Eastward Shift Research Articles

Inter-model robustness of the forced change of the ENSO-Indian Summer Monsoon Teleconnection

Concerning the robustness of predicting the forced response of the El Niño—Southern Oscillation-Indian summer monsoon (ENSO-ISM) teleconnection based on 9 CMIP-class models, we come to distinguish three time periods. (1) In the late 20th century, the trend was insignificant in most models, which does not permit a statement on robustness in this period. Thus the weakening of the teleconnection reported from the observational data might not be truly forced. (2) Furthermore, we find it typical that under global warming in the first part of the 21st century, the teleconnection is strengthening or non-decreasing. This considerable inter-model robustness is owed to an increasing ENSO variability as well as coupling strength. (3) At the end of the 21st century, however, under strong forcing, the teleconnection change is not robustly modeled: the ENSO variability change is not projected robustly across models, either with respect to the start or the rate of the ENSO variance decline, competing this time with an increase of the coupling strength. The difference in the projected coupling coefficient between models is mainly attributed to the disagreement in the projected ENSO-induced changes in the regional Hadley cell and SST patterns over the ISM domain, despite the agreement on the projected eastward shift of the Walker cell over the Pacific Ocean.

The combined influence of west Pacific subtropical high and tropical cyclones over the northwest Pacific on Indian summer monsoon rainfall

AbstractWe examined the interrelationship between the Indian summer monsoon rainfall (ISMR), the west Pacific subtropical high (WPSH), and tropical cyclone (TC) activity over the western north Pacific (WNP) Ocean during the peak monsoon season in 1951–2019. When WNP TCs are inactive (active), there is a noticeable 10° westward (eastward) shift observed along with intensification (weakening) of the WPSH. The WPSH and WNP TC activities are divided into four categories—an eastward shift of WPSH with active TCs (EA) and inactive TCs (EI), and a westward shift of WPSH with active TCs (WA) and inactive TCs (WI)—in order to investigate the combined influence of the WPSH and WNP TCs on ISMR during non‐El Niño–Southern Oscillation (non‐ENSO), El Niño, and La Niña phases. In the EA non‐ENSO cases, a surplus (deficit) rainfall was noticed over central (southern peninsular) India as a result of moisture convergence (low convective available potential energy, abnormal moisture divergence and downdraft); however, the rainfall is above normal over the Indian subcontinent. During the EI non‐ENSO case, an excess (deficit) regional rainfall activity was observed over east‐central India and parts of north India (southern peninsular India) through regional changes in atmospheric circulations and midtropospheric vertical velocity. In contrast, in WI (WA) non‐ENSO cases, the majority of India (southern peninsular and northeast India) experiences excessive precipitation while east‐central India (east and west central India) undergoes a deficit rainfall. This pattern is consistent with the spatial distribution of moisture flux convergence, convective available potential energy, and midtropospheric vertical velocity. In the case of non‐ENSO, the westward shift of the WPSH associated with inactive TCs is one of the favourable conditions for ISMR. In general, the effect of an eastward (westward) shift of the WPSH along with more (less) TCs during the non‐ENSO case is favourable to ISMR. On the other hand, rainfall patterns during ENSO are significantly associated with the circulation changes teleconnected to El Niño and La Niña conditions.

Global Per Capita CO2 Emission Trends

In recent years, carbon emissions have become a hot spot issue, and countries have made efforts to control the increasing rate of CO2 concentration. Prior studies have mainly focused on the national total carbon emissions, but per capita carbon emissions are still poorly known. Here, we used multiple economic development indices to investigate the dynamics of per capita carbon emissions. Additionally, we used the Mann–Kendall test to assess the directions and magnitudes of trends and to investigate abrupt changes in per capita carbon emissions. Our results showed the highest positive growth rate of 0.439 mts/yr in Oman, and the highest negative growth rate of −0.462 mts/yr in the United Arab Emirates. Hurst Index analysis showed that about 86% of countries will keep the current trends of carbon emissions if current mitigation measures remain unchanged. Furthermore, we analyzed the shift in the center of gravity for per capita carbon emissions and used the contribution decomposition method to identify the drivers for the shift, which changed direction in 2004. The main driver behind the westward shift in the gravity center before 2004 was the fact that carbon emissions grew more strongly in the west than in the east before 2004, while the driver for behind the eastward shift in the gravity center after 2004 was a combination of emission reductions in the west and emission increases in the east. Our results highlighted the importance of understanding that the per capita CO2 emissions are clearly defined within the context of global carbon neutrality, which can help policymakers set more reasonable targets with which to better achieve carbon neutrality goals.

Prospective Evolution of Meteorological Drought in the Haihe River Basin and Its Connection With Large‐Scale Atmospheric Circulations Using CMIP6 Multimodel Ensemble

AbstractClimate change modifies monsoon rainfall patterns, leading to significant impacts on future meteorological droughts. This study investigated the spatiotemporal pattern of future precipitation, drought features, and the dynamic mechanisms governing their evolution induced by teleconnected atmospheric circulation in the Haihe River Basin, situated in the north China monsoon region. The investigation was conducted under SSP1‐2.6, SSP2‐4.5, and SSP5‐8.5 scenarios of CMIP6, utilizing the Standardized Precipitation Index and an improved run theory at seasonal and annual scales. The findings revealed that high‐emission scenarios cause a wetter climate trend, particularly in autumn and winter, related to the attenuation of the East Asian Trough from climate warming. The uneven intra‐annual precipitation patterns within the basin, induced by the Asian monsoon climate, are expected to improve in the far future, particularly under the SSP2‐4.5 scenarios. The drought frequency, intensity, and duration of future meteorological drought are expected to improve compared to historical conditions under all three scenarios. SSP2‐4.5 shows the shortest duration and lightest intensity of annual droughts. Extreme droughts are primarily driven by strong subsidence with low‐level moisture divergence. However, in the far future, the eastward shift of the western Pacific subtropical high results in reducing moisture transport from the western Pacific, leading to increasing contribution of advection term to atmospheric drying, particularly under the SSP1‐2.6. In winter, the increase in radiative forcing leads to enhanced evapotranspiration from the Eurasian continent, providing additional moisture and alleviating drought, especially in the far future under the SSP1‐2.6 and SSP2‐4.5 scenarios.

Eastward shift in Juniperus virginiana distribution range under future climate conditions in the Southern Great Plains, United States

Eastern redcedar (Juniperus virginiana, redcedar) is a major woody species encroaching upon the native grasslands and forests of the southern Great Plains (SGP), representing a significant threat to regional ecosystem services. Future climate change is anticipated to influence redcedar habitat suitability, changing the probability of further encroachment and reshaping its spatial distribution. In this study, we trained seven Species Distribution Models (SDMs) with redcedar records from the USDA Forest Inventory Analysis database and used the ensemble of these SDMs to simulate redcedar distribution probability under current and future climate conditions in Kansas, Oklahoma, and Texas. Results reveal a distinct east-to-west gradient of decreasing distribution probability in the study domain, primarily driven by climate aridity. Throughout the 21st century, the optimal range of aridity for redcedar habitat is projected to shift eastwards by 0.7° (≈ 58 km) under the RCP45 climate scenario and 1.3° (≈ 108 km) under the RCP85. Accordingly, the suitable habitat will shift eastward by 0.6° (≈ 49 km) in the RCP45 and by 1.2° (≈ 103 km) in the RCP85. The proportion of unsuitable habitat will increase from 40.2 % of the study domain during 2000 – 2019 to 48 % in the RCP45 and 54.2 % in the RCP85 during 2080 – 2099. Additionally, highly suitable land areas will decrease from 10.4 % of the study domain during 2000 – 2019 to 1.3 % in the RCP45 and 0 % in the RCP85 by the end of this century. This study suggests a low likelihood of further redcedar encroachment in the west of the SGP states under future climates, while anticipating continued expansion in the east, gradually replacing the existing oak forests and rangelands. The findings provide valuable insights for prioritizing WPE management resources and contribute to our understanding of future changes in the SGP vegetation composition and their impacts on ecosystem dynamics.

Interdecadal change in the relationship between the boreal winter North Pacific Oscillation and the following summer El Niño

AbstractThe boreal winter North Pacific Oscillation (NPO) has a significant impact on the tropical Pacific large scale air-sea interaction in the following spring and summer. But it is unclear whether the boreal winter NPO is associated with the El Niño development or decaying during following summer. This study confirms the relationship between the winter NPO-like sea level pressure anomalies and following summertime El Niño and reveals an interdecadal change in this relationship. It tends to promote the development of sea surface temperature anomaly in central equatorial Pacific in the following summer when the subtropical lobe of the NPO located west of its average position. But after a significant eastward shift of NPO’s subtropical lobe, it is more conducive to the development of sea surface temperature anomaly in eastern equatorial Pacific. The eastward shift of the NPO’s subtropical lobe altered both the seasonal foortprint mechanism and the trade wind charging mechanism associated with the NPO, thus profoundly influenced the summertime El Niño. The findings in the present study have implications for a better understanding of the relationship between the boreal winter NPO and the El Niño in developing summer.

Interdecadal Variability in the Interface Between the Indian Summer Monsoon and the East Asian Summer Monsoon

AbstractThis study investigates the interdecadal variability (IDV) of the interface between the Indian summer monsoon and the East Asian summer monsoon (IIE). Results suggest that the IDV of the IIE is characterized by a uniform zonal movement associated with seesaw variations between the Indian summer monsoon (ISM) and the East Asian summer monsoon (EASM). The IDV of the IIE is closely linked to two air–sea coupled modes: one resembles the Asian–Pacific Oscillation (APO) and the other resembles the North Atlantic tripole (NAT) pattern. Both the APO‐like and NAT‐like patterns facilitate an eastward shift of the IIE during their positive phase. The APO‐like mode strengthens the western North Pacific subtropical high (WNPSH), which further enhances the climatological southwesterly wind over East Asia and leads to an intensification of the EASM. The simultaneous anticyclonic anomaly over the India and Bay of Bengal (BOB) region weakens the ISM. The NAT‐like mode forces a wave train of alternating cyclonic and anticyclonic anomalies across Eurasia, causing southwesterly anomalies over East Asia that favors a stronger EASM. The atmospheric response is reversed during the negative phases of the APO‐like and NAT‐like patterns. Recent decades have seen a weakening influence of the APO‐like mode, but a growing impact of the NAT‐like mode on the IIE‐IDV. The interdecadal transition of the IIE–APO and IIE–NAT relationships has a smaller influence on the IIE than that of the phase change of the APO‐like and NAT‐like patterns. Modeling results confirm the influence of the APO‐like and NAT‐like patterns on the IIE‐IDV.

Diagnosing observed extratropical stationary wave changes in boreal winter

Stationary waves are time-averaged zonally asymmetric component of the climatological mean atmospheric circulation, primarily due to the unevenly distributed topography and diabatic heating. Stationary waves are subject to influence from long-term external forcing. In this study, the temporal evolution of the winter (January) Northern Hemisphere stationary waves during 1961–2020 is diagnosed with the fifth generation European Centre for Medium-range Weather Forecasts reanalysis data (ERA5), which shows an overall strengthening in amplitude and an eastward shift in phase. A stationary wave model is used to attribute the stationary wave response to changes in the zonal mean basic state (ΔZM) and the zonally asymmetric diabatic heating forcing (). The pattern of stationary wave changes is well captured by the response to ΔZM alone, whereas the contribution of to the amplitude increases in height and becomes dominant in the stratosphere. is also found to be important in driving stationary wave changes in the North Pacific and Western Europe regions. Furthermore, changes in tropospheric stationary waves are probably a result of internal variability, whereas stratospheric changes are more likely to be driven by external forcing.

Diverse Impacts of ENSO on the Intensity of Tropical Western North Pacific Synoptic‐Scale Disturbances During Boreal Summer

AbstractPresent study analyzes diverse impacts of El Niño–Southern Oscillation (ENSO) on the intensity of synoptic‐scale disturbances (SSDs) over the tropical western North Pacific (TWNP) during boreal summer. Asymmetric changes in the SSD intensity are detected in El Niño (EN) and La Niña (LN) developing summers. The increase in the SSD intensity is larger and located more eastward in EN developing summers compared to the decrease in LN developing summers. The asymmetric SSD intensity changes are associated with an eastward shift of anomalous low‐level cyclone and mid‐level ascent during EN developing summers relative to opposite anomalies during LN developing summers. The above difference is attributed to zonally asymmetric anomalous equatorial central‐eastern Pacific heating and cooling in EN and LN years. Sensitivity experiments with an atmospheric general circulation model illustrate that the major reason for asymmetric TWNP SSD intensity changes is the asymmetric atmospheric response to opposite sea surface temperature (SST) anomalies in EN and LN years. Comparisons between strong and moderate ENSO events show an obvious dependence of the SSD intensity change on the amplitude of EN, but not on the amplitude of LN. This indicates a stronger sensitivity to warmer SST than to colder SST. The enhancement of the TWNP SSD intensity is confined to a more westward longitude in Central than Eastern Pacific EN years with a comparable magnitude.

ENSO–Rainfall Teleconnection over the Maritime Continent Enhances and Shifts Eastward under Warming

Abstract The Maritime Continent (MC), located in the heart of the Indo-Pacific warm pool, plays an important role in the global climate. However, the future MC climate is largely unknown, in particular the ENSO–rainfall teleconnection. ENSO induces a zonal dipole pattern of rainfall variability across the Indo-Pacific Ocean, that is, positive variability in the tropical Pacific and negative variability toward the MC. Here, new CMIP6 models robustly project that, for both land and sea rainfall, the negative ENSO teleconnection over the MC (drier during El Niño and wetter during La Niña) could intensify significantly under the Shared Socioeconomic Pathway 5–8.5 (SSP585) warming scenario. A strengthened teleconnection may cause enhanced droughts and flooding, leading to agricultural impacts and altering rainfall predictability over the region. Models also project that both the Indo-Pacific rainfall center and the zero crossing of dipole-like rainfall variability shift eastward; these adjustments are more notable during boreal summer than during winter. All these projections are robustly supported by the model agreement and scale up with the warming trend.

Testing heavy rainfall change in Jeju Island, Korea and its linkage to typhoon activity over East Asia during the Holocene

Understanding the spatiotemporal variability of extreme hydrologic events, especially those driven by typhoons over Asia, and their controlling factors is essential to testing and predicting their future changes under global warming. Here, we present a series of direct heavy-rainfall records over the past ca. 10,000 years based on lake sediments from a volcanic cone (Sara Oreum) on Jeju Island, Korea, where orographic amplification of precipitation is dominant and sensitive to present typhoon activity. The reconstructed heavy rainfall index based on the high-resolution elemental ratios (e.g., Ti/Al and Sr/Si) shows clear variability at centennial timescales and is similar to records of coastal flooding events along the southern coast of Korea, typhoon-driven overwash events along the south-western coast of Japan, indicating strong typhoon influence on the heavy rainfall events in Jeju Island during the Holocene. Furthermore, this heavy rainfall-typhoon linkage has been influenced by past El Niño–Southern Oscillation (ENSO) activity and sea surface temperature (SST) in the western Tropical Pacific, showing time-varying influences. This study suggests that on decadal to multi-centennial timescales, stronger ENSO activity is responsible for eastward shift in the location of typhoon genesis, resulting in more frequent recurving tracks of typhoon and increased landfalls in Korea and Japan, whereas SST affects the intensification rate of typhoon. The heavy rainfall index reconstructed from the volcanic cones of Jeju Island may be used as an indicator of past frequency and track changes of typhoon over highly populated East Asia.

Spatiotemporal Evolution of Land Use Efficiency in Southwest Mountain Area of China: A Case Study of Yunnan Province

The study of land use efficiency (LUE) evaluation and coupled coordination (CC) relationships under the perspective of urbanization can reasonably allocate land resources and contribute to the solution for agriculture, rural areas, and farmers. The LUE evaluation index system is constructed in three aspects: economy, society, and ecology. Then the LUE and CC degrees of Yunnan Province from 2010 to 2020 are measured, and the characteristics of LUE and the relationship of CC in each administrative region at each level are analyzed in space. Besides, the overall LUE and CC relationship in Yunnan Province is described. The study concludes that (1) The urbanization process in Yunnan Province is accelerating, unused land is decreasing, and construction land is increasing. (2) During the study period, the LUE of Kunming was much higher than that of other regions. The economic efficiency of the inner circle cities centered on Kunming is higher, while the economic efficiency of the outer circle cities is lower; social efficiency is increasing year by year except for Nujiang and Diqing, showing a higher pattern in the east than in the west; ecological efficiency is not increasing year by year except for Kunming, Qujing, and Lijiang, showing a higher pattern in the east than in the west; comprehensive efficiency is on the rise, with Kunming and Qujing leading the way with the overall pattern of “east > central > west”. The high-value area is relatively stable, and the low-value area has a clear tendency to shift eastward. (3) The coupling level of economic, social, and ecological efficiency of land use in administrative regions of Yunnan Province is low, but the coupling relationship is gradually optimized, showing the “contiguous effect” and realizing the state of extreme disorder to severe disorder in a large area. (4) The overall CC of three subsystems in Yunnan Province shows a fluctuating upward trend; the comprehensive efficiency index has an upward trend except for a slight decrease in 2017–2018; from 2010 to 2019, ecological and social efficiency is better than economic efficiency.

Assessing the influence of variation in forage availability on spatial patterns of beehive migration using a hybrid modelling approach – B-Agent

Bees and beekeeping are increasingly recognised as important contributors to sustainable development. Beekeeping is a landscape-scale process that involves complex interconnectivities between beekeepers, beehives and bee forage. Yet, accounting for these interactions within beekeeping system models is challenging as interactions are dynamic and often influenced by human behaviour and decision making. To this end, this research describes a spatially explicit modelling approach B-Agent, which draws upon multiple stakeholder engagement, a machine-learning algorithm and an agent-based model to simulate beehive migration processes. The Western Australian beekeeping sector provides a case study for model development and testing, to examine changes in (i) distances travelled by beekeepers, (ii) the frequency of beehive migration, and (iii) the spatial distribution of harvest locations resulting from climate related impacts on forage availability. The results indicate an increase in travel distance and frequency of hive migrations for commercial beekeepers under a moderate emissions climate scenario and indicated an eastward shift in the spatial distribution of harvest locations. The approach provides an evidence-base for better-informed management decisions in order to improve the long-term sustainability of beekeeping systems in Western Australia and beyond.

Regional Persistent Extreme Precipitation Events over Southwest China under Different Low-Latitude Intraseasonal Oscillations during the Rainy Season

Abstract This study investigates the mechanisms of low-latitude intraseasonal oscillations affecting regional persistent extreme precipitation events (RPEPEs) over Southwest China (SWC) during rainy seasons. Most of the RPEPEs over SWC are dominated by 7–20-day variability. The RPEPEs over SWC are preconditioned by two different types of 7–20-day Rossby waves with almost opposite phases over the western North Pacific (WNP). The two types of 7–20-day Rossby waves have direct and indirect effects on type-1 and -2 RPEPEs, respectively. For type 1, a coupled 7–20-day low-level anticyclone and suppressed convection originating from the tropical WNP propagate northwestward and cover the region from the South China Sea (SCS) to the Bay of Bengal before the RPEPEs. The anticyclone triggers ascending motion over SWC and transports more moisture to SWC, favoring the SWC RPEPEs. Before the type-2 RPEPEs, a coupled 7–20-day low-level cyclone and enhanced convection propagates from the tropical WNP to the SCS. The enhanced convection over the SCS leads to the westward extension of the western Pacific subtropical high (WPSH) and the eastward shift of the South Asian high (SAH). The variations in the WPSH and the SAH directly cause SWC RPEPEs by inducing ascending motion and transporting moisture. The mechanisms for type-2 RPEPEs tend to work under the background with a strong WPSH. Using a Lagrangian model, we found that both the 7–20-day oscillations and their background atmospheric circulations result in significant differences in moisture sources for the two types of RPEPEs. These findings benefit a better understanding of SWC extreme precipitation events.

Meteorological Analysis of the Pacific Northwest June 2021 Heatwave

Abstract During the last week of June 2021, the Pacific Northwest region of North America experienced a record-breaking heatwave of historic proportions. All-time high temperature records were shattered, often by several degrees, across many locations, with Canada setting a new national record, the state of Washington setting a new record, and the state of Oregon tying its previous record. Here we diagnose key meteorology that contributed to this heatwave. The event was associated with a highly anomalous midtropospheric ridge, with peak 500-hPa geopotential height anomalies centered over central British Columbia. This ridge developed over several days as part of a large-scale wave train. Back trajectory analysis indicates that synoptic-scale subsidence and associated adiabatic warming played a key role in enhancing the magnitude of the heat to the south of the ridge peak, while diabatic heating was dominant closer to the ridge center. Easterly/offshore flow inhibited marine cooling and contributed additional downslope warming along the western portions of the region. A notable surface thermally induced trough was evident throughout the event over western Oregon and Washington. An eastward shift of the thermal trough, following the eastward migration of the 500-hPa ridge, allowed an inland surge of cooler marine air and dramatic 24-h cooling, especially along the western periphery of the region. Large-scale horizontal warm-air advection played a minimal role. When compared with past highly amplified ridges over the region, this event was characterized by much higher 500-hPa geopotential heights, a stronger thermal trough, and stronger offshore flow.

A Regional Air‐Sea Coupled Model Developed for the East Asia and Western North Pacific Monsoon Region

AbstractIn this study, we developed a regional coupled model for the western North Pacific (WNP) and East Asian region. The atmospheric/oceanic component of the coupled model was the Weather Research and Forecasting and the Regional Ocean Modeling System, coupled through the National Center for Atmospheric Research Coupler version 7 (CPL7). An evaluation is provided through the simulation of the climatology and interannual variability of the summer monsoon climate from 1982 to 2015. The coupled model is also compared with a solely atmospheric run, which is driven by the observed sea surface temperature (SST) as the surface boundary. The results show that the coupled model has good capability in modeling the climate in the WNP and East Asian domain, including the climatology of summer precipitation and circulation, the subseasonal (month‐to‐month) variation in the western Pacific subtropical high and associated precipitation, and the seasonal cycle of the East Asian rain belt. One merit of this model is its ability to simulate the northward and eastward shift from early to late summer. With respect to the interannual variability, the model captures the spatial pattern of the leading mode of summer precipitation, with a north–south dipole mode in the studied region. The model also reproduces the larger SST variability in the northern part of this region. The temporal correlation coefficient between the coupled simulation and observation was 0.70 for the precipitation and 0.53 for the SST leading mode. The coupled model also captures the precipitation–SST relationship, which results from reasonably considering the air–sea coupling processes in the coupled run.

Effects of an eastward shift in the Agulhas retroflection region on chlorophyll-a bloom on its south flank.

As observed by remote sensing images in December 2013 and January 2014, chlorophyll-a (Chl-a) bloom occurred on the south side of the Agulhas Current (38°S-45°S). The dynamic mechanisms of Chl-a bloom were studied by satellite remote sensing data, reanalysis data and Argo data. The periodic shedding of the Agulhas ring led to a significant eastward shift of the Agulhas retroflection from December 2013 to January 2014, without the obstruction of flowing complex eddies and with increased current flow. Then, the horizontal transfer of Chl-a occurred along the south side of the Agulhas Current (38°S-45°S). Nitrate concentrations reached 10-15 μmol·L-1 on the south side of the Agulhas Current, where a deepened mixed layer and upwelling and the vertical transport of nutrients contributed to the Chl-a bloom. In addition, sufficient light and suitable precipitation provide good conditions for Chl-a bloom on the south side of the Agulhas Current.

Distinct characteristics of western Pacific atmospheric rivers affecting Southeast Asia

The dynamic characteristics of atmospheric rivers (ARs) have been researched over the western North Pacific and East Asia due to their close linkage to disastrous precipitation extremes, while very little attention has been paid to the AR features from the western Pacific to Southeast Asia. This study aims to quantify the climatology, long-term trends and variability of different AR properties from the western Pacific to Southeast Asia using an objective identification algorithm, the ERA5 reanalysis dataset and the APHRODITE precipitation dataset for the period 1951-2015. The results indicate a belt of frequent AR activities from the western Pacific to the Andaman Sea during the boreal autumn-winter season. The long-term trend analyses show a significantly increasing trend in AR frequency and an eastward shift of AR plumes. These dynamic changes contribute to the increasing trend of extreme precipitation amounts in the coastal areas surrounding the South China Sea. The intraseasonal variability of the AR associated with the Madden-Julian oscillation (MJO) shows a pronounced enhancement of AR activity in the MJO phase-2 to phase-3 due to the steeper gradient of low-level geopotential height between the Northwestern Pacific and the tropical Indian Ocean. The modulation is partly explained by the enhanced MJO convection and the adiabatic heating in the vicinity of the trough of the 200-500 hPa geopotential thickness of the region. This study shows that ARs are important mechanisms behind the climatology, trends and variability of the regional precipitation in Southeast Asia. This study implies that more attention is required toward the dynamics of these tropical weather systems, particularly for their interactions with other synoptic processes and their response to future climate warming.

Regional tropical rainfall shifts under global warming: an energetic perspective

Future climate simulations feature pronounced spatial shifts in the structure of tropical rainfall. We apply a novel atmospheric energy flux analysis to diagnose late 21st century tropical rainfall shifts in a large ensemble of simulations of 21st century climate. The method reconstructs 2D spatial changes in rainfall based on horizontal shifts in the lines of zero meridional and zonal divergent energy flux, called the energy flux equator (EFE) and energy flux prime meridian (EFPM), respectively. Two main sources of future atmospheric energy flux changes, and hence rainfall shifts, are identified by the analysis: the high-latitude North Atlantic due to a weakened Atlantic Meridional Overturning Circulation that shifts tropical rainfall southwards over the greater Tropical Atlantic sector and eastern Pacific; and the eastern tropical Pacific due to a permanent El-Niño-like response that produces zonal shifts over the Maritime Continent and South America. To first order, the shifts in the EFE and EFPM mirror gross distributional changes in tropical precipitation, with a southward shift in rainfall over the tropical Atlantic, West Africa, and eastern tropical Pacific and an eastward shift over the Maritime Continent and western Pacific. When used to reconstruct future rainfall shifts in the tropical Atlantic and Sahel, the method reasonably represents the simulated meridional structure of rainfall shifts but does not do so for the zonal structures.

On the relationship between ENSO and overland accumulated cyclone energy of landfalling tropical cyclones over the western North Pacific

This study investigates the relationship between El Niño-Southern Oscillation (ENSO) and overland accumulated cyclone energy (ACE) of tropical cyclones (TCs) over the western North Pacific (WNP). We find that there is only a weak correlation between ENSO and overland ACE during 1979–2019, compared to the significant relationship between ENSO and basinwide ACE over the WNP as reported in previous publications. Overland ACE is generally smaller in El Niño and La Niña years than that in neutral years, which mainly results from lower landfall frequency and shorter duration after landfall. Relative to neutral years, overland ACE is lower over almost the entire China mainland in both El Niño and La Niña years, which can be related to the changes in the formation and movement of landfalling TCs. During El Niño and La Niña years, fewer landfalling TCs form over the western WNP, mainly resulting from reduced 850-hPa humidity, which leads to a less chance of TCs making landfall over China mainland. In addition, the eastward (westward) shift of the western Pacific subtropical high in El Niño (La Niña) years steers more TCs to make landfall over the southern (northern) China.