Impacts of the Indian Ocean Dipole (IOD), two different types of El Niño/Southern Oscillation (ENSO): canonical ENSO and ENSO Modoki, on the year-to-year winter wheat yield variations in Australia ...have been investigated. It is found that IOD plays a dominant role in the recent three decades; the wheat yield is reduced (increased) by -28.4% (12.8%) in the positive (negative) IOD years. Although the canonical ENSO appears to be responsible for the wheat yield variations, its influences are largely counted by IOD owing to their frequent co-occurrence. In contrast, the ENSO Modoki may have its distinct impacts on the wheat yield variations, but they are much smaller compared to those of IOD. Both the observed April-May and the predicted September-November IOD indices by the SINTEX-F ocean-atmosphere coupled model initialized on April 1st just before the sowing season explain ~15% of the observed year-to-year wheat yield variances. The present study may lead to a possible scheme for predicting wheat yield variations in Australia in advance by use of simple climate mode indices.
During austral spring of 2019, an extreme positive Indian Ocean Dipole (pIOD) event occurred, with cold sea surface temperature (SST) anomalies over the eastern equatorial Indian Ocean (EEIO) and ...warming in the west. Although the growth of the EEIO cold anomalies involves forcing by equatorial nonlinear advection, unique to the 2019 pIOD is an air‐sea heat flux that was a forcing to the EEIO cold anomalies, rather than a damping as in previous extreme events. This unique thermodynamic forcing is due to a large latent cooling, which is supported by an unusually strong wind speed contributed by a large southerly anomaly as part of a long‐term trend. The wind trend is underpinned by a mean state SST change featuring slower warming off Sumatra‐Java. Given that a similar SST trend pattern is projected under greenhouse warming, the likelihood of such thermodynamical forcing operating more frequently in the future needs to be considered.
Plain Language Summary
The occurrence of 2019 extreme pIOD event features the strongest easterly wind anomalies and southerly wind anomalies on record, leading to the strongest wind speed that facilitates the latent cooling to overcome the increased radiative warming over the eastern equatorial Indian Ocean, leading to the unique thermodynamical forcing. This is the first time seen in such extreme pIOD event and is part of a long‐term increasing trend, supported by background changes in SST. As most climate models project a similar SST pattern over the Indian Ocean, it suggests that this unique thermodynamical forcing may operate more frequently under global warming.
Key Points
The 2019 positive Indian Ocean Dipole is a rare extreme event since 1900, second only to the strongest in 1997
Unique to the 2019 event is an air‐sea heat flux forcing the growth of cold anomalies in the eastern Indian Ocean, rather than damping
The unique feature is due to a windspeed‐induced increase in evaporation, supported by a warming pattern as projected for a warming climate
The Indian Ocean dipole is a prominent mode of coupled ocean-atmosphere variability, affecting the lives of millions of people in Indian Ocean rim countries. In its positive phase, sea surface ...temperatures are lower than normal off the Sumatra-Java coast, but higher in the western tropical Indian Ocean. During the extreme positive-IOD (pIOD) events of 1961, 1994 and 1997, the eastern cooling strengthened and extended westward along the equatorial Indian Ocean through strong reversal of both the mean westerly winds and the associated eastward-flowing upper ocean currents. This created anomalously dry conditions from the eastern to the central Indian Ocean along the Equator and atmospheric convergence farther west, leading to catastrophic floods in eastern tropical African countries but devastating droughts in eastern Indian Ocean rim countries. Despite these serious consequences, the response of pIOD events to greenhouse warming is unknown. Here, using an ensemble of climate models forced by a scenario of high greenhouse gas emissions (Representative Concentration Pathway 8.5), we project that the frequency of extreme pIOD events will increase by almost a factor of three, from one event every 17.3 years over the twentieth century to one event every 6.3 years over the twenty-first century. We find that a mean state change--with weakening of both equatorial westerly winds and eastward oceanic currents in association with a faster warming in the western than the eastern equatorial Indian Ocean--facilitates more frequent occurrences of wind and oceanic current reversal. This leads to more frequent extreme pIOD events, suggesting an increasing frequency of extreme climate and weather events in regions affected by the pIOD.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, KISLJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The influence of local conditions and remote climate modes on the interannual variability of oil palm fresh fruit bunches (FFB) total yields in Malaysia and two major regions (Peninsular Malaysia and ...Sabah/Sarawak) is explored. On a country scale, the state of sea-surface temperatures (SST) in the tropical Pacific Ocean during the previous boreal winter is found to influence the regional climate. When El Niño occurs in the Pacific Ocean, rainfall in Malaysia reduces but air temperature increases, generating a high level of water stress for palm trees. As a result, the yearly production of FFB becomes lower than that of a normal year since the water stress during the boreal spring has an important impact on the total annual yields of FFB. Conversely, La Niña sets favorable conditions for palm trees to produce more FFB by reducing chances of water stress risk. The region of the Leeuwin current also seems to play a secondary role through the Ningaloo Niño/ Niña in the interannual variability of FFB yields. Based on these findings, a linear model is constructed and its ability to reproduce the interannual signal is assessed. This model has shown some skills in predicting the total FFB yield.
Many parts of East Africa experienced extremely dry conditions during the short rains season of October–December 2021. It was predicted a few months before by the ensemble seasonal prediction system ...based on the SINTEX‐F climate model. The analysis of co‐variability of inter‐member anomalies has revealed that the 2021 negative Indian Ocean Dipole was responsible for these unusually dry conditions over East Africa. We also show that a hybrid statistical‐dynamical framework is more skillful than the SINTEX‐F model at predicting drought in East Africa on longer lead time, which may help people to take necessary mitigation measures to reduce the devastating impact of the drought.
Plain Language Summary
Many parts of East Africa experienced extremely dry conditions during the short rains season (October–December) of 2021. Such a devastating drought in East Africa leads to unsafe drinking water, food insecurity, and other socio‐economic issues. We found the 2021 negative Indian Ocean Dipole (IOD) was responsible for these unusually dry conditions over East Africa. The IOD is an intrinsic ocean–atmosphere coupled climate phenomenon in the tropical Indian Ocean with cold (warm) sea surface temperature anomalies and reduced (enhanced) rainfall in the western (eastern) tropical Indian Ocean during its negative phase. Some of the devastating droughts (severe floods) in East Africa are observed during negative (positive) IOD years, respectively. Improved predictions of the IOD and its impacts may help us develop necessary mitigation measures to reduce the devastating impacts.
Key Points
East Africa suffered from an extreme drought during the short rains season of October–December 2021
The 2021 negative Indian Ocean Dipole was responsible for the devastating drought and played a key role in its seasonal predictability
A hybrid statistical‐dynamical prediction of drought in East Africa on longer lead time may help people to take mitigation measures
Many parts of East Asia, including Japan, experienced extremely warm conditions during the 2019–2020 winter. These were successfully predicted in October of 2019 by the 108‐member ensemble seasonal ...prediction system based on the SINTEX‐F climate model. By analyzing covariability of intermember anomalies defined as deviations from the ensemble mean, we have found that the active convection over the western pole of the Indian Ocean Dipole (IOD) caused these unusual conditions over East Asia by generating the meander of the subtropical jet.
Plain Language Summary
The Indian Ocean Dipole (IOD) is an intrinsic ocean‐atmosphere coupled climate phenomenon in the tropical Indian Ocean with warm (cold) sea surface temperature anomalies with enhanced (reduced) rainfall in the western (eastern) tropical Indian Ocean during a positive phase. A strong and long‐lasting positive IOD event occurred in 2019, which caused climate‐related disasters in countries not only around the Indian Ocean but also East Asia, including Japan. Successful prediction of the teleconnection of such a super event may contribute to reducing the risks of socioeconomic losses under suitable measures for adaptation and mitigation.
Key Points
Many parts of East Asia, including Japan, experienced extremely warm conditions during the 2019–2020 winter
Warm SST anomalies associated with the super Indian Ocean Dipole in 2019 persisted even through the winter
Prolonged active convection over the western pole of the Indian Ocean Dipole may explain the unusual winter
Present work uses 1979-2005 monthly observational data to study the impacts of El Nino Modoki on dry/wet conditions in the Pacific rim during boreal summer. The El Nino Modoki phenomenon is ...characterized by the anomalously warm central equatorial Pacific flanked by anomalously cool regions in both west and east. Such zonal SST gradients result in anomalous two-cell Walker Circulation over the tropical Pacific, with a wet region in the central Pacific. There are two mid-tropospheric wave trains passing over the extratropical and subtropical North Pacific. They contain a positive phase of a Pacific-Japan pattern in the northwestern Pacific, and a positive phase of a summertime Pacific-North American pattern in the northeastern Pacific/North America region. The western North Pacific summer monsoon is enhanced, while the East Asian summer monsoon is weakened. In the South Pacific, there is a basin-wide low in the mid-latitude with enhanced Australian high and the eastern South Pacific subtropical high. Such an atmospheric circulation pattern favors a dry rim surrounding the wet central tropical Pacific. The El Nino Modoki and its climate impacts are very different from those of El Nino. Possible geographical regions for dry/wet conditions influenced by El Nino Modoki and El Nino are compared. The two phenomena also have very different temporal features. El Nino Modoki has a large decadal background while El Nino is predominated by interannual variability. Mixing-up the two different phenomena may increase the difficulty in understanding their mechanisms, climate impacts, and uncertainty in their predictions.
Anatomy of Indian heatwaves Ratnam, J V; Behera, Swadhin K; Ratna, Satyaban B ...
Scientific reports,
04/2016, Letnik:
6, Številka:
1
Journal Article
Recenzirano
Odprti dostop
India suffers from major heatwaves during March-June. The rising trend of number of intense heatwaves in recent decades has been vaguely attributed to global warming. Since the heat waves have a ...serious effect on human mortality, root causes of these heatwaves need to be clarified. Based on the observed patterns and statistical analyses of the maximum temperature variability, we identified two types of heatwaves. The first-type of heatwave over the north-central India is found to be associated with blocking over the North Atlantic. The blocking over North Atlantic results in a cyclonic anomaly west of North Africa at upper levels. The stretching of vorticity generates a Rossby wave source of anomalous Rossby waves near the entrance of the African Jet. The resulting quasi-stationary Rossby wave-train along the Jet has a positive phase over Indian subcontinent causing anomalous sinking motion and thereby heatwave conditions over India. On the other hand, the second-type of heatwave over the coastal eastern India is found to be due to the anomalous Matsuno-Gill response to the anomalous cooling in the Pacific. The Matsuno-Gill response is such that it generates northwesterly anomalies over the landmass reducing the land-sea breeze, resulting in heatwaves.
This paper explores merits of 100-ensemble simulations from a single dynamical seasonal prediction system by evaluating differences in skill scores between ensembles predictions with few (~10) and ...many (~100) ensemble members. A 100-ensemble retrospective seasonal forecast experiment for 1983–2015 is beyond current operational capability. Prediction of extremely strong ENSO and the Indian Ocean dipole (IOD) events is significantly improved in the larger ensemble. It indicates that the ensemble size of 10 members, used in some operational systems, is not adequate for the occurrence of 15% tails of extreme climate events, because only about 1 or 2 members (approximately 15% of 12) will agree with the observations. We also showed an ensemble size of about 50 members may be adequate for the extreme El Niño and positive IOD predictions at least in the present prediction system. Even if running a large-ensemble prediction system is quite costly, improved prediction of disastrous extreme events is useful for minimizing risks of possible human and economic losses.
Celotno besedilo
Dostopno za:
BFBNIB, DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
El Niño Modoki and its possible teleconnection Ashok, Karumuri; Behera, Swadhin K.; Rao, Suryachandra A. ...
Journal of Geophysical Research - Oceans,
November 2007, Letnik:
112, Številka:
C11
Journal Article
Recenzirano
Using observed data sets mainly for the period 1979–2005, we find that anomalous warming events different from conventional El Niño events occur in the central equatorial Pacific. This unique warming ...in the central equatorial Pacific associated with a horseshoe pattern is flanked by a colder sea surface temperature anomaly (SSTA) on both sides along the equator. empirical orthogonal function (EOF) analysis of monthly tropical Pacific SSTA shows that these events are represented by the second mode that explains 12% of the variance. Since a majority of such events are not part of El Niño evolution, the phenomenon is named as El Niño Modoki (pseudo‐El Niño) (“Modoki” is a classical Japanese word, which means “a similar but different thing”). The El Niño Modoki involves ocean‐atmosphere coupled processes which include a unique tripolar sea level pressure pattern during the evolution, analogous to the Southern Oscillation in the case of El Niño. Hence the total entity is named as El Niño–Southern Oscillation (ENSO) Modoki. The ENSO Modoki events significantly influence the temperature and precipitation over many parts of the globe. Depending on the season, the impacts over regions such as the Far East including Japan, New Zealand, western coast of United States, etc., are opposite to those of the conventional ENSO. The difference maps between the two periods of 1979–2004 and 1958–1978 for various oceanic/atmospheric variables suggest that the recent weakening of equatorial easterlies related to weakened zonal sea surface temperature gradient led to more flattening of the thermocline. This appears to be a cause of more frequent and persistent occurrence of the ENSO Modoki event during recent decades.
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