Hurricane Research Division
FY-2002 Publications
(October 1, 2001-September 30, 2002)
(names of HRD authors appear in capital letters)

	[1]	Atlas, D., C.W. Ulbrich, and F.D. MARKS.  Reply to comment by S.E. Yuter and R.A. Houze Jr. On “Partitioning tropical oceanic convective and stratiform rains by draft strength.” Journal of Geophysical Research, 107(D1):4006, doi:10.1029/2001JD000658 (2002).
No abstract.
	[2]	BLACK, M.L., J.F. GAMACHE, F.D. MARKS, C.E. Samsury, and H.E. WILLOUGHBY.  Eastern Pacific Hurricanes Jimena of 1991 and Olivia of 1994: The effect of vertical shear on structure and intensity. Monthly Weather Review, 130(9):2291-2312 (2002).
Shear is a key inhibitor of tropical cyclone intensification. Although its signature is readily recognized in satellite imagery and theoretical or modeling studies provide some insight, detailed observations have been limited. Airborne radar and in-situ observations in Hurricanes Jimena of 1991 and Olivia of 1994 are a step toward better understanding. Each storm was observed on two consecutive days. Initially, both had small eyes, 16-18 km radius, and maximum winds of 57 m s-1 over sea surface temperatures (SST) >28C in easterly environmental shear. Jimena maintained constant intensity or weakened gradually for 2 days in 13-20 m s-1 easterly shear. Olivia intensified in 8 m s-1 shear on the first day. Overnight, the shear diminished to reverse and became westerly. On the second day, Olivia weakened as the shear increased to >15 m s-1 from the west, the storm moved over cooler SST, and became surrounded by dryer air. As convection weakened and the outer rainbands ceased to be effective barriers, relative flow due to the environmental shear penetrated more deeply into the vortex core.  In both storms, shear controlled the convective structure. Convection organized itself into axisymmetric rings as Olivia intensified in weak shear. When both storms encountered stronger shear, radar reflectivity and vertical motion had strong wavenumber-1 components. Highest reflectivity lay generally to the left of the shear. Most radar echoes and updrafts formed in the downshear quadrant of the storm and advected around the eye with 60-80% of the swirling wind, consistent with vortex Rossby wave propagation. The buoyant updrafts accelerated and reflectivity increased as they passed through the left-of-shear semicircle. On the upshear side, the updrafts rose through the 0C isotherm, and hydrometeors fell out or froze. Reflectivity declined as the echoes transformed into lower-tropospheric downdrafts overlain by glaciated upper-tropospheric updrafts in the right-of-shear semicircle.  In relatively weak shear, clusters of echoes could be tracked completely around the eye. Each time the clusters passed through the downshear and left-of-shear quadrants, new echoes would form. In strong shear, all echoes were short lived, and none could be tracked around the eye. Echoes appeared downshear of the center and completed their life cycles on the left side of the shear vector where the composite reflectivities were greatest.
	[3]	DUNION, J.P., and C.S. Velden.  Application of surface-adjusted GOES low-level cloud-drift winds in the environment of Atlantic tropical cyclones.  Part I:  Methodology and validation. Monthly Weather Review, 130(5):1333-1346 (2002).
Beginning with the 1997 hurricane season, the Cooperative Institute for Meteorological Satellite Studies at the University of Wisconsin-Madison began demonstrating the derivation of real-time Geostationary Operational Environmental Satellite (GOES) low-level cloud-drift winds in the vicinity of Atlantic tropical cyclones. The winds are derived from tracking low-level clouds in sequential, high-resolution GOES visible channel imagery. Since then, these data have been provided to the National Oceanic and Atmospheric Administration (NOAA) Hurricane Research Division (HRD) for evaluation in their real-time tropical cyclone surface wind objective analyses (H*Wind) that are disseminated to forecasters at the NOAA National Hurricane Center on an experimental basis. These wind analyses are proving useful as guidance to support forecasters’ tropical cyclone advisories and warnings. The GOES satellite wind observations often provide essential near-surface coverage in the outer radii of the tropical cyclone circulation where conventional in-situ observations (e.g., ships and buoys) are frequently widely spaced or nonexistent and reconnaissance aircraft do not normally fly. The GOES low-level cloud-tracked winds are extrapolated to the surface using a planetary boundary layer model developed at HRD for hurricane environments.  In this study, the unadjusted GOES winds are validated against wind profiles from the newly deployed global positioning system dropwindsondes, and the surface-adjusted winds are compared with collocated in-situ surface measurements. The results show the ability of the GOES winds to provide valuable quantitative data in the periphery of tropical cyclones. It is also shown that the current scheme employed to extrapolate the winds to the surface results in small biases in both speed and direction. Nonlinear adjustments to account for these biases are presented.
	[4]	DUNION, J.P., S.H. Houston, C.S. Velden, and M.D. POWELL.  Application of surface-adjusted GOES low-level cloud-drift winds in the environment of Atlantic tropical cyclones.  Part II: Integration into surface wind analyses.  Monthly Weather Review, 130(5):1347-1355 (2002).
The Cooperative Institute for Meteorological Satellite Studies at the University of Wisconsin-Madison recently (1997 season) began providing real-time Geostationary Operational Environmental Satellite (GOES) low-level cloud-drift winds in the vicinity of tropical cyclones on an experimental basis to the National Oceanic and Atmospheric Administration’s (NOAA) Hurricane Research Division (HRD). The cloud-drift winds are derived from sequential high-resolution GOES visible channel imagery. These data were included in many of HRD’s real-time tropical cyclone surface wind objective analyses, which were sent to NOAA’s National Hurricane Center and the Central Pacific Hurricane Center on an experimental basis during the 1997-2001 hurricane seasons. These wind analyses were used to support the forecasters’ tropical cyclone advisories and warnings. The satellite wind observations provide essential low-level coverage in the periphery of the tropical cyclone circulation where conventional in-situ observations (e.g., ships, buoys, and Coastal-Marine Automated Network stations) are often widely spaced or nonexistent and reconnaissance aircraft do not normally fly. Though winds derived from microwave channels on polar-orbiting satellites provide valuable surface wind data for HRD surface wind analyses, their swath coverage and orbital passes are limited spatially and temporally. GOES low-level visible (GLLV) winds offer nearly continuous spatial and temporal coverage in the western Atlantic and eastern Pacific basins. The GLLV winds were extrapolated to the surface using a planetary boundary layer model developed at HRD.  These surface-adjusted satellite data were used in real-time surface wind analyses of 1998 Hurricane Georges, as well as in post-storm analyses of 1996 Hurricane Lili and 1997 Tropical Storm Claudette. The satellite observations often helped to define the spatial extent of the 17.5 m s!1 (34 kt) surface wind radii and also redefined the 25.7 m s!1 (50 kt) wind radius for one case. Examples of the impact of these data on real-time hurricane surface wind fields provided to the NHC will be discussed.

	[5]	Eastin, M.D., P.G. BLACK, and W.M. Gray.  Flight-level thermodynamic instrument wetting errors in hurricanes.  Part I: Observations.  Monthly Weather Review, 130(4):825-841 (2002).
Flight-level thermodynamic errors caused by the wetting of temperature and moisture sensors immersed within the airstream are studied using data from 666 radial legs collected in 31 hurricanes at pressure levels ranging from 850 to 500 mb. Concurrent measurements from a modified Barnes radiometer and a Rosemount 102 immersion thermometer are compared to identify regions, called instrument wetting events (IWE), in which Rosemount temperatures are significantly cooler than radiometer-derived temperatures by a specified amount. A total of 420 IWE are identified in the data set. Roughly 50% of the radial legs contain at least one instrument wetting event. More than 90% of IWE are associated with updrafts containing cloud water and are confined to scales less than 10 km. IWE are also found to be more frequent in eyewalls and intense hurricanes.  Thermodynamic errors within IWE and convective updrafts and downdrafts are summarized as distributions of average temperature, specific humidity, virtual potential temperature, and equivalent potential temperature error. Distributions are skewed toward larger error values at all levels. Median average errors within IWE indicate that the thermodynamic quantities are typically too low by -1EC, 1 g kg!1, -1.5 K, and -5 K, respectively. The largest errors (>90% of the distribution) are nearly twice the median values. Error magnitudes tend to increase with height, but rarely achieve theoretical predictions. In addition, more than 65% of updrafts and 35% of downdrafts are found to contain significant thermodynamic errors. A correction method used in earlier studies was found to be inadequate at removing the majority of errors, but reduced the errors by 30%-50% on average.
	[6]	Eastin, M.D., P.G. BLACK, and W.M. Gray.  Flight-level thermodynamic instrument wetting errors in hurricanes.  Part II: Implications.  Monthly Weather Review, 130(4):842-851 (2002).
The implications of flight-level instrument wetting error removal upon the mean thermodynamic structure across the eyewall, buoyancy of rainband vertical motions, and vertical energy fluxes near the top of the inflow layer, are studied. Thermodynamic quantities across the mean eyewall are found to increase at all levels. As a result, maximum radial gradients of each quantity are shifted from the center of the eyewall cloud toward the outer edge. The increase in equivalent potential temperature lifts eyewall values to comparable magnitudes observed in the eye. The mean virtual potential temperature deviation of rainband updrafts increases from slightly negative to slightly positive. This increase and shift in sign are more pronounced in stronger updrafts. The mean deviation in rainband downdrafts decreases slightly toward neutral conditions. Vertical sensible heat fluxes near the top of the inflow layer are found to shift from downward to upward. Upward latent heat fluxes increase. Implications of these results upon hurricane structure and evolution are discussed.
	[7]	Katsaros, K.B., P.W. Vachon, W.T. Liu, and P.G. BLACK.  Microwave remote sensing of tropical cyclones from space.  Journal of Oceanography, 58(1-2):137-151 (2002).
This article reviews several microwave instruments employed in research and analysis of tropical cyclones (TCs), typhoons, and hurricanes. The instruments discussed include scatterometers, microwave radiometers, synthetic aperture radars (SAR), and rain radar from space.  Examples of the particular contribution by one or more of these instruments in analysis of several storms illustrate the comprehensive new views provided by the SeaWinds scatterometers, the detailed high-resolution wind field provided by RADARSAT-1 SAR, particularly inside and in the vicinity of hurricane “eyes,” and the presence of secondary flows in the region between rainbands in TCs.  The high spatial resolution of precipitation data from the Tropical Rainfall Measuring Mission’s rain radar, combined with scatterometer or SAR data, give a significant improvement in the details that can be seen from space, at the surface, and in the precipitating areas of TCs.  The microwave instruments provide the penetrating view below the upper level cirrus clouds.
	[8]	Lawrence, J.R., S.D. Gedzelman, J.F. GAMACHE, and M.L. BLACK.  Stable isotope ratios: Hurricane Olivia.  Journal of Atmospheric Chemistry, 41(1):67-82 (2002).
The oxygen and hydrogen isotopic compositions of rains from Hurricane Olivia (1994) in the eastern Pacific were measured. The rains were collected on 24 and 25 September during airplane flights conducted at an elevation of 3 km. Hurricane Olivia peaked in intensity to a category-4 storm between the two dates. Isotope ratios of rains from Hurricane Olivia were markedly lower (δ18O = –13.9‰ to –28.8‰) than that of rain collected from a thunderstorm at an elevation of 2.3 km outside the influence of Olivia (δ18O = –3.8‰). A distinct decrease in isotope ratios from the first day to the next (δ18O = –18.4‰ to –21.9‰) in Hurricane Olivia was attributed to decreased updraft velocities and outflow aloft. This shifted the isotopic water mass balance so that fewer hydrometeors were lifted and more ice descended to flight level. A decrease in the average deuterium excess from the first day to the next (δ = 15.5 to 7.1‰) was attributed to an increase in the relative humidity of the water vapor “source” area. We hypothesize that the “source” region for the rain was in the boundary layer near the storm center and that because the hurricane was at peak intensity prior to the second day the relative humidity was higher.
	[9]	POWELL, M.D., and S.D. ABERSON.  Accuracy of United States tropical cyclone landfall forecasts in the Atlantic Basin (1976-2000).  Bulletin of the American Meteorological Society, 82(12):2749-2768 (2001).
About 13% of all Atlantic basin tropical cyclone forecasts issued from 1976 to 2000 are for landfalls along the United States coastline, and 2% more are for storms forecast to make landfall in the United States but that remain at sea. Landfall position and time forecasts are skillful at all forecast time periods and are more skillful than Atlantic basin track forecasts as a whole, but within 30 h of predicted landfall, timing errors demonstrate an early bias of 1.5-2.5 h. Landfall forecasts are most accurate for storms moving at oblique or normal angles to the coastline and slow-moving storms. During the last quarter century, after adjustment for forecast difficulty, no statistically significant improvement or degradation is noted for landfall position forecasts. Time of landfall forecasts indicate no degradation at any period and significant improvement for the 19-30 h period. The early bias and lack of improvement are consistent with a conservative or “least regret” forecast and warning strategy to account for possible storm accelerations. Landfall timing uncertainty is ~11 h at 24 and 36 h, which suggests that hurricane warnings could be disseminated about 12 h earlier (at 36 h, rather than 24 h, before predicted landfall) without substantial loss of lead time accuracy (although warning areas necessarily would be larger). Reconsideration of the National Weather Service Strategic Plan and United States Weather Research Program track forecast goals is recommended in light of these results.
	[10]	ROGERS, R.F., S.D. ABERSON, J. KAPLAN, and S.B. GOLDENBERG.  A pronounced upper-tropospheric warm anomaly encountered by the NOAA Gulfstream-IV aircraft in the vicinity of deep convection.  Monthly Weather Review, 130(1):180-187 (2002).
Recent flights near deep convection by the National Oceanic and Atmospheric Administration's Gulfstream-IV surveillance aircraft have occasionally experienced significant positive temperature anomalies that sometimes impact the aircraft performance. One such event occurred over the Bahamas on 23 August 1999. During a 20-s time period, when the plane was cruising at an altitude of 175 hPa, the flight-level ambient temperature rose 15EC and returned to ambient values, concurrent with significant fluctuations in the horizontal and vertical winds. Large temperature anomalies such as that reported here can cause the avionics on the aircraft to compensate with a sudden decrease in air speed and a loss of altitude. Possible explanations for this anomaly include instrument error and convectively forced gravity waves or upper-level subsidence.
	[11]	Schecter, D.A., M.T. Montgomery, and P.D. REASOR.  A theory for the vertical alignment of a quasigeostrophic vortex.  Journal of the Atmospheric Sciences, 59(2):150-168 (2002). 
This article presents a new theory for the rate at which a quasigeostrophic vortex realigns, under conservative dynamics, after being tilted by an episode of external vertical shear. The initial tilt is viewed as the excitation of a three-dimensional “vortex Rossby mode.” This mode, that is, the tilt, decays exponentially with time during its early evolution. The decay rate γ is proportional to the potential vorticity gradient at a critical radius, where the fluid rotation is resonant with the mode. The decay rate γ also depends on the internal Rossby deformation radius lR, which is proportional to the stratification strength of the atmospheric or oceanic layer containing the vortex. The change of γ with lR is sensitive to the form of the vortex. For the case of a “Rankine-with-skirt” vortex, the magnitude of γ increases (initially) with increasing lR. On the other hand, for the case of a “Gaussian” vortex, the magnitude of  γ decreases with increasing lR. The relevance of this theory to tropical cyclogenesis is discussed.
	[12]	Schubert, W.H., S.A. Hausman, M. Garcia, K.V. OOYAMA, and H.-C. Kuo.  Potential vorticity in a moist atmosphere.  Journal of the Atmospheric Sciences, 58(21):3148-3157 (2001).
The potential vorticity principle for a nonhydrostatic, moist, precipitating atmosphere is derived. An appropriate generalization of the well-known (dry) Ertel potential vorticity is found to be P = ρ!1 (2Ω + L × u) @ Lθρ, where ρ is the total density, consisting of the sum of the densities of dry air, airborne moisture (vapor and cloud condensate), and precipitation; u is the velocity of the dry air and airborne moisture; and θρ = Tρ (p0/p)Ra/CPa is the virtual potential temperature, with Tρ = p/(ρRa) the virtual temperature, p the total pressure (the sum of the partial pressures of dry air and water vapor), p0 the constant reference pressure, Ra the gas constant for dry air, and cPa the specific heat at constant pressure for dry air. Since θρ is a function of total density and total pressure only, its use as the thermodynamic variable in P leads to the annihilation of the solenoidal term, that is, Lθρ @(Lρ × Lp) = 0. In the special case of an absolutely dry atmosphere, P reduces to the usual (dry) Ertel potential vorticity. For balanced flows, there exists an invertibility principle that determines the balanced mass and wind fields from the spatial distribution of P. It is the existence of this invertibility principle that makes P such a fundamentally important dynamical variable. In other words, P (in conjunction with the boundary conditions associated with the invertibility principle) carries all the essential dynamical information about the slowly evolving balanced part of the flow.
	[13]	Smith, D.R., M.C. Hayes, M.K. Ramamurthy, J.W. Zeitler, K.A. Murphy, P.J. Croft, J.M. Nese, H.A. FRIEDMAN, H.W. Robinson, C.D. Thormeyer, P.A. Ruscher, and R.E. Pandya.  Meeting summary:  10th AMS symposium on education.  Bulletin of the American Meteorological Society, 82(12):2817-2824 (2001).
The American Meteorological Society held its 10th Symposium on Education in conjunction with the 82nd Annual Meeting in Albuquerque, New Mexico. The theme of 2001’s symposium was “enhancing public awareness of the atmospheric and oceanic environments.”  Thirty-six oral presentations and 38 poster presentations summarized a variety of educational programs or examined educational issues at both the precollege and university levels. There was a special session on increasing awareness of meteorology and oceanography through popular and informal educational activities, as well as a joint session with the 17th International Conference on Interactive Information and Processing Systems (IIPS) for Meteorology, Oceanography, and Hydrology on using the World Wide Web to deliver information pertaining to the atmosphere, oceans, and coastal zone. Over 200 people representing a wide spectrum of the Society attended one or more of the sessions in this two-day conference. The program for the 10th Symposium on Education can be viewed in the November 2000 issue of the Bulletin.
	[14]	Walsh, E.J., C.W. Wright, D. Vandemark, W.B. Krabill, A.W. Garcia, S.H. Houston, S.T. MURILLO, M.D. POWELL, P.G. BLACK, and F.D. MARKS.  Hurricane directional wave spectrum spatial variation at landfall.  Journal of Physical Oceanography, 32(6):1667-1684 (2002).
The NASA Scanning Radar Altimeter (SRA) flew aboard one of the NOAA WP-3D hurricane research aircraft to document the sea surface directional wave spectrum in the region between Charleston, South Carolina, and Cape Hatteras, North Carolina, as Hurricane Bonnie was making landfall near Wilmington, North Carolina, on 26 August 1998. Two days earlier, the SRA had documented the hurricane wave field spatial variation in open water when Bonnie was 400 km east of Abaco Island, Bahamas.  Bonnie was similar in size during the two flights. The maximum wind speed was lower during the landfall flight (39 m s-1) than it had been during the first flight (46 m s-1). Also, Bonnie was moving faster prior to landfall (9.5 m s-1) than when it was encountered in the open ocean (5 m s-1). The open ocean wave height spatial variation indicated that Hurricane Bonnie would have produced waves of 10 m height on the shore northeast of Wilmington had it not been for the continental shelf. The gradual shoaling distributed the wave energy dissipation process across the shelf so that the wavelength and wave height were reduced gradually as the shore was approached. The wave height 5 km from shore was about 4 m. Despite the dramatic differences in wave height caused by shoaling and the differences in the wind field and forward speed of the hurricane, there was a remarkable agreement in the wave propagation directions for the various wave components on the two days. This suggests that, in spite of its complexity, the directional wave field in the vicinity of a hurricane may be well behaved and lend itself to be modeled by a few parameters, such as the maximum wind speed, the radii of the maximum and gale force winds, and the recent movement of the storm.