Definition
Species introduced into an ecosystem (e.g., an estuary)
where they do not occur naturally.
An exotic species, with respect to a particular ecosystem, refers to any species, including its larvae, seeds, eggs,
spores, or other biological material capable of propagating
the species, which is not native to that ecosystem (Beck
et al., 2008). An exotic species does not necessarily cause
economic or environmental harm to an ecosystem.
Bibliography
Beck, K. G., Schardt, K. J. D., Stone, J., Lukens, R. R., Reichard, S.,
Randall, J., Cangelosi, A. A., Cooper, D., and Thompson, J. P.,
2008. Invasive species defined in a policy context: recommendations from the federal invasive species advisory committee.
Invasive Plant Science and Management, 1, 414–421.
Cross-references
Introduced Species
Invasive Species
EXTRATROPICAL STORMS
Harry C. Friebel
U.S. Army Corps of Engineers, Philadelphia District,
CENAP-EC-EH, Philadelphia, PA, USA
Synonyms
Extratropical cyclone; Midlatitude cyclone
Definition
Extratropical storms are cyclones that originate in mid to
high latitudes, discernible by a distinct front due to the
contrast in temperature between adjacent air masses.
Extratropical cyclones are low-pressure systems that
originate outside of the tropics, resulting from the interaction of warm and cold air masses. The center of these
storms contains the lowest pressure and is colder than the
surrounding storm system. In the Northern Hemisphere,
winds rotate counterclockwise (opposite in the Southern
Hemisphere), pulling and mixing warm air from the tropics with cold air from northern latitudes. The boundary
where warm and cold masses meet is termed a “front.”
The resulting front produces severe weather with extensive precipitation, with the strongest winds located in the
upper atmosphere. Extratropical storms generally move
west to east (in the Northern Hemisphere) across the globe
and are the dominant storm system for much of fall, winter,
and spring outside of the tropics (NHC, 2013).
Bibliography
National Hurricane Center (NHC), (2013). National Oceanic &
Atmospheric Administration (NOAA), U.S. Department of
Commerce. Available at http://www.nhc.noaa.gov. Accessed
5 May 2013.
Cross-references
Extreme Events (Hurricanes)
Storm Surges
EXTREME EVENTS (HURRICANES)
Harry C. Friebel
U.S. Army Corps of Engineers, Philadelphia District,
CENAP-EC-EH, Philadelphia, PA, USA
Synonyms
Cyclone; Tropical cyclone; Typhoon
Definition
Tropical cyclones are storms with a minimum sustained
surface wind speed of 74 mph (64 kt) in the Atlantic and
eastern Pacific Oceans. The sustained wind speed is the
average wind speed in a 2-minute period.
Hurricanes are a type of tropical cyclone. Tropical
cyclones are low-pressure weather systems that develop
over warm, tropical, or subtropical waters. A tropical
cyclone with sustained wind speeds of 38 mph (33 kt) or
less is termed a “tropical depression,” between 39 and
73 mph (34–63 kt) a “tropical storm,” and above 74 mph
(64 kt) a “hurricane.” Hurricanes are classified according
to the Saffir–Simpson Hurricane Scale. A Category
1 storm with winds between 74 and 95 mph (64–82 kt)
will produce some damage; a Category 2 storm with winds
between 96 and 110 mph (83–95 kt) will cause extensive
damage; a Category 3 storm with winds between 111 and
129 mph (96–112 kt) will cause devastating damage;
a Category 4 storm with winds between 130 and
156 mph (113–136 kt) will cause catastrophic damage;
and a Category 5 storm with winds of 157 mph or higher
(137 kt or higher) will cause catastrophic damage.
Extreme tropical cyclones are called “hurricanes” in the
Atlantic and eastern Pacific Oceans, “typhoons” in the
Western Pacific, and “Cyclones” in the Indian Ocean
(NOAA, 2013a). The Atlantic Ocean hurricane season
begins June 1 and ends November 30th, while the Eastern
Pacific season begins May 15th and ends November 30th
(NOAA, 2013a).
Hurricanes have winds that rotate counterclockwise
(in the Northern Hemisphere) and inward towards the
storm’s center where the strongest winds are located near
the earth’s surface. The center or core of a hurricane is
termed the “eye.” The eye is the warmest part of
a hurricane, relatively calm, thunderstorm-free, and
surrounded by an “eyewall.” The eyewall contains the
strongest winds of the hurricane. Hurricanes can vary in
size as rainbands, consisting of high winds and thunderstorms extending outward from the hurricane’s eye
(NOAA, 2013b). Hurricanes may produce microbursts,
tornadoes, flooding from excessive rainfall, and severe
storm surge and waves (FEMA, 2013). In the Northern
312
EXTRATROPICAL STORMS
Species introduced into an ecosystem (e.g., an estuary)
where they do not occur naturally.
An exotic species, with respect to a particular ecosystem, refers to any species, including its larvae, seeds, eggs,
spores, or other biological material capable of propagating
the species, which is not native to that ecosystem (Beck
et al., 2008). An exotic species does not necessarily cause
economic or environmental harm to an ecosystem.
Bibliography
Beck, K. G., Schardt, K. J. D., Stone, J., Lukens, R. R., Reichard, S.,
Randall, J., Cangelosi, A. A., Cooper, D., and Thompson, J. P.,
2008. Invasive species defined in a policy context: recommendations from the federal invasive species advisory committee.
Invasive Plant Science and Management, 1, 414–421.
Cross-references
Introduced Species
Invasive Species
EXTRATROPICAL STORMS
Harry C. Friebel
U.S. Army Corps of Engineers, Philadelphia District,
CENAP-EC-EH, Philadelphia, PA, USA
Synonyms
Extratropical cyclone; Midlatitude cyclone
Definition
Extratropical storms are cyclones that originate in mid to
high latitudes, discernible by a distinct front due to the
contrast in temperature between adjacent air masses.
Extratropical cyclones are low-pressure systems that
originate outside of the tropics, resulting from the interaction of warm and cold air masses. The center of these
storms contains the lowest pressure and is colder than the
surrounding storm system. In the Northern Hemisphere,
winds rotate counterclockwise (opposite in the Southern
Hemisphere), pulling and mixing warm air from the tropics with cold air from northern latitudes. The boundary
where warm and cold masses meet is termed a “front.”
The resulting front produces severe weather with extensive precipitation, with the strongest winds located in the
upper atmosphere. Extratropical storms generally move
west to east (in the Northern Hemisphere) across the globe
and are the dominant storm system for much of fall, winter,
and spring outside of the tropics (NHC, 2013).
Bibliography
National Hurricane Center (NHC), (2013). National Oceanic &
Atmospheric Administration (NOAA), U.S. Department of
Commerce. Available at http://www.nhc.noaa.gov. Accessed
5 May 2013.
Cross-references
Extreme Events (Hurricanes)
Storm Surges
EXTREME EVENTS (HURRICANES)
Harry C. Friebel
U.S. Army Corps of Engineers, Philadelphia District,
CENAP-EC-EH, Philadelphia, PA, USA
Synonyms
Cyclone; Tropical cyclone; Typhoon
Definition
Tropical cyclones are storms with a minimum sustained
surface wind speed of 74 mph (64 kt) in the Atlantic and
eastern Pacific Oceans. The sustained wind speed is the
average wind speed in a 2-minute period.
Hurricanes are a type of tropical cyclone. Tropical
cyclones are low-pressure weather systems that develop
over warm, tropical, or subtropical waters. A tropical
cyclone with sustained wind speeds of 38 mph (33 kt) or
less is termed a “tropical depression,” between 39 and
73 mph (34–63 kt) a “tropical storm,” and above 74 mph
(64 kt) a “hurricane.” Hurricanes are classified according
to the Saffir–Simpson Hurricane Scale. A Category
1 storm with winds between 74 and 95 mph (64–82 kt)
will produce some damage; a Category 2 storm with winds
between 96 and 110 mph (83–95 kt) will cause extensive
damage; a Category 3 storm with winds between 111 and
129 mph (96–112 kt) will cause devastating damage;
a Category 4 storm with winds between 130 and
156 mph (113–136 kt) will cause catastrophic damage;
and a Category 5 storm with winds of 157 mph or higher
(137 kt or higher) will cause catastrophic damage.
Extreme tropical cyclones are called “hurricanes” in the
Atlantic and eastern Pacific Oceans, “typhoons” in the
Western Pacific, and “Cyclones” in the Indian Ocean
(NOAA, 2013a). The Atlantic Ocean hurricane season
begins June 1 and ends November 30th, while the Eastern
Pacific season begins May 15th and ends November 30th
(NOAA, 2013a).
Hurricanes have winds that rotate counterclockwise
(in the Northern Hemisphere) and inward towards the
storm’s center where the strongest winds are located near
the earth’s surface. The center or core of a hurricane is
termed the “eye.” The eye is the warmest part of
a hurricane, relatively calm, thunderstorm-free, and
surrounded by an “eyewall.” The eyewall contains the
strongest winds of the hurricane. Hurricanes can vary in
size as rainbands, consisting of high winds and thunderstorms extending outward from the hurricane’s eye
(NOAA, 2013b). Hurricanes may produce microbursts,
tornadoes, flooding from excessive rainfall, and severe
storm surge and waves (FEMA, 2013). In the Northern
312
EXTRATROPICAL STORMS