Ha-Hm

 

habitat

The space used by an organism together with the other organisms with which it co-exists and the landscape and climate elements that affect it. See Heywood (1995).

 

haboob

A name applied to duststorms in the Sudan north of about 13 deg. N. These storms occur from about May to September and are most frequent in the afternoon and evening. The name is derived from the Arabic habb meaning to blow.

 

Hadley Cell

A part of the atmospheric circulation system extending from the Equator to 30 deg. latitude on both sides of the Equator. It is a thermally-driven system in which heated air rises at the Equator, flows poleward, cools and descends at subtropical latitudes, and then flows back towards the Equator. This description was suggested by Hadley in the 18th century.

 

Hale cycle

A 22-year cycle in solar activity which is a combination of the 11-year cycle in sunspot number and the reversal of the magnetic polarity of adjacent pairs of sunspots between alternate cycles. See Burroughs (1992).

 

half-life

The time in which half of the atoms of a given quantity of radioactive nuclide undergo at least one disintegration.

 

haline

Related to salinity.

 

Halmahera Sea

More later.

 

halocarbon

Any of several radiatively-active (i.e. greenhouse) gases that are compounds of carbon with fluorine and chlorine.

 

halocline

In oceanography, a relatively sharp change in salinity with depth.

 

HALOE

Abbreviation for Halogen Occultation Experiment, an ozone measuring experiment performed using UARS. See Russell (1993).

 

halophytes

Plants which find their optimum growth condition in saline soils.

 

HAPEX-MOBILHY

Acronym for the Hydrological Atmospheric Pilot Experiment-Modelisation du Bilan Hydrique. See Noilhan et al. (1991).

 

HAPEX-Sahel

Acronym for Hydrological and Atmospheric Pilot Experiment in the Sahel, a land-surface-atmosphere observation program that was undertaken in western Niger in the west African Sahel region. The goals of the project were to improve understanding of the role of the Sahel on the general circulation, in particular the effects of the large interannual fluctuations of land surface conditions in this region and, in turn, to develop ideas about how the general circulation is related to the persistent droughts that have affected the Sahel during the last 25 years. The field program measured atmospheric, surface and sub-surface properties in a 1 deg. by 1 deg. grid that incorporated examples of many of the major land surface types found throughout the Sahel. See the HAPEX-Sahel Web site.

 

harbor wave

A type of seiche found in harbors. The Japanese word ``tsunami'' means ``harbor wave'' but is a misnomer for what is really a seismic sea wave, more popularly (and even more incorrectly) known as a tidal wave.

 

harmattan

A dry wind blowing from a northeast or sometimes easterly direction over northwest Africa. The southern limit is about 5 deg. N in January and 18 deg. N in July. It is dry and cool and thus a welcome relief from the steady damp heat of the tropics, and as such is is known locally as ``the doctor'' for its supposed health-giving powers. This is in spite of the fact that it carries with it great quantities of dust from the desert, often carried in sufficient quantity to form a thick haze and impede navigation on the rivers.

 

harmonic

A frequency that is a simple multiple of a fundamental frequency. A second harmonic, for example, would have twice the frequency of the fundamental.

 

Hartley bands

The spectral bands in which solar radiation is most strongly absorbed by ozone. These cover the region from 2000 to 3000 Angstroms and are centered at 2553 Angstroms. The absorption of solar flux in these bands takes place primarily in the upper stratosphere and the mesosphere. See Liou (1992).

 

Hauterivian

The third of six ages in the Early Cretaceous epoch, lasting from 131 to 124 Ma. It is preceded by the Valanginian age and followed by the Barremian age.

 

HDP

Abbreviation for Human Dimensions of Global Environmental Change Programme, an ISSC program.

 

heat capacity

The heat capacity of a body is the product of its mass and its specific heat.

 

heat equator

See thermal equator.

 

HEIFE

Acronym for the Heihe River Basin Field Experiment. See Chou et al. (1992).

 

Heinrich Events

This refers to a set of sedimentary layers in cores from the North Atlantic that Heinrich (1988) first conjectured corresponded to the melting of six huge armadas of icebergs during the last 130,000 years. Further investigations Broecker (1994) have suggested that each event triggered a climate response of global extent during the last glaciation.

 

Helium-3

An isotope of helium that is useful in ocean tracer studies. There are two sources for Helium-3 in the ocean: volcanic sources at mid-ocean ridge crests and the decay of man-made tritium. The former source makes helium-3 a unique tracer due to its being injected into the middle of the water column. This leads, for example, to a stark contrast in helium-3 content between incoming and outgoing deep waters in the Pacific. It also provides a dramatic picture of the relative movement of helium poor NADW and helium rich (due to sources in the Pacific) ACC water. The helium-3 tritium decay (sometimes called trituigenic) source is much larger than the deep sea sources, with the global average of the latter being about 4 at/cm2/s as opposed to a northern hemisphere average of about 32 at/cm2/s for the former.

Helium-3 is used in combination with tritium to date water on timescales of 0-10 years with a resolution of around 0.1 years (in North Atlantic surface waters). It is better to treat them as separate but related tracers on longer timescales or in the presence of extensive mixing. Their relationship is a diagnostic of vertical versus horizontal mixing, and has been used to assess an upper limit to vertical mixing that is consistent with physical estimates. This has also been used to show that horizontal mixing is the dominant mechanism of thermocline ventilation in subtropical gyres. See Sarmiento (1988) and Broecker and Peng (1982).

 

Helland-Hansen, Bjorn

More later.

 

hemipelagic

Or or pertaining to continental margins and the adjacent abyssal plains.

 

Henry's law

To be completed.

 

Hesse's Rule

An ecogeographical rule, also known as the heart-weight rule, that states that extra metabolic work done to maintain heat in a cold environment causes a greater volume and mass of heart in animals living there as compared with their counterparts in warmer regions. This was propounded by Richard Hesse in 1937 and is basically an extension of Bergmann's Rule.

 

heterochrony

In paleobiology, the phenomenon of changes through time in the appearance or rate of development of ancestral characters. It involves the decoupling of the three elements of growth: size, shape, and time, or the extension or contraction of these elements. Temporal changes of size and shape relative to one another produce heterochrony, when either size or shape, or both, are affected by changes in their rate of ontogenetic development. The two basic forms are differentiative and growth heterochrony. See Briggs and Crowther (1990), pp. 111-119, or McKinney and McNamara (1991) for a book-length treatment.

 

heterogeneous nucleation

See GPC.

 

heterosphere

One of two atmospheric layers in a classification scheme based on homogeneity of composition. This is the atmospheric layer that starts at about 80-90 km in which molecules can be dissociated into atoms and/or ionized by absorption of energetic short-wave radiation. This is almost coincident with the ionosphere, although the ionosphere is usually thought to start a little lower at around 70-85 km. This sits above the homosphere, the lower level in this scheme.

 

heterotroph

Descriptive of a phytoplankton species which obtains the nutrients it needs (e.g. carbon, nitrogen, phosphorous, sulfur, etc.) from dissolved or particulate organic sources. Heterotrophs which feed on phytoplankton or detritus are called phagotrophs.

 

heterotrophic respiration

The form of respiration by which organic matter is converted back into CO2, mainly by soil micro-organisms.

 

heton

To be completed.

 

HF

Abbreviation for high frequency, an electromagnetic spectrum waveband ranging from 3 to 30 MHz.

 

high

Abbreviated form for high pressure center.

 

high pressure center

In meteorology, a region of relatively high barometric pressure. These are characterized by subsidence at altitude and by divergence near the surface. They predominate at 30 and 90 latitude where the global generation circulation patterns exhibit downward motion. This type of circulation feature is also known as an anticyclone and as such rotates clockwise/counterclockwise in the norther/southern hemisphere. High pressure systems are generally characterized by clear skies and fair weather since cloud development is impeded therein, and winds are also generally light.

 

HIMSS

Acronym for High-Resolution Microwave Spectrometer Sounder.

 

HIRDLS

Acronym for High-Resolution Dynamics Limb Sounder, an infrared limb-scanning radiometer designed to sound the upper troposphere, stratosphere, and mesosphere to determine temperature; the concentrations of O3, H2O, CH4, N2O, NO2, HNO3, N2O5, CFC11, CFC12, and aerosols; and the locations of polar stratospheric clouds and cloud tops. The goals are to provide sounding observations with horizontal and vertical resolution superior to that previously obtained; to observe the lower stratosphere with improved sensitivity and accuracy; and to improve understanding of atmospheric processes through data analysis, diagnostics, and use of two- and three-dimensional models. This is due to fly on NASA's EOS around the year 2002. See the HIRDLS Web site.

 

HIRIS

Acronym for High Resolution Imaging Spectrometer.

 

HIRLAM

Acronym for HIgh Resolution Limited Area Model, an international project to develop and maintain a numerical short-range weather forecasting for operational use by participating institutes. The project was started in 1985 and is now in the third phase. The HIRLAM model is at version 2.5 (as of 12/95) and the reference or standard version is kept at the ECMWF. See the HIRLAM Web site.

 

HIRS

Abbreviation for High Resolution infrared Sounder, a 20 channel scanning radiometer with infrared channels in the 15 and 4 micrometer regions plus 1 visible channel. The nadir resolution of HIRS is 17.4 km. This is part of the TOVS instrument package.

 

HIS

Acronym for High-resolution Interferometer Sounder, an instrument that obtains vertical profiles of atmopheric temperature and moisture from measurements of upwelling atmospheric radiation. It is currently flown aboard the NASA ER2 aircraft. See the HIS Web site.