Atmospheric Forcing Research Articles

A hybrid statistical–dynamical framework for compound coastal flooding analysis

Abstract Compound coastal flooding due to astronomic, atmospheric, oceanographic, and hydrologic forcings poses severe threats to coastal communities. While physics-driven approaches are able to dynamically simulate temporally and spatially varying compound flooding generated by multiple partially correlated drivers, computational burdens limit their capability to explore the full range of conditions that contribute to compound coastal hazards. Data-driven statistical approaches address some of these computational challenges, however they are also unable to explore all possible forcing combinations due to short observational records, and projections are typically limited to a few locations. This study proposes a hybrid statistical-dynamical framework for compound coastal flooding analysis that integrates a stochastic generator of compound flooding drivers, a hydrodynamic model, and a machine learning-based surrogate model. The framework is demonstrated in San Francisco (SF) Bay over the past 500 years with high accuracy and computational efficiency. The stochastic generator of compound flooding drivers is developed by coupling a sea surface temperature (SST) reconstruction model with a climate emulator, weather generator, and hydrologic model. Using reconstructed SSTs as input, the generator of compound flooding drivers is employed to simulate time series of the forcing factors contributing to compound flooding in SF Bay. A process-based hydrodynamic model is built to predict total water levels (TWLs) varying in time and space throughout SF Bay based on the stochastically generated drivers. A machine learning-based surrogate model is then developed from a relatively small library of hydrodynamic model simulations to efficiently predict water levels (WLs) for compound flooding analysis under the full range of stochastic drivers. This study contributes a hybrid statistical-dynamical framework to better understand the spatial distribution and temporal evolution of compound coastal flooding, along with the relative contributions of the forcing drivers in complex nearshore, estuarine, and river environments for centennial timescales under past, present, and future climates.

The Sea of Azov’s Hydrodynamic Response to Different Atmospheric Forcing Resolutions

This article is devoted to the analysis of the simulated meteorological and hydrodynamic characteristics of the Sea of Azov using the WRF (Weather Research and Forecasting) model and INMOM (Institute of Numerical Mathematics Ocean Model). The goal is to investigate the sea’s response to atmospheric forcing using two different horizontal resolutions. A comparison of the atmospheric simulation results with available meteorological in situ data from the land-based hydrometeorological stations (HMSs) did not reveal any significant differences between the simulations with different atmospheric forcing resolutions. A spatiotemporal analysis of the WRF model and INMOM results showed the most prominent differences along the entire coastal zone, especially in Taganrog Bay, along the spits in the north part of the sea, and in the Kerch Strait. Here, the wind speed obtained at a high spatial resolution (3.3 km) was ~10–15% higher than that obtained at a coarse resolution (10 km), and the surface and bottom currents were up to ~40% and ~15% higher. In marine coastal zones, the greatest differences were noted in a band of ~5 km, and differences in the rest of the Sea of Azov were negligible. An analysis of the bottom current speed revealed the presence of a counter-current flowing into Taganrog Bay. This shows the necessity of using three-dimensional marine circulation models to study the Sea of Azov’s dynamics.

Regional modelling of extreme sea levels induced by hurricanes

Abstract. Coastal zones are increasingly threatened by extreme sea level events, with storm surges being among the most hazardous components, especially in regions prone to tropical cyclones. This study aims to explore the factors influencing the performance of numerical models in simulating storm surges in the tropical Atlantic region. The maxima, durations, and time evolutions of extreme storm surge events are evaluated for four historical hurricanes against tide gauge records. The Advanced Circulation (ADCIRC) and Nucleus for European Modelling of the Ocean (NEMO) ocean models are compared using similar configurations in terms of domain, bathymetry, and spatial resolution. These models are then used to perform sensitivity experiments on oceanic and atmospheric forcings, physical parameterizations of wind stress, and baroclinic/barotropic modes. NEMO and ADCIRC demonstrate similar abilities in simulating storm surges induced by hurricanes. Storm surges simulated with ERA5 atmospheric reanalysis forcing are generally more accurate than those simulated with parametric wind models for the simulated hurricanes. The inclusion of baroclinic processes improves storm surge amplitudes at some coastal locations, such as along the southeastern Florida peninsula (USA). However, experiments exploring different implementations of wind stress and interactions among storm surges, tides, and mean sea level have shown minimal impacts on hurricane-induced storm surges.

Computing Method Applied for Simulation and Forecast of Hydrophysical Fields in the Southeastern Black Sea

In this paper, a numerical regional model of the Black Sea hydrodynamics with a spatial resolution of 1 km is applied to simulate and forecast the mesoscale circulation and thermohaline structure in the southeastern part of the Black Sea. The regional model is based on a nonlinear nonstationary system of differential equations in z coordinates, describing the evolution of three-dimensional fields of currents, temperature, salinity, and density. The solution of the equation system is based on the use of finite-difference methods, in particular, on the method of multicomponent splitting of the differential operator of the original problem into simpler operators. To illustrate the implementation of the numerical model, the paper presents the calculated fields of flow, temperature, and salinity for the summer season of 2020 under real atmospheric forcing derived from the atmospheric model SCIRON. The influence of basin-scale processes on regional processes was taken into account by boundary conditions on the liquid boundary separating the regional area from the open part of the sea basin. A comparison of the forecast results with available satellite data shows that the model reproduces well the basic peculiarities of hydrophysical fields.

Development of a daily coastal ocean model for Mississippi Sound and Bight

The Mississippi Sound and Bight is a complex coastal system with shallow estuarine waters that are highly vulnerable to the effects of climate change and anthropogenic influences. In order to further our understanding of the system and provide natural resource managers and decision-makers with science-based guidance, a pre-operational coastal ocean forecast system has been developed using the Coupled Ocean Atmosphere Wave Sediment Transport Modeling System (COAWST). The COAWST application for Mississippi Bight (msbCOAWST) can be run in hindcast mode, pre-operational near real-time mode, or forecast mode and relies on other operational models including the National Water Model (NWM) for river forcing, the High Resolution Rapid Refresh model (HRRR) for atmospheric forcing, and the Navy Coastal Ocean Model (NCOM) for open ocean boundary forcing. msbCOAWST is being validated using data from a variety of in situ measurements that quantify coastal processes, including tides and water quality parameters (i.e. temperature and salinity). The highest model skill is obtained for temperature followed by water levels and salinity. msbCOAWST has been used to provide guidance for quantifying how freshwater influences derived from river diversion operations impact water quality in estuarine waters. While the model is initially developed to study water quality and circulation in pre-operational near real-time and forecast modes, it is currently being extended to include waves, sediment transport, and biogeochemistry and also linked with habitat suitability models and ecological models in hindcast mode so as to comprehensively reveal consequential environmental concerns due to the onset and persistence of hypoxia, seasonal and storm-induced waves with their associated impacts on the region’s fisheries and shellfisheries.

Emission location affects impacts on atmosphere and climate from alternative fuels for Norwegian domestic aviation

Aviation emissions contribute to climate change and local air pollution, with important contributions from non-CO2 emissions. These exhibit diverse impacts on atmospheric chemistry and radiative forcing (RF), varying with location, altitude, and time. Assessments of local mitigation strategies with global emission metrics may overlook this variability, but detailed studies of aviation emissions in areas smaller than continents are scarce. Integrating the AviTeam emission model and OsloCTM3, we quantify CO2, NOx, BC, OC, and SOx emissions, tropospheric concentration changes, RF, region-specific metrics, and assess alternative fuels for Norwegian domestic aviation. Mitigation potentials for a fuel switch to LH2 differ by up to 3.1×108kgCO2-equivalents (GWP20) when using region-specific compared to global metrics. These differences result from a lower, region-specific contribution of non-CO2 emissions, particularly related to NOx. This study underscores the importance of accounting for non-CO2 variability in regional assessments, whether through region-specific metrics or advanced atmospheric modelling techniques.

Investigations on Stubble-Burning Aerosols over a Rural Location Using Ground-Based, Model, and Spaceborne Data

Agriculture crop residue burning has become a major environmental problem facing the Indo-Gangetic plain, as well as contributing to global warming. This paper reports the results of a comprehensive study, examining the variations in aerosol optical, microphysical, and radiative properties that occur during biomass-burning events at Amity University Haryana (AUH), at a rural station in Gurugram (Latitude: 28.31° N, Longitude: 76.90° E, 285 m AMSL), employing ground-based observations of AERONET and Aethalometer, as well as satellite and model simulations during 7–16 November 2021. The smoke emissions during the burning events enhanced the aerosol optical depth (AOD) and increased the Angstrom exponent (AE), suggesting the dominance of fine-mode aerosols. A smoke event that affected the study region on 11 November 2021 is simulated using the regional NAAPS model to assess the role of smoke in regional aerosol loading that caused an atmospheric forcing of 230.4 W/m2. The higher values of BC (black carbon) and BB (biomass burning), and lower values of AAE (absorption Angstrom exponent) are also observed during the peak intensity of the smoke-event period. A notable layer of smoke has been observed, extending from the surface up to an altitude of approximately 3 km. In addition, the observations gathered from CALIPSO regarding the vertical profiles of aerosols show a qualitative agreement with the values obtained from AERONET observations. Further, the smoke plumes that arose due to transport of a wide-spread agricultural crop residue burning are observed nationwide, as shown by MODIS imagery, and HYSPLIT back trajectories. Thus, the present study highlights that the smoke aerosol emissions during crop residue burning occasions play a critical role in the local/regional aerosol microphysical and radiation properties, and hence in the climate variability.

Evaluation of sea surface temperature from ocean reanalysis products over the North Indian Ocean

Ocean and sea ice reanalyses (ORAs or ocean syntheses) are reconstructions of the ocean and sea ice states using an ocean model integration constrained by atmospheric surface forcing and ocean observations via a data assimilation method. Ocean reanalyses are a valuable tool for monitoring and understanding long-term ocean variability at depth, mainly because this part of the ocean is still largely unobserved. Sea surface temperature (SST) is the key variable that drives the air–sea interaction process on different time scales. Despite improvements in model and reanalysis schemes, ocean reanalyses show errors when evaluated with independent observations. The independent evaluation studies of SST from ocean reanalysis over the Indian Ocean are limited. In this study, we evaluated the SST from 10 reanalysis products (ECCO, BRAN, SODA, NCEP-GODAS, GODAS-MOM4p1, ORAS5, CGLORS, GLORYS2V4, GLOSEA, and GREP) and five synthetic observation products (COBE, ERSST, OISST, OSTIA, and HadISST) and from the pure observation-based product AMSR2 for 2012–2017 with 12 in-situ buoy observations (OMNI) over the Arabian Sea and Bay of Bengal. Even though the reanalysis and observational products perform very well in the open ocean, the performance is poorer near the coast and islands. The reanalysis products perform comparatively better than most of the observational products. COBE and OISST perform better among the synthetic observational products in the northern Indian Ocean. GODAS-MOM4p1 and GREP performs best among the reanalysis products, often surpassing the observational products. ECCO shows poorer performance and higher bias in the Bay of Bengal. Comparing the BRAN daily and monthly SST, the monthly SST performance of reanalysis is better than the daily time scale.

Characterizing Model Uncertainties in Simulated Coast-to-Offshore Wind over the Northeast U.S. Using Multi-platform Measurements from the TCAP Field Campaign

Numerical weather prediction models, such as the Weather Research and Forecasting model, are widely used to provide estimates of the offshore wind energy resource owing to their large spatial coverage compared to available observations. Nevertheless, spatiotemporal distribution of model biases is highly dependent on factors including model configuration, location, and the interplay of multiscale physical processes. Here we focus on the characterization of model uncertainties in simulated coast-to-offshore winds over the northeast United States by varying sea surface temperature (SST) forcings and surface layer (SL) and planetary boundary layer (PBL) parameterizations, as well as identifying biases that may be directly passed from initial and boundary conditions. Multiple measurements, including aircraft data collected during the U.S. Department of Energy's Two-Column Aerosol Project experiment, are used to constrain the model results, and facilitate quantitative comparisons. Our analysis indicates that while SST forcing has notable impacts on simulated air temperature and moisture within PBL, the modeled winds are in general more sensitive to the choices of SL and PBL physics than to SST. The model’s forcing data not only controls the vertical dependence of wind speed errors, but also alters regional variability in the wind speed’s spatial correlation, which underscores the impact of initial and boundary conditions on simulated winds. Coastal and offshore near-surface wind speed biases tend to exhibit much higher similarity in winter than in summer due to the presence of much stronger and more persistent synoptic wind conditions. This study highlights the importance of accurate atmospheric forcing and parameterization choices in improving wind forecasts and suggests the potential for extrapolating coastal wind biases to offshore locations, aiding wind energy forecasting and informing the third Wind Forecast Improvement Project.

Influence of Lower Atmospheric Variability: An Investigation of Delayed Ionospheric Response to Solar Activity

AbstractThis study aims to examine the impact of lower atmospheric forcing on upper atmospheric variability using the Thermosphere‐Ionosphere‐Electrodynamics General Circulation Model (TIEGCM). We conducted numerical experiments comparing induced variability due to Hough Mode Extension (HME) tides constrained by winds and temperatures from Ionospheric Connection Explorer‐Michelson Interferometer for Global High‐Resolution Thermospheric Imaging (ICON‐MIGHTI) observations. Our model comparisons focus on the changes in the composition of the thermosphere‐ionosphere and the delayed ionospheric response to the 27‐day solar EUV flux variations during periods of low solar activity. We report the results of model simulations with and without tidal forcing at the approximate 97 km lower boundary of the TIEGCM. The differences led to changes in thermosphere‐ionosphere parameters such as electron density, peak electron density, and the ratio. The results show that the impact of tidal forcing is mainly observed in the low‐ and mid‐latitude regions, affecting the correlation between and NmF2. This change in correlation affects the amount of ionospheric delay. When tidal forcing is included, the modeled delay improves compared to the observed delay during low solar activity. The spatial variation of ionospheric delay due to induced tidal effects highlights the importance of understanding lower atmospheric forcing in thermosphere‐ionosphere models. This is crucial for predicting and understanding the ionospheric response to solar flux.

Subpolar North Atlantic Mean State Affects the Response of the Atlantic Meridional Overturning Circulation to the North Atlantic Oscillation in CMIP6 Models

Abstract The Atlantic meridional overturning circulation (AMOC) plays an important role in climate, transporting heat and salt to the subpolar North Atlantic. The AMOC’s variability is sensitive to atmospheric forcing, especially the North Atlantic Oscillation (NAO). Because AMOC observations are short, climate models are a valuable tool to study the AMOC’s variability. Yet, there are known issues with climate models, like uncertainties and systematic biases. To investigate this, preindustrial control experiments from models participating in the phase 6 of Coupled Model Intercomparison Project (CMIP6) are evaluated. There is a large, but correlated, spread in the models’ subpolar gyre mean surface temperature and salinity. By splitting models into groups of either a warm–salty or cold–fresh subpolar gyre, it is shown that warm–salty models have a lower sea ice cover in the Labrador Sea and, hence, enable a larger heat loss during a positive NAO. Stratification in the Labrador Sea is also weaker in warm–salty models, such that the larger NAO-related heat loss can also affect greater depths. As a result, subsurface density anomalies are much stronger in the warm–salty models than in those that tend to be cold and fresh. As these anomalies propagate southward along the western boundary, they establish a zonal density gradient anomaly that promotes a stronger delayed AMOC response to the NAO in the warm–salty models. These findings demonstrate how model mean state errors are linked across variables and affect variability, emphasizing the need for improvement of the subpolar North Atlantic mean states in models.

On the Inverse Correlation Between the Thermosphere Winter Helium Bulge and Solar Activity: Impact of Gravity Wave Drag From the Mesosphere

AbstractUnderstanding the temporal and spatial variations in the ideal inert tracer helium can provide insight into the dynamic evolution of the thermosphere. The magnitude of the thermospheric winter helium bulge was inversely correlated with the level of solar activity. However, this feature has been found to be not reproduced by the Thermosphere‐Ionosphere Electrodynamic General Circulation Model (TIEGCM), and the associated physical mechanisms remain unknown. Using the Thermosphere‐Ionosphere‐Mesosphere Electrodynamic General Circulation Model (TIME‐GCM), we found that mesospheric gravity wave drag (GWD) is a factor contributing to this inverse correlation. Specifically, the summer‐to‐winter circulation in thermosphere becomes the main cause of the helium bulge, as mesospheric GWD can play a role in strengthening this circulation. The GWD contributions to temperature change below the lower thermosphere do not depend prominently on solar activity. However, because the temperature impacts on the pressure gradient force are height‐integrated according to the background temperature of the neutral gas, the higher background temperature in the thermosphere at the solar maximum corresponds to a relatively weaker response in pressure gradient force in the thermosphere. Therefore, the response of the thermospheric circulation that might be expected to accompany increasing solar activity is suppressed due to the influence of mesospheric GWD, which results in a decrease in the magnitude of the winter helium bulge with increasing solar activity. Thus, our results demonstrated that lower atmosphere forcing can play a significant role in the response of thermospheric helium to solar activity.

Competing effects of wind and buoyancy forcing on ocean oxygen trends in recent decades

Ocean deoxygenation is becoming a major stressor for marine ecosystems due to anthropogenic climate change. Two major pathways through which climate change affects ocean oxygen are changes in wind fields and changes in air-sea heat and freshwater fluxes. Here, we use a global ocean biogeochemistry model run under historical atmospheric forcing to show that wind stress is the dominant driver of year-to-year oxygen variability in most ocean regions. Only in areas of water mass formation do air-sea heat and freshwater fluxes dominate year-to-year oxygen dynamics. The deoxygenation since the late 1960s has been driven mainly by changes in air-sea heat and freshwater fluxes. Part of this deoxygenation has been mitigated by wind-driven increases in ventilation and interior oxygen supply, mainly in the Southern Ocean. The predicted slowdown in wind stress intensification, combined with continued ocean warming, may therefore greatly accelerate ocean deoxygenation in the coming decades. The fact that the model used here, along with many state-of-the-art forced ocean models, underestimates recent ocean deoxygenation indicates the need to use forcing fields that better represent pre-industrial conditions during their spin-up.

A drop in Antarctic sea ice extent at the end of the 1970s

After a period of relative stability, the Antarctic sea ice extent has abruptly decreased in 2016 and has remained low since then. Both atmospheric and oceanic processes likely contributed to this drop but many questions remain regarding the underlying dynamics and it is unknown if this drop is unprecedented. Here we produce a new multi-variate spatial reconstruction covering 1958–2023 and show that a similar drop in sea ice extent occurred at the end of the 1970s, albeit with a smaller magnitude. Both drops show similar spatial patterns, with a higher sea ice loss in the East Antarctic sector than in the West Antarctic sector where the variability is strongly modulated by wind-driven changes. The ocean integrates the atmospheric forcing and provides memory that amplifies the magnitude of both drops.

Marine heatwaves suppress ocean circulation and large vortices in the Gulf of Alaska

Large-scale anticyclonic vortices forming along the Gulf of Alaska continental slope serve as fertile ecosystems for marine life, significantly shaping the distribution of primary productivity, with 40–80% of the gulf’s open ocean surface chlorophyll-a concentrated in their cores. Between 2013 and 2023, Alaska experienced some of the largest and longest marine heatwaves ever recorded in the world’s oceans, persistently altering its ecosystem and fisheries. Here, using 30 years of satellite and reanalysis data, we find that the coastal upwelling atmospheric forcing conditions associated with the heatwaves have also significantly suppressed the Gulf of Alaska’s ocean circulation and the formation of large anticyclones. Climate model simulations spanning from 1850 to 2100 suggest that future changes in the Aleutian Low pressure system will lead to a 60% increase in upwelling extremes (>2 standard deviations), further weakening the ocean anticyclones. However, large uncertainties remain in the mechanisms controlling the Aleutian Low’s response to climate forcing in the models.

Early emergence and determinants of human-induced Walker circulation weakening

The Walker circulation is projected to slow down in response to greenhouse gas warming. However, detecting the impact of human activities on changes in the Walker circulation is challenging due to the significant influence of internal variability. Here, based on ensembles of multiple climate models from the Coupled Model Intercomparison Project Phase 6 (CMIP6), we show evidence that the emergence of the human-induced weakening of Walker circulation tends to occur earlier in the middle-upper troposphere than at the surface. This earlier emergence is attributed to a more pronounced initial weakening response of the middle-upper tropospheric Walker circulation to atmospheric CO2 radiative forcing. We further reveal that the emergence time of a weaker Walker circulation varies across models. This intermodel spread is governed by an ocean thermostat that operates by modulating the zonal sea surface temperature gradient over the tropical Indo-Pacific region. Our findings address the key question of whether and how to detect human-induced large-scale atmospheric circulation changes and provide valuable insights for assessing the associated risks.

Enhanced eddy activity along the Subantarctic Front under intensified westerly winds

The westerlies in the southern hemisphere have intensified and shifted southward since the middle of the twentieth century. Previous studies have indicated that the expected increase in isopycnal slopes and acceleration of the Antarctic Circumpolar Current (ACC) is considerably weakened by the strengthening of mesoscale eddies and that this “eddy saturation” occurs mainly downstream of the major bottom topographic features such as the Kerguelen Plateau. Such eddy “hotspots” are thus considered to regulate the ACC responses to changes in external forcing. To improve our understanding of the ACC response to intensified winds, a sensitivity study is conducted using an eddy-resolving quasi-global ocean general circulation model named “OFES.” The reference run is driven by a climatological atmospheric forcing and the sensitivity run is driven by artificially intensified climatological westerlies. Our new finding is that the baroclinic energy pathway is enhanced over the Subantarctic Front (SAF) as well as over the hotspots identified by previous studies. A linear stability analysis indicates that the spin-up of the subtropical gyres north of the SAF and the enhanced Ekman upwelling south of the SAF by the intensified wind stress curl increase the vertical shear of zonal velocity along the SAF, enhancing baroclinic instability. We have also performed the same stability analysis comparing the 1985–2018 and 1955–1984 periods of a hindcast run of OFES, confirming the result from the climatological sensitivity study. These results suggest that the SAF is another eddy hotspot when the wind stress curl keeps increasing.

Прогноз толщины ледяного покрова в прибрежных областях Карского и Охотского морей

Based on the CICE viscoplastic sea ice model, the ice cover of the Gulf of Ob and the northwestern Okhotsk Sea was simulated for the winter seasons of 2021/2022, 2022/2023, and 2023/2024. The description of the seasonal variability of sea ice characteristics in these areas and examples of their numerical modeling are given. Using atmospheric forcing based on the WRF-ARW nonhydrostatic atmospheric model, the sea ice thickness in the northwestern Okhotsk Sea was predicted for April 2024. A comparison of the forecasts with the ice maps of the Hydrometcentre of Russia and sea ice thickness measurements at the Ayan and Bolshoy Shantar stations gave satisfactory results.

Wintertime atmospheric forcing of subtropical northeastern Pacific SST variability

Wintertime atmospheric forcing of subtropical northeastern Pacific SST variability

Molecular Insights into Gas-Particle Partitioning and Viscosity of Atmospheric Brown Carbon.

Biomass burning organic aerosol (BBOA), containing brown carbon chromophores, plays a critical role in atmospheric chemistry and climate forcing. However, the effects of evaporation on BBOA volatility and viscosity under different environmental conditions remain poorly understood. This study focuses on the molecular characterization of laboratory-generated BBOA proxies from wood pyrolysis emissions. The initial mixture, "pyrolysis oil (PO1)", was progressively evaporated to produce more concentrated mixtures (PO1.33, PO2, and PO3) with volume reduction factors of 1.33, 2, and 3, respectively. Chemical speciation and volatility were investigated using temperature-programmed desorption combined with direct analysis in real-time ionization and high-resolution mass spectrometry (TPD-DART-HRMS). This novel approach quantified saturation vapor pressures and enthalpies of individual species, enabling the construction of volatility basis set distributions and the quantification of gas-particle partitioning. Viscosity estimates, validated by poke-flow experiments, showed a significant increase with evaporation, slowing particle-phase diffusion and extending equilibration times. These findings suggest that highly viscous tar ball particles in aged biomass burning emissions form as semivolatile components evaporate. The study highlights the importance of evaporation processes in shaping BBOA properties, underscoring the need to incorporate these factors into atmospheric models for better predictions of BBOA aging and its environmental impact.