Decadal Time Scales Research Articles

How is the relationship between rainfall and water vapor in the Indian monsoon influenced by changes in lapse rate during global warming?

Most climate models have shown that the Indian Summer Monsoon Rainfall (ISMR) will increase on account of global warming. The primary reason is the increase in column water vapor (CWV). The rainfall increase is not, however, proportional to the increase in column water vapor; for a given amount of CWV, rainfall will be lower in the future, according to model simulations. This suggests that other there are factors are at play. We have used a diagnostic model based on moist static energy (MSE) and moisture conservation to examine the impact of changes in the vertical lapse rate of temperature. Our results indicate that on decadal time scales, changes in ISMR are mediated by changes in CWV and temperature lapse rates. This is consistent with previous studies that showed the impact of column-mean temperature on the rainfall-CWV relationship. Findings are significant for climate model projections of ISMR, as correct estimation of lapse rate changes in models is necessary to predict ISMR changes accurately.

N-fertilization and disturbance exert long-lasting complex legacies on subarctic ecosystems

Subarctic ecosystems are subjected to increasing nitrogen (N) enrichment and disturbances that induce particularly strong effects on plant communities when occurring in combination. There is little experimental evidence on the longevity of these effects. We applied N-fertilization (40 kg urea-N ha−1 year−1 for 4 years) and disturbance (removal of vegetation and organic soil layer on one occasion) in two plant communities in a subarctic forest-tundra ecotone in northern Finland. Within the first four years, N-fertilization and disturbance increased the share of deciduous dwarf shrubs and graminoids at the expense of evergreen dwarf shrubs. Individual treatments intensified the other’s effect resulting in the strongest increase in graminoids under combined N-fertilization and disturbance. The re-analysis of the plant communities 15 years after cessation of N-fertilization showed an even higher share of graminoids. 18 years after disturbance, the total vascular plant abundance was still substantially lower and the share of graminoids higher. At the same point, the plant community composition was the same under disturbance as under combined N-fertilization and disturbance, indicating that multiple perturbations no longer reinforced the other’s effect. Yet, complex interactions between N-fertilization and disturbance were still detected in the soil. We found higher organic N under disturbance and lower microbial N under combined N-fertilization and disturbance, which suggests a lower bioavailability of N sources for soil microorganisms. Our findings support that the effects of enhanced nutrients and disturbance on subarctic vegetation persist over decadal timescales. However, they also highlight the complexity of plant–soil interactions that drive subarctic ecosystem responses to multiple perturbations across varying timescales.

Large‐Scale Channel Response to Erosion‐Control Measures

AbstractErosion‐control measures in rivers aim to provide sufficient navigation width, reduce local erosion, or to protect neighboring communities from flooding. These measures are typically devised to solve a local problem. However, local channel modifications trigger a large‐scale channel response in the form of migrating bed level and sediment sorting waves. Our objective is to investigate the large‐scale channel response to such measures. We consider the lower Rhine River from Bonn (Germany) to Gorinchem (the Netherlands), where numerous erosion‐control measures have been implemented since the 1980s. We analyze measured bed level data (1999–2020) around four erosion‐control measures, comprising scour filling, bendway weirs, and two fixed beds. To get further insight on the physics behind the observed behavior, we set up an idealized one‐dimensional numerical model. Finally, we study how the geometry and spacing of the measures affect channel response. We show that erosion‐control measures reduce the sediment flux due to (a) lack of erosion over the measure and (b) sediment trapping upstream of the measure, resulting in downstream‐migrating incision waves that travel tens of kilometers at decadal timescales. When the measures are in close proximity, their downstream effects may be amplified. We conclude that, despite fulfilling erosion‐control goals at the local scale, erosion‐control measures may worsen large‐scale channel‐bed incision.

Beyond Point Masses. III. Detecting Haumea’s Nonspherical Gravitational Field

The dwarf planet Haumea is one of the most compelling trans-Neptunian objects to study, hosting two small, dynamically interacting satellites, a family of nearby spectrally unique objects, and a ring system. Haumea itself is extremely oblate due to its 3.9 hr rotation period. Understanding the orbits of Haumea’s satellites, named Hi’iaka and Namaka, requires detailed modeling of both satellite–satellite gravitational interactions and satellite interactions with Haumea’s nonspherical gravitational field (parameterized here as J 2). Understanding both of these effects allows for a detailed probe of the satellites’ masses and Haumea’s J 2 and spin pole. Measuring Haumea’s J 2 provides information about Haumea’s interior, possibly determining the extent of past differentation. In an effort to understand the Haumea system, we have performed detailed non-Keplerian orbit fitting of Haumea’s satellites using a decade of new, ultra-precise observations. Our fits detect Haumea’s J 2 and spin pole at ≳2.5σ confidence. Degeneracies present in the dynamics prevent us from precisely measuring Haumea’s J 2 with the current data, but future observations should enable a precise measurement. Our dynamically determined spin pole shows excellent agreement with past results, illustrating the strength of non-Keplerian orbit fitting. We also explore the spin–orbit dynamics of Haumea and its satellites, showing that axial precession of Hi’iaka may be detectable over decadal timescales. Finally, we present an ephemeris of the Haumea system over the coming decade, enabling high-quality observations of Haumea and its satellites for years to come.

The ozone hole and a phase change in lower stratospheric temperature

Depletion of ozone over Antarctica was first observed in the late 1970s, and discovery of the Antarctic ozone hole was announced in the 1980s as having started in 1979. The ozone hole was defined as the area with total column ozone less than 220 Dobson units. Analysis of ozone, temperature, chlorofluorocarbon and nitrous oxide data from 1963 onwards suggests that the annual ozone minimum at the South Pole is related to lower stratospheric temperature independently of chlorofluorocarbons and nitrous oxide. There were ozone holes, ie. column ozone less than 220 Dobson Units, at the South Pole in several years before 1979 (the date that the ozone hole is reported to have first appeared) when chlorofluorocarbon concentrations were much lower than today and lower than in 1979. An early 1980s phase change in the lower stratospheric temperature at the South Pole at altitudes between 250 hPa and 100 hPa, and at some lower altitudes, coincides with a phase change in the annual South Pole ozone minimum. The phase change is not visible in chlorofluorocarbon or nitrous oxide data. This raises the possibility that, over a multi-annual or decadal timescale, lower stratospheric temperature has more effect than chlorofluorocarbons or nitrous oxide on atmospheric ozone concentration over the South Pole. Alternatively, temperature and ozone may both be reacting to some other influence.

Relationship between the Pacific Meridional Mode and El Niño–Southern Oscillation on different timescales

Previous studies have shown that the Pacific Meridional Mode (PMM) has a crucial impact on the central Pacific El Niño–Southern Oscillation (ENSO). In this study, we redefined the PMM index used previously by focusing on the sea surface temperature in the subtropical northeastern Pacific (NEP), and found that the correlations between the PMM and ENSO are distinct on different timescales. We refer to this redefined index as PMMNEP. Results show that a positive PMM is weakly related to El Niño, while a negative PMM is more convincingly related to La Niña, specifically, the equatorial negative SSTAs possibly affecting negative PMM events. Moreover, the cause–effect relation between the PMMNEP and ENSO is much more significant on a decadal timescale than on an interannual timescale, and their interaction may be related to the equatorial zonal wind field. Our finding indicates that a La Niña-like decadal pattern is established through the combined actions of the PMM and ENSO, rather than an El Niño-like decadal pattern.

Evaluating risks to seabirds on the urban–coastal interface: Modelling dog attacks on little penguin populations in Tasmania

Abstract Tasmania (including offshore islands) has the largest breeding population of little penguins (Eudyptula minor) in Australia, but coastal development around nesting areas has led to habitat loss, often resulting in smaller, fragmented colonies. Colonies have also been subject to predation by introduced domestic species. This study assessed whether historical levels of domestic dog predation could threaten the viability of penguin populations. Data collected since the 1980s detailing little penguin kills by domestic dogs were used to inform the extent of individual mortality events. The potential impact of dog attacks on the viability of little penguin colonies of the sizes typically found on mainland Tasmania was explored using an age‐based population model. Simulation was conducted over decadal timescales to assess the impact of attacks at varying frequencies and intensities on small (100 birds), medium (300 birds) and large (500 birds) colonies that were stable, growing or decreasing. Results suggested that frequent and intense dog attacks markedly increased the probability of colony decline, regardless of colony size. Even large, growing penguin colonies were at risk of decline. The risk of extinction was <10% for medium and large stable colonies if no more than 15–25 penguins were killed per attack and there were no more than 20 attacks per 50 years. For small‐sized colonies, the risk of extinction was <10% if fewer than 10 attacks occurred per 50‐year period and no more than 15 birds were killed per attack. Importantly, results suggested that for small colonies especially, even low levels of predator attack could lead to colony collapse in 10–15 years. For large colonies that were already decreasing, the average time to extinction was markedly increased with additional mortalities from dogs, highlighting the need for ongoing management measures that reduce or eliminate dog attacks to help conserve this iconic species.

Satellite Remote Sensing Shows Maintenance of Fish Pond Area Improves Persistence of Eurasian Otters in Hong Kong

Urbanization and land cover change are significantly affecting the availability of habitats for wildlife worldwide. However, linking species persistence to large-scale habitat changes is challenging, especially when wildlife monitoring data is lacking. In China, the Eurasian otter (Lutra lutra) is a species of conservation concern and is listed as endangered as a consequence of declining populations across the country. Hong Kong is home to a small population of Eurasian otters, which are primarily restricted to a set of wetlands in the inner Deep Bay area. However, the drivers of their historical distribution changes are largely unknown. We combined otter spraint data from 2018 to 2019 with historical records of otter data spanning 1959–2018 to examine otter habitat preference and changes in their distribution, relating this with land cover changes measured by Landsat-5 and Landsat-8 satellite remote sensing in the past (1986 and 1995) and present (2018) using supervised random forest classification. We found that otters showed habitat preference for fish ponds and watercourses, and persisted in areas where fish pond area was more readily available. We also found no significant effect of the extent of land cover changes on otter persistence, suggesting that the species is resilient to some level of fish pond loss and find value in available terrestrial habitats. Our results demonstrate the utility of relating satellite remote sensing data to species distribution data over decadal time scales and highlight the importance of managing terrestrial and wetland habitats for otters and other key species in increasingly urbanized landscapes.

Rockfall from an increasingly unstable mountain slope driven by climate warming

Rockfall in high-mountain regions is thought to be changing due to accelerating climate warming and permafrost degradation, possibly resulting in enhanced activity and larger volumes involved in individual falls. Yet the systematic lack of long-term observations of rockfall largely hampers an in-depth assessment of how activity may have been altered by a warming climate. Here we compile a continuous time series from 1920 to 2020 of periglacial rockfall activity using growth-ring records from 375 trees damaged by past rockfall at Täschgufer (Swiss Alps). We show that the ongoing warming favours the release of rockfall and that changes in activity correlate significantly with summer air temperatures at interannual and decadal timescales. An initial increase in rockfall occurred in the late 1940s to early 1950s following early twentieth century warming. From the mid-1980s, activity reached new and hitherto unprecedented levels. This long-term record of rockfall activity can help to inform the design of vital mitigation and risk reduction measures in inhabited mountain environments.

The climatological renewable energy deviation index (credi)

We propose an index to quantify and analyse the impact of climatological variability on the energy system at different timescales. We define the climatological renewable energy deviation index (credi) as the cumulative anomaly of a renewable resource with respect to its climate over a specific time period of interest. For this we introduce the smooth, yet physical, hourly rolling window climatology that captures the expected hourly to yearly behaviour of renewable resources. We analyse the presented index at decadal, annual and (sub-)seasonal timescales for a sample region and discuss scientific and practical implications. credi is meant as an analytical tool for researchers and stakeholders to help them quantify, understand, and explain, the impact of energy-meteorological variability on future energy system. Improved understanding translates to better assessments of how renewable resources, and the associated risks for energy security, may fare in current and future climatological settings. The practical use of the index is in resource planning. For example transmission system operators may be able to adjust short-term planning to reduce adequacy issues before they occur or combine the index with storyline event selection for improved assessments of climate change related risks.

Spatiotemporal Variability of Tropical Cyclone Genesis Density in the Northwest Pacific

Abstract The small sample size of tropical cyclone (TC) genesis in the observations prevents us from fully characterizing its spatiotemporal variations. Here we take advantage of a large ensemble of 60-km-resolution atmospheric simulations to address this issue over the northwest Pacific (NWP) during 1951–2010. The variations in annual TC genesis density are explored separately on interannual and decadal time scales. The interannual variability is dominated by two leading modes. One is characterized by a dipole pattern, and its temporal evolution is closely linked to the developing ENSO. The other mode features high loadings in the central part of the basin, with out-of-phase changes near the equator and date line, and tends to occur during ENSO decay years. On decadal time scales, TC genesis density variability is primarily controlled by one mode, which exhibits an east–west dipole pattern with strong signals confined to south of 20°N and is tied to the interdecadal Pacific oscillation–like sea surface temperature anomalies. Further, we investigate the seasonal evolution of the ENSO effect on TC genesis density. The results highlight the distinct impacts of the two types of ENSO (i.e., eastern Pacific vs central Pacific) on TC genesis density in the NWP during a specific season and show the strong seasonal dependency of the TC genesis response to ENSO. Although the results from the observations are not as prominent as those from the simulations because of the small sample size, the high consistency between them demonstrates the fidelity of the model in reproducing TC statistics and variability in the observations.

Enhancing ENSO predictions with self-attention ConvLSTM and temporal embeddings

El Niño-Southern Oscillation (ENSO), a cyclic climate phenomenon spanning interannual and decadal timescales, exerts substantial impacts on the global weather patterns and ecosystems. Recently, deep learning has brought considerable advances in the accurate prediction of ENSO occurrence. However, the current models are insufficient to characterize the evolutionary behavior of the ENSO, particularly lacking comprehensive modeling of local-range and longrange spatiotemporal interdependencies, and the incorporation of calendar monthly and seasonal properties. To make up this gap, we propose a Two-Stage SpatioTemporal (TSST) autoregressive model that couples the meteorological factor prediction with ENSO indicator prediction. The first stage predicts the meteorological time series by leveraging self-attention ConvLSTM network which captures both the local and the global spatial-temporal dependencies. The temporal embeddings of calendar months and seasonal information are further incorporated to preserves repeatedly-occurring-yet-hidden patterns in meteorological series. The second stage uses multiple layers to extract higher level of features from predicted meteorological factors progressively to generate ENSO indicators. The results demonstrate that our model outperforms the state-of-the-art ENSO prediction models, effectively predicting ENSO up to 24 months and mitigating the spring predictability barrier.

Decadal‐Scale Influence of the Kuroshio and Oyashio Extension Fronts on Atmospheric Circulation and Storm Track

Decadal‐Scale Influence of the Kuroshio and Oyashio Extension Fronts on Atmospheric Circulation and Storm Track

Reassessing and Extending the Composite Rainfall Record of Manchester, Northwest England: 1786–Present

A monthly composite rainfall record for the period 1786–present representative of Manchester, northwest England is presented. The 235-year record ranks as the second-longest instrumental rainfall record available for northern England, and the fifth-longest for the UK, and contributes to a growing network of long homogenous rainfall series. A composite record is constructed, extended, and homogenised, and the record is analysed in terms of annual and seasonal variability, with a focus on extreme wet/dry events. Three primary meteorological stations in Manchester, located within 2 km of one another, form the basis of the reconstruction, with other records identified for infilling and extension based on their longevity, continuity, and proximity to the primary stations. A linear regression analysis is applied to produce a continuous record, and adjustment factors are applied to ensure homogeneity. Record homogeneity is assessed via cross-comparison with long-term records from the region (Carlisle, Chatsworth House and HadNWEP), and the methods are applied to assess relative homogeneity include the double-mass curve and Standard Normal Homogeneity tests. The Manchester record is deemed to be homogenous overall but includes two periods of increased uncertainty: 1786–1819, comprising the earliest observations and greatest number of different stations, and 1883–1911, which encompasses multi-year and multi-decadal drought events of (1883–1885 and 1890–1910) as identified by other long-term meteorological studies. The analysis of the entire record reflects long-term rainfall variability with an increasing, although not significant, trend in annual rainfall observed. Seasonally, a significant increase in winter rainfall is exhibited, in keeping with patterns observed in other regional studies. Seasonal rainfall totals are found to be highly variable at the decadal timescale. Several well-documented extreme wet (e.g., autumn 2000) and dry (e.g., summer 1976) seasons are identified, including historic events (e.g., the floods of summer 1872 and drought of summer 1887) from the less-well documented eighteenth and nineteenth centuries.

Rates of diagenesis of tropical insectivorous bat guano accumulations: implications for potential paleoenvironmental reconstruction

Cave guano deposits are increasingly being recognized as valuable repositories of paleo-climatic and paleo-environmental information. However, that value is constrained by rates of guano decomposition, and these rates have not been previously well-studied. Here we show that field and laboratory studies of deep insectivorous bat guano sequences in the caves of Borneo demonstrate the extreme dependence of decomposition rate on guano water content. Under tropical conditions, moist guanos exhibit decomposition coefficients (k) values of ~ 0.01, implying the loss of most of the organic content on decadal timescales. Under similar temperatures but drier conditions, k values drop to ~3 x 10-6, permitting significant organic (chitin) content to persist for tens of thousands of years. One of the implications of these findings for paleo-environmental records older than the limit of carbon dating is that a value for k can be calculated based on a single carbon date, which then allows an estimate of likely age at base of deposit.

A multiregressed COA-SAM model for predicting seasonal streamflow variability: A case study over Murray river basin

<p>Streamflow of the Murray River (MR) was investigated from 1978 to 2017, using statistical analysis based on Indian Ocean modes of variability. During the cool season, June to August (JJA), observations and reanalysis products have been used to analyse the relation of streamflow of MR with Indian Ocean High (IOH) and Southern Annular Mode (SAM) over South Australia (SA). Recently, the river has suffered from severe drought, whereas drought drivers differ significantly in terms of interannual and decadal timescales. As a defining feature of atmospheric general circulation, the IOH is quantitatively simulated in all global climate models. Variations in the streamflow of MR have been linked to the variability of intensity and positions of Indian Ocean high pressure (IOHP) meridionally and the impact of SAM across the Indian Ocean. It is found that the correlation of streamflow with IOHP is (r = -0.41), SAM (r = -0.52) and shows the strongest correlation with Indian Ocean High Longitude (IOHLN), which is -0.56. Moreover, SAM explains only 27% of streamflow variability, while IOHP and IOHLN indices calculated by the Center of Action (COA) approach explain 39% of the variation. This paper examines the decline of the inflow rate of MR in SA by applying the COA approach, Mann-Kendall (MK) test and Pearson correlation. We further investigate the impact of significant predictors over the flow of MR. Inflow rate of the hydrology of MR is influenced by the period of time, which shows a decreasing trend with -1.976 by applying autocorrelation. Overall, monthly and annual streamflows have also investigated a significant decreasing trend. Cross-correlation is also used to verify the relationship between streamflow and significant predictors of MR.</p>

Time Variability of FUV Emission from Cool Stars on Multi-year Timescales

The physical and chemical properties of planetary atmospheres are affected by temporal evolution of ultraviolet (UV) radiation inputs from their host stars at all time scales. While studies of X-ray/UV flare properties and long-term stellar evolution of exoplanet host stars have provided new constraints regarding stellar inputs to exoplanetary systems, the UV temporal variability of cool stars on the timescale of stellar cycles remains largely unexplored. To address this gap in our understanding of the UV temporal variability of cool stars, we analyze far-ultraviolet (FUV) emission lines of ions that trace the chromosphere and transition region of nearby stars (C ii, Si iii, Si iv, and N v; formation temperatures ∼ 20–150 kK) using data from the Hubble Space Telescope (HST) and International Ultraviolet Explorer (IUE) archives spanning temporal baselines of months to years. We select 33 unique stars of spectral types F-M with observing campaigns spanning over a year, and create ionic light curves to evaluate the characteristic variability of cool stars on such timescales. Screening for large flare events, we observe that the relative variability of FUV light curves decreases with increasing stellar effective temperature, from 30% to 70% variability for M-type stars to <30% variability for F and G-type stars. We also observe a weak trend in the temporal variability with the Ca ii RHK′ stellar activity indicator, suggesting that stars with lower Ca ii activity exhibit a smaller range of FUV flux variability. Screening for data sets with optimal temporal spread, and a sufficient number of individual observations, we select 5 data sets for further periodicity analysis (HST α Centauri A, HST α Centauri B, IUE α Centauri B, IUE ϵ Eri, IUE ξ Boo). Various periodic structures within the FUV flux were detected, with most significant being a 79 days frequency present within the IUE observations of ξ Boo, with a significance of 6σ, and a periodic signal in the FUV observations of α Centauri B, for both HST and IUE measurements, at ≈210 days frequency with significance of 3σ and 3.7σ, respectively. Our results suggest that extreme ultraviolet flux from cool stars varies by less than a factor of two on decade timescales, significantly smaller than variations on flare or stellar evolutionary timescales.

Soil carbon, nutrient, and vegetation dynamics of an old Anogeissus grove in Mole National Park, Ghana

AbstractFormation of forest islands in West Africa has been linked to anthropogenic soil improvement resulting in luxuriant tree growth in otherwise open savanna landscapes. However, there is limited understanding of how such unique ecosystems modulate soil carbon (C) dynamics and nutrient cycling. In this study, we report soil nutrient characteristics and two distinct soil organic carbon pools of Anogeissus grove (forest island) associated with abandoned village sites of the Mole National Park in the Guinea savanna or tropical continental climatic zone of Ghana, taking opportunity of a previously published study in Biotropica in 1978. We compared present‐day differences in soil characteristics between the previously studied forest grove and adjoining open savanna in the Park and evaluated vegetation dynamics since first measurement in 1974. Overall, we see changes related to self‐thinning and expansion of the grove on a decadal timescale. Soil organic matter and available phosphorus contents were greater in the grove and increased by 19.6% and 18.7%, respectively over time, showing persistence after four decades. Mineral‐associated organic carbon (MAOC) differed significantly (p &lt; .05) between the vegetation types, being 3.44% in the grove and 2.34% in the savanna. The grove was ca. 25% greater in particulate organic carbon (POC) content than the savanna. In both vegetation types, &gt;55% of carbon was stabilized in the mineral fraction. Our study demonstrates long‐term human impacts on soil and vegetation and offers a clear nature‐based solution for climate change mitigation through sustainable land management by indigenous people toward achievement of the “4p1000” initiative.

Detecting Relationship between the North–South Difference in Extreme Precipitation and Solar Cycle in China

The sun plays a crucial role as the primary source of energy for the Earth’s climate system and the issue of the influence of solar activity on the climate has been actively discussed recently. However, the precise impact of solar activity on extreme precipitation on the decadal timescale remains insufficiently confirmed. In this study, we investigate the relationship between summer extreme precipitation events exceeding 20 mm (R20mm) in China and the 11-year sunspot number (SSN) cycle from 1951 to 2018. Results showed that the first mode of June–July R20mm, a “south-drought and north-flooding (SDNF)” distribution, exhibited a significant correlation with the SSN cycle (p = 0.02). The fundamental driver is likely the pronounced periodic response of stratospheric ozone to solar forcing. During summer of the high-solar-activity years (HSY), there is a notable increase in ozone concentration and high temperatures in the stratosphere, particularly in the Southern Hemisphere. This phenomenon leads to a layer of anomalous temperature inversion, suppressing convection at the subtropics. This induced downward anomalous airflow toward the north stimulates convective activity in the equatorial region and generates northward wave activities. These wave activities produce rising and sinking anomalies at different latitudes in the Northern Hemisphere troposphere, finally causing the “SDNF” pattern in China.

CMIP3 and CMIP5 representation of sea surface temperature in the Tropical Atlantic Ocean

This study evaluates WCRP-CMIP3 and CMIP5 representation of the Sea Surface Temperature (SST) in the Atlantic Tropical Basin. The Atlantic Ocean presents thermal variability modes on intraseasonal, interannual and decadal time-scales that affect the climate of the North Atlantic, Caribbean, Western Africa, Northeast Brazil, the Gulf of Guinea Region and Southeast Atlantic (region of the Angolan resurgence). Two main SST modes in the Atlantic are the equatorial and meridional dipoles. These principal modes of SST interannual variabilities are investigated principally by empirical orthogonal function analysis (EOFs) to periods December-January and March-May. For the period of March-May, this study too analyses the relationships of these modes from coupled models of WCRP as rainfall in Northeastern Brazil compared to the observations (1971-2000 - ERSST). This investigation showed principally that although some models showed high value correlations (above 0.8 in absolute value) for both CMIP3 and CMIP5 with observations using their first two auto values EOFs coefficients of SST in the Tropical Atlantic basin, the simulations in most CMIP3-5 models do not represented the spatial thermal configuration in the basin compared to the observations, and also largely do not reproduce the pattern of correlation between to March-May between precipitation in northern of the NEB and the TSMs in the Tropical Atlantic.