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 Theoretical aspects of the onset of Indian summer monsoon from perturbed orography simulations in a GCM

2006 ◽  
Vol 24 (8) ◽  
pp. 2075-2089 ◽  
Author(s):  
A. Chakraborty ◽  
R. S. Nanjundiah ◽  
J. Srinivasan
Keyword(s):  
Summer Monsoon ◽  
Indian Summer Monsoon ◽  
General Circulation ◽  
Large Scale ◽  
Vertical Motion ◽  
Circulation Model ◽  
Threshold Value ◽  
The Earth ◽  
Static Energy ◽  
The Impact

Abstract. A theory is proposed to determine the onset of the Indian Summer Monsoon (ISM) in an Atmospheric General Circulation Model (AGCM). The onset of ISM is delayed substantially in the absence of global orography. The impact of orography over different parts of the Earth on the onset of ISM has also been investigated using five additional perturbed simulations. The large difference in the date of onset of ISM in these simulations has been explained by a new theory based on the Surface Moist Static Energy (SMSE) and vertical velocity at the mid-troposphere. It is found that onset occurs only after SMSE crosses a threshold value and the large-scale vertical motion in the middle troposphere becomes upward. This study shows that both dynamics and thermodynamics play profound roles in the onset of the monsoon.

scholarly journals Role of Indian and Pacific SST in Indian Summer Monsoon Intraseasonal Variability

2011 ◽  
Vol 24 (12) ◽  
pp. 2915-2930 ◽  
Author(s):  
Deepthi Achuthavarier ◽  
V. Krishnamurthy
Keyword(s):  
Indian Ocean ◽  
Summer Monsoon ◽  
Indian Summer Monsoon ◽  
General Circulation ◽  
Singular Spectrum Analysis ◽  
Intraseasonal Variability ◽  
Circulation Model ◽  
The Pacific ◽  
The Indian Ocean

Abstract Three regionally coupled experiments are conducted to examine the role of Indian and Pacific sea surface temperature (SST) in Indian summer monsoon intraseasonal variability using the National Centers for Environmental Prediction’s Climate Forecast System, a coupled general circulation model. Regional coupling is employed by prescribing daily mean or climatological SST in either the Indian or the Pacific basin while allowing full coupling elsewhere. The results are compared with a fully coupled control simulation. The intraseasonal modes are isolated by applying multichannel singular spectrum analysis on the daily precipitation anomalies. It is found that the amplitude of the northeastward-propagating mode is weaker when the air–sea interaction is suppressed in the Indian Ocean. The intraseasonal mode is not resolved clearly when the Indian Ocean SST is reduced to daily climatology. Intraseasonal composites of low-level zonal wind, latent heat flux, downward shortwave radiation, and SST provide a picture consistent with the proposed mechanisms of air–sea interaction for the northward propagation. The Pacific SST variability does not seem to be critical for the existence of this mode. The northwestward-propagating mode is obtained in the cases where the Indian Ocean was prescribed by daily mean or daily climatological SST. Intraseasonal SST composites corresponding to this mode are weak.

scholarly journals Meridionally Extending Anomalous Wave Train over Asia During Breaks in the Indian Summer Monsoon

2019 ◽  
Vol 3 (3) ◽  
pp. 353-366 ◽  
Author(s):  
Uppara Umakanth ◽  
Ramesh K. Vellore ◽  
R. Krishnan ◽  
Ayantika Dey Choudhury ◽  
Jagat S. H. Bisht ◽  
...  
Keyword(s):  
Summer Monsoon ◽  
Indian Summer Monsoon ◽  
General Circulation ◽  
Wave Train ◽  
Eastern China ◽  
Circulation Model ◽  
Cyclonic Circulation ◽  
The Arctic ◽  
Indian Landmass ◽  
Central Eastern

Abstract Anomalous interactions between the Indian summer monsoon (ISM) circulation and subtropical westerlies are known to trigger breaks in the ISM on subseasonal time-scales, characterised by a pattern of suppressed rainfall over central-north India, and enhanced rainfall over the foothills of the central–eastern Himalayas (CEH). An intriguing feature during ISM breaks is the formation of a mid-tropospheric cyclonic circulation anomaly extending over the subtropical and mid-latitude areas of the Asian continent. This study investigates the mechanism of the aforesaid Asian continental mid-tropospheric cyclonic circulation (ACMCC) anomaly using observations and simplified model experiments. The results of our study indicate that the ACMCC during ISM breaks is part of a larger meridional wave train comprising of alternating anticyclonic and cyclonic anomalies that extend poleward from the monsoon region to the Arctic. A lead–lag analysis of mid-tropospheric circulation anomalies suggests that the meridional wave-train generation is linked to latent heating (LH) anomalies over the CEH foothills, Indo-China, and the Indian landmass during ISM breaks. By conducting sensitivity experiments using a simplified global atmospheric general circulation model forced with satellite-derived three-dimensional LH, it is demonstrated that the combined effects of the enhanced LH over the CEH foothills and Indo-China and decreased LH over the Indian landmass during ISM breaks are pivotal for generating the poleward extending meridional wave train and the ACMCC anomaly. At the same time, the spatial extent of the mid-latitude cyclonic anomaly over Far-East Asia is also influenced by the anomalous LH over central–eastern China. While the present findings provide interesting insights into the role of LH anomalies during ISM breaks on the poleward extending meridional wave train, the ACMCC anomaly is found to have important ramifications on the daily rainfall extremes over the Indo-China region. It is revealed from the present analysis that the frequency of extreme rainfall occurrences over Indo-China shows a twofold increase during ISM break periods as compared to active ISM conditions.

Tropical Connections to Climatic Change in the Extratropical Southern Hemisphere: The Role of Atlantic SST Trends

2014 ◽  
Vol 27 (13) ◽  
pp. 4923-4936 ◽  
Author(s):  
Graham R. Simpkins ◽  
Shayne McGregor ◽  
Andréa S. Taschetto ◽  
Laura M. Ciasto ◽  
Matthew H. England
Keyword(s):  
Climatic Change ◽  
Atmospheric Circulation ◽  
Southern Hemisphere ◽  
Geopotential Height ◽  
General Circulation ◽  
Rossby Waves ◽  
Circulation Model ◽  
Hadley Cell ◽  
Austral Spring ◽  
The Impact

The austral spring relationships between sea surface temperature (SST) trends and the Southern Hemisphere (SH) extratropical atmospheric circulation are investigated using an atmospheric general circulation model (AGCM). A suite of simulations are analyzed wherein the AGCM is forced by underlying SST conditions in which recent trends are constrained to individual ocean basins (Pacific, Indian, and Atlantic), allowing the impact of each region to be assessed in isolation. When forced with observed global SST, the model broadly replicates the spatial pattern of extratropical SH geopotential height trends seen in reanalyses. However, when forcing by each ocean basin separately, similar structures arise only when Atlantic SST trends are included. It is further shown that teleconnections from the Atlantic are associated with perturbations to the zonal Walker circulation and the corresponding intensification of the local Hadley cell, the impact of which results in the development of atmospheric Rossby waves. Thus, increased Rossby waves, forced by positive Atlantic SST trends, may have played a role in driving geopotential height trends in the SH extratropics. Furthermore, these atmospheric circulation changes promote warming throughout the Antarctic Peninsula and much of West Antarctica, with a pattern that closely matches recent observational records. This suggests that Atlantic SST trends, via a teleconnection to the SH extratropics, may have contributed to springtime climatic change in the SH extratropics over the past three decades.

scholarly journals The Role of Tropical Interbasin SST Gradients in Forcing Walker Circulation Trends

2017 ◽  
Vol 30 (2) ◽  
pp. 499-508 ◽  
Author(s):  
Lei Zhang ◽  
Kristopher B. Karnauskas
Keyword(s):  
General Circulation ◽  
Circulation Model ◽  
Walker Circulation ◽  
Equatorial Pacific ◽  
Trade Winds ◽  
Low Level ◽  
The Pacific ◽  
Indian Ocean Warming ◽  
Tropical Sea ◽  
Sst Gradient

The effects of externally forced tropical sea surface temperature (SST) anomalies on long-term Walker circulation changes are investigated through numerical atmospheric general circulation model (AGCM) experiments. In response to the observed tropics-wide SST trend, which exhibits a prominent interbasin warming contrast (IBWC) with smaller warming in the Pacific than the Indian and Atlantic Oceans that includes a weak La Niña–like pattern in the equatorial Pacific, pronounced low-level easterly anomalies emerge over the equatorial Pacific. Through sensitivity experiments, the intensification of the Pacific trade winds (PTWs) is attributable to the IBWC, whereas the slightly enhanced zonal SST gradient within the equatorial Pacific plays a small role relative to the observed IBWC. It is further demonstrated that the greater Indian Ocean warming forces low-level easterly anomalies over the entire equatorial Pacific, while the greater tropical Atlantic warming-driven enhancement of PTWs is located over the central equatorial Pacific. In contrast to observations, a negligible IBWC emerges in the tropical SST trends of CMIP5 historical simulations due to a strong El Niño–like warming in the tropical Pacific. Lacking the observed IBWC (and the observed enhancement of the zonal SST gradient within the equatorial Pacific), the PTWs in the CMIP5 ensemble can only weaken.

scholarly journals On the bias correction of general circulation model output for Indian summer monsoon

2012 ◽  
Vol 20 (3) ◽  
pp. 349-356 ◽  
Author(s):  
Nachiketa Acharya ◽  
Surajit Chattopadhyay ◽  
U. C. Mohanty ◽  
S. K. Dash ◽  
L. N. Sahoo
Keyword(s):  
General Circulation Model ◽  
Summer Monsoon ◽  
Indian Summer Monsoon ◽  
Bias Correction ◽  
General Circulation ◽  
Circulation Model ◽  
Model Output ◽  
General Circulation Model Output

scholarly journals Impact of solar variability on the frequency variability of the Indian summer monsoon

MAUSAM ◽  
2021 ◽  
Vol 52 (1) ◽  
pp. 67-82
Author(s):  
J. R. KULKARNI ◽  
M. MUJUMDAR ◽  
S. P. GHARGE ◽  
V. SATYAN ◽  
G. B. PANT
Keyword(s):  
Time Series ◽  
Summer Monsoon ◽  
Solar Irradiance ◽  
General Circulation ◽  
Large Scale ◽  
Monsoon Season ◽  
Circulation Model ◽  
Solar Constant ◽  
Good Correspondence ◽  
The Impact

Earlier investigations into the epochal behavior of fluctuations in All India Summer Monsoon Rainfall (AISMR) have indicated the existence of a Low Frequency Mode (LFM) in the 60-70 years range. One of the probable sources of this variability may be due to changes in solar irradiance. To investigate this, time series of 128-year solar irradiance data from 1871-1998 has been examined. The Wavelet Transform (WT) method is applied to extract the LFM from these time series, which show a very good correspondence. A case study has been carried out to test the sensitivity of AISMR to solar irradiance. The General Circulation Model (GCM) of the Center of Ocean-Land-Atmosphere (COLA) has been integrated in the control run (using the climatological value of solar constant i.e., 1365 Wm-2) and in the enhanced solar constant condition (enhanced by 10 Wm-2) for summer monsoon season of 1986. The study shows that the large scale atmospheric circulation over the Indian region, in the enhanced solar constant scenario is favorable to good monsoon activity. A conceptual model for the impact of solar irradiance on the AISMR at LFM is also suggested.

scholarly journals Atmospheric Blocking: The Impact of Topography in an Idealized General Circulation Model

2020 ◽  
Author(s):  
Veeshan Narinesingh ◽  
James F. Booth ◽  
Spencer K. Clark ◽  
Yi Ming
Keyword(s):  
High Pressure ◽  
General Circulation ◽  
Storm Track ◽  
Circulation Model ◽  
Wave Activity ◽  
Stationary Waves ◽  
Atmospheric Blocking ◽  
The Pacific ◽  
The Impact ◽  
Wave Activity Flux

Abstract. Atmospheric blocking can have important impacts on weather hazards, but the fundamental dynamics of blocking are not yet fully understood. As such, this work investigates the influence of topography on atmospheric blocking in terms of dynamics, spatial frequency, duration and displacement. Using an idealized GCM, an aquaplanet integration, and integrations with topography are analyzed. Block-centered composites show midlatitude aquaplanet blocks exhibit similar wave activity flux behavior to those observed in reality, whereas high-latitude blocks do not. The addition of topography significantly increases blocking and determines distinct regions where blocks are most likely to occur. These regions are found near high-pressure anomalies in the stationary waves and near storm track exit regions. Focusing on block duration, blocks originating near topography are found to last longer than those that are formed without or far from topography but have qualitatively similar evolutions in terms of nearby geopotential height anomalies and wave activity fluxes in composites. Integrations with two mountains have greater amounts of blocking compared to the single mountain case, however, the longitudinal spacing between the mountains is important for how much blocking occurs. Comparison between integrations with longitudinally long and short ocean basins show that more blocking occurs when storm track exits spatially overlap with high-pressure maxima in stationary waves. These results have real-world implications, as they help explain the differences in blocking between the Northern and Southern Hemisphere, and the differences between the Pacific and Atlantic regions in the Northern Hemisphere.

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