North Pacific SST Anomalies Research Articles

Characteristics and mechanisms of the severe compound cold-wet event in southern China during February 2022

A severe compound cold-wet event occurred in southern China (hereafter referred to as CWESC ) in February 2022, leading to enormous socioeconomic losses. In this study, we proposed a new index to denote the severity of the compound cold-wet event. Based on the multivariate survival method, the CWESC in February 2022 is identified as the severest event during the past six decades. Our results indicate that the CWESC in 2022 is jointly regulated by the La Niña-like SST condition in the tropical Pacific and the warm SST anomalies in the North Atlantic, and a teleconnection in the Northern Hemisphere during winter (hereafter referred to as TNHW) plays the key role. The TNHW pattern originates from the tropical Pacific, and it splits into two routes over the North Atlantic. The northern branch of TNHW propagates via the Arctic and Siberia, causing intensified near-surface northerly wind and partially inducing an anomalous anticyclone over the western North Pacific (WNP). The southern branch of TNHW propagates via the Mediterranean and western Asia, inducing a deepened India–Burma trough and partially inducing the anomalous anticyclone over WNP. The intensified near-surface northerly wind causes enhanced cold advection over southern China, while the deepened India–Burma trough and the anomalous anticyclone over WNP cause increased southerly warm and moist air flow towards southern China, resulting in the CWESC in 2022. Moreover, four groups of numerical experiments forced by tropical Pacific, North Pacific, and North Atlantic SST anomalies are conducted based on the Community Atmosphere Model version 5. The results confirm the important roles of the La Niña-like condition and the warm SST anomalies in the North Atlantic in causing the CWESC in 2022.

Decadal change of spring dust activity in western Iran and its mechanism

Western Iran is an important dust source region in Middle East, with strong dust activities occurring in springtime. Based on a three-hourly meteorological station data, remarkable decadal change of dust frequency in the spring season has been found in the west and southwest of Iran, with less dust activities during 1992–2005 (hereafter as “P1”) and more frequent dust activities occurring during 2006–2015 (hereafter as “P2”). The decadal change signal in dust activities is closely associated with the corresponding decadal difference in precipitation and atmospheric moisture transportation in the region. Compared with P1 period during 1992–2005, anomalous moisture divergence over the center of Middle East can be found in P2 period during 2006–2015, suggesting less moisture transport to the western Iran from the Arabian Sea, Red Sea, and the Persian Gulf, hence there is relatively less precipitation and dry soil moisture over the main dust source regions in the study region, which is favorable for more frequent dust emissions in P2 period. Meanwhile, westerly anomaly in P2 period can also be found in western Iran and upstream regions, such as Iraq and Syria, which is favorable for more dust transport to western Iran from upstream dust source region in Middle East. Furthermore, negative SST anomalies in central and western North Pacific and positive SST anomalies in the eastern North Pacific can be found in P1 period, which is corresponding to positive phase of Pacific Decadal Oscillation (PDO). Conversely, a negative phase of PDO can be found during P2 period. This suggests that PDO is the key influential factor for the decadal change of spring dust activities in western Iran.

The influence of Pacific-North American teleconnection on the North Pacific SST anomalies in Wintertime under the global warming

The impact of the enhancing Pacific-North American teleconnection (PNA) on the intensity of the first mode of SST anomalies (SSTa) in wintertime North Pacific [known as the Pacific decadal oscillation (PDO)-like SST pattern] under global warming is studied using reanalysis datasets and 12 selected CMIP5 models. The robust observational result of the PNA one month ahead of the PDO shows that the PNA has a great effect on the PDO-like SSTa. The intensities of PNA and PDO are defined with elimination of the ENSO signals to evaluate the direct impact of PNA on the PDO in the North Pacific under global warming. By comparing RCP8.5 and historical scenario of selected multi-models (PNA enhanced models), future projection illustrates that the PDO intensity will intensify 2.2 times its internal variability. Approximately 67% of the increase in PDO variations is contributed by the PNA-induced SSTa in the future warming scenario of multi-models ensemble mean. Models with stronger intensification of PNA variability tends to have larger magnitude of SSTa response in the North Pacific, which has more contributions to the enhancement of PDO intensity change in a warmer climate. This may shed some light on the projection of PDO variability and the relative role of PNA forcing under the global warming.

Modulation of Atmospheric Response to North Pacific SST Anomalies under Global Warming: A Statistical Assessment

Abstract In this study the modulation of ocean-to-atmosphere feedback over the North Pacific in early winter from global warming is investigated based on both the observations and multiple climate model simulations from a statistical perspective. It is demonstrated that the basin-scale atmospheric circulation displays an equivalent barotropic ridge in response to warm SST anomalies in the Kuroshio–Oyashio Extension (KOE) region. This warm SST–ridge response in early winter can be enhanced significantly by global warming, indicating a strengthening of air–sea coupling over the North Pacific. This enhancement is likely associated with the intensification of storm tracks and, in turn, the amplification of atmospheric transient eddy feedback in a warm climate, although the secular trend of enhanced storm-track activity over the North Pacific is suggested to be biased in reanalysis product.

Relationship between North Pacific SST anomalies and the atmospheric circulation anomalies in January 2008

Based on the NCEP (National Centers for Environmental Prediction) data, the relationship between the Sea Surface Temperature Anomalies (SSTAs) in the North Pacific and the atmospheric circulation anomalies in January 2008 is analyzed in this study. The SSTA mode most correlated with the Geopotential Height anomalies (GHAs) in January 2008 in the North Pacific exhibited a basin-wide horseshoe pattern with a warm center in November 2007. This persistent SSTA pattern would induce positive GHAs in the Aleutian Low area and East Asia and the northward extension of the West Pacific Subtropical High in January 2008 by maximum diabatic heating in the atmosphere over the Kuroshio Oyashio Extension (KOE) area, leading to the occurence of the circumpolar trough-ridge wave train anomaly in January 2008.

On the relationship between the interannual and decadal SST variability in the North Pacific and tropical Pacific Ocean

To address the relationship between the North Pacific and tropical SST anomalies on decadal and interannual timescales, we analyzed observed SST during the period 1950–2000. The SST variability in the North Pacific has two fairly well separated timescales: (1) decadal and (2) interannual, and each has a markedly different relationship with tropical variability. Both the decadal and interannual variability in the North Pacific is connected to the evolution of tropical SST variability with different lead‐lag relationships. The decadal SST variability in the North Pacific is found to lead tropical decadal variability by approximately 5 ∼ 7 years; however, the interannual SST variability is in the North Pacific in equilibrium with the tropical interannual variability. It is also shown that the spatial structure of the decadal variability in the North Pacific is significantly different from the interannual variability.

North Pacific Atmospheric and SST Anomalies in 1997: Links to ENSO?

In the summer of 1997, positive sea surface temperature anomalies (SSTA) extended across the Gulf of Alaska (GOA) and into the eastern Bering Sea (EBS). The SSTA in the EBS are at least in part due to atmospheric causes. Anomalously high 925 mb temperatures and 700 mb geopotential heights and low 925 mb relative humidities, and hence decreased low cloud cover, occurred over the region during April to August. This resulted in enhanced warming of the GOA and EBS owing to increased insolation. The anomalous solar heating was particularly great in the EBS from mid‐May to mid‐July. The pattern of positive 700 mb height anomalies for April to August 1997 is similar to its counterpart formed by compositing the April to August anomalies that occurred during previous El Niños. The positive equatorial SSTA for 1997 was one of the strongest on record for summer months. The existence of an equatorial/high‐latitude connection and the strength of the summer equatorial SSTA in 1997 suggest an El Niño/Southern Oscillation (ENSO) influence in the GOA and EBS. The warming in the Bering Sea and North Pacific during summer 1997 appears to be due in part to the confluence of three meteorological factors which favoured clear skies. There was not only an El Niño influence, but also a decadal trend toward higher 700 mb geopotential heights and a particularly strong blocking ridge weather pattern over the Gulf of Alaska in May.

Teleconnections between El Niño and La Niña events and summer extended dry spells on the Canadian Prairies

Teleconnections among El Niño and La Niña events, North Pacific sea surface temperature anomalies, and summer (June, July, August) extended dry spells on the Canadian Prairies are documented and analysed. For the period 1948–1991, results show the majority of El Niño events associated with a persistent North Pacific SST anomaly pattern consisting of anomalously cold water in the east-central North Pacific and anomalously warm water along the west coast of North America. The average number of summer extended dry spells on the Prairies associated with El Niño events is significantly higher than for non-El Niño periods. This relationship occurs during the second summer following the mature stage of El Niño events. Further analysis reveals that La Niña events are associated with opposite North Pacific SST anomaly patterns that also tend to persist for several seasons. The average number of summer extended dry spells associated with these events is significantly lower than for non-La Niña periods. Even though the relationships among El Niño, La Niña, North Pacific SST anomalies, and extended dry spells show high variability, the results of this study may be considered as an initial step towards contributing to a long-range forecasting technique of summer extended dry spells on the Canadian Prairies. Copyright © 1999 Royal Meteorological Society

Teleconnections between El Niño and La Niña events and summer extended dry spells on the Canadian Prairies

Teleconnections among El Nino and La Nina events, North Pacific sea surface temperature anomalies, and summer (June, July, August) extended dry spells on the Canadian Prairies are documented and analysed. For the period 1948-1991, results show the majority of El Nino events associated with a persistent North Pacific SST anomaly pattern consisting of anomalously cold water in the east-central North Pacific and anomalously warm water along the west coast of North America. The average number of summer extended dry spells on the Prairies associated with El Nino events is significantly higher than for non-El Nino periods. This relationship occurs during the second summer following the mature stage of El Nino events. Further analysis reveals that La Nina events are associated with opposite North Pacific SST anomaly patterns that also tend to persist for several seasons. The average number of summer extended dry spells associated with these events is significantly lower than for non-La Nina periods. Even though the relationships among El Nino, La Nina, North Pacific SST anomalies, and extended dry spells show high variability, the results of this study may be considered as an initial step towards contributing to a long-range forecasting technique of summer extended dry spells on the Canadian Prairies. Copyright © 1999 Royal Meteorolog- ical Society.

An analysis of North Pacific SST anomalies by means of a linear thermodynamic stochastic two-dimensional model

An analysis of North Pacific SST anomalies by means of a linear thermodynamic stochastic two-dimensional model

An analysis of North Pacific SST anomalies by means of a linear thermodynamic stochastic two-dimensional model

The evolution of sea surface temperature anomalies (SSTA) in the North Pacific is studied with a 2-D linear heat transport equation with seasonally varying feedback and constant diffusion. The extension of the model to include an average cyclo-stationary SSTA advection field, estimated from seasonal ship-drift data of surface currents, does not improve the fit to the data. The model parameters are determined by an optimal fit of the observed SSTA lag-time auto-correlation function and the optimal model turns out to be statistically satisfactory (at the 95% confidence level) in most (83%) of the analysed region. The model is also able to explain the lag-time SSTA auto-covariances. Additionally, by applying the model operator to the observed monthly SSTA time series we obtain the actual stochastic forcing. This forcing is consistent with the usual concept of midlatitude atmospheric behaviour. In particular, the basic hypothesis of the stochastic approach, that the forcing is uncorrelated in the SSTA time scale, is verified. Both the success of the model hierarchy fitting procedure and the comparison of the best-fit value of the feedback parameter with mixed-layer depth data suggest that the feedback can be seen as an essentially local process closely related to the thermal inertia of the ocean mixed-layer. DOI: 10.1034/j.1600-0870.1995.00007.x

Impact of localized tropical and extratropical SST anomalies in ensembles of seasonal GCM integrations

AbstractA series of 120‐day ensemble integrations of a general circulation model, designed to assess the impact of geographically localized sea‐surface‐temperature (SST) anomalies in both the tropics and extratropics, are described. These experiments contribute firstly to an appraisal of the relative roles of tropical and extratropical SST anomalies on interannual variability of the large‐scale circulation in the northern extratropics, and secondly to an assessment of the role of quasi‐stationary diabatic‐heating anomalies on model systematic error, including blocking activity.Overall it is found that SST anomalies associated with El Niño and La Niña have a larger and more reproducible impact on the extratropics than the chosen extratropical SST anomalies. These extratropical anomalies were localized to the north‐west Pacific, and north‐west Atlantic, with realistic amplitude. However, unlike earlier studies, a response to the extratropical North Pacific SST anomalies has been obtained over the North Pacific which is correlated with the sign of the imposed SST anomaly. The response to extratropical SST anomalies in the north‐west Atlantic are similar to the results obtained from an earlier study. The downstream responses to the extratropical Pacific and Atlantic SST anomalies are qualitatively similar to one another. Overall it is concluded that the northern large‐scale flow is influenced by such extratropical SST anomalies.The response to idealized tropical SST anomalies was also studied. In particular, a localized anomaly over Indonesia had a very substantial impact on the Hadley circulation, on zonal flow, and on blocking frequency over the North Pacific and Europe. This response was such as to reduce model systematic error: locally in the vicinity of the SST anomaly, remotely around the tropics, and remotely in the extratropics. A similar, though weaker, impact on Euro‐Atlantic blocking was obtained with an idealized Caribbean SST anomaly.Further statistical and dynamical analyses suggested that the extratropical response to the Indonesian SST anomaly occurs through the creation of two distinct planetary‐scale regimes, in one of which the formation of blocks is much favoured by increased ridges on the north‐eastern side of the oceans.

On the Roles of Tropical and Midlatitude SSTs in Forcing Interannual to Interdecadal Variability in the Winter Northern Hemisphere Circulation

Three numerical experiments have been conducted to explore the relative roles of midlatitude and tropical SSTs in producing atmospheric variability. In these experiments, anomalous observed SSTs were prescribed in 1) the tropical oceans only, 2) the midlatitude oceans only, and 3) globally. These simulations were conducted with the same atmospheric model and covered the period 1970–88. Although each simulation reproduced some aspects of the observed circulation variability, the results from the two experiments including tropical SSTs performed best by most measure particularly in showing temporal signals that agreed with those seen in the observations. The results indicate that the response of the observed atmospheric circulation to North Pacific SST anomalies is much smaller and much less systematic than the response to tropical SSTs. It is suggested that the apparent links between North Pacific SSTs and the observed winter circulation am due primarily to the effects on oceanic forcing by the recurrent patterns of atmospheric variability remotely forced by changes in tropical SSTs. The results are consistent with the idea that the major shift in the winter circulation during the mid-1970s was forced by changes in tropical SSTS.

Modeling North Pacific SST anomalies as a response to anomalous atmospheric forcing

Large-scale sea surface temperature anomalies (SSTA) in the North Pacific ocean are often persistent for several months during wintertime. There is observational evidence that these patterns are forced by anomalous atmospheric circulation. Since the latter is in part related to the tropical El Niño/Southern Oscillation (ENSO) phenomenon it is hypothesized that part of the North Pacific SSTA's may be interpreted as remote oceanic response to anomalous equatorial Pacific SSTA's. Two experiments with a multi-level primitive equation model of the North Pacific have been conducted to study the influence of such anomalous atmospheric circulation on the SST. In both experiments anomalous wind stress as derived from the 1950–1979 COADS subset is specified as anomalous forcing. In experiment 1 no anomalous heat flux is introduced whereas in experiment 2 anomalous heat fluxes are estimated from anomalous surface winds and a simple advective atmosphere. In both experiments the GCM SSTA response are able to reproduce the main features of the time series of observed SSTA, in particular in winter. In experiment 1, however, the magnitudes are systematically too low. The addition of anomalous heat fluxes in experiment 2 significantly improves the simulation. The ENSO signal is clearly present in both simulations.