scholarly journals Large scale aspects of the monsoon-2011 Relevant to the objectives of the CTCZ

MAUSAM ◽  
2021 ◽  
Vol 64 (4) ◽  
pp. 687-698
Author(s):  
DR SIKKA ◽  
CS TOMAR ◽  
SI LASKAR ◽  
SUMAN GOYAL ◽  
AJIT TYAGI
Keyword(s):  
Large Scale ◽  
Weather Prediction ◽  
Lower Troposphere ◽  
La Niña ◽  
Seasonal Fluctuations ◽  
Gangetic Plain ◽  
Ocean Science ◽  
La Nina ◽  
Air Stream ◽  
The Pacific

Hkkjr esa xzh"edkyhu ekulwu ds nkSjku flukWfIVd vkSj mi&ekSleh mrkj p<+koksa dks le>us ds fy, o"kZ 2011 esa egk}hih; m".kdfVca/kh; vfHklj.k {ks= ¼lh-Vh-lh-tsM-½ ds uke ls Hkkjrh; ok;qeaMyh;&leqnzh foKku leqnk; us ,d QhYM dk;Zdze vk;ksftr fd;kA bl dk;Zdze dk ,d mís'; ekulwu ds flukWfIVd vkSj varjk&ekSleh mrkj&p<+koksa ls lacaf/kr c`greku ifjlapj.k ds dzfed fodkl ds ckjs esa tkudkjh izkIr djuk Hkh jgk gSA bl 'kks/k i= esa ekulwu 2011 ds le; cM+s iSekus ij gq, mrkj&Pk<+koksa ds ckjs esa Hkh crk;k x;k gSA o"kZ 2011 esa ekuwlu esa ekSle dh yxHkx lkekU; o"kkZ gqbZ rFkkfi mi&ekSleh eku ij twu ekg esa vPNh o"kkZ gqbZ] rRi'pkr tqykbZ ekg esa de o"kkZ gqbZ vksj fQj vxLr ekg ds vkjaHk ls ysdj flracj ekg ds var rd fQj ls vPNh o"kkZ gqbZA ekSle ds iwokZ)Z esa djhc&djhc U;wVªy yk&fuuk fLFkfr;k¡ cuhA rFkkfi vxLr ekg ls ysdj flracj ekg ds var rd Hkwe/;js[kh; iwohZ iz'kkar egklkxj esa leqnz lrg rkieku ¼,l-,l-Vh-½ lkekU; ls de ¼yk&fuuk fLFkfr;k¡½ esa ifjofrZr gks x,A gkykafd xaxk ds eSnkuh Hkkxksa esa fuEu {kksHkeaMy ij leqnz dh rjQ ls vkus okyh ok;q dk izokg cuk] ij iwjh _rq esa ok;q foy; yksM lkekU; ls cgqr de cus jgsA bl 'kks/k i= esa flukWfIVd ds fofHkUu igyq] iz'kkar egklkxj esa ,l-,l-Vh ds lqnwj izHkko ls lacaf/kr ekulwu ds miekSleh mrkj&p<+koksa rFkk Hkkjrh; leqnzh f}/zkqo ¼vkbZ-vks-Mh-½ ds LFkkuh; izHkko ij fopkj&foe'kZ fd;k x;kA blds lkFk&lkFk izpkyukRed lkaf[;dh; ekSle izkxqfDr ¼,u-MCY;w-ih-½ fun'kksZa] ;wjksih; e/; vof/k ekSle iwokZuqeku dsUnz ¼bZ-lh-,e-MCY;w-,Q-½] HkweaMyh; iwokZuqeku iz.kkyh ¼th-,Q-,l-½ vkSj ekSle vuqla/kku vkSj iwokZuqeku ¼MCY;w-vkj-,Q-½ ds fu"iknu ij Hkh fopkj&foe'kZ fd;k x;kA lh-Vh-lh-tsM- vkadM+ksa dk mi;ksx djrs gq, ekulwu 2011 ds fu"iknu ds vk/kj ij vkxs fd, tkus okys vuqla/kku ds dbZ {ks=ksa ds fo"k; esa Hkh lq>ko j[ks x,A  Indian atmosphere-ocean science community organised a field programme known as Continental Tropical Convergence Zone (CTCZ) during 2011 to understand the synoptic and sub-seasonal fluctuations of summer monsoon over India. One of the objectives of the programme was to understand the evolution of the large scale circulation in relation to synoptic & intra-seasonal fluctuations of the monsoon. The paper addresses the large scale fluctuations of Monsoon-2011. The Monsoon-2011 performed very close to the normal rainfall of the season. However, on the sub-seasonal scale its performance was good during June, became deficient during July and it recovered from the beginning of August to the end of September. The early part of the season was accompanied by near neutral La-Nina conditions. However, sea surface temperatures (SSTs) in the Equatorial Eastern Pacific Ocean shifted to below normal (La-Nina conditions) from August to the end of September. As the Gangetic Plain was swept by marine origin air stream in the lower troposphere, the aerosol load remained much below the normal during the entire season. The paper discusses different aspect of synoptic, sub-seasonal fluctuations of monsoon in relation to remote forcing of the SSTs in the Pacific and the local forcing of the Indian Ocean Dipole (IOD). Also the performance of the operational numerical weather prediction (NWP) models:  European Centre for Medium-Range Weather Forecasts (ECMWF), Global Forecast System (GFS) and Weather Research and Forecasting (WRF) is discussed. Several areas of further research using CTCZ data are also suggested based on the performance of the Monsoon-2011.

scholarly journals Simulation of ENSO teleconnections to precipitation extremes over the US in the high resolution version of E3SM

2021 ◽  
pp. 1-62
Author(s):  
Qi Tang ◽  
Noel D. Keen ◽  
Jean-Christophe Golaz ◽  
Luke P. van Roekel
Keyword(s):  
El Niño ◽  
Large Scale ◽  
El Nino ◽  
Storm Track ◽  
La Niña ◽  
Model Bias ◽  
Enso Teleconnections ◽  
La Nina ◽  
The Pacific ◽  
Storm Track Activity

Abstract We evaluate the simulated teleconnection of El Niño Southern Oscillation (ENSO) to winter season precipitation extremes over the United States in a long (98 years) 1950-control high resolution version (HR, 25 km nominal atmosphere model horizontal resolution) of US Department of Energy’s (DOE) Energy Exascale Earth System Model version 1 (E3SMv1). Model bias and spatial pattern of ENSO teleconnections to mean and extreme precipitation in HR overall are similar to the low-resolution model’s (LR, 110 km) historical simulation (4-member ensemble, 1925-1959). However, over the Southeast US (SE-US), HR produces stronger El Niño associated extremes, reducing upon LR’s model bias. Both LR and HR produce weaker than observed increase in storm track activity during El Niño events there. But, HR improves the ENSO associated variability of moisture transport over SE-US. During El Niño, stronger vertical velocities in HR produce stronger large-scale precipitation causing larger latent heating of the troposphere that pulls in more moisture from the Gulf of Mexico into the SE-US. This positive feedback also contributes to the stronger mean and extreme precipitation response in HR. Over the Pacific Northwest, LR’s bias of stronger than observed La Niña associated extremes is amplified in HR. Both models simulate stronger than observed moisture transport from the Pacific Ocean into the region during La Niña years. The amplified HR bias there is due to stronger orographically driven vertical updrafts that create stronger large scale precipitation, despite weaker La Niña induced storm track activity.

scholarly journals Atmospheric Conditions Associated with Labrador Sea Deep Convection: New Insights from a Case Study of the 2006/07 and 2007/08 Winters

2016 ◽  
Vol 29 (14) ◽  
pp. 5281-5297 ◽  
Author(s):  
Who M. Kim ◽  
Stephen Yeager ◽  
Ping Chang ◽  
Gokhan Danabasoglu
Keyword(s):  
North America ◽  
North Atlantic ◽  
Large Scale ◽  
Initial Conditions ◽  
Deep Convection ◽  
La Niña ◽  
Labrador Sea ◽  
Atmospheric Conditions ◽  
Circulation Anomaly ◽  
La Nina

Abstract Deep convection in the Labrador Sea (LS) resumed in the winter of 2007/08 under a moderately positive North Atlantic Oscillation (NAO) state. This is in sharp contrast with the previous winter with weak convection, despite a similar positive NAO state. This disparity is explored here by analyzing reanalysis data and forced-ocean simulations. It is found that the difference in deep convection is primarily due to differences in large-scale atmospheric conditions that are not accounted for by the conventional NAO definition. Specifically, the 2007/08 winter was characterized by an atmospheric circulation anomaly centered in the western North Atlantic, rather than the eastern North Atlantic that the conventional NAO emphasizes. This anomalous circulation was also accompanied by anomalously cold conditions over northern North America. The controlling influence of these atmospheric conditions on LS deep convection in the 2008 winter is confirmed by sensitivity experiments where surface forcing and/or initial conditions are modified. An extended analysis for the 1949–2009 period shows that about half of the winters with strong heat losses in the LS are associated with such a west-centered circulation anomaly and cold conditions over northern North America. These are found to be accompanied by La Niña–like conditions in the tropical Pacific, suggesting that the atmospheric response to La Niña may have a strong influence on LS deep convection.

scholarly journals Role of the Indo-Pacific Interbasin Coupling in Predicting Asymmetric ENSO Transition and Duration

2012 ◽  
Vol 25 (9) ◽  
pp. 3321-3335 ◽  
Author(s):  
Masamichi Ohba ◽  
Masahiro Watanabe
Keyword(s):  
El Niño ◽  
General Circulation ◽  
El Nino ◽  
Southern Oscillation ◽  
La Niña ◽  
La Nina ◽  
The Pacific ◽  
Enso Asymmetry ◽  
Sst Anomalies

Warm and cold phases of El Niño–Southern Oscillation (ENSO) exhibit a significant asymmetry in their transition/duration such that El Niño tends to shift rapidly to La Niña after the mature phase, whereas La Niña tends to persist for up to 2 yr. The possible role of sea surface temperature (SST) anomalies in the Indian Ocean (IO) in this ENSO asymmetry is investigated using a coupled general circulation model (CGCM). Decoupled-IO experiments are conducted to assess asymmetric IO feedbacks to the ongoing ENSO evolution in the Pacific. Identical-twin forecast experiments show that a coupling of the IO extends the skillful prediction of the ENSO warm phase by about one year, which was about 8 months in the absence of the IO coupling, in which a significant drop of the prediction skill around the boreal spring (known as the spring prediction barrier) is found. The effect of IO coupling on the predictability of the Pacific SST is significantly weaker in the decay phase of La Niña. Warm IO SST anomalies associated with El Niño enhance surface easterlies over the equatorial western Pacific and hence facilitate the El Niño decay. However, this mechanism cannot be applied to cold IO SST anomalies during La Niña. The result of these CGCM experiments estimates that approximately one-half of the ENSO asymmetry arises from the phase-dependent nature of the Indo-Pacific interbasin coupling.

scholarly journals Tropical Cyclone Activity in the Fiji Region: Spatial Patterns and Relationship to Large-Scale Circulation

2009 ◽  
Vol 22 (14) ◽  
pp. 3877-3893 ◽  
Author(s):  
Savin S. Chand ◽  
Kevin J. E. Walsh
Keyword(s):  
Tropical Cyclone ◽  
El Niño ◽  
Large Scale ◽  
El Nino ◽  
Southern Oscillation ◽  
Vertical Wind Shear ◽  
Relative Vorticity ◽  
La Niña ◽  
Factors Affecting ◽  
La Nina

Abstract This study examines the variations in tropical cyclone (TC) genesis positions and their subsequent tracks for different phases of the El Niño–Southern Oscillation (ENSO) phenomenon in the Fiji, Samoa, and Tonga region (FST region) using Joint Typhoon Warning Center best-track data. Over the 36-yr period from 1970/71 to 2005/06, 122 cyclones are observed in the FST region. A large spread in the genesis positions is noted. During El Niño years, genesis is enhanced east of the date line, extending from north of Fiji to over Samoa, with the highest density centered around 10°S, 180°. During neutral years, maximum genesis occurs immediately north of Fiji with enhanced genesis south of Samoa. In La Niña years, there are fewer cyclones forming in the region than during El Niño and neutral years. During La Niña years, the genesis positions are displaced poleward of 12°S, with maximum density centered around 15°S, 170°E and south of Fiji. The cyclone tracks over the FST region are also investigated using cluster analysis. Tracks during the period 1970/71–2005/06 are conveniently described using three separate clusters, with distinct characteristics associated with different ENSO phases. Finally, the role of large-scale environmental factors affecting interannual variability of TC genesis positions and their subsequent tracks in the FST region are investigated. Favorable genesis positions are observed where large-scale environments have the following seasonal average thresholds: (i) 850-hPa cyclonic relative vorticity between −16 and −4 (×10−6 s−1), (ii) 200-hPa divergence between 2 and 8 (×10−6 s−1), and (iii) environmental vertical wind shear between 0 and 8 m s−1. The subsequent TC tracks are observed to be steered by mean 700–500-hPa winds.

scholarly journals Influence of ENSO on the Diurnal Cycle of Rainfall over the Maritime Continent and Australia

2013 ◽  
Vol 26 (4) ◽  
pp. 1304-1321 ◽  
Author(s):  
Surendra P. Rauniyar ◽  
Kevin J. E. Walsh
Keyword(s):  
Diurnal Cycle ◽  
El Niño ◽  
Large Scale ◽  
El Nino ◽  
Walker Circulation ◽  
La Niña ◽  
Boreal Winter ◽  
Maritime Continent ◽  
La Nina ◽  
Rainfall Anomalies

Abstract This study examines the influence of ENSO on the diurnal cycle of rainfall during boreal winter for the period 1998–2010 over the Maritime Continent (MC) and Australia using Tropical Rainfall Measuring Mission (TRMM) and reanalysis data. The diurnal cycles are composited for the ENSO cold (La Niña) and warm (El Niño) phases. The k-means clustering technique is then applied to group the TRMM data into six clusters, each with a distinct diurnal cycle. Despite the alternating patterns of widespread large-scale subsidence and ascent associated with the Walker circulation, which dominates the climate over the MC during the opposing phases of ENSO, many of the islands of the MC show localized differences in rainfall anomalies that depend on the local geography and orography. While ocean regions mostly experience positive rainfall anomalies during La Niña, some local regions over the islands have more rainfall during El Niño. These local features are also associated with anomalies in the amplitude and characteristics of the diurnal cycle in these regions. These differences are also well depicted in large-scale dynamical fields derived from the interim ECMWF Re-Analysis (ERA-Interim).

Intraseasonal Transitions of the Wintertime Pacific Jet Stream

2020 ◽  
Author(s):  
Maria Madsen ◽  
Jonathan Martin
Keyword(s):  
General Circulation ◽  
Large Scale ◽  
Weather Prediction ◽  
Intraseasonal Variability ◽  
Extreme Weather Events ◽  
Jet Stream ◽  
The Pacific ◽  
Basin Scale ◽  
Jet Variability ◽  
The Impact

&lt;p&gt;The deficiency in predictability at subseasonal-to-seasonal timescales, as compared to prediction at conventional weather prediction timescales, is significant. Intraseasonal variability of atmospheric features like the jet stream, occurring within this gap, lead to extreme weather events that present considerable hazards to society. As jets are an important feature at the interface of the large-scale general circulation and the life cycle of individual weather systems, there is strong incentive to more comprehensively understand their variability.&lt;/p&gt;&lt;p&gt;The wintertime Pacific jet manifests its intraseasonal variability in two predominant modes: a zonal extension or retraction and a meridional shift by as much as 20&amp;#176; of the jet exit region. These two leading modes are associated with basin-scale anomalies in the Pacific that directly impact weather in Hawaii and continental North America. Although recent work has demonstrated the impact intramodal changes of the Pacific jet have on large-scale structure, sensible weather phenomena, and forecast skill in and around the vast North Pacific Basin, the transitions between the leading modes have hardly been considered and, therefore, are poorly understood. Consequently, this work examines the nature and predictability of transitions between modes of wintertime Pacific jet variability as well as their associated synoptic environments.&lt;/p&gt;&lt;p&gt;We apply two distinct but complementary statistical analyses to 70 cold seasons (NDJFM 1948/49-2017/18) of daily 250-hPa zonal winds from the NCEP/NCAR Reanalysis to investigate such transitions. Empirical orthogonal analysis (EOF)/principal component (PC) analysis is used to depict the state of the daily Pacific jet as a point in a two dimensional phase space defined by the two leading modes.&amp;#160; Supporting this technique is a self-organizing maps (SOMs) analysis that identifies non-orthogonal, synoptically recurring patterns of the Pacific jet. Together, these analyses show that there are, in fact, preferred transitions between these leading modes of variability. Composite and individual case analyses of preferred transition evolutions provides new insight into the synoptic-scale environments that drive Pacific jet variability.&lt;/p&gt;

scholarly journals A Bayesian Regression Approach to Seasonal Prediction of Tropical Cyclones Affecting the Fiji Region

2010 ◽  
Vol 23 (13) ◽  
pp. 3425-3445 ◽  
Author(s):  
Savin S. Chand ◽  
Kevin J. E. Walsh ◽  
Johnny C. L. Chan
Keyword(s):  
Tropical Cyclones ◽  
El Niño ◽  
Large Scale ◽  
El Nino ◽  
Seasonal Prediction ◽  
Bayesian Regression ◽  
La Niña ◽  
Annual Number ◽  
La Nina ◽  
Neutral Conditions

Abstract This study presents seasonal prediction schemes for tropical cyclones (TCs) affecting the Fiji, Samoa, and Tonga (FST) region. Two separate Bayesian regression models are developed: (i) for cyclones forming within the FST region (FORM) and (ii) for cyclones entering the FST region (ENT). Predictors examined include various El Niño–Southern Oscillation (ENSO) indices and large-scale environmental parameters. Only those predictors that showed significant correlations with FORM and ENT are retained. Significant preseason correlations are found as early as May–July (approximately three months in advance). Therefore, May–July predictors are used to make initial predictions, and updated predictions are issued later using October–December early-cyclone-season predictors. A number of predictor combinations are evaluated through a cross-validation technique. Results suggest that a model based on relative vorticity and the Niño-4 index is optimal to predict the annual number of TCs associated with FORM, as it has the smallest RMSE associated with its hindcasts (RMSE = 1.63). Similarly, the all-parameter-combined model, which includes the Niño-4 index and some large-scale environmental fields over the East China Sea, appears appropriate to predict the annual number of TCs associated with ENT (RMSE = 0.98). While the all-parameter-combined ENT model appears to have good skill over all years, the May–July prediction of the annual number of TCs associated with FORM has two limitations. First, it underestimates (overestimates) the formation for years where the onset of El Niño (La Niña) events is after the May–July preseason or where a previous La Niña (El Niño) event continued through May–July during its decay phase. Second, its performance in neutral conditions is quite variable. Overall, no significant skill can be achieved for neutral conditions even after an October–December update. This is contrary to the performance during El Niño or La Niña events, where model performance is improved substantially after an October–December early-cyclone-season update.

Processes in the Pacific La Niña onset triggered by the Atlantic Niño

2014 ◽  
Vol 44 (1-2) ◽  
pp. 115-131 ◽  
Author(s):  
Irene Polo ◽  
Marta Martin-Rey ◽  
Belen Rodriguez-Fonseca ◽  
Fred Kucharski ◽  
Carlos Roberto Mechoso
Keyword(s):  
La Niña ◽  
La Nina ◽  
The Pacific ◽  
Atlantic Niño

scholarly journals PDO–ENSO Effects in the Climate of Mexico

2006 ◽  
Vol 19 (24) ◽  
pp. 6433-6438 ◽  
Author(s):  
Edgar G. Pavia ◽  
Federico Graef ◽  
Jorge Reyes
Keyword(s):  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
La Niña ◽  
Climate Anomalies ◽  
Enso Events ◽  
La Nina ◽  
Mean Temperature ◽  
The Pacific

Abstract The role of the Pacific decadal oscillation (PDO) in El Niño–Southern Oscillation (ENSO)-related Mexican climate anomalies during winter and summer is investigated. The precipitation and mean temperature data of approximately 1000 stations throughout Mexico are considered. After sorting ENSO events by warm phase (El Niño) and cold phase (La Niña) and prevailing PDO phase: warm or high (HiPDO) and cold or low (LoPDO), the authors found the following: 1) For precipitation, El Niño favors wet conditions during summers of LoPDO and during winters of HiPDO. 2) For mean temperature, cooler conditions are favored during La Niña summers and during El Niño winters, regardless of the PDO phase; however, warmer conditions are favored by the HiPDO during El Niño summers.

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