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Joseph E. Salah

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E. Joseph Metzger and Harley E. Hurlburt

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A ⅛°, 6-layer Pacific version of the Naval Research Laboratory Layered Ocean Model is used to investigate the nondeterministic nature of Kuroshio intrusion and eddy shedding into the South China Sea (SCS) on annual and interannual timescales. Four simulations, which only differ in the initial state, are forced with 1979–93 European Centre for Medium-Range Weather Forecasts reanalysis 1000 hectopascal (hPa) winds and then continued in 1994–97 with ECMWF operational 1000-hPa winds. The model shows differing amounts of Kuroshio penetration across all four simulations for the yearly means, indicating a large degree of nondeterminism at this timescale. This nondeterminism is quantified by a technique that separates the variability of a model variable into deterministic (caused by direct atmospheric forcing) and nondeterministic (caused by mesoscale flow instabilities) components. Analysis indicates substantial nondeterministic sea surface height and upper-layer velocity variability in the vicinity of Luzon Strait. A quantitative measure of Kuroshio intrusion into the SCS is presented that allows interexperiment comparisons and investigation of interannual variability, and attempts are made to positively correlate it with the oceanic and atmospheric environment. Yearly mean Kuroshio intrusion is not strongly linked to Luzon Strait transports or to changes in the North Equatorial Current bifurcation latitude (which is related to the northward Kuroshio transport east of Luzon). Likewise, no relationship could be found that linked interannual variability of yearly mean Kuroshio intrusion or monsoon season mean Luzon Strait transport with the corresponding zonal or meridional wind components, wind stress magnitude, or wind stress curl. However, there was a close relationship between the mean seasonal cycles of the Luzon Strait transport and the northeast–southwest monsoon. Eddy shedding and deep Kuroshio intrusion are rare events during the period of ECMWF reanalysis forcing, but are persistent features during the ECMWF operational time frame. While the wind stress is consistent across the reanalysis/operational time boundary, large differences exist in the wind stress curl pattern over the Luzon Strait and interior of the SCS basin. For contemporaneous years, the ECMWF operational winds produce higher curl extrema (by a factor of 2) and a much sharper north–south gradient in Luzon Strait. The net effect is to produce more Ekman pumping, a deepening of the thermocline, and a more deeply penetrating Kuroshio during the 1994–97 ECMWF operational forcing time frame. Thus, while normal interannual variations of the wind curl did not produce a deterministic response of simulated Kuroshio intrusion, the marked differences in curl between the two atmospheric products did have a substantial impact.

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Danielle E. Nagele and Joseph E. Trainor

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In 2007, the National Weather Service (NWS) began using storm-based warnings (SBWs) rather than countywide warnings. Some analysts have examined the effects of this change, but little empirical research has yet to focus on the public response. Using a random digit dialing sample and a computer-assisted telephone interviewing (CATI) system, data were collected that focused on protective action decision making in counties that were affected by a severe storm or tornado warning. Based on those data, the following paper examines the influence of these new storm-based warnings on protective action decision making by the public. While a significant relationship between being inside the warning polygon and taking protective action was not found, the authors were able to conclude that polygon size is an important factor. Given these mixed results, it is suggested that future work on storm-based warnings focus on the warnings’ dissemination and reception, as well as the optimization of the polygons themselves. It is suggested that the complexities associated with communicating with these risk areas complicate the dissemination process and create difficulties in the public understanding of the warning. The possible need for optimization is reinforced by the significance of the track proximity and polygon-sized variables. In addition, a smaller polygon resulted in protective action, in particular, sheltering. With regard to the preparedness and sociodemographic variables, the study’s results agreed with previous findings on the importance of a family emergency plan. Unlike earlier research this study did not find past experience or education level significant within the regression model and showed mixed results of gender.

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GEORGE E. DAVIS and JOSEPH L. MCCARTHY

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Joseph R. Patton and Henry E. Fuelberg

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Thunderstorms in central Florida frequently halt outdoor activities, requiring that one wait some prescribed time after an assumed last flash before safely resuming activities. The goal of this research is to develop a high-skill probabilistic method that can be used in high pressure real-world operations to terminate lightning warnings more quickly while maintaining safety. Probabilistic guidance tools are created for isolated warm season storms in central Florida using dual-polarized radar data at 1-min intervals. The parameters examined are maximum reflectivity and graupel presence at the 0°, −5°, −10°, −15°, and −20°C levels as well as composite reflectivity. Random samples of the radar data are used to train a generalized linear model (GLM) to make a probabilistic prediction whether a given flash is the storm’s last flash. The most statistically significant predictors for lightning cessation are found to be the storm’s maximum reflectivity in the composite and the 0°C levels, along with graupel presence or absence at the −5°, −10°, −15°, and −20°C levels. Statistical verification is used to analyze the performance of the two GLMs at different probability thresholds (95.0%, 97.5%, and 99.0%). When applying the cessation guidance as though storms are occurring in real time, results showed ~99% of the storms produced no additional lightning after the GLM suggested cessation had already occurred. Although these results are encouraging, the procedure must be tested on much larger datasets having different convective modes and different areal coverages to prove its value compared to operational forecasters.

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Zhitao Yu, E. Joseph Metzger, and Yalin Fan

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A more complete wind stress τ n formulation takes into account the ocean surface currents V o, while the conventional wind stress τ c popularly used in ocean circulation models is only a function of 10-m winds V 10. An analytical solution is derived for the difference of Sverdrup transport induced by using τ n instead of τ c. A scaling analysis of the analytical solution indicates a 6% reduction of the Sverdrup transport in the North Pacific (i.e., the Kuroshio transport in the East China Sea) when Ekman velocity dominates the ocean surface currents. Because of the quadratic nature of wind stress, four nonlinear terms contribute equally to this difference: two vorticity torque terms and two speed gradient torque terms. A pair of 12.5-yr (July 2002–14) Hybrid Coordinate Ocean Model simulations that only differ in the wind stress formulation are used to test the analytical solution. The model results (2004–14) confirm that using τ n instead of τ c reduces the Sverdrup transport in the North Pacific by 8%–17% between 23° and 32°N. The reduction rate of the simulated 11-yr mean Kuroshio transport through the East Taiwan Channel and Tokara Strait is 8.0% (−2.5 Sv; 1 Sv ≡ 106 m3 s−1) and 12.8% (−4.8 Sv), respectively, in good agreement with the Sverdrup transport reduction rate, which is 7.4% (−2.6 Sv) and 15.4% (−6.3 Sv) at the corresponding latitude. The local effect of changing wind stress/wind work and Ekman transport due to the inclusion of V o in the wind stress formulation is negligible compared to the Kuroshio volume transport change estimated in this study.

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Joseph H. Pierluissi and Rufus E. Bruce

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Weinreb and Neuendorffer have demonstrated a new method for applying infrared homogeneous band models to slant path atmospheric attenuation calculations. The relation between this and the Curtis-Godson equivalence method is examined, and it shown that they are identical in the limits of weak- and strong-line absorption.

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Paul E. Roundy and Joseph R. Kravitz

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The Pacific Ocean intraseasonal Kelvin wave is a leading oceanic mode that links intraseasonal tropical atmospheric variations with interannual variations in the coupled ocean–atmosphere system. This study considers the premise that these waves may evolve differently with their associated weather patterns during different phases of El Niño–Southern Oscillation (ENSO). If atmospheric and oceanic intraseasonal modes interact and evolve differently during various stages of ENSO, this result may provide useful information with regard to the role of these intraseasonal processes in ENSO evolution. This work utilizes signals of the oceanic Kelvin wave as a statistical basis for a simple composite averaging technique that is applied during different phases of ENSO to objectively analyze the evolution of oceanic and the associated portions of atmospheric intraseasonal oscillations. Results confirm the above premise and suggest that coupling between Kelvin waves and atmospheric convection evolves differently during different stages of ENSO. Further, intraseasonal zonal wind anomalies across the east Pacific timed with oceanic Kelvin waves are stronger during adjustment toward El Niño than during adjustment away from El Niño. These and other patterns in the composites suggest the possibility that systematic changes in the evolution of intraseasonal variations over the course of ENSO might feed back upon this interannual mode to influence the evolution of ENSO itself.

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Toshiaki Shinoda, Weiqing Han, E. Joseph Metzger, and Harley E. Hurlburt
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Toshiaki Shinoda, Weiqing Han, E. Joseph Metzger, and Harley E. Hurlburt

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The seasonal variation of Indonesian Throughflow (ITF) transport is investigated using ocean general circulation model experiments with the Hybrid Coordinate Ocean Model (HYCOM). Twenty-eight years (1981–2008) of ⅓° Indo-Pacific basin HYCOM simulations and three years (2004–06) from a global HYCOM simulation are analyzed. Both models are able to simulate the seasonal variation of upper-ocean currents and the total transport through Makassar Strait measured by International Nusantara Stratification and Transport (INSTANT) moorings reasonably well. The annual cycle of upper-ocean currents is then calculated from the Indo-Pacific HYCOM simulation. The reduction of southward currents at Makassar Strait during April–May and October–November is evident, consistent with the INSTANT observations. Analysis of the upper-ocean currents suggests that the reduction in ITF transport during April–May and October–November results from the wind variation in the tropical Indian Ocean through the generation of a Wyrtki jet and the propagation of coastal Kelvin waves, while the subsequent recovery during January–March originates from upper-ocean variability associated with annual Rossby waves in the Pacific that are enhanced by western Pacific winds. These processes are also found in the global HYCOM simulation during the period of the INSTANT observations. The model experiments forced with annual-mean climatological wind stress in the Pacific and 3-day mean wind stress in the Indian Ocean show the reduction of southward currents at Makassar Strait during October–November but no subsequent recovery during January–March, confirming the relative importance of wind variations in the Pacific and Indian Oceans for the ITF transport in each season.

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