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Words begining with "T"
TDRSS
See Tracking and Data Relay Satellite System.
Telemetry
- Telecommunications transmission to a distance of measured
magnitude by radio or telephony with
suitably coded modulation,
e.g., amplitude, frequency,
phase, pulse.
- Transmission of data collected at a remote location over
communications channels to a central station.
- Surveying measurement of linear distances by use of
tellurometer - a device that uses microwaves to measure
distance.
Telephony
Used to transmit sounds between widely removed points with or
without connecting wires.
Television and Infrared Observation Satellite (TIROS)
A series of NASA and NOAA
satellites launched to monitor Earth's weather from outer space. The
era of the meteorological satellites began with the launch of TIROS-1
on April 1, 1960. For the first time, it was possible to monitor
weather conditions over most of the world regularly from space. A
series of these satellites were launched throughout the 1960s, those
funded by NASA for research and development were called TIROS, and
those funded by the Environmental Science Services Administration
(ESSA, the predecessor of NOAA) for the operational system were
called ESSA.
A second generation of ITOS/NOAA* environmental satellites was
initiated by the launch of ITOS-1 in 1970, followed by a number of
NOAA satellites. The third generation of TIROS-N/NOAA environmental
satellites was initiated by the launch of TIROS-N in 1978.
* Pairs of acronyms such as ITOS/NOAA arise because NASA funds and
names its prototype satellites and then the operating agency funds
and names the rest of the series.
TIROS-N/NOAA Satellites
NOAA satellites that continuously orbit the Earth from North to
South Pole (hence, polar orbiting) at an altitude of approximately
470 nautical miles (870.44 km or 540.86 statute miles). These
environmental satellites collect visible and infrared imagery and
provide atmospheric-sounding data and meteorological data relay and
collection. A primary mission of TIROS-N/NOAA is to monitor the 70
percent of the globe covered by water-where weather data is sparse
and provide continuous data to the National Weather Service for use
in numerical forecast modeling. Each TIROS- N/NOAA carries six
primary systems:
- The Advanced Very High Resolution Scanning Radiometer
(AVHRR) senses clouds over both
ocean and land, using the visible and infrared parts of the
spectrum. It stores measurements on tape, and later plays them
back to NOAAs command and data acquisition stations. The
satellites also broadcast in real time, and the broadcasts can be
received around the world by anyone equipped with a direct readout
receivinq station.
- The TIROS Operational Vertical Sounder (TOVS)
is a 3-part TIROS system to measure:
- Temperature profile of the Earth's atmosphere from the
surface to 10 millibars,
- Water content of the Earth's atmosphere
- Total ozone content of the Earth's atmosphere
- The ARGOS Data Collection and Platform Location System (DCS)
collects data from sensors placed on fixed and moving platforms,
including ships, buoys, and weather balloons, and transmits data
to a ground station antenna. Because ARGOS also determines the
precise location of these moving sensors, it can serve wildlife
managers by monitoring and tracking the transmitters placed on
birds and animals.
- The Space Environment Monitor (SEM)
measures energetic particles emitted by the sun over essentially
the full range of energies and magnetic field variations in the
Earth's near-space environment. Readings made by these instruments
are invaluable in measuring the sun's radiation activity.
- Search and Rescue
Tracking (COSPAS/SARSAT)
equipment receives emergency signals from persons in distress. The
satellites transmit the signals to ground receiving stations. The
signals then are forwarded to rescue coordination centers. The
rescue centers compute the location of the signals and provide the
coordinates of the emergency site (usually within a few miles).
- Earth Radiation Budget Experiment (ERBE)
is a radiometer, flown on
NOAA 9 and 10, designed to measure all radiation striking and
leaving the Earth. This enables scientists to measure the loss or
gain of terrestrial energy to space. Shifts in this energy
"budget" affect the Earth's average temperatures. Even slight
changes can affect climatic patterns.
Temperature
Measure of the energy in a substance. The more heat energy in the
substance, the higher the temperature. The Earth receives only one
two-billionth of the energy the sun produces. Much of the energy that
hits the Earth is reflected back into space. Most of the energy that
isn't reflected is absorbed by the Earths surface. As the surface
warms, it also warms the air above it.
Terabit
A trillion ( 1,000,000,000,000) bits.
Thematic Mapper (TM)
A Landsat multispectral scanner
designed to acquire data to categorize the Earths surface. Particular
emphasis was placed on agricultural applications and identification
of land use. The scanner continuously scans the surface of the Earth,
simultaneously acquiring data in seven spectral channels. Overlaying
two or more bands produces a false color image. The ground resolution
of the six visible and shortwave bands of the Thematic Mapper is 30
meters, and the resolution of the thermal infrared band is 120
meters. Thematic mappers have been flown on Landsats-4 and -5.
Thermal Infrared
Electromagnetic radiation with wavelengths between about 3 and 25
micrometers.
Thunder
The sound that results from lightning.
Lightning bolts (static electricity) produce intense heat. This burst
of heat makes the air around the bolt expand explosively, producing
the sound we hear as thunder. Since light travels faster than sound,
we see the lightning before we hear the thunder
Thunderstorm
Local storm resulting from warm humid air rising in an unstable
environment. Air may start moving upward because of unequal surface
heating, the lifting of warm air along a frontal zone, or diverging
upper-level winds (these diverging winds draw air up beneath them).
The scattered thunderstorms that develop in the summer are called
air-mass thunderstorms because they form in warm, maritime tropical
air masses away from other weather fronts. More violent severe
thunderstroms form in areas wih a strong verical wind shear that
forces the updraft into the mature stage, the most intense stage of
the thunderstorm. Severe thunderstorms can produce large hail,
forceful winds, flash floods, and tornadoes.
TIROS
See Television and Infrared Observation
Satellite.
TM
See Thematic Mapper
TNL
Thermal Noise Level.
TOGA
See Tropical Ocean Global Atmosphere
Program.
TOMS
See Total Ozone Mapping Spectrometer.
TOPEX/Poseidon
Ocean Topography Experiment, United States (NASA)/
France (CNES). Launched in 1992, the mission carrries a radar sensor
- called an altimeter - to measure the ocean's surface topography
wiht unprecedented precision. TOPEX/Poseidon is a core element of the
international World Ocean Circulation Experiment (WOCE)
and the Tropical Ocean Global Atmosphere (TOGA)
seagoing measurements program.
Mission objectives are to:
- Study ocean circulation and its interaction with the
atmosphere to understand climate change better
- Improve our knowledge of heat transport in the ocean
- Model global ocean tides
- Study the marine gravity field
- Calculate sea-level variations on both global and local
scales
Tornado
A twisting, spinning funnel of low pressure air. The most
upredictable weather event, tornadoes are created during powerful
thunderstorms As a column of warm air
rises, air rushes in at ground level and begins to spin. If the storm
gathers energy, a twisting, spinning funnel develops. Because of the
funnel's cloud and rain composition and the dust, soil, and debris it
draws up, the funnel appears blackish in color. The most energetic
storms result in the funnel touching the ground. In these tornadoes,
the roaring winds in the funnel can reach 300 mph, the stronges winds
on Earth. Funnels usually travel at 20 to 40 mph, moving toward the
northeast. When tornadoes form over lakes or oceans they suck water
into the funnel cloud and are called waterspouts.
Total Ozone Mappping Spectrometer
Flown on NASA's Nimbus-7
satellite, its primary goal is to continue the high-resolution global
mapping of total ozone on a daily
basis. The Nimbus-7 launch in 1978 enabled TOMS to begin delivering
data in 1979 and continue providing information until 1993. TOMS has
mapped the total amount of ozone between the ground and the top of
the atmosphere, provided the first maps of the ozone hole, and
continues to monitor this phenomenon.
Because of its longevity, TOMS also has obtained information on
the more subtle trends in ozone outside the ozone hole region. This
results from development of a powerful new calibration technique that
removes the instrument measurement drift that developed over the
years. With this technique applied to the TOMS 14.5 year data record,
a global ozone decrease of 2.69 percent per decade was detected.
To ensure that ozone data will be available through the next
decade, NASA will continue the TOMS program using U.S. and foreign
launches. In 1991, the former Soviet Union launched a Meteor-3
satellite carrying a TOMS instrument provided by NASA. A third TOMS
will be launched onboard a NASA Earth probe in 1994, and the Japanese
Advanced Earth Observations Satellite /ADEOS) will carry a fourth
TOMS when it launches in 1996.
TOVS
TIROS Operational Vertical Sounder. See Television
Infrared Operational Satellite /TIROS).
Tracking and Data Relay Satellite System (TDRSS)
An orbiting communications satellite, developed by NASA, used to
relay data from satellite sensors to ground stations and to track the
satellites in orbit.
Trade Winds
Surface air from the horse
latitudes that moves back toward the equator and is deflected by
the Coriolis Force, causing
the winds to blow from the Northeast in the Northern Hemisphere and
from the Southeast in the Southern Hemisphere. These steady winds are
called trade winds because they provided trade ships with an ocean
route to the New World. See wind.
TRMM
See Tropical Rainfall Measuring Mission.
Tropical Ocean-Global Atmosphere (TOGA)
TOGA is a program jointly sponsored by the United Nations World
Meteorological Organization (WMO); the International Council of
Scientific Unions (ICSU); the United Nations Educational, Scientific,
and Cultural Organization (UNESCO) Intergovernmental Oceanographic
Commission (IOC); and the ICSU Scientific Committee on Oceanic
Research (SCOR). TOGA has four major objectives:
- To collect and catalog observations of the tropical atmosphere
and ocean
- To assess the evolution of the tropical atmosphere/ocean
system in real time
- To promote the development of short-term climate-prediction
computer models for the tropics
- To study the influence of the tropical atmosphere/ocean system
on the climate at hiqher latitudes.
Tropical Rainfall Measuring Mission (TRMM)
A joint NASA/NASDA mission planned for launch in 1997. The goal of
TRMM is to obtain a minimum of 3 years of climatologically
significant observations of rainfall in the tropics. Because rainfall
is such a variable phenomenon, adequate sampling is a difficult
problem.
By averaging the instantaneous rainfall rates for 30 days over a 5
degree by 5 degree grid, TRMM will obtain observations that meet
climatological requirements. TRMM measurements, used together with
cloud models, also will provide accurate estimates of vertical
distributions of latent heating in the atmosphere.
The present uncertainty about the quantity and distribution of
precipitation, especially in the tropics, prohibits definition of the
mass and energy exchange between the tropical ocean and atmosphere.
Since the tropical atmosphere and oceans are closely coupled, cloud
radiation and rainfall are likely to have significant effects on
ocean circulation and marine biomass.
TRMM data will play a significant role in global change studies,
especially in developing an interdisciplinary understanding of
atmospheric circulation, ocean-atmospheric coupling, and tropical
biology. TRMM data on tropical clouds, evaporation, and heat transfer
will be used to understand the larger scale coupling of the
atmosphere to oceans. See Earth Probes.
Tropical Storm Formation
Tropical storms generally form in the eastern portion of tropical
oceans and track westward. Hurricanes, typhoons, and willy-willies
all start out as weak low pressure areas that form over warm tropical
waters (e.g., surface water temperature of at least 80 degrees F).
Initially, winds and cloud formations over the warm tropical waters
are minimal. Both intensify with time. Formation of tropical storms
also requires a significant Coriolis
effect to induce proper spin in the wind formation. As the storm
begins to organize itself into a coherent pattern, it will experience
increased activity and intensity.
When a storm develops a clearly recognizable pattern, it is
referred to as a tropical depression. When wind speeds reach 35 knots
(40.3 mph), it is called a tropical storm and is given a name When
wind speed equals or exceeds 74 mph, the storm is called a hurricane.
In the western Pacific, a hurricane is referred to as a
typhoon. In waters around Australia it is
called a cyclone or
willy-willy.
Hurricanes intensify when moving over areas of increased water
temperatures, and weaken over colder water surfaces. Upper atmosphere
wind shear (different wind direction and speeds at different
elevations) will frequently prevent or slow intensification of
tropical storms by "spreading out" the storm horizontally and
preventing the formation of strong updrafts of warm, humid air.
Movement over a land-mass will weaken hurricane winds but will result
in large-scale rain that can result in large-scale flooding. When
encountering a strong frontal system (such as a polar front) the
hurricane will curve and track along the leading edge of the front or
become implanted in it.
Satellite infrared imagery can identify surface water temperatures
that will foster tropical storm development.
Tropics
The area between 23.5 degrees north and south of the equator. This
region has small daily and seasonal changes in temperature, but great
seasonal changes in precipitation.
Troposhere
The lower atmosphere, to a height of 8-15 km above Earth, where
temperature generally decreases with altitude, clouds form,
precipitation occurs, and convection currents are active. See
atmosphere.
Tropospheric Emission Spectrometer
A high-resolution infrared spectrometer for monitoring the minor
components of the lower atmosphere.
Trough
Elongated area of low atmospheric pressure, either at the surface
or in the upper atmosphere.
True Anomaly (aka J)
One of six Keplerian
elements, it locates a satellite on an orbit. True anomaly is the
true angular distance of a satellite (planet) from its perigee
(perihelion) as seen from the center of the Earth (sun).
Typhoon
Hurricanes in the Western Pacific Ocean.
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