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Craig Mattocks
and
Rainer Bleck

Abstract

A numerical experiment is described which explores the relationship between upper-level potential vorticity advection and cyclogenesis on the leeward side of mountain barriers. A multilevel primitive equation model framed in isentropic coordinates is used to simulate the growth of a wave disturbance on the cold front associated with a preexisting “parent” cyclone. The effect of a mountain barrier placed in the path of the advancing cold front and the effect of an enhanced upper-level jet streak on the growth rate of the disturbance are investigated. Enhancement of the jet streak is accomplished by altering the geostrophic potential vorticity in a region upstream of the mountain barrier and solving for the corresponding man and geostrophic velocity field. The experiment suggests a strong connection between the intensity of the jet weak impinging on the barrier and the pressure fall in the lee. We also find that the strongest leeside pressure fall in this experiment is not accompanied by a conversion of available potential energy to kinetic energy. This suggests that geostrophic adjustment processes, rather than baroclinic instability, may cause the rapid initial growth of some, though possibly not all, lee cyclones.

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Jennifer M. Cram
,
Michael L. Kaplan
,
Craig A. Mattocks
, and
John W. Zack

Abstract

Conventional synoptic rawinsonde data do not have a fine enough temporal or spatial resolution to accurately resolve mesoscale features. Profiling networks are one potential source of these data although they provide only wind information. A methodology following Fankhauser and Kuo and Anthes is used to retrieve height and temperature analyses from actual profiler wind data using the full divergence equation. Simulation experiments were fist completed to test the feasibility of using the available profiler network spacing to define mesoscale atmospheric structure and to test the boundary conditions used in the retrieval process. Real profiler and rawinsonde data were then used to retrieve height analyses. The real-data results are compared to independent microbarograph surface pressure data and radiometer height data. Retrieved heights on 13 April 1986 from the four-node Colorado profiler network revealed the presence of a mesoscale trough that was not resolvable by the standard rawinsonde network, but was corroborated by PROFS mesonet data and Denver radiometer data. This study differs from previous work in that actual profiler data were used in the height retrievals, and the retrieved heights were verified against independent asynoptic data.

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Cristina Forbes
,
Richard A. Luettich Jr.
,
Craig A. Mattocks
, and
Joannes J. Westerink

Abstract

The evolution and convergence of modeled storm surge were examined using a high-resolution implementation of the Advanced Circulation Coastal Ocean and Storm Surge (ADCIRC) model for Hurricane Gustav (2008). The storm surge forecasts were forced using an asymmetric gradient wind model (AWM), directly coupled to ADCIRC at every time step and at every grid node. A total of 20 forecast advisories and best-track data from the National Hurricane Center (NHC) were used as input parameters into the wind model. Differences in maximum surge elevations were evaluated for ensembles comprised of the final 20, 15, 10, and 5 forecast advisories plus the best track. For this particular storm, the final 10–12 forecast advisories, encompassing the last 2.5–3 days of the storm’s lifetime, give a reasonable estimate of the final storm surge and inundation. The results provide a detailed perspective of the variability in the storm surge due to variability in the meteorological forecast and how this changes as the storm approaches landfall. This finding is closely tied to the consistency and accuracy of the NHC storm track forecasts and the predicted landfall location and, therefore, cannot be generalized to all storms in all locations. Nevertheless, this first attempt to translate variability in forecast meteorology into storm surge variability provides useful insights for guiding the potential use of storm surge models for forecast purposes. Model skill was also evaluated for Hurricane Gustav by comparing observed water levels with hindcast modeled water levels forced by river flow, tides, and several sources of wind data. The AWM (which ingested best-track information from NHC) generated winds that were slightly higher than those from NOAA’s Hurricane Research Division (HRD) H*Wind analyses and substantially greater than the North American Mesoscale (NAM) model. Surge obtained using the AWM more closely matched the observed water levels than that computed using H*Wind; however, this may be due to the neglect of the contribution of wave setup to the surge, especially in exposed areas. Several geographically distinct storm surge response regimes, some characterized by multisurge pulses, were identified and described.

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