Ocean Feedback Research Articles

Dynamics of ENSO Phase–Locking and Its Biases in Climate Models

AbstractThe contributions of different oceanic feedbacks to the El Niño–Southern Oscillation (ENSO) phase‐locking are examined by deriving ENSO dynamics based on the recharge‐discharge framework. In observations, the significant winter preference of the ENSO peak is determined by a strong seasonal modulation of SST growth rate, which is controlled by the zonal advective and thermodynamic feedbacks. However, the majority of climate models fail to simulate ENSO phase‐locking because the contribution of zonal advective feedback to the seasonal modulation of the SST growth rate is much smaller compared to observations. The weak annual cycle of the SST‐current coupling coefficient and small annual mean of the negative climatological zonal SST gradient are two factors contributing to the weak‐biased seasonality of zonal advective feedback. Further analysis shows that the Niño3.4 SSTA has better phase‐locking performance than Niño3 SSTA in the climate models due to the better simulation of zonal advection feedback in the Niño3.4 region.

Distinct Surface Warming Response Over the Western and Eastern Equatorial Pacific to Radiative Forcing

AbstractThis study examines regional characteristics of atmospheric and oceanic feedback processes in the western and eastern equatorial Pacific, by applying a localized surface heating in the respective region in a hierarchy of climate models. A western Pacific forcing is largely offset by a negative shortwave cloud radiative effect and damping via wind‐evaporation‐SST feedback. In contrast, an eastern Pacific forcing, while being partially compensated for by ocean dynamical adjustments, induces an amplified warming extending to the central Pacific due to weak local damping mechanisms. As for the inter‐model spread of the future tropical Pacific surface warming pattern, the ocean heat uptake response in the east can explain much of the spread both on fast (<5 years) and slow (>100 years) timescales. Our results suggest that an “El Niño‐like” warming pattern is probable in response to increasing greenhouse gases owing to the strong negative feedback intrinsic to the western Pacific.

Impact of a Mixed Ocean Layer and the Diurnal Cycle on Convective Aggregation.

We investigate how ocean feedbacks and the diurnal cycle impact convective aggregation using a slab ocean coupled to a cloud resolving model. With a 20 m mixed layer ocean, aggregation occurs after 25 days. Thinner ocean layers slow the onset of clustering, with a 1 m ocean layer needing around 43 days. The delay is due to anomalous solar radiation in clear sky regions, causing a relative surface warming balanced by a matching cooling in cloudy areas. The resulting gradient in surface heat fluxes opposes low level convergence into convecting regions. On aggregation, the convective regions are surrounded by moist, clear sky regions with the hottest SSTs, toward which convection migrates, while a cold SST patch forms under dry suppressed regions due to enhanced latent heat fluxes and longwave radiation. The next experiment allows a diurnal cycle of 2.5°C in the domain mean SST. This causes convective rainfall to shift from a weak morning maximum to a sharper evening peak, reminiscent of undisturbed tropical observations. However, convection reverts to a weak early morning maximum once aggregation starts due to spatially heterogeneous radiative forcing. This implies thin mixed ocean layers are a necessary but non‐sufficient condition for an afternoon maximum of convection; limited spatial water vapor variability is also necessary. The imposition of the mean diurnal cycle has no statistically significant impact on the mean timing of clustering onset.

The Influence of Ocean Coupling on Simulated and Projected Tropical Cyclone Precipitation in the HighResMIP–PRIMAVERA Simulations

AbstractThis study aims to quantify the impacts of atmosphere–ocean coupling on simulated and projected tropical cyclone (TC) precipitation globally. We used global climate model (GCM) simulations over 1950–2050 from the High Resolution Model Intercomparison Project (HighResMIP) and compared its fully coupled atmosphere–ocean GCMs (AOGCMs) with atmosphere‐only GCMs (AGCMs). We find that ocean coupling generally leads to decreased TC precipitation over ocean and land. Large‐scale sea surface temperature (SST) biases are critical drivers of the precipitation difference, with secondary contributions from local TC–ocean feedbacks via SST cold wakes. The two driving factors, attributed to ocean coupling in the AOGCMs, influence TC precipitation in association with decreased TC intensity and specific humidity. The AOGCMs and AGCMs consistently project TC precipitation increases in 2015–2050 relative to 1950–2014 over ocean for all basins, and for landfalling TCs in the North Atlantic and western North Pacific.

The Increased Likelihood in the 21st Century for a Tropical Cyclone to Rapidly Intensify When Crossing a Warm Ocean Feature—A Simple Model’s Prediction

A warm ocean feature (WOF) is a blob of the ocean’s surface where the sea-surface temperature (SST) is anomalously warmer than its adjacent ambient SST. Examples are warm coastal seas in summer, western boundary currents, and warm eddies. Several studies have suggested that a WOF may cause a crossing tropical cyclone (TC) to undergo rapid intensification (RI). However, testing the “WOF-induced RI” hypothesis is difficult due to many other contributing factors that can cause RI. The author develops a simple analytical model with ocean feedback to estimate TC rapid intensity change across a WOF. It shows that WOF-induced RI is unlikely in the present climate when the ambient SST is ≲29.5 °C and the WOF anomaly is ≲+1 °C. This conclusion agrees well with the result of a recent numerical ensemble experiment. However, the simple model also indicates that RI is very sensitive to the WOF anomaly, much more so than the ambient SST. Thus, as coastal seas and western boundary currents are warming more rapidly than the adjacent open oceans, the model suggests a potentially increased likelihood in the 21st century of WOF-induced RIs across coastal seas and western boundary currents. Particularly vulnerable are China’s and Japan’s coasts, where WOF-induced RI events may become more common.

Impacts of UV Irradiance and Medium-Energy Electron Precipitation on the North Atlantic Oscillation during the 11-Year Solar Cycle

Observational studies suggest that part of the North Atlantic Oscillation (NAO) variability may be attributed to the spectral ultra-violet (UV) irradiance variations associated to the 11-year solar cycle. The observed maximum surface pressure response in the North Atlantic occurs 2–4 years after solar maximum, and some model studies have identified that atmosphere–ocean feedbacks explain the multi-year lag. Alternatively, medium-to-high energy electron (MEE) precipitation, which peaks in the declining phase of the solar cycle, has been suggested as a potential cause of this lag. We use a coupled (ocean–atmosphere) climate prediction model and a state-of-the-art MEE forcing to explore the respective roles of irradiance and MEE precipitation on the NAO variability. Three decadal ensemble experiments were conducted over solar cycle 23 in an idealized setting. We found a weak ensemble-mean positive NAO response to the irradiance. The simulated signal-to-noise ratio remained very small, indicating the predominance of internal NAO variability. The lack of multi-annual lag in the NAO response was likely due to lagged solar signals imprinted in temperatures below the oceanic mixed-layer re-emerging equatorward of the oceanic frontal zones, which anchor ocean–atmosphere feedbacks. While there is a clear, yet weak, signature from UV irradiance in the atmosphere and upper ocean over the North Atlantic, enhanced MEE precipitation on the other hand does not lead to any systematic changes in the stratospheric circulation, despite its marked chemical signatures.

Subsurface Oceanic Structure Associated With Atmospheric Convectively Coupled Equatorial Kelvin Waves in the Eastern Indian Ocean

AbstractAtmospheric convectively coupled equatorial Kelvin waves (CCKWs) are a major tropical weather feature strongly influenced by ocean–atmosphere interactions. However, prediction of the development and propagation of CCKWs remains a challenge for models. The physical processes involved in these interactions are assessed by investigating the oceanic response to the passage of CCKWs across the eastern Indian Ocean and Maritime Continent using the NEMO ocean model analysis with data assimilation. Three‐dimensional life cycles are constructed for “solitary” CCKW events. As a CCKW propagates over the eastern Indian Ocean, the immediate thermodynamic ocean response includes cooling of the ocean surface and subsurface, deepening of the mixed layer depth, and an increase in the mixed layer heat content. Additionally, a dynamical downwelling signal is observed two days after the peak in the CCKW westerly wind burst, which propagates eastward along the Equator and then follows the Sumatra and Java coasts, consistent with a downwelling oceanic Kelvin wave with an average phase speed of 2.3 m s−1. Meridional and vertical structures of zonal velocity anomalies are consistent with this framework. This dynamical feature is consistent across distinct CCKW populations, indicating the importance of CCKWs as a source of oceanic Kelvin waves in the eastern Indian Ocean. The subsurface dynamical response to the CCKWs is identifiable up to 11 days after the forcing. These ocean feedbacks on time scales longer than the CCKW life cycle help elucidate how locally driven processes can rectify onto longer time‐scale processes in the coupled ocean–atmosphere system.

Can a Warm Ocean Feature Cause a Typhoon to Intensify Rapidly?

The hypothesis that a warm ocean feature (WOF) such as a warm eddy may cause a passing typhoon to undergo rapid intensification (RI), that is, the storm’s maximum 1-min wind speed at 10-m height increases by more than 15.4 m/s in 1 day, is of interest to forecasters. Testing the hypothesis is a challenge, however. Besides the storm’s internal dynamics, typhoon intensity depends on other environmental factors such as vertical wind shear and storm translation. Here we designed numerical experiments that exclude these other factors, retaining only the WOF’s influence on the storm’s intensity change. We use a storm’s translation speed Uh = 5 m/s when surface cooling is predominantly due to 1D vertical mixing. Observations have shown that the vast majority (70%) of RI events occur in storms that translate between 3 to 7 m/s. We conducted a large ensemble of twin experiments with and without ocean feedback and with and without the WOF to estimate model uncertainty due to internal variability. The results show that the WOF increases surface enthalpy flux and moisture convergence in the storm’s core, resulting in stronger updrafts and intensity. However, the intensification rate is, in general, insufficiently rapid. Consequently, the number of RIs is not statistically significantly different between simulations with and without the WOF. An analytical coupled model supports the numerical findings. Furthermore, it shows that WOF-induced RI can develop only over eddies and ambient waters that are a few °C warmer than presently observed in the ocean.

The atmospheric blocking influence over the South Brazil Bight during the 2013–2014 summer

The 2013–2014 summer in the Southeast Brazil region set records for negative precipitation anomalies and the highest sea surface temperatures. Such event was attributed to the anomalous presence of atmospheric blocking, which prevented the propagation of a cold front towards the Equator and the establishment of the South Atlantic Convergence Zone, two phenomena that regulate the precipitation regime in this area. These blocking episodes are relatively important to the climate in mid-latitudes, but the feedback of the coastal ocean is still poorly understood under these anomalous conditions. This paper investigates, from a numerical perspective, the impacts on the thermohaline properties and circulation in the South Brazil Bight (SBB). We found that enhanced shortwave radiation leads to intense surface heating and that the presence of northeasterly winds strengthens the coastal upwelling nearby Cabo Frio. The South Atlantic Coastal Waters, transported into the SBB, regulate the extreme heating in the northern half of the domain, while, in the southern half, the absence of cold waters leads to the development of a warm-water pool. The final thermohaline structure induced an enlargement and intensification of the northwestward currents south of São Sebastião Island. Between Ubatuba and Cabo Frio, in the northern half, the northeasterly winds developed an intense surface advection towards offshore, and in the northern region, compensated by an opposite advection, towards the coast. We conclude that the coastal ocean feedback could present extreme anomalous conditions during atmospheric blocking events, leading to impacts upon the thermodynamical properties. Further studies are needed to understand the impacts of these events on biogeochemical properties.

Depth Structure of Ningaloo Niño/Niña Events and Associated Drivers

AbstractMarine heatwaves along the coast of Western Australia, referred to as Ningaloo Niño, have had dramatic impacts on the ecosystem in the recent decade. A number of local and remote forcing mechanisms have been put forward; however, little is known about the depth structure of such temperature extremes. Utilizing an eddy-active global ocean general circulation model, Ningaloo Niño and the corresponding cold Ningaloo Niña events are investigated between 1958 and 2016, with a focus on their depth structure. The relative roles of buoyancy and wind forcing are inferred from sensitivity experiments. Composites reveal a strong symmetry between cold and warm events in their vertical structure and associated large-scale spatial patterns. Temperature anomalies are largest at the surface, where buoyancy forcing is dominant, and extend down to 300-m depth (or deeper), with wind forcing being the main driver. Large-scale subsurface anomalies arise from a vertical modulation of the thermocline, extending from the western Pacific into the tropical eastern Indian Ocean. The strongest Ningaloo Niños in 2000 and 2011 are unprecedented compound events, where long-lasting high temperatures are accompanied by extreme freshening, which emerges in association with La Niñas, that is more common and persistent during the negative phase of the interdecadal Pacific oscillation. It is shown that Ningaloo Niños during La Niña phases have a distinctively deeper reach and are associated with a strengthening of the Leeuwin Current, while events during El Niño are limited to the surface layer temperatures, likely driven by local atmosphere–ocean feedbacks, without a clear imprint on salinity and velocity.

The Effect of Anthropogenic Aerosols on the Aleutian Low

AbstractPast studies have suggested that regional trends in anthropogenic aerosols can influence the Pacific decadal oscillation (PDO) through modulation of the Aleutian low. However, the robustness of this connection is debated. This study analyzes changes to the Aleutian low in an ensemble of climate models forced with large, idealized global and regional black carbon (BC) and sulfate aerosol perturbations. To isolate the role of ocean feedbacks, the experiments are performed with an interactive ocean and with prescribed sea surface temperatures. The results show a robust weakening of the Aleutian low forced by a global tenfold increase in BC in both experiment configurations. A linearized steady-state primitive equation model is forced with diabatic heating anomalies to investigate the mechanisms through which heating from BC emissions influences the Aleutian low. The heating from BC absorption over India and East Asia generates Rossby wave trains that propagate into the North Pacific sector, forming an upper-tropospheric ridge. Sources of BC outside of East Asia enhance the weakening of the Aleutian low. The responses to a global fivefold and regional tenfold increase in sulfate aerosols over Asia show poor consistency across climate models, with a multimodel mean response that does not project strongly onto the Aleutian low. These findings for a large, idealized step increase in regional sulfate aerosol differ from previous studies that suggest the transient increase in sulfate aerosols over Asia during the early twenty-first century weakened the Aleutian low and induced a transition to a negative PDO phase.

Assessment of Ocean-Atmosphere Interactions for the Boreal Summer Intraseasonal Oscillations in CMIP5 Models over the Indian Monsoon Region

The boreal summer intraseasonal oscillations (BSISO) are the prominent features of South Asian summer monsoon and mainly governed by the internal atmospheric dynamics and air-sea interactions. The present study aims to understand and evaluate the relationship between the convection and the associated air-sea interactions during the BSISO over the Indian monsoon region. To accomplish this, the present study utilizes observations and the 22 general circulation model (GCM) simulations from the Coupled Model Intercomparison Project Phase 5 (CMIP5). Representation of Indian monsoon season rainfall, sea surface temperature (SST) and latent heat fluxes in CMIP5 models such as climatological and intraseasonal are assessed using Global Precipitation Climatology Project rainfall by Taylor diagram metric. Results suggest that the majority of CMIP5 models simulated the northward propagation of precipitation and zonal wind at 850 hPa. However, models bias of BSISO variance shows significant spatial heterogeneity over the regions of the Arabian Sea (AS), Sub-Continent of India (SCI) and Bay of Bengal (BoB). The CMIP5 model which shows large biases in the mean state is degrading the northward propagation of BSISO. The phase relationship of ocean (land) and atmospheric interactions are diagnosed with lead-lag regression analysis. On ISO timescales over north Indian Ocean (NIO) convection leads the turbulent fluxes and westerly winds by a week. However, the majority of the models shows large uncertainty to represent this prominent feature over AS and SCI. Further, improper representation of the lead-lag relationship of SST and precipitation on ISO scales over the AS, BoB, and NIO in the CMIP5 models are attributing for significant bias variances. The present study advocates that BSISO propagation in CMIP5 models is mainly attributing from the internal atmospheric dynamics and air-sea interactions. However, for the realistic amplitude simulation of BSISO, proper representation of air-sea feedback mechanisms is crucial in CMIP5 models. The present study further suggests that the oceanic feedback processes of the CMIP5 models need to be improved for the accurate prediction of the intraseasonal variations.

Reevaluating the impacts of oceanic vertical resolution on the simulation of Madden–Julian Oscillation eastward propagation in a climate system model

The upper ocean plays a critical role in determining the Madden–Julian Oscillation (MJO) characteristics through modulating the tropical atmosphere–ocean interaction. By increasing the oceanic vertical resolution, its impacts on the MJO eastward propagation are discussed in this study by using a climate system model. With a refined vertical resolution in the upper ocean, warmer surface ocean and shallower mixed layer depth are produced in the tropics, which induces associated atmospheric changes as the response to the ocean feedbacks. Enhanced November–April-mean vertically-integrated specific humidity is found around the equatorial region with the increased vertical resolution, which strengthens the zonal and meridional moisture gradients. The lead-lag correlation of MJO precipitation demonstrates that the simulated MJO eastward propagation is improved with increased oceanic vertical resolution by improving the simulations of convective instability at the east of the MJO convective center, the boundary layer moisture convergence, the low- and upper-level circulation, and the vertical structure of equivalent potential temperature and diabatic heating. Moreover, the zonal asymmetry of the tendency of specific humidity is also improved by increasing the oceanic vertical resolution. The vertically-integrated moisture budget analysis is applied to further investigate the dominance of the moistening and drying processes. Results reveal that the drying processes are successfully reproduced over the central Indian Ocean in the case of increased oceanic vertical resolution, whilst the moistening processes are not well captured over the Maritime Continent and the MJO “detour” region. It suggests that additional modifications are needed to further improve the MJO simulation.

Volcanism and global plague pandemics: Towards an interdisciplinary synthesis

Understanding the prevalence and dissemination of bacterial pathogens such as Yersinia pestis, the bacterial agent of plague, is key to identifying the origins and demographic impact of historic pandemic episodes and mitigating future risk. Climate may influence the spread of Yersinia pestis through impact upon bacterial, vector, and rodent host populations prior to human infection. Large climate-forcing volcanic eruptions have the potential to influence global climate for several years following the eruption with evidence increasingly suggesting that, through oceanic feedback mechanisms, some eruptions can influence climate for decades to centuries. This article assesses the potential mechanistic links between some of the largest volcanic eruptions of the Common Era and the three recorded plague pandemics. The article uses proxy records of climate and volcanic forcing along with historic data to suggest mechanisms by which each of the pandemic episodes may have been influenced by volcanism. Commonalities between the pandemic episodes are surprisingly rare, but it is suggested that the influence of volcanism on climate may be an important factor and may aid in understanding the complex array of factors which caused plague pandemics.

Changes to the Madden‐Julian Oscillation in Coupled and Uncoupled Aquaplanet Simulations With 4xCO2

AbstractThe impacts of rising carbon dioxide (CO2) concentration and ocean feedbacks on the Madden‐Julian Oscillation (MJO) are investigated with the Community Atmospheric Model Version 5 (CAM5) in an idealized aquaplanet configuration. The climate response associated with quadrupled CO2 concentrations and sea surface temperature (SST) warming are examined in both the uncoupled CAM5 and a version coupled to a slab ocean model. Increasing CO2 concentrations while holding SST fixed produces only small impacts to MJO characteristics, while the SST change resulting from increased CO2 concentrations produces a significant increase in MJO precipitation anomaly amplitude but smaller increase in MJO circulation anomaly amplitude, consistent with previous studies. MJO propagation speed increases in both coupled simulations with quadrupling of CO2 and uncoupled simulations with the same climatological surface temperature warming imposed, although propagation speed is increased more with coupling. While climatological SST changes are identical between coupled and uncoupled runs, other aspects of the basic state such as zonal winds do not change identically. For example, climate warming produces stronger superrotation and weaker mean lower tropospheric easterlies in the coupled run, which contributes to greater increases in MJO eastward propagation speed with warming through its effect on moisture advection. The column process, representing the sum of vertical moist static energy (MSE) advection and radiative heating anomalies, also supports faster eastward propagation with warming in the coupled run. How differing basic states between coupled and uncoupled runs contribute to this behavior is discussed in more detail.

Investigating the impact of atmosphere–wave–ocean interactions on a Mediterranean tropical-like cyclone

Understanding the governing mechanisms of atmosphere–wave–ocean​ interactions is critical for unravelling the formation and evolution mechanisms of severe weather phenomena. This study aims at investigating the effects of atmosphere–wave–ocean​ feedbacks on a Mediterranean tropical-like cyclone (medicane), occurred on 27–30 September 2018 at the central-eastern Mediterranean Sea and characterized by severe environmental and socioeconomic impact. To unveil the interactions across the air–sea interface, the medicane was simulated by an integrated modelling system consisting of the Chemical Hydrological Atmospheric Ocean wave System (CHAOS), upgraded by embedding to it the Nucleus for European Modelling of the Ocean (NEMO) as ocean circulation component. Coupled simulations revealed that air–seaheat transfer and Ekman pumping, bringing sub-surface cold waters in upper ocean layers (upwelling), caused SST cooling (∼2–3 °C). SST cooling triggered a negative feedback loop procedure tending to balance between atmospheric and ocean processes. It also attenuated the cyclone and, subsequently, reduced the atmospheric energy embedded in ocean through the upper ocean vertical stratification weakening, thus, upper ocean vertical mixing, upwelling and SST cooling. The waves adjusted this feedback loop making the system more resistant in air–sea flux variations. Waves additionally weakened the cyclone not only due to the kinetic energy loss in the lower-atmosphere but also due to the enhancement of SST cooling which is attributed to the strengthening of Ekman pumping and vertical mixing, forced by wind stress increase. Nevertheless, waves partially balanced the air–wave–sea exchanges through the slight enthalpy flux gain under high wind conditions which is explained by considering the increase of enthalpy transfer coefficient in rougher sea areas.

Dynamics and oceanic response of the Madeira tip‐jets

AbstractMadeira island is a well‐known source of atmospheric and oceanic eddy activity, with relevant downstream impact in both media. Previous studies focused on the dynamics of the island wake environment, suggesting the relevance of different atmosphere–ocean interactions in its maintenance. Here, results from one summer (two months) of fully coupled atmosphere–ocean high‐resolution simulations are used to explore such interactions and to further understand the dynamics of Madeira's wake. Those results, validated against available in situ and remote‐sensing data, indicate that the atmospheric and ocean circulations near Madeira are dominated by the variability of two quasi‐permanent features, its tip‐jets, and more so by the variability of its eastern jet. While both jets are of comparable magnitude and present similar intraseasonal variability at the multi‐week time‐scale, they are associated with qualitatively different forcing. The jets dominate the atmosphere forcing over the upper ocean, leading to enhanced mixing and deeper mixed‐layer depth. Oceanic eddies are more frequent in the east jet region, as shedding anticyclones, confirming observational evidence. A comparison with a similar one‐way coupled atmospheric simulation indicates that atmosphere–ocean feedbacks are relevant to the coastal surface temperature.

The role of oceanic feedbacks in the 2014–2016 El Niño events as derived from ocean reanalysis data

Why did the predicted “super El Nino” fade out in the summer 2014 and the following year develop into one of the three strongest El Nino on record? Although some hypotheses have been proposed in previous studies, the quantitative contribution of oceanic processes to these events remains unclear. We investigated the role of various oceanic feedbacks, especially in response to intra-seasonal westerly wind busts, in the evolution of the 2014–2016 El Nino events, through a detailed heat budget analysis using high temporal resolution Estimating the Circulation and Climate of the Ocean—Phase II (ECCO2) simulation outputs and satellite-based observations. Results show that the Ekman feedback and zonal advective feedback were the two dominant oceanic processes in the developing phase of the warm event in the spring of 2014 and its decay in June. In the 2015–2016 super El Nino event, the zonal advective feedback and thermocline feedback played a significant role in the eastern Pacific warming. Moreover, the thermocline feedback tended to weaken in the central Pacific where the zonal advection feedback became the dominant positive feedback.

Effects of Model Coupling on Typhoon Kalmaegi (2014) Simulation in the South China Sea

Typhoon Kalmaegi (2014) in the South China Sea (SCS) is simulated using a fully coupled atmosphere–ocean–wave model (COAWST). A set of sensitivity experiments are conducted to investigate the effects of different model coupling combinations on the typhoon simulation. Model results are validated by employing in-situ data at four locations in the SCS, and best-track and satellite data. Correlation and root-mean-square difference are used to assess the simulation quality. A skill score system is defined from these two statistical criteria to evaluate the performance of model experiments relative to a baseline. Atmosphere–ocean feedback is crucial for accurate simulations. Our baseline experiment successfully reconstructs the atmospheric and oceanic conditions during Typhoon Kalmaegi. Typhoon-induced sea surface cooling that weakens the system due to less heat and moisture availability is captured best in a Regional Ocean Modeling System (ROMS)-coupled run. The Simulated Wave Nearshore (SWAN)-coupled run has demonstrated the ability to estimate sea surface roughness better. Intense winds lead to a larger surface roughness where more heat and momentum are exchanged, while the rougher surface causes more friction, slowing down surface winds. From our experiments, we show that these intricate interactions require a fully coupled Weather Research and Forecasting (WRF)–ROMS–SWAN model to best reproduce the environment during a typhoon.

Nonlinear Impacts of Surface Exchange Coefficient Uncertainty on Tropical Cyclone Intensity and Air‐Sea Interactions

AbstractTropical cyclone maximum intensity is believed to result from a balance between the surface friction, which removes energy, and a temperature/moisture (enthalpy) difference between the sea surface and the air above it, which adds energy. The competing processes near the air‐sea interface are controlled by both the near surface wind speed and the surface momentum (Cd) and enthalpy (Ck) exchange coefficients. Unfortunately, these coefficients are currently highly uncertain at high wind speeds. Tropical cyclone winds also apply a force on the ocean surface, which results in ocean surface cooling through vertical mixing. Using coupled atmosphere‐ocean and uncoupled (atmosphere only) ensemble simulations we explore the complex influence of uncertain surface exchange coefficients on storm‐induced ocean feedback and tropical cyclone intensity. We find that the magnitude of ocean cooling increases with storm intensity and Cd. Additionally, the simulated maximum wind speed uncertainty does not necessarily decrease when ocean feedback are considered.