Negative Precipitation Anomalies Research Articles

Does Climate Variability Influence Internal Migration Flows in Senegal? An Empirical Analysis

This paper aims to estimate the total effect of climate variability on interregional migration flows in Senegal. We match regional climate data at origin, represented by normalised rainfall and normalised temperatures (maximum and minimum), with regional migration flow data from Senegal’s Agence Nationale de la Statistique et de la Démographie (ANSD) censuses to construct a panel database covering the five-yearly internal migration waves of 1976, 1988, 2001 and 2013. Using a gravity equation model where migration flows are explained by measures of climatic variability at origin, controlled for geographical, socioeconomic and demographic factors traditionally identified in the literature. Our results show that only negative precipitation anomalies at the origin area act as a push factor and accelerate emigration. In the predominantly agricultural regions, rainfall deficits appear, alongside traditional socioeconomic variables, as an additional significant factor shaping mobility across the country.

The Changing Influence of Precipitation on Soil Moisture Drought With Warming in the Mediterranean and Western North America

AbstractAnthropogenic climate change has already affected drought severity and risk across many regions, and climate models project additional increases in drought risk with future warming. Historically, droughts are typically caused by periods of below‐normal precipitation and terminated by average or above‐normal precipitation. In many regions, however, soil moisture is projected to decrease primarily through warming‐driven increases in evaporative demand, potentially affecting the ability of negative precipitation anomalies to cause drought and positive precipitation anomalies to terminate drought. Here, we use climate model simulations from Phase Six of the Coupled Model Intercomparison Project (CMIP6) to investigate how different levels of warming (1, 2, and 3°C) affect the influence of precipitation on soil moisture drought in the Mediterranean and Western North America regions. We demonstrate that the same monthly precipitation deficits (25th percentile relative to a preindustrial baseline) at a global warming level of 2°C increase the probability of both surface and rootzone soil moisture drought by 29% in the Mediterranean and 32% and 6% in Western North America compared to the preindustrial baseline. Furthermore, the probability of a dry (25th percentile relative to a preindustrial baseline) surface soil moisture month given a high (75th percentile relative to a preindustrial baseline) precipitation month is 6 (Mediterranean) and 3 (Western North America) times more likely in a 2°C world compared to the preindustrial baseline. For these regions, warming will likely increase the risk of soil moisture drought during low precipitation periods while simultaneously reducing the efficacy of high precipitation periods to terminate droughts.

Influence of Eastern, Central and Mix El Niño on the variability of rainfall in southeastern South America

El Niño/Southern Oscillation (ENSO) plays a very important role in modulating rainfall variability in South America. Although the effects of conventional ENSO are well known, there are significant variations in rainfall patterns when sea surface temperature anomalies manifest over the different regions along the equatorial Pacific, namely, Niño 3 (East), Niño 3 and Niño 4 (Mix), and Niño 4 (Central) ENSO. This work aims to analyze the variability of precipitation in southeastern South America associated with different types of El Niño (EN). For this, composite analyzes of precipitation, winds at low and high levels, vertical velocity and geopotential height were carried out. The results indicate that the rainfall pattern associated with Eastern Pacific (EP) El Niño shows the classic features expected from EN described in previous literature, i.e., a stronger and well-defined positive precipitation anomaly over southeast South America, while Central Pacific (CP) El Niño shows weaker and even an opposite sign over the region. Mix (MX) El Niño events present a spatial pattern of precipitation anomalies similar to EP El Niño events, but with lower intensity in the study area. The heterogeneity of EN-related precipitation effects results from a change in large-scale atmospheric circulation patterns: the Walker cell in the tropics, the Rossby waves in the extratropics, and the circulation of low and high-level jet streams. EP El Niño events feature a configuration similar to the South American Low-Level Jet, the strengthening of the subtropical jet, better structured Rossby waves and the Pacific-South America pattern. These characteristics are observed in MX El Niños, but in a weaker way compared to EP El Niños. CP El Niño events, on the other hand, present a weakening and spatial displacement of the aforementioned conditions, which is reflected in negative precipitation anomalies in most seasons. Thus, more significant rainfall variations are noted between the EP El Niños and CP El Niños, with a predominance of positive and negative rainfall anomalies in the study area, respectively.

The Location of Large‐Scale Soil Moisture Anomalies Affects Moisture Transport and Precipitation Over Southeastern South America

AbstractSoutheastern South America (SESA) is a highly productive agricultural region and a hot spot for land‐atmosphere interactions. To evaluate the impact of dry soil moisture anomalies (SMAs) on SESA climate and the sensitivity of the regional climate response to the location of SMAs, we perform three experimental simulations using the Community Earth System Model (CESM) with prescribed dry SMAs over (a) SESA, (b) western SESA, and (c) eastern SESA. The dry SESA and eastern SESA simulations show widespread negative precipitation anomalies. In contrast, the dry western SESA simulation shows positive precipitation anomalies over northeastern Argentina, which are associated with the enhanced southward moisture flux co‐located with the South American low‐level jet exit region. A composite analysis of extremely dry cases over western SESA using reanalysis data agrees with the findings from our CESM experiment. These findings have potential implications for subseasonal forecasting in this region.

The contrast responses of August precipitation over Northeast China to strong and moderate developing El Niño

Northeast China (NEC), which is identified as China's largest granary, has the biggest interannual variability in precipitation in August, which is low on predictive skill. El Niño–Southern Oscillation (ENSO) is the prime source of climate predictability and its temporal evolution is critical to improving the forecasting of summer NEC precipitation. At present, the impacts of a developing-ENSO on August NEC precipitation are unclear. Hence, this study investigates the complex relationship between a developing-ENSO and NEC precipitation in August. The results show that a strong (moderate) developing-El Niño can lead to positive (negative) August precipitation anomalies over NEC, while a neutral ENSO or La Niña have a weak influence on NEC August precipitation. Specifically, a strong developing-El Niño can cause cyclonic/southerly anomalies over NEC by stimulating northwestward wave propagation in the lower troposphere and Circumglobal Teleconnection (CGT) in the upper troposphere. While in a moderate developing-El Niño, the opposite CGT results in anticyclonic/northerly anomalies over NEC; and the warming Indian Ocean associated with the moderate developing-El Niño could excite Pacific-Japan patten. Consequently, southerly (northerly) anomalies can generate positive (negative) anomalous advection of climatological moist enthalpy in a strong (moderate) developing-El Niño, which then contributes to ascending (descending) motion and positive (negative) precipitation anomalies. However, in the neutral ENSO and La Niña phases, the zonal or weak meridional wind anomalies cannot exert a great influence on NEC precipitation in August. The complex relationship between August precipitation over NEC and developing ENSO can be well reproduced by numerical simulations, which demonstrate the robustness of the proposed physical mechanism.

Flash Drought in the South of Yangtze River and the Potential Impact of North Atlantic Sea Surface Temperature

AbstractFlash droughts (FDs), a type of drought with rapid onset, occurred in growing season have damaging impacts on crops, ecosystem and hence livelihoods. However, the associated physical mechanism were not well understood, which prohibits a skillful early warning. Based on the reanalysis data for 1961–2022, we diagnosed the characteristics, antecedent meteorological conditions and large‐scale atmospheric circulation of FDs over the region south of Yangtze River (SYR), a hotspot region of FDs. The FDs tend to occur during the periods before (i.e., from April to mid‐June) and after (i.e., early July–September) Meiyu season (B‐Meiyu and A‐Meiyu periods). Large precipitation deficits and rapid elevated temperature caused by anomalous subsidence and moisture divergence are responsible for the onset of FDs during the two periods. The North Atlantic tripole‐like sea surface temperature anomaly (SSTA) modes have potential impact on the anomalous circulations via modulating Rossby wave trains, but with different locations among the two periods. During B‐Meiyu period, the SSTA mode is characterized by positive SSTA over subtropical North Atlantic and negative SSTAs over the tropical and mid‐latitude ocean, triggering a “+ − + − + −” circulation pattern over North Atlantic–Eurasia, which reinforces the East Asian trough (EAT). Anomalous northeasterly winds dominate the SYR suppressing moisture transport from the tropics. The SSTA mode locates farther to the north during A‐Meiyu period, inducing a “+ − + − +” wave train over mid‐latitude North Atlantic‐Eurasia, leading to the strengthening of the western Pacific subtropical high. The high‐pressure anomalies control the SYR, resulting in anomalous subsidence and hence negative precipitation anomalies.

Persistent warm and cold spells in the Northern Hemisphere extratropics: regionalisation, synoptic-scale dynamics and temperature budget

Abstract. Persistent warm and cold spells are often high-impact events that may lead to significant increases in mortality and crop damage and can put substantial pressure on the power grid. Taking their spatial dependence into account is critical to understand the associated risks, whether in present-day or future climates. Here, we present a novel regionalisation approach of 3-week warm and cold spells in winter and summer across the Northern Hemisphere extratropics based on the association of the warm and cold spells with large-scale circulation. We identify spatially coherent but not necessarily connected regions where spells tend to co-occur over 3-week timescales and are associated with similar large-scale circulation patterns. We discuss the physical drivers responsible for persistent extreme temperature anomalies. Cold spells systematically result from northerly cold advection, whereas warm spells are caused by either adiabatic warming (in summer) or warm advection (in winter). We also discuss some key mechanisms contributing to the persistence of temperature extremes. Blocks are important upper-level features associated with such events – co-localised blocks for persistent summer warm spells in the northern latitudes; downstream blocks for winter cold spells in the eastern edges of continental landmasses; and upstream blocks for winter cold spells in Europe, northwestern North America and east Asia. Recurrent Rossby wave patterns are also relevant for cold and warm spell persistence in many mid-latitude regions, in particular in central and southern Europe. Additionally, summer warm spells are often accompanied by negative precipitation anomalies that likely play an important role through land–atmosphere feedbacks.

Long-Term Trends and Variability of Hydroclimate Variables and Their Linkages with Climate Indices in the Songhua River

The long-term trends and variability of hydroclimate variables are critical for water resource management, as well as adaptation to climate change. Three popular methods were used in this study to explore the trends and variability of hydroclimate variables during last 122 years in the Songhua River (SHR), one of most important river systems in China. Results show the followings: (1) There was an obvious pattern of decadal oscillations, with three positive and three negative precipitation and streamflow anomalies. The lengths of these phases vary from 11 to 36 years. (2) Annual temperature demonstrated a statistically significant increasing trend in the last 122 years, and the trend magnitude was 0.30 °C/10 years in the last 50–60 years, being larger than that of the global surface temperature. It has increased much faster since 1970. (3) Monthly precipitation in the winter season in recent years was almost the same as that in earlier periods, but a significantly increasing monthly streamflow was observed due to snowmelt under a warming climate. (4) A statistically significant correlation between hydroclimate variables and climate indices can be determined. These results could be used to make better water resource management decisions in the SHR, especially under future climate change scenarios.

The Relationship Between the Saharan Air Layer, Convective Environmental Conditions, and Precipitation in Puerto Rico

AbstractThe Saharan Air Layer (SAL) is a hot, dry, and dust‐laden feature that advects large concentrations of dust across the Atlantic annually to destination regions in the Americas and Caribbean. However, recent work has suggested the SAL may be a contributing factor to high‐impact drought in the Caribbean basin. While the SAL's characteristic dust loadings have been the focus of much previous research, fewer efforts have holistically engaged the co‐evolution of the dust plume, its associated convective environment, and resultant rainfall in Caribbean islands. This study employs a self‐organizing map (SOM) classification to identify the common trans‐Atlantic dust transport typologies associated with the SAL during June and July 1981–2020. Using the column‐integrated dust flux, termed integrated dust transport (IDT), from MERRA‐2 reanalysis as a SAL proxy, the SOM resolved two common patterns which resembled trans‐Atlantic SAL outbreaks. During these events, the convective environment associated with the SAL, as inferred by the Gálvez‐Davison Index, becomes less conducive to precipitation as the SAL migrates further away from the west African coast. Simultaneously, days with IDT patterns grouped to the SAL outbreak typologies demonstrate island‐wide negative precipitation anomalies in Puerto Rico. The SOM's most distinctive SAL outbreak pattern has experienced a statistically significant increase during the 40‐year study period, becoming roughly 10% more frequent over that time. These results are relevant for both climate scientists and water managers wishing to better anticipate Caribbean droughts on both the long and short terms.

To what extent can the ozone valley over the Tibetan Plateau influence the East Asian summer precipitation?

The ozone valley over the Tibetan Plateau (OVTP) has experienced significant interannual variations during the past decades. Previous studies have primarily focused on the origins of OVTP rather than its climate impact. This study reveals that OVTP during its peak season (May–July) explains up to 15% of the summer precipitation variability in East Asia. The results suggest that the surface temperature (Ts) anomaly over the Tibetan Plateau (TP) acts as a link between OVTP and East Asian precipitation. Through the positive land-atmosphere feedback, the Ts anomaly over the TP is amplified. The anomalous Ts pattern persists into summer (June–August) due to the land memory effect and impacts the East Asian precipitation by modulating the local circulation. The Specified-Chemistry version of the Whole Atmosphere Community Climate Model is employed to validate that MJJ OVTP results in a substantial increase of Ts over TP and induces an anomalous anti-cyclone centered over the Yangtze-Huaihe River Basin during summer. Consequently, negative precipitation anomalies are observed in the Yangtze River Basin, while positive precipitation anomalies occur in Southern China. The linear baroclinic model further demonstrates that the diabatic heating over the TP serves as the link between MJJ OVTP and East Asian summer precipitation patterns. Our analysis of Coupled Model Intercomparison Project Phase 6 models reveals that a more accurate prediction of East Asian precipitation requires an improved understanding of the relationship between OVTP and TP Ts.

Interannual impact of the Victoria mode on the winter-spring surface air temperature over Eurasia and North America

Variations of the Victoria mode (VM) have received considerable attention due to their profound impacts on the climate systems in the pan-North Pacific. However, works about its impact on surface air temperature (SAT) variability over Eurasia and North America, which may be responsible for extreme weather and climate events, are limited. Here we show a significant positive and negative relationship between the VM and the winter-spring SAT anomalies over mid-to-high-latitude east-central Eurasia (MEE) and eastern North America (ENA), respectively. A local energy budget analysis shows that the contribution of the surface heat fluxes associated with the VM to the SAT anomalies is confined mainly to MEE and may not explain the formation of SAT anomalies over ENA. Furthermore, VM-induced anomalous atmospheric circulations play a crucial role in the formation of notable SAT anomalies. The positive (negative) VM is linked to negative (positive) precipitation and upper-tropospheric wind convergence (divergence) anomalies over the western North Pacific, which contribute to positive (negative) Rossby wave source (RWS) anomalies near the East Asian westerly jet core. These RWS anomalies act as disturbances that propagate eastward, exciting a wave train-like pattern. The high-level positive and negative geopotential height anomalies of the Rossby wave dominate MEE and ENA, respectively, leading to the variation in SAT anomalies. These results could advance our understanding of the relationship between the VM and SAT over the Northern Hemisphere and inspire us to pay more attention to the VM climate impacts.

Impact of Arctic Sea Ice Interannual Variation on Nonmonsoonal Winter Precipitation over the Eurasian Continent

Abstract The present study analyzes the impact of interannual variation in autumn (September–November) Arctic sea ice concentration (SIC) on early winter (November–January) precipitation over nonmonsoonal Eurasian (NME) regions based on both observations and numerical model experiments. An energy budget analysis shows that negative autumn SIC anomalies in the Beaufort–Chukchi–East Siberian Seas (BCES) induce heating in the overlying atmospheric column, which excites a Rossby wave that propagates from the BCES through the Atlantic Ocean to the mid- and high-latitude Eurasian continent. This Rossby wave obtains energy from the mean flow by both baroclinic and barotropic energy conversions. In comparison, the baroclinic energy conversion is more important than the barotropic energy conversion. The low-level anomalous cyclone and anticyclone of the Rossby wave dominate the eastern North Atlantic Ocean–southern Europe and western Russia, respectively. Anomalous westerly wind along the south flank of the anomalous cyclone transports moisture from the North Atlantic Ocean to the continent, resulting in a water vapor flux convergence and positive precipitation anomaly over southern Europe in early winter. Pronounced anomalous northerly winds in the eastern part of the western Russian anticyclone cause negative precipitation anomalies over vast regions of central Asia and the west Siberian plain in early winter. The Rossby wave ray tracing experiment and numerical sensitivity experiments support the above BCES SIC–NME precipitation connection.

Has Arctic sea ice loss affected summer precipitation in North China?

AbstractArctic sea ice loss is one of the most striking features in changing of the climate system and affects weather and climate in the midlatitudes through complex interactions and feedback processes. However, it is not clear whether Arctic sea ice loss has affected summer precipitation in East Asia. This study shows that summer regional precipitation in North China exhibits obvious features of phasic variations. Before 1998, positive and negative precipitation anomalies appeared alternately. While from 1999 to 2011, negative precipitation anomalies were dominant. Since 2012, increased summer precipitation has been observed frequently. A direct cause of increases of summer precipitation in North China is an enhancement of water vapour transport from South China and China's marginal seas, which can be attributed to the strengthening and northward shifting of the northwestern Pacific subtropical high and the spatial configuration with west low–east high and north low–south high in East Asian height fields. Although summer atmospheric circulation anomalies in high latitudes are dominant during the sea ice melting phase, their contributions to summer precipitation variations in North China are little. Simulation experiments show that Arctic sea ice loss can significantly affect the atmospheric circulation in high latitudes; however, it cannot be regarded as a major cause of observed recent increases in precipitation in North China. Additionally, Arctic sea ice loss has little impact on summer precipitation in the Yangtze River valley and South China.

Distinct impacts of two kinds of El Niño on precipitation over the Antarctic Peninsula and West Antarctica in austral spring

Based on multiple reanalysis data, the authors investigated the distinct impacts of central Pacific (CP) and eastern Pacific (EP) El Niño events on precipitation over West Antarctica and the Antarctic Peninsula in austral spring (September–November). The results demonstrate that EP and CP events have similar impacts on precipitation over the Amundsen–Bellingshausen seas, but opposite impacts on that over the Weddell Sea, especially the Antarctic Peninsula. Mechanistically, the tropical heat sources associated with EP events drive two branches of Rossby wave trains, causing an anomalous anticyclone and cyclone over the Ross–Amundsen–Bellingshausen seas and the Weddell Sea, respectively. Anomalous southerly winds to the east (west) of the anomalous anticyclone (cyclone) advect colder and drier air into the Bellingshausen–Weddell seas and the Antarctic Peninsula, which jointly result in negative precipitation anomalies there. CP events, however, trigger only one weak and westward-shifted Rossby wave train, which induces an anomalous anticyclone and cyclone in the Ross–Amundsen seas and Bellingshausen–Weddell seas, respectively, both 20°–30° west of those generated by EP events. Consequently, anomalous northerly (southerly) winds to the east (west) of the anomalous cyclone cause an increase (a decrease) in precipitation over the Weddell Sea (Amundsen–Bellingshausen seas).摘要本文基于多种再分析资料, 研究了中部型 (CP) 和东部型 (EP) El Niño事件对南半球春季 (9–11月) 西南极和南极半岛降水的不同影响. 结果显示, EP和CP事件对阿蒙森-别林斯高晋海的降水具有相似影响, 而对威德尔海, 特别是南极半岛的降水影响相反. 由于EP事件激发两支罗斯贝波列, 分别引起罗斯-阿蒙森-别林斯高森海和威德尔海上空的异常反气旋和气旋, 从而导致别林斯高晋-威德尔海和南极半岛受到干冷的异常偏南风影响, 降水减少. 然而, CP事件仅激发一支相对较弱且偏西的罗斯贝波列, 分别引起罗斯-阿蒙森海和别林斯高晋-威德尔海上空的异常反气旋和气旋, 从而导致南极半岛以西 (东) 受异常偏南 (北) 风影响, 降水减少 (增加).

Influence of the Antarctic oscillation on summer precipitation over East Asia

As the strongest atmospheric mode in the extratropical Southern Hemisphere, the Antarctic oscillation (AAO) can affect regional and even global climate through zonal asymmetric and symmetric dynamic mechanisms. Observational analysis indicates that AAO can affect the zonal-mean vertical velocity of the Northern Hemisphere through eddy-induced meridional circulation in boreal summer, corresponding to the out-of-phase zonal precipitation anomaly at approximately 20°N and the in-phase zonal precipitation anomalies at approximately 30°N and 50°N. In particular, the precipitation anomalies related to AAO in East Asia are much stronger than those in the other regions at the same latitude, and the AAO-related precipitation anomaly agrees well with the precipitation leading mode over East Asia. The strong meridional circulation anomaly in the East Asia sector associated with the asymmetry of AAO results in strong subsidence over the Philippine Sea, and the tropical cooling triggers a Pacific-Japan-like (PJ-like) pattern anomaly, which is conducive to moisture transport over East Asia. In addition, the transient eddy forcing related to AAO causes abnormal circulation over East Asia, which further strengthens the PJ-like pattern. The zonal precipitation anomalies in the Northern Hemisphere are superimposed on the moisture transport and precipitation anomalies related to the PJ-like pattern, hence promoting positive precipitation anomalies in the Yangtze River valley, northeastern China, South Korea and southern Japan. In contrast, negative precipitation anomalies occur in southern China and North China. Our results indicate that AAO is a potential indicator for the East Asian summer precipitation anomaly.

Effects of Extreme Temperature and Precipitation Events on Daily CO2 Fluxes in the Tropics

The effects of anomalous weather conditions (such as extreme temperatures and precipitation) on CO2 flux variability in different tropical ecosystems were assessed using available reanalysis data, as well as information about daily net CO2 fluxes from the global FLUXNET database. A working hypothesis of the study suggests that the response of tropical vegetation can differ depending on local geographical conditions and intensity of temperature and precipitation anomalies. The results highlighted the large diversity of CO2 flux responses to the fluctuations of temperature and precipitation in tropical ecosystems that may differ significantly from some previously documented relationships (e.g., higher CO2 emission under the drier and hotter weather, higher CO2 uptake under colder and wetter weather conditions). They showed that heavy precipitation mainly leads to the strong intensification of mean daily CO2 release into the atmosphere at almost all stations and in all types of study biomes. For the majority of considered tropical ecosystems, the intensification of daily CO2 emission during cold and wet weather was found, whereas the ecosystems were predominantly served as CO2 sinks from the atmosphere under hot/dry conditions. Such disparate responses suggested that positive and negative temperature and precipitation anomalies influence Gross Primary Production (GPP) and Ecosystem Respiration (ER) rates differently that may result in various responses of Net Ecosystem Exchanges (NEE) of CO2 to external impacts. Their responses may also depend on various local biotic and abiotic factors, including plant canopy age and structure, plant biodiversity and plasticity, soil organic carbon and water availability, surface topography, solar radiation fluctuation, etc.

Projected relationship between ENSO and following-summer rainfall over the middle reaches of the Yangtze River valley based on CMIP6 simulations

El Niño–Southern Oscillation (ENSO) events have a strong impact on the middle reaches of Yangtze River summer rainfall (YRSR). The authors project how this impact might vary in the future. As in the historical period of 1979–2014, the middle reaches of the Yangtze River are projected to experience positive (negative) precipitation anomalies in post-El Niño (post-La Niña) summers in 2015–2100 under SSP5-8.5, and three related physical processes—namely, ENSO–tropical Indian Ocean (TIO) sea surface temperature (SST), TIO SST–Philippine Sea convection (PSC), and PSC–YRSR relationships—continue to have an impact. First, because the above three processes are projected to be significant, the ENSO–YRSR relationship is significant at the 90% confidence level over most periods of 2015–2100 under SSP5-8.5, according to the median of five reasonable CMIP6 models and the median of 20 reasonable EC-Earth3 runs. Second, due to the aforementioned three stronger relationships, the ENSO–YRSR relationship is projected to be somewhat stronger in 2015–2100 than in 1979–2014, based on both the median of all 30 CMIP6 models and the median of all 56 EC-Earth3 runs. Third, the ENSO–YRSR relationship projected by the median of five reasonable models remains stronger than that projected by the median of all CMIP6 models, owing to the former's stronger TIO SST–PSC and PSC–YRSR relationships under SSP5-8.5. Additionally, future assessments of uncertainty of projections in ENSO–YRSR relationship are still necessary.摘要厄尔尼诺—南方涛动 (ENSO) 对长江中游夏季降水 (YRSR) 的年际变化影响较大. 基于CMIP6模式数据, 本文预估了未来ENSO与长江中游夏季降水关系的变化. 与1979∼2014年相似, SSP5-8.5高排放情景下ENSO−YRSR的关系仍表现为前冬发生厄尔尼诺 (拉尼娜) 后, 长江中游夏季降水为正异常 (负异常). 同时, 仍然受三个物理过程影响:前冬ENSO影响次年夏季印度洋海温 (ENSO−TIO SST), 印度洋海温异常进而影响菲律宾对流 (TIO SST−PSC) , 菲律宾对流对长江中游夏季降水产生影响 (PSC−YRSR). 例如, (1) 5个CMIP6好模式的中位数和20个EC-Earth3好子集的中位数均预估ENSO−YRSR在2015∼2100年大部分时段保持显著正相关关系, 因为上述三个物理过程的相关关系在未来也显著. (2) 30个CMIP6模式的中位数和56个EC-Earth3子集的中位数预估ENSO−YRSR关系略有增强; 主要是因为上述三个物理过程在未来变强. (3) 5个CMIP6好模式的中位数预估ENSO−YRSR关系仍强于30个CMIP6模式的中位数结果, 主要是因为前者预估的TIO SST−PSC和PSC−YRSR关系更强. 未来将关注ENSO−YRSR预估的不确定性来源.

The influence of the El Niño-Southern Oscillation phase transitions over the northern South America hydroclimate

The transitions between the phases of the El Nino-Southern Oscillation (ENSO) are abrupt changes in the Sea Surface Temperature (SST) conditions, which lead to opposite SST anomalies from the boreal winter of one year to the next boreal winter. In this work, we studied the influence of these transitions of ENSO over the general circulation and three Low-Level Jets (LLJs) over northern South America. We carry out a composite analysis of seasonal anomalies for climatic variables such as SSTs, vertical wind speed, precipitation, water vapor transport, and low-level winds to evaluate changes in the hydroclimatic features. We found that the ENSO phase transitions may induce changes in the vertical wind speeds associated with the Walker cells over the far-eastern Pacific Ocean, which gradually increases (reduces) their downward velocities during the transition from El Niño to La Niña (La Niña to El Niño), and increases(reduces) their upward velocity over northern South America. During the El Niño to La Niña transition (La Niña to El Niño), we found that the low-level water vapor transport changes over the zones of the Caribbean LLJ, the Orinoco LLJ, and the Chocojet with distinctive patterns during the transition years. Moreover, we found a precipitation dipole around the latitude 5°N over the far-eastern Pacific ocean (western Colombian coast) that persists throughout JJA and SON, especially for the El Niño to La Niña transition whereas negative precipitation anomalies predominate over the continental territory of northern South America during the La Niña to El Niño transition. This work contributes to the characterization of ENSO during its abrupt transitions and provides new information about the effects of those transitions on tropical hydroclimatology, which can be used to improve diagnosis, analysis, and modeling of the influence of ENSO over the far-eastern Pacific and northern South America.

Characteristics of summer tropopause folds over southeastern Central Asia and their influences on precipitation

Tropopause folding activities in the summer play a significant role in atmospheric circulations and weather anomalies. Using rain gauge data and the Climate Prediction Center (CPC) precipitation observations as well as the ERA5 reanalysis dataset during July–August (JA) of 1979–2020, three-dimensional circulation structure during 592 frequent tropopause fold days that occurred over southeastern Central Asia and their impacts on precipitation over Central Asia and western China are investigated. During the frequent tropopause fold days, a significant dipole precipitation anomaly pattern is observed with negative precipitation anomalies over Central Asia and positive precipitation anomalies over western China. The contribution of precipitation (extreme precipitation) in the frequent tropopause fold days to the JA climatology over the northwestern slope of the Tibetan Plateau (TP) and the southern Tarim Basin can reach above 40% (50%). Compared with that in no fold days, daily mean precipitation in the frequent tropopause fold days can increase to three times over the northwestern TP and the Tarim Basin. Strong upward motions associated with low level convergence (high level divergence) and high specific humidity are found downstream of the fold region, which is favorable for the occurrence of precipitation, especially extreme precipitation over western China. In contrast, strong downward motions associated with low level divergence (high level convergence) and low specific humidity suppress the occurrence of precipitation over Central Asia. Further analysis reveals that precipitation over western China is closely related to the strength of tropopause fold, with significant positive correlation over the northwestern TP and the Tarim Basin. As the tropopause fold strengthens, the intensity of upward motion and specific humidity in the middle to lower troposphere downstream of the fold region increase, resulting in changes in the frequency and location of precipitation over western China. These findings highlight important impacts of the atmosphere around the tropopause on precipitation over western China.

Dynamics and Characteristics of Compound Heatwaves over Asia

The increasing frequency of heat waves in East Asia (EA) affects agriculture, water management, and people's livelihoods. In recent years, record-breaking heatwaves have occurred corresponding to extreme drought and are increasing in frequency. The two leading modes of heatwavesoverEA are closely related to dry conditions, but their temporal developments are somewhat different. The first major mode of heatwaves appears over northern EA, starting in early summer and lasting throughout the summer. The second mode of heatwaves occurs over central China and Korea and is closely related to negative precipitation anomalies during late summer and startsin July or August.This study investigated the quantitative feedback attribution of heatwave-related surface temperature anomalies using the coupled air-surface climate feedback-response analysis (CFRAM). The warming anomalies related tothe first mode of heatwaves are usually controlled by cloud, latent heat, and surface dynamics processes. It can be explained by reducing heat release from the surface to the atmosphere due to the lack of soil moisture under severe dry conditions.While surface warming related to the second mode of heatwaves is contributed by cloud feedback and atmospheric dynamic process. Reduction in cloud area associated with anticycloniccirculation anomalies induces increased insolation and it affects surface warming. However, the effect of humidity on high-temperature events has not yet been fully explored. Thus, this study identifiedcompound heatwaves that are described simultaneously with relative humidity conditions and suggested the future projections of two types of heatwaves over EA using phase six of the Coupled Model Intercomparison Project (CMIP6) model simulation. CMIP6 models projected intensification of dry heatwaves and increased moist heatwave days in response to projected increases in greenhouse gas concentrations.