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A defining feature of Earth’s present-day climate is that the Southern Hemisphere is stormier than the Northern Hemisphere. Consistently, the Southern Hemisphere has a stronger jet stream and more extreme weather events than the Northern Hemisphere. Understanding the relative importance of land–ocean contrast, including topography, radiative processes, and ocean circulation for determining this storminess asymmetry is important and may be helpful for interpreting projections of future storminess. Here, we show that the stormier Southern Hemisphere is induced by nearly equal contributions from topography and the ocean circulation, which moves energy from the Southern to Northern Hemisphere. These findings are based on 1) diagnostic energetic analyses applied to observations and climate model simulations and 2) modifying surface (land and ocean) boundary conditions in climate model simulations. Flattening topography and prescribing hemispherically symmetric surface energy fluxes (the manifestation of ocean energy transport on the atmosphere) in a climate model reduce the storminess asymmetry from 23 to 12% and 11%, respectively. Finally, we use the energetic perspective to interpret storminess trends since the beginning of the satellite era. We show that the Southern Hemisphere has become stormier, consistent with implied ocean energy transport changes in the Southern Ocean. In the Northern Hemisphere, storminess has not changed significantly consistent with oceanic and radiative (increased absorption of sunlight due to the loss of sea ice and snow) changes opposing one another. The trends are qualitatively consistent with climate model projections.

The Bohai Bay is particularly vulnerable to storm surges triggered by extratropical storms or cold-air outbreaks. A coupled atmosphere–ocean–wave model with high resolution is presented and applied to simulate a cold-air outbreak that happened in late November 2004. The surge dynamics are examined in detail. Each model component is separately validated, demonstrating that the triply coupled system can reproduce intense winds, storm surge amplitudes, and significant surface waves with high fidelity. The potential coupling effects on the simulation results are investigated. Six experiments are performed covering various coupling models, and a two-way nesting technique is utilized during simulation. After comparison it shows that there is little difference in wind speed between the three numerical models and that the reanalysis data may significantly underestimate extreme winds. The evident improvements are obtained for peak values of water level when using the atmosphere–ocean coupled configuration versus uncoupled model simulation. It also can be found that the negative surge can be captured by each of the coupled and uncoupled models. The ocean–wave coupled configuration yields significant wave heights that closely match in situ measurements, underscoring the critical role of ocean–wave interaction in storm wave prediction. Our findings confirm that the fully coupled model is well-suited for forecasting extratropical storm surge in Bohai Bay. Northeast winds emerge as the primary driver, with the western coast of Bohai Bay bearing the greatest impact.

Cheng, J. and Wang, P., 2022. Factors controlling storm-induced morphology changes at an erosional hot spot on a nourished beach, Sand Key barrier island, west-central Florida. Journal of Coastal Research, 38(4), 750–765. Coconut Creek (Florida), ISSN 0749-0208. Beach nourishment has become the dominant sandy shore protection method over the past 40 years. The performance of nourished beaches and therefore the design of renourishment projects are significantly controlled by the presence of erosional hot spots and storm impacts. Based on 5.5-year bimonthly beach profile surveys, along a nourished beach spanning an erosional hot spot, this study examines the hydrodynamic conditions of extratropical (winter) and tropical (summer) storms that cause significant morphology changes. The sand volume loss above the short-term closure depth averaged along the 1.8-km stretch erosional hot spot was 178 m3/m over the 5.5 years after the nourishment. A large portion of this volume loss was caused by several extratropical storms and Hurricane Irma in 2017, when the high, northerly approaching waves were associated with a depressed water level. The northerly approaching waves induced a large longshore sediment transport gradient along the generally north-south trending coast due to wave refraction over a nearby ebb tidal delta. The energetic Hurricane Irma induced a large negative surge and also transported sediment seaward beyond the short-term closure depth. On the other hand, during the passages of typical tropical storms, the southerly approaching waves superimposed on elevated water levels caused substantial beach volume loss above the mean sea level. The eroded sediment deposited on the nearshore sandbar, resulting in conserved sand volume above the short-term closure depth. Understanding the different beach response to extratropical and tropical storms would benefit beach management, especially under the circumstance of increasing storm activities due to climate change.

Prediction of severe natural hazards requires accurate forecasting systems. Recently, there has been a tendency towards more integrated solutions, where different components of the Earth system are coupled to explicitly represent the physical feedbacks between them. This study focuses on rapidly developing waves under extratropical storms to understand the impact of different wave source term parameterisations in the WAVEWATCH III (WWIII) model (ST4 and ST6) and coupling strategies (surface roughness closure versus surface stress closure) on the accuracy of the Met Office regional atmosphere-ocean-wave coupled research system for the north-west (NW) European shelf (UKC4). Results of a study focused on simulations during winter 2013/14 demonstrate that ST6 allows for a faster wave growth than the ST4 parameterisation but might degrade low to mid energy wave states. The difference between ST6 and ST4 in wave growth is larger for higher wind speeds and short fetches. The experiment with ST4 and roughness closure consistently under-predicts the wave growth in those locations where fetch dependence is an important factor (i.e., seas at the East (E) of Ireland and the UK for storms coming from the NW-WNW). The implementation in the wave model of ST6 physics with the stress closure coupling strategy appears to improve growth of young wind-seas, reducing bias in those locations where the storms are underestimated. The slower wave growth when using surface roughness closure seems to be related to an underestimation of the momentum transfer computed by the wave model when coupling the wind speeds. For very young to young wind seas, this can be overcome when the surface stress is computed by the atmospheric model and directly passed to the ocean.

The Bohai Sea is extremely susceptible to storm surges induced by extratropical storms and tropical cyclones in nearly every season. In order to relieve the impacts of storm surge disasters on structures and human lives in coastal regions, it is very important to understand the occurring of the severe storm surges. The previous research is mostly restricted to a single type of storm surge caused by extratropical storm or tropical cyclone. In present paper, a coupled atmosphere-ocean model is developed to study the storm surges induced by two types of extreme weather conditions. Two special cases happened in the Bohai Sea are simulated successively. The wind intensity and minimum sea-level pressure derived from the Weather Research and Forecasting (WRF) model agree well with the observed data. The computed time series of water level obtained from the Regional Ocean Modeling System (ROMS) also are in good agreement with the tide gauge observations. The structures of the wind fields and average currents for two types of storm surges are analyzed and compared. The results of coupled model are compared with those from the uncoupled model. The case studies indicate that the wind field and structure of the ocean surface current have great differences between extratropical storm surge and typhoon storm surge. The magnitude of storm surge in the Bohai Sea is shown mainly determined by the ocean surface driving force, but greatly affected by the coastal geometry and bathymetry.

Analyses of hourly measurements of ocean wave heights along the U.S. East Coast, collected since the 1970s by three buoys of the National Data Buoy Center, document a progressive increase during the summer months when hurricanes are most important to wave generation. In contrast, the waves measured during the winter, generated by extratropical storms, have not experienced a statistically significant change. Summer waves with significant wave heights greater than 3 m, which can be directly attributed to specific hurricanes, have increased at a rate of 0.059 m/y (1.8 m in 30 years) according to records from buoy 41002 offshore from Charleston, South Carolina, with a lower rate of 0.024 m/y (0.7 m in 30 years) recorded by the Cape Hatteras buoy (41001); both trends are statistically significant at the 90% level. A still lower rate is found for the Cape May buoy (44004), 0.017 m/y, suggesting that there is a systematic latitude variation. Histograms of the ranges of significant wave heights measured during the hurricane season show that the most extreme occurrences during the 1996–2005 decade are both higher and more common than occurred 30 years ago, at the beginning of buoy measurements, having increased from about 7 m to higher than 10 m. The waves recorded by the buoys depend on the annual numbers of hurricanes that followed tracks northward into the central Atlantic, how close their tracks approached the buoys, and the intensities (categories) of those hurricanes. Examinations of the storms that have occurred since 1980 indicate that the primary explanation for the progressive increase in wave heights has been an intensification of the hurricanes, with increased numbers of storms a contributing factor.

Li, H.; Lin, L., and Burks-Copes, K.A., 2013. Modeling of coastal inundation, storm surge, and relative sea-level rise at Naval Station Norfolk, Norfolk, Virginia, U.S.A. The potential risk and effects of storm-surge damage caused by the combination of hurricane-force waves, tides, and relative sea-level-rise (RSLR) scenarios were examined at the U.S. Naval Station, Norfolk, Virginia. A hydrodynamic and sediment transport modeling system validated with measured water levels from Hurricane Isabel was used to simulate two synthesized storms representing 50-year and 100-year return-period hurricanes, a northeaster, and five future RSLR scenarios to evaluate the combined impacts of inundation on this military installation in the lower Chesapeake Bay. The naval base topography and nearshore water body of Hampton Roads were included in the coastal modeling system (CMS), a suite of surge, circulation, wave, sediment transport, and morphology evolution models. The modeling domain was a rectangular area covering the entire Naval Station Norfolk in the Hampton Roads and the mouths of the James and Elizabeth rivers. A variable-resolution grid system was created with a finer resolution of 10 m in the naval base and a coarser resolution of 300 m in the regions away from the base. The boundary-forcing conditions to the CMS were regional storm surge produced by the ADvanced CIRCulation (ADCIRC),and wave conditions by the Simulating WAve Nearshore (SWAN) model. The CMS calculated the local water-surface elevation and storm-surge inundation for combined RSLR, surge, waves, and wind. Results indicate that synthetic storms would cause extensive inundation of coastal land around the naval base. Approximately 60% of the land would be under water with the 100-year storm for the present sea level, and 80% for estimated RSLR of 2 m.

This study examines the variability of freak wave parameters around the eye of northern hemisphere extratropical cyclones. The data was obtained from a hindcast performed with the WAve Model (WAM) model forced by the wind fields of the Climate Forecast System Reanalysis (CFSR). The hindcast results were validated against the wave buoys and satellite altimetry data showing a good correlation. The variability of different wave parameters was assessed by applying the empirical orthogonal functions (EOF) technique on the hindcast data. From the EOF analysis, it can be concluded that the first empirical orthogonal function (V1) accounts for greater share of variability of significant wave height (Hs), peak period (Tp), directional spreading (SPR) and Benjamin-Feir index (BFI). The share of variance in V1 varies for cyclone and variable: for the 2nd storm and Hs V1 contains 96 % of variance while for the 3rd storm and BFI V1 accounts only for 26 % of variance. The spatial patterns of V1 show that the variables are distributed around the cyclones centres mainly in a lobular fashion.

The present study extends the applicability of a statistical model for prediction of storm surge originally developed for The Battery, NY in two ways: I. the statistical model is used as a biascorrection for operationally produced dynamical surge forecasts, and II. the statistical model is applied to the region of the east coast of the U.S. susceptible to winter extratropical storms. The statistical prediction is based on a regression relation between the “storm maximum” storm surge and the storm composite significant wave height predicted ata nearby location. The use of the statistical surge prediction as an alternative bias correction for the National Oceanic and Atmospheric Administration (NOAA) operational storm surge forecasts is shownhere to be statistically equivalent to the existing bias correctiontechnique and potentially applicable for much longer forecast lead times as well as for storm surge climate prediction. Applying the statistical model to locations along the east coast shows that the regression relation can be “trained” with data from tide gauge measurements and near-shore buoys along the coast from North Carolina to Maine, and that it provides accurate estimates of storm surge.

Six major storms occurred between 1997 and 2000 offshore from the Pacific Northwest (PNW) of the United States, each generating deep-water significant wave heights greater than 10 m, the approximate height of the 100-year storm event determined from wave data collected up through 1996. Part of this apparent sudden increase in storm-wave heights was found to be associated with a progressive increase that has spanned the past 25 years (Allan and Komar, 2000), and a progressive increase in the magnitude and frequency of North Pacific cyclones since the late 1940s (Graham and Diaz, 2001), but also may have been affected by successive occurrences of a strong El Niño (1997-98) and moderate La Niña (1998-99). The objective of this paper is to document in detail the meteorological conditions and wave generation of these recent storms, due to their unusual strengths and because they produced substantial erosion along the coast. The paper focuses primarily on the two severest storms that crossed the PNW coast; the 19-20 November 1997 El Niño storm that generated 10.5 m significant wave heights, and a storm on 2-3 March 1999 (La Niña) that produced 14.1 m significant wave heights. With the presence of several NDBC buoys close offshore, the movement of each storm can be followed as it developed, and there is good spatial documentation of the meteo-rological conditions and generated waves. The measured wave heights and periods are used to calculate the along-coast variations in wave runup on PNW beaches. In addition, tide gauges permit analyses of the accompanying storm surge produced by the high winds and low atmospheric pressures of the storms. The largest storm surge occurred during the strongest storm in March 1999, which produced a peak surge of 0.6 m along the Oregon coast and 1.6 m on the Washington coast. Important to the resulting coastal erosion are analyses undertaken of the total water levels reached during the storms, produced by the wave runup above and beyond the elevated tides. Analyses of the 19-20 November 1997 El Nino storm and 2-3 March 1999 La Niña storm yielded estimated wave runup elevations that ranged from 2.8 to 4.1 m, while the total water levels (wave runup plus tides) reached 6.4 m relative to the NGVD 1929 vertical datum. These high water levels were a major cause of extreme erosion observed along the coasts of Oregon and Washington.