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Statistical models are an alternative to numerical models for reconstructing storm surges at a low computational cost. These models directly link surges to metocean variables, i.e., predictors such as atmospheric pressure, wind and waves. Such reconstructions usually underestimate extreme surges. Here, we explore how to reduce biases on extremes using two methods—multiple linear regressions and neural networks—for surge reconstructions. Models with different configurations are tested at 14 long-term tide gauges in the North-East Atlantic. We found that (1) using the wind stress rather than the wind speed as predictor reduces the bias on extremes. (2) Adding the significant wave height as a predictor can reduce biases on extremes at a few locations tested. (3) Building on these statistical models, we show that atmospheric reanalyses likely underestimate extremes over the 19th century. Finally, it is demonstrated that neural networks can effectively predict extreme surges without wind information, but considering the atmospheric pressure input extracted over a sufficiently large area around a given station. This last point may offer new insights into air-sea interaction studies and wind stress parametrization. [ABSTRACT FROM AUTHOR]

On December 8th, 2022, a meteotsunami caused significant damage to the southern beaches of Mar del Plata city, Argentina, and the Montevideo Port in Uruguay. The event was observed over a wide area, from Puerto Belgrano in the south of Buenos Aires Province, Argentina, to La Paloma, Uruguay, including locations in the upper Río de la Plata estuary. The meteotsunami was driven by a relatively long perturbation of the surface atmospheric pressure caused by the movement of an elongated high-pressure anomaly running parallel to a low-pressure system associated with an atmospheric frontal zone. The atmospheric perturbation propagated faster than the meteotsunami between Mar del Plata and Montevideo, but both velocities may have been similar between Mar del Plata and Santa Teresita, where the maximum meteotsunami wave height of 0.92 m was recorded, likely due to the Proudman resonance mechanism. The propagation direction of the front from SW to NE partially explains the negligible response of the water level on the Argentinean Río de la Plata coast, where observation sites are close to the shore from where the forcing originates, as well as the almost identical starting time of the water level activity in the upper Río de la Plata and the outer sector of the estuary. This event was different from other past events in the study region, as there was no evidence of atmospheric gravity wave propagation. One significant limitation in understanding the observed atmosphere–ocean interaction in the study region is the nonexistence of high-frequency atmospheric pressure data. [ABSTRACT FROM AUTHOR]

In recent decades, rise of sea surface temperature (SST) in the Kuroshio region of the East China Sea (ECS), which is associated with global warming, has attracted considerable attention. Despite its relevance to air‐sea interaction phenomena, the atmospheric consequences of this SST increase remain largely unexplored. Using the ERA5 reanalysis data set in conjunction with a moisture budget analysis, we found that during 1979–2022, warming in the ECS‐Kuroshio has contributed to the intensification of the East Asian Meiyu‐Baiu rainband in June. This intensification is attributed to augmented wind convergence in the low‐level free troposphere (950–700 hPa). Importantly, the atmospheric responses to ECS‐Kuroshio warming penetrated the deep troposphere (to approximately 300 hPa), suggesting an enhancement of deep convection. Furthermore, ECS‐Kuroshio warming likely strengthened the overlying atmospheric low pressure, resulting in wind convergence enhancement. The findings clarified the important role of the ECS‐Kuroshio in driving East Asian climate change amid global warming. Plain Language Summary: In response to global warming, East Asian summer precipitation is increasing along with an increase in extreme precipitation events, which poses a significant threat to agriculture and economic development. Understanding the mechanisms underlying the increased precipitation trend in East Asia is crucial for sustainable human development in this region. The findings of this study revealed that East Asian precipitation induced by the Meiyu‐Baiu rainband has intensified continuously during the past four decades, particularly in the marine areas around the East China Sea (ECS) and the south of Japan. We further established that the continuous increase in sea surface temperature over the Kuroshio in the ECS, which was related to global warming, strengthened the atmospheric low‐pressure system overlying the current, contributing to an increase in rainfall around the ECS. The findings of this study highlighted the important role of the Kuroshio Current in influencing climate change in East Asia. Key Points: The Meiyu‐Baiu rainband in June intensified over the marine areas around the Kuroshio and south of Japan during 1979–2022The intensified Meiyu‐Baiu rainband was caused mainly by the wind convergence accompanied by enhanced deep convectionKuroshio warming in the East China Sea likely intensified the Meiyu‐Baiu rainband by a pressure adjustment mechanism [ABSTRACT FROM AUTHOR]

Sea surface temperature (SST) is characterized by abundant warm and cold structures that influence the overlying atmospheric boundary layer dynamics through two different mechanisms. First, turbulence and large eddies in the lower troposphere are affected by atmospheric stability, which can be modified by local SST, resulting in enhanced vertical mixing and larger surface winds over warmer waters. Second, the thermodynamic adjustment of air density to the underlying SST structures and the subsequent changes in atmospheric pressure drive secondary circulations. This paper aims to disentangle the effects of these processes and explore the environmental conditions that favor them. Two main environmental variables are considered: the large-scale air–sea temperature difference (proxy for stability) and wind speed. Using 5 years of daily reanalyses data, we investigate the 10-m wind response to SST structures. Based on linear regression between wind divergence and SST derivatives, we show that both mechanisms operate over a large spectrum of conditions. Ten-meter wind divergence is strongly impacted by the local SST via its effect on vertical mixing for midwind regimes in slightly unstable to near-neutral conditions, whereas the secondary circulation is important in two distinct regimes: low wind speed with a slightly unstable air column and high background wind speed with a very unstable air column. The first regime is explained by the prolonged Lagrangian time that the air parcel stays over an SST structure while the second one is related to strong heat fluxes at the air–sea interface, which greatly modify the marine atmospheric boundary layer properties. Location and frequency of the environmentally favorable conditions are discussed, as well as the response in low-cloud cover and rainfall. Significance Statement: The main objective of this study is to explore the wind response to thermal structures at the sea surface under different environmental conditions using the latest atmospheric reanalysis. Recent literature suggests that fine-scale air–sea interactions affect a large spectrum of atmospheric dynamics, from seasonal to weather-type regimes. It is thus important to characterize the atmospheric response to ocean surface variability. Our findings describe the environmental conditions for which the two main physical processes through which the atmosphere responds to sea surface temperature structures are active the most and can guide the development of high-resolution observing missions and campaigns in specific geographical locations and seasons to retrieve data that can be used to improve parameterization in models. [ABSTRACT FROM AUTHOR]

This paper presents experimental observations to improve typhoon prediction accuracy and to understand interactions between atmosphere and ocean directly under typhoons. Two unmanned surface vehicles (Wave Gliders (WGs)) equipped with interchangeable sensors were sailed toward the path of an approaching Category 5 typhoon (Hinnamnor), which began on 29 August 2022 and subsided on 6 September, reaching a minimum pressure of 920 hPa and a maximum wind speed of 55 m/s (105 knots). Sensors on WGs measured atmospheric pressure, wind speed, atmospheric and seawater temperature, wave height, currents, salinity, and chlorophyll-a concentrations in different parts of the typhoon. These observations made it possible to clarify changes in various phenomena as the typhoon approached and to compare differences in storm characteristics measured by the two WGs. Sea surface pressure in the core of a typhoon is useful as an initial predictor of its intensity. Data assimilation into numerical models and other observations are expected to improve prediction accuracy of typhoon phenomena. Furthermore, simultaneous observations of atmosphere and ocean will also be useful for modeling interactions. [ABSTRACT FROM AUTHOR]

To advance the understanding of the interplay among clouds, convection, and circulation, and its role in climate change, the Elucidating the role of clouds–circulation coupling in climate campaign (EUREC 4 A) and Atlantic Tradewind Ocean–Atmosphere Mesoscale Interaction Campaign (ATOMIC) collected measurements in the western tropical Atlantic during January and February 2020. Upper-air radiosondes were launched regularly (usually 4-hourly) from a network consisting of the Barbados Cloud Observatory (BCO) and four ships within 6–16 ∘ N, 51–60 ∘ W. From 8 January to 19 February, a total of 811 radiosondes measured wind, temperature, and relative humidity. In addition to the ascent, the descent was recorded for 82 % of the soundings. The soundings sampled changes in atmospheric pressure, winds, lifting condensation level, boundary layer depth, and vertical distribution of moisture associated with different ocean surface conditions, synoptic variability, and mesoscale convective organization. Raw (Level 0), quality-controlled 1 s (Level 1), and vertically gridded (Level 2) data in NetCDF format are available to the public at AERIS (10.25326/137). The methods of data collection and post-processing for the radiosonde data set are described here. [ABSTRACT FROM AUTHOR]

Understanding the dynamics of the flow-dependent forecast error covariance across the air–sea interface is beneficial toward revealing the potential influences of strongly coupled data assimilation on tropical cyclone (TC) initialization in coupled models, and the fundamental dynamics associated with TC air–sea interactions. A 200-member ensemble of convection-permitting forecasts from a coupled atmosphere–ocean regional model is used to investigate the forecast error covariance across the oceanic and atmospheric domains during the rapid intensification of Hurricane Florence (2018). Forecast uncertainties in both atmospheric and oceanic domains, from an Eulerian perspective, increase with forecast lead time, mainly from TC displacement errors. In a storm-relative framework, the ensemble forecast uncertainties in both domains are predominantly caused by differences in the simulated storm intensity and structure. The largest ensemble spread in the atmospheric pressure, temperature, and wind fields can be found within the TC inner-core region. Alternatively, the largest ensemble spread in the upper-ocean currents and temperature fields are located along the cold wake behind the storm. Cross-domain ensemble correlations between simulated atmospheric (oceanic) observations and oceanic (atmospheric) state variables in the storm-relative coordinates are highly anisotropic, variable dependent, and ultimately driven by the dynamics of TC air–sea interactions. Meaningful and dynamically consistent cross-domain ensemble correlations suggest that it is possible to use atmospheric and oceanic observations to simultaneously update state variables associated with the coupled ocean–atmosphere prediction of TCs using strongly coupled data assimilation. Sensitivity experiments demonstrate that at least 60–80 ensemble members are required to represent physically consistent cross-domain correlations and minimize sampling errors. [ABSTRACT FROM AUTHOR]

Madden-Julian oscillation (MJO) is an atmospheric oscillation due to atmospheric phenomenon that occurs due to the uniformity of solar energy received at the surface of the earth, MJO is a natural occurrence in the seaatmosphere system. When the MJO is active, in general there will be a disturbance in the upper air which is then followed by an anomaly at sea surface pressure causing the changes in the wind on the surface. The changes in the surface wind affect the sea surface currents which then cause the occurrence of coastal upwelling downwelling. The upwelling process itself is a process whereby a sea mass is pushed upward along the continent, when the beach is to the left of the wind direction, the ecological transport leads to the mass of water away from the coast. As a result, there is a mass vacuum (divergence) in the coastal area. This mass void will be filled by the mass of water from the inner layer that moves to the surface. Indonesian territory itself is passed by MJO in phases 3, 4 and 5, while for Sumatra region is passed by MJO phase 3 and 4. This research aims to identify the propagation of coastal upwelling during MJO on the west coast of Sumatera, therefore the data of geopotential height, surface pressure sea (MSLP), zonal and meridional components and sea surface temperature are used to analyze how the MJO effect on the coastal upwelling occurs in the research area. The analysis was conducted in June, July and August by comparing the atmospheric conditions at the time of strong MJO in phases 3 and 4 with normal viewing of anomaly geopotential height and MSLP and then seeing the anomaly surface wind changes from zonal wind (u) and meridional wind (v) and changes in SST in Sumatra region. The result shows that there is a change of GH and MSLP when MJO passes the west coast of Sumatra and then follows the change in the value of u and v and SST to identify the upwelling, while the anomaly change negative SST does not occur when MJO is active but has time lag (lag). In this analysis it was found that SST anomaly occurs when the anomaly changes in both the upper and surface water occurring after 5 days in phases 3, 4 and 5. [ABSTRACT FROM AUTHOR]

Oceanic, nonisostatic responses to near 5-day Rossby-Haurwitz atmospheric pressure waves have been observed in open oceans; however, such responses based on observations in marginal seas such as the South China Sea have not been reported, owing to the limited ocean bottom pressure Pbot records. The Pbot measurements from pressure recording inverted echo sounders (PIESs) at sites in the northern South China Sea revealed a nonisostatic-like response near 5 days, although the coastal-trapped waves (CTWs) appeared to obscure it because their broadband periods include the near 5-day band. Cross-spectral analysis revealed that the PIES Pbot records and the sea level (SL) records of Hong Kong all correlate strongly with the atmospheric pressure and winds over the East China Sea. This is indicative of remotely forced CTWs. The PIES Pbot records showed higher coherence near 5 days with the zonal low-pass wavelength filters applied to the atmospheric pressure, and the phase analysis results strongly suggest nonisostatic oceanic responses to the westward-propagating Rossby-Haurwitz waves. Effective separation of CTWs and the nonisostatic responses from the Pbot records at the near 5-day period was achieved. The oceanic responses to the Rossby-Haurwitz waves in the northern South China Sea were nonisostatic; a 1-mbar change in air pressure resulted in a 1.58-mbar change in Pbot with a phase lag of 14.8°. The mean phase speed of CTWs from Hong Kong to station P3 was estimated to be 9.9 m s−1. [ABSTRACT FROM AUTHOR]

The impacts of El Niño-Southern Oscillation (ENSO) on the northwest Pacific (NWP) climate during ENSO decay summers are investigated based on the outputs of 37 coupled general circulation models (CGCMs) from phase 5 of the Coupled Model Intercomparison Project (CMIP5). Large intermodel spread exists in the 37 state-of-the-art CGCMs in simulating the ENSO-NWP relationship. Eight high-skill and eight low-skill models are selected to explore how the bias arises. By comparing the results among high-skill models, low-skill models, and observations, the simulation skill of the ENSO-NWP relationship largely depends on whether the model can reasonably reproduce the ENSO decay pace. Warm SST anomaly bias in the equatorial western Pacific (EWP) is found to persist into the ENSO decay summer in the low-skill models, obstructing the formation of an anomalous anticyclone in the NWP. Further analysis shows that the warm EWP SST anomaly bias is possibly related to the excessive westward extension of cold tongue in these models, which increases climatological zonal SST gradient in the EWP. Under westerly wind anomalies, the larger climatological zonal SST gradient could lead to warmer zonal advections in the low-skill models than that in the high-skill models, which could lead to warm EWP SST anomaly bias in the low-skill models. And the warm EWP SST anomaly bias could strengthen westerly wind anomalies over the western Pacific by triggering convection and atmospheric Rossby waves, which, in turn, could maintain the warm SST anomaly bias in the EWP. [ABSTRACT FROM AUTHOR]

El Niño-Southern Oscillation (ENSO) is the dominant mode of interannual variability in the tropical Pacific. However, the models in the ensemble from phase 5 of the Coupled Model Intercomparison Project (CMIP5) have large deficiencies in ENSO amplitude, spatial structure, and temporal variability. The use of stochastic parameterizations as a technique to address these pervasive errors is considered. The multiplicative stochastically perturbed parameterization tendencies (SPPT) scheme is included in coupled integrations of the National Center for Atmospheric Research (NCAR) Community Atmosphere Model, version 4 (CAM4). The SPPT scheme results in a significant improvement to the representation of ENSO in CAM4, improving the power spectrum and reducing the magnitude of ENSO toward that observed. To understand the observed impact, additive and multiplicative noise in a simple delayed oscillator (DO) model of ENSO is considered. Additive noise results in an increase in ENSO amplitude, but multiplicative noise can reduce the magnitude of ENSO, as was observed for SPPT in CAM4. In light of these results, two complementary mechanisms are proposed by which the improvement occurs in CAM. Comparison of the coupled runs with a set of atmosphere-only runs indicates that SPPT first improve the variability in the zonal winds through perturbing the convective heating tendencies, which improves the variability of ENSO. In addition, SPPT improve the distribution of westerly wind bursts (WWBs), important for initiation of El Niño events, by increasing the stochastic component of WWB and reducing the overly strong dependency on SST compared to the control integration. [ABSTRACT FROM AUTHOR]

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Characteristics of El Niño-Southern Oscillation (ENSO) have changed since the late 1970s as it synchronized with the Pacific Decadal Oscillation (PDO). In order to investigate the primary feedback process responsible for the interdecadal change in ENSO characteristics according to the PDO, using the ocean assimilation data (SODA) and the reanalysis data (NCEP/NCAR), we performed Bjerknes linear stability index (BJ index) analysis of two decadal periods: one before the late 1970s (the nPDO period) and the other after the late 1970s (the pPDO period). The BJ index for the pPDO period (−0.07 year for the growth rate of the eastern Pacific SST anomaly) is significantly larger than that for the nPDO period (−0.25 year). The larger BJ index value is primarily due to the enhanced zonal advection feedback (ZA; +0.44 year), thermocline feedback (TH; +0.33 year), and the reduced damping by the mean meridional current (MD; +0.16 year). The increases in ZA and TH are mainly attributed to the shoaling of the mean thermocline depth, which increased the sensitivity of the ocean dynamic fields to the wind forcing; and the reduced MD is related to the reduced mean meridional current associated with the weakened trade wind. The enhanced positive feedback is partly compensated by the enhanced thermodynamic damping including the shortwave, sensible heat flux and latent heat flux (collectively, −0.88 year). Interestingly, the change in air-sea coupling strength from the nPDO to the pPDO period was small. Without the two extreme El Niño events (1982-1983 and 1997-1998) in the pPDO period (pPDO_noBIG), the difference in BJ index between nPDO and pPDO_noBIG periods became smaller (~0.07 year), indicating that the two extreme El Niño events largely contribute to the larger ENSO variability of the pPDO period, possibly due to nonlinear feedback processes. Nevertheless, qualitative similarity in each of the feedback and damping components of BJ index exists between the pPDO and pPDO_noBIG periods, which suggests that the tropical climate states of the pPDO period provided more favorable conditions for the emergence of extreme El Niño events by intensifying the linear feedback processes. [ABSTRACT FROM AUTHOR]

Observations of ocean-atmosphere coupling across persistent mesoscale sea surface temperature (SST) gradients are used to examine the controls of atmospheric stability, pressure gradient force, and heat flux that are considered central to oft-observed coupling between wind and SST. Moored air-sea flux measurements near the Gulf Stream are combined with QuikSCAT satellite scatterometer equivalent neutral wind (ENW) data to assess correlations between SST, air-sea fluxes, pressure, and wind perturbations at scales of 10-100 days. The net effect of ocean fronts meandering past the site enabled buoy observation of SST impacts on wind, with coupling coefficients of 0.3-0.5 similar to past studies. Wind stress-SST and ENW-SST correlation coefficients are slightly higher, and roughly 20% of the ENW perturbation is attributed to stratification impacts predicted by Monin-Obukhov (MO) similarity theory. Significantly higher correlation is observed when relating wind or stress perturbations to buoyant heat flux variation. Atmospheric pressure perturbation with SST of order 0.5 hPa °C−1 is observed, as well as high negative correlation between wind and pressure variations. Length and time scales associated with the coupling indicate that peak correlations occur at 50-70 days and 300-500 km, consistent with mesoscale meander scales. Coupling coefficient values vary significantly depending on analysis time scale and exhibit a range near to recently observed interbasin variability. This variability is attributed to the extent of oceanic length scales permitted in the analysis. Together, results affirm the central role of SST-induced turbulent heat flux in controlling pressure field adjustments and thereby the wind perturbations over SST fronts. [ABSTRACT FROM AUTHOR]

The role of extreme surface turbulent fluxes in total oceanic heat loss in the North Atlantic is studied. The atmospheric circulation patterns enhancing ocean-atmosphere heat flux in regions with significant contributions of the extreme heat fluxes (up to 60% of the net heat loss) are analyzed. It is shown that extreme heat fluxes in the Gulf Stream and the Greenland and Labrador Seas occur in zones with maximal air pressure gradients, i.e., in cyclone-anticyclone interaction zones. [ABSTRACT FROM AUTHOR]

It is commonly accepted that there is a need for a better understanding of the factors that contribute to air-sea interactions and their feedbacks. In this context it is important to develop advanced numerical prediction systems that treat the atmosphere and the ocean as a unified system. The realistic description and understanding of the exchange processes near the ocean surface requires knowledge of the sea state and its evolution. This can be achieved by considering the sea surface and the atmosphere as a continuously crosstalking dynamic system. Following and adapting concepts already developed and implemented in large-scale numerical weather models and in hurricane simulations, this study aims to present the effort towards developing a new, highresolution, two-way fully coupled atmosphere-ocean wave model in order to support both operational and research activities. A specific issue that is emphasized is the determination and parameterization of the air-sea momentum fluxes in conditions of extremely high and time-varying winds. Software considerations, data exchange as well as computational and scientific performance of the coupled system, the so-called WEW(worketa-wam), are also discussed. In a case study of a high-impact weather and sea-state event, the wind-wave parameterization scheme reduces the resulted wind speed and the significant wave height as a response to the increased aerodynamic drag over rough sea surfaces. Overall, WEW offers a more realistic representation of the momentum exchanges in the ocean wind-wave system and includes the effects of the resolved wave spectrum on the drag coefficient and its feedback on the momentum flux. [ABSTRACT FROM AUTHOR]

ABSTRACT While researchers have identified teleconnections between El Niño-Southern Oscillation ( ENSO) and extended winter precipitation extremes in North America using generalized extreme value ( GEV) models, the regional form of the statistical relationship remains an open question. Past work has shown that relatively warm ENSO conditions may be needed to trigger a nonlinear response over North America. However, studies that stratify winters into La Niña, neutral, and El Niño phases have found that precipitation extremes in neutral/La Niña winters respond differently than in El Niño winters, whereas studies that stratify ENSO data into cold/warm conditions have not found evidence for a coherent nonlinear response. Data and methodological differences have made direct comparison between results difficult. In this study, evidence for a nonlinear association between ENSO and precipitation extremes is reassessed by fitting stationary and linear/nonlinear GEV regression models, with the Niño3.4 index as a covariate, to 1-, 5-, and 10-day extended winter precipitation maxima. Two types of nonlinear model - both one-sided GEV regressions where linear relationships are allowed to differ above/below a Niño3.4 index threshold - are considered. In the first, following past work, the breakpoint is fixed at zero, that is stratifying data into warm/cold conditions. In the second, to see whether there is evidence for a differential neutral/La Niña and El Niño response, the breakpoint is allowed to vary freely. Due to the non-nested nature of the set of models, the Akaike Information Criterion is used to assess the relative support for each model. Depending on accumulation time-scale, the strength of evidence favours nonlinear models at 28%-30% of stations when the Niño3.4 breakpoint is free to vary, versus just 3% with a fixed breakpoint. Optimum Niño3.4 breakpoints are positive (> +0.4°C) in the majority of the nonlinear models, confirming that ENSO/precipitation relationships differs between La Niña/neutral and El Niño winters. [ABSTRACT FROM AUTHOR]

ABSTRACT Twenty-one climate models from Coupled Model Intercomparison Project Phase 3 ( CMIP3) and thirty-one models from the project's Phase 5 ( CMIP5) were used to evaluate model reproducibility in assessing interannual variability of summer precipitation in Pan-Asian monsoon region. The results show that both the multi-model ensemble means of the best eight models and of the thirty-one CMIP5 models are more skilful than those of the CMIP3 models in simulating the climatological pattern and the dominant mode of summer precipitation in Pan-Asian monsoon region. CMIP5 models show improved skill in representing the main characteristic of the first mode of summer precipitation in Pan-Asian monsoon region, which is a meridional tripole pattern from north to south occurring east of the 80°E region. That is, owing to the improved El Niño-Southern Oscillation ( ENSO) pattern and the relationship between Antarctic oscillation in the southern Pacific Ocean ( AAOSP) and ENSO, the first dominant mode of summer precipitation in Pan-Asian monsoon region are captured by CMIP5 models, which indicates that these models are more skilful in simulating the air-sea interaction of the Southern Hemisphere. [ABSTRACT FROM AUTHOR]

This study evaluates the relative contributions to the Indian Ocean dipole (IOD) mode of interannual variability from the El Niño-Southern Oscillation (ENSO) forcing and ocean-atmosphere feedbacks internal to the Indian Ocean. The ENSO forcing and internal variability is extracted by conducting a 10-member coupled simulation for 1950-2012 where sea surface temperature (SST) is restored to the observed anomalies over the tropical Pacific but interactive with the atmosphere over the rest of the World Ocean. In these experiments, the ensemble mean is due to ENSO forcing and the intermember difference arises from internal variability of the climate system independent of ENSO. These elements contribute one-third and two-thirds of the total IOD variance, respectively. Both types of IOD variability develop into an east-west dipole pattern because of Bjerknes feedback and peak in September-November. The ENSO forced and internal IOD modes differ in several important ways. The forced IOD mode develops in August with a broad meridional pattern and eventually evolves into the Indian Ocean basin mode, while the internal IOD mode grows earlier in June, is more confined to the equator, and decays rapidly after October. The internal IOD mode is more skewed than the ENSO forced response. The destructive interference of ENSO forcing and internal variability can explain early terminating IOD events, referred to as IOD-like perturbations that fail to grow during boreal summer. The results have implications for predictability. Internal variability, as represented by preseason sea surface height anomalies off Sumatra, contributes to predictability considerably. Including this indicator of internal variability, together with ENSO, improves the predictability of IOD. [ABSTRACT FROM AUTHOR]

The northern annular mode (NAM) influences wintertime climate variability in the Northern Hemisphere, and understanding the processes controlling its sign and amplitude is of critical importance. Mounting evidence supports a robust teleconnection between the El Niño-Southern Oscillation (ENSO) and the NAM, while internal variability generated in the tropical Indian Ocean (TIO) may be associated with a NAM response of the opposite sign. This study uses a coupled ocean-atmosphere model to separate the influence on the NAM from teleconnections driven by ENSO and the TIO. In composites constructed using a long preindustrial control integration, increased December-February precipitation in the central/eastern Pacific drives a negative late-winter NAM response. When isolated from ENSO variability, increased precipitation over the western-central TIO drives a strong and persistent positive NAM response throughout the winter. Opposite linear interference of the anomalous wave teleconnections explains most of the opposite-signed planetary wavedriving of the NAM responses. The case with combined ENSO and TIO variability yields cancellation of the wave interference and a weak NAM response. This mechanism is confirmed using experiments where the tropical ocean is nudged separately over the Pacific and TIO to the large-amplitude 1997/98-1998/99 ENSO cycle. The phases of the Rossby wave and NAM responses in these two cases are of opposite sign, providing strong evidence that internal variability over the TIO can induce teleconnections independent of-and with opposite sign to-those associated with ENSO. [ABSTRACT FROM AUTHOR]

Subsurface ocean observations in the equatorial tropical Pacific Ocean dramatically increased after the 1990s because of the completion of the TAO moored array and a steady increase in Argo floats. In this analysis the question explored is whether a steady increase in ocean observations can be discerned in improvements in skill of predicting sea surface temperature (SST) variability associated with El Niño-Southern Oscillation (ENSO)? The analysis is based on the time evolution of skill of sea surface temperatures in the equatorial tropical Pacific since 1982 based on a seasonal prediction system. It is found that for forecasts up to a 6-month lead time, a clear fingerprint of increases in subsurface ocean observations is not readily apparent in the time evolution of prediction skill that is dominated much more by the signal-to-noise consideration of SSTs to be predicted. Finding no clear relationship between an increase in ocean observations and prediction skill of SSTs, various possibilities for why it may be so are discussed. This discussion is to motivate further exploration on the question of the tropical Pacific observing system, its influence on the skill of ENSO prediction, and the capabilities of the current generation of coupled models and ocean data assimilation systems to take advantage of ocean observations. [ABSTRACT FROM AUTHOR]

Complex oceanic circulation and air--sea interaction make the eastern tropical Pacific Ocean (ETPO) a highly variable source of CO2 to the atmosphere. Although the scientific community have amassed 70 000 surface partial-pressure of carbon dioxide (pCO2) datapoints within the ETPO region over the past 25 years, the spatial and temporal resolution of this dataset is insufficient to fully quantify the seasonal to inter-annual variability of the region, a region where pCO2 has been observed to fluctuate by >300 µatm. Upwelling and rainfall events dominate the surface physical and chemical characteristics of the ETPO, with both yielding unique signatures in sea surface temperature and salinity. Thus, we explore the potential of using a statistical description of pCO2 within sea-surface salinity-temperature space. These SSS/SST relationships are based on in-situ SOCAT data collected within the ETPO. This statistical description is then applied to high resolution (0.25°) SMOS sea surface salinity and OSTIA sea surface temperature in order to compute regional pCO2. As a result, we are able to resolve pCO2 at sufficiently high resolution to elucidate the influence various physical processes have on the pCO2 of the surface ETPO. Normalised (to 2014) oceanic pCO2 between July 2010 and June 2014 within the entire ETPO was 41 µatm supersaturated with respect to 2014 atmospheric partial pressures. Values of pCO2 within the ETPO were found to be broadly split between southeast and a northwest regions. The north west, central and South Equatorial Current regions were supersaturated, with wintertime wind jet driven upwelling found to be the first order control on pCO2 values. This contrasts with the southeastern/Gulf of Panama region, where heavy rainfall combined with rapid stratification of the upper water-column act to dilute dissolved inorganic carbon, and yield pCO2 values under-saturated with respect to atmospheric partial pressures of CO2. [ABSTRACT FROM AUTHOR]

Partial pressure of CO2 (pCO2) in surface water and vertical profiles of the carbonate system parameters were measured during austral summer in the Indian sector of the Southern Ocean (64-67° S, 32-58° E) in January 2006 to understand the CO2 dynamics of seawater in the seasonal ice zone. Surface-water pCO2 ranged from 275 to 400 μatm, and longitudinal variations reflected the dominant influence of water temperature and dilution by sea ice meltwater between 32 and 40° E and biological productivity between 40 and 58° E. Using carbonate system data from the temperature minimum layer (-1.9 °C < T <-1.5 °C, 34.2 < S < 34.5), we examined the winter-to-summer evolution of surface-water pCO2 and the factors affecting it. Our results indicate that pCO2 increased by as much as 32 µatm, resulting mainly from the increase in water temperature. At the same time as changes in sea ice concentration and surface-water pCO2, the air-sea CO2 flux, which consists of the exchange of CO2 between sea ice and atmosphere, changed from -1.1 to +0.9 mmolCm-2 day-1 between winter and summer. These results suggest that, for the atmosphere, the seasonal ice zone acts as a CO2 sink in winter and a temporary CO2 source in summer immediately after the retreat of sea ice. Subsequent biological productivity likely decreases surface-water pCO2 and the air-sea CO2 flux becomes negative, such that in summer the study area is again a CO2 sink with respect to the atmosphere. [ABSTRACT FROM AUTHOR]

High-resolution global climate modeling holds the promise of capturing planetary-scale climate modes and small-scale (regional and sometimes extreme) features simultaneously, including their mutual interaction. This paper discusses a new state-of-the-art high-resolution Community Earth System Model (CESM) simulation that was performed with these goals in mind. The atmospheric component was at 0.25° grid spacing, and ocean component at 0.1°. One hundred years of 'present-day' simulation were completed. Major results were that annual mean sea surface temperature (SST) in the equatorial Pacific and El-Niño Southern Oscillation variability were well simulated compared to standard resolution models. Tropical and southern Atlantic SST also had much reduced bias compared to previous versions of the model. In addition, the high resolution of the model enabled small-scale features of the climate system to be represented, such as air-sea interaction over ocean frontal zones, mesoscale systems generated by the Rockies, and Tropical Cyclones. Associated single component runs and standard resolution coupled runs are used to help attribute the strengths and weaknesses of the fully coupled run. The high-resolution run employed 23,404 cores, costing 250 thousand processor-hours per simulated year and made about two simulated years per day on the NCAR-Wyoming supercomputer 'Yellowstone.' [ABSTRACT FROM AUTHOR]

Atlantic tropical cyclone (TC) activity is influenced by interannual tropical Pacific sea surface temperature (SST) variability characterized by the El Niño-Southern Oscillation (ENSO), as well as interannual-to-decadal variability in the interhemispheric gradient in tropical Atlantic SST characterized by the Atlantic meridional mode (AMM). Individually, the negative AMM phase (cool northern and warm southern tropical Atlantic SST anomalies) and El Niño each inhibit Atlantic TCs, and vice versa. The impact of concurrent strong phases of the ENSO and AMM on Atlantic TC activity is investigated. The response of the atmospheric environment relevant for TCs is evaluated with a genesis potential index. Composites of observed accumulated cyclone energy (ACE) suggest that ENSO and AMM can amplify or dampen the influence of one another on Atlantic TCs. To support the observational analysis, numerical simulations are performed using a 27-km resolution regional climate model. The control simulation uses observed SST and lateral boundary conditions (LBCs) of 1980-2000, and perturbed experiments are forced with ENSO phases through LBCs and eastern tropical Pacific SST and AMM phases through Atlantic SST. Simultaneous strong El Niño and strongly positive AMM, as well as strong concurrent La Niña and negative AMM, produce near-average Atlantic ACE suggesting compensation between the two influences, consistent with the observational analysis. Strong La Niña and strongly positive AMM together produce extremely intense Atlantic TC activity, supported largely by above average midtropospheric humidity, while strong El Niño and negative AMM together are not necessary conditions for significantly reduced Atlantic tropical cyclone activity. [ABSTRACT FROM AUTHOR]

High-temporal resolution analysis of different climatic tracers (pollen, foraminiferal-based winter sea surface temperature (SST), benthic foraminiferal δ18O) from marine core MD95-2042, retrieved off SW Iberia, allows us to directly compare, without any chronological ambiguity, Mediterranean vegetation and eastern North Atlantic winter SST changes for the last 14.2 kyr. We identify on land and in the ocean several climatic phases such as the end of the warm and humid Bølling–Allerød, the cold and dry Younger Dryas, and the warm and humid Holocene with the Mediterranean forest (MF) optimum between 9.6 and 8.1 kyr. This record shows that, at multi-centennial timescale (~800 years), declines in forest cover generally related to dry and cool periods in southern Iberia are synchronous with cold SST in the eastern part of the North Atlantic subtropical gyre. At multi-centennial timescale, changes in thermohaline circulation, via freshwater content fluctuations, appear to be responsible for the coupling between dryness in Iberia and SST cooling in eastern North Atlantic subtropical gyre. In contrast, some Holocene events include centennial-scale oscillations (~100 years) marked by MF declines in southern Iberia concomitant with SST warming in the eastern North Atlantic subtropical gyre. This climatic pattern is similar to that observed at decadal timescale under the influence of the positive mode of the North Atlantic Oscillation (NAO). We suggest, therefore, that synchronous SW Iberian dryness and SST warming at centennial timescale could be explained by atmospheric fluctuations related to NAO changes. [ABSTRACT FROM PUBLISHER]

The interplay between density and climate in shaping the dynamics of herbivore populations is widely acknowledged, and current research is fueled by the identification of mechanisms underlying their effects on individuals and populations. We assessed whether forage availability mediated the effects of density and winter climate on body mass of whitetailed deer (Odocoileus virginianus) yearlings by experimentally reducing deer density to 7.5 and 15 deer/km2 during eight growing seasons, and by using causal (graphical) hierarchical models and Bayesian hierarchical modeling to assess relationships. The abundance of preferred forage decreased with deer density and varied quadratically (positive parabola) with winter North Atlantic Oscillation (NAO), whereas the fall mass of yearlings increased with forage abundance and spring mass. Fall mass did not differ between experimentally reduced deer densities, yet experimental yearlings were 30% heavier than yearlings harvested at ambient densities. Hence, forage abundance simultaneously mediated the effects of density and climate on fall body mass, which was also infiuenced by carry-over effects of spring body mass. Our findings increase our ability to anticipate how temperate large herbivores will respond to ongoing changes in intrinsic (e.g., large-herbivore density) and extrinsic (e.g., climate) factors. [ABSTRACT FROM AUTHOR]

We evaluated evidence of an effect of climate on the numerical response of a coyote (Canis latrans) population to their keystone prey, snowshoe hares (Lepus americanus), in a Canadian boreal forest. Six a priori hypotheses of the coyote numerical response were developed that postulated linear, nonlinear, additive, and interactive effects of prey and climate. Model selection procedures showed the North Atlantic Oscillation (NAO) had the strongest effect on the coyote numerical response via its interaction with snowshoe hare density, while other large-scale climate indices had very weak effects. For a given snowshoe hare density, a negative value of the NAO amplified the abundance of coyote and a positive NAO decreased coyote abundance. We hypothesize that the coyote numerical response is ultimately determined by the coyote functional response influenced by winter conditions determined by the NAO. [ABSTRACT FROM AUTHOR]

Long records of the latitude and speed of the North Atlantic eddy-driven jet stream since 1871 are presented from the newly available Twentieth Century Reanalysis. These jet variations underlie the variability associated with patterns such as the North Atlantic Oscillation (NAO) and have considerable societal impact through variations in the prevailing westerly winds. While the NAO combines variations in the latitude and speed of the jet, these two characteristics are shown to have quite different seasonal cycles and interannual variability, suggesting that they may have different dynamical influences. In general, the features exhibited in shorter records are shown to be robust, for example the strong skewness of the NAO distribution. Related to this is a clear multimodality of the jet latitude distribution, which suggests the existence of preferred positions of the jet. Decadal variations in jet latitude are shown to correspond to changes in the occurrence of these preferred positions. However, it is the speed rather than the latitude of the jet that exhibits the strongest decadal variability, and in most seasons this is clearly distinct from a white-noise representation of the seasonal means. When viewed in this longer term context, the variations of recent decades do not appear unusual and recent values of jet latitude and speed are not unprecedented in the historical record. [ABSTRACT FROM AUTHOR]

The Eastern Seaboard (ESB) of Australia is a distinct climate entity, with little relationship between rainfall in this area and the major drivers of rainfall elsewhere in Australia such as the El Niño-Southern Oscillation (ENSO). One potential cause is the influence of East Coast Lows (ECLs), major coastal weather systems that can produce a significant proportion of rainfall in this region. In this article, a novel approach is used to separate the ECL component of rainfall on the ESB from other sources of rainfall. This method is used to quantify the influence of ECLs on rainfall in this region, with ECLs responsible for 23% of rainfall in the ESB and 40% of widespread heavy rain events. While ECLs are particularly important in the southern ESB and during the cool season (May-October) they can occur in any month, particularly in northern areas of the ESB. ECLs are identified as a significant factor in the weakened relationship between ENSO and rainfall in the ESB, particularly in southern parts; however, these are not the only factor, with local topographic effects also likely to play a role. [ABSTRACT FROM AUTHOR]

The Oceanic Flux Program (OFP) sediment trap time series, the longest running time series of its kind, has continuously measured particle fluxes in the deep Sargasso Sea since 1978. OFP results provided the first direct observation of seasonality in the deep ocean, and they have documented the tight coupling between deep fluxes and upper ocean processes and the intensity of biological reprocessing of sinking flux in the ocean interior. The synergy among OFP and other research programs co-located at the Bermuda time-series site has provided unprecedented opportunities to study the linkages among ocean physics, biology, and chemistry; particle flux generation; and particle recycling in the ocean interior. The OFP time series is beginning to reveal how basin-scale climatic forcing, such as the North Atlantic Oscillation, affects the deep particle flux [ABSTRACT FROM AUTHOR]

ABSTRACT Interannual variability of the seasonal surface air-temperature over the Indian subcontinent is investigated using observations for the period of 1900-2005. Our results demonstrate that air-temperature over India is remotely influenced by the El Niño-Southern Oscillation and locally through Indian Ocean sea surface temperature ( SST) anomalies. The leading mode of variability ( EOF-1, empirical orthogonal function) in the observed air-temperature displays a country-wide warming in all four seasons. The spatial pattern of EOF-1 is similar to that of composite air-temperature anomalies of warm/cold years. Above-normal air-temperature in India (country-wide warming) is positively correlated to a simultaneous El Niño conditions in the eastern Pacific during boreal summer. El Niño induced strong subsidence, weaker low-level winds, less moisture availability and enhanced incoming shortwave radiation over the north Indian Ocean and Indian subcontinent are responsible for air-temperature warming in summer. It is observed that during fall, air-temperature pattern of EOF-1 over India is highly correlated with SST over the tropical oceans. SST correlation is maximum in central Pacific and north Indian Ocean, indicating the importance of both remote and local forcing. During boreal spring and winter, air-temperature warming ( EOF-1) is mainly influenced by Indian Ocean SST anomalies. Low moisture and negative sea level pressure anomalies over India indicate the existence of heat low with strong dry winds convergence, which are favourable for air-temperature warming in spring. Although El Niño peaks during winter, its impact on the air-temperature over the Indian subcontinent is weak during this season. The second EOF mode shows dipole-like air-temperature pattern with warming over the south-east and cooling in the north-western India during summer and winter, whereas spring shows opposite polarity. In case of boreal fall, EOF-2 of air-temperature displays a south-west and north-east orientation. Mechanisms responsible for these variabilities are studied in detail. [ABSTRACT FROM AUTHOR]

There is evidence that the observed changes in winter North Atlantic Oscillation (NAO) drive a significant portion of Atlantic Multi Decadal Variability (AMV). However, whether the observed decadal NAO changes can be forced by the ocean is controversial. There is also evidence that artificially imposed multi-decadal stratospheric changes can impact the troposphere in winter. But the origins of such stratospheric changes are still unclear, especially in early to mid winter, where the radiative ozone-impact is negligible. Here we show, through observational analysis and atmospheric model experiments, that large-scale Atlantic warming associated with AMV drives high-latitude precursory stratospheric warming in early to mid winter that propagates downward resulting in a negative tropospheric NAO in late winter. The mechanism involves stratosphere/troposphere dynamical coupling, and can be simulated to a large extent, but only with a stratosphere resolving model (i.e., high-top). Further analysis shows that this precursory stratospheric response can be explained by the shift of the daily extremes toward more major stratospheric warming events. This shift cannot be simulated with the atmospheric (low-top) model configuration that poorly resolves the stratosphere and implements a sponge layer in upper model levels. While the potential role of the stratosphere in multi-decadal NAO and Atlantic meridional overturning circulation changes has been recognised, our results show that the stratosphere is an essential element of extra-tropical atmospheric response to ocean variability. Our findings suggest that the use of stratosphere resolving models should improve the simulation, prediction, and projection of extra-tropical climate, and lead to a better understanding of natural and anthropogenic climate change. [ABSTRACT FROM AUTHOR]

During late boreal summer (July-October), the intraseasonal oscillation (ISO) exhibits maximum variability over the western North Pacific (WNP) centered in the South China Sea and Philippine Sea, but many numerical models have difficulty in simulating this essential feature of the ISO. To understand why this maximum variability center exists, the authors advance a simple box model to elaborate the potential contribution of the mean-state-dependent atmosphere-ocean interaction. The model results suggest that the WNP seasonal mean monsoon trough plays an essential role in sustaining a strong stationary ISO, contributing to the existence of the maximum intraseasonal variability center. First, the monsoon trough provides abundant moisture supply for the growing ISO disturbances through the frictional boundary layer moisture convergence. Second, the cyclonic winds associated with the monsoon trough provide a favorable basic state to support a negative atmosphere-ocean thermodynamic feedback that sustains a prominent stationary ISO. In an active phase of the ISO, anomalous cyclonic winds enhance the monsoon trough and precipitation, which reduce shortwave radiation flux and increase evaporation; both processes cool the sea surface and lead to an ensuing high pressure anomaly and a break phase of the ISO. In the wintertime, however, the wind-evaporation feedback is positive and sustains the Philippine Sea anticyclone. The result here suggests that accurate simulation of the boreal summer climatological mean state is critical for capturing a realistic ISO over the WNP region. [ABSTRACT FROM AUTHOR]

The representation of the CFSv2 ocean-atmosphere ensemble hindcasts is investigated during Dec-Jan-Feb (DJF) and Jun-Jul-Aug (JJA) from 1983 to 2010. The skill anomaly correlations showed that in some continents the forecasts do not have dependency with changes in the initial conditions. Also, in both seasons the model has a higher skill at the 0-month lead time with the largest spatial biases occurring over the North America, South America, and Oceania. Over the continents the largest biases in the nonlinearity of El Nino minus La Nina events are found over the eastern South Africa, part of Oceania, and central-southeastern parts of South America. During DJF the main biases are related to double-ITCZ, strengthening of SPCZ, and deepening of the Aleutian and Icelandic low pressures. The simulation of a warmer SST on the eastern of most austral oceans, the strengthening (weakening) of the Subtropical (Polar) Jet over the Southern Hemisphere, and the weakening of the zonal circulation near the Antarctic continent are also found in both seasons. Over the central-eastern Equatorial Pacific a cooler bias in SST is found during JJA. These biases are interpreted by analyses of the simulated global mean-state and their impact on the main patterns of variability. [ABSTRACT FROM AUTHOR]

ABSTRACT An effort is made to identify the 'more predictable' signals in seasonal precipitation in the Eastern Yangtze-Huaihe River Valley of China based on the observations recorded for the period of 1951-2004 at a network of 23 stations in this region. A recently developed methodology for decomposing the interannual variance of seasonal mean climate fields is applied to precipitation time series at the stations. This allows the total interannual variance to be separated into the variance of a slow component, or predictable signal, and the variance of a more noisier component of rainfall associated with intraseasonal variability. The potential predictability (signal-to-total ratio) is generally moderate in this region and is lower during winter from January to March ( JFM) and higher in summer from May to July ( MJJ) and autumn from November to January ( NDJ). Empirical orthogonal function ( EOF) analysis is then applied to the predictable-, intraseasonal- and total-covariance matrices, respectively. Leading EOF modes of the total component more often resemble the EOF modes of the intraseasonal component when the potential predictability is lower and vice versa. Temporal variation of the leading modes in the predictable components is more closely linked to the interannual variability of Eastern Pacific sea surface temperature ( SST) in early summer ( MJJ), North Atlantic SST in late summer ( JAS) and El Niño/Southern oscillation in late autumn ( NDJ). The rainfall SST connections found in these seasons persist throughout the entire 54-year period. The predictable rainfall modes also have apparent linkages to the intensity and position of the Western Pacific subtropical high during the early summer and late autumn with more rainfall occurring in the region when the height pattern is more intensive and extends further west. During the late summer, the predictable rainfall variability is accompanied by a large variation of tropospheric advection from north of the region, indicating the impact of an anomalous atmospheric circulation associated with the variation of summer North Atlantic Oscillation. [ABSTRACT FROM AUTHOR]

Multidecadal and longer changes to the Atlantic interhemispheric sea surface temperature gradient (AITG) in phase 5 of the Coupled Model Intercomparison Project (CMIP5) historical simulations are investigated. Observations show a secular trend to this gradient over most of the twentieth century, with the southern lobe warming faster relative to its northern counterpart. A previous study of phase 3 of the CMIP (CMIP3) suggests that this trend is partially forced by anthropogenic sulfate aerosols. This analysis collectively confirms the partially forced trend for the CMIP5 and by anthropogenic aerosols. Like the CMIP3, the CMIP5 also simulates a reversal in the AITG trend in the late 1970s, which was attributed to a leveling off of the anthropogenic aerosol influence and increased influence of greenhouse gases in the late twentieth century. Two (of 25) CMIP5 models, however, systematically simulate a twentieth-century trend opposite to observed, leading to some uncertainty regarding the forced nature of the AITG trend. The observed AITG also exhibits a pronounced multidecadal modulation on top of the trend, associated with the Atlantic multidecadal oscillation (AMO). Motivated by a recent suggestion that the AMO is a forced response to aerosols, the causes of this multidecadal behavior were also examined. A few of the CMIP5 models analyzed do produce multidecadal AITG variations that are correlated to the observed AMO-like variation, but only one, the Hadley Centre Global Environmental Model, version 2 (HadGEM2), systematically simulates AMO-like behavior with both the requisite amplitude and phase. The CMIP5 simulations thus point to a robust aerosol influence on the historical AITG trend but not to the AMO-like multidecadal behavior. [ABSTRACT FROM AUTHOR]

The El Niño Southern Oscillation (ENSO) phenomenon is a natural part of the global climate system resulting from the interactions between large-scale ocean atmospheric circulation processes in the equatorial Pacific and Indian Oceans. In Guyana, for all the adverse weather and extreme hydrological events, the blame goes to El Niño or La Niña. This paper investigates the relationship between ENSO and three Guyanese river flows; the Demarara, Essequibo and Mazaruni. This work sheds some light on the effects of this phenomenon on these river flows which may be useful for the adaptation policies dealing with the impacts of ENSO. [ABSTRACT FROM AUTHOR]

Highlights: [•] A novel modeling approach to examine scale-dependence of ocean–atmosphere coupling. [•] Large-scale and mesoscale coupling are important in the vertical mixing mechanism. [•] Mesoscale coupling is predominant in the pressure adjustment mechanism. [•] For latent heat flux-SST coupling, mesoscale and large-scale features are important. [•] Precipitation anomalies coincide with 10m wind convergence rather than SST anomalies. [Copyright &y& Elsevier]

Recent studies have shown that the impact of the Indian Ocean dipole (IOD) on southern Australia occurs via equivalent barotropic Rossby wave trains triggered by convective heating in the tropical Indian Ocean. Furthermore, the El Niño-Southern Oscillation (ENSO) influence on southern Australian climate is exerted through the same pathway during austral spring. It is also noted that positive phase [positive IOD (pIOD) and El Niño] events have a much larger impact associated with their respective skewness. These phenomena play a significant role in the region's rainfall reduction in recent decades, and it is essential that climate models used for future projections simulate these features. Here, the authors demonstrate that climate models do indeed simulate a greater climatic impact on Australia for pIOD events than for negative IOD (nIOD) events, but this asymmetric impact is distorted by an exaggerated influence of La Niña emanating from the Pacific. The distortion results from biases in the Pacific in two respects. First, the tropical and extratropical response to La Niña is situated unrealistically too far westward and hence too close to Australia, leading to an overly strong impact on southeast Australia that shows up through the nIOD-La Niña coherence. Second, the majority of models simulate a positive sea surface temperature skewness in the eastern Pacific that is too weak, overestimating the impact of La Niña relative to that of El Niño. As such, the impact of the positive asymmetry in the IOD only becomes apparent when the impact of ENSO is removed. This model bias needs to be taken into account when analyzing projections of regional Australian climate change. [ABSTRACT FROM AUTHOR]

Ice core data are combined with Regional Atmospheric Climate Model version 2 (RACMO2) output (1958-2010) to develop a reconstruction of Greenland ice sheet net snow accumulation rate, Ât( G), spanning the years 1600-2009. Regression parameters from regional climate model (RCM) output regressed on 86 ice cores are used with available cores in a given year resulting in the reconstructed values. Each core site's residual variance is used to inversely weight the cores' respective contributions. The interannual amplitude of the reconstructed accumulation rate is damped by the regressions and is thus calibrated to match that of the RCM data. Uncertainty and significance of changes is measured using statistical models. A 12% or 86 Gt yr−1 increase in ice sheet accumulation rate is found from the end of the Little Ice Age in ~1840 to the last decade of the reconstruction. This 1840-1996 trend is 30% higher than that of 1600-2009, suggesting an accelerating accumulation rate. The correlation of Ât( G) with the average surface air temperature in the Northern Hemisphere (SATNH t) remains positive through time, while the correlation of Ât( G) with local near-surface air temperatures or North Atlantic sea surface temperatures is inconsistent, suggesting a hemispheric-scale climate connection. An annual sensitivity of Ât( G) to SATNH t of 6.8% K−1 or 51 Gt K−1 is found. The reconstuction, Ât( G), correlates consistently highly with the North Atlantic Oscillation index. However, at the 11-yr time scale, the sign of this correlation flips four times in the 1870-2005 period. [ABSTRACT FROM AUTHOR]

Variations in power input to the ocean using a recent global 'reanalysis' extending back to 1871 show a strong trend in the net power input since then, a trend dominated by the Southern Ocean region. This trend is interpreted as a spurious result of the changing observational system. Focusing therefore on the North Atlantic Ocean, where the database is somewhat more secure, it is found that the input power in the subpolar North Atlantic varies significantly in time, showing a strong relationship to the North Atlantic Oscillation (NAO). During positive NAO index years, power input is greater owing to enhanced synoptic activity. Furthermore, cumulative power input to the subpolar North Atlantic is found to correlate significantly with both the eddy kinetic energy there and the Atlantic multidecadal oscillation (AMO), although the physical mechanism at work remains unclear. The assumption that the changing ocean can be neglected relative to the changing atmosphere in calculating the power input is found to be a usefully accurate approximation over the two decades for which changing ocean state estimates are available. Strong dependence on synoptic weather systems of monthly-mean stress distributions implies that past and future climate simulations must account properly for changes in weather systems, not just the large-scale variations. [ABSTRACT FROM AUTHOR]

This study explores the possible effects of the North Atlantic Oscillation (NAO) on the quality of Spanish Cava. We found a significant negative relationship between the mean NAO for the months of March through August of each year between 1970 and 2008 and the probability of obtaining a top quality Cava. The NAO is associated with temperature and rainfall variations in the Cava region, which affect vine physiological processes during grape maturity. The probability of obtaining a top quality Cava was highest when the mean value of the NAO was negative, which causes the mean temperature in the Cava area to decrease, with positive consequences on Cava quality. Although the overall discrimination capacity and explanatory power of the model were low, 80 % of clearly favorable years were classified correctly as corresponding to top quality Cava, and 70 % of clearly unfavorable years were classified correctly as non top quality Cava. [ABSTRACT FROM AUTHOR]

The authors propose the use of a 'climate filter' concept to enhance prediction skill of a multimodel ensemble (MME) suite for the East Asian summer monsoon (EASM) precipitation and temperature at 850 hPa. The method envisages grading models on the basis of the degree of reproducibility of the association of EASM variability with a few relevant climate drivers with the respective model hindcasts for the period 1981-2003. The analysis identifies the previous winter Niño-3.4 and spring North Atlantic Oscillation indices as the most suitable climate drivers in designing a climate filter for evaluating models that replicate the observed teleconnections to EASM well. The results show that the hindcast skills of a new MME with the better-performing models are significantly higher than those from the nonperforming models or from an all-inclusive operational MME. [ABSTRACT FROM AUTHOR]

The two-dimensional nonhydrostatic compressible dynamical core for the atmosphere has been developed by using a new nodal-type high-order conservative method, the so-called multimoment constrained finite-volume (MCV) method. Different from the conventional finite-volume method, the predicted variables (unknowns) in an MCV scheme are the values at the solution points distributed within each mesh cell. The time evolution equations to update the unknown point values are derived from a set of constraint conditions based on the multimoment concept, where the constraint on the volume-integrated average (VIA) for each mesh cell is cast into a flux form and thus guarantees rigorously the numerical conservation. Two important features make the MCV method particularly attractive as an accurate and practical numerical framework for atmospheric and oceanic modeling. 1) The predicted variables are the nodal values at the solution points that can be flexibly located within a mesh cell (equidistant solution points are used in the present model). It is computationally efficient and provides great convenience in dealing with complex geometry and source terms. 2) High-order and physically consistent formulations can be built by choosing proper constraints in view of not only numerical accuracy and efficiency but also underlying physics. In this paper the authors present a dynamical core that uses the third- and the fourth-order MCV schemes. They have verified the numerical outputs of both schemes by widely used standard benchmark tests and obtained competitive results. The present numerical core provides a promising and practical framework for further development of nonhydrostatic compressible atmospheric models. [ABSTRACT FROM AUTHOR]

The linkages between the El Niño Southern Oscillation (ENSO) and the sea ice extent (SIE) in the Weddell Sea (South Atlantic) and the Bellingshausen-Amundsen Sea (South-Eastern Pacific) sectors of the Southern Ocean have been studied for the period 1979-2005 using crosswavelet analysis. The analysis showed that the relationship between the tropical expression of ENSO and the SIE in these two areas are different before and after 1992. Further, we investigated the structure and strength of the regional Ferrel cell (RFC) during El Niño and La Niña episodes using composite latitude-pressure cross-sections of wind anomalies for these two periods. Contrasting features were observed in the structure and strength of the RFC before and after 1992 in both, the South Atlantic and the South-Eastern Pacific. These modulations in the RFC control the heat transport from the tropics to high latitudes and hence the extent of sea ice in both the regions. We propose that the modulation of the RFC is responsible for the phase shift in the tropical-polar teleconnection. Copyright © 2012 Royal Meteorological Society [ABSTRACT FROM AUTHOR]

A Singular value decomposition (SVD) analysis was performed jointly on the daily intensity of extreme rainfall (DIER) over Argentina and the sea surface temperature (SST) of all the oceans from 17.5°N to 90°S in order to identify the large-scale variability of the SSTs related to extreme rainfall, in the period 1962-2005. The main objective of the article is to objectively recognize regions of the tropical and subtropical oceans that could be related with the extreme rainfall over Argentina. Spring is the season that is best represented by the first mode, accounting for up to 45% of the covariance between the DIER and SST. The first SVD mode of spring, summer and autumn presents a pattern of SST relating to the El Niño-Southern Oscillations (ENSO) phenomena with an enhanced DIER in different zones of centre and east of Argentina. In the second SVD mode of spring and summer, the SST patterns show cold conditions in the tropical and subtropical Atlantic and near Indonesia with an enhancement of the DIER in the centre and east of Argentina. These modes show a significant decadal variability. In the third SVD mode of spring and summer, the SST patterns present warm and cold conditions in the Indian Ocean and the centre and western Pacific Ocean (PO) with decreased rainfall in the northern and eastern portion of Argentina, respectively. This mode shows a significant period of temporal variability of around 14 years. The third mode of autumn presents warm conditions in the tropical Atlantic and the southwest PO with a low DIER in the centre and east of Argentina. This mode also presents temporal variability of around 14 years. The correlation between each mode derived from analysis of SVD and climate indices related with SST were computed. Copyright © 2012 Royal Meteorological Society [ABSTRACT FROM AUTHOR]

The Western Antarctic Peninsula is one of the most rapidly warming regions on earth. It is therefore important to analyze long-term trends and inter-annual patterns of change in major environmental parameters to understand the process underlying climate change in Western Antarctica. Since many polar long-term data series are fragmented and cannot be analysed with common time series analysis tools, we present statistical approaches that can deal with missing values. We applied U-statistics after Pettit and Buishand to detect abrupt changes, dynamic factor analysis to detect functional relationships, and additive modelling to detect patterns in time related to climatic cycles such as the Southern Annular Mode and El Niño Southern Oscillation in a long-term environmental data set from King George Island (WAP), covering 20 years. Our results not only reveal sudden changes for sea surface temperature and salinity, but also clear patterns in all investigated variables (sea surface temperature, salinity, suspended particulate matter and Chlorophyll a) that can directly be related to climatic cycles. Our results complement previous findings on climate related changes in the King George Island Region and provide insight into the environmental conditions and climatic drivers of system change in the study area. Hence, our statistical analyses may prove valuable for other polar environmental data sets and contribute to a better understanding of the regional variability of climate change and its impact on coastal systems. [ABSTRACT FROM AUTHOR]