1200 m depending on density structure.
The diameter of maximum swirl velocity ranges from 20 to 50 km, and
beyond the region of solid body rotation swirl velocities appear to
decay exponentially with radius. Some axes have been observed to
tilt due to the background geostrophic shear.
The mean lifetime of a newly formed meddy has been estimated to be
about 1.7 years, although some have been observed to last over
5 years. An estimated 17 meddies form each year, which when
combined with the typical lifetime suggests that about 29 meddies
coexists in the North Atlantic at any one time. Some meddies
have been observed to coalesce and others to split, although
there are no percentage estimates for these phenomena.
Over the long
term these meddies, each slowly releasing its surplus of
heat and salt, inject their contents into and serve to
partially form the upper part of
North Atlantic Deep Water
The term `meddy' originated with the discovery by
() of a subsurface eddy containing a clockwise
rotating core of warm salty water in the western North Atlantic north
After concluding that the eddy water had characteristics of Mediterranean
Water from the eastern Atlantic, they called it a meddy.
See Richardson et al. (1991) and
Richardson et al. (2000).
- The first academic remotely operated vehicle (ROV)
MEDEA/JASON was developed in 1982 and included a dynamically controlled
surface ship, shipboard control center, fiber optic wire and winch
system, the MEDEA relay vehicle, the ROV JASON, a satellite link, and
shore-based control and data processing centers.
The long-term objective of the program is to permit scientists to
have full access to the at-sea operations from shore-based satellite
downlink sites, including full control of the vehicles from shore.
The primary purpose for the original development was to bridge the
gap between seafloor data gathered by acoustic and visual imaging systems.
It was found to be difficult to cross-correlate acoustic and visual
data sets. Although the former allowed the mapping of a much larger
area than the latter, the latter offered much greater detail on smaller
scales. Thus the goal was to combine the use of high-frequency
acoustic sensors and low-light level large-area visual sensors on
the same platform.
See Ballard (1993).
- A sea level program for the
Mediterranean and Black Seas under the
auspices of the CIESM and
- A directory of information about marine related datasets that consists
of metadata, i.e. data about other datasets.
The aims of MEDI are to catalog which data is available, when and
where it was collected, and where it is located.
It is intended as a reference point for locating marine and coastal
datasets, and as a means for advertising the availability of new
- mediolittoral zone
- The second (from the surface) of seven zones into which the
benthos has been divided.
In this zone organisms are more or less regularly emerged
and submerged, usually by the action of the tides.
Species are here adapted to resist prolonged emersion
and are generally incapable of living if continually
See Fairbridge (1966).
- See Millot et al. (1997).
- mediterranean sea
- A generic term used to describe a class of ocean basins that
have limited communication with the major ocean basins and
in which the circulation is dominated by thermohaline
forcing. This causes a circulation that is the reverse of
that found in the major basins, i.e. it is driven by salinity
and temperature differences and only modified by wind action.
Mediterranean seas exhibit the dynamics of estuaries rather
than those of open oceans.
Examples include the
Arctic Mediterranean Basin,
Australasian Mediterreanan Basin, and of course the
Mediterranan seas can be further distinguished by their
balance of precipitation and evaporation. If evaporation
exceeds precipitation, the deep vertical convection occurs and
the water below the sill depth is frequently renewed. The
open ocean connection features inflow in the upper layer and
outflow in the lower layer since the inflow is driven by the
freshwater loss in the upper layer. This is called a
If precipitation exceeds evaporation, then the surplus of
fresh water in the upper layer drives an outflow of surface
water into the connecting major basin. The decrease in surface
density also results in an increased pressure difference at the
connecting sill which in turn results in inflow in the lower
layer and even more outflow in the upper layer. A very
sharp pycnocline is established which inhibits the renewal
of the deep waters. This type of basin can be depleted in
oxygen even to the point of anoxia in the lower layer.
This is known as a dilution basin.
- Mediterranean Sea
- A semi-enclosed basin containing many of the characteristics
found in the open ocean, e.g. deep and intermediate water formation,
jets, eddies, and intense air-sea interaction.
It is an evaporation basin wherein the average heat loss is
-7 W m, with the most significant heat loss occuring in
the northern portion, particularly in the Gulfe de Lion and northern
Adriatic Sea were deep water is formed.
The general pattern of the circulation of the deep and intermediate
waters in the Mediterranean was first schematized by Wüst (1961).
Relatively fresh water from the Atlantic flows in through the
Strait of Gibraltar and through a series of eddies and jets to
replace the water convectively overturned by intense air-sea
interaction, with the latter flowing out of the Mediterranean
through the Strait of Gibraltar.
Deep water is produced in the Gulfe du Lion and the
Adriatic Sea. It fills the deepest portions of the western
and eastern Mediterranean basins which are separated by the
Strait of Sicily.
Levantine Intermediate Water (LIW) is
formed in the eastern Mediterranean near the Rhodes gyre and spreads
at intermediate depths, i.e. near 300 m in the eastern basin and between
200 and 800 m in the western basin. Most of the Mediterranean outflow
is LIW, with only about 10% consisting of
Western Mediterranean Deep Water (WMDW).
A more recent summary is provided by Theocharis et al. (1998):
A schematic pattern of the Mediterranean circulation can be described
in terms of four basic constituents:
- The nonreturn flow of the low-salinity
Modified Atlantic Water (MAW) from the
Gibraltar to the eastern end of the Levantine in the upper 150-200 m.
- The formation and westward spreading of the warm and saline
Levantine Intermediate Water (LIW)
from the formation region in the northwest Levantine and South Aegean
Seas to the Gibraltar, where it enters the Atlantic Ocean.
- The formation of a cold and dense water in the Adriatic Sea and
the subsequent southward and then eastward spreading as it fills the
deepest parts of the East Mediterranean to form the
East Mediterranean Deep Water (EMDW).
- The formation in the Gulf of Lions of the
West Mediterranean Deep Water (WMDW),
which then spreads to the deep layers of the West Mediterranean
and occasionally participates in the Mediterranean outflow into the
The actual circulation picture, however, is rather complex, consisting
of basin-scale, subbasin-scale and mesocale structures. Permanent,
recurrent and transitional cyclonic and anticylonic gyres and eddies,
usually locked over topographic escarpments are interconnected by
currents and jets. The complexity of the circulation is caused by the
combination of the wind forcing with the surface and lateral thermohaline
fluxes imposed by water exchange through straits and river input, the
topographic and coastal effects, and the internal dynamics characterized
by a Rossby internal deformation radius around 10-15 km.
There is strong evidence of seasonal, interannual and multiannual
variability. The water formation processes are active in both the
open-sea and shelf areas under the influence of intense winter
air-sea interactions and local circulation patterns that favor the
atmospheric exposure of subsurface water.
See Wüst (1961),
Robinson et al. (1992),
Theocharis et al. (1998),
Baringer and Price (1999),
Send et al. (1999) and
Balopoulos et al. (1999).
- Mediterranean Surface Water
- See Perkins and Pistek (1990).
- Mediterranean Undercurrent
- A current originating from the dense Mediterranean Sea water
overflowing the Strait of Gibraltar It cascades down the continental
slope and equilibrates at depths of 500-1500 m in the northern
Gulf of Cadiz, forming a westward flowing boundary current.
Large segments of the Undercurrent separate from the boundary in
the form of 40-100 km diameter lenses of warm, salty
Mediterreanean Water called meddies.
See Baringer and Price (1997),
Baringer and Price (1999) and
Richardson et al. (2000).
- Mediterranean Water (MW)
- In physical oceanography, a
water mass formed in the arid eastern
Mediterranean Sea that flows westward and sinks in the Algero-Ligurian
and Alboran basins to depth of about 500 m due to its relatively
high salinity of 36.5 to 39.1. It continues westward into
the Atlantic Ocean through the shallow Straits of Gibraltar (at
depths below 150 m) where it sinks to about 1000 m, forming a
distinctive water mass with a temperature of 11-12 C
and a salinity of 36.0-36.2. It can be recognized as a salinity
and temperature maximum near 1000 m. This is also denoted as
EMW or Eurafrican MW to distinguish it from Australasian MW.
See Tomczak and Godfrey (1994).
- Acronym for Mediterranean Models Evaluation Experiment, whose aim is
to achieve an intercomparison of existing models that have been
applied to the Mediterranean Sea.
- Acronym for MEDiterranean Ocean Circulation.
See Group (1970).
- Acronym for Marine Environmental Data Service, a branch of
Canada's DFO whose mandate is to manage and
archive physical and chemical oceanographic data collected by DFO
regions or acquired through various arrangements from Canadian
researchers and from foreign research conducted in the major
ocean areas adjacent to Canada.
MEDS Web site.
- An experiment taking place in the Pacific subarctic frontal zone
See Maximenko et al. (2001).
- Meinardus Line
- See Polar Front.
- Abbreviation for
Modified East Icelandic Water.
- Menai Strait
- See Campbell et al. (1998).
- Menard, Henry (1920-1986)
- A marine geologist at Scripps who in 1958 suggested a
continuous process of mid-ocean ridge development.
- Acronym for the Marine Ecosystem Response program, a research
initiative jointly supported by NOAA and NSF geared toward
the generation of quantitative scenarios for the impact of
the climate system on marine ecosystems such as the economically
significant fisheries in the northeast U.S. See the
MER Web site.
- Merian's formula
- In the study of seiches and harbor resonance, this is an
equation that gives the natural period of a
long and narrow basin in terms
of its length and depth for the various modes of oscillation.
It is given by
where is the period, is the length of the basin,
is the mode number, gravitational acceleration,
and the basin depth.
See Raichlen (1966).
- Acronym for Medium Resolution Imaging Spectrometer, an ocean color
sensor. It is a push-broom instrument that measures the radiation
reflected from the Earth's surface and from clouds in the visible
and near-infrared range during the daytime.
The 1150 km wide swatch of the instrument is divided into 5 segments
covered by 5 identical cameras having corresponding fields of
view with slight overlap between adjacent cameras.
The geophysical parameters derived from MERIS measurements
include ocean color in open and coastal waters, e.g. chlorophyll,
gelbstoffe, and other pigments, qualitative parameters such as
presence ofclouds and emerged land, and atmospheric parameters
like aerosol optical thickness, cloud albedo, Angstrom exponent,
top pressure, and water vapor column contents.
MERIS Web site.
- Acronym for Mediterreanean Eddy Resolving Modeling and Interdisciplinary
Studies, a study whose main goal is to assess the internal variability
of the Mediterranean thermohaline circulation as induced by deep and
intermediate water formation processes and the inflow/outflow system
at Gibraltar on the seasonal and interannual time scales.
- Mersa Matruh Gyre
- The strongest sub-basin scale feature of the Eastern Mediterranean
general circulation. This gyre exhibits upper thermocline velocities
reaching 20-30 cm s and is located in the southwestern
It is found north of the Egyptian coast and generally between
26-30E and 32-34.5N, and has a diameter of 250-350 km.
There are variabilities associated with the location, orientation,
strength and number of centers of the gyre, but it is a quasi-permanent
feature of the circulation in the area.
This gyre was defined and named during phase I of the international
research program POEM.
See Golnaraghi (1993).
- mesopelagic zone
- One of five vertical ecological zones into which the
deep sea is sometimes divided.
This is the uppermost aphotic zone from 200 to 1000 m deep where little light
penetrates and the temperature gradient is even and gradual with
little seasonal variation. This zone contains an oxygen minimum
layer and usually the maximum concentrations of the nutrients
nitrate and phosphate.
This overlies the
bathypelagic zone and
is overlain by the
See Bruun (1957).
- To be completed.
- Meteor Expedition
- See Spiess (1985).
- meteoric water
- Water produced by or derived from the atmosphere. Meteoric waters
start as precipitation in the hydrologic cycle, and the source
thereof is evaporation from oceanic surfaces.
- Meteoric Water Line
- An equation expressing a correlation between deuterium and
oxygen-18 in meteoric waters. The equation is expressed as
del D = 8 * del oxygen-18 + 10. See Bowen (1991).
- meteorological equator
- The latitude of the mean annual position of the
This is located at about N rather than on the geographical
See Riehl (1954).
- meteorological tsunami
- The excitation of short period (on the order of minutes) sea level
oscillations near a coast by the passage of atmospheric pressure
See Rabinovich and Monserrat (1996).
- A European geostationary meteorological satellite operated by
- method of dynamic sections
- See dynamic method.
- Mexican Current (MC)
- See Badan-Dangon (1998).
- Abbreviation for the marine geophysical data format established
in 1977 for the exchange of digital underway geophysics data.
It was created at a workshop held at the NGDC in January, 1977 and
is sanctioned by the IOC.
The later HYD93 data format was based on this.
Documents providing the details of the standard are available at the
MGD77 FTP site.
- Michael Sars
- A Norwegian research vessel with which the first meticulous systematic
measurements were made at many stations in the Norwegian Sea.
See Murray and Hjort (1912) and
- Acronym for the Miami Isopycnic Coordinate Ocean Model, a ocean
circulation model that uses isopycnic coordinates in the vertical.
MICOM Web site.
- Mostly nitrate, phosphate and silicic acid.
See Spencer (1975).
- Middle Atlantic Bight
- The region of the continental shelf off the eastern United States
beginning at Cape Hatteras and extending northeast to Cape Cod.
The shelf topography is relatively smooth throughout the Bight,
with depth increasing linearly from shore to shelf break except
near submarine canyons. Several estuaries provide fresh water
to the shelf, with the most important being Chesapeake Bay.
The Bight has a mean along-shelf current moving southwest towards
Cape Hatteras, except during periods of strong northward winds and low river
discharge. The along-shelf current turns offshore as it approaches
Cape Hatteras, entraining the relatively cool and fresh shelf water into
the warmer and saltier Gulf Stream.
A sharp frontal boundary exists along the shelf break, separating
the cooler shelf water from the warmer, more saline slope water.
Most of the variability observed in the MAB is due to forcing by
strong winds from synoptic storms.
The waters are well mixed in the winter, with the coolest water
near the shore. Stratification increases during the summer as
increased fresh water discharge and solar heating induce buoyancy
forcing at the surface. The stratification is destroyed in the fall
by storm passages and surface cooling.
See Beardsley and Boicourt (1981).
- Mid-Japan Sea Current
- A slow southward cold water movement into the Polar Front in the
Japan Sea. This is also known as
the Maritime Province Current.
- Milankovitch forcing
- The name given to the changes in the amount or seasonal distribution
of solar radiation that reaches the Earth as caused by the orbital
changes predicted by Milankovitch theory.
- Milankovitch theory
- The theory
that changes in the geographic distribution of solar insolation
due to planetary perturbations of the Earth's orbital characteristics
are the primary driving force for the cycles of glaciation seen
in geological and fossil records. See Berger (1988).
- mild slope equation
- See Mei (1990).
- Acronym for MIxed Layer Dynamics EXperiment, multi-institutional
cooperative experiment which took place in a deep water region
(4700 m) about 650 km off Pt. Conception in central California.
Two ships and two floating platforms were used to make
measurements of the surface meteorological forcing and the
temperature and current response of the near-surface layers
in the ocean.
See Paduan et al. (1989).
- Acronym for MIxed Layer Experiment.
See Levine et al. (1983) and
Halpern et al. (1981).
- Abbreviation for Multifrequency Imaging Microwave Radiometer, a
passive microwave radiometer successor to the Special Sensor
Microwave/Imager (SSM/I) that provides greater frequency diversity,
improved spatial resolution, increased swatch width, and improved
antenna performance. It is used to observe atmospheric and oceanic
parameters such as precipitation, soil moisture, global ice and
snow cover, SST, wind speed, atmospheric cloud water,
and water vapor. See the
MIMR Web site.
- Mindanao Current
- A southward flowing boundary current along the Philippine coast
(from about 13 to 8 N at about 127 W) that closes
the counterclockwise wind-driven gyre of which the
North Equatorial Current (NEC)
North Equatorial Countercurrent (NECC) are the northern and southern
limbs, respectively. The westward flowing NEC splits at the
Philippine coast and the Mindanao Current (MC) flows southward,
carrying North Pacific subtropical thermocline and surface waters
toward a region of confluence with South Pacific waters near
5 N. Part of the flow continues along the Philippines and on
into the Celebes Sea, with the remainder
turning eastward at the confluence and contributing to the
NECC as well as the
Equatorial Undercurrent and the
Northern Subsurface Countercurrent. This eastward turn also
serves to spin-up a recirculation feature historically called the
Mindanao Eddy, although the Eddy
may be an intermittent rather than a persistent feature.
The MC is an energetic coastally trapped jet with speeds
reaching over 0.9 m s at the shelf break, with a standard
deviation of measured velocities of less than 0.1 m s
indicating low current variability. It is
broadest at the surface and narrows to a width of 150 km at
300 m depth.
The average transport above the thermocline has been estimated from
direct measurements to be
kg s, with the estimate
from hydrographic surveys virtually identical.
The MC contains distinct cores of high salinity
North Pacific Central Water (NPCW) and low-salinity
North Pacific Intermediate Water (NPIW), with each salinity
core associated with elevated concentrations of dissolved
oxygen indicative of the source connection with the
See Wijffels et al. (1995).
- Mindanao Dome
- See Mindanao Eddy.
- Mindanao Eddy
- A cyclonic circulation gyre or eddy
sometimes found to the east of Mindanao
centered at about 8 N and 135 E.
The southward flowing section near the coast is part of
the Mindanao Current,
and the Eddy can be thought of as the recirculation cell
of this current.
The southward flow does not extend
beyond a depth of 250 m and is underlain by a deep western boundary current
flowing northward (from about 250 to 500 m) at a rate
of 16-18 Sv.
The transport has been estimated at
around 25-35 Sv with strong interannual variations.
At least one investigation of the Mindanao Current at
8 N noted the absence of the Eddy, and as such it
may be an intermittent feature of the circulation field.
This has also been called the Mindanao Dome.
See Tomczak and Godfrey (1994) and Wijffels et al. (1995).
- Mindanao Sea
- See Bohol Sea.
- Mindanao Undercurrent
- A northward flowing current beneath and offshore of the
This has been estimated by some investigators to have speeds ranging
from 0.15 to 0.30 m s and transports between
8 and 22
kg s, although others have found
it to be more of a transient phenomena than a permanent circulation
See Wijffels et al. (1995).
- A northwesterly or northerly wind which blows offshore along the
north coast of the Mediterranean from the Ebro to Genoa. In the
region of its chief development its characteristics are its frequency,
its strength, and its dry coldness. It is most intense on the coasts
of Languedoc and Provence, especially near the Rhone delta. Its speeds
are usually around 40 knots, but can reach over 75 knots in the delta.
- mixed layer
- In oceanography, a nearly isothermal surface layer of around
40 to 150 m depth caused by wind stirring and convection.
Brainerd and Gregg (1995) defined this as ``the envelope of
maximum depths reached by the
mixing layer on time scales of
a day or more, i.e. the zone that has been mixed in the recent past.
It generally corresponds to the zone above the top of the
In the winter, low surface temperatures and large waves (with
their accompanying turbulent mixing) can deepen the mixed
layer all the way to the
Higher temperatures and a less energetic wave climate in the
summer can lead to the development of a
at the base of the mixed layer that overlies the
Various objective definitions for the mixed layer depth have
been proposed and used, e.g.:
The general criteria that have been used are summarized by
Brainerd and Gregg (1995):
- Price et al. (1986) defined the mixed layer as a
quasi-homogeneous surface layer where the temperature was uniform
to within 0.2C (with the stratified layer between the mixed
layer and the undisturbed fluid beneath called the transition layer);
- Levitus (1982) defined the mixed layer depth as the depth
at which the density increases by 0.125 density units from the
Two types of mixed and mixing layer depth definitions have been most
commonly used. The first is based on specifying a difference in
temperature or density from the surface value; for density
is the value of the surface and
is the specified difference.
This type of criterion suffers from difficulties in defining the
surface value, particularly during convection. The
second type of criterion is based on specifying a gradient in the
temeprature or density;
is the difference in
vertical bin of thickness and
is the specified gradient
criterion. This criterion is sensitive to the vertical scale over which
the (first-differenced) gradients are computed.
Criteria of both types based on temperature rather than density have been
extensively used, as temperature has been easier to measure reliably than
density. This works well in many locations, as both the daily and
seasonal cycles in surface forcing have large heat fluxes, and weak
salt fluxes. However, intense rainfall can produce strongly stratified
pools of fresh water that necessitate accounting for salinity in determining
both mixed and mixing layer depths.
They state that the density difference criteria is more stable than
the gradient criteria, with values of
= 0.005 and 0.01 kg m giving the
best results for determining
mixing layer depths.
The best mixed layer depth results were
= 0.05 to 0.5 kg m.
They conclude, however, that while both criteria are able to find
the mixed layer depth rather well, neither consistently returns
the mixing layer depth. The latter requires measurements that
resolve the turbulent overturns within the mixing layer.
Peter Rhines reviewed recent progress in understanding the
mixed layer (at the APROPOS conference).
The ocean mixed layer is one of the ...
... The double turbulent boundary layers through which the ocean
and atmosphere communicate. Classical models begin with the Ekman
layer, still a viable object because of its robust (integral)
independence from the detailed turbulent stress. The Krauss-Turner process of
"solving" the energy equation with assumed dependence of
energy dissipation and mixing on the surface stress led to the most widely
used models, particularly after later inclusion of bulk momentum
dynamics. More detai led attempts at modelling effects of fully
developed turbulence have led to more complex mixed-layer models,
and a generation of "large-eddy-simulation" models. Here and in
the atmospheric boundary layer community the power of theory seems
not up to the task of relating fluxes of heat, momentum, tracers to
their mean gradients, given the variety of environments in which
boundary layers occur. Important observations of mixed-layer structure
made in the 1980s began to "test" or "calibrate" the models, and
emphasized the importance of time-dependence, including diurnal
heating effects on stability.
The difficulties of turbulence have been soothed, at least, by
direct turbulence measurement. But of greater
importance was the discovery or rediscovery of distinct events
in the mixed layer, particularly Langmuir roll vortices aligned with the
wind. Innovative observations of bubble clouds with acoustic imaging,
and 3-dimensional Lagrangian particle histories with floats, in
company with a series of theories involving surface-wave/mean flow
interaction and with laboratory experiments in wave flumes, have
led to significant advances. Key elements of the Craik-Leibovitch
theory of their generation appear to be present, yet with important
contributions from wave-breaking.
Theory has moved on, in other directions, by taking more seriously the
large-scale environment in which the boundary layers are
embedded. Stable density stratification and convection, and
time-dependent forcing produce a new set of constraints. We see "Ekman
demon" interaction of downward pumping by wind-stress and seasonal
mixing and a family of calculations trying to relate water-mass
creation to surface boundary conditions ("warm", subtropical- and
"cold", subpolar subduction). A group of "geostrophic adjustment"
theories, developed after the pattern of Rossby's original
calculations, add vital time-dependence. The study of sharp density fronts
begun in atmospheric sciences is found to have many applications in
the oceanic mixed layer: determining for example whether lateral
wind-driven Ekman transport remains at the surface or is channeled to
the interior when it encounters a front. These are familiar lessons
of oceanographic theory: we cannot and should not wait for a 'theory
of turbulence' before working on the many aspects of theory of the
communication of the mixed layer and the geostrophic interior. Often,
by proceeding with a GFD problem with new physical effects
added, one can circumscribe and perhaps avoid the missing
elements of turbulence.
See Kara et al. (2000).
- mixed layer models
- According to Ranvindran et al. (1999), models of the surface
layer of the ocean can be classified into two groups: differential
models and depth-integrated bulk models.
The bulk models originate with Kraus and Turner (1967), and are
developed by integrating the heat and energy conservation equations
over the mixed layer.
These models are limited by the assumptions used in the model formulations,
two notable ones being that (i) a well-mixed layer exists a priori and
(ii) there is a density discontinuity at the base of the mixed layer.
The differential models can be traced to the paper of Mellor and Yamada (1974)
on turbulent closure models for boundary layers.
These are useful but limited by substantial computational
See Ranvindran et al. (1999).
- mixed layer ocean
- See slab ocean.
- mixing layer
- Brainerd and Gregg (1995) define this as ``the depth zone being
actively mixed from the surface at a given time, generally corresponding
to the depth zone in which there is strong turbulence directly driven
by surface forcing.''
Compare to mixed layer.
- mixing length
- A concept used in the parameterization of turbulent transport
processes. According the this model, fluid masses called
eddies, distinguishable from the ambient fluid, spring into
existence in some undefined way and then, after moving unchanged
over a certain path length, become indistinguishable from the
surrounding fluid. This path length, over which the eddy
mixes with the surrounding fluid, is called the mixing length.
This model is analogous to the mean free path of a molecule
or atom between collisions.
See Liou (1992), p. 219.
- mixing ratio
- See water vapor mixing ratio.
- Abbreviation for
marginal ice zone.
- Acronym for Marginal Ice Zone Experiment.
See Quadfasel et al. (1987) and
- See Modified Levantine Intermediate Water.
- Abbrevation for Marine Light-Mixed Layers, a research program
designed to study mixed layer dynamics and bioluminescent
plankton production. The program focuses on seasonal changes
in upper layer physics and the successive populations that
are responsible for bioluminescence.
See Marra (1989).