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Droughts and climate change are causing severe and persistent dust storms in the arid and hot regions. The potential existence of significant relationships between the Oceanic Niño Index (ONI), Indian Ocean Dipole (IOD), and the MERRA-2 dust column mass density data are thus investigated in the State of Kuwait during 1990–2021 as a study case in the hot and arid regions. The findings show that the correlation starts from ONI-DJF (December–January-February) with the Pearson test value of -0.36 and increasing to a value of -0.55 on ONI-AMJ (April-May-June), the same results were obtained when applying the Spearman correlation test. The correlation exists between the July dust column mass density and IOD-January with a value of -0.484 and − 0.544 over Pearson and ' 'Spearman's test, respectively, all estimated p-values are lower than 0.05. The results of the One-Way ANOVA show that the output is pretty straightforward and statistically significant at p > 0.05, which was confirmed by the nonparametric Kruskal–Walli's test and Mann-Whitney Test. This considerable correlation means that active dust storms are linked with La Niña, while light dust storms occur during the El Niño event. A positive correlation occurs between precipitation and ONI - SON (September-October-November), while a negative correlation is found between precipitation and IOD-July. Our preliminary findings in this paper indicate that an appearance of -0.7°C in ONI-DJF could serve as a definitive marker of the La Nina phase and an indicator for at-risk communities to prepare for the expected activity dust storm. [ABSTRACT FROM AUTHOR]

This paper describes the use of a web application system, called 4-Dimensional Visual Delivery (4DVD), to visualize and deliver climate data. The focus of this paper is on the monthly data from the NOAA-CIRES-DOE Twentieth Century Reanalysis (20CR) project Version 2c. The 20CR is a global model at a spatial resolution about 2° latitude-longitude. The temporal coverage is from January 1851 to December 2014. The monthly data include numerous climate variables, such as temperature, pressure, precipitation rate, zonal wind, meridional wind, albedo, and longwave radiation flux. We show how to use the 4DVD system to conveniently visualize, deliver, and analyze the 20CR data of these parameters on a globe or on a 2D latitude-longitude map. We analyze the temporal and spatial patterns of zonal wind and precipitation over Niño 4 region (5° N-5° S, 160° E-150° W). The monthly NASA Global Precipitation Climatology Project (GPCP) data are used to compare the results from 20CR. GPCP data used in this 4DVD application are defined on 2.5° latitude-longitude grid boxes from January 1979 to January 2019. The 4DVD figures successfully show the reverse of zonal wind direction from the east-to-west wind to the west-to-east wind on the grid box (2° S, 176° W) in the Niño 4 region during an El Niño event. The spectral analysis shows the annual and semi-annual cycles in the zonal wind data on this grid box. The GPCP data are used to support the analysis results of 20CR zonal data. The precipitation data over the grid box (1.25° S, 176.25° W) in the Niño 4 region show clear El Niño signals (persistent extreme precipitation more than 6 mm/day) and clear La Niña signals (persistent "dry" with near-zero precipitation). The spectral analysis of the precipitation data time series over this grid box shows no annual cycle. [ABSTRACT FROM AUTHOR]

This paper discussed the use of stable isotope compositions of precipitation (δ2H and δ18O) to understand its characteristics and the parameters controlling meteorological conditions in Malaysia. The meteoric water line for Malaysia, or MMWL established in this study are δ2H = (7.43 ± 0.05)δ18O + (7.33 ± 0.11) (n = 595, r2 = 0.97) for individual values, and δ2H = (7.07 ± 0.20)δ18O + (4.90 ± 0.75) (n = 51, r2 = 0.96) for annual precipitation weighted means. No major variations in local meteoric water lines established between the stations, except for one (i.e., Cameron Highlands), which was found to be significantly different due to its high deuterium excess, or d value, attributed to moisture recycling (re–evapotranspiration) from the surrounding dense rainforest area. The precipitation moisture came from the two monsoon systems; the Northeast monsoon (NEM) and Southwest monsoon (SWM). They differ only slightly in their isotope signatures, where the NEM (winter monsoon) is 0.38‰ more negative than the SWM (summer monsoon), and the rainfall amount and temperature have a relatively weak influence on the stable isotopes in precipitation. Rainfall δ18O is poorly correlated with the monthly rainfall amount and temperature, with very low r2 values (–0.4‰/100 mm; 0.09 and 0.7‰/°C; 0.06, respectively). The seasonal variability of isotopic compositions of precipitation in this region is controlled by the insubstantial but conspicuous inverse correlation amount effect. The seasonal patterns of δ2H and δ18O are evident, with higher values observed during the NEM and lower values observed during SWM. However, the temporal variations of rainfall δ2H and δ18O during NEM and SWM are almost indistinguishable due to local climatic conditions, prevailing atmospheric circulations, and sources of precipitation. The apparent sign of El Niño and La Niña events (2015 and 2017, respectively) of the El Niño–Southern Oscillation (ENSO) cycle were successfully identified from this study, indicated by the heavier δ18O from the peaks in the annual precipitation amount versus δ18O annual precipitation weighted mean plot, while La Niña corresponds to the lighter values of the rainfall isotopes. [ABSTRACT FROM AUTHOR]

The purpose of this paper is to determine the impact of rare disaster risks, captured by the El Niño-Southern Oscillation (ENSO) cycle, on the volatility of Treasury securities of the United States (US) involving 1- to 360-month maturities. We use a random coefficient panel-data-based heterogeneous autoregressive-realized variance (HAR-RV) model over the monthly period of 1961:06 to 2019:12, with the monthly RV derived from the sum of squared daily changes in yield within a month. Our results show a positive and statistically significant (at the 1% level) impact of the ENSO cycle on RV, with the results being robust to alternative metrics of the ENSO, consideration of lagged values, and decomposition of the ENSO cycle into El Niño and La Niña phases, with the former having a relatively stronger effect. Based on the panel estimation method using heterogeneous slope coefficients, we find that the impact on the entire term-structure is positive yet stronger at the two-ends and the middle-part of the term-structure. Our findings have important implications for investors in US Treasury securities. [ABSTRACT FROM AUTHOR]

Understanding past changes in the characteristics of climate extremes forms an essential part of viable countermeasures to cope with climate-induced risks in a rapidly warming world. Thus, this paper endeavored to explore possible non-monotonic trend components in heavy rainfall events over the Central Highlands (Vietnam) by employing Şen's innovative trend analysis method in conjunction with the well-defined extreme rainfall indices. The outcomes show less spatially coherent trends in the intensity, frequency, and duration of extreme rainfall events across the study area, and most analyzed indices exhibited non-monotonic trend forms. The overall trends in the intensity and frequency, represented by maximum 1-day, 5-day precipitation amount (Rx1day, Rx5day), very and extremely wet days (R95p and R99p), and the number of very and extremely heavy precipitation days (R20mm and R50mm), were characterized by significant increases at three or four sites. Concerning dry and wet extremes, observed increases in consecutive dry days (CDD) and decreases in consecutive wet days (CWD) were identified significantly simultaneously at three sites. There is high domination of significant increases in high-value subgroups of these indices. Several sites also exposed significantly increasing trend behaviors in these indices within all low-, medium-, and high-value subgroups, thereby implying the intensity and frequency have intensified over recent decades. This study also indicated potential linkages between annual peaks of several extreme rainfall indices, characterizing intensity, frequency, and wet duration, usually coincided with negative Indian Ocean Dipole and La Niña events, while dry extremes were usually found during El Niño events based on correlation analysis. [ABSTRACT FROM AUTHOR]

The impact of the Indian Ocean Dipole (IOD) and El Niño Southern Oscillation (ENSO) on tropical cyclone activities in the North Indian Ocean (NIO) basin including the Bay of Bengal (BoB) and Arabian Sea (AS) are investigated using data from 1891 to 2020 of the cyclone e-Atlas developed by India Meteorological Department, Niño 3.4, and the Indian Ocean Dipole mode indices (DMI). A total of 657 tropical cyclones are observed over the NIO basin with an annual frequency of 5.05 while the annual frequencies over BoB and AS are 4.03 and 1.02, respectively. The years from 1891 to 2020 have been classified as years of ENSO [El Niño (EN), La Niña (LN), and neutral ENSO (nENSO)] and IOD [positive IOD (pIOD), negative IOD (nIOD), and noIOD] years. The frequency is higher in EN (nIOD) followed by LN (noIOD) years in the NIO basin. LN (EN) events and nIOD (pIOD) events favor tropical cyclone cases in the BoB (AS). Tropical cyclone genesis has a peak density covering 10–15° N in the BoB and AS during ENSO and IOD years. Wavelet coherence (WTC) analysis between the frequency of tropical cyclones over the NIO basin and the DMI/Niño 3.4 index shows high coherence with DMI and in-phase relationship for the period 2006–2020 while it shows higher coherence with Niño 3.4 index and out-of-phase relationship for the period 1991–2020. The WTC analysis is also performed separately for BoB and AS. Multiple linear regression analysis of the frequency of tropical cyclones and Niño 3.4 index/DMI shows a significant correlation between the frequency and the DMI. A strong coherence between DMI and Niño 3.4 index is also found for the period 1991–2001 over the NIO basin. [ABSTRACT FROM AUTHOR]

La Niña was forecasted to be one of the predominant climatic modes in the 2020 boreal autumn, taking into consideration its impact on the short rain (October to November rainfall) in eastern Africa. Parallel to La Niña and just 2 months before the start of the 2020 short rain, the Greater Horn of Africa Regional Outlook Forum published extremely strong projections of below-normal rainfall in Burundi, Rwanda, most parts of Uganda, Kenya's southern region, and Tanzania. On the other hand, several regions of East Africa (EA) saw above average rainfall, especially in November. The current study examines the core and potential drivers causing the 2020 November rainfall to deviate from its historical response to the La Niña event. The driving force responsible for the wetter-than-anticipated 2020 November rainy conditions was identified. Although the ocean surface favors a negative phase of the Indian Ocean Dipole mode, it normally acts to suppress the short rain in EA, the mode decayed sooner than its life cycle in October. Lastly, the Madden–Julian Oscillation (MJO) in the Indian Ocean acted to reverse or weaken the Walker circulation (WC), the surface westerly (northeasterly) wind flow from the Congo Basin (central Indian Ocean) which conveys moist (warm) unstable air to EA, thereby promoting convective activity and rainfall. The study further identifies the reasons for dry conditions in October and December. In October, the MJO strength in the Maritime Continent and Western Pacific was associated with Somali low-level jet-like and WC across the Indian Ocean. The latter caused subsidence in EA, whereas the former triggered a strong friction-induced sinking motion along the eastern coast of Africa. To create a dry condition, they both collaborated. In December, La Niña strengthened WC across the Indian Ocean which induced subsidence in EA and resulted in poor rainfall. The diversity of mechanisms of MJO influence is relevant to problems of sub-seasonal weather forecasts for EA. [ABSTRACT FROM AUTHOR]

Large-scale oceanic effects of El Niño Southern Oscillation and Indian Ocean Dipole on local rainfall and streamflow variability at the catchment scale have not been well studied. This study assesses the effects of El Niño Southern Oscillation and Indian Ocean Dipole on rainfall and streamflow variability in Geba catchment Tigray Ethiopia. Modified Mann–Kendall and Pettit's tests were used to generally understand the overall trends and expected abrupt changes in rainfall and streamflow. We also applied correlation, explained variance, and multiple regression methods to evaluate the linkages, performance, and strengths between the sea surface temperatures and station rainfall and streamflow records. The rainfall trend of the study site did not change significantly. However, the streamflow showed a significant change with the mixed increase or decrease trends. The abrupt changes in rainfall and streamflow are strongly linked with El Niño Southern Oscillation and La Niña episode events. Rainfall in the rainy season (July, August, and September) enhanced due to La Niña events and suppressed with El Niño episodes. The stream flow of the study catchment gets declined during strong El Niño years (e.g., 1982, 1983, 1987, 1997, and 2015) while also reach its peak during the strong La Niña years (1988, 1999, 2000, 2008, and 2011). Our finding ratified that 39% of rainfall and 38% of streamflow variabilities in the Geba catchment are explained by the combined effects of El Niño Southern Oscillation and Indian Ocean Dipole signals. [ABSTRACT FROM AUTHOR]

Climate modes like ENSO (El Nino Southern Oscillation) and IOD (Indian Ocean Dipole) produce an impact on the monsoon rainfall over India. Monsoon rainfall is extremely important for the agriculture of our country. The impact of these climate modes on monsoon rainfall thus in turn affects the rain-fed crops (kharif). In this study, four kharif season crops namely rice (Oryza sativa), maize (Zea mays), pulses and sugarcane (Saccharum officinarum) are chosen over four arid/semi-arid agro-climatic zones of western India to study the effect of the climate modes on selected crops. The detailed analysis has been carried out to show the impact of rainfall in the El Nino/La Nina (phases of ENSO) and IOD years on the crop productions over the mentioned zones viz. (Central plateau and hills region; Western plateau and hills region; Gujarat hills and plains region; Western dry region) from 1966–2011. The results show that rice productions which require hot and humid conditions have been largely affected during drought years associated with El Nino which results in poor rainfall over all the zones. The production of pulses which does not require excess humid conditions shows marginal improvement during the neutral years or non-El Nino/non-La Nina years. Maize production seems to be better in La Nina years and worst in the El Nino years as La Nina years are responsible for good rainfall in all zones. El Nino years provide a minor impact on sugarcane productions in different zones. La Nina years are well suited for sugarcane production in all zones of our study as sugarcane requires a good amount of moisture. Positive IOD years are associated with poor crop productions as compared to negative IOD years mostly in all zones as most of the positive IOD years happen to be El Nino years. El Nino-rainfall relation being dominant than positive IOD-rainfall relation is, therefore, responsible for negative rainfall anomalies over the selected zones. [ABSTRACT FROM AUTHOR]

Distinctive annual weather patterns in the Western Kenya Highlands have been attributed to El Niño Southern Oscillation (ENSO) teleconnections. A novel application of a recently developed analytical approach is used to identify statistically significant differences between temperature and rainfall patterns in the Kakamega District during the El Niño and La Niña periods of the ENSO cycle. This approach separates the seasonal trend and 1-day autocorrelation from the statistical noise in an annual data set. The standard deviation of this noise is further analyzed for its own seasonal trend. Thirty-eight years of reanalysis data are analyzed, and statistical comparisons are made on all three aspects of this analysis. El Niño years were characterized by a phase shift in temperature patterns. Larger random variation was detected in El Niño years during the long rains than in La Niña years, leading to a higher probability of anomalously high rainfall. Larger random variation was detected in La Niña years during the short rains, leading to both a higher probability of anomalously high rainfall and a higher probability of no rainfall. The method appears to be a promising tool for analyzing not only the effects of distant teleconnections but also the nature of those effects. [ABSTRACT FROM AUTHOR]

Precipitation is considered one of the most important forcing data in scientific investigations involving agriculture, water management, and climate variability. Knowledge of precipitation variation during rainy seasons is the key to the understanding of the precipitation variability under the effect of climate change. This study evaluated some rainy season features (e.g., onset, retreat, and rainy-season precipitation) over the Yellow River basin (YRB), China, and the influence of the El Niño-Southern Oscillation (ENSO). The multi-scale moving t-test was applied to capture the onset and retreat of rainy season. The possible linkage between ENSO-induced precipitation and monsoon and atmospheric circulation was also explored. From the analysis, four conclusions can be drawn: (1) Rainy season began the earliest (latest) and ended the latest (earliest) in the southern (northern) YRB, with rainy-season precipitation increasing from northwest to southeast. (2) Rainy-season precipitation showed strong correlation to SST in Niño regions. Precipitation can reach up to 20% above the average precipitation for decaying central Pacific warming (CPW) and down to 35% below the average precipitation for developing eastern Pacific warming (EPW) in most areas of the YRB. (3) Developing El Niño showed the strongest dry signals among developing ENSO and ENSO Modoki phases. Decaying El Niño and El Niño Modoki indicated overall increasing precipitation, with La Niña and La Niña Modoki during the corresponding period showing the opposite tendency. (4) Different performances of ENSO-induced precipitation attributed to the combined influence of the monsoon from the India Ocean and the atmospheric circulation in the Western North Pacific (WNP). Stronger anti-cyclone and monsoon are related to increasing rainy-season precipitation. These findings can improve the predictability of rainy season features and ENSO-induced precipitation. [ABSTRACT FROM AUTHOR]

Regional climate variability is generally controlled by atmospheric water vapor (WV), which sources and transport pathways are primarily driven by different large-scale teleconnection processes, particularly the El Niño-Southern Oscillation (ENSO). Hence, this study investigated spatial, temporal, and vertical variations in atmospheric WV during cold months of December through March in Iran over the period 2002–2020 and their relationships with the ENSO. Accordingly, we analyzed the atmospheric WV and cloud type data sets provided by the Atmospheric Infrared Sounder (AIRS) and the CloudSat, respectively, over different three atmospheric WV regions of Iran: Mountainous region (R1), the interior region as well as the Caspian Sea (R2), and southern seas (R3). Moreover, two of the strongest El Niño and La Nina events were selected for synoptic analysis and cloudiness monitoring over all three regions of R1, R2, and R3 in Iran. The results showed that atmospheric WV ranged from less than 8 kg/m2 over the R1 to higher than 14 kg/m2 over the R3. The atmospheric WV showed statistically insignificant (p > 0.05) decreasing trends across all three regions of R1, R2, and R3. The ENSO positively correlated with the atmospheric WV during both December in the R3 and March in the R2. The vertical atmospheric WV showed the highest anomalies at pressure levels of below 850 and above 500 hPa during the El Niño and La Nina events, respectively. The atmospheric WV over the mountainous regions in different longitudes of Iran was strongly affected by the La Nina events. However, across the southern seas, interior region, and mountains in eastern, central, and western Iran, respectively, the El Niño events influence the atmospheric WV. The Sudanese and the Eastern Mediterranean troughs (the Siberia and Arabia high-pressure systems) were highly contributed to atmospheric WV variability over Iran during the strong El Niño (La Nina) events in December 2015 (2010) and March 2016 (2011). The precipitable stratocumulus and nimbostratus clouds were mostly dominant over Iran (particularly across the R3) during the El Niño events in December. In conclusion, the warm (cold) phases of ENSO or the El Niño (La Nina) events effectively increase (decrease) the atmospheric WV over Iran during cold months, particularly both December and March. [ABSTRACT FROM AUTHOR]

There are several important large-scale oceanic and atmospheric processes like El Niño-Southern Oscillation (ENSO), Madden–Julian Oscillation (MJO), and Indian Ocean Dipole (IOD) which have significant impact on global weather and climate system. This article reviews the mechanism and dynamics of ENSO, MJO, and IOD processes and their impact on global and regional weather and climate particularly the Indian summer monsoon rainfall. Generally, these processes are coupled ocean–atmosphere phenomenon and associated dynamics control the global weather and climate system. Sea surface temperature (SST) anomaly in the central and equatorial pacific region respectively results the warm (El Niño) and cold (La Niña) events and it has strong impacts globally. Similarly, MJO is a dominant phase of intra-seasonal variability in the tropical region and also has significant impacts on the global system like strong wind, convective waves, extreme rainfall, cyclones, and ENSO. The IOD is often termed as the counterpart of pacific El Niño and La Niña in Indian Ocean which mainly measures the SST gradient between Arabian Sea and the eastern Indian Ocean. IOD also linked to ENSO and the shifting warm/cool pool results in the summer monsoon rainfall variability in the India Ocean as well as continental Indian region. All these phenomena have direct impact on the Indian monsoon circulation system, so in this work, these impacts are quantified using the India Meteorological Department (IMD) observed rainfall data over Indian subcontinent as a case study. This work also provides the review of the studies using observation and modelling to understand the dynamics of all the three processes. This review and analysis work will help in understanding the process feedback on the regional rainfall distribution and there is a need of near-future modelling research on these processes and their impacts on weather and climate system and associated sectors. [ABSTRACT FROM AUTHOR]

The Botswana High is an important component of the regional atmospheric circulation during austral spring, summer and autumn. While the high tends to be stronger during El Niño and weaker during La Niña, its direct response to El Niño Southern Oscillation (ENSO) remains unknown. To that end, a variable resolution global climate model (Model Prediction Across Scales version 7, hereafter MPAS) is applied with relatively high resolution (48-km grid spacing) over Southern Africa and a coarser resolution (240-km grid spacing) over the rest of the globe for the study period 1980–2010. The first model experiment uses observed sea surface temperatures (SSTs) everywhere during the study period, while the second experiment uses observed SSTs everywhere except over the Pacific Ocean, where monthly climatological SSTs are imposed. The model results were validated against satellite data (Global Precipitation Climatology Project, GPCP) and reanalysis datasets (Climate Forecast System Reanalysis, CFSR; European Centre for Medium-Range Weather Forecasts version 5, ERA5). The results of the study show that the MPAS model gives a credible simulation of the temporal variability of the Botswana High, the seasonal rainfall and 500-hPa geopotential heights over Southern Africa. In the absence of ENSO forcing, the amplitude of the Botswana High variability reduces but the signal of the variability remains. Hence, this study shows that ENSO enhances the strength of the Botswana High but does not aid in the formation of the high. [ABSTRACT FROM AUTHOR]

The present study analyzed a long-term record of major floods over Bangladesh under the influence of El Niño–Southern Oscillation (ENSO). Bangladesh is highly vulnerable to floods, and ENSO has a great influence on it. El Niño (La Niña) represents the warm (cold) phase of the ENSO cycle. Southern Oscillation Index data and a long-term flood records have been identified from National Oceanic and Atmospheric Administration, Bureau of Meteorology, Australia, and historical archives, respectively. Synoptic features—precipitation, wind, geopotential height, precipitable water, relative humidity, and surface runoff data—were used to examine the influence of ENSO. Result shows that the Indian summer monsoon contributes the major flood events and largely influenced by both El Niño and La Niña events, with a slightly higher frequency for the latter. Physical mechanisms (distribution of precipitation, wind, geopotential height, precipitable water, relative humidity, and surface runoff) supported these flood events; however, they are quite distinct during El Niño and La Niña condition. Moreover, ENSO's impacts to the Bangladesh region are different to the west part of the monsoon region. Therefore, if ENSO forecast is reliable, the predictability of the monsoon-related flood events can be improved. [ABSTRACT FROM AUTHOR]

The study of the maximum number of consecutive dry days (MCDDs) is one approach to analyze precipitation behavior in arid and semi-arid regions of Iran. This study is a first attempt to investigate the MCDDs and their relationship with the El Niño/Southern Oscillation (ENSO) in winter months over Iran. The study was carried out using Tropical Rainfall Measuring Mission (TRMM) satellite data on a daily basis at 1° latitude × 1° longitude spatial resolution and reanalysis data for the period 1998–2019. Results showed that the highest values of MCDDs are observed in southeastern Iran and the lowest in northwestern Iran. Based on the coefficients of the linear trend of the MCDDs, the significant increasing trends are remarkably more abundant than declining trends, especially in the northern half of the country in December and January. The results regarding the relationship between ENSO and MCDDs indicated a non-stationary behavior, with a significant negative correlation for December (especially in the southwest) and positive correlation for January and February (especially in the southeast). The largest differences in the correlation coefficients were observed between December and January. In general, during El Niño (La Niña) phases, the length of MCDDs decreases (increases) in December and increases (decreases) in January especially in the southern half. By comparing different large-scale climate parameters for the 2 months, we found that during El Niño (La Niña) phases, a negative (positive) anomaly of geopotential height and a positive (negative) anomaly of zonal wind and specific humidity are observed over the region in December, while the opposite situation occurs in January. The innovation of this study is the use of satellite data that provide a continuous spatial coverage of the region and the consideration of the ENSO teleconnection pattern in regards to dry spells. We find that El Niño (La Niña) has contradictory effects on MCDDs in different winter months in the southern half of the country. These findings are of great importance for a country like Iran that lies in arid and semi-arid regions, as they can be useful for water resources management. [ABSTRACT FROM AUTHOR]

The fidelity of the eight Asia-Pacific Economic Cooperation (APEC) Climate Center (APCC) models in representing the inter-annual variability and decadal shift in the northeast monsoon (NEM; October–December) rainfall over Southern Peninsular India (SPI) is evaluated. The hindcast data is used for the period of 28 years from 1983 to 2010 based on September initial conditions. The observations showed a clear inter-annual and inter-decadal variability of NEM rainfall during the study period. The analysis suggests that most of the models exhibited poor skill in representing the inter-annual variability. Only APCC model rainfall is in phase with observed SPI rainfall variations on the inter-annual time scale. It is noticed from the observed NEM rainfall time series that the period 1990–1999 (first decade) displays an above-normal rainfall and the period 2000–2010 (second decade) displays a below normal rainfall over the SPI region. It is also evident from the observations that NEM rainfall for most of the years displayed negative anomalies in the second decade including El Niño and La Niña years, while in the first decade positive anomalies are noted, suggesting the presence of decadal variability in the NEM. Rainfall variations in most of the coupled models are in phase with the observations during the second decade but are out of phase during the first decade. As evidenced from the observations that the intensified deep convection over the Indo-western Pacific region results in too far southward movement of the intertropical convergence zone (ITCZ) during the second decade. The southward shift in the strong upper-level divergence associated with lower-level convergence over the south Indian Ocean caused negative rainfall anomalies over the SPI in this decade. Further, the difference between the second and first decade demonstrates that an anomalous anticyclonic circulation over the Indian subcontinent is accountable for the vigorous dry northerly flow towards the SPI region and the resultant decadal shift in the rainfall pattern. Though the southward shift in the rainfall and large-scale circulation patterns are mildly captured by some models from decade to decade, most of the models completely misrepresented it. This study suggests that the coupled models displayed a very limited skill not only in capturing the inter-annual variability but also in representing the decadal variability of NEM rainfall. [ABSTRACT FROM AUTHOR]

The present study investigates the contributions of four types of precipitation events with different consecutive days (1–3-day, 4–7-day, 8–14-day, and over-14 day) of precipitation to April–October rainfall anomalies over Asia and roles of the three factors (intensity, number, duration) in area-mean rainfall anomalies of four types of precipitation events in El Niño and La Niña years. It is found that precipitation tends to be below normal in the entire tropical and extratropical regions except for northeastern Asia and east and west Indochina Peninsula during El Niño years. During La Niña years, precipitation tends to increase in eastern China, India, the south hills of the Himalayas, west Indochina Peninsula-southwest China, and the Maritime Continent, but decreases in northeast China, east Kazakhstan, Afghanistan, and east Indochina Peninsula. The precipitation change at the low latitudinal regions has a larger contribution from the over-14-day events. The number of events is a main factor in changes of precipitation of primary events during El Niño years. The precipitation changes in El Niño and La Niña years are consistent with changes in the activity of cyclonic wind anomalies corresponding to the precipitation events. The intraseasonal wind anomalies leading to the precipitation events in China are preceded by northwestward move of cyclonic systems from the tropical western North Pacific that promotes the start of precipitation in the concerned regions. The present study points to the impacts of intraseasonal wind systems with various lifespans on precipitation changes over Asia in El Niño and La Niña years. [ABSTRACT FROM AUTHOR]

Haze pollution in recent decades varies largely with both pollutant emissions and meteorological conditions. Using the discrete wavelet transform (DWT) method, we separate these two influences on haze variations in southern China in the time series of haze observations from 1981 to 2011. This helps us to identify the meteorological influence on interannual variation in haze occurrences in southern China and thus observe a teleconnection between the thermal forcing of sea surface temperature (SST) in the central and eastern Pacific and wintertime haze occurrences in southern China (R = − 0.51, p < 0.05). The total haze days in winter is highest among all seasons over southern China and the climotological mean of number of winter haze days is 7.5 days for the region. Compared with the normal winters, the regional mean of the number of haze days in southern China is reduced by ~ 5 days in the winters with above-normal Niño3.4 SST (during El Niño phases), but increased by ~ 4 days in the winters with below-normal Niño3.4 SST (during La Niña phases). In the warm SST winters, the cumulative consequences of strong winds, more precipitation, and a more unstable atmosphere with an "upper colder and lower warmer" vertical pattern leading to more ascendance can all hinder haze formation, whereas in the cold SST winters, opposite meteorological conditions are favorable to haze formation. These meteorological conditions induced by anomalous SST make wintertime haze pollution in southern China vary from year to year to a large extent. This study suggests a strong sensitivity of winter haze occurrences in southern China to the viability of the SST in the central and eastern Pacific. [ABSTRACT FROM AUTHOR]

For proactive prevention of water shortage problems, it is important to understand the spatiotemporal variabilities of droughts and their development mechanisms. This study identified an interannual variation of spring drought-prone condition in each region of East Asia (EA)—northern, mid, and southern EA—for the period 1979–2015 by using the standardized precipitation evapotranspiration index (SPEI) and a hierarchical clustering analysis. According to our analyses, spring drought-prone condition in the northern EA region mainly depends on local surface heating and precipitation deficit due to adiabatic compression by a high-pressure anomaly over the region during the preceding winter to spring. The high-pressure anomaly was driven by an upper-level wave train propagating from the Europe related to a positive phase of the Arctic Oscillation. For drought-prone conditions in the mid and the southern EA regions, the local precipitation deficit caused by the negative moisture advection/convergence therein acts as a primary factor. During the preceding winter, the negative moisture advection/convergence anomalies both in mid and southern EA regions were induced by anomalous low-level cyclonic circulations over the western North Pacific related to the La Niña. In spring, however, the moisture condition in the southern EA region was affected by persistent La Niña while that in the mid-EA region was by the negative phase of North Pacific Oscillation. This gap makes the main location of the negative moisture advection/convergence anomalies just slightly different, but considerably alter the region exposed to the drought-prone condition. [ABSTRACT FROM AUTHOR]

Diversifying impacts of El Niño/La Niña events on northeast monsoon (NEM; October to December) rainfall over southern peninsular India (SPI) are explored in observations and Coupled Model Inter-comparison Project Phase 5 (CMIP5) models. Analysis of observations suggests that about 30 to 40% of El Niño–Southern Oscillation (ENSO) events co-occurred with Indian Ocean Dipole (IOD) during the NEM season (October to December). It is found from the observations that approximately half of the pure El Niño events show above-normal rainfall and remaining show below-normal rainfall over the SPI region, indicating the diversifying effect of El Niño on NEM rainfall. In the case of pure La Niña events, below-normal NEM rainfall is seen in 86% of events and above-normal rainfall in the remaining 14% of events. All El Niño–positive IOD (La Niña–negative IOD) co-occurrence years have witnessed positive rainfall anomalies over the SPI region. The strength and position of cyclonic/anticyclonic circulation over the South China Sea associated with positive/negative moisture anomalies are mainly responsible for the differences in rainfall patterns over SPI during ENSO events. It is found that in CMIP5 models the diversity in SPI rainfall pattern is not just limited to only pure El Niño and La Niña cases but also prominent in ENSO-IOD co-concerning years. CMIP5 models displayed strong skewness towards negative rainfall over the SPI region as compared with the observations during pure El Niño events. This would certainly limit the CMIP5 models' ability to accurately represent ENSO teleconnections to NEM rainfall over the SPI region. [ABSTRACT FROM AUTHOR]

Ocean interactions are known to play a major role in the modulation of intraseasonal variability. The role of sea surface temperature (SST) and major oceanic processes like ENSO (El Niño-Southern Oscillation) and IOD (Indian Ocean Dipole) on intraseasonal oscillations like Madden-Julian Oscillation (MJO) and convectively coupled equatorial waves (Kelvin wave, equatorial Rossby (ER), mixed-Rossby gravity and tropical depressions (together MT)) is explored using 32 years of satellite observations and reanalysis data. It is shown that the relationship between wave activity and SST is highly seasonal and region dependent. The study also shows that the global wave activity is more related to major oceanic phenomena like ENSO and IOD, while regionally, local intensification of the waves is observed to be directly associated with corresponding regional SST. But this relation is mostly limited to the western hemisphere. Globally, while Kelvin and Rossby waves intensify during El Niño, MT waves are shown to intensify during La Niña. MJO and ER are suppressed and MT is intensified during positive IOD. It is shown that the zonal and meridional distribution of moist static energy (MSE) during different phases of ENSO and IOD is the major factor in modulating the observed changes in the intensity of waves along with the distribution of vertical shear. Seasonal variations in these relationships are also explored. [ABSTRACT FROM AUTHOR]

The relationship between blocking events and mean precipitation frequency (MPF) was investigated in this work for Turkey during 1977–2016. The overall MPF for the examined stations during blocked days (nonblocked days) fluctuated between 0.15 and 0.43 (0.12 and 0.38). The ratio of MPF during the blocked days to nonblocked days ranges between 12 and 38%. During the winter season, the country has higher MPF values during blocked days. The greatest ratio of MPF values during blocked days to nonblocked days is observed in summer due to smaller values of MPF occurring during this season overall. Higher MPF occurs when the event center was located between 0o and 30o E (mean 0.27, range 0.17–0.51). There is no relationship between blocking duration and MPF for all seasons. There is a positive relationship between blocking intensity and MPF during summer (CC = 0.35, significant at the 95% level) and fall (CC = 0.43, significant at the 95% level). The relationship between blocking longitudinal extent and MPF is significant at the 95% confidence level during the summer and fall seasons with correlation coefficients of 0.29 and 0.25, respectively. A composite of the 10 blocking events associated with the largest MPF demonstrated that there is moist advection via westerly flow into Turkey in all seasons. During winter, a greater proportion of these events is observed during the La Niña phase of El Niño Southern Oscillation, but during El Niño in spring and summer. For the blocking case study (31 October to 5 November 2009) associated with the largest MPF, the mean value across the country was 0.73. The mean total precipitation during this period was 63.4 mm. [ABSTRACT FROM AUTHOR]

In this study, rainfed wheat and barley yields response to severity and persistence of cold temperature extremes in the January-February-March (JFM) and high temperature, low rainfall, and soil water shortage extremes in the October-November-December (OND) and March-April-May (MAM) was evaluated. For this purpose, the associations between the yields and the extreme indices were tested using Pearson's correlation coefficient for 10 sites located in the western Iran over 1982–2013. The FAO-56 soil water balance model was employed to develop the soil water deficit extreme indices. The impacts of extremes on the yields were also investigated under El Niño–Southern Oscillation (ENSO) phases. The yields were anti-correlated significantly (p < 0.05) with the soil water shortage and rainfall deficit extreme indices, but not with the temperature-related extreme indices, for the majority of sites. On average, a more negative association also existed between the yields and the soil moisture-related indices relative to the rainfall and temperature extreme indices. The yields seem, therefore, to be more adversely impacted by agricultural droughts. Compared with the OND extremes, the high temperature, precipitation shortage, and soil water deficit extremes in MAM had more negative effects on the yields. This can be attributable to strong sensitivity of reproductive processes commonly occurring during MAM to such stresses. In most cases, the yields were more adversely influenced by the short-term extremes. The results also revealed that more frequent occurrence of high temperature and drought-related extremes during La Niña can well explain the substantial yield loss in cold ENSO years. [ABSTRACT FROM AUTHOR]

The annual cycle and interannual variability of stratification in Bay of Bengal (BoB) are studied using both observations and Global Ocean Data Assimilation System (GODAS) analysis during 2003-2012. Annual cycle of stratification and sea surface temperature (SST) evolve coherently, highlighting its role on modulating air-sea interaction over this climatologically important region. Spatial distribution of stratification shows strong seasonality in ARGO observations, whereas it is highly underestimated in GODAS with highest discrepancies during fall and spring. The annual cycle of sea surface salinity (SSS) in GODAS is out of phase with observations implying potential feedbacks. During La Niña years, SSS drop in fall and winter and are lesser than those reported during El Niño years. All these features are misrepresented in GODAS. As stratification modulates air-sea interaction over BoB especially during El Niño and La Niña years, such misrepresentation of ocean stratification may lead to unrealistic thermocline-SST coupling in the models. The mean stratification and its interannual variability in GODAS are weaker than observed even though interannual variability in freshwater flux (P-E) is higher in GODAS. Detailed analysis of GODAS with in situ observations reveals that upper ocean current shear (vertical) is overestimated in GODAS, leading to unrealistically strong mixing which is primarily responsible for the deeper penetration of surface warm and freshwater resulting weaker stratification. As GODAS is used to initialize the ocean component of the coupled forecasting system for seasonal prediction of Asian monsoon, proper representation of stratification is essential. This study advocates the need of accurate representation of upper ocean salinity in GODAS for improved stratification. We speculate that improved stratification and mixing in the BoB improve summer monsoon forecast. [ABSTRACT FROM AUTHOR]

An exploration of the temporal evolution of the El Niño Southern Oscillation (ENSO) from January 1876 to November 2011 by means of a new time domain called natural time reveals that the major ENSO extremes provide precursory signals that are maximized in a time window of almost 2 years. This finding may be used to improve the accuracy of the short-term prediction models of the ENSO extremes, thus enabling steps to be taken to ameliorate its disastrous impacts. [ABSTRACT FROM AUTHOR]

Based on composite analysis using categories of solar inactivity and activity, the responses of surface temperature to different categorized solar activity and a plausible mechanism have been discussed. The results show the increasing solar sunspot activity during solar cycles 13 to 24 (1880-2010) and it seemed to make a positive contribution to rising global temperature. However, the sunspots were fewer in number, if we focused on the most recent 60 years (1950-2010), and the decreasing solar activity did not contribute to a cooler Earth. This result indicates that the connection between sunspots and the Earth's climate is sensitive to the study period. An extreme analysis was performed in an attempt to gain a better understanding of solar impacts. The extreme top 10 composite analysis demonstrated that the surface temperature response to solar activity is spatially different and is highly sensitive to El Niño-Southern Oscillation (ENSO) events. The most sensitive areas in the Pacific sector revealed a significant difference between including and excluding ENSO years. During the solar inactive years, the tropical eastern Pacific was observed as a weak El Niño-like (strong La Niña-like) pattern in the composite including (excluding) ENSO events. Another interesting feature is the strong similarity in the composites which include or exclude ENSO events during the sunspot active years, but it differs from the La Niña-like pattern observed in previous studies. The bottom-up mechanism associated with the response of the surface dynamical circulation and the heat balance when compared to the total solar irradiance forcing partially explains the connection. [ABSTRACT FROM AUTHOR]

Subsurface ocean temperature indices are developed to identify two distinct types of tropical Pacific warming (El Niño) and cooling (La Niña) events: the Eastern-Pacific (EP) type and the Central-Pacific (CP) type. Ocean temperature anomalies in the upper 100 m are averaged over the eastern (80°W-90°W, 5°S-5°N) and central (160°E-150°W, 5°S-5°N) equatorial Pacific to construct the EP and CP subsurface indices, respectively. The analysis is performed for the period of 1958-2001 using an ocean data assimilation product. It is found that the EP/CP subsurface indices are less correlated and show stronger skewness than the sea surface temperature (SST)-based indices. In addition, while both quasi-biennial (∼2 years) and quasi-quadrennial (∼4 years) periodicities appear in the SST-based indices for these two types, the subsurface indices are dominated only by the quasi-biennial periodicity for the CP type and by the quasi-quadrennial (∼4 years) periodicity for the EP type. Low correlation, high skewness, and single leading periodicity are desirable properties for defining indices to separate the EP and CP types. Using the subsurface indices, major El Niño and La Niña events identified by the Niño-3.4 SST index are classified as the EP or CP types for the analysis period. It is found that most strong El Niño events are of the EP type while most strong La Niña events are of the CP type. It is also found that strong CP-type La Niña events tend to occur after strong EP-type El Niño events. The reversed subsequence (i.e., strong EP El Niño events follow strong CP La Niña events) does not appear to be typical. This study shows that subsurface ocean indices are an effective way to identify the EP and CP types of Pacific El Niño and La Niña events. [ABSTRACT FROM AUTHOR]

A study of the skill of the ECHAM version 4 atmospheric general circulation model and two reanalyses in simulating Indonesian rainfall is presented with comparisons to 30 years of rain gauge data. The reanalyses are those performed by the European Centre for Medium-Range Weather Forecasts and of the National Centers for Environmental Prediction jointly with National Center for Atmospheric Research. This study investigates the skill of the reanalyses and ECHAM4 with regard to three climate regions of Indonesia, the annual and interannual variability of rainfall and its responses to El Niño-Southern Oscillation (ENSO) events. The study is conducted at two spectral resolutions, T42 and T106. The skill of rainfall simulations in Indonesia depends on the region, month and season, and the distribution of land and sea. Higher simulation skills are confined to years with ENSO events. With the exception of the northwest region of Indonesia, the rainfall from June (Molucca) and July (south Indonesia) to November is influenced by ENSO, and is more sensitive to El Niño than La Niña events. Observations show that the Moluccan region is more sensitive to ENSO, receives a longer ENSO impact and receives the earliest ENSO impact in June, which continues through to December. It is found that the reanalyses and the climate model simulate seasonal variability better than monthly variability. The seasonal skill is highest in June/July/August, followed by September/October/November, December/January/February and March/April/May. The correlations usually break down in April (for monthly analysis) or in the boreal spring (for seasonal analysis). This period seems to act as a persistent barrier to Indonesian rainfall predictability and skill. In general, the performance of ECHAM4 is poor, but in ENSO sensitive regions and during ENSO events, it is comparable to the reanalyses. [ABSTRACT FROM AUTHOR]