Results 1 - 10 of 374
Results 1 - 10 of 374. Search took: 0.062 seconds
|Sort by: date | relevance|
[en] The question of whether it is possible to intentionally modify the El Nino/Southern oscillation (ENSO) cycle is explored as a case study in the dynamics of climate intervention beyond simple temperature adjustment. A plausible control strategy is described, including an estimate of the energy it would require to implement. The intent here is not to suggest that we should do so, but rather that the scale of the required intervention is such that we could intentionally influence ENSO. Simulations use the Cane-Zebiak intermediate complexity model, and demonstrate that depending on the parameter regime, a feedback strategy that dynamically deflects less than 1% of the sunlight over the Nino-3 region of the eastern tropical Pacific could be used to reduce the probability of extreme ENSO events (T>2 deg. C) to near zero, or conversely to enhance the cycle.
[en] Relationships between tropical cyclogenesis (TCG) in the Australian region and modes of various atmospheric and oceanic parameters are investigated for the period 1968-2006. Seven thermal and seven dynamic variables describing the state of moisture transport and wind flow patterns in the atmosphere were analysed. In order to identify the dominant modes of each variable, an empirical orthogonal function (EOF) is applied. The three leading modes of each variable were then considered. This study corroborates previous work showing that El Nino-Southern Oscillation (ENSO) is the leading contributor to TCG in the all-Australian, Western and Eastern Australian regions. The ENSO-linked first EOF of the streamfunction at sigma level 0.2101 shows the strongest relationship with TCG variations in the all-Australian and Eastern regions correlating at 0.73 and 0.62, respectively. In the western Australian region, the first EOF of environmental vertical wind shear shows the strongest skill. TCG frequency in the Northern region is mainly affected by the large-scale wind patterns of the subtropics and mid-latitudes such as the subtropical jet and the Rossby wave train.
[en] Since February 2016, the equatorial quasi-biennial oscillation (QBO) in zonal wind of the lower stratosphere exhibited anomalous behavior. In more detail, it broke down from its typical pattern and the eastward stratospheric winds unexpectedly reversed to a westward direction. We herewith attempt to detect whether this unprecedented event could be considered as a result of plausible long-range correlations in the QBO temporal evolution. The analyses performed using all the available QBO data sets showed that such an interpretation could not be inferred, because the temporal evolution of the equatorial zonal wind in the lower stratosphere does not exhibit power-law behavior. Further, the natural time analysis of the QBO data indicates precursory behavior before the maximization of the zonal wind velocity and that the recent strong El Niño event might be related with the aforementioned unprecedented behavior.
[en] The temporal variability of daily mean maximum and minimum temperatures and seasonal rainfall totals in summer (June to September) measured at 25 stations from 1950 to 2010 was analyzed in light of five climate indices. Long-term trend analysis using the Mann-Kendall method revealed a significant increase in maximum temperatures at 44% of stations and in minimum temperatures at 68% of stations. In contrast, a significant decrease in rainfall totals is observed for 16% of stations. The Lombard test revealed that shifts in mean values of maximum and minimum temperatures occurred after the 1970s decade whereas shifts in mean values of rainfall occurred before that decade. Daily mean maximum and minimum temperatures primarily show a positive correlation with summer (June to September) Atlantic Multidecadal Oscillation (AMO) and Arctic Oscillation (AO) indices, whereas rainfall totals are negatively correlated with the Southern Oscillation Index (SOI). The study shows that, contrary to the generally accepted view, summer warming is more widespread than winter warming in southern Quebec. Climate models used to predict future temperatures must take this into account.
[en] This paper investigates the optimal observational array for improving the initialization of El Niño-Southern Oscillation predictions by exploring the sensitive areas for target observations of two types of El Niño predictions. The sensitive areas are identified by calculating the optimally growing errors (OGEs) of the Zebiak–Cane model, as corrected by the optimal forcing vector that is determined by assimilating the observed sea surface temperature anomalies (SSTAs). It is found that although the OGEs have similar structures for different start months of predictions, the regions covered by much large errors for the SSTA component tend to locate at different zonal positions and depends on the start months. Furthermore, these regions are also in difference between two types of El Niño events. The regions covered by large errors of OGEs represent the sensitive areas for target observations. Considering the dependence of the sensitive areas on related El Niño types and the start months of predictions, the present study propose a quantitative frequency method to determine the sensitive areas for target observations associated with two types of El Niño predictions, which is expected to be applicable for both types of El Niño predictions with different start months. As a result, the sensitive areas that describe the array of target observations are presented with a reversal triangle-like shape locating in the eastern Pacific, specifically the area of 120°W–85°W, 0°S–11°S, and an extension to the west along the equator and then gathering at the 180° longitude and the western boundary. “Hindcast” experiments demonstrated that such observational array is very useful in distinguishing two types of El Niño and superior to the TAO/TRITON array. It is therefore suggested that the observational array provided in the present study is towards the optimal one and the original TAO/TRITON array should be further optimized when applied to predictions of the diversities of El Niño events.
[en] The feasibility of using tree-ring data as a proxy for regional precipitation and ENSO events in the Mediterranean region of California is explored. A transect of moisture-sensitive tree-ring sites, extending from southwestern to north-central California, documents regional patterns of winter precipitation and replicates the regional response to ENSO events in the 20. century. Proxy records of ENSO were used with the tree-ring data to examine precipitation/ENSO patterns in the 18. and 19. centuries. Results suggest some temporal and spatial variability in the regional precipitation response to ENSO over the last three centuries