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Words begining with "H"
Habitat
The area or region where a particular type of plant or animal
lives and grows.
Hail
Precipitation composed of balls or irregular lumps of ice. Hail is
produced when large frozen raindrops, or almost any particles, in
cumulonimbus clouds act as embryos
that grow by accumulating supercooled liquid droplets. Violent
updrafts in the cloud carry the particles in freezing air, allowing
the frozen core to accumulate more ice. When the piece of hail
becomes too heavy to be carried by upsurging air currents it falls to
the ground.
Hardware
The electrical and mechanical components of a system, as opposed
to software.
Haze
Fine dry or wet particles of dust, salt, or other impurities that
can concentrate in a layer next to the Earth when air is stable.
Heat Balance
The equilibrium existing between the radiation received and
emitted by a planetary system.
Heat Capacity Mapping Mission (HCMM)
A two-channel radiometer launched by NASA to measure the thermal
properties of the terrestrial surface. It had an application to
identify and locate rocks and minerals. One radiometer channel was in
the visible to near infrared (0.5 - 1.1 micrometers), and the other
in the thermal infrared (10.5 - 12.5 micrometers). The instantaneous
field of view (IFOV) was about 600 meters.
Hemisphere
Half of the Earth, usually conceived as resulting from the
division of the globe into two equal parts, north and south or east
and west.
Hertz (Hz)
The international unit of frequency equal to one cycle per second.
Radio frequencies are usually expressed in kilohertz/kHz (1,000
cycles per second) or megahertz/MHz (1,000,000 cycles per second).
Hertzian Waves
Radio waves or other electromagnetic radiation resulting from the
oscillations of electricity in a conductor.
High
A digital logic state corresponding to a binary "l" See low.
High Resolution Doppler Imager (HRDI)
Carried on UARS, it measures
stratospheric winds.
High-Resolution Infrared Radiation Sounder (HIRS)
Instrument carried by NOAA polar-orbiting satellites that detects
and measures energy emitted by the atmosphere to construct a vertical
temperature profile from the Earths surface to an altitude of about
40 km. Measurements are made in 20 spectral reqions in the infrared
band.
High-Resolution Picture Transmission (HRPT)
Real-time, 1.1 - kilometer resolution, digital images provided by
NOAAs polar-orbiting environmental satellites, containing all five
spectral channels and telemetry data transmitted as high-speed
digital transmissions. The Advanced Very High Resolution Radiometer
(AVHRR} provides the primary imaging
system for APT and HRPT. See TIROS.
Horse Latitudes
The subtropical latitudes (30-35 degrees), where winds are light
and weather is hot and dry. According to legend, ships traveling to
the New World often stagnated in this region and had to throw dead
horses overboard or eat them to survive, hence the name horse
latitudes. See wind.
HRDI
See High Resolution Doppler Imager.
HRPT
See High Resolution Picture Transmission.
Humidity
The amount of water vapor in the air. The higher the temperature,
the greater the number of water molecules the air can hold. For
example: at 60 degree F (15 degree C), a cube of air one yard on each
side can hold up to 4.48 ounces of water At 104 degrees F (40
degreesC), the same cube of air can hold up to 17.9 ounces of water.
Relative humidity describes the amount of water in the air compared
with how much the air can hold at the current temperature. Example:
50% relative humidity means the air holds half the water vapor that
it is capable of holding; 100% relative humidity means the air holds
all the water vapor it can. At 100% humidity, no more evaporation can
occur until the temperature rises, or until the water vapor leaves
the air through condensation. Absolute humidity is the ratio of the
mass of water vapor present in a system of moist air to the volume
occupied by the mixture, that is, the density of water vapor.
Hurricanes
Severe tropical storms whose winds exceed 74 mph. Hurricanes
originate over the tropical and subtropical North Atlantic and North
Pacific oceans, where there is high humidity and light wind. These
conditions prevail mostly in the summer and early fall. Since
hurricanes can take days or even weeks to form, time is usually
available for preventive or protective measures.
From space, hurricanes look like giant pinwheels, their winds
circulating around an eye that is between 5 and 25 miles in diameter
The eye remains calm with light winds and often a clear sky.
Hurricanes may move as fast as 50 mph, and can become incredibly
destructive when they hit land. Although hurricanes lose power
rapidly as soon as they leave the ocean, they can cause high waves
and tides up to 25 feet above normal. Waves and heavy flooding cause
the most deaths during a hurricane. The strongest hurricanes can
cause tornadoes.
Hydrochlorofluorocarbon (HCFC)
One of a class of compounds used primarily as a CFC
substitute. Work on CFC alternatives began in the late 1970s after
the first warnings of CFC damage to stratospheric ozone. By adding
hydrogen to the chemical formulation, chemists made CFCs less stable
in the lower atmosphere enabling them to break down before reaching
the ozone layer. However, HCFCs do release chlorine and have
contributed more to atmospheric chlorine buildup than originally
predicted. Development of non-chlorine based chemical compounds as a
substitute for CFCs and HCFCs continues.
Hydrologic Cycle
The pathways through which water is cycled in the terrestrial
biosphere.
Hydroshpere
The totality of water encompassing the Earth, comprising all the
bodies of water, ice, and water vapor in the atmosphere.
Hygrometer
Instrument that measures water vapor content in the air and
communicates changes in humidity visibly and immediately through a
graph or a dial. There are three types of hygrometers:
- The hair hygrometer uses a human hair as the sensing
instrument. The hair lengthens when the air is moist and contracts
when the air is dry, but remains unaffected by air temperature.
However, the hair hygrometer cannot respond to rapid fluctuations
in humidity.
- An electric hygrometer uses a plate coated with carbon.
Electrical resistance of the carbon coating changes as the
moisture content of the air changes - changes that translate into
relative humidity. This type of hygrometer is used frequently in
the radiosonde.
- An infrared hygrometer uses a beam of light containing two
separate wave lengths to gauge atmospheric humidity. One of the
wavelengths is absorbed by water vapor, the other is unaffected,
providing an extremely accurate index of water vapor for paths of
a few inches or thousands of feet. See psychrometer
Hz
See Hertz.
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