چکیده:
The impact of the ENSO phenomenon on summer and autumn precipitation anomalies in the southeast region of Iran Ghayour Hassan Ali, Khosravi Mahmoud The present study was conducted to evaluate the effects and signals of the El Niño-Southern Oscillation (ENSO) phenomenon on precipitation amounts and related factors in the southeast region of Iran during the autumn and summer seasons. To achieve a correct understanding regarding the mechanisms of the impact or non-impact of the ENSO phenomenon, precipitation-related anomalies and the factors affecting them during cold and warm phases were evaluated in this study. Using multiple documents and data, and through their analysis, processing, and the application of various statistical test inferences, the existence of specific anomalies during different ENSO phases during the summer and autumn seasons was confirmed. Furthermore, correlation coefficients for precipitation time series, precipitable water, and outgoing longwave radiation (OLR) were calculated, and the relationship between them and ENSO-related indices and patterns was clarified. The present investigation proves that precipitation amounts during warm phases in the autumn season are significantly higher than normal conditions and ENSO cold phases. Although regional differences in responses to ENSO exist. In the summer seasons during warm phases, summer drought conditions generally persist and summer precipitation reaches its minimum; whereas in cold phases, contrary to the autumn season, wetter and more humid conditions than usual occur in parts of the region that receive these precipitations. The above findings were tested using statistical methods based on the proposed hypotheses, and detailed results confirm the aforementioned hypotheses in most cases. Due to the length of the discussion, it is not possible to address all synoptic aspects. Therefore, in this article, the changes in the paths of the Subtropical Jet (STJ) and Polar Jet (PEJ) during warm and cold ENSO phases, and their impact on moisture transport and the creation or non-occurrence of precipitation, were investigated. The evidence and analyses conducted show that warm ENSO phases during the autumn season are usually accompanied by higher-than-average rainfall and atmospheric falls due to the shifting of jet stream paths to more southern latitudes and more zonal movements. \Maximum autumn precipitation in most stations of the region has been associated with the strongest El Niños (1997 and 1982). Given the variable nature of the ENSO phenomenon and the assumption that no two El Niño events are exactly alike, it is evident that the intensity and extent of their impacts also differ.
خلاصه ماشینی:
The evidence and analyses conducted show that ENSO warm phases during the autumn season are usually accompanied by higher-than-average rainfall and atmospheric precipitation due to the shifting of jet stream paths to lower latitudes and more zonal movements.
This means that warm phases (El Nino) are generally accompanied by an increase in precipitable water, especially in the parts (Refer to the page image) Map 1: Correlation coefficient of Columnar Precipitable Water (CPW) in the southeast Iran region with the (NINO3-4) index during the autumn season (Source: CDC is the eastern desert part of the region.
Table 2: Difference in Columnar Precipitable Water (CPW) levels during autumn and summer seasons in the southeast Iran region during ENSO and non-ENSO phases (Refer to the page image) Map 2: Precipitable water anomalies (kg/m2) in the southeast Iran region during 4 strong El Nino autumn events C: Jet Stream Jet streams play an important role in atmospheric movements.
To test the hypothesis that the jet stream path changes under ENSO conditions, maps of wind direction and speed at the 500, 300, and 200 hPa levels in the Northern Hemisphere during warm, cold, and normal conditions, as well as index El Nino events, were prepared.
The results of calculations, interpretation of maps, and statistical analysis of various atmospheric levels of elements related to precipitation, some of the most important of which were discussed in this article, indicate the direct and indirect effects of the ENSO phenomenon and its teleconnection patterns on the climatic conditions of the autumn and summer seasons in the region.
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