Interdecadal Scales Research Articles

Interannual and interdecadal atmospheric circulation anomalies of autumn dry/wet over the loess plateau and its multi-scalar correlation to SST

The ecological environment is vulnerable and extremely sensitive to climate change in the loess plateau. The interannual and interdecadal variations of dry/wet index are particularly obvious in this region. Up to now, the analisis of the dry/wet variation in the loess plateau has been basically understood during summer, but the autumn dry/wet evolution of the loess plateau and the atmospheric circulation characteristic are still laking in its knowledge. Based on the monthly mean rainfall and temperature of 589 China weather stations, the NCEP/NCAR reanalysis dataset and NOAA extended reconstructed sea surface temperature (SST) data from 1961 to 2010, using the EOF/REOF, bandpass filtering, wavelet technique and regression methods, the autumn dry/wet evolution of the loess plateau and the atmospheric circulation characteristic associated with them, and the multi-scale relationship between dry/wet index and SST were analyzed on the basis of classification of dry/wet over China region in autumn. The continuous wavelet transform shows that the autumn wet/dry index exists has ～4 a and 8 a period over the loess plateau, and the ～8 year oscillation from 1970–1990 is rather obvious. On the interannual scales, the atmospheric circulation anomalies of 500 hPa associated with the wet years exhibit a ’double-blocking’ in the mid-high latitude, and the westerly jet stream turns to be weakened and the jet axis moves to the north significantly. Japan-Okhotsk Sea is featured with anticyclone, and the east wind at the bottom of the anticyclone provides favorable moisture for the middle Loess plateau. On the interdecadal scales, the atmospheric circulation anomalies associated with the wet years show the negative geopotential height anomaly over East Asian, and the East Asian subtropical westerly jet stream of 200 hPa is weakened and moves north too. The vapour of the middle Loess plateau comes from two paths, one is the westerly water vapor transport in the middle latitude, and the other is the southerly water vapor transport from the Bay of Bengal and turns to the north at the Indo-China Peninsula. When the Nino3 index (Nino3I) is in advance of dry/wet index for 5 months, there is a significantly negative correlation between them. When the Bay of Benga and South China Sea SST index (BayI) goes shead of dry/wet index for 3 months, there is a significantly negative correlation between them. On the interannual scales, the cross wavelet transform indicates that both the Nino3I and BayI have significant connections with the dry/wet index (～4 a and 4–6 a cycles). On the interdecadal scales, only BayI has significant connections with dry/wet index (～10 a cycles). By establishing the interannual and interdecadal variations of dry/wet cycle of the loess plateau, recognizing the atmospheric circulation anomalies, and building the relationship between the dry/wet index and SST, this paper reveals the physical mechanism of the dry/wet variation and finds the early waring signals for drought climate change in the region.

Reconstructing changes in Atlantic thermohaline circulation during the 20th century under two possible scenarios

Atlantic thermohaline circulation (THC) is a key component of the Earth Climate System and identification of its changes during the 20th Century is critical to the understanding of its variation characteristics and the corresponding climatic impacts. Previous researches have been inconclusive, with the results varying depending on the approach used to measure THC. The results for the two established approaches for measurement of the phenomenon (direct observation and indirect reconstruction) are contradictive (weakening and non-weakening), and their credibility needs improving. Based on the tight relationship between THC anomaly and “see-saw” intensities of Sea Surface Temperature (SST) and Surface Air Temperature (SAT), we first diagnose their quantitative relationship in the model experiments, which is corresponding to its two possible scenarios, and then reconstruct the changes of THC during the 20th Century respectively with multiple observed datasets of SST and SAT. Model results show that THC anomaly and SST/SAT “see-saw” intensities are well correlated in timescales longer than 10/40 years under scenarios of weakening/non-weakening respectively. Two kinds of reconstructions here are consistent with each other, and we propose that THC has undergone a 2-cycle oscillation with inter-decadal scale since the Industrial Revolution with a magnitude of about 1 Sv. The transformation times of decadal trend are around the mid-1910s, the 1940s, and the mid-1970s. This research further validates the main results of previous reconstructions, and points out that THC does not have a long-term weakening during the 20th Century.

지구시스템 모형을 이용한 21세기 동중국해와 남해의 수온과 일차생산 변화 평가

Using results from an Earth System model, we investigated change in primary production in the East China Sea, under a global warming scenario. As global warming progresses, the vertical stratification of water becomes stronger, and nutrient supply from the lower part to the upper part is reduced. Consequently, so is the primary production. In addition to the warming trend, there is strong decadal to interdecadal scale variability, and it takes a few decades before the warming trend surpasses natural variability. Thus, it would be very hard to investigate the global warming trend using data of several years' length.

Multiple temporal scale analysis of main driving factors of eutrophication in Meiliang Bay, Lake Taihu

采用太湖湖泊生态系统研究站太湖梅梁湾富营养化四种主要驱动因子叶绿素a(Chl.a)、水温、总磷(TP)、总氮浓度1992-2010年的监测数据,利用小波变换方法,分析了四种因子不同时间尺度上的时间格局特征.结果表明,四种驱动因子在年际和年代际尺度上都具有清晰的多时间尺度特征,主周期各不相同,但Chl.a和TP浓度的小波实部变化趋势具有较高的一致性.本文分析了各因子在不同时间尺度上的强弱分布以及高低交替,并在此基础上从时间尺度的角度预测出在未来3~5年内,太湖梅梁湾湖区的富营养化程度将保持在一个比较平稳的水平,为太湖富营养化的认识和治理提供更加可靠的科学依据.;Concentration of chlorophyll-a (Chl. a), total phosphorus (TP), total nitrogen and water temperature are the four main driving factors resulting in eutrophication in Meiliang Bay, Lake Taihu. Based on the observation data in the period of 1992 -2010, the temporal pattern characteristics of the four factors in different temporal scales were analyzed respectively using wavelet analysis. Results showed that the temporal patterns of the four factors were obvious in the inter-annual and inter-decadal scales and the primary periods were different, but the real parts of wavelet coefficients of Chl. a and TP were consistent. The distributions and the periodic oscillation were analyzed and it was predicted that the eutrophication condition in Meiliang Bay would keep stable in the future 3-5 years. This method will provide reliable scientific evidence to the management of Lake Taihu.

Multitime scale variations of sea surface temperature in the China seas based on the HadISST dataset

The variability of the sea surface temperature (SST) in the China seas has been studied in seasonal, interannual and interdecadal scales based on the monthly data of HadISST spanning from 1870 to 2007. The main results obtained are SST in the China offshore changes most actively at the seasonal scale with the intensity diminishing from north to south, as the temperature differences between summer and winter reaching 17 and 4°C in the northern and southern areas, respectively. Moreover, seasonal variation near the coastal regions seems relatively stronger than that far from the coastline; significant interannual variations are detected, with the largest positive anomaly occurring in 1998 in the overall area. But as far as different domains are concerned, there exists great diversity, and the difference is also found between winter and summer. Differed from the seasonal variations, where the strongest interannual variability takes place, resides to the south of that of the seasonal ones in the northern section, nevertheless in the South China Sea, the most significant interannual variability is found in the deep basin; interdecadal changes of summer, winter and annual mean SST in different domains likewise present various features. In addition, a common dominant warming in recent 20 a are found in the overall China offshore with the strongest center located in the vicinity of the Changjiang Estuary in the East China Sea, which intensifies as high as 1.3°C during the past 130 a.

Inter-decadal variability of summer rainfall in Eastern China detected by the Lepage test

On the basis of the latest observational datasets, the inter-decadal changes of summer rainfall in East China in the past 50 years are analyzed using the Lepage test. The two traditional methods moving t-test and Mann-Kendall test are also performed on the rainfall data as a comparison. Results indicate four inter-decadal abrupt changes of summer rainfall that occurred near 1979, 1983, 1993, and 1999, and each of them is characterized by remarkable regional features. The abrupt change of summer rainfall around 1979 is accompanied by significant rainfall increase in Yangtze–Huai River Valley and a decrease in its flank. The one near 1983 shows similar structures of the rainfall changes to that near 1979, but with more significant changes in the South China and Northeast China (NEC). The inter-decadal change around 1993 brings a notable increase of summer rainfall to the South China; and the abrupt shift near 1999 exhibits significant decrease in summer rainfall over a large part of North China and NEC. The spatial–temporal features of the inter-decadal changes in summer rainfall are also investigated. Consistent results are observed. Moreover, results indicate that, on the inter-decadal scale, the rainfall variability mode changes from typical tripole to dipole structure since the early 1990s.

Interdecadal variations of the western Pacific subtropical high and surface heat flux over East Asia and their relationship

The interdecadal variation of intensity of the western Pacific subtropical high (WPSH) during the period 1951–2001 is studied by using data from the National Climate Center (NCC), China Meteorological Administration. The characteristics of the circulations at 500 hPa and the surface heat flux over East Asia are also analyzed based on the NCEP/NCAR monthly reanalysis data. The results reveal that the WPSH and the circulations exhibit interdecadal variations around 1978, with enhancing intensities. The interseasonal persistence of the WPSH intensity alters correspondingly to some extent, which is more significant during 1978–2001 than during 1951–1978. The surface heat flux over East Asia also displays a remarkable interdecadal variation, which leads that of the WPSH intensity. The key variation areas of the surface sensible heat flux (SSHF) are mainly located over the eastern and western Tibetan Plateau around the late 1960s. However, the difference of the SSHF between the eastern and western Plateau exhibits a change in the mid 1970s, close to the time of the abrupt climate change of the WPSH intensity. The SSHF of the Plateau stably increases in the west and decreases in the east before the mid-late 1960s, while it stably increases in the east and decreases in the west after the mid-1970s. On the other hand, the key variation area of the surface latent heat flux (SLHF) is mainly situated over the West Pacific (WP), where the SLHF anomaly in spring changes from positive to negative in the south before 1978, but from negative to positive in the north after 1978; while in summer it turns from positive to negative all over the WP after 1978. The interdecadal variation of SLHF in both spring and summer corresponds well to the interdecadal variation of the WPSH intensity in the same season. The notable correlation between the WPSH intensity and SSHF (or SLHF) maintains without any change although each of these qnantities varies on the interdecadal scale.

A possible cause of decreasing summer rainfall in northeast Australia

AbstractThe NCEP/NCAR reanalysis and precipitation data from the Australian Bureau of Meteorology are used to analyse variability in rainfall during the austral summer (December–March, DJFM) in northeast Australia (NEA). NEA rainfall shows a marked decrease over the past 50 years, mainly in the austral summer. Our analysis reveals that the summer rainfall decrease in NEA is generally an interdecadal phenomenon. The declining trend has an imprint in the tropical Australian summer monsoon (TASM). Not only does TASM have a phase‐to‐phase influence on NEA summer rainfall at the interannual scale, it is also closely linked with interdecadal variation in NEA summer rainfall. Thus, the decrease in NEA at the interdecadal scale could be attributed to corresponding variation in TASM. Moreover, the coupled linkage between TASM and NEA summer rainfall appears to be largely independent of El Niño–Southern Oscillation. One possible reason for the interdecadal weakening trend in TASM is a sustained interdecadal warming trend in sea surface temperature (SST) over the Wharton Basin (100°–130°E, 20°–5°S). When the Wharton Basin is in a cold state, anomalous westerlies occur in the lower troposphere in the TASM region, and cyclonic circulation anomalies and rising flows occur in the low and middle troposphere over NEA, which are associated with a strong TASM situation, consequently favouring enhanced rainfall over NEA; the opposite occurs in the case of a warm Wharton Basin. SST over the Wharton Basin has shown a continuous warming trend over the past 60 years, contributing to the weakening of TASM and, consequently, a decrease in NEA summer rainfall. Copyright © 2011 Royal Meteorological Society

Changes in hot days and heat waves in China during 1961–2007

AbstractBased on the daily maximum temperature (DMT) records at 512 stations during 1961–2007, the geographical patterns and temporal variations of hot days (HDs) and heat waves (HWs, including those persisting for 3–5 days and longer) over mainland China were studied. The HD (and hence HW) was defined in two ways, one by an absolute criterion, DMT > 35 °C, as applied in the nationwide meteorological agencies and another in a relative sense, DMT > the 90th percentile threshold of a local daily temperature distribution around the day. Two centers of high frequencies (over 5 days per year) of the absolute HDs during June–September were found in the regions of Xinjiang and the mid‐lower reaches of the Yangtze River. The highest frequencies of the absolute HWs were about 1.5 times per year in the Xinjiang region and to the south of the mid‐lower reaches of the Yangtze River. The frequencies of the relative HWs were about 1–1.5 times per year in most of China. The HDs and HWs increased significantly during the studied period in most of China, especially over the southeastern coast and northern China (by over 4 days per decade for relative HDs and 0.4 times per decade for relative HWs), but decreased significantly at some stations in the lower reaches of the Yellow River. Over most of China except northwestern China, the frequency of HDs was high during the 1960s–1970s, low in the 1980s, and high afterwards, with strong interannual variations. A remarkable increasing trend of HDs occurred after the 1990s in all regions. The changes in HDs and HWs were closely related to those in rain days and atmospheric circulation patterns at the interannual and interdecadal scales. Copyright © 2009 Royal Meteorological Society

Quantitative assessment of impacts of regional climate and human activities on saline-alkali land changes: A case study of Qian’an County, Jilin Province

Interdecadal and interannual variations of saline-alkali land area in Qian’an County, Jilin Province, China were comprehensively analyzed in this paper by means of satellite remote sensing interpretation, field flux observations and regional climate diagnosis. The results show that on the interannual scale, the impact of climate factors accounts for 71.6% of the total variation of the saline-alkali land area, and that of human activities accounts for 28.4%. Therefore the impact of climate factors is obviously greater than that of human activities. On the interdecadal scale, the impact of climate factors on the increase of the saline-alkali land area accounts for 43.2%, and that of human activities accounts for 56.8%. The impact of human activities on the variation of saline-alkali land area is very clear on the interdecadal scale, and the negative impact of human activities on the environment should not be negligible. Besides, changes in the area of heavy saline-alkali land have some indication for development of saline-alkali land in Qian’an County.

The Role of Pacific Climate on Low-Frequency Hydroclimatic Variability and Predictability in Southern Alberta, Canada

Abstract Wavelet and rank correlation analysis were used to identify the links between primary Pacific climate variability modes and low-frequency hydroclimatic variability in the South Saskatchewan River basin (SSRB) of southern Alberta. The April–September average streamflow shows strong interdecadal oscillations with dominant scales of 19–22, 41–42, and 62 yr whereas statistically significant wavelet power in the interannual scale was organized on a background scale of approximately 20–25 yr. At interannual scales, strong coherency is observed between streamflow and the Niño-3 index prior to the 1940s, and in the 1950s, 1970s, and 1980s. However, a change in the phase difference from near 0° in the 1950s to near 180° in the 1980s indicates that the relationship between streamflow and the El Niño–Southern Oscillation (ENSO) is not consistent. Streamflow–Pacific–North America pattern (PNA) and streamflow–Pacific decadal oscillation (PDO) relationships at interannual scales also exhibit similar inconsistencies in phase difference. At interdecadal scales, PDO and streamflow exhibited consistently strong coherence with a stable phase difference of 180° for scales >20 yr. From the period of 1913–2001, the median partial correlation between streamflow and PDO|Niño-3 (read as PDO given Niño-3) was −0.36, whereas it was zero between streamflow and Niño-3|PDO, suggesting that PDO is the primary mode of importance in streamflow variability and predictability in the SSRB. Precipitation variability was also dominated by interdecadal oscillations; however, there is less spatial coherence for dominant scales. Correlations between the basin’s winter precipitation and climate indices are also weaker than with streamflow.

Recent developments in understanding sea level rise at the Adriatic coasts

Sea level observations from tide-gauge records located at the Adriatic coasts are analysed. The estimated sea level trends show variability in time and space. Spatial variability is assessed by estimating the differential trends by reference to Trieste. For many of the stations the differential trends become smaller than the corresponding error bars. This indicates that the land, atmospheric and oceanic contributors to sea level change are, at long scales, uniform in the basin.Observed trends in the longer records differ significantly for the periods before 1960 and after 1960. Atmospheric forcing has been a significant contribution in sea level variability for the period 1960 onwards. The atmospheric trends account for −0.8mm/year for the period 1960–2000. No significant atmospheric trends appear to be present at the period 1900–1960. Changes in the atmospheric forcing alone are not capable of explaining fully the difference in the sea level trends for the periods before and after 1960.Steric trends for the period 1960–2000 have also been identified. Their magnitude depends on the depth used for their estimation. Steric trends range between −0.4mm/year for the upper 100m to −2.4mm/year for the whole water column. The residual sea level after the removal of atmospheric and steric effects ranges between 2 and 3.4mm/year at various stations with an associated error bar of 1mm/year. This residual must be accounted for by land movements and incoming signals through the strait of Otranto.The coherence of high frequency sea level signals in the north part of the Adriatic Sea is also analysed for the period 2002–2005 using eight tide gauges. The first empirical orthogonal function contains 71% of the variability indicating that the known coherency at inter-annual and inter-decadal scales extends partly to the higher frequency too.

Coherence between lake ice cover, local climate and teleconnections (Lake Mendota, Wisconsin)

Summary Ice duration has shortened and the ice-off date has become earlier for Lake Mendota from 1905 to 2000 as air temperatures have warmed and snowfall has increased. In addition, the ice record has cyclic components at inter-annual and inter-decadal scales. We examined the frequency domain relations between ice, local climate and the teleconnections, Southern Ocean Oscillation (SOI), Pacific Decadal Oscillation (PDO), North Atlantic Oscillation (NAO), and Northern Pacific Index (NP), through a three-tiered analysis of coherence. The coherence results provide evidence of linear relations between the three levels at inter-annual and inter-decadal frequencies. Of the three local climate variables analyzed, namely temperature, snowfall and snow depth, temperature is the variable that most significantly affects ice duration and ice-off date, at both inter-annual and inter-decadal frequencies. The most significant effect of teleconnections on local climate are the effects of PDO on snowfall and snow depth, and SOI on temperature, at inter-annual frequencies, and the effect of NAO on snowfall at inter-decadal frequencies. The teleconnections that most significantly affect ice-cover duration and ice-off date, particularly at inter-decadal frequencies, are the PDO and the NAO. The influence of PDO on ice-cover appears to be transmitted through temperature, while the influence of the NAO appears to be transmitted through temperature and snowfall. A cascading set of links between teleconnections, local climate, and lake ice explain some, but not all, of the dynamics in these time series.

An assessment of the functional variability of selected coastal ecosystems in the context of local environmental changes

Abstract Baird, D. (2009) An assessment of the functional variability of selected coastal ecosystems in the context of local environmental changes. – ICES Journal of Marine Science, 66: 1520–1527. The functioning of coastal ecosystems is greatly dependent on a wide variety of external pulses (e.g. tides, freshwater influx, seasonal trends in temperature, nutrient input, etc.). Assessments of the effect of a selection of environmental characteristics driven by natural and/or anthropogenic forces on ecosystem function are given using selected ecosystem properties, such as total system throughput, system organization, productivity, recycling, and trophic efficiency, derived from ecological network analysis (ENA) of several coastal ecosystems on monthly, intra-seasonal, seasonal, and interdecadal scales. Each ecosystem was modelled depicting data of standing stocks, the flows between the constituent living and non-living components in the system, exports, and imports. Results from ENA revealed considerable differences of the same property (or properties) resulting from physical changes (e.g. temperature, salinity, oxygen, rate of freshwater inflow) over time. A small temperature increase in a Florida seagrass bed, for example, resulted in increases in system throughput, the P/B ratio, and in the rate of carbon recycling, but also in a significant decrease in system organization. The effect of seasonal increases in water temperature and of measured decrease/increase in river run-off to a few selected estuaries is discussed using ENA.

Sensitivity of marine systems to climate and fishing: Concepts, issues and management responses

Modern fisheries research and management must understand and take account of the interactions between climate and fishing, rather than try to disentangle their effects and address each separately. These interactions are significant drivers of change in exploited marine systems and have ramifications for ecosystems and those who depend on the services they provide. We discuss how fishing and climate forcing interact on individual fish, marine populations, marine communities, and ecosystems to bring these levels into states that are more sensitive to (i.e. more strongly related with) climate forcing. Fishing is unlikely to alter the sensitivities of individual finfish and invertebrates to climate forcing. It will remove individuals with specific characteristics from the gene pool, thereby affecting structure and function at higher levels of organisation. Fishing leads to a loss of older age classes, spatial contraction, loss of sub-units, and alteration of life history traits in populations, making them more sensitive to climate variability at interannual to interdecadal scales. Fishing reduces the mean size of individuals and mean trophic level of communities, decreasing their turnover time leading them to track environmental variability more closely. Marine ecosystems under intense exploitation evolve towards stronger bottom–up control and greater sensitivity to climate forcing. Because climate change occurs slowly, its effects are not likely to have immediate impacts on marine systems but will be manifest as the accumulation of the interactions between fishing and climate variability — unless threshold limits are exceeded. Marine resource managers need to develop approaches which maintain the resilience of individuals, populations, communities and ecosystems to the combined and interacting effects of climate and fishing. Overall, a less-heavily fished marine system, and one which shifts the focus from individual species to functional groups and fish communities, is likely to provide more stable catches with climate variability and change than would a heavily fished system.

A 694-year tree-ring based rainfall reconstruction from Himachal Pradesh, India

We developed ring-width chronologies of Cedrus deodara [(Roxb.) G. Don] and Pinus gerardiana (Wall. Ex. Lamb) from a homogeneous moisture stressed area in Kinnaur, Himachal Pradesh. Running correlation using a 50-year window with overlap of 25 years showed strong correlations between these species chronologies during the entire common period (ad 1310–2005). Response function analysis indicated that except for January–February, precipitation has a direct relationship with growth of these species. We therefore combined both the species chronologies to develop a statistically calibrated reconstruction of March–July precipitation that spans from ad 1310–2004, and explains 46% of the variance contained in the instrumental data from the calibration period 1951–1994. In the past 694 years of the reconstruction, the wettest period was in the twentieth century (1963–1992) and the driest in the eighteenth century (1773–1802). The relationships observed between reconstructed precipitation and Indian summer monsoon on interdecadal scale, SOI, PDO and NAO indicate the potential utility of such long-term reconstructions in understanding the large-scale climate variability. Multi-taper method (MTM) spectral analysis indicated significant (p < 0.05) spectral peaks at 2–4, 6, 8, 10, 30, 33, 37 and 40–42 years in the reconstructed precipitation data.

Influence of volcanic activity on climate change in the past several centuries: Assessments with a climate model of intermediate complexity

The climate model of intermediate complexity developed at the A.M. Obukhov Institute of Atmospheric Physics of the Russian Academy of Sciences (IAP RAS CM) is supplemented by a scheme which takes into account the volcanic forcing of climate. With this model, ensemble experiments have been conducted for the 1600s–1900s, in which, along with the volcanic forcing, the anthropogenic forcing due to greenhouse gases and sulfate aerosols and the natural forcing due to variations in solar irradiance were taken into account. The model realistically reproduces the annual mean response of surface air temperature and precipitation to major eruptions both globally and regionally. In particular, the decreases in the annual mean global temperature Tg in the IAP RAS CM after the largest eruptions in the latter half of the 20th century, the Mt. Agung (1963), El Chichon (1982), and Mt. Pinatubo (1991) volcanic eruptions, are 0.28, 0.27, and 0.46 K, respectively, in agreement with estimates from observational data. Moreover, in the IAP RAS CM, the volcanic eruptions result in a general precipitation decrease, especially over land in the middle and high latitudes of the Northern Hemisphere. The seasonal distribution of the response shows good agreement with observations for high-latitude eruptions and worse agreement for tropical and subtropical volcanoes. On interdecadal scales, volcanism leads to variations in Tg on the order of 0.1 K. In numerical experiments with anthropogenic and natural forcings, the model reproduces a general change in surface air temperature over the past several centuries. Taking into account the volcanic forcing, along with that due to variations in solar irradiance, the model has partly reproduced the nonmonotonic global warming for the 20th century.

Monsoon-ocean coupled modes in the South China Sea and their linkage with the eastern Indian Ocean-western Pacific warm pool

Monsoon-ocean coupled modes in the South China Sea (SCS) were investigated by a combined singular value decomposition (CSVD) analysis based on sea surface temperature (SST) and sea surface wind stress (SWS) fields from SODA (Simple Ocean Data Assimilation) data spanning the period of 1950–1999. The coupled fields achieved the maximum correlation when the SST lagged SWS by one month, indicating that the SCS coupled system mainly reflected the response of the SST to monsoon forcing. Three significant coupled modes were found in the SCS, accounting for more than 80% of the cumulative squared covariance fraction. The first three SST spatial patterns from CSVD were: (I) the monopole pattern along the isobaths in the SCS central basin; (II) the north-south dipole pattern; and (III) the west-east seesaw pattern. The expansion coefficient of the SST leading mode showed interdecadal and interannual variability and correlation with the Indo-Pacific warm pool (IPWP), suggesting that the SCS belongs to part of the IPWP at interannual and interdecadal time scales. The second mode had a lower correlation coefficient with the warm pool index because its main period was at intra-annual time scales instead of the interannual and interdecadal scales with the warm pools. The third mode had similar periods to those of the leading mode, but lagged the eastern Indian Ocean warm pool (EIWP) and western Pacific warm pool (WPWP) by five months and one year respectively, implying that the SCS response to the warm pool variation occurred from the western Pacific to the eastern Indian Ocean, which might have been related to the variation of Indonesian throughflow. All three modes in the SCS had more significant correlations with the EIWP, which means the SCS SST varied much more coherently with the EIWP than the WPWP, suggesting that the SCS belongs mostly to part of the EIWP. The expansion coefficients of the SCS SST modes all had negative correlations with the Nino3 index, which they lag by several months, indicating a remote response of SCS SST variability to the El Nino events.

Climatic Variability in the Meridional Mode of Global Atmospheric Circulation During Recent 60 Years

AbstractThe climatic variability in the meridional mode of global atmospheric circulation is investigated by using the monthly geopotential height fields at 1000, 500, and 100 hPa during 1948 and 2004. The data are taken from the NCEP/NCAR Reanalysis. The leading meridional mode shows opposite characteristics in its spatial and temporal distributions at the high and low latitudes at the three levels. The latitude differences are significantly enlarged in recent 60 years. An abrupt change occurred in the mid‐1970s, leading to the phases of the first mode reversed at the low and high latitudes in both hemispheres. The variability is generally larger in SH at 1000 and 500 hPa, but in NH at 100 hPa. In contrast, the second meridional mode shows different features in its spatial and temporal distributions. It mainly manifests as the AAO and AO at 1000 and 100 hPa. The two oscillations have a negative correlation at interannual and interdecadal scales, and show strong anti‐phase variations at the SH and NH high latitudes at 100 hPa level, suggesting that the mode could connect the SH and NH circulation at mid‐ and high latitudes and affect global climate change.

Sensitivity of Interannual and Interdecadal Precipitation Variability over China to Spatial Scale

AbstractWith the precipitation observation of 740 stations over China, the interannual and interdecadal precipitation variabilities over 6 climate subregions are calculated with respect to 5 resolutions separately. The analysis shows that the sensitivity of the interannual precipitation variability to spatial scales in all the subregions over China decreases gradually with the increasing spatial scales and there is a significant seasonal change, whereas the sensitivity of the interdecadal variability increases with the increasing spatial scales and there is no seasonal change. Because of the particularities of precipitation, there are some significant differences in the sensitivities of the interannual and interdecadal precipitation variability to spatial scales for different climate subregions over China. On the interannual and interdecadal scales, the highest sensitivity of the precipitation variability to spatial scales is in southwestern China. So it is the most difficult region to test the signals of the interannual and interdecadal precipitation variability there, whereas in southern China, there is a relatively high sensitivity on the interannual scale, and little sensitivity on the interdecadal scale. Nevertheless, the inhomogeneity of precipitation over southern China is most sensitive to spatial scales both on interannual and interdecadal timescales.