Va-Vm

 

VACM

See Vector Averaging Current Meter.

 

Vaisala frequency

See buoyancy frequency.

 

Valanginian

The second of six ages in the Early Cretaceous epoch, lasting from 138 to 131 Ma. It is preceded by the Berriasian age and followed by the Hauterivian age.

 

vapor concentration

See absolute humidity.

 

vapor pressure

The vapor pressure of water vapor in moist air is given by

where p is the pressure and r the mixing ratio.

 

Varen, Bernhard (1622-1650?)

A German physician who is commonly accredited with being the founder of modern general geography. He summarized, amongst many other things, the current state of knowledge about the sea in his book Geographia Generalis (later published in English as A Compleat System of General Geography), first published in 1650. The book was important for being the first comprehensive and objective collection of geographical knowledge since the Greek Classical Age and for its reflection of a growing appreciation and use of empirical knowledge to guide explanations rather than the reliance on fantasy and speculation that had prevailed for more than a millenia (although Varen did indeed lapse into the latter on more than a few occasions).

Varen's most important contribution to oceanography was probably the discussions in his book about steady currents being driven by the wind, the first time this notion had seen print. This led to motions in the sea finally being considered in terms other than Aristotle's primum mobile. He also attempted to categorize the motions of the sea, separating them into a continuous western flow, an observed periodic rise and fall of the sea surface that is the tide (although their connection with the moon was suspected though not as yet well-known), and various special flows including what are now known as the Florida, Kuroshio and Mozambique Currents.

Varen also discussed varying theories as to the causes of the perceived general westward flow and the tides. The explanations for the former included a magnetic pull from the moon, thermal expansion as a result of moonlight, downward pressure from the moon as trasmitted through an endless atmosphere, the sun pulling the water after it, the inability of the sea to keep up with the earth's rotation, and more. He concluded that the cause was uncertain although he favored the wind as a cause at least of the general westward currents in the tropics as well as of other non-tidal currents flowing counter to the supposed general western flow. He considered the moon as responsible for the tides although via a mechanism as yet unknown (and to be identified by Newton in 1687). See Peterson et al. (1996).

 

variance ellipse

 

VAS

Abbreviation for VISSR Atmospheric Sounder, a combined imaging and sounding device on the GOES series of geosynchronous satellites operated by NOAA. It is an advanced version of the VISSR flown on earlier geosynchronous satellites that retains the imaging function while expanding the number of infrared channels that allow the 3-D structure of the atmospheric temperature and water-vapor distribution to be determined. It has one channel in the visible spectrum (0.55 m to 0.75 m) which comprises signals from eight detectors and six infrared detectors which make up 12 channels by use of a filter wheel. The spectral channels are chosen to permit the measurement of atmospheric profiles of temperature and humidity as well as surface temperature. The vertical flux divergence of infrared radiation, i.e. the cooling-rate profile, can also be estimated. See the VAS Web site.

 

vascular plant

A plant containing vascular tissue, the conducting system which enables water and minerals to move through it.

 

vardarac

A cold northerly wind which blows from the mountains down to the valleys of Macedonia, especially through the Morava-Vardar gap, in the rear of a depression and affects the Thessalonika region. It is a type of ravine wind. It is similar to the mistral wind.

 

varve

A sedimentary bed or lamina or sequence of laminae deposited in a body of still water within one year's time. More specifically, a thin pair of graded glaciolacustrine layers seasonally deposited, usually by meltwater streams, in a glacial lake or other body of still water in front of a glacier. The lower layer is coarser material deposited by rapid melting of ice in the warmer months, and the upper layer more fine-grained deposited from suspended particles in quiet water in the winter months.

 

VCI

Abbreviation for vegetation condition index, an index derived from AVHRR data for drought detection and tracking in many countries of the world. See Kogan (1990).

 

Vector Averaging Current Meter

A current meter used in oceanography that senses speed with a Savonius rotor and direction relative to its case with a vane assembly. An internal compass senses the orientation of the case relative to magnetic north. Temperature is also recorded. The data recorded by the internal electronics is a true vector average with the sampling rate for speed and direction partly determined by the rotor rotation rate. See Heinmuller (1983).

 

Vector Measuring Current Meter

A current meter used in oceanography that is effective at measuring near-surface currents since it is not as susceptible as some other meters to contamination from vertical currents and high frequency horizontal currents. It uses two orthogonal propellors to achieve insensitivity to current flow at right angles to the propellor axis. See Weller and Davis (1980).

 

veering

Said of the clockwise change of the direction of a wind, as opposed to backing.

 

vegetation

The kind of plant cover in an area, e.g. forest, grassland, etc., as opposed to the flora. See Collinson (1988).

 

VEGETATION

A program to monitor, on a daily basis, terrestrial vegetation over through remote sensing at regional and global levels. The instrument will be part of the SPOT 4 payload to be launched during the last quarter of 1998. See the VEGETATION Web site.

 

vegetation physiognomy

The suite of morphological and physiological characteristics that have evolved in resonse to climate variables, notably temperature and rainfall. Salient characteristics include leaf longevity, leaf dimension, and temperature sensitivity. See Woodward (1992).

 

VEI

Abbreviation for volcanic explosivity index. See Newhall and Self (1982).

 

VEINS

Acronym for Variability of Exchanges in Northern Seas.

 

velocity potential

A scalar function that exists in irrotational fluid motion. If we denote the velocity potential by , then it is defined by the equation

where is the velocity vector. This equation implies that is normal to the equipotential lines and is directed from high to low potential.

 

Vema Gap

A deep-sea channel that connects the Hatteras Abyssal Plain to the Nares Abyssal Plain in the North American Basin. This is an important passasge for northward traveling deep water formed in the Antarctic. See Fairbridge (1966).

 

VEMAP

Acronym for the Vegetation/Ecosystem Modeling and Analysis Project, a research group formed to compare biogeography and biogeochemistry models in the context of global climate change. The project objectives are the comparison of model output for current conditions, intercomparison of the climate and CO2 sensitivity of three biogeochemistry models and three vegetation lifeform distribution models, and linking vegetation distribution and ecosystem physiology models to evaluate the joint response of these processes to altered conditions. VEMAP is a designated activity of the GCTE Core Project. See Group (in press) and the VEMAP Web site.

 

vendavales

A name given to strong, squally, southwest winds in the Straits of Gibraltar and off the east coast of Spain. It is associated with depressions and occurs mainly between September and March. They usually bring stormy weather and heavy rain.

 

VENTEX

Acronym for Vent Experiment.

 

ventilated thermocline

See Luyten et al. (1983) for the original concept and Huang (1991) and Pedlosky (1990) for reviews.

 

VENTS

A NOAA PMEL program established in 1984 to focus research on determining the oceanic impacts and consequences of submarine hydrothermal venting, with most of the effort directed towards achieving an understanding of the chemical and thermal effects of venting along northeast Pacific Ocean seafloor spreading centers. See the VENTS Web site.

 

vernal equinox

See equinox.

 

Vertebrata

A subphylum of marine vertebrates of phylum Chordata. The classes containing marine species include Cyclostomata, Elasmobrachii, Pisces, Reptilia, Aves and Mammalia.

 

VERTEX

A multidisciplinary study of VERtical Transport and EXchange of material in the upper ocean performed in the California Current. See Martin et al. (1987).

 

VHF

Abbreviation for very high frequency, an electromagnetic spectrum waveband ranging from 30 to 300 MHz.

 

Vienna Convention

Known fully as the Vienna Convention for the Protection of the Ozone Layer, this was a meeting that took place in March 1985 which started an intensive effort by chemical manufacturers to produce alternative refrigerants to ozone-depleting CFCs.

 

VIRR

Abbreviation for Visible and IR Radiometer, an instrument that flew aboard SEASAT. It produced imagery for the identification of cloud and geographic features.

 

virtual potential temperature

A temperature defined to include the buoyant effects of liquid water in the air. It is calculated identically to the virtual temperature.

 

virtual temperature

The temperature a sample of dry air at pressure P would have in order that its density equal that of the sample of moist air at temperature T, pressure P, and water vapor mixing ratio r. It is given by

a If there is also liquid water in the air this is modified as

where is the liquid water mixing ratio (in grams of liquid water per gram of dry air). The virtual temperature is thus defined because it allows the ideal gas law to be used for situations in which the air is not dry, i.e. moist air of temperature T behaves identically to dry air of temperature .

 

Visayan Sea

A small sea located in the midst of the Visayan Islands that comprise the central portion of the Philippines. It is centered at about 124 E and 12 N and connected to the Sibuyan Sea to the northwest, the Samar Sea to the northeast, the the Camotes Sea to the southeast, the Bohol Sea to the southwest via the Tanon Strait, and to the Panay Gulf to the southwest via the Guimaras Strait. Prominent geographic features include the Asid Gulf (in Masbate Island) and Bantayan Island.

 

viscous sublayer

That part of a boundary layer where the viscous stress is much larger than the Reynolds stress. See Kagan (1995).

 

VISSR

Abbreviation for Visible Infrared Spin-Scale Radiometer, an imaging device on the METEOSAT, GOES and GMS platforms. It is used for obtaining 2-D cloud cover pictures from a geosynchronous altitude and provides for both day and night time observations of clouds and the determination of temperatures, cloud heights, and wind fields. The instrument consists of a scanning system, a telescope, and infrared and visible sensors. It is a radiometer with 2.5 x 2.5 km resolution in the visible and 5 x 5 km resolution in the infrared. The spectral range is 0.5 to 12.5 m and the temporal resolution 30 minutes (48 images per day). See the VISSR Web site.

 

vital effects

Semantic rug under which disequilibrium isotope fractionations of stable oxyen and carbon isotopes in the calcareous shells of some organisms are swept. This obviates the use of some organisms for paleothermometric purposes. Several mechanisms have been proposed as culprits but none have yet garnered the preponderance of evidence necessary for conviction. See Bowen (1991).

 

VLBI

Abbreviation for Very Long Baseline Interferometry.

 

VLF

Abbreviation for very low frequency, an electromagnetic spectrum waveband below 30 kHz.

 

VMCM

See Vector Measuring Current Meter.