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Ma-Mm

Mach number
More later.

MADAM
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 MAST projects. 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.

[http://bali.cetiis.fr/madam/]
[http://www.gets.cadrus.fr/madam/]

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 meteorological tsunami phenomenon in the Strait of Sicily. See Candela et al. (1999).

maestro
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.

MAGE
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:

[http://web.mit.edu/igac/www/sub_pages/mage.html]

MAHLOVS
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$ ^\circ$ S. This is also called the Falkland Current. See Tomczak and Godfrey (1994) and Vivier and Provost (1999).

MAMBO
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 distinct characteristics. 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.

MARGINEX
Acronym for Margin Experiment, an Antarctic CRC large-scale hydrographic experiment along the continental shelf and slope region of Antarctica from 80$ ^\circ$ to 165$ ^\circ$ E whose objectives include:

The MARGINEX experiment consisted of two components. The first was carried out from March through April 1995 in the eastern region from 150$ \deg$ to 165$ \deg$ 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 continental shelf. The hydrographic measurements covered the region from 80 to 150$ \deg$ 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$ \deg$ of latitude and were designed to extend from the coast to the Antarctic Divergence.

[http://www.antcrc.utas.edu.au/antcrc/research/polar/oceanproc/marginex.html]

Margules' equation
In physical oceanography, an equation that allows the estimation of the slope of the surface density discontinuity associated with geostrophic motions 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

$\displaystyle {{\delta z}\over{\delta n}}\,=\,{f \over g}
{ {{\rho ' c'}\,-\,\rho c} \over {\rho\,-\,\rho '} }$

where $ \delta z$ is a finite increment of vertical distance, $ \delta n$ a finite increment of horizontal distance along the dip of the interfacial slope, $ f$ the Coriolis parameter, $ g$ the gravitational acceleration, $ \rho$ the density, and $ c$ 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 $ \mu$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.

[http://ioc.unesco.org/iode/activities/marine_xml.htm]

MARIS
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$ ^\circ$ E and 40.5$ ^\circ$ N whose primary significance is to serve as part of the connection between the Black Sea and the Mediterranean Sea. It reaches 75 km in width, 250 km in length, has a surface area of about 11,500 km$ ^2$, 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 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).

Marrobbio
See Mad Sea.

MARSEN
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 90 days. 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 water waves. See Hasselmann and Shemdin (1982) and Geernaert (1990).

Count Marsigli (1658-1730)
See Peterson et al. (1996), p. 32.

MARVOR
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 ballast. See Ollitrault and et al. (1994).

[http://www.ifremer.fr/lpo/eurofloat/technic.html]

MASIG
Abbreviation for Mesoscale Air-Sea Interaction Group.

masl
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.

MATE
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 acoustic transmissions. See Ewart and Reynolds (1984).

Maury, Matthew Fontaine (1806-1873)
See Peterson et al. (1996), p. 79.

MAW
Abbreviation for Modified Atlantic Water.

MBL
1. Abbreviation for Marine Biology Laboratory, located at WHOI. 2. Abbreviation for marine boundary layer.

MCDW
Abbreviation for Modified Circumpolar Deep Water.

MCM
Abbreviation for mechanical current meter.

MCSST
Abbreviation for multichannel sea surface temperature, a satellite SST data set derived from the TIROS-N/NOAA series satellite AVHRR. 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 0.3$ ^\circ$C. See Wick et al. (1992).

[http://podaac.jpl.nasa.gov/mcsst/]

MCTEX
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 North Territory. 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.

[http://www.atmos.washington.edu/~gcg/Mctex.site/]

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 geodesy. 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 isostatic rebound). In geodesy, MSL usually means the local height of the global Mean Sea Surface (MSS) above a level reference surface called the geoid. See Lisitzin (1963).

[http://www.nbi.ac.uk/psmsl/puscience/]

MECBES
Acronym for Marine Environment Changes and Basin Evolution in the East Sea of Korea, a KORDI project.

[http://key.kordi.re.kr/home/mecbes.htm]

MECCA
Acronym for Model for Estuarine and Coastal Circulation Assessment.

MEDATLAS
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.

[http://www.ifremer.fr/sismer/program/medatlas/gb/gb_medat.htm]
[http://ioc.unesco.org/medar/]

meddy
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 13.0$ ^\circ$C in the depth range 800-1400 m. As they translate westward from the eastern boundary of the Atlantic into cooler and fresher water, their core waters become apparent as large anomalies that can reach 1 psu and 4$ ^\circ$C. The anomalously warm and salty meddy core water extends vertically from around 600 to 1700 m, and density sections show the lens shape frequently extending from the surface down to at least 2000 m, with the dynamical structure extending beyond the layers occuped by temperature and salinity anomalies. They are often found in the vicinity of the Azores Current which flows eastward near 34$ ^\circ$N, 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 $ \sim$ 30 cm/s are found near the central depth of the core, i.e. $ \sim$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 (NADW). 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 of Hisponola. 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).

MEDEA/JASON
The first academic remotely operated vehicle (ROV) system. 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).

MedGLOSS
A sea level program for the Mediterranean and Black Seas under the auspices of the CIESM and IOC.

[http://medgloss.ocean.org.il/]

MEDI
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 datasets.

[http://www.aodc.gov.au/IODE/MEDI/]

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 emerged. See Fairbridge (1966).

MEDIPROD
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 Mediterranean Sea.

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 concentration basin.

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$ ^2$, 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:
  1. 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.
  2. 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.
  3. 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).
  4. 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 Atlantic.

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$ ^\circ$ 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).

MEDMEX
Acronym for Mediterranean Models Evaluation Experiment, whose aim is to achieve an intercomparison of existing models that have been applied to the Mediterranean Sea.

[http://modb.oce.ulg.ac.be/MEDMEX/]
[http://sit.iuav.unive.it/mednet/ocean/medmex.html]

MEDOC
Acronym for MEDiterranean Ocean Circulation. See Group (1970).

MEDS
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. See the MEDS Web site.

Megapolygon-87
An experiment taking place in the Pacific subarctic frontal zone in 1987. See Maximenko et al. (2001).

Meinardus Line
See Polar Front.

MEIW
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.

[http://scilib.ucsd.edu/sio/archives/siohstry/menard-biog.html]

MER
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

$\displaystyle T\,=\,{ {2a} \over {n\sqrt{gh}} }$

where $ T$ is the period, $ a$ is the length of the basin, $ n$ is the mode number, $ g$ gravitational acceleration, and $ h$ the basin depth. See Raichlen (1966).

MERIS
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. See the MERIS Web site.

MERMAIDS
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.

[http://www.imbc.gr/biblio_serv/mast/X0043_172.html]
[http://www.imga.bo.cnr.it/mermaids/SYNFIN.html]

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$ ^{-1}$ and is located in the southwestern Levantine Basin. It is found north of the Egyptian coast and generally between 26-30$ ^\circ$E and 32-34.5$ ^\circ$N, 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 epipelagic zone. See Bruun (1957).

mesoscale
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 equatorial trough. This is located at about $ {5^\circ}$ N rather than on the geographical equator. 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 gravity waves. See Rabinovich and Monserrat (1996).

Meteosat
A European geostationary meteorological satellite operated by EUMETSAT.

method of dynamic sections
See dynamic method.

Mexican Current (MC)
See Badan-Dangon (1998).

MGD77
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 ().

MICOM
Acronym for the Miami Isopycnic Coordinate Ocean Model, a ocean circulation model that uses isopycnic coordinates in the vertical. See the MICOM Web site.

micronutrients
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).

MILDEX
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).

MILE
Acronym for MIxed Layer Experiment. See Levine et al. (1983) and Halpern et al. (1981).

MIMR
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$ ^\circ$ N at about 127$ ^\circ$ W) that closes the counterclockwise wind-driven gyre of which the North Equatorial Current (NEC) and the 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$ ^\circ$ 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 aforementioned 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$ ^{-1}$ at the shelf break, with a standard deviation of measured velocities of less than 0.1 m s$ ^{-1}$ 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 $ 24\,\pm\,4\,\times\,{{10}^9}$ kg s$ ^{-1}$, 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 subtropical gyre. 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$ ^\circ$ N and 135$ ^\circ$ 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 $ ^\circ$ 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 Mindanao Current. This has been estimated by some investigators to have speeds ranging from 0.15 to 0.30 m s$ ^{-1}$ and transports between 8 and 22 $ X\,{{10}^9}$ kg s$ ^{-1}$, although others have found it to be more of a transient phenomena than a permanent circulation feature. See Wijffels et al. (1995).

mistral
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 seasonal pycnocline.''

In the winter, low surface temperatures and large waves (with their accompanying turbulent mixing) can deepen the mixed layer all the way to the permanent thermoclinethermocline. Higher temperatures and a less energetic wave climate in the summer can lead to the development of a seasonal thermocline at the base of the mixed layer that overlies the permanent thermocline.

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):
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

$\displaystyle {\sigma_\theta}(D)\,-\,{\sigma_\theta^0}\,=\, {{\left(\delta{\sigma_\theta}\right)}_C}$ (13)

where $ \sigma_\theta^0$ is the value of the surface and $ {{\left(\delta{\sigma_\theta}\right)}_C}$ 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;

$\displaystyle { {\delta{\sigma_\theta}} \over {\delta z} }\,=\, {{\left( { {\delta{\sigma_\theta}} \over {\delta z} } \right)}_C}$ (14)

where $ \delta{\sigma_\theta}$ is the difference in $ \sigma_\theta$ within a vertical bin of thickness $ \delta z$ and $ {(\delta{\sigma_\theta}/\delta z)}_C$is the specified gradient criterion. This criterion is sensitive to the vertical scale over which the (first-differenced) gradients are computed.

$ \cdots$

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 $ {(\delta{\sigma_\theta})}_C$ = 0.005 and 0.01 kg m$ ^{-3}$ giving the best results for determining mixing layer depths. The best mixed layer depth results were obtained with $ {(\delta{\sigma_\theta})}_C$ = 0.05 to 0.5 kg m$ ^{-3}$. 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 requirements. 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.

MIZ
Abbreviation for marginal ice zone.

MIZEX
Acronym for Marginal Ice Zone Experiment. See Quadfasel et al. (1987) and Geernaert (1990).

MLIW
See Modified Levantine Intermediate Water.

ML-ML
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).

[http://uop.whoi.edu/data/mlml/mlml.html]


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