scholarly journals The ENSO teleconnections to the Indian summer monsoon climate through the Last Millennium as simulated by the PMIP3

2018 ◽  
Author(s):  
Charan Teja Tejavath ◽  
Karumuri Ashok ◽  
Supriyo Chakraborty ◽  
Rengaswamy Ramesh
Keyword(s):  
Summer Monsoon ◽  
Indian Summer Monsoon ◽  
Little Ice Age ◽  
Walker Circulation ◽  
Summer Monsoon Rainfall ◽  
Ice Age ◽  
Boreal Summer ◽  
Last Millennium ◽  
Enso Teleconnections ◽  
The Mean

Abstract. Using seven model simulations from the PMIP3, we study the mean summer (June–September) climate and its variability in India during the Last Millennium (LM; CE 850–1849) with emphasis on the Medieval Warm Period (MWP) and Little Ice Age (LIA), after validation of the simulated current day climate and trends. We find that the above (below) LM-mean summer global temperatures during the MWP (LIA) are associated with relatively higher (lower) number of concurrent El Niños as compared to La Niñas. The models simulate higher (lower) Indian summer monsoon rainfall (ISMR) during the MWP (LIA). This is notwithstanding a strong simulated negative correlation between the timeseries of NINO3.4 index and that of the area-averaged ISMR, Interestingly, the percentage of strong El Niños (La Niñas) causing negative (positive) ISMR anomalies is higher in the LIA (MWP), a non-linearity that apparently is important for causing higher ISMR in the MWP. Distribution of simulated boreal summer velocity potential at 850 hPa during MWP in models, in general, shows a zone of anomalous convergence in the central tropical Pacific flanked by two zones of divergence, suggesting a westward shift in the Walker circulation as compared to the simulations for LM as well as and a majority of historical simulations, and current day observed signal. The anomalous divergence centre in the west also extends into the equatorial eastern Indian Ocean, resulting in an anomalous convergence zone over India and therefore excess rainfall during the MWP as compared to the LM; the results are qualitative, given the inter-model spread.

scholarly journals The Indian summer monsoon climate during the Last Millennium, as simulated by the PMIP3

2017 ◽  
Author(s):  
Charan Teja Tejavath ◽  
Ashok Karumuri ◽  
Supriyo Chakraborty ◽  
Rengasamy Ramesh
Keyword(s):  
Summer Monsoon ◽  
Indian Summer Monsoon ◽  
Walker Circulation ◽  
Summer Monsoon Rainfall ◽  
Tropical Pacific ◽  
Ice Age ◽  
Boreal Summer ◽  
Last Millennium ◽  
Strong Negative Correlation ◽  
Summer Temperatures

Abstract. In this study, using the available model simulations from the PMIP3, we study the mean summer (June–September; JJAS) climate and its variability in India during the Last Millennium (CE 850–1849; LM) for which conventional observations are unavailable, with emphasis on the Medieval Warm Period (MWP; CE 1000–1199 as against the CE 950–AD1350 from the proxy-observations) and Little Ice Age (LIA; CE 1550–1749 as against the CE 1500–1850 proxy observations. Out of the eight available models, by validating the corresponding simulated global and Indian mean summer temperatures and mean Indian summer monsoon rainfall (ISMR), and their respective trends, from historical simulations (CMIP5) against the various observed/reanalysed datasets for the 1901–2005 period. From this exercise, we identify seven realistic models. The models simulate higher (lower) mean summer temperatures in India as well as globally during the MWP (LIA) as compared to the corresponding LM statistics, in conformation with several proxy studies. Our Analysis shows a strong negative correlation between the NINO3.4 index and the ISMR and a positive correlation between NINO3.4 and summer temperature over India during the LM, as is observed in the last one-and-half centuries. The magnitude of the simulated ISMR-NINO3.4 index correlations, as seen from the multi-model mean, is found to be higher for the MWP (−0.19; significant at 95 % confidence level) as compared to that for the LIA (−0.09; insignificant). Our analysis also shows that the above (below) LM-mean summer temperatures during the MWP (LIA) are associated with relatively more (less) number of concurrent El Niños as compared to the La Niñas. Distribution of boreal summer velocity potential at 850 hPa in the central tropical pacific and a zone of anomalous convergence in the central tropical pacific, flanked by two zones of divergence in the equatorial pacific, suggesting a westward shift in Walker circulation as compared to the current day signal. The anomalous divergence centre in the west also extends into the equatorial eastern Indian Ocean, which results in an anomalous convergence zone over India and therefore excess rainfall during the MWP as compared to the LM. The results are qualitative, given the inter-model spread.

Dependence of Indian summer monsoon rainfall forecast skill of CFSv2 on initial conditions and the role of bias in SST boundary forcing

2021 ◽  
Author(s):  
Stella Jes Varghese ◽  
Kavirajan Rajendran ◽  
Sajani Surendran ◽  
Arindam Chakraborty
Keyword(s):  
Summer Monsoon ◽  
Indian Summer Monsoon ◽  
Lead Time ◽  
Monsoon Rainfall ◽  
Indian Summer Monsoon Rainfall ◽  
Initial Conditions ◽  
Summer Monsoon Rainfall ◽  
Forecast Skill ◽  
Boreal Summer ◽  
Central Pacific

<p>Indian summer monsoon seasonal reforecasts by CFSv2, initiated from January (4-month lead time, L4) through May (0-month lead time, L0) initial conditions (ICs), are analysed to investigate causes for the highest Indian summer monsoon rainfall (ISMR) forecast skill of CFSv2 with February (3-month lead time, L3) ICs. Although theory suggests forecast skill should degrade with increase in lead-time, CFSv2 shows highest skill with L3, due to its forecasting of ISMR excess of 1983 which other ICs failed to forecast. In contrast to observation, in CFSv2, ISMR extremes are largely decided by sea surface temperature (SST) variation over central Pacific (NINO3.4) associated with El Niño-Southern Oscillation (ENSO), where ISMR excess (deficit) is associated with La Niña (El Niño) or cooling (warming) over NINO3.4. In 1983, CFSv2 with L3 ICs forecasted strong La Niña during summer, which resulted in 1983 ISMR excess. In contrast, in observation, near normal SSTs prevailed over NINO3.4 and ISMR excess was due to variation of convection over equatorial Indian Ocean, which CFSv2 fails to capture with all ICs. CFSv2 reforecasts with late-April/early-May ICs are found to have highest deterministic ISMR forecast skill, if 1983 is excluded and Indian monsoon seasonal biases are also reduced. During the transitional ENSO in Boreal summer of 1983, faster and intense cooling of NINO3.4 SSTs in L3, could be due to larger dynamical drift with longer lead time of forecasting, compared to L0. Boreal summer ENSO forecast skill is also found to be lowest for L3 which gradually decreases from June to September. Rainfall occurrence with strong cold bias over NINO3.4, is because of the existence of stronger ocean-atmosphere coupling in CFSv2, but with a shift of the SST-rainfall relationship pattern to slightly colder SSTs than the observed. Our analysis suggests the need for a systematic approach to minimize bias in SST boundary forcing in CFSv2, to achieve improved ISMR forecasts.</p>

A PMIP3 narrative of modulation of ENSO teleconnections to the Indian summer monsoon by background changes in the Last Millennium

2019 ◽  
Vol 53 (5-6) ◽  
pp. 3445-3461 ◽  
Author(s):  
Charan Teja Tejavath ◽  
Karumuri Ashok ◽  
Supriyo Chakraborty ◽  
Rengaswamy Ramesh
Keyword(s):  
Summer Monsoon ◽  
Indian Summer Monsoon ◽  
Last Millennium ◽  
Enso Teleconnections

Speleothem Evidence for Changes in Indian Summer Monsoon Precipitation over the Last ∼2300 Years

2000 ◽  
Vol 53 (2) ◽  
pp. 196-202 ◽  
Author(s):  
Rhawn F. Denniston ◽  
Luis A. González ◽  
Yemane Asmerom ◽  
Ram H. Sharma ◽  
Mark K. Reagan
Keyword(s):  
Summer Monsoon ◽  
Indian Summer Monsoon ◽  
Little Ice Age ◽  
Ice Age ◽  
Monsoon Precipitation ◽  
The Past ◽  
Central Nepal ◽  
Monsoon Variability ◽  
Cave Environment ◽  
Pokhara Valley

AbstractSpeleothems from a well-ventilated dolomitic cave in the Pokhara Valley, central Nepal, preserve a mineralogic record of Indian summer monsoon variability over the past 2300 yr. Annually deposited aragonite layers formed between 2300 and 1500 yr B.P., indicating reduced monsoon precipitation and increased cave aridity, whereas alternating calcite/aragonite laminae deposited after 1500 yr B.P. record elevated summer monsoon precipitation and increased cave humidity. Dense, optically clear calcite layers deposited from 450 ± 5 to 360 ± 20 yr B.P. (1550 to 1640 A.D.) indicate a less-evaporative cave environment and suggest moister and/or cooler conditions, possibly related to climatic change associated with the onset of the Little Ice Age.

scholarly journals The Indian Summer Monsoon in MetUM-GOML2.0: Effects of air-sea coupling and resolution

2018 ◽  
Author(s):  
Simon C. Peatman ◽  
Nicholas P. Klingaman
Keyword(s):  
Indian Ocean ◽  
Summer Monsoon ◽  
Indian Summer Monsoon ◽  
Seasonal Cycle ◽  
Global Ocean ◽  
Boreal Summer ◽  
Correction Technique ◽  
The Indian Ocean ◽  
The Mean ◽  
Mean State

Abstract. The fidelity of the simulated Indian Summer Monsoon is analysed in the UK Met Office Unified Model Global Ocean Mixed Layer configuration (MetUM-GOML2.0), in terms of its boreal summer mean state and propagation of the Boreal Summer IntraSeasonal Oscillation (BSISO). The model produces substantial biases in mean June--September precipitation, especially over India, in common with other MetUM configurations. Using a correction technique to constrain the mean seasonal cycle of ocean temperature and salinity, the effects of regional air-sea coupling and atmospheric horizontal resolution are investigated. Introducing coupling in the Indian Ocean degrades the atmospheric basic state, compared with prescribing the observed seasonal cycle of sea surface temperature (SST). This degradation of the mean state is attributable to small errors (±0.5 C) in mean SST. However, coupling slightly improves the simulation of northward BSISO propagation over the Indian Ocean, Bay of Bengal and India. Increasing resolution from 200 km to 90 km grid spacing (approximate value at the equator) improves the atmospheric mean state, but increasing resolution again to 40~km offers no substantial improvement. The improvement to intraseasonal propagation at finer resolution is similar to that due to coupling.

scholarly journals The Indian summer monsoon in MetUM-GOML2.0: effects of air–sea coupling and resolution

2018 ◽  
Vol 11 (11) ◽  
pp. 4693-4709 ◽  
Author(s):  
Simon C. Peatman ◽  
Nicholas P. Klingaman
Keyword(s):  
Indian Ocean ◽  
Summer Monsoon ◽  
Indian Summer Monsoon ◽  
Seasonal Cycle ◽  
Global Ocean ◽  
Boreal Summer ◽  
Correction Technique ◽  
The Indian Ocean ◽  
The Mean ◽  
Mean State

Abstract. The fidelity of the simulated Indian summer monsoon is analysed in the UK Met Office Unified Model Global Ocean Mixed Layer configuration (MetUM-GOML2.0) in terms of its boreal summer mean state and propagation of the boreal summer intraseasonal oscillation (BSISO). The model produces substantial biases in mean June–September precipitation, especially over India, in common with other MetUM configurations. Using a correction technique to constrain the mean seasonal cycle of ocean temperature and salinity, the effects of regional air–sea coupling and atmospheric horizontal resolution are investigated. Introducing coupling in the Indian Ocean degrades the atmospheric basic state compared with prescribing the observed seasonal cycle of sea surface temperature (SST). This degradation of the mean state is attributable to small errors (±0.5 ∘C) in mean SST. Coupling slightly improves some aspects of the simulation of northward BSISO propagation over the Indian Ocean, Bay of Bengal, and India, but degrades others. Increasing resolution from 200 to 90 km grid spacing (approximate value at the Equator) improves the atmospheric mean state, but increasing resolution again to 40 km offers no substantial improvement. The improvement to intraseasonal propagation at finer resolution is similar to that due to coupling.

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