Complicated ENSO models do not significantly outperform very simple ENSO models

Recent studies arising from both statistical analysis and dynamical disease models indicate that there is a link between the incidence of cholera, a paradigmatic waterborne bacterial illness endemic to Bangladesh, and the El Niño–Southern Oscillation (ENSO). Cholera incidence typically increases following boreal winter El Niño events for the period 1973–2001. Observational and model analyses find that Bangladesh summer rainfall is enhanced following winter El Niño events, providing a plausible physical link between El Niño and cholera incidence. However, rainfall and cholera incidence do not increase following every winter El Niño event. Substantial variations in Bangladesh precipitation also occur in simulations in which identical sea surface temperature (SST) anomalies are prescribed in the central and eastern tropical Pacific. Bangladesh summer precipitation is thus not uniquely determined by forcing from the tropical Pacific, with significant implications for predictions of cholera risk. Nonparametric statistical analysis is used to identify regions of SST anomalies associated with variations in Bangladesh rainfall in an ensemble of pacemaker simulations. The authors find that differences in the response of Bangladesh summer precipitation to winter El Niño events are strongly associated with the persistence of warm SST anomalies in the central Pacific. Also there are significant differences in the SST patterns associated with positive and negative Bangladesh rainfall anomalies, indicating that the response is not fully linear. SST anomalies in the Indian Ocean also modulate the influence of the tropical Pacific, with colder Indian Ocean SST tending to enhance Bangladesh precipitation relative to warm Indian Ocean SST for identical conditions in the central and eastern tropical Pacific. This influence is not fully linear. Forecasts of Bangladesh rainfall and cholera risk may thus be improved by considering the Niño-3 and Niño-4 indices separately, rather than the Niño-3.4 index alone. Additional skill may also be gained by incorporating information on the southeast Indian Ocean and by updating the forecast with information on the evolution of the SST anomalies into spring.

Sea surface temperature and rainfall anomaly over the Bay of Bengal during the El Niño-Southern Oscillation and the extreme Indian Ocean Dipole events between 2002 and 2016

The coupling between sea surface temperature (SST) anomalies and rainfall is an important driver of tropical climate variability. Observations however reveal inconsistencies, such as decreased convective rainfall in regions with positive SST anomalies in the tropical Indian and Atlantic Oceans during and after El Niño–Southern Oscillation (ENSO) events. The upper troposphere warms during El Niño events, stabilizing the atmosphere. SST anomalies only account for the influence of the surface. Using theoretical arguments, we show that relative SST (RSST; defined as SST minus its tropical mean) anomalies, by also accounting for the influence of upper tropospheric temperature anomalies on gross moist stability, explain tropical convection interannual variations better than SST anomalies in observations and climate models. This relation further improves when RSST anomalies are weighted by the precipitation climatology to account for low and high‐precipitation regimes. Using RSST is thus essential to understand El Niño–Southern Oscillation teleconnections and interactions between modes of tropical climate variability.

El Niño Southern Oscillation (ENSO) impacts the supply of and, to some extent, the demand for primary commodities. But what are the consequences of ENSO shocks for these commodity price dynamics? I consider monthly series of 43 primary commodity prices and sea surface temperature (SST) anomalies in the Niño3.4 region from January 1980 to December 2016. The SST anomalies serve as a proxy for ENSO, as persistent positive (negative) SST deviations from their historical mean are associated with El Niño (La Niña) events. I apply a time‐varying smooth transition autoregressive modeling framework to account for potentially complex dynamic relationships between SST anomalies and prices. The estimated models reveal more amplified price responses during El Niño events, and at the onset of the ENSO cycle. I find statistically significant linkages between SST anomalies and a subset of agricultural commodity prices, which manifests in a better price forecasting for the commodities produced in the tropics. While I also find some in‐sample evidence for prices of selected nonagricultural commodities, for example, timber and metals, the ability of SST anomalies to predict these commodity prices in an out‐of‐sample setting is lacking. These findings carry important welfare implications, especially for developing economies that have been historically linked to the behavior of primary commodity prices, and offer valuable insights to policy makers working in areas related to economic growth and foreign aid programs, as well as those concerned with issues of farm income and rural poverty.

Anomalous seasonal patterns of precipitation variability over South America (SA) associated with El Niño‐Southern Oscillation (ENSO) and non‐ENSO (residual) conditions were assessed during 1951–2016. Patterns were obtained from empirical orthogonal functions analysis of total and residual precipitation seasonal anomalies. In austral spring and summer, precipitation variability is dominated by a dipolar anomaly mode with a centre extending from northwestern to northeastern SA and another in central‐eastern Brazil and part of southeastern SA (SESA) during spring, and a centre in northwestern SA and another extending from northeastern SA to central and eastern Brazil and central SESA, during summer. These modes are associated with ENSO to a greater extent during spring than summer. In summer, there is a strong association of the dipolar precipitation pattern with sea surface temperature (SST) anomalies on the east coast of Brazil, which indicates local influence. In austral fall, SST anomalies in the tropical South Atlantic relate to precipitation anomalies in northeast SA, and those in the tropical north Atlantic (TNA) to precipitation anomalies in northwestern SA, through the intertropical convergence zone anomalous position modulated by SST anomalies. In this same condition, the ENSO acts only to intensify or weaken the dominant precipitation pattern, depending on its phase, mainly over SESA. In contrast, the second variability mode in fall is characterized by positive SST anomalies in the Indian Ocean and equatorial and southern Atlantic Ocean and negative in the TNA. The importance of ENSO and the Indian Ocean in the characterization of the SST dipole in the tropical Atlantic explains the main changes in precipitation patterns over northeastern Brazil not been discussed in previous studies.

While significant improvements have been made in understanding how the El Nino–Southern Oscillation (ENSO) impacts both North American and Asian climate, its relationship with the North Atlantic Oscillation (NAO) remains less clear. Observations indicate that ENSO exhibits a highly complex relationship with the NAO-associated atmospheric circulation. One critical contribution to this ambiguous ENSO/NAO relationship originates from ENSO’s diversity in its spatial structure. In general, both eastern (EP) and central Pacific (CP) El Nino events tend to be accompanied by a negative NAO-like atmospheric response. However, for two different types of La Nina the NAO response is almost opposite. Thus, the NAO responses for the CP ENSO are mostly linear, while nonlinear NAO responses dominate for the EP ENSO. These contrasting extra-tropical atmospheric responses are mainly attributed to nonlinear air-sea interactions in the tropical eastern Pacific. The local atmospheric response to the CP ENSO sea surface temperature (SST) anomalies is highly linear since the air-sea action center is located within the Pacific warm pool, characterized by relatively high climatological SSTs. In contrast, the EP ENSO SST anomalies are located in an area of relatively low climatological SSTs in the eastern equatorial Pacific. Here only sufficiently high positive SST anomalies during EP El Nino events are able to overcome the SST threshold for deep convection, while hardly any anomalous convection is associated with EP La Nina SSTs that are below this threshold. This ENSO/NAO relationship has important implications for NAO seasonal prediction and places a higher requirement on models in reproducing the full diversity of ENSO.

The East African ‘short rains’ in October–December (OND) exhibit large interannual variability. Drought and flooding are not unusual, and long-range rainfall forecasts can guide planning and preparedness for such events. Although seasonal forecasts based on dynamical models are making inroads, statistical models based on sea surface temperature (SST) precursors are still widely used, making it important to better understand the strengths and weaknesses of such models. Here we define a simple statistical forecast model, which is used as a tool to shed light on the dynamics that link SSTs and rainfall across time and space, as well as on why such models sometimes fail. Our model is a linear regression, where the August states of El Niño-Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD) predict about 40% of the short rains variability in 1950–2020. The forecast errors are traced back to the initial SSTs: too-wet (too-dry) forecasts are linked linearly to positive (negative) initial ENSO and IOD states in August. The link to the initial IOD state is mediated by changes in the IOD between August and OND, highlighting a physical mechanism for prediction busts. We also identify asymmetry and nonlinearity: when ENSO and/or the IOD are positive in August, the range and variance of OND forecast errors are larger than when the SST indices are negative. Upfront adjustments of predictions conditional on initial SSTs would have helped in some years with large forecast busts, such as the dry 1987 season during a major El Niño, for which the model erroneously predicts copious rainfall, but it would have exacerbated the forecast in the wet 2019 season, when the IOD was strongly positive and the model predicts too-dry conditions.

SST Anomalies and Blocking

The response of both the time of onset, and the strength of the Asian summer monsoon, to regional aspects of the sea surface temperature (SST) anomalies in the tropical Pacific Ocean associated with El Niño/Southern Oscillation (ENSO) has been investigated through a series of sensitivity experiments with the Universities Global Atmospheric Modelling Programme (UGAMP) General Circulation Model (UGCM). This paper builds on the work of Ju and Slingo (1995) and on their hypothesis that the relationship between the Asian summer monsoon and ENSO involved the latitudinal position and strength of the tropical convective maximum (TCM) over Indonesia and the west Pacific in the preceding spring. the inference from their results was that the modulation of the TCM might be associated either with changes in the Walker circulation through the influence of the east Pacific SST anomalies, or with changes in the local Hadley circulation associated with the in situ SST anomalies in the west Pacific. the investigation has focused on the particular contrasting years of 1983 and 1984. the experiments described in this paper are designed to isolate the effects of the principal SST anomalies in the east and central Pacific, associated with El Niño/La Niño, from those of opposite sign which develop in the west Pacific as a complementary pattern during the mature phase of El Niño/La Niño.The results of the experimentation suggest that, at least for the test cases of 1983 and 1984, the modulation of the Walker circulation, with implied additional subsidence over the eastern hemisphere, is the dominant mechanism whereby the Asian summer monsoon is weakened during El Niñño years. However, the late onset during El Niño years may also be associated with the complementary cold SST anomalies in the west Pacific which delay the northwards transition of the TCM. During La Niño, the modulation of the Walker circulation appears not to be the controlling factor which determines the stronger monsoons. the UGCM results suggest that the complementary warm SST anomalies in the west Pacific enhance the TCM, and it is this in situ response by the TCM that leads to an early onset and stronger monsoon. the importance of warm anomalies in the west Pacific in the development of a strong monsoon has been investigated further through a case‐study of the 1994 season. the year 1994 was an El Niño year in which the monsoon was unexpectedly active, but which was also marked by warmer than normal SSTs in the west Pacific.The sensitivity experiments have also elucidated the role of El Niño in influencing the precursory signature of stronger subtropical westerlies over India and south‐east Asia during the winter and spring preceding weak monsoons. the results suggested that the equatorwards shift of the subtropical jet is a remote response to the warm SST anomalies in the central and east Pacific associated with El Niño.

The response of both the time of onset, and the strength of the Asian summer monsoon, to regional aspects of the sea surface temperature (SST) anomalies in the tropical Pacific Ocean associated with El Niño/Southern Oscillation (ENSO) has been investigated through a series of sensitivity experiments with the Universities Global Atmospheric Modelling Programme (UGAMP) General Circulation Model (UGCM). This paper builds on the work of Ju and Slingo (1995) and on their hypothesis that the relationship between the Asian summer monsoon and ENSO involved the latitudinal position and strength of the tropical convective maximum (TCM) over Indonesia and the west Pacific in the preceding spring. the inference from their results was that the modulation of the TCM might be associated either with changes in the Walker circulation through the influence of the east Pacific SST anomalies, or with changes in the local Hadley circulation associated with the in situ SST anomalies in the west Pacific. the investigation has focused on the particular contrasting years of 1983 and 1984. the experiments described in this paper are designed to isolate the effects of the principal SST anomalies in the east and central Pacific, associated with El Niño/La Niño, from those of opposite sign which develop in the west Pacific as a complementary pattern during the mature phase of El Niño/La Niño. The results of the experimentation suggest that, at least for the test cases of 1983 and 1984, the modulation of the Walker circulation, with implied additional subsidence over the eastern hemisphere, is the dominant mechanism whereby the Asian summer monsoon is weakened during El Niñño years. However, the late onset during El Niño years may also be associated with the complementary cold SST anomalies in the west Pacific which delay the northwards transition of the TCM. During La Niño, the modulation of the Walker circulation appears not to be the controlling factor which determines the stronger monsoons. the UGCM results suggest that the complementary warm SST anomalies in the west Pacific enhance the TCM, and it is this in situ response by the TCM that leads to an early onset and stronger monsoon. the importance of warm anomalies in the west Pacific in the development of a strong monsoon has been investigated further through a case-study of the 1994 season. the year 1994 was an El Niño year in which the monsoon was unexpectedly active, but which was also marked by warmer than normal SSTs in the west Pacific. The sensitivity experiments have also elucidated the role of El Niño in influencing the precursory signature of stronger subtropical westerlies over India and south-east Asia during the winter and spring preceding weak monsoons. the results suggested that the equatorwards shift of the subtropical jet is a remote response to the warm SST anomalies in the central and east Pacific associated with El Niño.

Effects of the ENSO on rainfall erosivity in the Fujian Province of southeast China

Spring Central Asian precipitation (SCAP) holds significant implications for local agriculture and ecosystems, with its variability mainly modulated by El Niño–Southern Oscillation (ENSO). The ENSO–SCAP relationship has experienced pronounced interdecadal shifts, though mechanisms remain elusive. Based on observations and climate model simulations, these shifts may result from transitions in ENSO-induced meridional circulation and Rossby wave trains triggered by North Atlantic (NA) sea surface temperature (SST) anomalies. During high (low) correlation periods, ENSO induces strong (weak) vertical motion anomalies over Central Asia, while NA SST anomalies exert a weak (strong) counteracting effect, modulated by the Pacific decadal oscillation (PDO). In the positive (negative) phase of PDO, a slow (fast) decaying ENSO triggers a strong (weak) NA horseshoe-like SST anomaly in the post-ENSO spring, affecting the ENSO–SCAP relationship. Our study identifies a strengthening trend in the ENSO–SCAP relationship since the 2000s, indicating improved predictability for SCAP in recent decades.

This study analyzes the frequency characteristics of tropical cyclone (TC) genesis in the southeastern part of the western North Pacific (SEWNP) during June–November from 1965 to 2019 and investigates the possible combined effect of the solar activity and El Niño-Southern Oscillation (ENSO). Results suggest that TCs generated in the SEWNP have the longest lifetime and greatest strength, and its frequency has apparent interannual and decadal variations, which is jointly affected by the solar activity and ENSO. In El Niño years during declining phases of solar cycle (1–3 years following the solar maximum), positive TC genesis frequency anomalies in the SEWNP are significantly strong and tend to occur in extremes. While the opposite is true for La Niña during ascending phases of solar cycle (1–3 years following the solar minimum). However, there exists no significant feature in the combined effect of La Niña (El Niño) and declining (ascending) phases of solar cycle. When declining (ascending) phases of solar cycle and El Niño (La Niña) are combined, the overlapping effect leads to apparently warmer (colder) sea surface temperature (SST) anomalies in the central equatorial Pacific and colder (warmer) SST anomalies in the western Pacific, so the SST anomalies gradient are stronger. It enhances low-level westerly (easterly) wind anomalies and upper-level easterly (westerly) wind anomalies, which is favorable for the further decrease (increase) of the vertical wind shear in the eastern (most) part of SEWNP. Moreover, the stronger and more westward low-level convergence (divergence) center appears in the Pacific, causing stronger low-level convergent (divergent) flow and upper-level divergent (convergent) flow anomalies, and strengthened (suppressed) ascending movement anomalies in the SEWNP. As a result, the TC genesis frequency in the SEWNP is much higher (lower). Further diagnoses show that absolute vorticity plays a leading role in El Niño years during declining phases of solar cycle, and its contribution is obviously much greater than other environmental factors. It is not perfectly symmetrical in La Niña years during ascending phases of solar cycle when the contribution of absolute vorticity is the greatest, but vertical wind shear is also important.

Abstract. Much has been written about the so-called hiatus or pause in global warming, also known as the stasis period, the start of which is typically dated to 1998. HadCRUT4 global mean temperatures slightly decreased over the 1998–2013 period, although a simple statistical model predicts that they should have grown by 0.016 ∘C/yr, in proportion to the increases in the concentrations of well-mixed greenhouse gases (WMGHGs) and ozone. We employ a statistical approach to assess the contributions of model forcings and natural variability to the hiatus. Our point estimates suggest that none of the model forcings explain more than one-third of the missing heat, accounting for the upper bound of the confidence interval on the effect of tropospheric aerosols, which is the most prominent yet most uncertainly measured of the model forcings that could explain the missing heat. The El Niño–Southern Oscillation (ENSO) explains up to about one-third of the missing heat, and two-thirds and possibly up to 81 % is explained by the unusually high temperature of 1998. Looking forward, the simple model also fails to explain the large increases since then (0.087 ∘C/yr from 2013 to 2016). This period coincides with another El Niño, but the ENSO fails to satisfactorily account for the increase. Instead, we propose a semiparametric cointegrating statistical model that augments an energy balance model with a novel multi-basin measure of the oceans' multidecadal temperature cycles. The model partially explains the recent slowdown and explains all of the subsequent warming. The natural cycle suggests the possibility – depending in part on the rate of increase of WMGHG concentrations – of a much longer hiatus over the period from roughly 2023 to 2061, with potentially important implications for policy evaluation.

Sea‐level pressure (SLP) anomalies over the North Atlantic and European (NAE) sector (25–70°N, 100°W–50°E) and over a larger domain encompassing the entire North Pacific domain are studied to demonstrate that SLP anomalies (SLPAs) during boreal winter (January–March) vary widely between years characterized by the same El Niño–southern oscillation (ENSO) phase. The typical cold ENSO signal tends to be more stable than the warm one during the 1874–1996 period. The typical cold ENSO pattern (e.g. positive SLPA south of 55°N across the North Atlantic and negative SLPA in the northern North Atlantic) is similar to the positive phase of the North Atlantic oscillation (NAO) and occurs throughout the 20th century, except during the 1950s and 1960s when the basinwide westerlies are particularly slow. On the contrary, the typical warm ENSO pattern (e.g. positive SLPA from central Canada to Scandinavia and negative SLPA from the southeastern USA to central Europe, corresponding to the negative phase of the NAO) occurs mainly from 1930 to 1970. Another robust warm ENSO pattern is associated with a large positive (negative) SLPA between Newfoundland and western Europe (between Greenland and Scandinavia), and occurs mainly at the beginning and the end of the 20th century when the basinwide North Atlantic westerlies are strengthened. All these patterns stay statistically significant when the multi‐decadal variability is removed from the North Atlantic SLPA. It is shown that the low‐frequency variability of the north tropical Atlantic sea‐surface temperature anomalies could exert a modulating effect on the ENSO teleconnection. NAE SLPAs tend to be strong during warm (cold) ENSO winters and consistent with a negative (positive) phase of the NAO when the north tropical Atlantic is anomalously warm (cold). Lastly, the magnitude of the SLPA patterns over the NAE sector appears poorly related to the intensity of sea‐surface temperature anomalies in the central and eastern equatorial Pacific. Copyright © 2003 Royal Meteorological Society