Impacts of the Indian Ocean Dipole (IOD), two different types of El Niño/Southern Oscillation (ENSO): canonical ENSO and ENSO Modoki, on the year-to-year winter wheat yield variations in Australia ...have been investigated. It is found that IOD plays a dominant role in the recent three decades; the wheat yield is reduced (increased) by -28.4% (12.8%) in the positive (negative) IOD years. Although the canonical ENSO appears to be responsible for the wheat yield variations, its influences are largely counted by IOD owing to their frequent co-occurrence. In contrast, the ENSO Modoki may have its distinct impacts on the wheat yield variations, but they are much smaller compared to those of IOD. Both the observed April-May and the predicted September-November IOD indices by the SINTEX-F ocean-atmosphere coupled model initialized on April 1st just before the sowing season explain ~15% of the observed year-to-year wheat yield variances. The present study may lead to a possible scheme for predicting wheat yield variations in Australia in advance by use of simple climate mode indices.
By using the observation, reanalysis data and numerical simulation, the inter‐decadal variations in El Niño–Southern Oscillation (ENSO) impacts on the eastern China (EC) precipitation during its ...developing autumn in the past 65 years have been investigated. Results show that ENSO is related to the significant dipole precipitation anomalies in EC in the early decades (1951–1981); El Niño/La Niña introduces more/less precipitation in the southern EC, but less/more in the northern EC. However, the significant dipole pattern disappears in the recent decades (1985–2015), mainly owing to loss of the significant positive influences of La Niña on the northern EC precipitation. Comparison of the atmospheric circulation anomalies in East Asia related to La Niña in the two periods shows that there are anticyclonic circulation anomalies in the northeastern Asia near Japan in the first period, while they shift to Mongolia in the second period. Hence, in the first period, the northern EC is under the influences of anomalous southwesterlies along the southwestern flank of the anticyclonic circulation anomalies that advect more moisture from the south to the northern EC and lead to more precipitation there. In contrast, in the second period, the northern EC is under the influences of anomalous northeasterlies along the southeastern edge of the anticyclonic circulation anomalies near Mongolia that impede the northwards transport of moisture and are not conducive to surplus precipitation. The westwards shift of the anticyclonic circulation anomalies may be closely related to the higher SST and thus convective anomalies related to La Niña in the tropical western North Pacific (WNP) east of the Philippines in the second than the first periods. The sensitivity experiment forced by the positive SST anomalies in the tropical WNP comparable to the observed in an atmospheric general circulation model can successfully simulate the anticyclonic circulation anomalies around Mongolia.
We have discovered that ENSO caused the significant dipole autumn precipitation anomalies in eastern China (EC) in the early decades (1951–1981); El Niño/La Niña introduces more/less precipitation in the southern EC, but less/more in the northern EC. However, the significant dipole pattern disappears in the recent decades (1985–2015). The decadal variations in the ENSO impacts are due to the decadal changes of SST anomalies related to La Niña in the tropical western North Pacific. In the figure, composite anomalies of SON precipitation (mm/day) in (a, c) El Niño and (b, d) La Niña years during (a, b) the first and (c, d) second periods, respectively. The anomalies significant at the 90% confidence level are stippled.
Because of the seasonal northward migration of the East Asian summer monsoon, the mean-state atmospheric circulation in South China (SC) is remarkably different between the early (May–June) and late ...(July–August) rainy seasons. This study presents distinct teleconnections between the SC precipitation in the two periods and the sea surface temperatures (SSTs) in the tropical oceans. In the early rainy season when the major monsoon rain belt is located in SC, the increased local precipitation is related to the tropical Indian Ocean Basin warming. The basin warming induces an anomalous anticyclone in the South China Sea–western North Pacific (SCS-WNP). The related southwesterly anomalies transport more moisture to SC and lead to more moisture convergence and precipitation there. In the late rainy season when the major monsoon rain belt migrates northward to the Yangtze River valley, the precipitation increase in SC can be caused by the dipole SST anomalies in the tropical Pacific with the cold anomalies near the Maritime Continent and warm ones near the date line. The dipole SST anomalies generate an anomalous cyclone in the WNP with its center more northward than that of the anomalous anticyclone in the early rainy season. The related northeasterly anomalies along its northwestern flank reduce the climatological northward transport of moisture flux out of SC, and increase the moisture convergence and precipitation there. The distinct teleconnections between the SC precipitation and the tropical SSTs in the early and late rainy seasons can be well reproduced in the sensitivity experiments by an atmospheric general circulation model.
Celotno besedilo
Dostopno za:
BFBNIB, DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Accurate detection and attribution of past climate change are crucial for projecting future climate change and formulating proper policies. In this study, we show that the warming of the tropical ...Indian Ocean contributes to the observed wetting trend in the Tibetan plateau. The warming tropical Indian Ocean can lead to more precipitation around the Arabian Sea. The associated diabatic heating triggers the cyclonic atmospheric response in the lower troposphere over the Arabian Sea and eastern Africa. It also causes the enhancement and westward extension of the western North Pacific subtropical high. The in‐between airflow transports more moisture northward to the plateau, leading to the increased precipitation over the plateau. These large‐scale circulation patterns can be detected from the long‐term trends based on the observations and the large‐ensemble historical simulations. They can also be simulated by an atmospheric general circulation model forced by the observed warming merely in the tropical Indian Ocean.
Plain Language Summary
The Tibetan plateau, often referred to the “Asian water tower,” is the source region of many major rivers in Asia. It has experienced an increasing precipitation trend over the past few decades. In this study, we show that the warming tropical Indian Ocean contributes to this wetting trend. The warming tropical Indian Ocean can cause more precipitation around the Arabian Sea. The associated diabatic heating not only triggers an anomalous cyclone in the lower troposphere around the Arabian Sea and eastern Africa, but also causes the enhancement and westward extension of western North Pacific subtropical high. Consequently, the northward airflow between them transports more moisture to the plateau and causes more precipitation there. Our findings underscore the significant role of the warming tropical Indian Ocean in shaping the changing climate under global warming. Further research efforts are warranted to deepen our understanding of this phenomenon.
Key Points
The warming tropical Indian Ocean increases the precipitation over the Arabian Sea
The associated large‐scale circulation anomalies transport more moisture northward to the plateau
Consequently, more moisture converges over the plateau, leading to the increased precipitation
Investigating the Indian Ocean Dipole (IOD) during the Last Interglacial (LIG) can advance knowledge of IOD behaviors in orbitally‐induced warmer‐than‐present scenarios. Based on multiple model ...outputs from the Paleoclimate Modeling Intercomparison Project Phase 4, the analysis suggests reduced frequencies of the IOD compared to the preindustrial period. Spatially, the whole growing and mature stages of the IOD feature suppressed variability over the west and westward expansions of eastern anomalies, while the eastern perturbation enhances only at the initial phase. The overall amplitude assessed by the dipole mode index shows only minor reductions. These changes are attributed to orbitally‐induced enhancement in mean‐state westward currents along the equator, which transport more anomalous cold water westward. In addition, the subdued El Niño–Southern Oscillation (ENSO) during the LIG is unlikely to cause a weakening of the IOD, in association with a less important role of ENSO in the formation of the IOD.
Plain Language Summary
The IOD is one of the leading modes of interannual climate variability in the tropical Indian Ocean, characterized by west–east contrasted sea surface temperature (SST) anomalies. The connection between changes in the IOD and mean states is an important issue to be addressed. This study examines IOD behaviors during an orbitally‐induced warm scenario, the LIG (∼127 ka BP), using the preindustrial period as the baseline. The results suggest significant reductions in IOD frequencies and structural changes, with westward extended eastern cooling and spatially uniform suppression in western warming throughout the growing and mature stages, accompanied by intensified eastern cooling at the initial phase. The overall amplitude of the IOD, as measured by the dipole mode index, exhibits only minor reductions. The main mechanism behind the change lies in enhanced equatorial easterlies over the Indian Ocean, which are triggered by orbitally‐induced amplifications in Pacific subtropical anticyclones and increases in northern Africa–South Asia summer monsoon precipitation. Subsequently, equatorial westward currents enhance, modulating the mean advection of SST anomalies during IOD events. Further composite analyses show that the concurrently subdued ENSO is unlikely to induce an IOD attenuation since the ENSO–IOD connections are diminished as indicated by decreased correlation coefficients.
Key Points
Spatial structural change and less frequency of Indian Ocean Dipole in Last Interglacial compared to preindustrial period
Main causes are that orbitally‐induced enhancement of equatorial westward currents intensifies mean advection of anomalous cold water
The concurrent suppression in El Niño–Southern Oscillation is unlikely to cause a weakening in the Indian Ocean Dipole
Resolution of global climate models (GCMs) significantly influences their capacity to simulate extreme weather such as tropical cyclones (TCs). However, improving the GCM resolution is ...computationally expensive and time-consuming, making it challenging for many research organizations worldwide. Here, we develop a downscaling model, MSG-SE-GAN, based on the Generative Adversarial Networks (GAN) together with Multiscale Gradient (MSG) technique and a Squeeze-and-Excitation (SE) Net, to achieve 10-folded downscaling. GANs consist of a generator and a discriminator network that are trained adversarially, and are often used for generating new data that resembles a given dataset. MSG enables generation and discrimination of multi-scale images within a single model. Inclusion of an attention layer of SE captures better underlying spatial structure while preserving accuracy. The MSG-SE-GAN is stable and fast converging. It outperforms traditional bilinear interpolation and other deep-learning methods such as Super-Resolution Convolutional Neural Networks (SRCNN) and MSG-GAN in downscaling low-resolution meteorological data in assessment metrics and power spectral density. The MSG-SE-GAN has been used to downscale the TC-related variables in the western North Pacific in the low-resolution GCMs of HadGEM3-GC31 and EC-Earth3P, respectively. The downscaled data show highly similar TC activities to the direct outputs of the high-resolution HadGEM3-GC31 and EC-Earth3P, respectively. These results not only suggest the validity of the MSG-SE-GAN but also indicate its possible portability among low-resolution GCMs.
The present study shows the existence of intrinsic coastal air-sea coupled phenomenon in the coastal ocean off Baja California and California in boreal summer for the first time. It contributes ...significantly to the interannual sea surface temperature (SST) anomalies there. An initial decrease/increase in the equatorward alongshore surface winds weakens/strengthens the coastal upwelling and raises/lowers the coastal SSTs through oceanic mixed-layer processes. The resultant coastal warming/cooling, in turn, heats/cools the overlying atmosphere anomalously, decreases/increases the atmospheric pressure in the lower troposphere, generates an anomalous cross-shore pressure gradient, and thus reinforces or maintains the alongshore surface wind anomalies. The regional air-sea coupled phenomenon seems to be analogous to the well-known El Niño/Southern Oscillation (ENSO) in the tropical Pacific but with much smaller time and space scales, and may be referred to as California Niño/Niña in its intrinsic sense.
In July and August 2022, the Yangtze River basin (YRB) experienced its hottest summer since 1961. The SINTEX‐F2 seasonal prediction system initialized in early May predicted the hotter‐than‐normal ...summer due to its successful prediction of central Pacific La Niña, negative Indian Ocean Dipole and the resultant warming in the tropical West Pacific‐East Indian Ocean (TWP_EIO). The common SST forcing explains only about 26% to the heatwave strength, while the internal variations in the anomalous warming in the TWP_EIO and Europe, surplus precipitation in Pakistan, and local land‐air interaction account for approximately 65%, based on the analysis of 108 ensemble members. These factors have collectively increased the maximum temperature over the YRB through the enhancement and westward expansion of western North Pacific subtropical high. Our findings quantify the relative contributions of external forcing and internal variations to the unprecedented hot event, offering insights into its forming mechanism and potential predictability.
Plain Language Summary
A record‐breaking heatwave event occurred in the YRB in July and August 2022, posing significant risks on human health, power supply, and social economic activities. Recognizing the importance of such an event, our study aims to identify key factors influencing its prediction using the SINTEX‐F2 system. The central Pacific La Niña, negative Indian Ocean Dipole and the resultant warming in the TWP_EIO provide the dominant predictability, but accounts only about 26% of the heatwave strength. However, internal variations in the anomalous warming in the TWP_EIO and Europe, surplus precipitation in Pakistan, and local land‐air interaction collectively explain about 65%. Our results suggest the necessity of large‐ensemble prediction in capturing this kind of unprecedented extreme event.
Key Points
The SINTEX‐F2 initialized on 2022 early May captures the warmer‐than‐normal air temperatures in Yangtze River basin
The model successfully predicts co‐occurrences of CP La Niña and negative IOD in 2022
However, the direct SST forcing contributes only 26% to the 2022 extreme event in Yangtze River basin
Discovery of Chile Niño/Niña Xue, Jiaqing; Luo, Jing‐Jia; Yuan, Chaoxia ...
Geophysical research letters,
16 March 2020, Letnik:
47, Številka:
5
Journal Article
Recenzirano
Odprti dostop
A new air‐sea coupled mode is discovered off the coast of northern Chile and named Chile Niño/Niña. It shows remarkable interannual variability in sea surface temperature (SST) with the peak in ...austral summer from January to March. The related warm (cold) SST anomalies are mainly generated by anomalous southward (northward) alongshore surface winds that suppress (enhance) the coastal upwelling and subsurface mixing and, in turn, reinforce the wind anomalies by heating (cooling) the overlying atmosphere and strengthening the anomalous cross‐shore pressure contrast. The positive feedback is called the coastal Bjerknes feedback in analogy to the equatorial Bjerknes feedback that is responsible for generation of El Niño–Southern Oscillation. The anomalous surface shortwave radiation through the SST‐low stratus cloud thermodynamic feedback and the variation in the mixed‐layer depth play positive roles in the evolution of Chile Niño (Niña). In contrast, the wind‐evaporation‐SST feedback plays almost no role in the evolution.
Plain Language Summary
The coastal air‐sea coupled modes occur along eastern boundaries of most of major subtropical oceans and have noticeable biogeochemical impacts on marine ecosystems. However, no such phenomenon has been reported in the southeast Pacific so far. Here, by carefully removing the influence of El Niño–Southern Oscillation, we have discovered a new coastal climate mode off northern Chile and named it Chile Niño/Niña. The intrinsic climate mode along the coast is generated by the coastal Bjerknes feedback among alongshore surface winds, coastal upwelling, and the SST anomalies. The anomalous surface shortwave radiation and the variation in the mixed‐layer depth contribute to the evolution of Chile Niño/Niña. Our results reveal the existence and generation mechanism of Chile Niño/Niña for the first time, which advance our knowledge of ocean‐atmosphere‐land coupled interactions and may provide new insights into the research of marine ecology and blue economy.
Key Points
A new intrinsic climate mode is discovered off the coast of northern Chile and named Chile Niño/Niña for the first time
The coastal Bjerknes feedback involving the ocean‐atmosphere‐land interaction plays an essential role in generating Chile Niño/Niña
The anomalous shortwave radiation by a stratus cloud feedback and variation of the mixed‐layer depth influence Chile Niño/Niña evolution
This study examined the predictive skill of a statistical Generalised Additive Model (GAM) by considering the impact of the Indian Ocean Dipole (IOD). The proposed technique is powerful but simple ...and considers both the linear and non-linear relations hidden in the data. The model considers tropical cyclogenesis through kernel density estimation, trajectories by velocity field, and landfall through a country mask approach. A lead–lag analysis for TC forecast potential confirms that the IOD is a good predictor for 2-month lead forecast. Result shows that TC occurrence increase (decrease) during the negative (positive) IOD events and that the landfall probability vary for each IOD phase. Altering convection, steering flow, and low-level vorticity influence the NIO TC activity. Result also highlights the importance and potential of the GAM approach (approximately 72% skill) in matching predicted landfall with the observations.
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