scholarly journals Nonlinear forced change and nonergodicity: The case of ENSO-Indian monsoon and global precipitation teleconnections

2021 ◽  
Author(s):  
Gabor Drotos ◽  
Tamas Bodai ◽  
Kyung-Ja Ha ◽  
June-Yi Lee ◽  
Eui-Seok Chung
Keyword(s):  
Correlation Coefficient ◽  
Summer Monsoon ◽  
Indian Summer Monsoon ◽  
Southern Oscillation ◽  
Function Analysis ◽  
Forced Response ◽  
Spatiotemporal Variability ◽  
Historical Period ◽  
Max Planck ◽  
Enso Variability

<p>We study the forced response of the teleconnection between the El Niño–Southern Oscillation (ENSO) and the Indian summer monsoon (IM) in the Max Planck Institute Grand Ensemble, a set of Earth system ensemble simulations under historical and RCP forcing. The forced response of the teleconnection, or a characteristic of it, is defined as the time dependence of a correlation coefficient evaluated over the ensemble. We consider the temporal variability of spatial averages and that with respect to dominant spatial modes in the sense of Maximal Covariance Analysis, Canonical Correlation Analysis and Empirical Orthogonal Function analysis across the ensemble. A further representation of the teleconnection that we define here takes the point of view of the predictability of the complete spatiotemporal variability of the Indian summer monsoon. We find that the strengthening of the ENSO-IM teleconnection is robustly or consistently featured in view of various teleconnection representations, whether sea surface temperature (SST) or sea level pressure (SLP) is used to characterise ENSO, and both in the historical period and under the RCP8.5 forcing scenario. It is found to be associated dominantly with the principal mode of ENSO variability. Concerning representations that involve an autonomous characterisation of the Pacific, in terms of a linear regression model, the main contributor to the strengthening} is the regression coefficient, which can outcompete even a declining ENSO variability when it is represented by SLP. We also find that the forced change of the teleconnection is typically nonlinear by (1) formally rejecting the hypothesis that ergodicity holds, i.e., that expected values of temporal correlation coefficients with respect to the ensemble equal the ensemble-wise correlation coefficient itself, and also showing that (2) the trivial contributions of the forced changes in means and standard deviations are insignificant here. We also provide, in terms of the test statistics, global maps of the degree of nonlinearity/nonergodicity of the forced change of the teleconnection between local precipitation and ENSO.</p>

scholarly journals Nonlinear Forced Change and Nonergodicity: The Case of ENSO-Indian Monsoon and Global Precipitation Teleconnections

2021 ◽  
Vol 8 ◽  
Author(s):  
Tamás Bódai ◽  
Gábor Drótos ◽  
Kyung-Ja Ha ◽  
June-Yi Lee ◽  
Eui-Seok Chung
Keyword(s):  
Correlation Coefficient ◽  
Summer Monsoon ◽  
Indian Summer Monsoon ◽  
Southern Oscillation ◽  
Function Analysis ◽  
Forced Response ◽  
Spatiotemporal Variability ◽  
Historical Period ◽  
Max Planck ◽  
Enso Variability

We study the forced response of the teleconnection between the El Niño–Southern Oscillation (ENSO) and the Indian summer monsoon (IM) in the Max Planck Institute Grand Ensemble, a set of Earth system ensemble simulations under historical and Representative Concentration Pathway (RCP) forcing. The forced response of the teleconnection, or a characteristic of it, is defined as the time dependence of a correlation coefficient evaluated over the ensemble. We consider the temporal variability of spatial averages and that with respect to dominant spatial modes in the sense of Maximal Covariance Analysis, Canonical Correlation Analysis and Empirical Orthogonal Function analysis across the ensemble. A further representation of the teleconnection that we define here takes the point of view of the predictability of the spatiotemporal variability of the Indian summer monsoon. We find that the strengthening of the ENSO-IM teleconnection is robustly or consistently featured in view of various teleconnection representations, whether sea surface temperature (SST) or sea level pressure (SLP) is used to characterize ENSO, and both in the historical period and under the RCP8.5 forcing scenario. It is found to be associated dominantly with the principal mode of ENSO variability. Concerning representations that involve an autonomous characterisation of the Pacific, in terms of a linear regression model, the main contributor to the strengthening is the regression coefficient, which can outcompete even a declining ENSO variability when it is represented by SLP. We also find that the forced change of the teleconnection is typically nonlinear by 1) formally rejecting the hypothesis that ergodicity holds, i.e., that expected values of temporal correlation coefficients with respect to the ensemble equal the ensemble-wise correlation coefficient itself, and also showing that 2) the trivial contributions of the forced changes in means and standard deviations are insignificant here. We also provide, in terms of the test statistics, global maps of the degree of nonlinearity/nonergodicity of the forced change of the teleconnection between local precipitation and ENSO.

scholarly journals Impact of Madden-Julian oscillations on the Indian summer monsoon sub-divisional rainfalls

MAUSAM ◽  
2021 ◽  
Vol 59 (2) ◽  
pp. 195-210
Author(s):  
K. SEETHARAM
Keyword(s):  
Summer Monsoon ◽  
Indian Summer Monsoon ◽  
Seasonal Variations ◽  
Monsoon Rainfall ◽  
Indian Summer Monsoon Rainfall ◽  
Southern Oscillation ◽  
Low Frequency ◽  
Summer Monsoon Rainfall ◽  
Dominant Mode ◽  
Oscillation Phenomenon

Indian summer monsoon rainfall exhibits inter-seasonal variations in the time scales of 2-7 years which are linked to quasi-biennial oscillations and El nino-Southern Oscillation phenomenon and also intra-seasonal variations in the time-scale of 30-60 days which are linked to activity of MJO which emerged as a dominant mode of intra-seasonal oscillations of Indian summer monsoon rainfall in addition to the other modes of low frequency oscillations. In this scenario, the inter and intra seasonal variability of 29 meteorological sub-divisional rainfalls has been investigated by correlating the MJO indices at 10 different longitudes covering Indian, Pacific and Atlantic Oceans with cumulative sub-divisional summer monsoon rainfall (1979 – 2000). The results were discussed.

On the relationship between Indian Ocean Dipole, Indian summer monsoon and ENSO

2021 ◽  
Author(s):  
Annalisa Cherchi ◽  
Pascal Terray ◽  
Satyaban Bishoyi Ratna ◽  
Virna Meccia ◽  
Sooraj K.P.
Keyword(s):  
Indian Ocean ◽  
Summer Monsoon ◽  
Indian Summer Monsoon ◽  
Indian Ocean Dipole ◽  
Climate Models ◽  
Southern Oscillation ◽  
Global Climate ◽  
Global Climate Models ◽  
The Future ◽  
The Indian Ocean

<p>The Indian Ocean Dipole (IOD) is one of the dominant modes of variability of the tropical Indian Ocean and it has been suggested to have a crucial role in the teleconnection between the Indian summer monsoon and El Nino Southern Oscillation (ENSO). The main ideas at the base of the influence of the IOD on the ENSO-monsoon teleconnection include the possibility that it may strengthen summer rainfall over India, as well as the opposite, and also that it may produce a remote forcing on ENSO itself. The Indian Ocean has been experiencing a warming, larger than any other basins, since the 1950s. During these decades, the summer monsoon rainfall over India decreased and the frequency of Indian Ocean Dipole (IOD) events increased. In the future the IOD is projected to further increase in frequency and amplitude with mean conditions mimicking the characteristics of its positive phase. Still, state of the art global climate models have large biases in representing IOD and monsoon mean state and variability, with potential consequences for properties and related teleconnections projected in the future. This works collects a review study of the influence of the IOD on the ISM and its relationship with ENSO, as well as new results on IOD projections comparing CMIP5 and CMIP6 models.</p>

scholarly journals Decreasing Indian summer monsoon on the northern Indian sub-continent during the last 180 years: evidence from five tree-ring cellulose oxygen isotope chronologies

2018 ◽  
Vol 14 (5) ◽  
pp. 653-664 ◽  
Author(s):  
Chenxi Xu ◽  
Masaki Sano ◽  
Ashok Priyadarshan Dimri ◽  
Rengaswamy Ramesh ◽  
Takeshi Nakatsuka ◽  
...  
Keyword(s):  
High Resolution ◽  
Oxygen Isotope ◽  
Tree Ring ◽  
Summer Monsoon ◽  
Indian Summer Monsoon ◽  
Southern Oscillation ◽  
Oxygen Isotope Fractionation ◽  
Northern India ◽  
Tree Ring Cellulose

Abstract. We have constructed a regional tree-ring cellulose oxygen isotope (δ18O) record for the northern Indian sub-continent based on two new records from northern India and central Nepal and three published records from northwestern India, western Nepal and Bhutan. The record spans the common interval from 1743 to 2008 CE. Correlation analysis reveals that the record is significantly and negatively correlated with the three regional climatic indices: all India rainfall (AIR; r  =  −0.5, p  <  0.001, n  =  138), Indian monsoon index (IMI; r  =  −0.45, p  <  0.001, n  =  51) and the intensity of monsoonal circulation (r  =  −0.42, p  <  0.001, n  =  51). The close relationship between tree-ring cellulose δ18O and the Indian summer monsoon (ISM) can be explained by oxygen isotope fractionation mechanisms. Our results indicate that the regional tree-ring cellulose δ18O record is suitable for reconstructing high-resolution changes in the ISM. The record exhibits significant interannual and long-term variations. Interannual changes are closely related to the El Niño–Southern Oscillation (ENSO), which indicates that the ISM was affected by ENSO in the past. However, the ISM–ENSO relationship was not consistent over time, and it may be partly modulated by Indian Ocean sea surface temperature (SST). Long-term changes in the regional tree-ring δ18O record indicate a possible trend of weakened ISM intensity since 1820. Decreasing ISM activity is also observed in various high-resolution ISM records from southwest China and Southeast Asia, and may be the result of reduced land–ocean thermal contrasts since 1820 CE.

scholarly journals Regional and Local Impacts of the ENSO and IOD Events of 2015 and 2016 on the Indian Summer Monsoon—A Bhutan Case Study

Atmosphere ◽  
2021 ◽  
Vol 12 (8) ◽  
pp. 954
Author(s):  
Katherine Power ◽  
Josefine Axelsson ◽  
Norbu Wangdi ◽  
Qiong Zhang
Keyword(s):  
Indian Ocean ◽  
Summer Monsoon ◽  
Indian Summer Monsoon ◽  
El Niño ◽  
Late Onset ◽  
El Nino ◽  
Southern Oscillation ◽  
Regional Scale ◽  
Local Scale ◽  
The Indian Ocean

The Indian Summer Monsoon (ISM) plays a vital role in the livelihoods and economy of those living on the Indian subcontinent, including the small, mountainous country of Bhutan. The ISM fluctuates over varying temporal scales and its variability is related to many internal and external factors including the El Niño Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD). In 2015, a Super El Niño occurred in the tropical Pacific alongside a positive IOD in the Indian Ocean and was followed in 2016 by a simultaneous La Niña and negative IOD. These events had worldwide repercussions. However, it is unclear how the ISM was affected during this time, both at a regional scale over the whole ISM area and at a local scale over Bhutan. First, an evaluation of data products comparing ERA5 reanalysis, TRMM and GPM satellite, and GPCC precipitation products against weather station measurements from Bhutan, indicated that ERA5 reanalysis was suitable to investigate ISM change in these two years. The reanalysis datasets showed that there was disruption to the ISM during this period, with a late onset of the monsoon in 2015, a shifted monsoon flow in July 2015 and in August 2016, and a late withdrawal in 2016. However, this resulted in neither a monsoon surplus nor a deficit across both years but instead large spatial-temporal variability. It is possible to attribute some of the regional scale changes to the ENSO and IOD events, but the expected impact of a simultaneous ENSO and IOD events are not recognizable. It is likely that 2015/16 monsoon disruption was driven by a combination of factors alongside ENSO and the IOD, including varying boundary conditions, the Pacific Decadal Oscillation, the Atlantic Multi-decadal Oscillation, and more. At a local scale, the intricate topography and orographic processes ongoing within Bhutan further amplified or dampened the already altered ISM.

scholarly journals Influence of the Pacific–Japan Pattern on Indian Summer Monsoon Rainfall

2018 ◽  
Vol 31 (10) ◽  
pp. 3943-3958 ◽  
Author(s):  
G. Srinivas ◽  
Jasti S. Chowdary ◽  
Yu Kosaka ◽  
C. Gnanaseelan ◽  
Anant Parekh ◽  
...  
Keyword(s):  
Summer Monsoon ◽  
Indian Summer Monsoon ◽  
General Circulation ◽  
Rossby Waves ◽  
Function Analysis ◽  
Circulation Model ◽  
Easterly Wind ◽  
Low Level ◽  
The Pacific ◽  
The Impact

Abstract This study discusses the impact of the Pacific–Japan (PJ) pattern on Indian summer monsoon (ISM) rainfall and its possible physical linkages through coupled and uncoupled pathways. Empirical orthogonal function analysis of 850-hPa relative vorticity over the western North Pacific (WNP) is used to extract the PJ pattern as the leading mode of circulation variability. The partial correlation analysis of the leading principal component reveals that the positive PJ pattern, which features anticyclonic and cyclonic low-level circulation anomalies over the tropical WNP and around Japan respectively, enhances the rainfall over the southern and northern parts of India. The northwestward propagating Rossby waves, in response to intensified convection over the Maritime Continent reinforced by low-level convergence in the southern flank of westward extended tropical WNP anticyclone, increase rainfall over southern peninsular India. Meanwhile, the anomalous moisture transport from the warm Bay of Bengal due to anomalous southerlies at the western edge of the low-level anticyclone extending from the tropical WNP helps to enhance the rainfall over northern India. The atmospheric general circulation model forced with climatological sea surface temperature confirms this atmospheric pathway through the westward propagating Rossby waves. Furthermore, the north Indian Ocean (NIO) warming induced by easterly wind anomalies along the southern periphery of the tropical WNP–NIO anticyclone enhances local convection, which in turn feeds back to the WNP convection anomalies. This coupled nature via interbasin feedback between the PJ pattern and NIO is confirmed using coupled model sensitivity experiments. These results are important in identifying new sources of ISM variability/predictability on the interannual time scale.

scholarly journals How large does a large ensemble need to be?

2020 ◽  
Vol 11 (4) ◽  
pp. 885-901
Author(s):  
Sebastian Milinski ◽  
Nicola Maher ◽  
Dirk Olonscheck
Keyword(s):  
Southern Oscillation ◽  
Surface Air Temperature ◽  
Internal Variability ◽  
Forced Response ◽  
Ensemble Size ◽  
Max Planck ◽  
Large Ensemble ◽  
Acceptable Error ◽  
Near Surface ◽  
Temperature And Precipitation

Abstract. Initial-condition large ensembles with ensemble sizes ranging from 30 to 100 members have become a commonly used tool for quantifying the forced response and internal variability in various components of the climate system. However, there is no consensus on the ideal or even sufficient ensemble size for a large ensemble. Here, we introduce an objective method to estimate the required ensemble size that can be applied to any given application and demonstrate its use on the examples of global mean near-surface air temperature, local temperature and precipitation, and variability in the El Niño–Southern Oscillation (ENSO) region and central United States for the Max Planck Institute Grand Ensemble (MPI-GE). Estimating the required ensemble size is relevant not only for designing or choosing a large ensemble but also for designing targeted sensitivity experiments with a model. Where possible, we base our estimate of the required ensemble size on the pre-industrial control simulation, which is available for every model. We show that more ensemble members are needed to quantify variability than the forced response, with the largest ensemble sizes needed to detect changes in internal variability itself. Finally, we highlight that the required ensemble size depends on both the acceptable error to the user and the studied quantity.

scholarly journals An Asian Summer Monsoon-Related Relative Humidity Record from Tree-Ring δ18O in Gansu Province, North China

Atmosphere ◽  
2020 ◽  
Vol 11 (9) ◽  
pp. 984
Author(s):  
Yan Wang ◽  
Yu Liu ◽  
Qiang Li ◽  
Huiming Song ◽  
Changfeng Sun ◽  
...  
Keyword(s):  
Relative Humidity ◽  
Tree Ring ◽  
Summer Monsoon ◽  
North China ◽  
Southern Oscillation ◽  
Asian Summer Monsoon ◽  
Function Analysis ◽  
Gansu Province ◽  
Pinus Tabulaeformis ◽  
Asian Summer

The monsoon fringe region in North China (NC) is also an ecologically fragile zone. Improving our comprehension of the paleoclimate variations and their driving mechanisms in this region has great significance for environmental protection and agricultural economic development. In order to provide more reliable data for future climate forecasting and reduce the effects of climatic disasters in NC, we established a 328-year stable oxygen isotope (δ18O) chronology based on four Pinus tabulaeformis Carr. from Mt. Hasi, Gansu Province, and found that the tree-ring δ18O inherited the signals of summer (July–August) monsoonal precipitation δ18O (δ18OP). Correlation function analysis indicated that the tree-ring δ18O series responded significantly to the observed local relative humidity from July to August (RHJA) with r = −0.65 (n = 55, p < 0.001). Based on the clear physiological mechanism, we reconstructed the RHJA variations from 1685 to 2012 using a transfer function. Our reconstruction was very stable and had strong spatial representativeness, it was significantly positively correlated with Asian summer monsoon (ASM) indices, indicating that our reconstruction reflected the variations of ASM to a large extent. The RHJA series successfully captured the weakening of the ASM since the 1930s. There was a close connection between the reconstructed sequence and the East Pacific sea surface temperature (SST). Further analyses revealed that El Niño–Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO) may play important roles in the summer monsoon precipitation in NC.

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