Passage Of Storm Research Articles

Underwater Optical Path Loss after Passage of a Tropical Storm

Underwater wireless optical communications (UWOCs) have attracted considerable attention in recent years as an alternative means for acoustic communication. However, optical path loss of light propagation from attenuation is in large part due to absorption and scattering in various water conditions. Identification of environmental effects, especially tropical storms on underwater optical path loss, is key to the success of using optics for UWOCs. Underwater inherent optical properties (IOPs), such as the beam attenuation coefficient for 470 nm light in the western North Pacific Ocean, were measured from U.S. Naval Oceanographic Office Seagliders deployed after Super Typhoon Guchol’s (June 7–20, 2012) passage from June 25 to June 30, 2012 and without any typhoon passage from January 9 to February 28, 2014. The two observed sets (with and without the super typhoon) of IOPs are taken as input for a recently developed radiative transfer equation solver. The simulated normalized received powers for the two durations show a large impact of typhoon passage on UWOCs.

After the Storm Has Passed: Translating Crisis Experience into Useful Knowledge

This virtual special issue (VSI) collects together 19 papers published in Organization Science that explore how organizations learn from crises. The objective is to discuss insights that can help us understand the COVID-19 pandemic crisis, implications that existing research carries for organizations’ abilities to keep hard-earned lessons after the storm passes, and opportunities that the current phenomenon offers for future inquiry in this domain. Organizations, large and small, in scores of countries, have suspended normal operations. To survive, many organizations have adapted by shifting almost all human-to-human interactions online while facing an ethical dilemma and a tense tradeoff between public health and economic well-being. We take stock of the research on organizational learning from crises, summarize useful knowledge for managing the current crisis, and provide directions for future research.

Winds, Waves, and Turbulence on a Shallow Continental Shelf during Passage of a Tropical Storm

AbstractMeasurements of collocated fields of atmospheric forcing, surface waves, and mean and turbulent velocities associated with passage of Tropical Storm (TS) Barry over the U.S. Navy Tower R2 on the Georgia continental shelf are presented. A vertical-beam ADCP enables computation of directional surface wave spectra and hence of directional Stokes functions of depth and time, as well as mean (including tidal) and turbulent velocities throughout the water column. Full-depth turbulent velocity and backscatter structures observed during TS Barry are determined to be Langmuir supercells (LS). The LS appear in the present observations and in similar observations from a shallower site only when a surface growth rate g* exceeds a critical value, providing a means of predicting how deep an unstratified water column must be before LS will not be expected. When observed, LS structures at Tower R2 are less organized than archetypical LS structures: we suggest that this result is due primarily to smaller near-bottom growth rate in the deeper water column. Despite g* values above the critical value, and appropriate values of Langmuir and Rayleigh numbers, full-depth velocity/backscatter structures disappear completely for a time between the two wind maxima associated with the TS, as wind veers rapidly clockwise with eye passage to the west of Tower R2. From the observations, the most likely explanation for this hiatus is decreased wave breaking during the period of wind veering, reducing surface supply of “effective” vertical vorticity that dominates generation of Langmuir circulation (LC). This result has significant implications for LES modeling of LC.

Biogeochemical Variability of the Upper Ocean Response to Typhoons and Storms in the Northern South China Sea

Satellite remote sensing of chlorophyll a (Chl) has produced evidence of typhoon-induced phytoplankton blooms in the tropical and subtropical ocean but it is difficult to evaluate if the particulate organic carbon (POC) fixed by marine organisms can be transported into deep waters. Recent field observations have shown enhancements in primary production, Chl and POC flux associated with the passage of typhoons over the shallow waters (< 200 m) of the continental shelf. However, it is still unclear whether typhoons, which originate beyond the continental margin, can transfer the newly fixed carbon to deeper waters. Here we report on nitrate+nitrite (N), Chl and POC fluxes in the northern South China Sea (NSCS) before and shortly after the passage of typhoons and storms, between September 2012 and June 2014. The integrated inventories of N (0–150 m) 8, 3, 2 and 5 days after passage of typhoons Tembin, Soulik, Knongrey were 0.44, 0.16, 0.36 and 0.48 mol m−2, and these values were not significantly different from inventories of N under normal, non-typhoon conditions (0.18 ~ 0.48 mol m−2). The integrated Chl values 8, 3, 2 and 5 days after passage typhoons Tembin, Soulik, Knongrey were 35, 24, 14 and 28 mg m−2, i.e. lower than Chl inventories when no typhoons occurred (29 ~ 40 mg m−2). POC fluxes after the passage of typhoons Tembin and Soulik were 78 ± 12 and 115 ± 16 mg-C m−2 d−1 (average ± 1 standard deviation), i.e. 1.6 and 2.4 times higher than those obtained before the typhoon. In addition, variations in both surface and depth-integrated Chl were decoupled from POC fluxes. This decoupling may be attributed to a change in the plankton community composition due to water column instability or to lateral inputs of particulate matter released from shelf or slope sediments. Overall, our analysis of this two-year dataset highlights the spatial and temporal variability of the factors controlling POC exports to the deep NSCS.

Simulation of the atmospheric parameters during passage of a tropical storm over the South China Sea: a comparison with MetOcean buoy and ERA‐Interim data

AbstractThe accuracy of Weather Research and Forecasting (WRF) model derived meteorological fields during the passage of a tropical storm, Pabuk, over the southern South China Sea is investigated. The European Centre for Medium‐Range Weather Forecasts’ ERA‐Interim data were also used for comparison. Data from a MetOcean buoy which captured tropical storm Pabuk were used to evaluate the accuracy of the WRF model. The period of study was from January 1, 2019 to January 5, 2019. Simulated parameters (surface temperature, wind speed and pressure) showed agreement with the buoy data before and after passage of the tropical storm. In contrast, model output shows differences from observations during the passage of the storm near 0600 UTC on January 3, 2019. Overall, surface pressure was simulated with a maximum correlation of 0.93 while the wind speed showed a minimum correlation of 0.76. The surface temperature was simulated with a correlation of 0.78. Weaker correlations arise due to differences in simulated and observed parameters during the storm. During the storm, model estimates overestimated the buoy wind speed and pressure data. The results show the inaccuracy of the simulation due to the vigorous conditions prevailing during the storm. The location of the centre of the storm differing between the model and the ERA‐Interim data could also contribute to the discrepancy of the WRF data. The MetOcean buoy provided a rare opportunity for validation of the WRF model during the storm over the understudied shallow tropical South China Sea.

Tropical cyclone enhanced vertical transport in the northwestern South China Sea I: Mooring observation analysis for Washi (2005)

Using mooring-observed horizontal velocities and temperature from July 28 to August 2, 2005, this study analyzes the temporal-vertical variation of the diagnostic vertical velocity and mass transport during passage of tropical storm Washi (2005) over the northwestern continental shelf of the South China Sea (SCS). The results show that the total vertical velocity is of the order of O(1×10−4) m s−1 in the mixed layer above 25 m, and of O(1×10−5) m s−1 in the lower layer. Dynamically, the geostrophic advection and unsteady behavior of density induced by near-inertial oscillation are dominant factors in the upper and lower layers, respectively. As tropical storm Washi (2005) passed by from July 29 to 31, 2005, the upward vertical velocity was dominant and significantly enhanced to the order of O(1×10−3) m s−1. The diagnosed vertical velocity in the upper layer is one order greater than the averaged Ekman pumping velocity, which occurred one day earlier. The vertical advection transport calculated from the diagnosed vertical velocity reaches O(1×10−5) kg s−1m−3, one order greater than that induced by turbulent mixing. Time-averaged transports by vertical advection and mixing are both upward in the layer above the thermocline during the storm passage.

I Am the Storm by Jane Yolen

Reviewed by: I Am the Storm by Jane Yolen Elizabeth Bush Yolen, Jane I Am the Storm; by Jane Yolen and Heidi E. Y. Stemple; illus. by Kristen and Kevin Howdeshell. Rise x Penguin Workshop, 2020 [32p] Trade ed. ISBN 9780593222751 $17.99 E-book ed. ISBN 9780593225400 $10.99 Reviewed from digital galleys R 3-7 yrs In this benevolent fictional take on disaster response, children from four families, representing parts of America prone to different natural disasters, describe their family’s experiences when trouble arrives. Tornado? Party together in the basement with flashlights and books and games. Wildfire? Camp by a lake and enjoy nature. Blizzard? Snuggle by the fireplace when the power goes out and roast hot dogs and marshmallows. Hurricane? Shelter with cousins further inland. It all sounds like a pretty good time, at least until the hurricane refugee, subdued next to his rollicking cousins, admits to being a bit scared. Yes, there’s lots of support and well-timed deflection from protective adults, but there’s also the reality of fear that the best intentions and amusing diversions can’t erase. Yolen and Stemple’s soothing text, combined with brief and plain spoken appended paragraphs on the four storms, is firmly focused on the optimistic, but that makes it just the ticket for parents seeking to approach this topic with sensitivity; the Howdeshells’ use of bright, contrasting color creates visual tension that acknowledges the jitters running through the cozy domestic scenes. The narrators celebrate their resilience, and even the most nervous of the lot attests, “when the storm passes, as it always does, I am the calm, too.” Copyright © 2020 The Board of Trustees of the University of Illinois

Observing and Modeling the Response of Placentia Bay to an Extratropical Cyclone

An extratropical cyclone reported to have the largest wind speed in Newfoundland in morethan a decade landed on the island of Newfoundland on 11 March 2017. The oceanic responses inPlacentia Bay on the southeast coast of Newfoundland to the winter storm were examined usingobserved data and the Finite-Volume Community Ocean Model (FVCOM). The peak non-tidal waterlevel increase, i.e., storm surge, reached 0.85mat St. Lawrence and 0.77mat Argentia on Placentia Bay.Sea surface temperature slightly decreased after the storm passage according to buoy and satellitemeasurements. Root mean square dierences (RMSD) of the magnitude of storm surge between modelresults and observations are 0.15 m. The model sea surface temperature showed a small decrease,consistent with observations, with RMSDs from 0.19 to 0.64 C at buoy stations. The simulatedsurface current changes agree with buoy observations, with model-observation velocity dierenceratios (VDR) of 0.75–0.88. It was found that, at Argentia (St. Lawrence), the peak storm surge inPlacentia Bay was dominantly (moderately) associated with the inverse barometric eect, and thesubsequent negative surge was mainly due to the wind eect at both stations. The sea surface coolingwas associated with oceanic heat loss. In the momentum balance, the Coriolis, pressure gradient,and advection terms were all important during the storm, while the first two terms were predominantbefore and after the storm.

Underwater optical detection after passage of tropical storm

Optical detection systems have the potential to get around some limitations of acoustic detection systems, especially with increased fleet and port security in noisy littoral waters. Identification of environmental effects especially tropical storms on underwater optical detection is a key to the success. A typhoon-influenced area is chosen in the western North Pacific Ocean with high ocean transparency and low seasonal optical variability. Underwater inherent optical properties (IOPs) such as the beam attenuation coefficient for 470 nm light are measured in the selected region from the U.S. Naval Oceanographic Office sea gliders deployed after super typhoon Guchol’s (June 7 to 20, 2012) passage from June 25 to 30, 2012, and with no typhoon activity from January 9 to February 28, 2014. The observed two sets (with and without typhoon) of IOPs are taken as the input into the Navy’s electro-optical detection simulator. The simulation shows low detection after the super typhoon Guchol-2012’s passage and high detection without typhoon passage.

Effects of wave-induced vertical Reynolds stress on upper-ocean momentum transfer over the Scotian Shelf during extreme weather events

The effects of wave-induced vertical Reynolds stress (WIVRS) on the upper-ocean momentum transfer over the Scotian Shelf (ScS) are examined using a coupled wave-circulation modeling system during two extreme storm events: Hurricane Earl and Winter Storm Echo. The effects of WIVRS are specified in the circulation model using the wave pressure-slope stress ( τP) suggested by Mellor (2013). The inclusion of τP enhances the downward momentum transfer within the surface layer when the storm passes overhead associated with strong vertical gradients of τP, leading to relatively weak vertical shears of horizontal currents and thus weak turbulent Reynolds stress (τT) in the upper-ocean layer. This in turn weakens the vertical momentum transfer to deeper water through τT just after the storm passage. The reduced downward momentum transfer after the storm due to the inclusion of τP is found to be in better agreements with both the ADCP observations and the HF-radar observations. The ADCP observations show a relatively slow decay of upper-ocean currents, and the HF-radar observations show relatively strong clockwise-rotating near-inertial surface currents over the offshore area of the ScS just after the storm passage. The model results also demonstrate that the effects of τP are more pronounced during Hurricane Earl due to deeper penetration depths of τP associated with stronger winds (up to 33 m/s) than those during Winter Storm Echo (wind speeds up to 25 m/s).

Unpacking storm damages on a developed shoreline: Relating dune erosion and urban runoff

Hurricane Matthew (2016) caused significant beach and dune erosion from Cape Hatteras, North Carolina, USA, to Cape Canaveral, Florida, USA. At Myrtle Beach, South Carolina, the storm caused beach recession, and much of the southern half of the city’s beaches appeared to be overwashed in post-storm surveys. Around half of the city’s beaches appeared overwashed following the storm; however, the Storm Impact Scale (SIS; Sallenger 2000) applied to a pre-storm elevation model suggests less than 10% of the city’s beaches should have experienced overwash. Spatial analysis of elevation and land cover data reveals dunes that were “overwashed” during Matthew drain from watersheds that are &gt;35% impervious, where those showing only dune recession are &lt;5% impervious. The densely developed downtown of Myrtle Beach sits on a low seaward-sloping terrace. Additionally, indurated strata beneath the downtown area can prevent groundwater from draining during excessive rain events. As a result, the most continuous impervious surface cover and near-surface strata lie within a half-kilometer of the beach and drain directly to the backshore. Along the U.S. Southeast coast, this is somewhat rare; many coastal systems feature a lagoon or low-lying bottomland along their landward border, which facilitates drainage of upland impervious surfaces following storm passage. At Myrtle Beach, all of the stormwater runoff is drained directly to the beach through a series of outfall pipes. Many of the outfall pipes are located along the backshore, near the elevation of storm surge during Matthew. Runoff from Matthew’s heavy rains was observed causing ponding on the landward side of the foredune and scouring around beach access walkways. Based on these observations, the severe dune erosion experienced near downtown Myrtle Beach during Hurricane Matthew may have been caused by runoff and/or groundwater flux rather than overwash. These results highlight an unexpected relationship between upland conditions and dune erosion on a developed shoreline. That is, dune erosion can be caused by mechanisms beside overwash during storm events.

Cyclone Enhanced Chlorophyll in the Bay of Bengal as Evidenced from Satellite and BGC-Argo Float Observations

Temporal evolution of biophysical properties of Bay of Bengal (BoB) was measured using an Argo float equipped with fluorescence sensor (BGC-float) during the winter monsoon of 2013–2014. This season was subjected to intense vertical mixing due to the passage of several cyclonic storms beginning with ‘Phailin’ in October to ‘Madi’ in December 2013. These events had resulted in anomalous chlorophyll bloom (> 0.9 mg/l) together with an increase of ~ 1 PSU in the surface salinity and a drop-in temperature (~ 1 °C) in the southwestern BoB. The event was well captured by a BGC-float (WMO ID 2902086) present in the region close to the tracks of cyclones ‘Leher’ and ‘Madi’. The presence of a strong cold-core eddy as observed from the sea level anomaly data played a vital role in spreading the bloom over a wider area and maintaining it for nearly two months from November 2013 to January 2014. This was also evident from the satellite observations of surface chlorophyll-a concentration and Ekman pumping velocity (~ 2 × 10–3 m/s). The intense mixing caused by the cyclonic storms has resulted in eroding the stratification and assisting the entrainment of nutrients into the euphotic layer, which was subsequently sustained by the mesoscale eddy. The present study reveals the strong synergistic application potential of BGC-float data together with satellite observations in monitoring the changes in the vertical structure of chlorophyll during the cyclonic storms and other mesoscale processes.

The Central Chile Mega Drought (2010–2018): A climate dynamics perspective

AbstractCentral Chile, home to more than 10 million inhabitants, has experienced an uninterrupted sequence of dry years since 2010 with mean rainfall deficits of 20–40%. The so‐called Mega Drought (MD) is the longest event on record and with few analogues in the last millennia. It encompasses a broad area, with detrimental effects on water availability, vegetation and forest fires that have scaled into social and economical impacts. Observations and reanalysis data reveal that the exceptional length of the MD results from the prevalence of a circulation dipole‐hindering the passage of extratropical storms over central Chile—characterized by deep tropospheric anticyclonic anomalies over the subtropical Pacific and cyclonic anomalies over the Amundsen–Bellingshausen Sea. El Niño Southern Oscillation (ENSO) is a major modulator of such dipole, but the MD has occurred mostly under ENSO‐neutral conditions, except for the winters of 2010 (La Niña) and 2015 (strong El Niño). Climate model simulations driven both with historical forcing (natural and anthropogenic) and observed global SST replicate the south Pacific dipole and capture part of the rainfall anomalies. Idealized numerical experiments suggest that most of the atmospheric anomalies emanate from the subtropical southwest Pacific, a region that has experienced a marked surface warming over the last decade. Such warming may excite atmospheric Rossby waves whose propagation intensifies the circulation pattern leading to dry conditions in central Chile. On the other hand, anthropogenic forcing (greenhouse gases concentration increase and stratospheric ozone depletion) and the associated positive trend of the Southern Annular Mode also contribute to the strength of the south Pacific dipole and hence to the intensity and longevity of the MD. Given the concomitance of the seemingly natural (ocean sourced) and anthropogenic forcing, we anticipate only a partial recovery of central Chile precipitation in the decades to come.

The Economic and Financial Costs of Climate Change in Small Island Developing States: Assessing the Effect of Hurricanes &amp;amp; Tropical Storms on Stock and Foreign Exchange Markets in Jamaica

During the year 2017, hurricanes Irma and Maria wreaked havoc in the Caribbean and severely disrupted entire societies. This study extends the literature on the impact of climate change on Small Island Developing States by investigating the impact of hurricanes and tropical storms on stock and foreign exchange markets in Jamaica. The study finds that in a majority of cases, the passage of hurricanes and tropical storms lead to significant losses on Jamaica’s stock and foreign exchange markets, and in some cases, exceed the widely reported losses from damage to property and infrastructure. The implication is that failure to account for financial market losses can significantly understate the economic and financial impact of natural disasters. The results reinforce the vulnerability of Small Island Developing States like Jamaica to natural disasters and provide another dimension to the scale of the negative impacts of climate change on these nations. The findings also suggest that measures to mitigate the effects of climate change and natural disasters not only minimize loss of life, property and infrastructure, but may also serve to protect the value of pensions and other investments held in the stock market, as well as help maintain the stability of the currency.

Internal gravity and infrasound waves during a hurricane in Moscow On May 29, 2017

The results of recording of internal gravity waves (IGWs) and infrasound waves from the warm and cold fronts associated with the atmospheric storm passing through Moscow on May 29, 2017 are presented. The waves were recorded by a network of 4 microbarographs IFA–MGU–MSR–ZNS located in Moscow and Moscow region, and compared with the data of measurements of the parameters of infrasound waves at infrasound station IS43 in Dubna. We study the temporal changes in the characteristics of IGWs and infrasound waves (coherence, direction of propagation,phase velocities, characteristic periods and frequency spectra) with the passage of warm and cold fronts through the network. The transition from the gravity to the acoustic dispersive branch of acoustic-gravity waves due to an increase in frequency and the temporal modulation of the phase velocity of infrasound waves caused by IGWs are also studied. The measurement data for PM10 aerosol concentrations and NO2 gas concentrations at various locations in Moscow during a passage of atmospheric storm are presented. The possibility of detecting wave precursors of atmospheric storms simultaneously in variations of atmospheric pressure, wind velocity and aerosol concentrations is studied.

The Impact of the Amazon–Orinoco River Plume on Enthalpy Flux and Air–Sea Interaction within Caribbean Sea Tropical Cyclones

Abstract The influence of the Amazon–Orinoco River plume in the Caribbean Sea on latent and sensible heat flux (enthalpy flux) and tropical cyclone (TC) intensity is investigated for Hurricanes Ivan (2004), Emily (2005), Dean (2007), and Felix (2007) using dropwindsonde data, satellite sea surface temperature (SST), and the SMARTS climatology. Relationships among enthalpy fluxes, ocean heat content relative to the 26°C isotherm depth (OHC), and SST during storm passage are diagnosed. Results indicate that sea surface cooling in the river plume, a low-OHC region, is comparable to that in the warm eddy region, which has high OHC. An isothermal layer heat budget shows that upper-ocean cooling in the river plume can be explained predominantly by sea-to-air heat flux, rather than by entrainment flux from the thermocline. The latter two findings suggest that relatively large upper-ocean stratification in the plume regime limited entrainment cooling, sustaining SST and enthalpy flux. Inspection of atmospheric variables indicates that deep moderate wind shear is prevalent, and equivalent potential temperature is enhanced over the river plume region for most of these storms. Thus, sustained surface fluxes in this region may have provided warm, moist boundary layer conditions, which may have helped these storms to rapidly intensify even over relatively low-OHC waters and moderate shear. These findings are important because several Caribbean Sea TCs, including these cases, have been underforecast with respect to intensity and/or rapid intensifications, yet minimal upper-ocean observations exist to understand air–sea interaction during TCs in the salinity-stratified Amazon–Orinoco plume regime.

Study of upper ocean parameters during passage of tropical cyclones over Indian seas

ABSTRACTThe primary energy supply for tropical cyclones is the upward latent heat fluxes that are directly related to Sea Surface Temperatures (SST). The strong winds induce a negative SST anomaly in the tropical cyclone wake. This is usually referred to as the ‘cold wake’. Many studies have suggested that the cold wake results in a significant reduction of upward latent heat fluxes that supply energy to the tropical cyclone, and hence provides a negative feedback on its intensity. The cold-wake feedback on the intensity of tropical cyclones is a strong motivation to understand the oceanic response to tropical cyclones. A recent study of re-examining the mechanisms controlling the cold wake has shown the importance of vertical Ekman pumping. Under the core of tropical cyclones (typically over a disk of 100 km radius), vertical pumping is responsible for a cooling of the entire water column, while surface heat fluxes and vertical mixing both contribute to the surface cooling during the cyclone passage. Farther away from the cyclone core, vertical mixing generally overwhelms the effect of vertical pumping, and also the effect of heat fluxes in the case of strong tropical cyclones. The study examines the Ekman pumping during the passage of few cyclonic storms in the Arabian Sea (AS) and Bay of Bengal (BOB) during last decade using different datasets such as Satellite (QuikScat) and reanalysis (ERA-Interim) data and calls up the value for satellite deliverables. Surface currents and subsurface temperature structure is examined further and for different Ekman pumping velocity (EPV), variable subsurface response is illustrated. The changes in ocean surface temperature, sea level and heat content obtained from the remote sensing data products, in the wake of cyclone are also reported and thus the usefulness of satellite products to study the coupled tropical system is demonstrated.

Performance evaluation of COSMO numerical weather prediction model in prediction of OCKHI: one of the rarest very severe cyclonic storms over the Arabian Sea—a case study

In the first week of December 2017, a very severe cyclonic storm, namely “OCKHI”, made its landfall over the western coastline of the Indian peninsula. In a climatological perspective, this was one of the very rarest cyclonic storms that developed over the Comorin Sea with rapid intensification from a deep depression into a cyclonic storm within 6 h. Here, we present a case study on the performance evaluation of a regional numerical weather prediction model, Consortium for Small-scale Modelling (COSMO) during the passage of this cyclonic storm from 29 November 2017 to 6 December 2017 over the Arabian Sea by comparing the model-simulated fields against concurrent observations from the India Meteorological Department and European Centre for Medium-Range Weather Forecasts—Interim Reanalysis, respectively. Results obtained from this case study indicate good credentials to the COSMO in capturing the progression of OCKHI from its genesis as a deep depression in the early hours [0230 Indian Standard Time (IST)] of 30 November 2017 to a very severe cyclonic storm in the afternoon (1430 IST) of 01 December 2017 with a lead time of about 18 h. However, the intensity of the storm simulated by COSMO in terms of wind speed magnitudes and convective rainfall was found to be low in magnitudes as against the observations. The mean deviation between the model-simulated and observed trajectory of the storm was about 74 km for a lead time of 24 h, whereas it was below 41 km for a lead time of 18 h. The progression of OCKHI and the prevailing meteorological conditions for its intensification and subsequent weakening are also discussed in this article.

Wind Pulse Effect on Coastal Current

Shallow water equations have been used to analyze the final stage of the response of a semi-infinite rotating basin to the wind impulse effect simulating the passage of a storm in the presence of a coastal current. It has been shown that the most significant effect upon a high storm intensity is that the coastal stream core shifts several kilometers toward the coast or from the coast, depending on the sign of the Ekman transport. The additional currents arising after the storm passage in the presence of an alongshore stream differ only quantitatively from the currents arising in its absence.

Hydrodynamics and Sediment Mobility Processes Over a Degraded Senile Coral Reef

AbstractCoral reefs can influence hydrodynamics and morphodynamics by dissipating and refracting incident wave energy, modifying circulation patterns, and altering sediment transport pathways. In this study, the sediment and hydrodynamic response of a senile (dead) barrier reef (Crocker Reef, located in the upper portion of the Florida Reef Tract) to storms and quiescent conditions was evaluated using field observations and the Coupled Ocean‐Atmosphere‐Wave‐Sediment Transport model. Waves, circulation, and resultant sediment mobility were modeled across different reef zones. Sediment mobility during quiescent periods and the passage of far‐field storms are driven by nonbreaking waves and, to a lesser degree, regional circulation. Spatial variability in these processes produces the present‐day distribution of sediment grain size at Crocker Reef, wherein finer‐grain material along a shallow central ridge is frequently mobilized (43% to 62% of the time), winnowed away, and deposited along the lower‐energy flanks and in the fore reef where sand mobility occurs less frequently (32% to 43% and 1% to 22% of the time, respectively). Analysis of wave conditions for the period of 2006–2014 supports that wave heights rarely exceed the threshold for breaking (0.1% and 0.3% at the reef crest and at the reef flat, respectively), predominantly during the passage of tropical storms. There is a shift to a wave‐breaking regime during near‐field storms, creating the potential for mobilization of larger material and enhanced reef degradation. Sediment mobility can be enhanced due to wave skewness or the generation of free infragravity waves during periods of depth‐induced wave breaking.