Eric Uhlhorn - Academia.edu (original) (raw)

Papers by Eric Uhlhorn

Bulletin of the American Meteorological Society, 2014

ABSTRACT The Hurricane Weather Research and Forecasting (HWRF) model is an operational model used... more ABSTRACT The Hurricane Weather Research and Forecasting (HWRF) model is an operational model used to provide numerical guidance in support of tropical cyclone forecasting at the National Hurricane Center. HWRF is a complex multi-component system, consisting of the Weather Research and Forecasting (WRF) atmospheric model coupled to the Princeton Ocean Model for Tropical Cyclones (POM-TC), a sophisticated initialization package including a data assimilation system, and a set of postprocessing and vortex tracking tools. HWRF's development is centralized at the Environmental Modeling Center of NOAA's National Weather Service, but it incorporates contributions from a variety of scientists spread out over several governmental laboratories and academic institutions. This distributed development scenario poses significant challenges: a large number of scientists need to learn how to use the model, operational and research codes need to stay synchronized to avoid divergence, and promising new capabilities need to be tested for operational consideration. This article describes how the Developmental Testbed Center has engaged in the HWRF developmental cycle in the last three years and the services it provides to the community in using and developing HWRF.

Offshore Technology Conference, 2001

Oceanographic conditions in the Gulf of Mexico have been extensively studied from the summer of 1... more Oceanographic conditions in the Gulf of Mexico have been extensively studied from the summer of 1999 through the fall of 2000. These studies included cradle to grave surveys of Juggernaut Eddy; surveys in the Caribbean by several consortia; oceanographic surveys in support of hurricane research in the Gulf; measurements of inflow/outflow through the Yucatan Strait; and regional nowcasts and hindcasts of circulation. Several interesting phenomena have been observed during this period, including energetic bottom currents in excess of 2 knots and bottom furrows on the continental slope; the intrusion of one of the strongest eddies in a decade into the north-central Gulf leases; and strong midwater-column currents in SE Ewing Bank (~140 cm/s). This paper describes the observational data available and summarizes ongoing efforts to understand the oceanographic conditions during this period. Eventually, it is hoped that these efforts will lead to a better estimation of offshore structure design currents; an understanding of the dynamical causes of the strong mid-water-column currents; determining whether there is a link between the strong bottom currents at the base of the Sigsbee Escarpment and the Loop Current; and assessing the skill of the regional forecast/nowcast/hindcast oceanographic models.

Journal of Atmospheric and Oceanic Technology, 2014

Monthly Weather Review, 2015

ABSTRACT Using dropsondes from 27 aircraft flights, in-situ and satellite data acquired during tr... more ABSTRACT Using dropsondes from 27 aircraft flights, in-situ and satellite data acquired during tropical cyclone Earl (category 4 hurricane), bulk air-sea fluxes of enthalpy and momentum are investigated in relation to intensity change and underlying upper-ocean thermal structure. During Earl’s rapid intensification (RI) period, ocean heat content (OHC) variability relative to the 26°C isotherm exceeded 90 kJ cm-2, and sea surface cooling was less than 0.5°C. Enthalpy fluxes of ~1.1 kW m-2 were estimated for Earl’s peak intensity. Daily sea surface heat losses of −6.5±0.8, −7.8±1.1, and +2.3±0.7 kJ cm-2 were estimated for RI, mature, and weakening stages, respectively. A ratio CK/CD of the exchange coefficients of enthalpy (Ck) and momentum (CD) between 0.54 and 0.7 produced reliable estimates for the fluxes relative to OHC changes, even during RI; a ratio CK/CD = 1 overestimated the fluxes. The most important result is that bulk enthalpy fluxes were controlled by the thermodynamic disequilibrium between the sea surface and the near-surface air, independently of wind speed. This disequilibrium was strongly influenced by underlying warm oceanic features; localized maxima in enthalpy fluxes developed over tight horizontal gradients of moisture disequilibrium over these eddy features. These regions of local buoyant forcing preferentially developed during RI. The overall magnitude of the moisture disequilibrium (Δq=qs-qa) was determined by the saturation specific humidity at sea surface temperature (qs) rather than by the specific humidity of the atmospheric environment (qa). These results support the hypothesis that intense local buoyant forcing by the ocean could be an important intensification mechanism in tropical cyclones over warm oceanic features.

IEEE International Geoscience and Remote Sensing Symposium, 2002

... The five straight lines &amp;ted to the data between nadir and 14&#x27;off-na... more ... The five straight lines &amp;ted to the data between nadir and 14&#x27;off-nadir (middle 213 of swath) almost coalesce in Fig. ... REFERENCES [ 1 ] RL Olsen, DV Rogers, DB Hodge, “The aRb relation in the calculation ofrain attenuation,” IEEE Trans. Ant. Propagation, vol. AP-26, pp. ...

This study uses an observing system simulation experiment (OSSE) approach to test the limitations... more This study uses an observing system simulation experiment (OSSE) approach to test the limitations of even nearly ideal observing systems to capture the peak wind speed occurring within a tropical storm or hurricane. The dataset is provided by a 1-km resolution simulation of an Atlantic hurricane with surface wind speeds saved every 10 s. An optimal observing system consisting of a dense field of anemometers provides perfect measurements of the peak 1-min wind speed as well as the average peak wind speed. Suboptimal observing systems consisting of a small number of anemometers are sampled and compared to the truth provided by the optimal observing system. Results show that a single, perfect anemometer experiencing a direct hit by the right side of the eyewall will underestimate the actual peak intensity by 10%-20%. Even an unusually large number of anemometers (e.g., 3-5) experiencing direct hits by the storm together will underestimate the peak wind speeds by 5%-10%. However, the peak winds of just one or two anemometers will provide on average a good estimate of the average peak intensity over several hours. Enhancing the variability of the simulated winds to better match observed winds does not change the results. Adding observational errors generally increases the reported peak winds, thus reducing the underestimates. If the average underestimate (negative bias) were known perfectly for each case, it could be used to correct the wind speeds, leaving only mean absolute errors of 3%-5%.

This study investigates the asymmetric structure of the hurricane boundary layer in relation to t... more This study investigates the asymmetric structure of the hurricane boundary layer in relation to the environmental vertical wind shear in the inner core region. Data from 1878 GPS dropsondes deployed by research aircraft in 19 hurricanes are analyzed in a composite framework. Kinematic structure analyses based on Doppler radar data from 75 flights are compared with the dropsonde composites. Shear-relative quadrantmean composite analyses show that both the kinematic and thermodynamic boundary layer height scales tend to decrease with decreasing radius, consistent with previous axisymmetric analyses. There is still a clear separation between the kinematic and thermodynamic boundary layer heights. Both the thermodynamic mixed layer and height of maximum tangential wind speed are within the inflow layer. The inflow layer depth is found to be deeper in quadrants downshear, with the downshear right (DR) quadrant being the deepest. The mixed layer depth and height of maximum tangential wind speed are alike at the eyewall, but are deeper outside in quadrants left of the shear. The results also suggest that air parcels acquire equivalent potential temperature u e from surface fluxes as they rotate through the upshear right (UR) quadrant from the upshear left (UL) quadrant. Convection is triggered in the DR quadrant in the presence of asymmetric mesoscale lifting coincident with a maximum in u e . Energy is then released by latent heating in the downshear left (DL) quadrant. Convective downdrafts bring down cool and dry air to the surface and lower u e again in the DL and UL quadrants. This cycling process may be directly tied to shear-induced asymmetry of convection in hurricanes.

This study presents a new approach for retrieving hurricane surface wind vectors utilizing C-band... more This study presents a new approach for retrieving hurricane surface wind vectors utilizing C-band dualpolarization (VV, VH) synthetic aperture radar (SAR) observations. The copolarized geophysical model function [C-band model 5.N (CMOD5.N)] and a new cross-polarized wind speed retrieval model for dual polarization [C-band cross-polarized ocean surface wind retrieval model for dual-polarization SAR (C-2POD)] are employed to construct a cost function. Minimization of the cost function allows optimum estimates for the wind speeds and directions. The wind direction ambiguities are removed using a parametric two-dimensional sea surface inflow angle model. To evaluate the accuracy of the proposed method, two RADARSAT-2 SAR images of Hurricanes Bill and Bertha are analyzed. The retrieved wind speeds and directions are compared with collocated Quick Scatterometer (QuikSCAT) winds, showing good consistency. Results suggest that the proposed method has good potential to retrieve hurricane surface wind vectors from dual-polarization SAR observations.

Weather and Forecasting, 2011

Geophysical Monograph Series, 2000

At the time of the Deepwater Horizon oil rig explosion, the Loop Current (LC), a warm ocean curre... more At the time of the Deepwater Horizon oil rig explosion, the Loop Current (LC), a warm ocean current in the Gulf of Mexico (GoM), extended to 27.5°N just south of the rig. To measure the regional scale variability of the LC, oceanographic missions were flown on a NOAA WP-3D research aircraft to obtain ocean structural data during the spill and provide thermal structure profiles to ocean forecasters aiding in the oil spill disaster at 7 to 10 day intervals. The aircraft flew nine grid patterns over the eastern GoM between May and July 2010 deploying profilers to measure atmospheric and oceanic properties such as wind, humidity, temperature, salinity, and current. Ocean current profilers sampled as deep as 1500 m, conductivity, temperature, and depth profilers sampled to 1000 m, and bathythermographs sampled to either 350 or 800 m providing deep structural measurements. Profiler data were provided to modeling centers to predict possible trajectories of the oil and vector ships to regions of anomalous signals. In hindcast mode, assimilation of temperature profiles into the Hybrid Coordinate Ocean Model improved the fidelity of the simulations by reducing RMS errors by as much as 30% and decreasing model biases by half relative to the simulated thermal structure from models that assimilated only satellite data. The synoptic snapshots also provided insight into the evolving LC variability, captured the shedding of the warm core eddy Franklin, and measured the small-scale cyclones along the LC periphery.

Ocean Engineering, 2010

As the most costly US natural disaster in history, Hurricane Katrina fostered the IPET forensic s... more As the most costly US natural disaster in history, Hurricane Katrina fostered the IPET forensic study to better understand the event. All available observations from several hundred space-, land-, sea-, and aircraft-based measurement platforms were gathered and processed to a common framework for height, exposure, and averaging time, to produce a series of wind field snapshots at 3 h intervals to depict the wind structure of Katrina when in the Gulf of Mexico. The stepped-frequency microwave radiometer was calibrated against GPS sondes to establish the upper range of the instrument and then used to determine the wind field in the storm's core region in concert with airborne Doppler radar winds adjusted to the surface from near the top of the PBL (500 m). The SFMR data were used to develop a method to estimate surface winds from 3 km level reconnaissance aircraft observations, taking into consideration the observed azimuthal variation of the reduction factor. The ''SFMR method'' was used to adjust reconnaissance flight-level measurements to the surface in the core region when SFMR and Doppler winds were not available. A variety of coastal and inland mesonet data were employed, including portable towers deployed by Texas Tech University, University of Louisiana at Monroe, and the Florida Coastal Monitoring Program, as well as fixed mesonet stations from Louisiana State Universities Marine Consortium, University of Southern Mississippi, and Agricultural Networks from Louisiana, Mississippi, and Alabama, and the Coastal Estuarine Network of Alabama and Mississippi. Also included were land-(WSR-88D VAD and GBVTD, ASOS, Metar, LLWAS, HANDAR), space-(QuikScat, GOES cloud drift winds, WindSat), and marine-(GPS sondes, Buoys, C-MAN, ships) platforms. The wind fields serve as an analysis of record and were used to provide forcing for wave and storm surge models to produce hindcasts of water levels in the vicinity of flood control structures.

Weather and Forecasting, 2009

Radial profiles of surface winds measured by the Stepped Frequency Microwave Radiometer (SFMR) ar... more Radial profiles of surface winds measured by the Stepped Frequency Microwave Radiometer (SFMR) are compared to radial profiles of flight-level winds to determine the slant ratio of the maximum surface wind speed to the maximum flight-level wind speed, for flight altitude ranges of 2-4 km. The radius of maximum surface wind is found on average to be 0.875 of the radius of the maximum flight-level wind, and very few cases have a surface wind maximum at greater radius than the flight-level maximum. The mean slant reduction factor is 0.84 with a standard deviation of 0.09 and varies with storm-relative azimuth from a maximum of 0.89 on the left side of the storm to a minimum of 0.79 on the right side. Larger slant reduction factors are found in small storms with large values of inertial stability and small values of relative angular momentum at the flight-level radius of maximum wind, which is consistent with Kepert's recent boundary layer theories. The global positioning system (GPS) dropwindsonde-based reduction factors that are assessed using this new dataset have a high bias and substantially larger RMS errors than the new technique. A new regression model for the slant reduction factor based upon SFMR data is presented, and used to make retrospective estimates of maximum surface wind speeds for significant Atlantic basin storms, including 1 Although the maximum inflow speed can reach 2-3 times the GPS sonde fall speed of 12 m s 21 , the maximum inflow occurs in a thin layer near the surface, and thus leads to only a modest inward displacement of the GPS sonde. Even in intense storms, the inward displacement of a GPS sonde trajectory is small; see, for example, Kepert (2006a, .