Pacific SSTs Research Articles

Interdecadal change in the relationship between the South China late rainy season rainfall and equatorial Pacific SSTs

Abstract The South China (SC) late rainy season rainfall (SCLR) is important to people’s livelihoods and properties of this densely populated and economically developed region. Based on observation and reanalysis datasets, this study identifies that the relationship between the SCLR and equatorial Pacific SSTs (EPSSTs) experiences an interdecadal change around the late 1970s. The SCLR is negatively correlated with the eastern EPSSTs during 1948–1977 (the previous epoch) but positively correlated with the central EPSSTs during 1978–2022, especially during the last three decades 1993–2022 (the post epoch). This is due to the interdecadal change in El Niño flavors and EPSSTs-tropical Atlantic SSTs (TASSTs) relationship. With the increasing frequency of central Pacific El Niños in the post epoch, the El Niño-related warm SST anomaly center shifts from the eastern equatorial Pacific (EEP) to the central equatorial Pacific (CEP). Correspondingly, the anomalous cyclone exerted by the CEP warming reaches SC and causes rainfall surplus there (westward propagation pathway). In contrast, the EEP warming in the previous epoch can’t influence the SCLR through the westward propagation pathway, but through shifting the westerly jet southward via heating the tropical troposphere. The southward shifted westerly jet crashes the Qinghai-Tibet Plateau, triggering cyclonic circulations across the northern East Asia and North Pacific, which in turn cause anticyclonic circulations over the western SC and reduce SC rainfall (eastward propagation pathway). On the other hand, the CEP warming in the post epoch barely influence the SCLR through the eastward propagation pathway because of the enhanced negative relationship between EPSSTs and TASSTs.

Shortwave Radiative Flux Variability Through the Lens of the Pacific Decadal Oscillation

AbstractThe variability of the shortwave radiative fluxes at the surface and top of atmosphere (TOA) is examined in a pre‐industrial modeling setup using the Pacific Decadal Oscillation (PDO) as a possible pacemaker of atmospheric decadal‐scale variability. Within models from the Coupled Model Intercomparison Project—Phase 6, downwelling shortwave radiation at the surface, the net shortwave fluxes at the surface and TOA, as well as cloud radiative effects show remarkably similar patterns associated with the PDO. Through ensemble simulations designed with a pure PDO pattern in the North Pacific only, we show that the PDO relates to about 20%–40% of the unforced year‐to‐year variability of these shortwave fluxes over the Northern Hemispheric continents. The sea surface temperature imprint on shortwave‐flux variability over land is larger for spatially aggregated time series as compared to smaller areas, due to the blurring effect of small‐scale atmospheric noise. The surface and TOA radiative flux anomalies associated with the PDO index range of [−1.64; 1.64] are estimated to reach up to ±6 Wm−2 for North America, ∓3 Wm−2 for India and ±2 Wm−2 for Europe. We hypothesize that the redistribution of clouds in response to a North Pacific PDO anomaly can impact the South Pacific and North Atlantic SSTs.

Holocene hydroclimatic variability recorded in sediments from Maddox Lake (northern California Coast Range)

AbstractPerspectives on past climate using lake sediments are critical for assessing modern and future climate change. These perspectives are especially important for water-stressed regions such as the western United States. One such region is northwestern California (CA), where Holocene-length hydroclimatic records are scarce. Here, we present a 9000-year, relative lake level record from Maddox Lake (CA) using a multi-indicator approach. The Early Holocene is characterized by variably low lake levels with a brief excursion to wetter climates/relative highstand ca. 8.4–8.06 cal ka BP, possibly related to the 8.2 ka cold event and changing Atlantic Meridional Overturning Circulation (AMOC). From 5.2–0.55 cal ka BP, Maddox Lake experienced a long-term regression, tracking changes in summer-winter insolation, tropical and northeast Pacific SSTs, and the southward migration of the ITCZ. This gradual regression culminated in a pronounced relative lowstand during the Medieval Climatic Anomaly (MCA). A marked relative highstand followed the MCA, correlative to the Little Ice Age. The latter reflects a far-field response to North Atlantic volcanism, solar variability, and possibly changes in AMOC and Arctic sea ice extent. Our results further confirm the hydroclimatic sensitivity of northwest California to various forcings including those emanating from the North Atlantic.

Atmospheric impacts of local sea surface temperatures versus remote drivers during strong South China Sea winter cold tongue events

AbstractSea surface temperatures (SSTs) in the western part of the South China Sea (SCS) are cooler than in the eastern part in boreal winter, owing to a winter climatological cold tongue (CT). In this study, using a regional atmospheric model configured for the Maritime Continent, we assess the atmospheric impacts of local (or SCS) SSTs versus those from remote drivers (e.g., western tropical Pacific SSTs) during strong CT events with anomalously cool SSTs. In the local run, more rainfall is observed over the eastern SCS, but no significant atmospheric impacts are found over the CT region when SSTs associated with strong CT events are imposed within the SCS while climatological conditions are imposed elsewhere. SCS SST anomalies during strong CT events do not significantly modify the regional wind circulation. The lack of atmospheric response to SSTs over the CT region may be explained by the wintertime mean SSTs (i.e., <27–28°C) over the CT region that are inadequate to trigger deep atmospheric convection, while eastern SCS SSTs are high enough. The increase of anomalous positive moist static energy (MSE) near the sea level over the eastern SCS indicates underlying warm eastern SCS SST anomalies could be influencing positive rainfall anomalies. In the remote run, imposing climatological SCS SSTs but remote SSTs and lateral boundary conditions linked to strong CT events results in cyclonic wind and positive rainfall anomalies over the eastern SCS and Philippines, which are a Matsuno–Gill response to the diabatic heating anomalies over the warm western tropical Pacific SST anomalies. Positive rainfall and cloud cover anomalies associated with the cyclonic wind anomalies are due to the anomalous positive MSE import into the eastern SCS by horizontal advection.

Revisiting mechanisms of the Mesoamerican Midsummer drought

Observations show that the seasonal cycle of precipitation in parts of southern Mexico and Central America exhibits a bimodal signal, known as the Midsummer drought (MSD), but there is no consensus on which processes are most relevant for the two-peak structure of the rainy season. This paper evaluates three hypotheses that could explain the MSD: the SST cloud-radiative feedback, the solar declination angle and the Caribbean Low-Level Jet (CLLJ) moisture transport hypotheses. Model experiments produced by the Met Office Hadley Centre (MOHC) for CMIP6 as well as ERA5 reanalysis data are used to critically assess the predictions of each hypothesis. The simulations capture the double peak signal of precipitation well and reasonably simulate the spatial and temporal variations of the MSD and other relevant climate features such as the CLLJ. Evidence from our analysis suggests that the Eastern Pacific SSTs do not increase in late summer in ERA5 data and only slightly increase in the simulations. More importantly, the Eastern Pacific SST variability in ERA5 and in the model experiments cannot explain the differences in the seasonality of precipitation. The net shortwave radiation at the surface shows a two-peak seasonal cycle; however, this behaviour appears to result from a strong anti-correlation of the incoming shortwave and convective activity due to cloud radiative-effects. There was no evidence found by this study of a causal link in which absorption of shortwave energy forces precipitation variations, as suggested by the solar declination angle hypothesis. The moisture convergence, CLLJ and the precipitable water vapor variations best explain the characteristics of the observed and simulated MSD, particularly for the onset of the MSD. The diagnosed variations of moisture convergence, which are synchronous with the timing of the MSD, point to a dynamic mechanism in which the low-level inflow from the Caribbean is more important for the MSD than other radiative mechanisms.

Dynamical mechanisms for the recent ozone depletion in the Arctic stratosphere linked to North Pacific sea surface temperatures

The stratospheric ozone layer, which prevents solar ultraviolet radiation from reaching the surface and thereby protects life on earth, is expected to recover from past depletion during this century due to the impact of the Montreal Protocol. However, how the ozone column over the Arctic will evolve over the next few decades is still under debate. In this study, we found that the ozone level in the Arctic stratosphere at 100–150 hPa during 1998–2018 exhibits a decreasing trend of − 0.12 ± 0.07 ppmv decade–1 from MERRA2, suggesting a continued depletion during this century. About 30% of this ozone depletion is contributed by the second leading mode of sea surface temperature anomalies (SSTAs) over the North Pacific with one month leading and therefore is dynamical in origin. The North Pacific SSTAs associated with this mode tend to result in a weakened Aleutian low, a strengthened Western Pacific pattern and a weakened Pacific–North American pattern, which impede the upward propagation of wavenumber-1 waves into the lower stratosphere. The changes in the stratospheric wave activity may result in decreased ozone in the Arctic lower stratosphere through weakening the Brewer-Dobson circulation. Our findings uniquely linked the recent ozone depletion in the Arctic stratosphere to the North Pacific SSTs and might provide new understanding of how dynamical processes control Arctic stratospheric ozone.

The role of interannual ENSO events in decadal timescale transitions of the Interdecadal Pacific Oscillation

The build-up of decadal timescale upper ocean heat content in the off-equatorial western tropical Pacific can provide necessary conditions for interannual El Niño/Southern Oscillation (ENSO) events to contribute to decadal timescale transitions of tropical Pacific SSTs to the opposite phase of the Interdecadal Pacific Oscillation (IPO). This can be viewed as a corollary to subseasonal westerly wind burst events contributing to El Niño interannual timescale transitions. A long pre-industrial control run with CESM1 is analyzed to show that there is a greater chance of ENSO activity to contribute to an IPO transition when off-equatorial western Pacific Ocean heat content reaches either a maximum (for El Niño to contribute to a transition to positive IPO) or minimum (for La Niña to contribute to a transition to negative IPO) as seen in observations. If above a necessary ocean heat content threshold, the convergence associated with westerly anomaly near-equatorial surface winds associated with El Niño activity can draw that heat content equatorward to sustain anomalously warm western and central Pacific SSTs. These are associated with positive precipitation and convective heating anomalies, a Gill-type response and wind stress curl anomalies that continue to feed warm water into the near-equatorial western Pacific. These conditions then sustain the decadal-timescale transition to positive IPO (with the opposite sign for transition to negative IPO). Associated central equatorial Pacific convective heating anomalies produce SLP and wind stress anomalies in the North and South Pacific that can excite westward-propagating off-equatorial oceanic Rossby waves to contribute to the western Pacific thermocline depth and consequent heat content anomalies.

The Impact of SST Biases in the Tropical East Pacific and Agulhas Current Region on Atmospheric Stationary Waves in the Southern Hemisphere

AbstractClimate models in phase 5 of the Coupled Model Intercomparison Project (CMIP5) vary significantly in their ability to simulate the phase and amplitude of atmospheric stationary waves in the midlatitude Southern Hemisphere. These models also suffer from a double intertropical convergence zone (ITCZ), with excessive precipitation in the tropical eastern South Pacific, and many also suffer from a biased simulation of the dynamics of the Agulhas Current around the tip of South Africa. The intermodel spread in the strength and phasing of SH midlatitude stationary waves in the CMIP archive is shown to be significantly correlated with the double-ITCZ bias and biases in the Agulhas Return Current. An idealized general circulation model (GCM) is used to demonstrate the causality of these links by prescribing an oceanic heat flux out of the tropical east Pacific and near the Agulhas Current. A warm bias in tropical east Pacific SSTs associated with an erroneous double ITCZ leads to a biased representation of midlatitude stationary waves in the austral hemisphere, capturing the response evident in CMIP models. Similarly, an overly diffuse sea surface temperature gradient associated with a weak Agulhas Return Current leads to an equatorward shift of the Southern Hemisphere jet by more than 3° and weak stationary wave activity in the austral hemisphere. Hence, rectification of the double-ITCZ bias and a better representation of the Agulhas Current should be expected to lead to an improved model representation of the austral hemisphere.

The dominant North Pacific atmospheric circulation patterns and their relations to Pacific SSTs: historical simulations and future projections in the IPCC AR6 models

The first two leading modes of the North Pacific atmospheric variability, the Aleutian Low (AL) and North Pacific Oscillation (NPO), in boreal winter and their relations to the North American and Eurasian surface temperature, El Nino–Southern Oscillation (ENSO), Pacific Decadal Oscillation (PDO), and Victoria Mode (VM) are explored in 20 coupled climate models which participated in the sixth Assessment Report of the Intergovernmental Panel on Climate Change. The historical simulations of these models can well reproduce spatial structures and amplitudes of the winter AL and NPO, as well as their associations with North American and Eurasian surface air temperatures. The close connections of the winter AL with ENSO and PDO, as well as the linkage between the NPO and VM could also be well simulated. However, most of the models lack the capability in simulating the impact of the winter ENSO on the NPO. This deficiency is mainly attributed to westward shifts of the ENSO-related sea surface temperature and precipitation anomalies in the tropics and ENSO-induced atmospheric teleconnections over the North Pacific in the models. Spread in the ENSO’s amplitude also contributes partly to the diversity of the ENSO–NPO relation among the models. Under the SSP2-RCP4.5 forced climate change projection, projected changes in the amplitudes and centers of the AL and NPO exhibit large uncertainties across the 20 models. The close connections of the AL with ENSO and PDO, and the NPO with VM are still robust in the warming climate. Most models project an increase (a decrease) in the AL–PDO (NPO–VM) relationship. However, there exists a large uncertainty in the projected changes of the AL–ENSO relationship, which is partly attributed to the large divergence in the projected changes of the ENSO’s amplitude among the models.

A Control of ENSO Transition Complexity by Tropical Pacific Mean SSTs Through Tropical‐Subtropical Interaction

AbstractEl Niño–Southern Oscillation (ENSO) transitions from one event to another in complex ways. Using observational analyses and forced atmospheric model experiments, we show that a preceding ENSO event can activate a subtropical Pacific forcing mechanism to trigger another ENSO event during the following year. These tropical‐subtropical Pacific interactions result in a cyclic ENSO transition if the two ENSO events are of opposite signs or a multiyear ENSO transition if they are of the same sign. The preceding ENSO event should excite deep convections in the tropical Pacific in order to activate the subtropical Pacific mechanism. This requirement enables mean temperatures in the cold tongue and warm pool to respectively control how easily the cyclic and multiyear transitions can occur. A future warmer tropical Pacific is projected to decrease the frequency of occurrence of multiyear ENSO transitions but increase the occurrence of cyclic ENSO transitions.

Contributions of tropical-extratropical oceans to the prediction skill of ENSO after 2000

The skill of most ENSO prediction models has declined significantly since 2000. This decline may be due to a weakening of the correlation between tropical predictors and ENSO. Moreover, the effects of extratropical ocean variability on ENSO have increased during this period. To improve ENSO predictability, the authors investigate the influence of the extratropical Atlantic and Pacific oceans on ENSO during the pre-2000 and post-2000 periods, and find that the influence of the northern tropical Atlantic sea surface temperature (NTA SST) on ENSO has significantly increased since 2000. Furthermore, there is a much earlier and stronger correlation between NTA SST and ENSO over the central-eastern Pacific during June-July-August in the post-2000 period compared with the pre-2000 period. The extratropical Pacific SST predictors for ENSO retain an approximate 10-month lead time after 2000. The authors use SST signals in the extratropical Atlantic and Pacific to predict ENSO using a statistical prediction model. This results in a significant improvement in ENSO prediction skill and an obvious decrease in the spring predictability barrier phenomenon of ENSO. These results indicate that extratropical Atlantic and Pacific SSTs can make substantial contributions to ENSO prediction, and can be used to enhance ENSO predictability after 2000.

Trends and interannual variability of extreme rainfall indices over Ghana, West Africa

Rainfall plays an important role in the socio-economic development of any nation. Below or above normal rainfall amounts have serious consequences on key socio-economic sectors. This is particularly true for countries such as Ghana where rainfall plays a key role in the agriculture and energy sectors. In this study, the Climate Hazards Group InfraRed Precipitation with Station data (CHIRPS)-homogenized daily rainfall series was used to determine the variability of ten extreme rainfall indices recommended by the World Meteorological Organization-Commission for Climatology (WMO-CCL) and the research project on Climate Variability and Predictability (CLIVAR). The trends of these indices and their links to SST anomalies at oceanic basins were also explored in this study. To understand the variability at interannual to decadal time scales and links with SST forcings, the sum of the first three principal components of the indices were correlated with SST anomalies at oceanic basins. The 35 years mean of frequency indices, CDD, CWD, R10mm and R20mm were found to be in a range of 10–125, 6–14, 30–60 and 8–24 days per year, respectively. On the other hand, the mean over the same period of intensity indices PRCPTOT, R95p, R99p, SDII, RX1day and RX5day were in the range of 900–1700 mm, 200–400 mm, 40–130 mm, 9–13 mm, 30–100 mm and 90–180 mm per year, respectively. The maximum of temporally averaged intensity indices covers southwestern Ghana, while the minimum of the indices lies over northwestern and eastern coasts. A significant decreasing trend in wet indices were observed over the Volta Lake and central portions of the country (7.5°N to 9.5°N), whereas low positive trends were observed over the Northern parts of the country. Wet indices over the country showed significant positive correlations with the Atlantic Ocean SST and negative correlations with the Pacific and Indian basins SSTs. Specifically, the NINO3.4 revealed significant negative correlations with the wet indices over the west-central portions of the country. IOD was observed to have a dipole effect on rainfall indices with the central and southern parts generally covered by negative correlations, while Northern and coastal regions showed positive correlations. The impacts of Atlantic SST on wet rainfall indices are significant over most parts of the country. These results have implications on the improvement of seasonal forecast of the Ghanaian rainfall and its extremes and also provide prior knowledge for better understandings of multidecadal modulations of global interannual teleconnections.

Quantification of Information Exchange in Idealized and Climate System Applications

Often in climate system studies, linear and symmetric statistical measures are applied to quantify interactions among subsystems or variables. However, they do not allow identification of the driving and responding subsystems. Therefore, in this study, we aimed to apply asymmetric measures from information theory: the axiomatically proposed transfer entropy and the first principle-based information flow to detect and quantify climate interactions. As their estimations are challenging, we initially tested nonparametric estimators like transfer entropy (TE)-binning, TE-kernel, and TE k-nearest neighbor and parametric estimators like TE-linear and information flow (IF)-linear with idealized two-dimensional test cases along with their sensitivity on sample size. Thereafter, we experimentally applied these methods to the Lorenz-96 model and to two real climate phenomena, i.e., (1) the Indo-Pacific Ocean coupling and (2) North Atlantic Oscillation (NAO)–European air temperature coupling. As expected, the linear estimators work for linear systems but fail for strongly nonlinear systems. The TE-kernel and TE k-nearest neighbor estimators are reliable for linear and nonlinear systems. Nevertheless, the nonparametric methods are sensitive to parameter selection and sample size. Thus, this work proposes a composite use of the TE-kernel and TE k-nearest neighbor estimators along with parameter testing for consistent results. The revealed information exchange in Lorenz-96 is dominated by the slow subsystem component. For real climate phenomena, expected bidirectional information exchange between the Indian and Pacific SSTs was detected. Furthermore, expected information exchange from NAO to European air temperature was detected, but also unexpected reversal information exchange. The latter might hint to a hidden process driving both the NAO and European temperatures. Hence, the limitations, availability of time series length and the system at hand must be taken into account before drawing any conclusions from TE and IF-linear estimations.

Dominant Modes of China Summer Heat Waves Driven by Global Sea Surface Temperature and Atmospheric Internal Variability

AbstractThis study applies the maximum temperatures at more than 2000 Chinese stations to investigate the dominant modes of China summer heat waves (HWs). The first empirical orthogonal function (EOF) mode of the HW days reflects an increased frequency of HWs in northern China (NC), while the second and third modes represent two distinct interannual modes, with key regions over the Yangtze River valley (YRV) and southern China (SC), respectively. The NC HWs are possibly associated with the Atlantic–Eurasian teleconnection, showing zonally propagating wave trains over the North Atlantic and Eurasian continent. The YRV HWs are proposed to be linked to the North Atlantic Oscillation, which may trigger a southeastward-propagating wave train over northern Russia and East Asia that results in a high pressure anomaly over the YRV. The SC HWs are obviously dominated by the Indian Ocean and northwest Pacific warm SSTs owing to the transition from the preceding El Niño to La Niña, which excites above-normal highs over SC. The anomalously high pressures over NC, the YRV, and SC are usually accompanied by descending air motions, clear skies, decreased precipitation, and increased solar radiation, which jointly cause a drier and hotter soil condition that favors the emergence of HWs. The GFDL HiRAM experiments are able to reproduce the historical evolution of NC and SC HWs, but fail to capture the YRV HWs. The correlation coefficient between model PC1 (PC2) and observed PC1 (PC3) for the period of 1979–2008 is 0.65 (0.38), which significantly exceeds the 95% (90%) confidence level, indicating that this model has a more faithful representation for the SST-forced HWs.

Role of Pacific SSTs in improving reconstructed streamflow over the coterminous US

Reconstructed annual streamflows using tree-ring chronologies provide useful information on moisture availability during the pre-historic period, but they have limitations in estimating high flows due to the upper bound on soil water holding capacity and trees’ metabolic growth limits. We propose a hybrid approach that uses tree-ring chronologies and climatic indices for improving high flows in 301 basins whose annual streamflows are modulated by ENSO and/or PDO. The hybrid decomposition approach relies on separating the moisture supply into the basin as outside-the-region moisture and within-the-region moisture with the former being estimated by SST indices and the latter being estimated by tree-ring chronologies. Analyses over the 301 stations from coterminous US show that the proposed approach improves the high flows and improves the overall error in the reconstructed streamflows. Potential utility of the improved reconstructed annual streamflows with improved high flows is also discussed.

한반도 홀로세 후기 기후와 적도 태평양 해수면 온도 간의 연관성

한반도 홀로세 후기 기후와 적도 태평양 해수면 온도 간의 연관성

Recent increased warming of the Alaskan marine Arctic due to midlatitude linkages

Alaskan Arctic waters have participated in hemispheric-wide Arctic warming over the last two decades at over two times the rate of global warming. During 2008–13, this relative warming occurred only north of the Bering Strait and the atmospheric Arctic front that forms a north–south thermal barrier. This front separates the southeastern Bering Sea temperatures from Arctic air masses. Model projections show that future temperatures in the Chukchi and Beaufort seas continue to warm at a rate greater than the global rate, reaching a change of +4°C by 2040 relative to the 1981–2010 mean. Offshore at 74°N, climate models project the open water duration season to increase from a current average of three months to five months by 2040. These rates are occasionally enhanced by midlatitude connections. Beginning in August 2014, additional Arctic warming was initiated due to increased SST anomalies in the North Pacific and associated shifts to southerly winds over Alaska, especially in winter 2015–16. While global warming and equatorial teleconnections are implicated in North Pacific SSTs, the ending of the 2014–16 North Pacific warm event demonstrates the importance of internal, chaotic atmospheric natural variability on weather conditions in any given year. Impacts from global warming on Alaskan Arctic temperature increases and sea-ice and snow loss, with occasional North Pacific support, are projected to continue to propagate through the marine ecosystem in the foreseeable future. The ecological and societal consequences of such changes show a radical departure from the current Arctic environment.

The Link between ENSO-like Forcing and Hydroclimate Variability of Coastal East Asia during the Last Millennium

Inconsistent reconstructions of East Asian hydroclimate for the last millennium significantly limit our understanding of the mechanisms behind climate variability during the medieval climate anomaly (MCA) and little ice age (LIA) in the region. In this study, we present new high-resolution multiproxy records (diatom, δ13C, C/N, TS) from the Mulyoungari swamp, Jeju Island, South Korea. Our results indicate that El Niño southern oscillation-like variations caused the dry MCA/wet LIA pattern in the study area. Recent paleo-ENSO studies generally support the hypothesis that the MCA was characterized by more persistent El Niño-like conditions. During El Niño events, the genesis of typhoons affecting coastal East Asia tends to diminish because of warm anomalies of eastern tropical Pacific (ETP) SSTs and downward motions over the western tropical Pacific. Therefore, coastal East Asia likely experienced a decline in typhoon-related precipitation during the MCA, in contrast to monsoon-dominated northern China. Our results additionally imply that SST anomalies in the ETP need to be carefully checked to better understand current hydroclimate variability in coastal East Asia, one of the most populated areas on earth.

Climate change and precipitation variability over the western ‘Pampas’ in Argentina

ABSTRACTThis work focuses on the analysis of spatial and temporal variability of precipitation in the central region of southern Central Argentina (SCA), a climate transition area which has experienced an important agricultural expansion. For this purpose, gauge station precipitation datasets available in the area were extensively used. The annual cycle shows a defined dry season (May–August) and wet season (September–April). Wet season represents over 85% of annual totals. A regionalization analysis of wet‐season precipitation suggests five subregions with spatially homogeneous precipitation variability in SCA. Three out the five subregions are located in central SCA. Conveniently devised precipitation indices for the latter subregions show the presence of significant precipitation jumps by the early 1970s, and to a minor extent, the mid‐1960s. Precipitation jumps are responsible for the observed long‐term trends in central SCA, which explain positive precipitation changes over 30–40% of regional averages in the period 1922–2012. The presence of stationary and non‐stationary components in SCA precipitation variability remotely connects the region mainly with variations in equatorial Pacific SSTs. The assessment of greenhouse gases concentration effects on future projections of wet‐season precipitation over central SCA is investigated by means of multi‐model analysis of historical experiment, and the representative concentration pathways 4.5 (RCP 4.5) and 8.5 (RCP 8.5), provided by the Coupled Model Intercomparison Project Phase 5. Results suggest an overall increased precipitation, roughly 15% respect to present climate, under most severe future scenario.

A meridional dipole in premonsoon Bay of Bengal tropical cyclone activity induced by ENSO

AbstractAnalysis of Bay of Bengal tropical cyclone (TC) track data for the months of May–June during 1979–2014 reveals a meridional dipole in TC intensification: TC intensification rates increased significantly in the northern region and decreased in the southern region. The dipole is consistent with changes in the large‐scale TC environment estimated using the Genesis Potential Index (GPI) for the same period. While an increase in lower troposphere cyclonic vorticity and midtroposphere humidity in the northern Bay of Bengal made the environment more favorable for TC intensification, enhanced vertical wind shear in the southern Bay of Bengal tended to reduce TC development. These environmental changes were associated with a strengthening of the monsoon circulation for the months of May–June, driven by a La Niña‐like shift in tropical Pacific SSTs and associated tropical wave dynamics. Finally, analysis of a suite of climate models from the Coupled Model Intercomparison Project Phase 5 archive shows that most models correctly reproduce the link between ENSO and premonsoon Bay of Bengal TC activity at interannual timescales, demonstrating the robustness of our main conclusions.