Warm Sea Surface Temperature Anomalies Research Articles

Anthropogenic forcing intensified internally driven concurrent heatwaves in August 2022 across the Northern Hemisphere

In August 2022, unprecedented and long-lasting extreme heatwaves attacked the Northern Hemisphere, with simultaneous record-breaking surface air temperature (SAT) in Eastern Europe (EE), Southern China (SC), and Western North America (WNA). However, the underlying physical mechanisms of these concurrent heatwaves, and the extent to which they are driven by anthropogenic forcing versus internal variability remain unclear. Our analysis using the HadGEM3-A-N216 large ensemble attribution model reveals that anthropogenic forcing is responsible for approximately 50% of the heatwaves in EE and SC, and over 80% in WNA. Furthermore, an internally-generated circumglobal atmospheric wave train is identified as a key circulation factor facilitating these simultaneous heatwaves. Observations and numerical simulations indicate that extreme warm sea surface temperature (SST) anomalies in the North Atlantic, North Pacific and Barents Sea, along with extreme cold SST anomalies in the tropical central Pacific, are critical in the formation and maintenance of this atmospheric teleconnection wave train. Under future high-emission scenarios, the influence of the internally-generated atmospheric teleconnection on concurrent heatwaves may be enhanced, particularly in WNA.

The cause of an extreme sea surface warming in the midlatitude western North Pacific during 2012 summer

This study investigated an extreme sea surface warming in the midlatitude western North Pacific (MLWNP) during the summer of 2012. The 2012 extreme event was characterized by warm sea surface temperature anomaly (SSTA) extending from the East/Japan Sea to central North Pacific. The SSTA box–averaged over the MLWNP (130–180°E, 33–50°N) in 2012 ranked as the third warmest in recent four decades, which has caused intense marine heatwaves in this region. During the summer of 2012, a positive Indian Ocean Dipole event co-occurred with El Niño, favoring anomalous moisture transport between the two basins that caused enhanced convection in the South China and Philippine Seas and western–to–central subtropical Pacific. The enhanced convective activities triggered two meridional atmospheric Rossby wave trains to form strong atmospheric blocking high–pressure systems in the MLWNP. This reduced the total cloud cover and surface wind speed, enhancing insolation and reducing the release of latent heat flux. In addition, the weakened wind strengthened the stratification and shoaled the mixed layer. As a result, the increased net heat flux into the ocean accompanied by a shallower mixed layer contributed to the upper ocean warming in the MLWNP. Meanwhile, the North Pacific was dominated by a negative phase of Pacific Decadal Oscillation (PDO), significantly contributing to warm SSTAs in the MLWNP in 2012. Consequently, the 2012 extreme warming in the MLWNP was the results of the combination of atmospheric Rossby waves and PDO. Our study highlighted the roles of high–frequency atmospheric teleconnection and low–frequency PDO in extreme sea surface warming in the MLWNP.

Comparative Evaluation of Niño1+2 and Niño3.4 Indices in Terms of ENSO Effects Over the Euro‐Mediterranean Region

ABSTRACTGlobal or regional impacts of El Niño Southern Oscillation (ENSO) have predominantly been investigated through the Niño3.4 index, representing the sea surface temperature (SST) variations in the central Tropical Pacific. In this study, we comparatively evaluated the usefulness of Niño1+2, a relatively less utilised index that represents SST variability in the Eastern Tropical Pacific. In our analyses, we focused on ENSO impacts on Euro‐Mediterranean (EM) climate variability during boreal winter, using data from the NCEP/NCAR Reanalysis. The correlation analysis involving Niño1+2 depicts more distinct temperature and precipitation patterns over the EM region. Amongst the SST‐based Niño indices, it has the highest correlation with the East Atlantic index (0.47, statistically significant at > 99% confidence level), a prominent regional teleconnection associated primarily with the strength of the East Atlantic ridge, which produces dipole‐type climate patterns between East Atlantic/Western Europe and Central/Eastern Mediterranean. Moreover, its lagged correlations with the following spring (0.39), summer (0.31), and autumn (0.36) are all statistically significant at ≥ 99% confidence levels. The composite analysis shows that different Niño regions have distinct effects on atmospheric circulation and climate in the EM region. The Niño1+2 index is particularly helpful in identifying the years when warm SST anomalies of El Niño extend to the Eastern Equatorial Pacific, which results in a reversal of temperatures across the EM region. Thus, this study suggests that Niño1+2 is a useful index for studying climate variability and predictability in the EM region, especially when used in conjunction with other Niño indices, as it captures some ENSO features that they may not encompass.

A framework for reconstructing marine heatwaves from individual foraminifera in sedimentary archives

Marine heatwaves (MHWs) are warm sea surface temperature (SST) anomalies with substantial ecological and economic consequences. Observations of MHWs are based on relatively short instrumental records, which limit the ability to forecast these events on decadal and longer timescales. Paleoclimate reconstructions can extend the observational record and help to evaluate model performance under near future conditions, but paleo-MHW reconstructions have received little attention, primarily because marine sediments lack the temporal resolution to record short-lived events. Individual foraminifera analysis (IFA) of paleotemperature proxies presents an intriguing opportunity to reconstruct past MHW variability if strong relationships exist between SST distributions and MHW metrics. Here, we describe a method to test this idea by systematically evaluating relationships between MHW metrics and SST distributions that mimic IFA data using a 2000-member linear inverse model (LIM) ensemble. Our approach is adaptable and allows users to define MHWs based on multiple duration and intensity thresholds and to model seasonal biases in five different foraminifera species. It also allows uncertainty in MHW reconstructions to be calculated for a given number of IFA measurements. An example application of our method at 12 north Pacific locations suggests that the cumulative intensity of short-duration, low-intensity MHWs is the strongest target for reconstruction, but that the error on reconstructions will rely heavily on sedimentation rate and the number of foraminifera analyzed. This is evident when a robust transfer function is applied to new core-top oxygen isotope data from 37 individual Globigerina bulloides at a site with typical marine sedimentation rates. In this example application, paleo-MHW reconstructions have large uncertainties that hamper comparisons to observational data. However, additional tests demonstrate that our approach has considerable potential to reconstruct past MHW variability at high sedimentation rate sites where hundreds of foraminifera can be analyzed.

Inter-Model Spread in Representing the Impacts of ENSO on the South China Spring Rainfall in CMIP6 Models

A major challenge for climate system models in simulating the impacts of El Niño–Southern Oscillation (ENSO) on the interannual variations of East Asian rainfall anomalies is the wide inter-model spread of outputs, which causes considerable uncertainty in physical mechanism understanding and short-term climate prediction. This study investigates the fidelity of 40 models from Phase 6 of the Coupled Model Intercomparison Project (CMIP6) in representing the impacts of ENSO on South China Spring Rainfall (SCSR) during the ENSO decaying spring. The response of SCSR to ENSO, as well as the sea surface temperature anomalies (SSTAs) over the tropical Indian Ocean (TIO), is quite different among the models; some models even simulate opposite SCSR anomalies compared to the observations. However, the models capturing the ENSO-related warm SSTAs over TIO tend to simulate a better SCSR-ENSO relationship, which is much closer to observation. Therefore, models are grouped based on the simulated TIO SSTAs to explore the modulating processes of the TIO SSTAs in ENSO affecting SCSR anomalies. Comparing analysis suggests that the warm TIO SSTA can force the equatorial north–south antisymmetric circulation in the lower troposphere, which is conducive to the westward extension and maintenance of the western North Pacific anticyclone (WNPAC). In addition, the TIO SSTA enhances the upper tropospheric East Asian subtropical westerly jet, leading to anomalous divergence over South China. Thus, the westward extension and strengthening of WNPAC can transport sufficient water vapor for South China, which is associated with the ascending motion caused by the upper tropospheric divergence, leading to the abnormal SCSR.

Signature of the western boundary currents in local climate variability.

The western boundary currents are characterized by narrow, intense ocean jets and are among the most energetic phenomena in the world ocean. The importance of the western boundary currents to the mean climate is well established: they transport vast quantities of heat from the subtropics to the midlatitudes1, and they govern the structure of the climatological mean surface winds2-6, precipitation4-6 and extratropical storm tracks7-13. Their importance to climate variability is much less clear, as the tropospheric response to extratropical sea surface temperature (SST) variability is generally modest relative to the internal variability in the midlatitude atmosphere12-14. Here we exploit novel local analyses based on high-spatial-resolution data to demonstrate that SST variability in the western boundary currents has a more robust signature in climate variability than has been indicated in previous work. Our results indicate that warm SST anomalies in the major boundary currents of both hemispheres are associated with a distinct signature of locally enhanced precipitation and rising motion anomalies that extend throughout the depth of the troposphere. The tropospheric signature closely mirrors that of ocean dynamical processes in the boundary currents. Thus, the findings indicate a distinct and robust pathway through which extratropical ocean dynamical processes influence local climate variability. The observational relationships are also reproducible in Earth system model simulations but only when the simulations are run at high spatial resolution.

Different Modulations of Arctic Oscillation on Wintertime Sea Surface Temperature Anomalies in the Northeast Pacific

AbstractPersistent positive sea surface temperature anomalies (SSTAs) in the mid‐latitude Northeast Pacific (NEP), also known as “warm blob” or “marine heatwave,” have substantial ecological and climate effects. This study delves into the spatiotemporal connection between Arctic Oscillation (AO) and SSTAs in the NEP. First, we conduct the lead‐lag correlation and maximum covariance analyses to disentangle the closest temporal relationship between October AO and wintertime SSTAs in the NEP. Then, we categorize the years in positive AO (pAO) phase into two groups: positive AO with warm anomaly (pAO&Blob) group and positive AO without warm anomaly (pAO&noBlob) group based on the October AO index and wintertime blob index. Results show that the positive phase of AO in October strongly influences the wintertime warm SSTAs in the NEP through local and remote pathways. The local pathway is contingent upon the longitudinal positioning of AO‐related high‐pressure anomaly (i.e., anomalous ridge) in the North Pacific. When easterly anomalies prevail at the southern flank of the anomalous ridge over the NEP, they foster warm SSTAs in the NEP. However, different locations of the high‐pressure anomalies may impede the NEP warming. Remote pathways indicate the teleconnections triggered by AO‐related precipitation increase in Greenland and decrease in East Asia, sustaining the high‐pressure anomaly and promoting the anomalous NEP warming. Hence, this study presents new evidence on polar and mid‐latitude climate connections, which may provide potential predictability for the warm SSTAs in the NEP.

Impact of an unprecedented marine heatwave on extremely hot summer over Northern Japan in 2023

Possible local influence of an extreme marine heatwave is investigated on unprecedentedly hot summer around northern Japan in 2023. Sea-surface temperatures (SSTs) and subsurface ocean temperatures around northern Japan were also unprecedentedly high in the summer. This was especially the case off the east coast of Japan, where cool Oyashio water was replaced with much warmer water due to a striking poleward meander of the Kuroshio Extension persistent from the spring. Particularly amplified near-surface air temperature anomalies and even stronger warm anomalies in the subsurface ocean suggest that the marine heatwave acted to sustain the atmospheric heatwave. Anomalous upward of latent and sensible heat fluxes from the warmed sea surface are indicative of local oceanic impact. The warm SST anomalies reduced the lower-tropospheric stratification to maintain unfavourable condition for low-level cloud formation, which in turn led to increased surface insolation for further SST warming as positive feedback. The increased moisture in the warmed lower troposphere contributed to the enhanced surface downward longwave radiation. This enhanced greenhouse effect acted not only as positive feedback on the warm SST anomalies that increased evaporation but also as a contributor for the extreme warmth over northern Japan landmass.

Moderate Indian Ocean Dipole dominates spring fire weather conditions in southern Australia

Patterns of the Indian Ocean Dipole (IOD) exhibit strong diversity, ranging from being dominated by the western tropical Indian ocean (WTIO) to by the eastern tropical Indian ocean. How the different types of the IOD variability patterns affect Australian fires differently is unknown, nor is it certain how the impacts may change under greenhouse warming. Here, we find that the moderate IOD, dominated by WTIO sea surface temperature (SST) variability, plays a primary role in affecting southern Australian fire weather conditions during austral spring. During a positive moderate IOD, broad-scaled warm SST anomalies in WTIO force an atmospheric stationary Rossby wave with a high-pressure anomaly over southern Australia. This elevated pressure and associated anomalous atmospheric conditions provide suitable fire weather with hot, dry, and windy conditions, raising fire risks in southern Australia. Such impact is distinctively different from that strong IOD-induced. As predicted by climate models, decreased moderate IOD variability in the future will result in weakened Australian fire weather responses.

Asymmetric Impacts of ENSO on Boreal Winter Southern Subtropical Cell in the Indian Ocean

AbstractThe interannual relationships between the southern subtropical cell (SSTC) in the Indian Ocean (IO) and the El Niño‐Southern Oscillation (ENSO) are examined. The results demonstrate that the impacts of ENSO on the boreal winter IO SSTC display a notable negative skewness, with the amplification of the SSTC during La Niña being far stronger than its reduction during El Niño. This difference is mainly attributed to an asymmetry in anomalous meridional geostrophic transport, characterized by more robust southward (weaker northward) geostrophic transport anomalies during La Niña (El Niño) events. Further analyses reveal that the differing longitudinal positions of the ENSO‐related sea surface temperature anomaly (SSTA) are the primary drivers of the asymmetry in anomalous meridional geostrophic transport via the oceanic and atmospheric teleconnections. Compared to the warm SSTA in El Niño events, the La Niña‐related cool SSTA in the central‐eastern equatorial Pacific displays a greater westward extension, which induces stronger surface easterlies over the western equatorial Pacific, and then initiates a more substantial sea surface height anomaly (SSHA) in the southeast Indian Ocean (SEIO) through oceanic waveguides. This leads to a heightened zonal SSHA gradient over the southern IO, resulting in a larger anomalous meridional geostrophic transport. On the other hand, the westward extension of negative SSTA during La Niña winters triggers anomalous cyclonic northerlies along the western coast of Australia by shifting the Walker circulation westward. These coastal northerlies amplify the positive SSHA signals in the SEIO and enhance the anomalous meridional geostrophic transport, ultimately contributing to a more robust IO SSTC response.

Weakened western Indian Ocean dominance on Antarctic sea ice variability in a changing climate.

Patterns of sea surface temperature (SST) anomalies of the Indian Ocean Dipole (IOD) exhibit strong diversity, ranging from being dominated by the western tropical Indian Ocean (WTIO) to the eastern tropical Indian Ocean (ETIO). Whether and how the different types of IOD variability patterns affect the variability of Antarctic sea ice is not known, nor is how the impact may change in a warming climate. Here, we find that the leading mode of austral spring Antarctic sea ice variability is dominated by WTIO SST variability rather than ETIO SST or El Niño-Southern Oscillation. WTIO warm SST anomalies excite a poleward-propagating Rossby wave, inducing a tri-polar anomaly pattern characterized by a decrease in sea ice near the Amundsen Sea but an increase in regions on both sides. Such impact has been weakening in the two decades post-2000, accompanied by weakened WTIO SST variability. Under greenhouse warming, climate models project a decrease in WTIO SST variability, suggesting that the reduced impact on Antarctic sea ice from the IOD will likely to continue, facilitating a fast decline of Antarctic sea ice.

The Contrast Precipitation Patterns in Yangtze River Valley Between the Two La Niña Decaying Summers in 2021 and 2022

AbstractAlthough the summers of 2021 and 2022 are both in the two successive La Niña decaying stages and under the same climate background of negative Pacific Decadal Oscillation (PDO) phase and global warming trend, they exhibit significantly different and even opposite precipitation patterns in the Yangtze River Valley (YRV) as well as in the Indian monsoon region (IMR). In contrast to the abundant precipitation and lower temperature in the YRV in summer 2021, in summer 2022 the YRV experiences severe drought and extremely high temperatures, which is also accompanied by Mega‐floods in the IMR. This study identifies the joint influence of sea surface temperature anomalies (SSTAs) in Niño4 and Barents Sea (BS) regions as the underlying cause for the contrast YRV precipitation anomalies in the summers of 2021 and 2022. Specifically, the cold SSTAs in both Niño4 and BS regions in summer 2021 favor stronger and southward shifted western North Pacific subtropical high (WNPSH), leading to more precipitation in the YRV, which is however generally reversed but more intense in summer 2022 because of the synergistic effect of cold Niño4 and warm BS SSTAs. Moreover, the induced extreme precipitation in the IMR in summer 2022, which is absent in summer 2021 due to the offsetting effect of cold SSTAs in both Niño4 and BS regions, in turn further strengthens the anomalous atmospheric circulations via its released large diabatic heating and serves as a relay pathway for the dramatic drought and heat wave in the YRV.

Seasonal predictability of SST anomalies and marine heatwaves over the Kuroshio extension region in the Copernicus C3S models

The warm sea surface temperature anomalies (SSTAs) and marine heatwaves (MHWs) in the Kuroshio Extension (KE) region have profound impacts on local and surrounding ecological and climatic systems. This study evaluates the seasonal prediction skills of KE-SSTAs and KE-MHWs based on six dynamical models from the Copernicus Climate Change Service (C3S) using different observational datasets for verification and further investigates the main sources of predictability. The results show that current dynamical models can provide reliable predictions for KE-SSTAs for up to about 4 months, but they are challenging to accurately predict the occurrence of KE-MHWs. Compared with single models, the C3S multi-model ensemble mean is usually more skillful in predicting KE-SSTAs and KE-MHWs at most lead times. With lead time increasing, the dynamical models tend to underestimate the mean intensity and annual frequency of the KE-MHWs and overestimate their mean duration. The performance of models in predicting KE-SSTAs is largely dependent on their ability to predict the Pacific Decadal Oscillation, Interdecadal Pacific Oscillation, and El Niño–Southern Oscillation which all significantly influence the KE-SSTAs. The results indicate that these three climate modes are the main sources of seasonal predictability for KE-SSTAs and KE-MHWs. These results provide a deeper understanding of the dynamical seasonal predictability of SSTAs and MHWs in the KE region.

The impact of tropical sea surface temperature on extreme precipitation in Pakistan during the summer of 2022

In August 2022, Pakistan experienced an unprecedented precipitation event that caused significant damage. Analysis of the observations reveals that this extreme rainfall is primarily driven by anomalous atmospheric zonal advection, resulting in an anomalous water vapor concentration in Pakistan. The climatological meridional advection also contributes to this flooding. Anomalous easterly winds and low-level vertical convection combine to be critical factors contributing to the moisture concentration over the country. Further investigation identifies the air-sea interaction over the tropical Indian Ocean and abnormal warming over the Arabian Sea are crucial factors influencing this extreme flooding event. The concurrent occurrence of a negative Indian Ocean Dipole event and the warming sea surface temperature anomalies in the northern Arabian Sea intensifies the easterly winds over Pakistan, helping to transfer the anomalous water vapor from the remote region into Pakistan, ultimately contributing to the extreme flooding in 2022.

ФОРМИРОВАНИЕ ПОЛОЖИТЕЛЬНЫХ АНОМАЛИЙ ТЕМПЕРАТУРЫ ПОВЕРХНОСТИ ЧЕРНОГО МОРЯ

Based on the satellite data at the points of a high-resolution regular grid for the period from 2008 to 2021, positive anomalies of the sea surface temperature (SST) in the northern Black Sea and off the southwestern coast of Crimea have been identified. It has been shown that there are vast areas with an exceeding of SST over the mean for the measurement period up to 4-5 and 5-6°C and a monthly total area (for example, in May 2018) about 200000 and 100000 km2, respectively, in the northern Black Sea. The analysis of available satellite data has led to the conclusion that warm SST anomalies occur mainly in May and October. The maximum (over the entire analyzed period) warm SST anomaly (exceeding 5°C) was reached in May 2012, when its area was 200000 km2. The spatial structure and some statistical characteristics of the identified SST anomalies have been described and analyzed. It has been shown that the typical frequency of vast SST anomalies is at least one case per several years, while they are generated by abnormal heat fluxes on the sea surface with the inflow of anomalously warm river water in shallow areas of the northwestern shelf and spread to the open sea areas due to the horizontal advection of predominantly wind-driven origin. The average annual SST anomalies off the northwestern coast of Crimea and in the northern Black Sea correlate at a level of 0.97.

Modulation of Western South Atlantic Marine Heatwaves by Meridional Ocean Heat Transport

AbstractMarine heatwaves and cold spells are extreme surface temperature events that have been associated with adverse societal and ecosystem impacts in several regions around the globe. Predicting these events presents a challenge because of their generally short‐lived nature and dependence on air‐sea interactions, both locally and remotely. Here we analyze oceanic propagating features that promote the occurrence of marine heatwaves and cold spells in the western subtropical South Atlantic. The main interannual feature detected from satellite sea level data since 1993 shows a westward propagating zonal pattern with a periodicity of 3–5 years. The pattern has a significant in‐phase correlation with sea surface temperature (SST) anomalies in the western South Atlantic, explaining 82% of the daily extreme warm (90th percentile) and cold (10th percentile) SST anomalies and consequently modulating interannual variations in the intensity and duration of marine heatwave and cold spell events. It is found that meridional oceanic advection plays an important role in the regional heat budget associated with the westward‐propagating mode, modulating the meridional exchange of tropical (warm) and extratropical (cold) waters in the western subtropical South Atlantic region and thereby setting a baseline for temperature extremes on interannual timescales. This propagating mode is well correlated (r > 0.6) with the strength of the meridional overturning circulation at 25°S and 30°S with a lag of approximately 3–9 months. The lagged response provides a potential source of predictability of extreme events in the western South Atlantic.

The Tropical Atlantic's Asymmetric Impact on the El Niño‐Southern Oscillation

AbstractUsing observations and Atlantic forced coupled model simulations, we show evidence for an asymmetry in the link between beginning of year tropical Atlantic sea surface temperature anomalies (SSTAs) and end of the year El Niño‐Southern Oscillation events. We find a greater tendency for warm Atlantic SSTAs to lead to a La Niña than for cold anomalies to lead to El Niño. The model experiments showed that the Atlantic had a greater chance to force the tropical Pacific if the Pacific was initially in a neutral state. In the model, a warm Atlantic from March–May was able to produce an atmospheric response leading to easterly wind anomalies in the western Pacific. This in turn induces a subsurface oceanic response, leading to La Niña at the end of the year. The atmospheric response does not occur for a cold Atlantic, leading to no impacts in the Pacific.

MJO-Induced Warm Pool Eastward Extension Prior to the Onset of El Niño: Observations from 1998 to 2019

Abstract The Madden–Julian oscillation (MJO) and El Niño–Southern Oscillation (ENSO) are the two most important tropical phenomena that affect global weather and climate on intraseasonal and interannual time scales. Although they occur on different time scales, the MJO-induced sea surface temperature (SST) anomalies over the equatorial Pacific have spatial scales similar to SST anomalies prior to El Niño. This study aims to address the question of whether the MJO plays an important role in the warm pool eastward extension (WPEE) leading up to El Niño. We use over 20 years of satellite observations, including optimum interpolated SST, TRMM-GPM precipitation, and the cross-calibrated multiplatform (CCMP) surface winds from 1998 to 2019, to quantify the spatial structure and duration of the MJO-induced warm SST anomalies over the equatorial Pacific (10°S–10°N, 130°E–180°). The intensity of the MJO is measured by the total rain volume and average surface westerly wind speed throughout its convectively active phase. Results show that 1) 61% of the 98 MJO events induced a WPEE over 1000–3000 km along the equator, which can last beyond 15–30 days after the MJO precipitation ended; 2) the MJO events prior to El Niño are generally stronger and produce significant WPEE far beyond its annual cycle and increasing SST warming in the Niño-3.4 region; 3) consecutive MJO events can produce much stronger WPEE prior to El Niño, which are observed in all El Niño events from 1998 to 2019; and 4) more frequent and stronger MJO-induced WPEE occurs in March–May than other seasons. These results can help better understand the MJO–ENSO interaction and, ultimately, improve the prediction of El Niño onset.

The Influence of Freshwater Input on the Evolution of the 1995 Benguela Niño

AbstractBenguela Niño events are characterized by strong warm sea surface temperature (SST) anomalies off the Angolan and Namibian coasts. In 1995, the strongest event in the satellite era took place, impacting fish availability in both Angolan and Namibian waters. In this study, we use direct observations, satellite data, and reanalysis products to investigate the impact that the up‐until‐now unnoticed mechanism of freshwater input from Congo River discharge (CRD) and precipitation had on the evolution of the 1995 Benguela Niño. In the onset phase of the event, anomalous rainfall in November/December 1994 at around 6°S, combined with a high CRD, generated a low salinity plume. The plume was advected into the Angola‐Namibia region in the following February/March 1995 by an anomalously strong poleward surface current generated by the relaxation of the southerly winds and shifts in the coastal wind stress curl. The presence of this low surface salinity anomaly of about −2 psu increased ocean stability by generating barrier layers, thereby reducing the turbulent heat loss, since turbulent mixing acted on a weak vertical temperature gradient. A mixed layer heat budget analysis demonstrates that southward advection of Angolan waters drove the warming at the onset, while reduced mixing played the main role at the event's peak. We conclude that a freshwater input contributed to the SST increase in this exceptionally strong event and suggest that this input can influence the SST variability in Angola‐Namibia waters through a combination of high CRD, precipitation, and the presence of a strong poleward surface current.

Influence of the Atlantic Multidecadal Oscillation on the Rapid Intensification Magnitude of Tropical Cyclones over the Western North Pacific

Abstract Rapid intensification (RI) of tropical cyclones (TCs), which refers to an explosive increase of TC intensity exceeding a certain threshold [e.g., 30 kt (1 kt ≈ 0.51 m s−1) in 24 h] within a short time period, poses a great challenge to both forecasting and disaster prevention efforts. Recent studies have documented a significant increase in the magnitude of TC RI (RIM; measured as the mean intensification rate of all TC RI records in a TC season) over the western North Pacific (WNP) since 1979, and have attributed it to the impacts of global warming. In this study, results from statistical analyses show that the TC RIM over the WNP during 1951–2021 exhibits significant interdecadal variability, which is found to be closely related to the Atlantic multidecadal oscillation (AMO). Further analyses indicate that the response of the local thermodynamic conditions to the AMO plays a dominant role in shaping this relationship. The positive AMO phase fosters a high TC RIM over the WNP by producing significant warm sea surface temperature (SST) anomalies, which in turn enhances TC heat potential and the midtropospheric relative humidity in the main region of TC RI occurrence. Results from both data analyses and numerical model experiments demonstrate that the AMO modulates thermodynamic conditions over the WNP, such as SST and ocean heat content, by affecting local heat fluxes and the Ekman heat transport in the WNP via the modulation of Walker circulation from the Atlantic to the Pacific.