Southern Oscillation Index Values Research Articles

The Characteristics Of The Mixed Layer Depth During La Niña, El Niño, And Normal Years In The North Natuna Sea

The Natuna Sea is one of the seas located in the northern part of Indonesia, which is influenced by several oceanographic climate phenomena, including the El Nino-Southern Oscillation (ENSO) system, such as La Nina and El Nino, which cause vertical temperature dynamics. This study aims to examine the relationship between La Nina, El Nino, and normal years on the variability of the mixed layer depth in the Natuna Sea. The study utilizes temperature data from the World Ocean Database (WOD) and Marine Copernicus for a period of 3 years, including years with La Nina, El Nino, and normal conditions, as well as mixed layer depth (defined by sigma theta) data from Marine Copernicus. The occurrence of La Nina, El Nino, and normal years is obtained from the Southern Oscillation Index (SOI). The research findings indicate a correlation between the SOI values and the Maximum Mixed Layer Depth (MLD) during weak and very weak El Nino and La Nina conditions, while the correlation is weak during normal years. During the La Nina, normal, and El Nino periods, the deepest MLD occurs during the west monsoon season at depths ranging from 7 to 60 meters. The shallowest MLD occurs during the first transition season at depths ranging from 7 to 25 meters. The MLD values during the east monsoon season range from 7 to 43 meters, and during the second transition season, the MLD ranges from 7 to 44 meters.

ENSO Signals Recorded by Ash Tree Rings in Iberian Riparian Forests

Climate–atmospheric patterns affect ecological processes. The El Niño Southern Oscillation (ENSO) represents the strongest global source of climate variability at annual scales, but its impacts on Mediterranean forests are still understudied. Here, ENSO signals recorded by river flow and radial growth series of Mediterranean riparian forests are uncovered in the middle Ebro basin, northeastern Spain. A chronology or mean series of tree ring widths (period 1970–2018, 27 trees) was built for narrow-leaved ash (Fraxinus angustifolia). Growth indices increased as the river flow did during the prior winter and from May to September. Ash growth indices and river flow of the hydrological year were positively related (r = 0.54, p < 0.001), suggesting that a higher soil moisture enhances growth. This correlation remained significant after taking out the influence of precipitation. Ash growth indices (r = −0.46, p = 0.001) and river flow during the hydrological year (r = −0.30, p = 0.03) were negatively associated with the January Southern Oscillation Index (SOI). These relationships suggest that high SOI values corresponding to La Niña events lead to reduced river flow, thus decreasing ash radial growth. Further approaches could be used to better understand how the ENSO impacts drought-prone riparian forests subjected to increasing aridity.

Spatiotemporal Environmental Drivers of Eastern Equine Encephalitis Virus in Central Florida: Towards a Predictive Model for a Lethal Disease.

Eastern equine encephalitis virus (EEEV) is a mosquito-borne virus that affects humans and horses, with a high case fatality rate in both species. The virus can be transmitted by several mosquito species and maintained in multiple reservoir hosts, making EEEV dynamics difficult to anticipate. In this study, we identified spatial and temporal factors that precede EEEV detection using sentinel chicken surveillance data from Orange County, Florida, from 2003 to 2017. We first examined the land cover and mosquito species composition associated with sentinel chicken sites. We then fit distributed lag nonlinear models of EEEV detection at the county scale, using monthly temperature, precipitation, and Southern Oscillation Index values, and at the sentinel flock-scale, using remotely sensed temperature and wetness indicators. We found positive associations between the percent wooded wetlands and the count of EEEV detections. We found Culiseta melanura (Diptera: Culicidae) were more abundant at positive sites in winter and summer, but Coquillettidia perturbans (Walker) were more abundant at positive sites in spring. In the county-wide model, precipitation, temperature, and Southern Oscillation Index values at lags of two, nine, and twelve months were significant, respectively, while temperature and wetness were significant at lags of eight and six months in the flock-specific models.

Hubungan Curah Hujan dan Titik Panas (Hotspot) Kebakaran di Hutan Lindung Gambut (HLG) Londerang, Provinsi Jambi

Jambi is one of the provinces that has high risk of forest fires in Indonesia.HLG Londerang is one of the protected peatland forests in Jambi that burned greatly in 2015. Precipitation become one of the climate factor that is affecting fires risk. This research is aimed to analyse the correlation between precipitation pattern peatland fires in HLG Londerang on 2013-2016. This research used hotspot data, precipitation, SPI (Standardized Precipitation Index), SOI (Southern Oscillation Index), and SSTA (Sea Surface Temperature Anomalies). Simple correlation test is used to acsess the relation between each parameters. This research showed that SPI-1 values could represent precipitation. In 2015, a great number of hotspot may relate to the El Nino event indicated by high positive value of SSTA and low SOI. There is a negative and weak correlation between precipitation and hotspot. Rainfall and SPI-1 has a positive and strong correlation. Combination of precipitation, SOI and SSTA is showing highest correlation with hotspot than other parameters.
 Keywords: fire, hotspot, precipitation, SOI, SPI, SSTA

Probabilistic El Niño effect on flood damages assessment

AbstractFlood ranks as the first natural disaster that causes economic losses to human societies. Meanwhile, Iran was reported to be the third country in the world with a high number of affected populations from the flood. In this article, a risk base analysis has been performed to investigate the probable influence of El Niño on the flood damages in Kan River basin (KRB). Doing so, annual precipitation data and Southern Oscillation Index values were gathered for 66 years from 1951 to 2017, then the precipitation change (PC) factor was calculated for every El Niño year. Using a cumulative distribution function of Gumble type fitted on the PC values El Niño changes the precipitation by −10, 8.2, and 31% with 30, 60, and 90% probability levels, respectively. It means that in limited cases El Niño has decreased the flood severity. Also, it could be interpreted that El Niño's influence on the precipitation intensity has been less than +31% by 90% probability and it is less than +8.2% by 60% probability. Considering the PC values with different probabilities, hydrologic and hydraulic models were used to evaluate the runoff, inundation areas, and economic losses to different properties located in the KRB. To have estimates of economic losses as a result of changed precipitation due to El Niño, the damage‐depth curves method was used. Flood damage assessment showed that the expected damage cost of a 50‐year flood has been reduced as much as −21.77% by a 30% probability. On the other hand, the flood damages may grow up to 40.94 and 73.74%, respectively, by 60 and 90% probability.

ANALISIS KEKERINGAN DI KABUPATEN SRAGEN DENGAN METODE PALMER, THORNTHWAITE, DAN STANDARDIZED PRECIPITATION INDEX

El Nino and La Nina in Indonesia are one of the reasons that caused climate changes, which has possibility of drought and flood disasters. Sragen Regency wherethe dry season occurs, drought happened meanwhile other areas experience floods and landslides. A study on drought needs to be carried out so as to reduce the risk of losses due to the drought hazard. This study is to determine the drought index in Sragen Regency based on several methods and the correlation of each methods and its suitability to the Southern Oscillation Index (SOI) and rainfall. Drought was analyzed using several methods such as Palmer Drought Severity Index (PDSI), Thornthwaite-Matter, and Standardized Precipitation Index (SPI) then correlated with SOI to determine the most suitable method for SOI. The variables are applied in this method are rainfall, temperature, and evapotranspiration. The results showed that the drought potential of the Palmer method is only in Near Normal conditions, which is 1%, Severe drought conditions are 29% for the Thornthwaite-Matter method, and Extreme Dry conditions only reach 1,11% for the SPI method. The PDSI and SPI methods are inversely proportional to the Thornthwaite-Matter method and the most suitable method for SOI values or rainfall is the SPI method. These three methods can be identified the potential for drought with only a few variables so that they could be applied if they only have those data.Keywords: Drought, PDSI, Thornthwaite-Matter, SPI, SOI

Effect of climate variability on water quality trends in New Zealand rivers

Associations between temporal variability in 10 water quality variables and the El Niño–Southern Oscillation (ENSO) climate pattern, quantified by the Southern Oscillation Index (SOI), were assessed at 56 river sites in New Zealand over a 31-year period (1989–2019). Fluctuations in monthly observations of water quality at each site were correlated to varying degrees with the corresponding SOI value (ro). Trends for rolling windows of 5-, 10- and 15-year duration were evaluated for each site and variable using Kendall’s tau (τw) and for the SOI using linear regression (δSOIw). Aggregate trends for each variable, duration and time window were quantified as proportions of site trends that were increasing (Pw). Fluctuations in τw and Pw between time windows for all durations were explained by the corresponding SOI trend (δSOIw). Between-site and between-variable differences in the trend responses to the SOI trends were explained by the corresponding ro values and the median of the ro values (MF21087_IE1.gif) respectively. These results indicate that climate variability makes a significant contribution to water quality trends, even at timescales longer than ENSO cycles. Our models can be used to quantify this contribution for individual sites (i.e. τw) and for aggregate trends (i.e. Pw).

River flows affect the growth of a tropical finfish in the wet-dry rivers of northern Australia, with implications for water resource development

Freshwater is a critical input to estuaries but is under increasing demand to support upstream human activities. In this study, otolith biochronology was used to quantify the relationship between river discharge and juvenile growth rates of barramundi (Lates calcarifer) in three regions of the Gulf of Carpentaria in northern Australia. In all regions, river discharge had a strong positive effect on juvenile growth rates. Models were also developed which incorporated the Southern Oscillation Index (SOI) and the Madden–Julian Oscillation (MJO). SOI values corresponding to La Niña events had strong positive consequences for juvenile barramundi growth rates in all regions, and the intensity of positive wet season MJO pulses had a strong positive effect on growth rates in the perennially flowing river, but not the intermittently flowing rivers. The consequences of three hypothetical water development scenarios were estimated for the perennial river. The model predicted a 12%, 8% and 1% reduction in annual barramundi growth rates under proposed scenarios for 18%, 8%, and 3% reduction in river discharge, respectively. Fish growth is a robust, quantitative metric that can be monitored pre and post water resource development to identify the least impactful development scenario and monitor its compliance and success through time.

Studi Analisa Kekeringan dengan Metode Standardized Precipitation Index (SPI) dan Palmer Drought Severity Index (PDSI) di DAS Kemuning Kabupaten Sampang

Drought is a natural disaster that occurs slowly but harms Sampang Regency people's life sustainability. Consider the negative impact of drought, analyze the drought index and its distribution are necessary. This study aims to know drought level using Standardized Precipitation Index (SPI) and Palmer Drought Severity Index (PDSI), then to know their correlation with Southern Oscillation Index (SOI) that can represent El Nino Southern Oscillation (ENSO). Drought index with bigger correlation mapped by Inverse Distance Weighting method to know the distribution. SPI method produced the most severe drought in April 2004 on one month deficit period (-3.651). PDSI method developed the most severe drought in September 2001 (-20.628). Based on the PDSI average analysis results for the 1998-2017 period, it is well-known that drought disasters generally start in July and end in October, while the peak of drought occurs in September. The PDSI method has 60% conformity to the SOI value derived from the graphical visualization of the annual average surplus and deficit index, better than the SPI method that only scores 53%. The visualization of the drought distribution map shows that the Districts of Sampang, Torjun, and Camplong need to become prioritized to mitigate future drought disasters because they have a great potential for drought disasters compared to other districts.

Impact of the Southern Oscillation Index, Temperature, and Precipitation on Eastern Equine Encephalitis Virus Activity in Florida.

Eastern equine encephalitis virus (EEEV), an Alphavirus from family Togaviridae, is a highly pathogenic arbovirus affecting the eastern United States, especially Florida. Effects of the Southern Oscillation Index (SOI), precipitation, and cooling degree days on EEEV horse case data in Florida from 2004 to 2018 were modeled using distributed lag nonlinear models (DLNMs). The analysis was conducted at statewide and regional scales. DLNMs were used to model potential delayed effects of the covariates on monthly counts of horse cases. Both models confirmed a seasonal trend in EEEV transmission and found that precipitation, cooling degree days, and the SOI were all predictors of monthly numbers of horse cases. EEEV activity in horses was associated with higher amounts of rainfall during the month of transmission at the statewide scale, as well as the prior 3 mo at the regional scale, fewer cooling degree days during the month of transmission and the preceding 3 mo and high SOI values during the month and the previous 2 mo, and SOI values in the prior 2 to 8 mo. Horse cases were lower during El Niño winters but higher during the following summer, while La Niña winters were associated with higher numbers of cases and fewer during the following summer. At the regional scale, extremely low levels of precipitation were associated with a suppression of EEEV cases for 3 mo. Given the periodicity and potential predictability of El Niño Southern Oscillation (ENSO) cycles, precipitation, and temperature, these results may provide a method for predicting EEEV risk potential in Florida.

Climatology of landfalling atmospheric Rivers and associated heavy precipitation over the Indian coastal regions

AbstractThe Indian coastal regions encountered frequently by extreme weather events such as heavy precipitation events (HPE). In the present study, an assessment has been made to understand the climatological relationship between atmospheric rivers (ARs) and HPEs for Indian coastal regions. For this purpose, India Meteorological Department gridded rainfall dataset, and four different reanalyses datasets for the occurrence of ARs were analysed for different seasons during 1980–2015. The influence of ARs towards the cause of HPEs was stronger over the West coast (WC) compared to the East coast of India (ECI). Over the WC the association between HPE with ARs is ~40% (for rainfall events >124.4·mm·day−1) than East coast (EC) by ~28%. The 64.4–124.4·mm·day−1 events are higher over the WC by ~18% compared to ~5% over the EC. While for the events (<64.4·mm·day−1), the percentage of occurrence is moreover the WC (~7%) compared to the EC (~2%). The study reveals that ARs is in good correlation with the occurrence of HPE. Using Poisson regression model, investigated the relationship between the AR totals in the summer and Northeast monsoon and the large‐scale climate indices. A sufficiently significant negative (positive) dependency observed between ARs and the Southern Oscillation Index (SOI) (Indian Ocean Dipole [IOD] and Niño 3.4 indices) with a larger rate of AR occurrence associated with lower SOI values and larger frequency of AR occurrence associated with larger IOD and Niño 3.4 values for both the coasts of India.

The Correlation of Southern Oscillation Index (SOI) with the Rainfall at Rainy and Dry Season Peak in Kintamani-Bangli Region period 1986-2015

A correlation study of the Southern Oscillation Index (SOI) on rainfall at the peak of the wet and dry season in the Kintamani-Bangli region has been carried out by taking SOI values and rainfall data for the period 1986-2015. The rainfall data used were recorded at 2 rain posts, namely Kembangsari and Kintamani. The research aimed to determine the relationship of fluctuations in the value of SOI with the intensity of rainfall, so that it can be used as a regional management plan when El Nino occurs. The method used in this study is correlation. The results obtained from the correlation that is the relationship between SOI value and rainfall in February were quite strong in the Kembangsari post with correlation coefficient of 0.409. Whereas for the Kintamani post the correlation obtained was weak with a correlation coefficient of 0.308. Then in August a weak correlation occurred in the Kembangsari post with a correlation coefficient of 0.2398 and was quite strong in the Kintamani post with a correlation coefficient of 0.4662. So that the influence of El Nino in the Kintamani area in February was more dominant in the Kembangsari post and in August at the Kintamani post.

Dampak Kejadian La Niña Terhadap Curah Hujan Di Kabupaten Jembrana

Rainfall variability in Indonesia could be affected by global phenomenon like La NiA±a by looking at the intensity value of Southern Oscillation Index (SOI) and anomaly value of SPL. The amount of these effect varies from one place to another. Jembrana Regency is one of the Regency of Bali Province. Jembrana Regency is located at 8°09'30 - 8°28'02 SL and 114°25'53 - 114°56'38 EL. The west and south border of Jembrana Regency are the sea which are Bali Strait and Indian Ocean, whereas the its east and north border are Buleleng Regency and Tabanan Regency. Rainfall pattern of Jembrana Regency has a peak of the rainy season between December - February and a valley of the dry season between June - August. From monthly rainfall data taken from the rain post of Poh Santen, Rambutsiwi, Palasari and Negara, descriptive statistical method was used to calculate the average monthly rainfall during the period of 30 years during period of 1981-2010. La NiA±a of 2010 affected the amounts of rainfall that is greater than its average in Jembrana Regency Bali. La NiA±a of 2010 affected the amounts of rainfall that is greater than La NiA±a period of the previous years.

Assessment of heavy precipitation events associated with floods due to strong moisture transport during summer monsoon over India

Integrated water vapor transport (IVT) detection algorithm is implemented over the Arabian Sea basin for the identification of strong moisture transport events (SMTs) over Indian subcontinent during 1979–2013. Attempt has been made through the spatiotemporal characteristics whether SMTs are responsible for the occurrence of heavy precipitation events (HPEs) and floods. The results demonstrated that the persistent SMTs are related to HPEs towards flooding over parts of Indian subcontinent during summer monsoon. In the study a total of 364 SMTs have been identified. It is seen that the SMT axes is reaching from eastward direction crosses over land mass of west coast of India and moves in north-westerly direction through Assam, Bihar and Uttarakhand. The results reveal a better correlation of occurrence of HPEs with the presence of SMTs and a large portion of SMTs lead to HPEs, as well as large fraction of HPEs occurs after SMTs. The characteristics of specific flood and rainfall events associated with the occurrence of SMTs show that existence of strong relation between presence of SMTs and extreme precipitation events for the western region where SMTs make landfalls (over Mumbai in 2005), for the north western region where SMTs penetrate inland (over Uttarakhand in 2013), whereas the relations is weakened in the north eastern region (e.g., over Bihar in 2008). The results emphasize that the existence of large amount of atmospheric moisture over the study regions 2–3 days before extreme precipitation events is due to SMTs. Given the narrowness of SMTs, the location of SMTs over each region is related to the occurrence or lack of extreme precipitation events. In addition, rainfall intensity enhanced with the duration of persistent SMTs of the majority of identified events. A significant negative (positive) dependence was found between SMT totals and the Southern Oscillation Index (SOI) (Indian Ocean Dipole (IOD)), with a greater frequency of SMTs associated with lower SOI (higher IOD) values. This study is helpful in inspiring more detailed analysis of the relationship between SMTs and extreme precipitation events over India.

The contribution of super typhoons to tropical cyclone activity in response to ENSO

Western North Pacific tropical cyclone (TC) activity is known to have a significant response to El Niño and Southern Oscillation (ENSO). Among the TC intensity classifications, “super typhoon”, is widely used as a symbolic word for warning people about the potential for experiencing the most severe typhoon. This study quantifies the contribution of super typhoons to TC activity in response to ENSO, where the Southern Oscillation Index (SOI) is used to indicate the internal variation of ENSO. It is found that the number and the genesis location of non-super typhoons are little influenced by ENSO, and the changes are mostly by the addition of super typhoons. Historical levels of El Niño and La Niña span from −2σ to +2σ of the SOI. Over this range of SOI values, the mean response is 5.6 super typhoons (7.1 for El Niño and 1.5 for La Niña) which nearly matches the mean response overall of 6 storms (24.6 for El Niño and 18.6 for La Niña). The spatial distribution of TC genesis locations for different ENSO conditions does not completely explain these results.

Local weather and regional climate influence breeding dynamics of Mountain Bluebirds (Sialia currucoides) and Tree Swallows (Tachycineta bicolor): a 35-year study

Many songbirds are under increasing pressure owing to habitat loss, land-use changes, and rapidly changing climatic conditions. Using citizen science data collected from 1980 to 2014, we asked how local weather and regional climate influenced the breeding dynamics of Mountain Bluebirds (Sialia currucoides (Bechstein, 1798)) and Tree Swallows (Tachycineta bicolor (Vieillot, 1808)). Mountain Bluebird reproduction was strongly associated with local weather: number of nestlings and fledglings both decreased in years of high rainfall. Clutch size and number of fledglings also declined over the study period. Abundance of Mountain Bluebirds was higher in years of lower early-season snowfall and warmer local temperatures, as well as more negative Southern Oscillation Index (SOI) values, indicating a positive influence of El Niño conditions. Tree Swallow reproduction (clutch size, number of nestlings, and number of fledglings) was negatively associated with SOI values, and the number of Tree Swallow nestlings decreased in years of higher rainfall and warmer temperatures. Tree Swallows also showed a marked decline in abundance over the period of the study, consistent with recent range-wide declines. Together, our results demonstrate that local weather and regional climate differentially affect the reproductive dynamics of Mountain Bluebirds and Tree Swallows and highlight the importance of long-term citizen science data sets.

Hubungan Indeks Osilasi Selatan dan Indeks Curah Hujan terhadap Kejadian Kekeringan di Kabupaten Indramayu, Jawa Barat, Indonesia

Indramayu district experiences frequent droughts that leads to many paddy fields harvest failure. Since the district is one of the national granary, this disaster needs to be addressed urgently. This study aimed to assess the level of dryness in Indramayu using Standard Precipitation Index (SPI) and its relation with the Southern Oscillation Index (SOI). The study used monthly rainfall data from 1996 to 2013 observed by 19 stations and the score of SOI that came from the Bureau of Meteorology of Australia. The method used quantitative approach using SPI and software SPI_sl_6.exe. Drought indices was measured in four different time scale which are 1, 3, and 6 month(s) (for the short term period) and the 12 months time scale (for the long term period). SPI’s assessment was classified in accordance with the classification of WMO (World Meteorological Organization) which consist of seven classes, ranging from wet extreme to dry extreme class. The results showed that the occurence of "very dry" to "dry extreme“ drought was occured mainly from February 1997 to January 1998 at most stations, while for some stations, it lasted until March 1998. The drought period was lasted from nine to ten months. In 2002 to 2003, the droughts that classified as "very dry" on a 3 and 6 months time scale lasted about five months, while the 12 months time scale was lasted about nine months. SPI value that obtained from different time scales has a strong relation with the value of SOI. The negative value of SOI tends to be followed by the negative value of SPI, and vice versa. SOI that has negative value below -7 and occured in a long period (more than three months) indicates a prolonged El Nino which occurred in 1997 and 2002/2003 when the research area was struck by "being dry" to "dry extreme" drought state.

The variable impact of ENSO events on regional dengue/DHF in Indonesia

Although studies have demonstrated significant associations between ENSO events and dengue fever, few have explored regional impacts on dengue fever of separate events. This study explores the impacts of two ENSO events on regional patterns of dengue/ dengue haemorrhagic fever (DHF) incidence in Indonesia. Data consist of monthly cases of dengue/DHF from 1992 to 2001 for each of Indonesia's 27 provinces, and monthly figures for rainfall, rainfall anomalies, temperature, relative humidity and the Southern Oscillation Index (SOI). We conducted Pearson correlation analyses for each independent variable against dengue/DHF incidence, using a direct month‐by‐month correlation and applying a lag of between one and six months to each variable with respect to dengue/DHF incidence. Based on the SOI value, we identified two ENSO events between 1992 and 2001. To explore each event, we created two dummy variables and in regression analyses for eight provinces. The variance of between 12.9 per cent and 24.5 per cent in provincial dengue/DHF incidence is explained by two or three climate variables in each of the provinces (p < 0.01 to 0.1). During the 1997/98 event, the explained variance increased by between 7 per cent and 15 per cent in provinces whose climate regimes were most affected by this event. This study demonstrates that indicators of ENSO such as the SOI may assist in the forecast of potential dengue/DHF incidence and distribution in Indonesia.

Climatic variability at the treeline of Monte Tlaloc, Mexico: a dendrochronological approach

An increase in winter-spring precipitation appears to have a positive effect on radial growth of P. hartwegii a treeline species in Mexican volcanoes. To address the degree to which high-elevation trees reflect climatic variability, a ring-width chronology of 308 years (1705–2012) was developed from a pure stand of Pinus hartwegii forest at the upper treeline of Monte Tlaloc in the Trans-Mexican Volcanic System. A series of variables were used to verify the climatic correlation of the chronology, including climate data, historical archives dealing with agricultural crises and climate anomalies in central Mexico, regional dendroclimatic reconstructions of precipitation, values of the Southern Oscillation Index (SOI), and Tropical Rainfall Index, which are estimators of El Nino/Southern Oscillation phenomena (ENSO). Correlations with local and regional climate data suggested that wet conditions in the winter–spring season had a positive effect on radial growth. Reduced growth was associated with extreme droughts in central Mexico, with some exceptions, such as in 1997, when, due to the massive warming of sea surface temperatures and low precipitation, growth did not begin until May or June and peaked during the cool season. The ring-width chronology indicated an increase in radial growth when SOI values were negative and precipitation was above-mean during the growing season. The lowest recorded growth measurements are associated with extreme droughts and strong warm ENSO events. Given the significant relationship between climate and radial growth of P. hartwegii, this study highlights the potential vulnerability of this high-elevation species to climate change.

El Niño–Southern Oscillation influence on tropospheric mercury concentrations

AbstractThe El Niño–Southern Oscillation (ENSO) affects the tropospheric concentrations of many trace gases. Here we investigate the ENSO influence on mercury concentrations measured in the upper troposphere during Civil Aircraft for the Regular Investigation of the atmosphere Based on an Instrumented Container flights and at ground at Cape Point, South Africa, and Mace Head, Ireland. Mercury concentrations cross‐correlate with Southern Oscillation Index (SOI) with a lag of 8 ± 2 months. Highest mercury concentrations are always found at the most negative SOI values, i.e., 8 months after El Niño, and the amplitude of the interannual variations fluctuates between ~5 and 18%. The time lag is similar to that of CO whose interannual variations are driven largely by emissions from biomass burning (BB). The amplitude of the interannual variability of tropospheric mercury concentrations is consistent with the estimated variations in mercury emissions from BB. We thus conclude that BB is a major factor driving the interannual variation of tropospheric mercury concentrations.