Role of Tidal Forcing in Determining the Internal Wave Spectrum in the Littoral Ocean

LONG-TERM GOALS: The goal of this proposed project is to examine the hypothesis that changes in tropical cyclone intensity and structure depend on: i) vertical alignment of the initial vortex ii) characteristics of the upper-level environment, iii) tropical cyclone structure, iv) phasing of the tropical cyclone and the environmental features, and iv) feedback of the tropical cyclone onto the environment.Award Number: N0001413AF0000

Assessment of the Potential for Prediction of Tropical Cyclone Formation in the Navy Global Model

4D.7Some of the recent increase in skill of tropical cyclone track predictions has been attributed to increased accuracy of guidance from global dynamical models. Indeed, as the skill in dynamical predictions has been extended into the medium ranges, requirements for fi ve-day track predictions are being contemplated. However, a tropical cyclone may form, intensify, and move a long distance in five days to become a serious threat to maritime activities and coastal locations.This research is sponsored by the Office of Naval Research, Marine Meteorology Program

Predictability associated with extratropical transition of tropical cyclones as defined by operational ensemble prediction systems

The poleward movement of a decaying tropical cyclone often results in a rapidly-moving, explosively-deepening midlatitude cyclone. The re-intensification of the remnant tropical cyclone as an extratropical cyclone depends on the phasing between the decaying tropical cyclone and a midlatitude environment that is favorable for midlatitude cyclogenesis (Klein et al. 2001). Because of the typical rapid translation speed (Jones et al. 2003) of the decaying tropical cyclone, accurate extended-range prediction of the phasing between the remnant tropical circulation and the midlatitude environment into which it is moving is critical.This research has been supported by the Office of Naval Research, Marine Meteorology

ITOP 2010 Field Experiment

LONG-TERM GOALS: The long-term goal of this project is to increase understanding of the interaction between the ocean and tropical cyclones over the tropical western North Pacific. Tropical cyclones produce a threedimensional response of the underlying ocean that includes surface currents, upwelling of the thermocline, and formation of a cold wake. These responses then impact the structure and intensity of the tropical cyclone. Specific objectives are to provide leadership to the ITOP field campaign in support of direct measurements of the ocean and tropical cyclone characteristics.Award Number: N0001410WX2133

The relationship of western Pacific monsoon and tropical cyclone activity to North Pacific and North American climate anomalies

This present study investigates the influence of western Pacific tropical cyclone activity as possible centers of anomalous tropical heating on the large-scale circulation over the Pacific region. The characterization of tropical cyclone activity via an index based on anomalous 700 mb zonal wind is described first. Patterns of anomalous large-scale extratropical circulation anomalies based on composites of similar periods of tropical cyclone activity are then presented, followed by general conclusions

In-Situ Wave Observations in the High Resolution Air-Sea Interaction DRI

Long-term goals: Ocean wave prediction models, based on a spectral energy balance, are widely used to obtain wind- wave forecasts and hindcasts on global and regional scales (e.g., Komen et al., 1994). However, these inherently stochastic models assume a Gaussian and homogeneous sea state and thus do not describe the nonlinear instability processes that can dramatically alter the structure of wave groups and produce anomalously large waves, also known as ‘freak’ or ‘rogue’ waves (e.g., Janssen, 2003). Fully deterministic modeling capabilities are now becoming available that incorporate these nonlinear effects and provide the detailed phase-resolved sea surface predictions needed in many applications. Concurrent with the development of new models, advances in radar remote sensing techniques are enabling the detailed observation of the sea surface on the scales of wave groups and individual waves. The long-term goal of this research is to test these emerging new models and measurement technologies in realistic sea states and use them to better understand and predict the wave group structure and occurrence of extreme waves in the ocean.N0001409WR20007N00014091034

A saturated stochastic simulator: synthetic US Gulf coast tropical cyclone precipitation fields

The space–time fields of rainfall during a hurricane and tropical storm (TC) landfall are critical for coastal flood risk preparedness, assessment, and mitigation. We present an approach for the stochastic simulation of rainfall fields that leverages observed, high-resolution spatial fields of historical landfalling TCs rainfall that is derived from multiple instrumental and remote sensing sources, and key variables recorded for historical TCs. Spatial realizations of rainfall at each time step are simulated conditional on the variables representing the ambient conditions. We use 6 hourly precipitation fields of tropical cyclones from 1983 to 2019 that made landfall on the Gulf coast of the US, starting from 24 h before landfall until the end of the track. A conditional K-nearest neighbor method is used to generate the simulations. The TC attributes used for conditioning are the preseason large-scale climate indices, the storm maximum wind speed, minimum central pressure, the latitude and speed of movement of the storm center, and the proportion of storm area over land or ocean. Simulation of rainfall for three hurricanes that are kept out of the sample: Katrina [2005], Rita [2005], and Harvey [2017] are used to evaluate the method. The utility of coupling the approach to a hurricane track simulator applied for a full season is demonstrated by an out-of-sample simulation of the 2020 season

An ocean coupling potential intensity index for tropical cyclones

© American Geophysical Union, 2013. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 40 (2013): 1878–1882, doi:10.1002/grl.50091.Timely and accurate forecasts of tropical cyclones (TCs, i.e., hurricanes and typhoons) are of great importance for risk mitigation. Although in the past two decades there has been steady improvement in track prediction, improvement on intensity prediction is still highly challenging. Cooling of the upper ocean by TC-induced mixing is an important process that impacts TC intensity. Based on detail in situ air-deployed ocean and atmospheric measurement pairs collected during the Impact of Typhoons on the Ocean in the Pacific (ITOP) field campaign, we modify the widely used Sea Surface Temperature Potential Intensity (SST_PI) index by including information from the subsurface ocean temperature profile to form a new Ocean coupling Potential Intensity (OC_PI) index. Using OC_PI as a TC maximum intensity predictor and applied to a 14 year (1998–2011) western North Pacific TC archive, OC_PI reduces SST_PI-based overestimation of archived maximum intensity by more than 50% and increases the correlation of maximum intensity estimation from r2 = 0.08 to 0.31. For slow-moving TCs that cause the greatest cooling, r2 increases to 0.56 and the root-mean square error in maximum intensity is 11 m s−1. As OC_PI can more realistically characterize the ocean contribution to TC intensity, it thus serves as an effective new index to improve estimation and prediction of TC maximum intensity.This work is supported by Taiwan’s National Science Council and National Taiwan University (grant numbers: NSC 101- 2111-M-002-002-MY2; NSC 101-2628-M-002-001-MY4; 102R7803) and US Office of Naval Research (ONR) under the Impact of Typhoons on Pacific (ITOP) program. PB’s support is provided by ONR under PE 0601153N through NRL Contract N00173-10-C-6019

The Extratropical Transition of Tropical Cyclones: Forecast Challenges, Current Understanding, and Future Directions

A significant number of tropical cyclones move into the midlatitudes and transform into extratropical cyclones. This process is generally referred to as extratropical transition (ET). During ET a cyclone frequently produces intense rainfall and strong winds and has increased forward motion, so that such systems pose a serious threat to land and maritime activities. Changes in the structure of a system as it evolves from a tropical to an extratropical cyclone during ET necessitate changes in forecast strategies. In this paper a brief climatology of ET is given and the challenges associated with forecasting extratropical transition are described in terms of the forecast variables (track, intensity, surface winds, precipitation) and their impacts (flooding, bush fires, ocean response). The problems associated with the numerical prediction of ET are discussed. A comprehensive review of the current understanding of the processes involved in ET is presented. Classifications of extratropical transition are described and potential vorticity thinking is presented as an aid to understanding ET. Further sections discuss the interaction between a tropical cyclone and the midlatitude environment, the role of latent heat release, convection and the underlying surface in ET, the structural changes due to frontogenesis, the mechanisms responsible for precipitation, and the energy budget during ET. Finally, a summary of the future directions for research into ET is given

Typhoon-ocean interaction in the western North Pacific : Part 1

Author Posting. © The Oceanography Society, 2011. This article is posted here by permission of The Oceanography Society for personal use, not for redistribution. The definitive version was published in Oceanography 24 no. 4 (2011): 24–31, doi:10.5670/oceanog.2011.91.The application of new technologies has allowed oceanographers and meteorologists to study the ocean beneath typhoons in detail. Recent studies in the western Pacific Ocean reveal new insights into the influence of the ocean on typhoon intensity.This work is supported by grants from the Office of Naval Research, N00014- 10-WX-20203 (Black), N00014-08-1- 0656 (Centurioni), N00014-08-1-0577 (D’Asaro), N00014-09-1-0816 (D’Asaro), N00014-10-WX-21335 (Harr), N00014-08-1-0614 (Jayne), N00014- 09-1-0133 (Lee), N00014-08-1-0560 (Lien), N00014-10-1-0313 (student support), N00014-08-1-0658 (Rainville), N00014-08-1-0560 (Sanford); the National Oceanic and Atmospheric Administration NA17RJ1231 (Centurioni); and the National Science Foundation OCE0549887 (D’Asaro)