Spring Sea Surface Temperature Anomalies Research Articles

Shift in the Relationship Between Summer Extreme Humid‐Heat Events in Eastern China and Tropical Sea Surface Temperature in the Mid‐1990s

AbstractThe social losses associated with extreme humid‐heat events (EHHE) increased sharply in recent decades. This study has explored the changing relationship between EHHE in eastern China and tropical sea surface temperature (SST) anomalies. Results show that the monopolar mode of EHHE is significantly associated with spring SST anomalies in Northwest Pacific (NWP) before the mid‐1990s, which can impact humid‐heat conditions in eastern China through an atmospheric meridional overturning circulation extending from NWP to eastern China. Then, the associated eastward shift of convection center after the mid‐1990s weakens connection between NWP SST anomalies and the monopolar mode. Further analysis reveals that the weakened Kelvin waves, induced by persistent SST anomalies from spring in tropical Indian Ocean after the mid‐1990s, cause the westward‐shifted anomalous convection in western Pacific, and then reinforce formation of the dipolar mode via exciting zonal wave trains. Numerical simulations via linear baroclinic model further validate atmospheric response to displacement of diabatic forcings.

Predicting Summer Precipitation Anomalies in the Yunnan–Guizhou Plateau Using Spring Sea-Surface Temperature Anomalies

By constructing a correlation network between global sea surface temperature anomalies (SSTAs) and summer precipitation anomalies in the Yunnan–Guizhou Plateau, key SST regions influencing summer precipitation anomalies in the Yunnan–Guizhou Plateau were selected. It was found that spring SSTAs in the Bay of Bengal, southwestern Atlantic, and eastern Pacific are crucial for influencing summer precipitation anomalies in the Yunnan–Guizhou Plateau. Setting SSTAs from these three regions as predictor variables 3 months in advance, we constructed multiple linear regression (MLR), ridge regression (RR), and lasso regression (LR) models to predict summer precipitation anomalies over the Yunnan–Guizhou region. The training phase involved data spanning from 1961 to 2005, which aimed to predict precipitation anomalies in the Yunnan–Guizhou Plateau for the period extending from 2006 to 2022. Based on MLR, RR, and LR models, the correlations between predicted values and observed summer precipitation anomalies in Yunnan–Guizhou were 0.48, 0.46, and 0.46, respectively. These values were all higher than the correlation coefficients of the NCC_CSM model’s predicted and observed values. Additionally, its performance in predicting summer precipitation anomalies over the Yunnan–Guizhou region, based on key SST regions, was assessed using performance metrics such as anomaly correlation coefficient (ACC), anomaly sign consistency rate (PC), and trend anomaly comprehensive score (PS score). The average ACC of MLR, RR, and LR models was higher than that of the NCC_CSM model’s predictions. For MLR, RR, LR, and NCC_CSM models, the PCs exceeding 50% of the year were 14, 14, 11, and 10, respectively. Furthermore, the average PS score for predicting summer precipitation anomalies over the Yunnan–Guizhou region using MLR, RR, and LR was approximately 73 points; 8 higher than the average PS score of the NCC_CSM model. Therefore, predicting summer precipitation anomalies over the Yunnan–Guizhou region based on key SST regions is of great significance for improving the prediction skills of precipitation anomalies in this region.

El Niño and La Niña asymmetry in short-term predictability on springtime initial condition

El Niño-Southern Oscillation (ENSO) asymmetry in predictability on springtime initial condition remains unclear. From the perspective of the spring predictability barrier (SPB), this paper investigates the ENSO asymmetry in SPB and explores the potential factors that may lead to this asymmetry. Both the observation and 29 Coupled Model Intercomparison Project Phase 6 (CMIP6) models show that the spring sea surface temperature (SST) persistence is significantly higher in El Niño years than that in La Niña years, and the SPB intensity is stronger in La Niña years than that in El Niño years. Through the recharge oscillator model, observation and CMIP6 models, we demonstrate that the nonlinear wind stress response to SST anomalies in spring is the main cause of the asymmetric SPB intensity. By the mixed-layer heat budget of the tropical Pacific in the spring, we further identify that a stronger response of zonal wind stress in El Niño events can cause a stronger zonal advection feedback, which finally leads to a weaker SPB and enhances the predictability of El Niño. In contrast, the cooling SST in the spring only leads to weak easterly anomalies, the zonal advection feedback is relatively weaker, thus SPB is stronger and the predictability of La Niña is lower. From the perspective of SPB, we suggest that El Niño is more predictable than La Niña.

Influence of boreal spring sea surface temperature anomalies over the tropical South Atlantic on the Meiyu onset

This study investigates the impact of boreal spring tropical South Atlantic surface sea temperature anomalies (TSA-SSTA) on the anticyclone over the western North Pacific (WNPAC) and the Meiyu onset date (MOD) based on reanalysis data and numerical experiments. The results indicate an intimate linkage between the MOD and TSA-SSTA, in which warmer spring TSA-SSTA are associated with an earlier MOD and vice versa, and the underlying mechanism is identified. Warm TSA-SSTA can trigger a Gill-type response and anomalous equatorial Walker circulation, which leads to anomalous upward motion and latent heating over the Maritime Continent. This anomalous condition over the Maritime Continent strengthens local Hadley circulation accordingly accompanied by anomalous descending motion over the western North Pacific. This descending motion reduces the local rainfall and enhances the equatorward northerly wind at low level. Further analysis reveals that local Sverdrup positive feedback between the anomalous diabatic cooling owing to reduced rainfall and the lower-level equatorward northerly wind is critical for sustaining the well-developed anomalous WNPAC. The abundant water vapor transport embedded in the northwestern flank of the anomalous WNPAC eventually favors an earlier MOD. Atmospheric conditions corresponding to cold TSA-SSTA produce the opposite effect. The spring TSA-SSTA can therefore prominently communicate with the subsequent East Asian MOD via the aforementioned mechanism, and the spring TSA-SSTA can be interpreted as a precursor signal of the East Asian MOD.

Impact of Internal Climate Variability on the Relationship between Spring Northern Tropical Atlantic SST Anomalies and Succedent Winter ENSO: The Role of the North Pacific Oscillation

Abstract Previous studies suggested that spring sea surface temperature anomalies (SSTAs) in the northern tropical Atlantic (NTA) have a marked influence on the succedent winter El Niño–Southern Oscillation (ENSO). In this study, we examine the spring NTA SSTA–winter ENSO connection in a 50-member large-ensemble simulation conducted with the Canadian Centre for Climate Modelling and Analysis second-generation Canadian Earth System Model (CanESM2) and a 100-member ensemble simulation conducted with the Max Planck Institute Earth System Model (MPI-ESM). The observed out-of-phase relation of spring NTA SSTA with winter ENSO can be captured by the multimember ensemble means of the large-ensemble simulations from both models. However, the relation shows a large diversity among different ensemble members attributing to the internal climate variability. The preceding winter North Pacific Oscillation (NPO) is suggested to be an important source of the internal climate variability that modulates the spring NTA SSTA–ENSO connection. The modulation of the winter NPO on the subsequent spring NTA SSTA–winter ENSO relation is seen in both climate modeling and observational datasets. When winter NPO and spring NTA SSTA indices have the same (opposite) sign, the linkage between the spring NTA SSTA and the following winter ENSO tends to be weak (strong). The NPO modulates the spring NTA SSTA–winter ENSO relation mainly via changing the zonal wind anomalies over the tropical western-to-central Pacific induced by the spring NTA SSTA. In addition, our analysis indicates that winter NPO may have a marked effect on the predictability of winter ENSO based on the condition of spring NTA SSTA.

Possible mechanisms for the coupling between late spring sea surface temperature anomalies over tropical Atlantic and East Asian summer monsoon

The relationship between the preceding late spring Sea Surface Temperature (SST) over the tropical Atlantic and the East Asian Summer Monsoon (EASM) is investigated based on the observational data and Coupled Model Intercomparison Project Phase 5 (CMIP5) historical simulations. The results show that warm (cold) tropical Atlantic SST (TASST) during May tends to be followed by a strong (weak) EASM with positive (negative) precipitation anomalies over the subtropical frontal area. Evidence is also provided that the atmospheric teleconnections propagating in both east and west directions are the key mechanisms linking the EASM with the preceding May TASST. That is, the warm TASST anomaly during late spring can persist through the subsequent summer, which, in turn, induces the Gill-type Rossby wave response in the eastern Pacific, exciting the westward relay of the Atlantic signal, as well as the eastward propagation of the Rossby wave along the jet stream. Furthermore, the westward (eastward) propagating teleconnection signal may induce the anomalous anticyclone in the lower troposphere over the Philippine Sea (anomalous tropospheric anticyclone with barotropic structure over the Okhotsk Sea). The anomalous anticyclonic circulation over the Philippine Sea (Okhotsk Sea) brings warm and humid (cold) air to higher latitudes (lower latitudes). These two different types of air mass merge over the Baiu-Meiyu–Changma region, causing the enhanced subtropical frontal rainfall. To support the observational findings, CMIP5 historical simulations are also utilized. Most state-of-the-art CMIP5 models can simulate this relationship between May TASST and the EASM.

An interdecadal change in the influence of the Central Pacific ENSO on the subsequent north tropical Atlantic spring SST variability around the mid-1980s

North tropical Atlantic (NTA) spring sea surface temperature (SST) tends to be warmer (cooler) than normal in Central Pacific (CP) El Nino decaying years during 1960s to mid-1980s. However, the relationship between the NTA spring SST and CP El Nino-Southern Oscillation (ENSO) is weakened after mid-1980s. This study presents this interdecadal change and investigates possible causes. Before the mid-1980s, above-normal NTA SST peaks in post-El Nino spring. The CP El Nino can affect NTA spring SST by inducing a negative phase of North Atlantic Oscillation (NAO) anomaly over North Atlantic from winter to spring. This negative NAO circulation weakens the Azores High and causes weaker than normal trade wind. As a result, less heat loses from the NTA Ocean and above-normal SST anomalies generated. In contrast, after the middle 1980s, the connection between CP ENSO and NAO-like anomaly has been disrupted. This leads to a weakening of CP ENSO influences on the NTA spring SST. The observed change in the relationship between NTA spring SST and CP ENSO is likely related to the state of the polar vortex. Before the middle 1980s, the polar vortex is weak, this favors the propagation of ENSO-related wave flux. The Rossby wave trains spread to the stratosphere during El Nino conditions and cause weaker than normal polar vortex, resulting in a negative NAO in the low levels. And the subtropical jet is enhanced and elongated which provides a potential waveguide for wave activity propagating to the Atlantic through a tropospheric way. However, the polar vortex is strong after mid-1980s, preventing the propagation of the ENSO-related wave trains through the stratosphere or the troposphere.

ENSO and Sea Surface Temperature Anomalies in Association with Canadian Wheat Yield Variability

ABSTRACTInterannual variations of spring wheat yields in Canadian agricultural regions are analyzed, together with the associated sea surface temperature (SST) anomalies in the northern hemisphere tropics and extratropics, from 1961 to 2015. The cubic trend is calculated and used to represent the trend related to advances in agricultural technology over this time period. The correlations between Canadian wheat yields at regional scales and the tropical El Niño–Southern Oscillation (ENSO) variability are not robust at any stage of the evolution of ENSO. Based on the power spectrum and cross-spectrum analysis, the most prominent yield variance is found in the Canadian Prairies, with a significant power peak of 4.5 years but does not co-vary significantly with interannual ENSO variability. ENSO weakly affects temperature and precipitation anomalies in the Canadian Prairie Region in summer—two important agroclimatic conditions for crop growth—and hence insignificantly impacts wheat yields. This indicates that there would be little benefit to including tropical ENSO indices in the operational wheat yield forecasting system. For Canadian wheat yield forecasting, attention should be paid to the preceding winter and spring SST anomalies in the northern extratropics. The SST anomalies associated with yields in the Canadian Prairie region and Central Region are generally stronger than those associated with yields in the Canadian Pacific Coast Region and eastern Maritime Region. In association with the Prairie Region and Central Region yields, SST shows pronounced anomalies in the mid-high latitudes of the North Pacific from winter to summer. The non-linearity of the SST anomalies associated with the Canadian yields is also clearly evident. Stronger (weaker) SST anomalies in the extratropical North Pacific correspond to low wheat yields in the Prairie (Central) Region, while weaker (stronger) SST anomalies correspond to high yields in the Prairie (Central) Region.

OLR perspective on the Indian Ocean Dipole with application to East African precipitation

Interannual variability of precipitation over eastern Africa (Somalia, Ethiopia, and Kenya) is impacted by the Indian Ocean dipole (IOD), which has its maximum amplitude during autumn. During northern spring, sea‐surface temperature (SST) in the tropical Indian Ocean is nearly always sufficiently high to sustain convection, but it exhibits no clear pattern of variability. Thus, precipitation variability over Eastern Africa during spring is not connected to any Indian Ocean interannual mode sustained by SST anomalies. Yet, seasonal variability in atmospheric convection might sustain interannual modes during spring independent of SST. We construct an index for the IOD based on outgoing long‐wave radiation anomaly (OLRA) instead of SST anomaly. During northern spring, analysis of this index shows that interannual precipitation over Eastern Africa is correlated with interannual variability similar to the IOD, as measured by OLR. The largest part of that relationship originates from the western Indian Ocean, with smaller contributions from the eastern Indian Ocean. Results indicate that atmospheric convection over the tropical Indian Ocean couples the atmospheric circulation over the eastern and western Indian basin irrespective of SST anomalies. Results from constructed analogue analysis show that positive SST anomaly during northern winter caused by persistence of subsidence and cloud–radiation–SST negative feedback over the southeastern Indian Ocean from the previous positive IOD is associated with formation of negative IOD later during the following autumn.

Possible impacts of spring sea surface temperature anomalies over South Indian Ocean on summer rainfall in Guangdong-Guangxi region of China

Based on observational and reanalysis data for 1979–2015, the possible impacts of spring sea surface temperature anomalies (SSTA) over the South Indian Ocean on the inter-annual variations of summer rainfall in Guangdong and Guangxi Provinces (i.e., the Guangdong-Guangxi area, GG) were analysed in this study. The physical mechanism behind these impacts was explored. Two geographic regions over [65°E–95°E, 35°S–25°S] and [90°E–110°E, 20°S–5°S] were defined as the western pole region and the eastern pole region, respectively, for the GG summer precipitation (PGG)-related South Indian Ocean dipole SSTA pattern (R-SIODP). The difference between springtime SST anomalies averaged over the western pole region and that averaged over the eastern pole region was defined as the R-SIODP index. The correlation between the spring R-SIODP index and GG summer precipitation can reach up to 0.52. In the spring of positive R-SIODP anomaly, southerly winds over the western pole of the R-SIODP weaken, whereas the southeast trade winds over the eastern pole strengthen. By means of the wind-evaporation-SST feedback mechanism, the enhanced southeast trade winds can weaken the evaporation over the western pole of the R-SIODP and enhance the evaporation over the eastern pole. This results in a sustained positive SSTA in the western pole of the R-SIODP and a sustained negative SSTA in the eastern pole, whereby the distribution of the SSTAs maintains until summer. The SST dipole abnormally enhances the cross-equatorial airflow near 105°E, which intensifies the anomalous anti-cyclonic circulation over South China Sea at 850 hPa and simultaneously results in abnormal enhancement of water vapour transport to GG. Additionally, the SST dipole promotes abnormal divergence in the lower troposphere and abnormal convergence in the upper troposphere over the maritime continent (MC) region. Moreover, the low-level convergence in GG is enhanced, which results in abnormal enhancement of ascending motion in the GG that is conducive to positive summer rainfall anomaly in this region. In this study, the spring R-SIODP index, the SST to the east of Australia and to the east of southern Africa, and the North Atlantic oscillation (NAO) index were used to construct a statistical prediction model for the inter-annual variability of the GG summer rainfall anomaly. This model can well predict the accuracy of the inter-annual variation of GG summer rainfall.

Two Types of Interannual Variability of South China Sea Summer Monsoon Onset Related to the SST Anomalies before and after 1993/94

Abstract An advance in the timing of the onset of the South China Sea (SCS) summer monsoon (SCSSM) during the period 1980–2014 can be detected after 1993/94. In the present study, the interannual variability of the SCSSM onset is classified into two types for the periods before and after 1993/94, based on their different characteristics of vertical coupling between the upper- and lower-tropospheric circulation and the differences in their related sea surface temperature anomalies (SSTAs). On the interannual time scale, type-I SCSSM onset is characterized by anomalous low-level circulation over the northern SCS during 1980–93, whereas type-II SCSSM onset is associated with anomalies of upper-level circulation in the tropics during 1994–2014. The upper-tropospheric thermodynamic field and circulation structures over the SCS are distinct between the two types of SCSSM onset, and this investigation shows the importance of the role played by the spring SSTAs in the southern Indian Ocean (SIO) and that of ENSO events in type-I and type-II SCSSM onset, respectively. In the early episode, the warming SIO SSTAs can induce an anomalous low-level anticyclone over the northern SCS that affects local monsoonal convection and rainfall over land to its north, demonstrating a high sensitivity of subtropical systems in type-I SCSSM onset. However, in type-II SCSSM onset during the later episode, the winter warm ENSO events and subsequent warming in the tropical Indian Ocean can influence the SCSSM onset by modulating the spring tropical temperature and upper-level pumping effect over the SCS.

Influence of the North Pacific Victoria mode on the Pacific ITCZ summer precipitation

AbstractThis study demonstrates the close connection between the second dominant mode of spring sea surface temperature anomalies (SSTAs) in the North Pacific poleward of 20°N, referred to as the Victoria mode (VM), and the Pacific Intertropical Convergence Zone (ITCZ) precipitation during the following summer. Our analysis shows that strong positive VM cases are followed by positive precipitation anomalies over the central‐eastern Pacific ITCZ region, in association with negative precipitation anomalies over the ITCZ regions of the tropical western Pacific and eastern North Pacific. The hypothesized physical mechanism through which the spring VM induces the Pacific ITCZ summer precipitation is similar to but slightly different from the seasonal footprinting mechanism. During strong positive VM cases, SSTAs in the subtropics associated with the spring VM persist until summer and develop toward the equator, where low‐level convergence and divergence caused by SSTA gradients give rise to enhanced precipitation over the central‐eastern Pacific ITCZ region and to reduced precipitation over the ITCZ regions of the tropical western Pacific and eastern North Pacific. The thermodynamic ocean‐atmosphere coupling between the ITCZ and SSTAs associated with the VM may play a vital role in the initiation of El Niño–Southern Oscillation (ENSO) events. The VM influence on tropical Pacific summer precipitation can be passed on to the next year through its influence on ENSO. A VM‐based linear model is established to predict the tropical Pacific summer precipitation, which yields skillful forecasts for summer precipitation across almost the entire tropical Pacific.

Different relationships between spring SST in the Indian and pacific oceans and summer precipitation in China

Observational and reanalysis data are used to investigate the different relationships between boreal spring sea surface temperature (SST) in the Indian and Pacific oceans and summer precipitation in China. Partial correlation analysis reveals that the effects of spring Indian Ocean SST (IO SST) and Pacific SST (PSST) anomalies on summer precipitation in China are qualitatively opposite. When IO SST anomalies are considered independently of PSST anomalies, precipitation decreases south of the Yangtze River, in most areas of Inner Mongolia, and in some parts of Liaoning Province, and increases in the Yangtze River valley, parts of southwestern and northern China, northeastern Inner Mongolia, and Heilongjiang Province. This results in a negative-positive-negative-positive pattern of precipitation anomalies in China from south to north. When PSST anomalies (particularly those in the Nino3.4 region) are considered independently of IO SST anomalies, the pattern of precipitation anomalies in China is positive-negative-positive-negative from south to north. The genesis of summer precipitation anomalies in China is also examined when El Nino-Southern Oscillation (ENSO) signals are removed from the ocean and atmosphere. An anticyclonic low-level wind anomaly forms in the South China Sea-Northwest Pacific area when the IO SST anomaly (SSTA) is warm and the Northwest Pacific SSTA is cold. This anticyclonic anomaly substantially influences summer precipitation in China. Anomalous warming of tropical IO SST induces positive geopotential height anomalies in the subtropics and an east-west dipole pattern in midlatitudes over Asia. These anomalies also affect summer precipitation in China.

Climate as a driver of population variability in breeding Gentoo Penguins Pygoscelis papua at the Falkland Islands

Detecting and predicting how populations respond to environmental variability are eminent challenges in conservation research and management. This is particularly true for wildlife populations at high latitudes, many of which demonstrate changes in population dynamics associated with global warming. The Falkland Islands (Southwest Atlantic) hold one of the largest Gentoo Penguin Pygoscelis papua populations in the world, representing c. 34% of the global population. The numbers of breeding Gentoo Penguins at the Falkland Islands have shown a high degree of inter‐annual variability since monitoring commenced in 1990. However, proximate causes of annual variability in breeding numbers have not been explored. Here we examine 21 years of Gentoo Penguin breeding surveys from the Falkland Islands and assess whether inter‐annual variability in the number of breeding pairs were correlated with proxies of environmental variability. There was a positive correlation between the number of breeding pairs and a broad‐scale climatic variation index, the Southern Oscillation Index (SOI). In turn, the SOI was significantly correlated with spring sea surface temperature anomalies, indicating a more immediate atmospherically forced response to El Niño Southern Oscillation variability in the Southwest Atlantic than previously reported. However, we also describe a non‐linear response to environmental variability that may highlight foraging plasticity and/or the complexity of regional ecosystem interactions that operate across a range of different scales.

Combined effects of fisheries and climate on a migratory long‐lived marine predator

Summary The impact of climate on marine ecosystems is now well documented, but remains complex. Climate change may interact with human activities to effect population dynamics. In addition, in migratory species conditions are different between the breeding and wintering grounds, resulting in more complex dynamics. All these possible effects should be considered to predict the future of endangered species, but very few studies have investigated such combined interactions. As a case study, we assessed the relative impact of fisheries and of oceanographic conditions in breeding and wintering sites on adult survival and breeding success of a population of the endangered black‐browed albatross Thalassarche melanophrys in the Kerguelen Islands, Southern Indian Ocean. This study was based on long‐term monitoring of individually marked individuals (1979–2005) and identification by tracking studies and band recoveries of the oceanic feeding zones used during breeding and non‐breeding seasons. Breeding success was variable until 1997 and then declined gradually, from 0·88 to 0·48 chicks per egg laid. It was favoured by positive sea‐surface temperature anomalies (SSTA) and trawl fishery during the breeding period, whereas it was negatively affected by positive SSTA around Tasmania, where the species winters. Adult survival was 0·918 ± 0·004 on average and increased with SSTA during incubation, but decreased significantly with high tuna longlining effort in the wintering zone. Our analyses show that demographic parameters were influenced by both climate and fisheries in both breeding and wintering grounds, but with different effect size. Black‐browed albatross breeding success was more favoured by trawlers’ offal and discards than by any of the seasonally/spatially oceanographic conditions, whereas their survival was equally affected by tuna longline fishery through incidental by‐catch and spring SSTA. Synthesis and applications. Our work underlines that a comprehensive knowledge of the life history of a species in all the habitats used is important to disentangle the respective roles of environmental conditions and human factors on population dynamics. Identification of these effects is required when proposing effective conservation measures, because the conservation of threatened species may depend on their wintering country's exclusive economic zones.

Investigating the link between early season Caribbean rainfall and the El Niño + 1 year

AbstractThe Caribbean rainfall season is best characterized by its bimodal nature, with an initial peak in May–June and a second more prominent one in September–October. This allows for a convenient division into an early and a late rainfall season. In this study we examine the rainfall patterns of the early rainfall season (mid April to July) for links with El Niño–Southern Oscillation (ENSO) events. Whereas traditionally ENSO events have been identified with dry conditions during the later Caribbean rainfall season, recent research suggests a second signal that manifests itself as a wet early rainfall season of the year of ENSO decline (the El Niño + 1 year). Two leading empirical orthogonal function modes of early season Caribbean rainfall are examined for evidence of this. Strong correlations are shown to exist between the first mode and wintertime equatorial Pacific anomalies. The first mode explains nearly half of the early season variability. The idea that the wintertime Pacific anomalies alter the early Caribbean rainfall season via the warm spring sea surface temperature anomalies they induce in the north tropical Atlantic is also investigated. An atmospheric general circulation model is also used to show that, when warm/cold anomalies exist across the north tropical Atlantic, this results in a large‐scale atmospheric circulation that is more/less favourable to rainfall production over the Caribbean. Copyright © 2002 Royal Meteorological Society.