Nino Years Research Articles

On the Relationship between Atmospheric Carbon Dioxide and Global Temperature

The study of dynamic relationships between the atmospheric carbon dioxide and the Earth’s global temperature in the current changing climate supported the notion that the trend in the global temperature followed the trend in the atmospheric CO2 before the climate hiatus that started in the beginning of the 21st century. During the hiatus period, the heat trapped by the atmospheric CO2 is going mostly to the ocean. This conclusion is supported by comparison of the CO2 trend with the trend in the ocean heat content. The phase relationships between the CO2 and temperature are more complicated after the removal of the trends. The phase relationships are chaotic on time scales shorter than the annual time scale. During 1986-2008, the atmospheric CO2 changed in an-ti-phase with the global temperature. The phase relationship reversed in 1979 and after 2010. The atmospheric CO2 was in-phase with the global temperature on the El Nino time scale (2.3 - 7 years) except during very strong El Nino years in 1991-1999 when CO2 led the global temperature.

Winter coastal upwelling off northwest Borneo in the South China Sea

Winter coastal upwelling off northwest Borneo in the South China Sea (SCS) is investigated by using satellite data, climatological temperature and salinity fields and reanalysis data. The upwelling forms in December, matures in January, starts to decay in February and almost disappears in March. Both Ekman transport induced by the alongshore winter monsoon and Ekman pumping due to orographic wind stress curl are favorable for the upwelling. Transport estimates demonstrate that the month-to-month variability of Ekman transport and Ekman pumping are both consistent with that of winter coastal upwelling, but Ekman transport is two times larger than Ekman pumping in January and February. Under the influence of El Nino-Southern Oscillation (ENSO), the upwelling shows remarkable interannual variability: during winter of El Nino (La Nina) years, an anticyclonic (a cyclonic) wind anomaly is established in the SCS, which behaves a northeasterly (southwesterly) anomaly and a positive (negative) wind stress curl anomaly off the northwest Borneo coast, enhancing (reducing) the upwelling and causing anomalous surface cooling (warming) and higher (lower) chlorophyll concentration. The sea surface temperature anomaly (SSTA) associated with ENSO off the northwest Borneo coast has an opposite phase to that off southeast Vietnam, resulting in a SSTA seesaw pattern in the southern SCS in winter.

Analysis of Climate Variability (ENSO) and Vegetation Dynamics in Gojjam, Ethiopia

This study analyses the regional climate variability, especially La Nina or El Nino Southern Oscillation events and their impact on rainfall variability and vegetation coverage. The temporal and spatial distributions of temperature, precipitation, and vegetation coverage have been investigated for the two agricultural productive seasons from (2000–2008), using data from 11 meteorological station and MODIS satellite data in Gojjam, Ethiopia. The normalized difference vegetation index (NDVI) is widely accepted as a good indicator for providing vegetation properties and associated changes for large spatial scale. The analyses indicated that climate variability is quite common particularly in the small rainy season, Belg and continues to affect the vegetation condition in the region. The statistical correlation analysis indicated that there is a strong positive correlation between NDVI and the seasonal rainfall in most years, whereas, the temperature increase decreases the vegetation coverage in both seasons. The effect of ENSO, climate variability has been high to the regional rainfall variability in mostly of the months or years. In the fully strong El Nino or La Nina episode years like 2000 and 2002 the SST and rainfall showed positive correlation with r2 values 0.75 and 0.63, respectively. The NDVI anomaly pattern is almost similar to that of the main documented precipitation and temperature anomaly pattern associated with ENSO. The spatial and temporal analyses of basic climate elements and NDVI values for the growing season showed that NDVI and rainfall are highly variable during the 9 years period. The ENSO analyses showed an increase in seasonal vegetation coverage during El Nino episodes contrasting to La Nina episodes. However, there has been a rainfall delay during El Nino episodes in the first one or two months of Kiremt season.

Impacts of drought on grape yields in Western Cape, South Africa

Droughts remain a threat to grape yields in South Africa. Previous studies on the impacts of climate on grape yield in the country have focussed on the impact of rainfall and temperature separately; meanwhile, grape yields are affected by drought, which is a combination of rainfall and temperature influences. The present study investigates the impacts of drought on grape yields in the Western Cape (South Africa) at district and farm scales. The study used a new drought index that is based on simple water balance (Standardized Precipitation Evapotranspiration Index; hereafter, SPEI) to identify drought events and used a correlation analysis to identify the relationship between drought and grape yields. A crop simulation model (Agricultural Production Systems sIMulator, APSIM) was applied at the farm scale to investigate the role of irrigation in mitigating the impacts of drought on grape yield. The model gives a realistic simulation of grape yields. The Western Cape has experienced a series of severe droughts in the past few decades. The severe droughts occurred when a decrease in rainfall occurred simultaneously with an increase in temperature. El Nino Southern Oscillation (ENSO) appears to be an important driver of drought severity in the Western Cape, because most of the severe droughts occurred in El Nino years. At the district scale, the correlation between drought index and grape yield is weak (r≈−0.5), but at the farm scale, it is strong (r≈−0.9). This suggests that many farmers are able to mitigate the impacts of drought on grape yields through irrigation management. At the farm scale, where the impact of drought on grape yields is high, poor yield years coincide with moderate or severe drought periods. The APSIM simulation, which gives a realistic simulation of grape yields at the farm scale, suggests that grape yields become more sensitive to spring and summer droughts in the absence of irrigation. Results of this study may guide decision-making on how to reduce the impacts of drought on food security in South Africa.

Relationships between drought disasters and crop production during ENSO episodes across the North China Plain

Studying the causes of drought is important because the formation of large regional droughts is linked to global atmospheric system abnormalities in China. Information about the effects of drought on crop production is needed in order to improve understanding of a region’s drought vulnerability and to improve food production safety in the North China Plain. This paper uses agricultural statistics and monthly Southern Oscillation Index data between 1961 and 2007 to quantitatively evaluate regional agricultural meteorological disasters and to assess the regressive models used to predict the grain yield and climatic yield losses caused by drought disasters. The data showed that the drought-covered area ratios declined, but the drought-affected area ratios rose. During the La Nina stage, the probability of a drought disaster was higher than during the El Nino stage, especially in Hebei. In the El Nino years, there were negative trends for the drought-covered, -affected and -destroyed area ratios in winter and positive trends in the other three seasons. In the La Nina years, the drought disaster area ratios were positive for all seasons. In Neutral years, there was more likely to be a drought event in autumn. The regression analyses for the three provinces showed that the grain climatic yield loss was significantly associated with the grain yield loss caused by drought disasters. This showed that regional grain yield simulations and evaluations of agro-meteorological disasters reliably predicted the field measured statistical data for drought disasters. Therefore, our results showed that there is a mixed seasonal trend in the drought disaster areas in the El Nino years, but a consistent upward trend for all seasons in the La Nina years. We also showed that the damage caused by drought disasters can be quantified by estimating the yield loss.

El Nino Southern Oscillation (ENSO) impact on tuna fisheries in Indian Ocean.

El Nino Southern Oscillation (ENSO) is an important driver of interannual variations in climate and ecosystem productivity in tropical regions. However, detailed information about this important phenomenon of the Indian Ocean is scarce. Consequently, the objective of this study is to improve understanding of the impact of warm event El Nino and cool event La Nina on annual tuna landings from the Indian Ocean from 1980 to 2010. In this study, maximum tuna landings were recorded during a weak El Nino year (1456054 t in 2006) and during a weak La Nina year (1243562 t in 2000), although the lowest tuna catch was followed during the strong El Nino year (1204119 t in 2009) and during a strong La Nina year (706546 t in 1988). Validation of predicted tuna landings and SST were showing a significant positive correlation (p < 0.01) was observed all the major tuna species except Southern Bluefin Tuna. Whereas the other relationships such as sea level pressure, Wind actions; Zonal Wind (U), Meridonial Wind (V), and Scalar Wind (W) are less well-defined. In contrast with principal component analysis we find that Principal Components 1 explains 75.5% of the total variance and suggest that sea surface temperature plays a major role in determining tuna availability in the region especially during warm event El Nino years; landings in Indian Ocean tend to be optimum SST 25 to 26°C in ENSO event. Our results confirm the ENSO impact on climate, tuna abundance and production in the Indian Ocean. However, among the oceanic variables SST explained the highest deviance in generalized additive models and therefore considered the best habitat predictor in the Indian Ocean followed by sea level pressure and Winds (U, V, W).Electronic supplementary materialThe online version of this article (doi:10.1186/2193-1801-3-591) contains supplementary material, which is available to authorized users.

Influence of ENSO SSTs on the spread of the probability density function for precipitation and land surface temperature

The impact of the interannual variations in ENSO SSTs on the spread of probability density function (PDF) for the seasonal mean of variables of societal relevance are analyzed based on a large set of the hindcasts from NCEP CFSv2. The study is focused on the analysis of global rainfall and 2-m temperature over land (T2m) for December–January–February (DJF) seasonal mean. For rainfall, the spatial distribution of the ENSO SST induced changes on the spread of PDF strongly resembles changes in the mean but have a smaller amplitude. Over the central-eastern equatorial Pacific, changes in the spread lead to a reduction in signal-to-noise ratio (SNR) during El Nino years while to an increase in the SNR during La Nina years. Over extratropics, year to year changes in the spread are relatively small. For T2m, the changes in spread have little systematic dependence on the ENSO SSTs and the amplitudes of the changes in spread are much smaller than corresponding changes in the ensemble mean. The results demonstrate small systematic year to year variations in the PDF spread, for example over extratropics for rainfall and over most of global land areas for T2m, and indicate that it might be a good practice in seasonal predictions to assume that the spread of seasonal means from year to year is constant and the skill in seasonal forecast information resides primarily in the shift of the first moment of the seasonal mean of the PDF.

Pacific and Atlantic oceanic anomalies and their interaction with rainfall and fire in Bolivian biomes for the period 1992–2012

Bolivia is located at the crossroad of the major climatic influences of Northern and Southern-South America, which turns this country into a natural laboratory to investigate the interactions between ocean-climate and fire variability. We chose two oceanic indices: MEI (multivariate ENSO Index) and AMO (Atlantic Multidecadal Oscillation) to select the three most representative years for four oceanic conditions: El Nino, La Nina, AMO, and standard years (understood as years with little ocean influences), for the period 1992–2012. We investigated how i) rainfall (dry vs wet seasons) and ii) fire responded in five Bolivian biomes (Tropical Moist Forests, Tropical Dry Forests, Tropical Grasslands, Tropical Montane, and Seasonally Flooded ecosystems) under these oceanic conditions. Bolivia showed a strong rainfall increase in El Nino years in both seasons (wet/dry), while AMO showed the strongest droughts in both seasons. La Nina showed a bipolar response with rainfall increases in the wet season and a very marked rainfall decrease in the dry season. Drought significantly increased fire numbers in AMO years, being the most significant fire condition and suggesting a larger fire influence of the Atlantic than the Pacific at the national level. Surprisingly, the amount of fire was very large under normal years (STD) and similar to fire levels under La Nina, suggesting generalized fire conditions in the country, except for El Nino years that bring rainfall excess and little fire. The most fire-affected biomes were the seasonally flooded and dry forests, followed by the grassland/savannah biome. Montane areas showed the least fire, but satellite fire omission is well known in the Andean region.

Storm track activity over the North Pacific associated with the Madden-Julian Oscillation under ENSO conditions during boreal winter

The present study investigates modulation by the Madden-Julian Oscillation (MJO) of storm track activity (STA) over the North Pacific (NP) during boreal winter for El Nino and La Nina periods. STA defined by vertically averaged synoptic eddy kinetic energy (EKE) greatly intensifies over the western North Pacific (WNP) and central eastern North Pacific during La Nina and El Nino years, respectively, when the MJO convection is located over the central Indian Ocean (IO)-Maritime Continent. When the MJO moves into the western central Pacific, the STA in La Nina years is suppressed (enhanced) at higher (lower) latitudes than in El Nino years. Diagnoses of EKE and eddy available potential energy budgets indicate that the difference in STA over the WNP for the MJO phases between El Nino–Southern Oscillation (ENSO) years is mainly contributed by baroclinic energy conversion and potential energy conversion between background and eddy (BCPE). We reveal that BCPE is mainly attributed to intraseasonal baroclinicity and eddy heat flux (EHF) anomalies and their interactions with strong winter mean baroclinic fields in the WNP. Through the EHF, synoptic eddies act to counterbalance an intraseasonal temperature that is primarily caused by the anomalous horizontal advection of mean temperature by MJO-related flow. The intraseasonal circulation and associated temperature and EHF anomalies dominate in northwest (southeast) portion of the NP during La Nina (El Nino), leading to BCPE difference. Changes in the spatial pattern and strength of the NP circulation and STA are caused by dominance of strong MJO amplification over the IO (central Pacific) during La Nina (El Nino).

An objective criterion for the identification of breaks in Indian summer monsoon rainfall

AbstractWe proposed a new objective criterion for discerning breaks in Indian summer monsoon rainfall, which is based on grid‐level rainfall threshold. The identified breaks reproduced all well‐known breaks discussed in the literature, but are relatively fewer in number. The correlation analysis between the number of break days and all‐India seasonal rainfall is not only high (R2 = −0.77) but also reproduced well‐known association between El Nino and bad monsoon years. The fraction of seasonal rainfall in break days is found to be smaller (&lt;10%) over most part of India than earlier studies, indicating that the discerned spells are valid for a large part of India.

Impacts of ENSO and IOD on tropical cyclone activity in the Bay of Bengal

The impacts of El Nino-Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD) on tropical cyclone (TC) activity (intensity, frequency, genesis location, track and average lifetime) in the Bay of Bengal (BoB) are studied for the period 1891–2007 using cyclone e-Atlas of India Meteorological Department, Nino3.4 Index, Oceanic Nino Index and Dipole Mode Index (DMI). TCs in the present study include cyclones with maximum sustainable wind (MSW) ≥34 knots (referred as cyclonic storms) and severe cyclonic storms with MSW ≥48 knots. The study shows a total of 502 TCs over BoB during the 117-year study period at the rate of 4.29 TC per year. Seven-year running mean of TCs for the period 1891–2007 shows a decreasing trend. Correlation between Nino3.4 Index and DMI for the 117-year period is significant and positive and the significance level is higher (lower) for the period with higher (lower) TC frequencies. One-third monthly interval analysis for the 117-year period indicates first third (1–10) of November as the most favoured period of TC formation over BoB. 117-year study period is divided into years of ENSO (El Nino, La Nina and neutral ENSO) and IOD (+ve IOD, −ve IOD and no IOD) categories. Maximum frequency of TC is observed during La Nina years, −ve IOD years and also when La Nina co-occurred with −ve IOD. More severe cyclones are formed during La Nina and +ve IOD years. Genesis location of TCs indicates that during La Nina (El Nino) years, the TCs are oriented in the south-east–north-west (south-west–north-east) direction. TCs in no IOD and −ve (+ve) IOD years are more (less) in northern BoB (north of 15° N), while in southern BoB (south of 15° N), TCs are more (less) during no IOD and +ve (−ve) IOD condition. BoB is divided into four quadrants, and number of TCs in each quadrant is computed under different ENSO–IOD events. Peak direction of track movement is observed as north-east followed by north–north-west which is corroborated from the dissipation of TCs in the specific quadrant. Total TC tracks in the peak direction of track movement are maximum during El Nino and no IOD years. The study reveals that TCs with shorter lifetime are observed during El Nino and −ve IOD years, while TCs with longer lifetime are observed during La Nina, neutral ENSO and +ve IOD years. The decade with maximum TC formation is observed as 1921–1930, and the impacts of ENSO and IOD on decadal variability are distinctly observed.

Influence of Pacific Decadal Oscillation on the relationship between ENSO and tropical cyclone activity in the Bay of Bengal during October–December

The relationship between ENSO and tropical cyclones (TCs) activity in the Bay of Bengal (BoB) during October–December under cold (1950–1974) and warm (1975–2006) phase of Pacific Decadal Oscillation (PDO) is investigated. A statistically significant difference in the formation of total number of TCs and intense TCs (Category-1 and above) between El Nino and La Nina years is observed when the PDO was in warm phase. Our analysis shows that, there is a tendency to form more number of TCs during La Nina years (2.62 TCs per season) than during El Nino years (1.6 TCs per season) under warm phase of PDO. Moreover, the difference is quite high for intense TCs cases, such as, relatively more number of intense TCs forms in the BoB during La Nina years (1.4 TCs per season) compared to El Nino years (0.10 TCs per season) under warm phase of PDO. However, the difference in the formation of total number of TCs and intense TCs between La Nina and El Nino years is not significant under cold phase of PDO. Significant enhancement in low level cyclonic vorticity and mid-troposphere humidity during La Nina years compared to El Nino years when the PDO was in warm phase, rather than the PDO was in cold phase leads to this difference. Our analysis further shows that how the ENSO related teleconnection to the Indian Ocean region differ under warm and cold phase of PDO.

ENSO Effect on Black Sea Precipitation

El Nino Southern Oscillation is one of the most important oceanic-atmospheric events on the world, which sometimes considerably affects the climates of the countries, i.e. the hydrologic parameters of the regions. Hence, the aim of this study was to determine the possible effects of ENSO events on the precipitation data of the Black Sea Region of Turkey by concerning 23 precipitation-recording stations at the Black Sea Region of Turkey. During the analysis, the synthetic monthly precipitation data corresponding to the El Nino years were generated using Feed Forward Back Propagation Artificial Neural Network model and replaced with the original data. In this way, two precipitation data sets for each station (synthetic and original) were obtained in order to compare their statistical parameters (variance, mean, population, autocorrelation) to find out whether the synthetic and the original data differ from each other or not. Consequently, significant El Nino effect was determined for the precipitation data of Turkey's Black Sea Region which should be taken into consideration for long term drinking water, irrigation, environmental planning, energy purposes, etc. This study can be extended for all the countries surrounding the Black Sea to obtain the regions affected from ENSO more precisely in the subsequent studies.

Droughts of Indian summer monsoon associated with El Niño and Non‐El Niño years

ABSTRACTUnderstanding the conditions of droughts are imperative for many purposes especially in planning and agricultural fields. In this paper an attempt is made to analyse rainfall distribution during droughts associated with El Niño and non‐El Niño events using India Meteorological Department (IMD) daily rainfall data set having a spatial resolution of 0.25° latitude × 0.25° longitude grid. Patterns of rainfall during drought years which are not associated with El Niño have below normal rainfall over most places of Indian subcontinent, except peninsular India and eastern region. Most of the drought conditions of the Indian summer monsoon rainfall are associated with El Niño (13 of the 18 years) indicating that about 72% of the drought years are associated with the influence of Pacific Ocean. North India and most of the central Indian regions are under below normal rainfall especially over west coastal stations there the severity of drought is strong. The drought that are associated with El Nino are much intense in most parts of the subcontinent, it severely affected the entire west coastal belts, monsoon zone and eastern regions than the droughts associated with non‐El Nino years. The spatial patterns of rainfall during flood years associated with La Niña events and drought years associated with El Niño reveal that the spatial structure of rainfall is highly non‐linear. These results are also verified using APHRODITE rainfall data. Over central India and Western Ghats (WGs), the drought associated with El Niño gives clear indication of droughts from the early June onward, however, in the case of non‐El Niño‐related droughts, the indication of drought can be seen only after the first week of July. The study suggests that droughts associated with El Niño events bring severe drought conditions over WG region. However, over central India, there is no considerable difference in cumulative rainfall associated with the two types of droughts. The intraseasonal properties of rainfall are prominently different from non‐El Niño to El Niño droughts. During El Niño droughts, the variance of rainfall in both the central Indian and WG regions is weaker than the droughts that are not associated with El Niño.

Evolucion geomorfologica y vegetacion costera de playa Palmeras, Parque Nacional Natural Isla Gorgona, Pacifico Colombiano

A study of the geomorphology and vegetation in Palmeras Beach was conducted from a digital elevation model, systematic measurements of beach profiles for 15 months, analysis of equilibrium shape and measurements of vegetation, electric conductivity of the floodwater and granulometry at 15 parcels established along the beach. The beach can be divided into two sectors. The NE is characterized by a concave shape, beach cusps, steeper slope, higher elevation, wider dry zone, greater variability of the shape in plan and profile, greater tendency for accretion and herbaceous vegetation dominated by Rhynchospora polystachys. The SW sector has a convex shape, lower elevation, minimal dry zone width, lower variability of the plan and profile, its shape tends to erosion. The herbaceous vegetation is dominated by Sphagneticola trilobata and it has a higher proportion of dead palms. Although the length of the observations limits the conclusions on the seasonal and interannual variability of the beach, in the wet season there is loss of sand and the sea level rises. Also during El Nino years increased wave energy, which could be associated with coastal erosion was evident. In the long term, there is evidence of a change in wave direction and a tilting of the beach with accretion to the NE and erosion to the SW.

Increasing autumn drought over southern China associated with ENSO regime shift

In the two most recent decades, more frequent drought struck southern China during autumn, causing an unprecedented water crisis. We found that the increasing autumn drought is largely attributed to an ENSO regime shift. Compared to traditional eastern-Pacific (EP) El Nino, central-Pacific (CP) El Nino events have occurred more frequently, with maximum sea surface temperature anomalies located near the dateline. Southern China usually experiences precipitation surplus during the autumn of EP El Nino years, while the CP El Nino tends to produce precipitation deficits. Since the CP El Nino has occurred more frequently while EP El Nino has become less common after the early 1990s, there has been a significant increase in the frequency of autumn drought. This has implications for increasing precipitation shortages over southern China in a warming world, in which CP El Nino events have been suggested to become more common.

Impact of intraseasonal oscillation on the tropical cyclone track in the South China Sea

This study investigates the impact of the intraseasonal oscillation (ISO) on tropical cyclone (TC) tracks in the South China Sea (SCS) during 1970–2010. About one third of TCs in the SCS move eastward, while the other two thirds move westward. In the TC genesis peak seasons of June–October (JJASO), the westward moving TCs are controlled by the background TC steering flow of easterly, and the eastward moving TCs by the TC steering flow induced by the ISO. The outgoing longwave radiation and wind fields show that the eastward moving TCs were mostly along the main axis of strong TC steering flow anomaly of westerly associated with the ISO, while the westward moving TCs were only weakly associated with the ISO. An experiment performed with a simple two-level model further confirmed the result. The interannual variation of TC tracks in the SCS is also discussed. It is found that the steering flow anomalies in the SCS mostly favor eastward moving TCs in central Pacific (CP) El Nino and eastern Pacific (EP) El Nino years. However, the eastward flow anomalies are too weak to have strong influence on the majority of the TCs. During La Nina years, TCs in the SCS tend to move westward, possibly related to the westward steering flow anomalies.

Modeling winter rainfall in Northwest India using a hidden Markov model: understanding occurrence of different states and their dynamical connections

A multiscale-modeling framework for daily rainfall is considered and diagnostic results are presented for an application to the winter season in Northwest India. The daily rainfall process is considered to follow a hidden Markov model (HMM), with the hidden states assumed to be an unknown random function of slowly varying climatic modulation of the winter jet stream and moisture transport dynamics. The data used are from 14 stations over Satluj River basin in winter (December–January–February–March). The period considered is 1977/78–2005/06. The HMM identifies four discrete weather states, which are used to describe daily rainfall variability over study region. Each state was found to be associated with a distinct atmospheric circulation pattern, with the driest and drier states, State 1 and 2 respectively, characterized by a lack of synoptic wave activity. In contrast, the wetter and wettest states, States 3 and 4 respectively, are characterized by a zonally oriented wave train extending across Eurasia between 20N and 40N, identified with ‘western disturbances’ (WD). The occurrence of State 4 is strongly conditioned by the El Nino and Indian Ocean Dipole (IOD) phenomena in winter, which is demonstrated using large-scale correlation maps based on mean sea level pressure and sea surface temperature. This suggests that there is a tendency of higher frequency of the wet days and intense WD activities in winter during El Nino and positive IOD years. These findings, derived from daily rainfall station records, help clarify the sequence of Northern Hemisphere mid-latitude storms bringing winter rainfall over Northwest India, and their association with potentially predictable low frequency modes on seasonal time scales and longer.

Short- and long-term response of phytoplankton to ENSO in Prydz Bay, Antarctica: Evidences from field measurements, remote sensing data and stratigraphic biomarker records

The study provides one of the first lines of evidence showing linkages between Antarctic phytoplankton abundance and composition in response to ENSO, based on historical reconstruction of sediment biomarkers. In addition to sediment biomarkers, field measured and remote sensing data of phytoplankton abundance were also recorded from Prydz Bay, Eastern Antarctica. Community structure of field measured phytoplankton showed significant El Nino/La Nina-related succession during 1990 to 2002. In general, the number of algae species decreased during El Nino and La Nina years compared to normal years. Austral summer monthly variation of remotely sensed chlorophyll-a (Chl-a), particulate organic carbon (POC), and sea surface temperature (SST) indicated that ENSO impacted the timing of phytoplankton blooms during 2007 to 2011. Phytoplankton blooms (indicated by Chl-a and POC) preceded the increases in SST during El Nino years, and lagged behind the SST increases during La Nina years. Stratigraphic record of marine sedimentary lipid (brassicasterol, dinosterol and alkenones) biomarkers inferred that the proportions of different algae (diatoms, dinoflagellates and haptophytes) changed significantly between El Nino and La Nina events. The relative proportion of diatoms increased, with that of dinoflagellates being decreased during El Nino years, while it was reversed during La Nina years.

Trends and extreme value analysis of rainfall pattern over homogeneous monsoon regions of India

Trends of pre-monsoon, monsoon and post-monsoon rainfall pattern were studied on decadal basis over different homogeneous monsoon regions in India for the period 1871-2008. It is attempted to understand the relation of monsoon rainfall with the global teleconnections of El Nino and La Nina, for which the correlation analysis has been carried out with Darwin pressure and Nino 3.4 sea surface temperature (Nino 3.4 SST). The correlation analysis inferred that the significant correlations were observed when monsoon rainfall is related to ENSO indices on decadal scale than on annual ones. The study also found that the north-west region is more affected by the moderate El Nino years compared to strong El Nino years. The regions Central North-East and North-East could not make any difference among weak, moderate and strong La Nina events. The authors also have carried out the extreme value analysis over different homogeneous monsoon regions of India as well as for whole India. The results show that the return values of rainfall are increasing with the return periods for the forthcoming 10, 20, 50 and 100 years. The heterogeneity in number of threshold years that were recorded for the extreme rainfall over north-east (humid climatic type) and north-west (arid climatic type) described the climate variability. The results of the present study may be useful for the policy makers in understanding the rainfall exceedance in different return periods for planning the risk management strategies.