Nn-Nz

 

NOAA

Acronym for the National Oceanic and Atmospheric Administration.

 

NOBREX

Acronym for NOrth BRazilian current EXperiment.

 

NODC

Acronym for National Oceanographic Data Center, a branch of the NESDIS division of the Office of Environmental Information Services of NOAA that develops and maintains a national marine database. More information can be found at the NODC Web page.

 

NODDS

Acronym for the Navy Oceanography Data Distribution System, a state-of-the-art methodology that makes environmental products and satellite data available worldwide via the Web. This was developed at the FNMOC for the distribution of their products. See the NODDS Web site.

 

NODS

Acronym for NASA Ocean Data System.

 

NOHRSC

Abbreviation for National Operational Hydrologic Remote Sensing Center, which operates under the Office of Hydrology of the National Weather Service, creates and distributes a variety of products that use remotely sensed data in support of the hydrological services mission of the NWS. See the NOHRSC Web page.

 

noise

In geophysical data processing this is most simply defined as any unwanted signal, and given that one person's signal can be another person's noise, this is ultimately a relative term. For example, if a time series is created by taking the temperature at some location every hour for five years, then the daily cycle of temperature that will be seen in such a record is a signal for someone looking for the daily cycle but is noise to someone looking for monthly or seasonal temperature variations.

 

nonlinear

Said of a system (an electronic circuit, the climate, etc.) in which the output is not strictly proportional to the input. One consequence of this is that small changes in input can lead to very large and unpredictable changes in output.

 

NOPEX

Acronym for the Northern Hemisphere Climate-Process Land-Surface Experiment, a BAHC coordinated large-scale land-surface experiment whose objective is to quantify the energy and mass budgets for a landscape dominated by the boreal forest. See the NOPEX Web site.

 

normal distribution

See Gaussian distribution.

 

normal modes

A decomposition solution procedure based on the eigenvectors of the linearized dynamical equations, i.e. an inherently linear concept. For example, the equations of large-scale motion in the atmosphere or ocean yield a sum of normal mode solutions for which each has a fixed vertical structure and behaves in the horizontal dimension and in time in the same way as a homogenous fluid with a free surface. Assuming the validity of the assumptions leading to the normal mode solution, the complete solution to the original differential equation is then approximated as a sum of the normal mode solutions. This technique can be applied to either a continuously or discretely stratified ocean model, with the former yielding an infinite set of normal modes and the latter a finite number of modes.

 

NORPAX

Acronym for the NORth PAcific eXperiment.

 

North Atlantic Deep Water

A water mass that fills the depth range between 1000 and 4000 m in the Atlantic Ocean. It is seen as a layer of relatively high salinity (above 34.9) and oxygen (above 5.5 ml/l) extending southward from the Labrador Sea to the Antarctic Divergence.

There are five regional sources for NADW: derivatives of salty Mediterranean Sea outflow, products of open ocean convection in the Labrador Sea (LSW), Iceland-Scotland overflow water from the Norwegian Sea (forming NEADW), Denmark Strait overflow water from the Iceland and Greenland Seas (forming NWABW, and remnants of deep water from the Antarctic circumpolar region (the freshest of the deep waters).

The resulting mixture is conventionally separated into upper, middle and lower NADW. Upper NADW comes from Mediterranean outflow spreading into the Central and North Atlantic at depths of 1000 to 1500m, while middle NADW is formed by ocean convection in the Labrador Sea flowing into the Western North Atlantic Basin. Lower NADW is formed by a complex series of mixing flows over the Greenland-Scotland Ridge and thereafter, and comprises the bulk of the totality of NADW. The middle and lower forms of NADW are additionally identified by two oxygen maxima in the subtropics at 2000-3000 m and 3500-4000 m, respectively. See Warren (1981) and Tomczak and Godfrey (1994).

 

North Atlantic Drift

More later.

 

North Equatorial Countercurrent

An eastward flow in the Atlantic and Pacific located approximately between 5 and 10 deg. N. It is located between the NEC and the SEC and called a countercurrent because it flows counter to the direction of the easterly trade winds. The NECC is strongest during July and August and weak in the northern winter and spring, and is known to migrate from a northernmost position in the northern summer to a position closest to the equator in the northern winter. Some evidence indicates that during this latter period the NECC is discontinuous and may even vanish in parts of the eastern Pacific. Even so, it is the most well developed of any of the equatorial currents. In the Indian Ocean this and the NEC are seasonally controlled by the monsoon circulation patterns. See Leetmaa et al. (1981),

 

North Equatorial Current

A westward flow in the Atlantic and Pacific located north of the past 10 deg. N. In the Indian Ocean this and the NECC are seasonally controlled by the monsoon circulation patterns. See Leetmaa et al. (1981),

 

North Equatorial Undercurrent

An eastward flow in the Atlantic Ocean whose core is located near 200 m depth a few degrees north of the Equator. A satisfactory dynamical explanation for this is as yet nonexistent. See Tomczak and Godfrey (1994), p. 260.

 

North Korea Current

A current that flows along the western coast in the Japan Sea. It is the southward continuation of part of the Liman Current and ultimately turns east and then northward (at around 38-40 deg. N) to become part of the flow in the Polar Front.

 

North Pacific Current

The eastward continuation of the Kuroshio and Oyashio Extensions, with which it forms the southern limb of the North Pacific subpolar gyre. This is a broad band of eastward flow around 2000 km wide that, at some not well known location east of the Emperor Seamounts, becomes well distinguished from the two aforementioned narrower and strongly frontal flows that eventually merge into its broader flow. This current eventually turns north and, along with the Alaska Current, forms the eastward limb of the North Pacific subpolar gyre. See Tomczak and Godfrey (1994).

 

North Pacific Equatorial Water

In physical oceanography, a water mass formed at the boundary between the subtropical gyres via mixing in the Equatorial Countercurrent and the Equatorial Undercurrent. NPEW is a mixture of WNPCW and SPEW. This combination of formation process and ancestral water masses makes NPEW one of the few water masses not formed through air-sea interaction. See Tomczak and Godfrey (1994), p. 166.

 

North Sea

More later.

 

North Subsurface Countercurrent

An eastward flow in the Pacific Ocean whose core is located near 600 m depth a few degrees north of the Equator. A satisfactory dynamical explanation for this is as yet nonexistent. See Tomczak and Godfrey (1994), p. 128.

 

Norwegian Coastal Current

See Skagerrak.

 

NEADW

Abbreviation for NorthEast Atlantic Deep Water.

 

NOS

Acronym for the National Ocean Service, a program office of NOAA that monitors, assesses and forecasts conditions in the coastal and oceanic environment. More information can be found at the NOS Web page.

 

NOSAMS

Acronym for the National Ocean Sciences Accelerator Mass Spectrometer Facility, established in 1989 at WHOI to serve the ocean sciences community with high-precision C-14 AMS measurements. See the NOSAMS Web site.

 

notch filter

In signal processing, a filter designed to remove a single narrow band of frequencies from a signal.

 

NPEW

See North Pacific Equatorial Water.

 

NPIW

Abbreviation for North Pacific Intermediate Water.

 

NPO

Abbreviation for North Pacific Oscillation.

 

NPOP

Abbreviation for NASA Polar Orbiting Platform

 

NPP

Abbreviation for Net Primary Productivity, the net annual uptake of carbon dioxide by vegetation. It is equal to the GPP minus autotrophic respiration. This is difficult to measure directly in terrestrial ecosystems, not only because it requires a direct measurement of gross photosynthesis, but also because it requires measurement of the respiration of the plant or plant community, including roots. See Woodwell (1995a).

 

NREN

Abbreviation for National Research and Education Network.

 

NROSS

Abbreviation for Navy Remote Ocean Sensing Satellite.

 

NSCAT

Acronym for NASA Scatterometer, an instrument that will measure wind speeds and directions over at least 90% of the ice-free global oceans every 2 days under all weather and cloud conditions. It is based on the Seasat scatterometer and uses an array of six stick-like antennas that radiate microwave pulses across the Earth's surface. It will orbit the Earth at an altitude of 800 km in a near-polar, sun-synchronous orbit. NSCAT will fly on the ADEOS mission. See the NSCAT Web site.

 

NSDW

Abbreviation for Norwegian Sea Deep Water, a water mass identifiable by being colder than 0 deg. C and saltier than 34.9.

 

NSF

Abbreviation for National Science Foundation. See the NSF Web site.

 

NSFNET

Abbreviation for NSF Network, a three-level network sponsored by the National Science Foundation that provides advanced scientific collaboration, access to NSF funded supercomputers, better sharing of research among researchers, teachers and the public, and leadership in networking technology.

 

NSIDC

Abbreviation for National Snow and Ice Data Center, a data and information resource for snow and ice processes, especially for interactions among snow, ice, atmosphere and ocean. This is one of the DAACs. See the NSIDC Web site.

 

NSRDB

Abbreviation for National Solar Radiation Data Base, a comprehensive data base with solar radiation data for 239 sites in the U.S. and its territories. See the NSRDB Web site.

 

NSSDC

Abbreviation National Space Science Data Center, a NASA facility located at the Goddard Space Flight Center in Greenbelt, MD. The location for GCMD.

 

NTF

Abbreviation for the Australian National Tidal Facility, which operates the Australian Baseline Sea Level Monitoring Network and is involved in several others. See the NTF Web site.

 

NTIS

Abbreviation for National Technical Information Service.

 

nuclear winter

The theory that large fires following a nuclear exchange would cause the input of large amounts of high elevation aerosols which would absorb solar radiation and heat the upper parts of the troposphere. This would simultaneously dramatically reduce solar input to the surface and cause the atmospheric lapse rate to become strongly stable. This stability would shut down convection processes and the cold surface of the earth would become decoupled from the atmosphere, a situation from which a very large amount of energy is needed to recover. The original scenario by the ``TTAPS'' (for the initials of the authors) group can be found in Turco et al. (1983) and a later appraisal in light of further work using more complex models in Turco et al. (1990) The results in the original paper were extrapolated from 1-D modeling simulations and were superseded and significantly mollified by later 2- and 3-D simulations, the upshot of which is definite but perhaps not catastrophic cooling should such an eventuality come about.

 

nucleation mode

One of three categories used to summarize the distribution of atmospheric aerosols in terms of production mechanism and particle size, the others being the coarse particle and accumulation modes. The nucleation mode ranges from 0.001 to 0.1 m in diameter and its production mechanism is by gas-to-particle conversion (GPC). See Jaenicke (1993b).

 

numerical stability

In numerical modeling, a numerical computational scheme is said to be stable if the infinite set of computed solutions of the discrete algebraic equations created by the process of discretization of some original continuum differential equations is always below some uniformly bounded upper-limit as the computational grid spacing is shrunk to zero. There are reasonably efficacious methods for exploring the stabilility of a given linear set of discretized equations, although it is much trickier with nonlinear equations, with the most popular option for the latter being the linearization thereof.

 

numerical taxonomy

A taxonomic scheme devised to establish a repeatable and objective methodology for classifying and comparing species of living or fossil things. This differs from classical taxonomy in that multiple unit characters or features are measured or qualitatively evaluated and then treated by statistical techniques such as multivariate analysis. The purpose is to establish similarities and difference between taxa, referred to as operational taxonomic units (OTUs). See Sokal and Sneath (1963) and Tasch (1980).

 

nunatak

A high-level region that is free of ice during a glacial stage. Constrast with enclave.

 

nutation

Oscillation of the Earth's pole about the mean position. It has a period of about 19,000 years and is superimposed on the precessional movement.

 

NWABW

Abbreviation for NorthWest Atlantic Bottom Water.

 

NWP

Abbreviation for Numerical Weather Prediction.

 

NWS

Acronym for the National Weather Service, a program office of NOAA that maintains a constant watch for life-threatening weather situations such as hurricanes, tornadoes, winter storms, and floods. More information can be found at the NWS Web page.

 

NWT

Abbreviation for northern warm tongue, a tongue of relatively warm water located at the eastern boundary of the WPWP. It is located at around 7 N. See Ho et al. (1995).

 

Nyquist frequency

In sampling theory, this is defined by

where is the sampling interval. It is the maximum frequency that can be detected from data sampled at time spacing . Higher frequencies are subject to aliasing which can cause the spectrum to differ from the true spectrum. See Nyquist theorem. See Peixoto and Oort (1992).

 

Nyquist theorem

In sampling theory, no information will be lost from a temporal or spatial series of data in the sampling interval is smaller than , where is the maximum frequency present in the series. In other words, the Nyquist frequency must be higher than the maximum frequency present in the series. See Peixoto and Oort (1992).

 

NZOI

Abbreviation for New Zealand Oceanographic Institute.