Hurricane Eye Research Articles

Vortical Swirls in Hurricane Eye Clouds

Abstract A collection of images depicting various swirling patterns within low-level cloud decks in hurricane eyes is presented and described. A possible causal mechanism for the presence of these cloud patterns is suggested by comparison of the observed cloud patterns with the evolution of passive tracers in a simple 2D barotropic model. The model is initialized with a barotropically unstable flow field that imitates the observed flows in hurricanes, and numerical integration of this field simulates vigorous mixing between eye and eyewall. During the mixing process, passive tracers initially embedded in the flow form swirling patterns in the eye that are strikingly similar to cloud patterns often observed in the eyes of hurricanes.

Symmetrization of lopsided vorticity monopoles and offset hurricane eyes

AbstractThis paper is a contribution towards better understanding of the continually occurring symmetrization processes in tropical cyclones. Before a tropical cyclone develops an eye, it can often possess an asymmetric monopolar vorticity distribution. As an idealized initial condition in a non‐divergent barotropic model, we use a lopsided monopole with different degrees of asymmetry of the monotonic vorticity field. We then study the axi‐symmetrization process which involves the ejection of a winding spiral band. For extreme asymmetric initial conditions, the band can produce regions of barotropic instability, resulting in nonlinear mixing of vorticity and the formation of polygonal structures. In a second series of experiments, we study the case of a tropical cyclone with a developed eye, modelled as a hollow‐tower vorticity distribution, i.e. an annular region of elevated vorticity, with low vorticity in the eye. If the eye is offset and the annular region of elevated vorticity is not of uniform width, complex symmetrization processes can occur, sometimes leading to a tripole structure of the hurricane's vorticity field. Long‐lived hurricane eyes are found for initial conditions with a slight offset. For such initial conditions, passive tracers can remain in the eye for as long as 72 hours, showing that in this model it is possible for air inside the eye to remain there for long periods of time, while moving coherently with the storm. Predictions of the axi‐symmetric final equilibrium states of the flow are obtained using the statistical mechanics theory of maximum Boltzmann mixing entropy. These predictions are then compared with results from the direct numerical integrations for both the lopsided monopole and the offset hurricane eye. The distribution of air‐parcel tracers initially placed in selective regions of vorticity for the direct numerical integrations are compared with results from the statistical theory.

Two Distinct Regimes in the Kinematic and Thermodynamic Structure of the Hurricane Eye and Eyewall

Abstract Using aircraft flight-level data, the present work demonstrates that the kinematic and thermodynamic distributions within the eye and eyewall of strong hurricanes are observed to evolve between two distinct regimes. In the first regime, angular velocity is greatest within the eyewall and relatively depressed within the eye. In the second regime, radial profiles of angular velocity are nearly monotonic, with maxima found at the eye center. Considering sequential profiles within individual hurricanes, the authors find that the evolution of the kinematic distribution is often marked by a transition from the first regime to the second. The transition can occur in less than 1 h. Also noted during the transition are dramatic changes in the thermodynamic structure of the hurricane. Prior to the transition (regime 1), the eye is typically very warm and dry, and the equivalent potential temperature is often elevated within the eyewall and relatively depressed within the eye. After the transition (regime 2...

A Numerical Study of the Effect of GOES Sounder Cloud-Cleared Brightness Temperatures on the Prediction of Hurricane Felix

The influence of Geostationary Operational Environmental Satellite (GOES) brightness temperature data on the numerical simulations of Hurricane Felix is investigated. Satellite data are included as an augmentation to a bogus data assimilation (BDA) procedure using a mesoscale adjoint modeling system. The assimilation of satellite data modified not only the environmental flow but also the structure of the initial vortex, which is located over a region devoid of satellite data. This modification resulted in a reduction of the 12-h forecast errors verified by radiosonde data. Despite the fact that the forecast using only the bogus surface low at the initial time was very good, track and intensity forecasts beyond 2 days of model integration were shown to be improved further by including satellite data in the initialization procedure. Differences in the prediction of Hurricane Felix with and without satellite data were also found in the prediction of the upper-level jet, the cold temperature trough ahead of the hurricane, the size of the hurricane eye, and the location of the maximum hydrometeor. Although the focus of this study is to assess the effect of the direct use of satellite brightness temperature data on hurricane prediction, it is also noted that the BDA experiment including only the bogus data shows a positive effect of the BDA vortex on the environmental flow during the forecast period, as verified by satellite observations.

Tropical Cyclone Eye Thermodynamics

In intense tropical cyclones, sea level pressures at the center are 50‐100 hPa lower than outside the vortex, but only 10‐30 hPa of the total pressure fall occurs inside the eye between the eyewall and the center. Warming by dry subsidence accounts for this fraction of the total hydrostatic pressure fall. Convection in the eyewall causes the warming by doing work on the eye to force the thermally indirect subsidence. Soundings inside hurricane eyes show warm and dry air aloft, separated by an inversion from cloudy air below. Dewpoint depressions at the inversion level, typically 850‐500 hPa, are 10‐30 K rather than the ;100 K that would occur if the air descended from tropopause level without dilution by the surrounding cloud. The observed temperature and dewpoint distribution above the inversion can, however, be derived by ;100 hPa of undilute dry subsidence from an initial sounding that is somewhat more stable than a moist adiabat. It is hypothesized that the air above the inversion has remained in the eye since it was enclosed when the eyewall formed and that it has subsided at most a few kilometers. The cause of the subsidence is the enclosed air’s being drawn downward toward the inversion level as the air below it flows outward into the eyewall. Shrinkage of the eye’s volume is more than adequate to supply the volume lost as dry air is incorporated into the eyewall or converted to moist air by turbulent mixing across the eye boundary. The moist air below the inversion is in thermodynamic contact with the sea surface. Its moisture derives from evaporation of seawater inside the eye, frictional inflow of moist air under the eyewall, and from moist downdrafts induced as condensate mixes into the eye. The moist air’s residence time in the eye is much shorter than that of the dry air above the inversion. The height of the inversion is determined by the balance between evaporation, inflow, and inward mixing on one hand and loss to the eyewall updrafts on the other.

Some Aspects of Hurricane Inner-Core Dynamics and Energetics

Abstract The energy cycle of the mature hurricane resides in the secondary circulation that passes through the storm’s eyewall. By equating the generation of energy in this cycle to boundary layer dissipation, an upper bound on wind speed is derived. This bound depends on the degree of thermodynamic disequilibrium between the tropical ocean and atmosphere, on the difference between sea surface and outflow absolute temperatures, and also on the ratio between the enthalpy exchange and surface drag coefficients. Such a bound proves to be an excellent predictor of maximum wind speeds in two different axisymmetric numerical models and does not appear to depend on the existence of the hurricane eye. But further consideration of the detailed dynamics of the eye and eyewall show that the intensification of hurricanes is accelerated by feedbacks associated with a component of eye subsidence forced by radial turbulent diffusion of momentum. This radial momentum diffusion is an inevitable by-product of the strong fr...

In the hurricane's eye: A supraparadigmatic integrative model.

In the hurricane's eye: A supraparadigmatic integrative model.

Impacts of Hurricane Andrew on carbonate platform environments, northern Great Bahama Bank

The northern (most energetic) quadrant of Hurricane Andrew (August 1992) passed over leeward-margin sand waves, bank-top sand shoals, reefs, and low islands of Great Bahama Bank for which an extensive prestorm data base exists. A reconnaissance survey seven weeks after Hurricane Andrew evaluated storm impacts on these bank-top settings. Resurveyed seismic profiles showed that positions, dimensions, and orientations of platform sand bodies were unchanged relative to fixed bedrock features. Surveys of reef communities indicated only minor storm-related disturbance. Coral bleaching may be due to storm-induced environmental stress. In addition, storm-wave plucking of boulders from emergent rocky cays resulted in localized crushing of reef biota. On low islands, beach erosion and storm surge were insignificant, and storm damage to Casuarina forests was minor and substrate-specific. Observed minimal hurricane impacts on northern Great Bahama Bank environments lying 10-75 km from the hurricane eye are reconciled by analysis of meteorological data, which show significant weakening of the storm (expressed as a rise in central barometric pressure of ∼20 mbar) during passage across the bank-top. This study demonstrates the importance of specific dynamic aspects of hurricanes (e.g., varying intensity, strength, size, forward speed, duration) which influence their geologic potential, even over relatively short distances along the storm track of an individual hurricane.

Physical Aspects of Hurricane Hugo in Puerto Rico

On 18 September 1989 the western part of Hurricane Hugo crossed eastern Puerto Rico and the Luquillo Experimental Forest (LEF). Storm-facing slopes on the northeastern part of the island that were within 15 km of the eye and received greater than 200 mm of rain were most affected by the storm. In the LEF and nearby area, recurrence intervals associated with Hurricane Hugo were 50 yr for wind velocity, 10 to 31 yr for stream discharge, and 5 yr for rainfall intensity. To compare the magnitudes of the six hurricanes to pass over Puerto Rico since 1899, 3 indices were developed using the standardized values of the product of: the maximum sustained wind speed at San Juan squared and storm duration; the square of the product of the maximum sustained wind velocity at San Juan and the ratio of the distance between the hurricane eye and San Juan to the distance between the eye and percentage of average annual rainfall delivered by the storm. Based on these indices, Hurricane Hugo was of moderate intensity. However, because of the path of Hurricane Hugo, only one of these six storms (the 1932 storm) caused more damage to the LEF than Hurricane Hugo. Hurricanes of Hugo's magnitude are estimated to pass over the LEF once every

Questions For My Country Cousin

Questions For My Country Cousin Have you spur-raked a wild stallion Bucking toward the sky? Have you raft-run white water, or Flown through hurricane eye? Have you voice-tracked hounds all night By light from the moon, Then beat brush for the grizzly You wounded next noon? If you've done all those things, Wouldst marry the tagalong Who walked by your side And did you no wrong? And then erect a log cabin (With a latch-bolt door) And beget you a family In that room with clay floor? Or, like me, will you go to town To make love to a whore. —Paul Lee Heaven Hill When my son died, I cried Cried for a long time. I prayed, prayed for regeneration, Then I walked and drank, drank And walked And staggering To a mountain top I lay down. Lying on rock-pillow, staring past the farthest pinpoint of light, I envisioned GOD. Rising up I danced, till exhausted, for glory of Him; Then dropping To my knees I prayed. I prayed again for Matthew's promised Heaven wine, Then fell into a stupor— But when I awoke My son was still dead; So I took another drink. —Paul Lee 48 ...

Over the eye of the storm

The force of Hurricane Josephine is clearly evident from the photograph on the cover. The center of the circulation at the surface is located at 33.5°N, 7l.7°W, 400 km east‐southeast of Cape Hatteras, North Carolina. When this photograph was taken on October 12, 1984, at 1631:34 UT, the camera was pointing toward the southwest from the orbital subpoint of 34.8°N, 70.1°W. The South Carolina coastline is faintly visible beyond all the clouds in the upper right‐hand corner. The south wall of the hurricane eye is practically nonexistent.

RADAR OBSERVATIONS OF HURRICANE WAVE DIRECTIONS

This paper presents an analysis of data collected in a hurricane wave research program. The data were collected with a synthetic aperture radar (SAR) during five aircraft flights into hurricanes in August and September, 1976. These data are the first collected on the directional distributions of waves throughout the region of active generation. The wave patterns in all of the storms are similar and show a marked radially asymmetry. The dominant waves propagate ahead of the storm in a broad arc that has an apparent center in a region of confused sea to the right and rear of the hurricane eye. The asymmetry in the wave patterns is attributed to the forward motion of the storms. The wave directions throughout the storms do not show a sensitive dependence on the forward speed of the storms or on their maximum wavespeeds. However, there is an increase in peak wavelength with increasing windspeed and forward velocity.

Ocean Wave Patterns Under Hurricane Gloria: Observation with an Airborne Synthetic-Aperture Radar

Surface imagery of ocean waves under Hurricane Gloria (September 1976) has been obtained with an airborne synthetic-aperture imaging radar. Observations were obtained over most of the area within a radius of 150 kilometers around the center of the eye. These direct observations made it possible to derive the wave patterns in the region around a hurricane eye.

The Hurricane’s Inner Core Region. II. Thermal Stability and Dynamic Characteristics

Abstract This is the second (Paper II) of two papers on the characteristics of the hurricane’s inner core region as revealed by the research flight data of the National Hurricane Research Laboratory. This paper presents information on the thermal stability and the dynamic characteristics of the hurricane’s inner core region from information derived from Paper I. Discussion is given on the hurricane’s inner core vertical stability, divergence, vertical motion, heating mechanism, wind-pressure acceleration, thermal wind balances, and other features. It is shown that large vertical moist instability is present in the eye-wall cloud. Large super-gradient winds are present at the radius of maximum winds. Substantial mixing occurs between eye and eye wall and the average hurricane eye ventilates itself by about half of its mass during the time it takes to move the distance of its eye diameter. Maximum heating does not occur at the radius of maximum updraft. Inner core heating comes from the sinking motion withi...

Eyes on Hurricane Eye

Eyes on Hurricane Eye

ON THE STRUCTURE OF HURRICANE DAISY ON 27 AUGUST 1958

Abstract An unusually large collection of aircraft-reconnaissance data was made in hurricane Daisy on 27 August 1958. These data consist primarily of detailed flight-level information collected by the research aircraft of the National Hurricane Research Project and radar films taken from the operational reconnaissance aircraft of the U. S. Navy. At this time, hurricane Daisy was a small, slow-moving storm off the Florida east coast with winds in excess of 100 kn in the lower troposphere. The concentrated nature of this vortex is clearly shown by the flight-level wind and temperature data and by the weather patterns shown on the radar films. The films from the search radar show a central, ring-like echo only a few miles wide which corresponds closely with the area of maximum observed winds. The height-finding radar shows this central echo—which is associated with the wall cloud surrounding the hurricane eye—to be nearly vertical and to extend above 60,000 ft.

ON THE STRUCTURE AND MAINTENANCE OF THE MATURE HURRICANE EYE

An attempt is made to derive the significant features of a mature hurricane eye in terms of a simplified model of the physical processes undergone by the air composing it. In particular, a quantitative relation is prescribed among the fields of motion, temperature, and humidity on the basis of assumptions concerning the exchange of mass and momentum between the eye and its surrounding cloud bands. The basic assumptions are that eye air mixes with the cloud wall on its descent; the latter is maintained by lower level outflow caused by unbalanced centrifugal and Coriolis forces, resulting from the incorporation into the eye of high cloud-wall momentum. Joint entrainment and angular momentum calculations for two hypothetical cases of stationary hurricanes of differing intensity show qualitative agreement in major features with existing incomplete observations and delineate a computational framework for real cases when available. Modifications of eye structure in moving storms are finally considered.