scholarly journals Seasonal Contrast in Precipitation Mechanisms over Nepal Deduced from Relationship with the Large-Scale Climate Patterns

2013 ◽  
Vol 13 (1) ◽  
pp. 115-123 ◽  
Author(s):  
Madan Sigdel ◽  
Motoyoshi Ikeda
Keyword(s):  
Indian Ocean ◽  
Large Scale ◽  
Southern Oscillation ◽  
Summer Precipitation ◽  
Walker Circulation ◽  
Moisture Flux ◽  
Rain Gauge ◽  
Western Region ◽  
Eastern Region ◽  
The Relationship

Summer precipitation dominates over winter one for the annual total in south Asia, while the winter condition is still important for agricultural productions. Rain gauge data over Nepal were analyzed with large-scale atmospheric patterns such as El Niño-Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD). In the period of June to September, summer monsoon rainfall over Nepal (SMRN) is generally higher in the eastern region along with a peak in the central region associated with the local orography. Its interannual variability was found to be correlated with the southern oscillation index (SOI): i.e., when La Niña occurs, eastward moisture flux is blocked over Bay of Bengal (BOB) by the anomalous Walker circulation extending from the Pacific. The local-scale condition for higher SMRN is implied by a main moisture route along the eastern arm of the low pressure in northeastern India, as proved by a significant correlation between SMRN and the northward moisture flux. In winter (DJFM), precipitation occurs more in the western region. The higher winter precipitation over Nepal (WPN) was correlated almost equally with positive Dipole Mode Index (DMI) over the Indian Ocean and also SOI, while the relationship with SOI is reversed from summer. A clear linkage was suggested with moisture flux from the Arabian Sea and the further western region. Thus, possible impacts of anomalous precipitation have to be predicted under the relationship with the large-scale indices depending on seasons. Nepal Journal of Science and Technology Vol. 13, No. 1 (2012) 115-123 DOI: http://dx.doi.org/10.3126/njst.v13i1.7450

A Monsoon-Like Southwest Australian Circulation and Its Relation with Rainfall in Southwest Western Australia

2010 ◽  
Vol 23 (6) ◽  
pp. 1334-1353 ◽  
Author(s):  
Juan Feng ◽  
Jianping Li ◽  
Yun Li
Keyword(s):  
Indian Ocean ◽  
Western Australia ◽  
Large Scale ◽  
Southern Oscillation ◽  
Southern Annular Mode ◽  
Late Winter ◽  
Early Winter ◽  
Winter Rainfall ◽  
Enso Modoki ◽  
Distinct Features

Abstract Using the NCEP–NCAR reanalysis, the 40-yr ECMWF Re-Analysis (ERA-40), and precipitation data from the Climate Prediction Center (CPC) Merged Analysis of Precipitation (CMAP) and the Australian Bureau of Meteorology, the variability and circulation features influencing southwest Western Australia (SWWA) winter rainfall are investigated. It is found that the climate of southwest Australia bears a strong seasonality in the annual cycle and exhibits a monsoon-like atmospheric circulation, which is called the southwest Australian circulation (SWAC) because of its several distinct features characterizing a monsoonal circulation: the seasonal reversal of winds, alternate wet and dry seasons, and an evident land–sea thermal contrast. The seasonal march of the SWAC in extended winter (May–October) is demonstrated by pentad data. An index based on the dynamics’ normalized seasonality was introduced to describe the behavior and variation of the winter SWAC. It is found that the winter rainfall over SWWA has a significant positive correlation with the SWAC index in both early (May–July) and late (August–October) winter. In weaker winter SWAC years, there is an anticyclonic anomaly over the southern Indian Ocean resulting in weaker westerlies and northerlies, which are not favorable for more rainfall over SWWA, and the opposite combination is true in the stronger winter SWAC years. The SWAC explains not only a large portion of the interannual variability of SWWA rainfall in both early and late winter but also the long-term drying trend over SWWA in early winter. The well-coupled SWAC–SWWA rainfall relationship seems to be largely independent of the well-known effects of large-scale atmospheric circulations such as the southern annular mode (SAM), El Niño–Southern Oscillation (ENSO), Indian Ocean dipole (IOD), and ENSO Modoki (EM). The result offers qualified support for the argument that the monsoon-like circulation may contribute to the rainfall decline in early winter over SWWA. The external forcing of the SWAC is also explored in this study.

scholarly journals Central-West Argentina Summer Precipitation Variability and Atmospheric Teleconnections

2012 ◽  
Vol 25 (5) ◽  
pp. 1657-1677 ◽  
Author(s):  
Eduardo A. Agosta ◽  
Rosa H. Compagnucci
Keyword(s):  
Indian Ocean ◽  
Southern Oscillation ◽  
Vertical Motion ◽  
Summer Precipitation ◽  
Western Indian Ocean ◽  
Stationary Wave ◽  
Precipitation Variability ◽  
South Atlantic ◽  
Spectral Variation ◽  
The South

The interannual-to-multidecadal variability of central-west Argentina (CWA) summer (October–March) precipitation and associated tropospheric circulation are studied in the period 1900–2010. Precipitation shows significant quasi cycles with periods of about 2, 4–5, 6–8, and 16–22 yr. The quasi-bidecadal oscillation is significant from the early 1910s until the mid-1970s and is present in pressure time series over the southwestern South Atlantic. According to the lower-frequency spectral variation, a prolonged wet spell is observed from 1973 to the early 2000s. The precipitation variability shows a reversal trend since then. In that wet epoch, the regionally averaged precipitation has been increased about 24%. The lower-frequency spectral variation is attributed to the climate shift of 1976/77. From the early twentieth century until the mid-1970s, the precipitation variability is associated with barotropic quasi-stationary wave (QSW) propagation from the tropical southern Indian Ocean and the South Pacific, generating vertical motion and moisture anomalies at middle-to-subtropical latitudes east of the Andes over southern South America. The QSW propagation could be related to anomalous convection partly induced by tropical anomalous SSTs in the western Indian Ocean (WIO). It could also be linked to another midlatitude source along the storm tracks, to the east of New Zealand. After 1976/77, the precipitation variability is associated with equatorial symmetric circulation anomalies linked to El Niño–Southern Oscillation (ENSO)-like warmer conditions. Positive moisture anomalies are consistently observed at lower latitudes in association with inflation of the western flank of the South Atlantic anticyclone. Outside of this, the precipitation variability is unrelated to ENSO.

The relationship between Indian Ocean sea–surface temperature and East African rainfall

2005 ◽  
Vol 363 (1826) ◽  
pp. 43-47 ◽  
Author(s):  
Emily Black
Keyword(s):  
Indian Ocean ◽  
Surface Temperature ◽  
Sea Surface Temperature ◽  
Southern Oscillation ◽  
Sea Surface ◽  
East African ◽  
African Rainfall ◽  
The Pacific ◽  
The Indian Ocean ◽  
The Relationship

Knowledge of the processes that control East African rainfall is essential for the development of seasonal forecasting systems, which may mitigate the effects of flood and drought. This study uses observational data to unravel the relationship between the Indian Ocean Dipole (IOD), the El Niño Southern Oscillation (ENSO) and rainy autumns in East Africa. Analysis of sea–surface temperature data shows that strong East African rainfall is associated with warming in the Pacific and Western Indian Oceans and cooling in the Eastern Indian Ocean. The resemblance of this pattern to that which develops during IOD events implies a link between the IOD and strong East African rainfall. Further investigation suggests that the observed teleconnection between East African rainfall and ENSO is a manifestation of a link between ENSO and the IOD.

scholarly journals Interannual and Interdecadal Variability of Thailand Summer Monsoon Season

2005 ◽  
Vol 18 (11) ◽  
pp. 1697-1708 ◽  
Author(s):  
Nkrintra Singhrattna ◽  
Balaji Rajagopalan ◽  
K. Krishna Kumar ◽  
Martyn Clark
Keyword(s):  
Summer Monsoon ◽  
El Niño ◽  
Large Scale ◽  
Monsoon Rainfall ◽  
El Nino ◽  
Southern Oscillation ◽  
Negative Relationship ◽  
Walker Circulation ◽  
Planning And Management ◽  
The Walker Circulation

Abstract Summer monsoon rains are a critical factor in Thailand’s water resources and agricultural planning and management. In fact, they have a significant impact on the country’s economic health. Consequently, understanding the variability of the summer monsoon rains over Thailand is important for instituting effective mitigating strategies against extreme rainfall fluctuations. To this end, the authors systematically investigated the relationships between summer monsoon precipitation from the central and northern regions of Thailand and large-scale climate features. It was found that Pacific sea surface temperatures (SSTs), in particular, El Niño–Southern Oscillation (ENSO), have a negative relationship with the summer monsoon rainfall over Thailand in recent decades. However, the relationship between summer rainfall and ENSO was weak prior to 1980. It is hypothesized that the ENSO teleconnection depends on the SST configuration in the tropical Pacific Ocean, that is, an eastern Pacific–based El Niño pattern, such as is the case in most of the post-1980 El Niño events, tends to place the descending limb of the Walker circulation over the Thailand–Indonesian region, thereby significantly reducing convection and consequently, rainfall over Thailand. It is believed that this recent shift in the Walker circulation is instrumental for the nonstationarity in ENSO–monsoon relationships in Thailand. El Niños of 1997 and 2002 corroborate this hypothesis. This has implications for monsoon rainfall forecasting and, consequently, for resources planning and management.

scholarly journals Effects of Atlantic and Pacific Ocean Teleconnections on Corn Yield East of Puebla, Mexico: Case Studies

2021 ◽  
pp. 85-99
Author(s):  
Ma De Los Ángeles Velasco-Hernández ◽  
Tomás Morales-Acoltzi ◽  
Miguel Ángel García-Castro ◽  
Rogelio Bernal-morales ◽  
Joaquín Zagoya-Martínez ◽  
...  
Keyword(s):  
Case Studies ◽  
Southern Oscillation ◽  
Geographical Location ◽  
Structured Interview ◽  
Growth Cycle ◽  
Corn Yield ◽  
Eastern Region ◽  
Hurricane Activity ◽  
Relationship Of ◽  
The Relationship

Ocean-atmospheric interactions have effects at different scales; forming microclimates, which can explain variations with climatic or natural anomalies, between meteorological processes. This research analyzes and identifies the relationship of the teleconnection hydrometeorological effects, which determine the distribution of precipitation in corn yield. The data were used from a semi-structured interview directed to corn producers, where seven years of case studies were identified for the eastern region of the state of Puebla, Mexico. The Graphics were made with “pentad scale distribution”. The results show the importance of geographical location for agricultural activities in relation to a valley with altitudinal gradient. In addition, the corn growth cycle is associated with tropical disturbances from east Puebla region as well as Hurricane activity. It was identified that the relationship of teleconnections and the distribution of rainfall are main factors that influence in the development good or bad of corn, showed in the yields, where the different phases of ENSO (EL NIÑO Southern Oscillation) have a differentiated impact on the availability of precipitation in this case studies of the present investigation.

scholarly journals Re-Examination of the Decadal Change in the Relationship between the East Asian Summer Monsoon and Indian Ocean SST

Atmosphere ◽  
2018 ◽  
Vol 9 (10) ◽  
pp. 395 ◽  
Author(s):  
Seogyeong Kim ◽  
Kyung-Ja Ha ◽  
Ruiqiang Ding ◽  
Jiangping Li
Keyword(s):  
Indian Ocean ◽  
Summer Monsoon ◽  
Southern Oscillation ◽  
Asian Summer Monsoon ◽  
Low Frequency ◽  
Decadal Change ◽  
Remote Forcing ◽  
The Indian Ocean ◽  
Asian Summer ◽  
The Relationship

This study examines the decadal change in the relationship between two major Indian Ocean (IO) sea surface temperature patterns, namely the Indian Ocean dipole (IOD) and northern IO and the East Asia summer monsoon (EASM) in the early 2000s. In 1991–1999, the former epoch, the interannual variability of EASM was associated with the IOD-like pattern in the original paper and its relationship weakened in 2000–2016. There are two possible causes for this decadal change; stronger land-sea thermal contrast as a local forcing in latter epoch, which may result in the weakening of the relationship between the IO and the EASM. In addition, the influence of El Niño-southern Oscillation (ENSO) on the western North Pacific subtropical high (WNPSH) could be changed depending on the frequency of ENSO. In the 2000s, the intensity of the low frequency (LF)-type ENSO (42–86 months period) events was weaker compared to the former epoch but that of quasi-biennial (QB)-type ENSO (16–36 months period) remained persistent. This could explain that the QB-type ENSO is remote forcing that modulates the change in the relationship between the tropical IO patterns and EASM in the 2000s.

scholarly journals The Relationship between the ITCZ and MJO Initiation over the Indian Ocean

2019 ◽  
Vol 76 (8) ◽  
pp. 2275-2294 ◽  
Author(s):  
Rachel C. Zelinsky ◽  
Chidong Zhang ◽  
Chuntao Liu
Keyword(s):  
Indian Ocean ◽  
Large Scale ◽  
Madden Julian Oscillation ◽  
Shallow Convection ◽  
Theoretical Understanding ◽  
Convective Initiation ◽  
Moist Condition ◽  
The Indian Ocean ◽  
The Relationship ◽  
Global Reanalysis

Abstract Understanding convective initiation of the Madden–Julian oscillation (MJO) remains an unmet challenge. MJO initiation has been perceived as a process starting from a convectively suppressed large-scale condition with gradual growth of shallow convection to congestus and to deep convective and stratiform systems that cover a large-scale area. During the DYNAMO field campaign over the Indian Ocean, MJO initiation was observed to start from an existing intertropical convergence zone (ITCZ) south of the equator. This raises a question of what possible role the ITCZ may play in convective initiation of the MJO. This study addresses this question through analysis of satellite observations of precipitation and a global reanalysis product. By setting several criteria, MJO and ITCZ events were objectively identified and grouped according to whether MJO initiation was immediately preceded by an ITCZ. The results demonstrate that an ITCZ is neither a necessary nor sufficient condition for convective initiation of the MJO. Nonetheless, evolution of the large-scale circulation, moisture, and convective characteristics during MJO initiation can be different with and without a preexisting ITCZ. Convective growth begins gradually before and during MJO initiation when there is a preexisting ITCZ whereas it is abrupt and slightly delayed without a preexisting ITCZ. Such differences are presumably related to the existing large-scale moist condition of the ITCZ. The results from this study suggest that there are multiple mechanisms for convective initiation of the MJO, which should be considered in theoretical understanding of the MJO.

The Amplification of the ENSO Forcing over Equatorial Amazon

2009 ◽  
Vol 10 (6) ◽  
pp. 1561-1568 ◽  
Author(s):  
Vasubandhu Misra
Keyword(s):  
South America ◽  
Diurnal Cycle ◽  
Land Surface ◽  
Large Scale ◽  
French Guiana ◽  
Southern Oscillation ◽  
Moisture Flux ◽  
Precipitation Anomalies ◽  
Upper Level

Abstract The remote influence of the El Niño–Southern Oscillation (ENSO) strongly manifests over the equatorial Amazon (EA)—including parts of southern Venezuela, Guyana, French Guiana, and Suriname—when there is a large-scale anomalous upper-level divergence over continental tropical South America. Modeling studies conducted in this paper suggest that it is because of the modulation of the local diurnal cycle of the moisture flux convergence, which results in the local amplification of the ENSO signal over the EA. Further, it is shown that the local land surface feedback plays a relatively passive but important role of maintaining these interannual precipitation anomalies over the EA region.

scholarly journals A CGCM Study on the Interaction between IOD and ENSO

2006 ◽  
Vol 19 (9) ◽  
pp. 1688-1705 ◽  
Author(s):  
Swadhin K. Behera ◽  
Jing Jia Luo ◽  
Sebastien Masson ◽  
Suryachandra A. Rao ◽  
Hirofumi Sakuma ◽  
...  
Keyword(s):  
Indian Ocean ◽  
General Circulation ◽  
Southern Oscillation ◽  
Walker Circulation ◽  
Tropical Pacific ◽  
Boreal Summer ◽  
Enso Variability ◽  
The Indian Ocean ◽  
Sst Anomalies ◽  
The Tropical Pacific

Abstract An atmosphere–ocean coupled general circulation model known as the Scale Interaction Experiment Frontier version 1 (SINTEX-F1) model is used to understand the intrinsic variability of the Indian Ocean dipole (IOD). In addition to a globally coupled control experiment, a Pacific decoupled noENSO experiment has been conducted. In the latter, the El Niño–Southern Oscillation (ENSO) variability is suppressed by decoupling the tropical Pacific Ocean from the atmosphere. The ocean–atmosphere conditions related to the IOD are realistically simulated by both experiments including the characteristic east–west dipole in SST anomalies. This demonstrates that the dipole mode in the Indian Ocean is mainly determined by intrinsic processes within the basin. In the EOF analysis of SST anomalies from the noENSO experiment, the IOD takes the dominant seat instead of the basinwide monopole mode. Even the coupled feedback among anomalies of upper-ocean heat content, SST, wind, and Walker circulation over the Indian Ocean is reproduced. As in the observation, IOD peaks in boreal fall for both model experiments. In the absence of ENSO variability the interannual IOD variability is dominantly biennial. The ENSO variability is found to affect the periodicity, strength, and formation processes of the IOD in years of co-occurrences. The amplitudes of SST anomalies in the western pole of co-occurring IODs are aided by dynamical and thermodynamical modifications related to the ENSO-induced wind variability. Anomalous latent heat flux and vertical heat convergence associated with the modified Walker circulation contribute to the alteration of western anomalies. It is found that 42% of IOD events affected by changes in the Walker circulation are related to the tropical Pacific variabilities including ENSO. The formation is delayed until boreal summer for those IODs, which otherwise form in boreal spring as in the noENSO experiment.

scholarly journals Compound high-temperature and low-chlorophyll extremes in the ocean over the satellite period

2021 ◽  
Vol 18 (6) ◽  
pp. 2119-2137
Author(s):  
Natacha Le Grix ◽  
Jakob Zscheischler ◽  
Charlotte Laufkötter ◽  
Cecile S. Rousseaux ◽  
Thomas L. Frölicher
Keyword(s):  
High Temperature ◽  
Indian Ocean ◽  
Extreme Events ◽  
Large Scale ◽  
Southern Oscillation ◽  
Chlorophyll Concentration ◽  
Equatorial Pacific ◽  
Compound Event ◽  
Eastern Equatorial Pacific ◽  
Compound Events

Abstract. Extreme events in the ocean severely impact marine organisms and ecosystems. Of particular concern are compound events, i.e., when conditions are extreme for multiple potential ocean ecosystem stressors such as temperature and chlorophyll. Yet, little is known about the occurrence, intensity, and duration of such compound high-temperature (a.k.a. marine heatwaves – MHWs) and low-chlorophyll (LChl) extreme events, whether their distributions have changed in the past decades, and what the potential drivers are. Here we use satellite-based sea surface temperature and chlorophyll concentration estimates to provide a first assessment of such compound extreme events. We reveal hotspots of compound MHW and LChl events in the equatorial Pacific, along the boundaries of the subtropical gyres, in the northern Indian Ocean, and around Antarctica. In these regions, compound events that typically last 1 week occur 3 to 7 times more often than expected under the assumption of independence between MHWs and LChl events. The occurrence of compound MHW and LChl events varies on seasonal to interannual timescales. At the seasonal timescale, most compound events occur in summer in both hemispheres. At the interannual timescale, the frequency of compound MHW and LChl events is strongly modulated by large-scale modes of natural climate variability such as the El Niño–Southern Oscillation, whose positive phase is associated with increased compound event occurrence in the eastern equatorial Pacific and in the Indian Ocean by a factor of up to 4. Our results provide a first understanding of where, when, and why compound MHW and LChl events occur. Further studies are needed to identify the exact physical and biological drivers of these potentially harmful events in the ocean and their evolution under global warming.

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