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Liyan Liu, Carlos Lozano, and Dan Iredell

Abstract

A 2-yr-long daily gridded field of sea surface temperature (SST) in the Atlantic centered for the year 2013 is projected onto orthogonal components: its mean, six harmonics of the year cycle, the slow-varying contribution, and the fast-varying contribution. The periodic function defined by the year harmonics, referred to here as the seasonal harmonic, contains most of the year variability in 2013. The seasonal harmonic is examined in its spatial and temporal distribution by describing the amplitude and phase of its maxima and minima, and other associated parameters. In the seasonal harmonic, the ratio of the duration of warming period to cooling period ranges from 0.2 to 2.0. There are also differences in the spatial patterns and dominance of the year harmonics—in general associated with regions with different insolation, oceanic, and atmospheric regimes. Empirical orthogonal functions (EOFs) of the seasonal harmonic allow for a succinct description of the seasonal evolution for the Atlantic and its subdomains. The decomposition can be applied to model output, allowing for a more incisive model validation and data assimilation. The decorrelation time scale of the rapidly varying signal is found to be nearly independent of the time of the year once four or more harmonics are used. The decomposition algorithm, here implemented for a single year cycle, can be applied to obtain a multiyear average of the seasonal harmonic.

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Julio Candela, Salvatore Mazzola, Chérif Sammari, Richard Limeburner, Carlos J. Lozano, Bernardo Patti, and Angelo Bonanno

Abstract

Sea level observations at Cape Bon, Tunisia, and Mazara del Vallo, Sicily, show that large, coherent oscillations exist across the Strait of Sicily with significant energy bands centered at periods of 35.3, 41.6, 50.6, 75.8, and 134.5 min, whose possible structure is confirmed by a numerical approximation to the gravitational barotropic normal modes with realistic topography. It is observed that these oscillations are related to the passage of synoptic weather systems over the region. An investigation on the configuration, phase velocity, and direction of approach of atmospheric disturbances over the region suggests that the oscillations in the Strait of Sicily could be forced by instabilities that develop in large-scale, low pressure fronts that propagate as pressure gravity waves with an approximate phase speed between 24 and 30 m s−1.

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Hyun-Sook Kim, Carlos Lozano, Vijay Tallapragada, Dan Iredell, Dmitry Sheinin, Hendrik L. Tolman, Vera M. Gerald, and Jamese Sims

Abstract

This paper introduces a next-generation operational Hurricane Weather Research and Forecasting (HWRF) system that was developed at the U.S. National Centers for Environmental Prediction. The new system, HWRF–Hybrid Coordinate Ocean Model (HYCOM), retains the same atmospheric component of operational HWRF, but it replaces the feature-model-based Princeton Ocean Model (POM) with the eddy-resolving HYCOM. The primary motivation is to improve enthalpy fluxes in the air–sea interface, by providing the best possible estimates of the balanced oceanic states using data assimilated Real-Time Ocean Forecast System products as oceanic initial conditions (IC) and boundary conditions.

A proof-of-concept exercise of HWRF–HYCOM is conducted by validating ocean simulations, followed by the verification of hurricane forecasts. The ocean validation employs airborne expendable bathythermograph sampled during Hurricane Gustav (2008). Storm-driven sea surface temperature changes agree within 0.1° and 0.5°C of the mean and root-mean-square difference, respectively. In-storm deepening mixed layer and shoaling 26°C isotherm depth are similar to observations, but they are overpredicted at similar magnitudes of their ICs. The forecast verification for 10 Atlantic hurricanes in 2008 and 2009 shows that HWRF–HYCOM improves intensity by 13.8% and reduces positive bias by 43.9% over HWRF–POM. The HWRF–HYCOM track forecast is indifferent, except for days 4 and 5, when it shows better skill (8%) than HWRF–POM. While this study proves the concept and results in a better skillful hurricane forecast, one well-defined conclusion is to improve the estimates of IC, particularly the oceanic upper layer.

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Daniel F. Steinhoff, Andrew J. Monaghan, Lars Eisen, Michael J. Barlage, Thomas M. Hopson, Isaac Tarakidzwa, Karielys Ortiz-Rosario, Saul Lozano-Fuentes, Mary H. Hayden, Paul E. Bieringer, and Carlos M. Welsh Rodríguez

Abstract

The mosquito virus vector Aedes (Ae.) aegypti exploits a wide range of containers as sites for egg laying and development of the immature life stages, yet the approaches for modeling meteorologically sensitive container water dynamics have been limited. This study introduces the Water Height and Temperature in Container Habitats Energy Model (WHATCH’EM), a state-of-the-science, physically based energy balance model of water height and temperature in containers that may serve as development sites for mosquitoes. The authors employ WHATCH’EM to model container water dynamics in three cities along a climatic gradient in México ranging from sea level, where Ae. aegypti is highly abundant, to ~2100 m, where Ae. aegypti is rarely found. When compared with measurements from a 1-month field experiment in two of these cities during summer 2013, WHATCH’EM realistically simulates the daily mean and range of water temperature for a variety of containers. To examine container dynamics for an entire season, WHATCH’EM is also driven with field-derived meteorological data from May to September 2011 and evaluated for three commonly encountered container types. WHATCH’EM simulates the highly nonlinear manner in which air temperature, humidity, rainfall, clouds, and container characteristics (shape, size, and color) determine water temperature and height. Sunlight exposure, modulated by clouds and shading from nearby objects, plays a first-order role. In general, simulated water temperatures are higher for containers that are larger, darker, and receive more sunlight. WHATCH’EM simulations will be helpful in understanding the limiting meteorological and container-related factors for proliferation of Ae. aegypti and may be useful for informing weather-driven early warning systems for viruses transmitted by Ae. aegypti.

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