scholarly journals Characteristics of the Northern Australian Rainy Season

2008 ◽  
Vol 21 (17) ◽  
pp. 4298-4311 ◽  
Author(s):  
I. N. Smith ◽  
L. Wilson ◽  
R. Suppiah
Keyword(s):  
Rainy Season ◽  
Climate Model ◽  
Southern Oscillation ◽  
Monsoon Season ◽  
Daily Rainfall ◽  
Summer Rainfall ◽  
Average Intensity ◽  
Australian Monsoon ◽  
Enso Events ◽  
Independent Features

Abstract A trend of increasing rainfall over much of north and northwest Australia over recent decades has contrasted with decreases over much of the rest of the continent. The increases have occurred during the summer months when the rainy season is dominated by the Australian monsoon but is also affected by other events such as tropical cyclones, Madden–Julian oscillations, and sporadic thunderstorms. The problem of diagnosing these trends is considered in terms of changes in the timing of the rainy season. While numerous definitions for rainy/monsoon season onset exist, most are designed to be useful in a predictive sense and can be limited in their application to diagnostic studies, particularly when they involve predetermined threshold amounts. Here the authors define indices, based on daily rainfall observations, that provide relatively simple, robust descriptions of each rainy season at any location. These are calculated using gridded daily rainfall data throughout the northern Australian tropics and also for selected stations. The results indicate that the trends in summer rainfall totals over the period from 1950 to 2005 appear to be mainly the result of similar trends in average intensity. Furthermore, the links between the September–October average Southern Oscillation index indicate that ENSO events affect season duration rather than average intensity. Because duration and average intensity are derived as independent features of each season, it is argued that the trends in rainfall totals are largely unrelated to trends in ENSO and most likely reflect the influence of other factors. Finally, diagnosing these features of the rainy season provides a basis for assessing the confidence one can attach to different climate model projections of changes to rainfall.

Decadal Variability of Rainfall in Senegal : beyond total seasonal amounts

2021 ◽  
Author(s):  
Aissatou Badji ◽  
Moussa Diakhaté ◽  
Amadou Tierno Gaye ◽  
Juliette Mignot ◽  
Elsa Mohino
Keyword(s):  
Rainy Season ◽  
Decadal Variability ◽  
Function Analysis ◽  
Monsoon Season ◽  
Daily Rainfall ◽  
Average Intensity ◽  
Main Mode ◽  
Clear Trend ◽  
Dry Spells ◽  
Rainy Days

<p>The intraseasonal characteristics of rainfall have important implications for agriculture in the Sahel. For example, the development and yield of millet, sorghum and maize depend not only on the rainfall seasonal total amounts, but also on the onset of the rainy season and the seasonal distribution of rainy days as well as the occurrence of dry spells. However, the decadal variability of intraseasonal rainfall characteristics in the Sahel and in particular in Senegal has received little attention in the literature so far. In this study, we analyze the decadal modulations of the intraseasonal characteristics of the monsoon season in Senegal over the period 1918-2000. From daily rainfall data measured at different stations in Senegal, we have defined indices characterizing, among others, the number of rainy days, the average intensity of rainy days, the starting day and ending day of the rainy season. The spatial patterns of the mean indices generally show a north/south gradient and their temporal modulations show a clear decadal signal. Application of EOF (Empirical Orthogonal Function) analysis provides a main mode of variability showing same-signed loads throughout the territory. The associated PCs show strong decadal variability for most indices with a strong link to the Atlantic Multidecadal Variability. The exception are the indices related to the duration of the monsoon season, which show a weaker decadal variability with a clear trend.</p>

The relationship between the El Niño Southern Oscillation and Australian monsoon rainfall on decadal time-scales

2021 ◽  
Author(s):  
Hanna Heidemann ◽  
Joachim Ribbe ◽  
Benjamin J. Henley ◽  
Tim Cowan ◽  
Christa Pudmenzky ◽  
...  
Keyword(s):  
Monsoon Rainfall ◽  
Decadal Variability ◽  
Southern Oscillation ◽  
Eastern Pacific ◽  
Central Pacific ◽  
Australian Monsoon ◽  
Enso Events ◽  
Pacific Decadal Variability ◽  
Prediction Systems ◽  
Different Response

<p>This research analyses the observed relationship between eastern and central Pacific El Niño Southern Oscillation (ENSO) events and Australian monsoon rainfall (AUMR) on a decadal timescale during the December to March monsoon months. To assess the decadal influence of the different flavours of ENSO on the AUMR, we focus on the phases of the Interdecadal Pacific Oscillation (IPO) over the period 1920 to 2020.  The AUMR is characterized by substantial decadal variability, which appears to be linked to the positive and negative phases of the IPO. During the past two historical negative IPO phases, significant correlations have been observed between central Pacific sea surface temperature (SST) anomalies and AUMR over both the northeast and northwest of Australia. This central Pacific SST-AUMR relationship has strengthened from the first negative IPO phase (mid-1940s to the mid-1970s) to the second (late 1990s to mid-2010s), while the eastern Pacific SST-AUMR influence has weakened. Composite rainfall anomalies over Australia reveal a different response of AUMR to central Pacific El Niño/La Niña and eastern Pacific La Niña events during positive IPO and negative IPO phases. This research clearly shows that ENSO's influence on AUMR is modulated by Pacific decadal variability, however this teleconnection, in itself, can change between similar decadal Pacific states.  Going forward, as decadal prediction systems improve and become more mainstream, the IPO phase could be used as a potential source for decadal predictability of the tendency of AUMR.  </p>

scholarly journals Coastal upwelling along the southwest coast of India – ENSO modulation

2008 ◽  
Vol 26 (6) ◽  
pp. 1331-1334 ◽  
Author(s):  
K. Muni Krishna
Keyword(s):  
Coastal Upwelling ◽  
Southern Oscillation ◽  
Monsoon Season ◽  
Trade Winds ◽  
Southwest Coast Of India ◽  
Southwest Coast ◽  
Enso Events ◽  
The Pacific ◽  
Basin Scale ◽  
Using Data

Abstract. An index of El Niño Southern Oscillation (ENSO) in the Pacific during pre monsoon season is shown to account for a significant part of the variability of coastal Sea Surface Temperature (SST) anomalies measured a few months later within the wind driven southwest coast of India coastal upwelling region 7° N–14° N. This teleconnection is thought to result from an atmospheric bridge between the Pacific and north Indian Oceans, leading to warm (cold) ENSO events being associated with relaxation (intensification) of the Indian trade winds and of the wind-induced coastal upwelling. This ENSO related modulation of the wind-driven coastal upwelling appears to contribute to the connection observed at the basin-scale between ENSO and SST in the Arabian Sea. The ability to use this teleconnection to give warning of large changes in the southwest coast of India coastal upwelling few months in advance is successfully tested using data from 1998 and 1999 ENSO events.

scholarly journals Black Carbon Increases Frequency of Extreme ENSO Events

2019 ◽  
Vol 32 (23) ◽  
pp. 8323-8333 ◽  
Author(s):  
Sijia Lou ◽  
Yang Yang ◽  
Hailong Wang ◽  
Jian Lu ◽  
Steven J. Smith ◽  
...  
Keyword(s):  
Black Carbon ◽  
Climate Models ◽  
Climate Model ◽  
Southern Oscillation ◽  
Global Climate ◽  
Global Climate Model ◽  
Co2 Concentration ◽  
Enso Events ◽  
Aerosol Forcing ◽  
Earth’S Climate

ABSTRACT El Niño–Southern Oscillation (ENSO) is the leading mode of Earth’s climate variability at interannual time scales with profound ecological and societal impacts, and it is projected to intensify in many climate models as the climate warms under the forcing of increasing CO2 concentration. Since the preindustrial era, black carbon (BC) emissions have substantially increased in the Northern Hemisphere. But how BC aerosol forcing may influence the occurrence of the extreme ENSO events has rarely been investigated. In this study, using simulations of a global climate model, we show that increases in BC emissions from both the midlatitudes and Arctic weaken latitudinal temperature gradients and northward heat transport, decrease tropical energy divergence, and increase sea surface temperature over the tropical oceans, with a surprising consequential increase in the frequency of extreme ENSO events. A corollary of this study is that reducing BC emissions might serve to mitigate the possible increasing frequency of extreme ENSO events under greenhouse warming, if the modeling result can be translated into the climate in reality.

Impact of Indo-Pacific Feedback Interactions on ENSO Dynamics Diagnosed Using Ensemble Climate Simulations

2012 ◽  
Vol 25 (21) ◽  
pp. 7743-7763 ◽  
Author(s):  
A. Santoso ◽  
M. H. England ◽  
W. Cai
Keyword(s):  
Indian Ocean ◽  
Climate Model ◽  
Southern Oscillation ◽  
Ocean Basin ◽  
Climate Feedback ◽  
Enso Events ◽  
Thermocline Feedback ◽  
Enso Dynamics ◽  
The Indian Ocean ◽  
The Impact

The impact of Indo-Pacific climate feedback on the dynamics of El Niño–Southern Oscillation (ENSO) is investigated using an ensemble set of Indian Ocean decoupling experiments (DCPL), utilizing a millennial integration of a coupled climate model. It is found that eliminating air–sea interactions over the Indian Ocean results in various degrees of ENSO amplification across DCPL simulations, with a shift in the underlying dynamics toward a more prominent thermocline mode. The DCPL experiments reveal that the net effect of the Indian Ocean in the control runs (CTRL) is a damping of ENSO. The extent of this damping appears to be negatively correlated to the coherence between ENSO and the Indian Ocean dipole (IOD). This type of relationship can arise from the long-lasting ENSO events that the model simulates, such that developing ENSO often coincides with Indian Ocean basin-wide mode (IOBM) anomalies during non-IOD years. As demonstrated via AGCM experiments, the IOBM enhances western Pacific wind anomalies that counteract the ENSO-enhancing winds farther east. In the recharge oscillator framework, this weakens the equatorial Pacific air–sea coupling that governs the ENSO thermocline feedback. Relative to the IOBM, the IOD is more conducive for ENSO growth. The net damping by the Indian Ocean in CTRL is thus dominated by the IOBM effect which is weaker with stronger ENSO–IOD coherence. The stronger ENSO thermocline mode in DCPL is consistent with the absence of any IOBM anomalies. This study supports the notion that the Indian Ocean should be viewed as an integral part of ENSO dynamics.

scholarly journals Prospects for Dynamical Prediction of Meteorological Drought

2012 ◽  
Vol 51 (7) ◽  
pp. 1238-1252 ◽  
Author(s):  
Xiao-Wei Quan ◽  
Martin P. Hoerling ◽  
Bradfield Lyon ◽  
Arun Kumar ◽  
Michael A. Bell ◽  
...  
Keyword(s):  
Great Plains ◽  
Climate Model ◽  
Southern Oscillation ◽  
Standardized Precipitation Index ◽  
Summer Rainfall ◽  
Northern Great Plains ◽  
Seasonal Forecasts ◽  
Wet Season ◽  
Antecedent Soil Moisture ◽  
Drought Prediction

AbstractThe prospects for U.S. seasonal drought prediction are assessed by diagnosing simulation and hindcast skill of drought indicators during 1982–2008. The 6-month standardized precipitation index is used as the primary drought indicator. The skill of unconditioned, persistence forecasts serves as the baseline against which the performance of dynamical methods is evaluated. Predictions conditioned on the state of global sea surface temperatures (SST) are assessed using atmospheric climate simulations conducted in which observed SSTs are specified. Predictions conditioned on the initial states of atmosphere, land surfaces, and oceans are next analyzed using coupled climate-model experiments. The persistence of the drought indicator yields considerable seasonal skill, with a region’s annual cycle of precipitation driving a strong seasonality in baseline skill. The unconditioned forecast skill for drought is greatest during a region’s climatological dry season and is least during a wet season. Dynamical models forced by observed global SSTs yield increased skill relative to this baseline, with improvements realized during the cold season over regions where precipitation is sensitive to El Niño–Southern Oscillation. Fully coupled initialized model hindcasts yield little additional skill relative to the uninitialized SST-forced simulations. In particular, neither of these dynamical seasonal forecasts materially increases summer skill for the drought indicator over the Great Plains, a consequence of small SST sensitivity of that region’s summer rainfall and the small impact of antecedent soil moisture conditions, on average, upon the summer rainfall. The fully initialized predictions for monthly forecasts appreciably improve on the seasonal skill, however, especially during winter and spring over the northern Great Plains.

scholarly journals Characteristic of the Regional Rainy Season Onset over Vietnam: Tailoring to Agricultural Application

2020 ◽  
Author(s):  
Nachiketa Acharya ◽  
Elva Bennett
Keyword(s):  
Rainy Season ◽  
Southern Oscillation ◽  
Practical Importance ◽  
Onset Date ◽  
Central Coast ◽  
Enso Events ◽  
South Central ◽  
Decadal Scale ◽  
Central Highlands ◽  
Agroclimatic Zones

Owing to its unique position within multiple monsoon regimes, latitudinal extent, and complex topography, Vietnam is divided into seven agroclimatic zones, each with distinct rainy season characteristics. Variation in the dominant rainfall system across zones affects the rainfall climatology, the primary water resource for regional crops. This study explores the creation of an agronomic rainy season onset based on high-resolution rainfall data for each agroclimatic zone for applications in an agricultural context. Onset information has huge practical importance for both agriculture and the economy. The spatiotemporal characteristics of zonal onset date are analyzed using integrated approaches of spatial and interannual variability, temporal changes, and estimation of predictability using teleconnection with Niño 3.4 sea surface temperature anomalies (SSTA) for 1980 to 2010. Results suggest that northern and southern zones experience regional onset dates in May, while the central zones experience rainy season onset in late August. The regional variability of rainy season onset is lower in a single dominant monsoon regime (northern and southern zones) and higher in latitudinally extended zones on the border of monsoon regimes (central zones). The interannual variation in rainy season onset date is found to be approximately 2 weeks across all agroclimatic zones. The significant negative trend in rainy season onset date is found for Central Coast and South Central Coast zones, suggesting that the onset date shifted earlier for the entire period. In the decadal scale, the zonal mean onset date shifted later in the Northwest and earlier in the Central Highlands. Out of the seven climate zones, a significant positive correlation is only noticed in the Central Highlands and South zones between zonal mean onset date and Niño 3.4 SSTA for Dec-Jan-Feb, suggesting the potential of seasonal scale predictability of rainy season onset date with respect to preceding El Niño-Southern Oscillation (ENSO) events.

scholarly journals Study of rainfall departure over catchments of Bihar plains

MAUSAM ◽  
2021 ◽  
Vol 61 (2) ◽  
pp. 187-196
Author(s):  
T. N. JHA ◽  
R. D. RAM
Keyword(s):  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
Monsoon Season ◽  
Daily Rainfall ◽  
La Niña ◽  
Rainfall Time Series ◽  
La Nina ◽  
Multivariate Enso Index ◽  
Rainfall Departure

Station wise daily rainfall data of sixty years is used to study rainfall departure and variability  in  Kosi, Kamala/Bagmati/Adhwara and  Gandak/Burhi Gandak catchments during  monsoon  season. Station and catchment wise rainfall time series have been made to compute rainfall departure and Coefficient of Variation (CV). Southern Oscillation Index (SOI), Multivariate ENSO Index (MEI) and ENSO strength based on percentile analysis are used to ascertain their impact on rainfall distribution in the category as excess, normal, deficient and scanty. Results indicate that the variability is greater over Kosi as compared to the other catchments. Probability of normal rainfall is found 0.75 and there is no possibility of scanty rain over the catchments during El Nino and La Nina year. Similarly probabilities of normal, deficient, excess rainfall are found as 0.67, 0.18 and 0.15 respectively during mixed year. SOI has emerged as principal parameter which modifies the departure during El Nino and La Nina year. MEI along with ENSO strength  are more prominent  during  mixed year  particularly to ascertain deficient and excess rain in weak and strong- moderate La Nina  respectively .   

scholarly journals Variability of the Australian Monsoon and Precipitation Trends at Darwin

2014 ◽  
Vol 27 (22) ◽  
pp. 8487-8500 ◽  
Author(s):  
Stuart Evans ◽  
Roger Marchand ◽  
Thomas Ackerman
Keyword(s):  
Monsoon Season ◽  
Intraseasonal Variability ◽  
Daily Rainfall ◽  
Precipitation Trend ◽  
Australian Monsoon ◽  
Northwestern Australia ◽  
Precipitation Trends

Abstract An atmospheric classification for northwestern Australia is used to define periods of monsoon activity and investigate the interannual and intraseasonal variability of the Australian monsoon, as well as long-term precipitation trends at Darwin. The classification creates a time series of atmospheric states, which two correspond to the active monsoon and the monsoon break. Occurrence of these states is used to define onset, retreat, seasonal intensity, and individual active periods within seasons. The authors demonstrate the quality of their method by showing it consistently identifies extended periods of precipitation as part of the monsoon season and recreates well-known relationships between Australian monsoon onset, intensity, and ENSO. The authors also find that onset and seasonal intensity are significantly correlated with ENSO as early as July. Previous studies have investigated the role of the Madden–Julian oscillation (MJO) during the monsoon by studying the frequency and duration of active periods, but these studies disagree on whether the MJO creates a characteristic period or duration. The authors use their metrics of monsoon activity and the Wheeler–Hendon MJO index to examine the timing of active periods relative to the phase of the MJO. It is shown that active periods preferentially begin during MJO phases 3 and 4, as the convective anomaly approaches Darwin, and end during phases 7 and 8, as the anomaly departs Darwin. Finally, the causes of the multidecadal positive precipitation trend at Darwin over the last few decades are investigated. It is found that an increase in the number of days classified as active, rather than changes in the daily rainfall rate during active monsoon periods, is responsible.

scholarly journals Characteristic of the Regional Rainy Season Onset over Vietnam: Tailoring to Agricultural Application

Atmosphere ◽  
2021 ◽  
Vol 12 (2) ◽  
pp. 198
Author(s):  
Nachiketa Acharya ◽  
Elva Bennett
Keyword(s):  
Rainy Season ◽  
Southern Oscillation ◽  
Practical Importance ◽  
Onset Date ◽  
Central Coast ◽  
Enso Events ◽  
South Central ◽  
Decadal Scale ◽  
Central Highlands ◽  
Agroclimatic Zones

Owing to its unique position within multiple monsoon regimes, latitudinal extent, and complex topography, Vietnam is divided into seven agroclimatic zones, each with distinct rainy season characteristics. Variation in the dominant rainfall system across zones affects the rainfall climatology, the primary water resource for regional crops. This study explores the creation of an agronomic rainy season onset based on high-resolution rainfall data for each agroclimatic zone for applications in an agricultural context. Onset information has huge practical importance for both agriculture and the economy. The spatiotemporal characteristics of zonal onset date are analyzed using integrated approaches of spatial and interannual variability, temporal changes, and estimation of predictability using teleconnection with Niño 3.4 sea surface temperature anomalies (SSTA) for 1980 to 2010. Results suggest that northern and southern zones experience regional onset dates in May, while the central zones experience rainy season onset in late August. The regional variability of rainy season onset is lower in the northern and southern zones and higher in the central zones which are latitudinally extended. The interannual variation in rainy season onset date is found to be approximately two weeks across all agroclimatic zones. The significant negative trend in rainy season onset date is found for Central Coast and South Central Coast zones, suggesting that the onset date shifted earlier for the entire period. In the decadal scale, the zonal mean onset date shifted later in the Northwest zone and earlier in the Central Highlands. Out of the seven climate zones, a significant positive correlation is only noticed in the Central Highlands and South zones between zonal mean onset date and Niño 3.4 SSTA for Dec–Jan–Feb, suggesting the potential of seasonal scale predictability of rainy season onset date with respect to preceding El Niño-Southern Oscillation (ENSO) events.

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