EM 1110-2-1100 (Part II)
(Change 1) 31 July 2003
Table II-2-2 (Concluded)
Monsoonal winds
Episodic wave generation can generate large wave
H 4-7m
conditions.
T 6 - 11 sec
Biannual outbursts of air from continental
Very important in the Indian Ocean, part of the Gulf
land masses.
of Mexico, and some U.S. east coast areas.
Long waves can be generated by moving
Long-wave generation
pressure/wind anomalies (such as can be associated
with fronts and squall lines) and can resonate with long
waves if the speed of frontal or squall line motion is
approximately %&& .
gd
Examples of this phenomenon have been linked to
inundations of piers and beach areas in Lake Michigan
and Daytona Beach in recent years.
U . 40 m/s
These winds may be extremely important in
Gap winds
generating waves in many U.S. west coast areas
Wind acceleration due to local topographic
not exposed to open-ocean waves.
funneling.
(Sheet 3 of 3)
h.
Winds in hurricanes.
(1) In tropical and in some subtropical areas, organized cloud clusters form in response to perturbations
in the regional flow. If a cloud cluster forms in an area sufficiently removed from the Equator, then Coriolis
accelerations are not negligible and an organized, closed circulation can form. A tropical system with a
developed circulation but with wind speeds less than 17.4 m/s (39 mph) is termed a tropical depression.
Given that conditions are favorable for continued development (basically warm surface waters, little or no
wind shear, and a high pressure area aloft), this circulation can intensify to the point where sustained wind
speeds exceed 17.4 m/s, at which time it is termed a tropical storm. If development continues to the point
where the maximum sustained wind speed equals or exceeds 33.5 m/s (75 mph), the storm is termed a
hurricane. If such a storm forms west of the international date line, it is called a typhoon. In this section, the
generic term hurricane includes hurricanes and typhoons, since the primary distinction between them is their
point of origin. Tropical storms will also follow some of the wind models given in this section, but since
these storms are weaker, they tend to be more poorly organized.
(2) Although it might be theoretically feasible to model a hurricane with a primitive equation approach
(i.e. to solve the coupled dynamic and thermodynamic equations directly), information to drive such a model
is generally lacking and the roles of all of the interacting elements within a hurricane are not well-known.
Consequently, practical hurricane wind models for most applications are driven by a set of parameters that
characterize the size, shape, rate of movement, and intensity of the storm, along with some parametric
representation of the large-scale flow in which the hurricane is imbedded. Myers (1954); Collins and
Viehmann (1971); Schwerdt, Ho, and Watkins (1979); Holland (1980); and Bretschneider (1990) all describe
and justify various parametric approaches to wind-field specification in tropical storms. Cardone,
Greenwood, and Greenwood (1992) use a modified form of Chow's (1971) moving vortex model to specify
winds with a gridded numerical model. However, since this numerical solution is driven only by a small set
of parameters and assumes steady-state conditions, it produces results that are similar in form to those of
parametric models (Cooper 1988). Cardone et al. (1994) and Thompson and Cardone (1996) describe
a more general model version that can approximate irregularities in the radial wind profile such as the double
maxima observed in some hurricanes.
(3) All of the above models have been shown to work relatively well in applications; however, the
Holland (1980) model appears to provide a better fit to observed wind fields in early stages of rapidly
Meteorology and Wave Climate
II-2-27
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