The Influence Of Boreal Summer Intraseasonal Oscillation On Heatwave And Tropical Cyclone And Its Prediction Application

China is located in the East Asian monsoon region,where weather and climate disasters occur frequently.Compared with weather forecast and climate prediction,the study of predictability and methods of extended-range predictions for weather disasters developed lately.Previous studies are more focused on the influence of intraseasoanl oscillation(ISO)on precipitation,but relatively less attention has been paid to the mechanism of intraseasonal variabilities of heatwave and tropical cyclones(TCs)in summer and their extended-range prediction methods.Based on several reanalysis datasets and intraseasonal forecast products,the mechanisms of intraseasonal variabilities of East Asia summer heatwave and tropical cyclones activities are deeply explored by conducting numerical sensitive experiments,and utilizing several climate diagnose methods.Based on these basics,the predictability source of extended-range prediction is also explored,and try to develop extended-range prediction model for TCs.Boreal summer intraseasonal oscillation(BSISO)is one of the most important predictability source of extended prediction in East Asia.BSISO contains two modes,which is the well-known Madden–Julian Oscillation(MJO),characterized by a periodicity of 30–90 days,and the 10–30 days' quasi-biweekly oscillation(QBWO).Compared with the MJO,which has had several real-time indices proposed for monitoring and predicting its state,there are very few equivalents for the QBWO.Firstly,new QBWO indices are proposed.These new QBWO indices and MJO index are used to reveal the general features of East Asia summer heatwave and related physical mechanism influenced by two modes of BSISO.The influence of BSISO to extended-range prediction skills of heatwave and its predictability are discussed,based on the heatwave prediction results from subseasonal-to-seasonal(S2S)operational forecast models.For the study of the influence of BSISO on the TC activity in the western North Pacific(WNP),the previous studies mainly focus on all the TCs(including TCs with different genesis regions and different trajectories)in the WNP.Different from previous studies,TCs in the WNP are classified into several track patterns by utilizing an objective statistical method in this paper,to explore how dose BSISO influence the genesis,moving trajectories and intensities of individual TC clusters.(1)New real-time indices based on the EEOF analysis for the QBWO over the Asian summer monsoon region are developed.Given that EEOF analysis is arguably more suitable than EOF analysis for capturing the canonical spatial and temporal structure of a propagating wave system,we introduce two new indices for real-time monitoring of the QBWO over the tropical western North Pacific(WNP)and Indian Ocean(IO),separately,by projecting outgoing longwave radiation(OLR)anomalies onto the two leading modes of EEOF analysis for the 10–30-day-filtered OLR anomalies over the two basins.The newly proposed QBWO indices faithfully represent the vigorous QBWO activities over the WNP and IO,which are underestimated and/or not necessarily well represented by existing indices.It is also shown that the indices are able to reveal the connections between the QBWO and other pronounced phenomena,such as the onset of the South China Sea and Indian monsoons,the occurrence of extreme rainfall events,and tropical cyclone genesis.Thus,monitoring and predicting the evolution of the QBWO in these two basins based on the new QBWO indices should help in the quest to mitigate future damage caused by weather-related disasters at an extended lead time.(2)Verifying the significant influence and modulation mechanisms of two BSISO modes on the occurrence probabilities,intensities and prone areas of East Asia summer heatwave,and their influence to the predictability of heatwave.The occurrence probabilities of heatwave in the East Asia in different phases of two BSISO modes are calculated based on the new BSISO index.The occurrence of heatwave events in the Yangtze River Basin is linked to the southwesterly anomaly of the high pressure,and anomalous adiabatic heating via anomalous downward,when the depressed convection of the northwestpropagating QBWO signal in the Yangtze River Basin.For MJO,when enhanced MJO convection located in the tropical WNP,the MJO heating also induce a Rossby wave with a high pressure anomaly in the mid-latitude region,resulting subsidence anomaly and clear sky favored increased diabetic heating.The prediction skills of BSISO in the S2 S models are critical to the predictability of heatwave extended-range forecast.(3)Revealing physical process of BSISO in influencing the genesis,moving and intensity of different TC clusters.Seven TC clusters are obtained based on the fuzzy c-means clustering method.The relative contributions of TC Genesis Potential Index(GPI)to individual TC clusters are diagnosed at intraseasonal time-scale.The diagnostic results suggest that the BSISO-related relative humidity is the leading factor contributing to the intraseasonal GPI anomalies for each cluster,followed by BSISO-related low-level absolute vorticity.Besides,BSISO could influence the background steering flow at intraseasonal time-scale by changing the relative strengths and locations of monsoon trough and WNP subtropical high.For the straight-moving TCs(Cluster1,Cluster 5,and Cluster 6),the BSISO-related cyclonic flows appear over the South China Sea and Philippine Sea in the low latitude,leading to enhanced easterly related to the westward extension of the WNP subtropical high.In contrast,the eastward shift of the WNP subtropical high induced by the strengthened BSISO cyclonic flow favors the recurving TCs of Cluster 4 and Cluster 7.The TC intensities for individual clusters are also influenced by the BSISO vertical temperature profile.(4)Developing statistical and hybrid dynamical-statistical TC extended-range prediction models,to forecast TC genesis counts and location and track frequency probability distributions in the WNP at lead time of 3–4 weeks.Based on the understanding of the physical mechanism of the modulation of BSISO to individual TC clusters,and the statistical correlations between previous BSISO-related large-scale fields and TC genesis counts,the statistical extended-range prediction model for TC genesis in the WNP are developed.On the other hands,by utilizing the prediction results from GFDL's FLOR dynamical model and the contemporaneous statistical correlations between TC counts and BSISO-related large-scale fields,the hybrid dynamical-statistical extended-range prediction model are developed.It is shows that the prediction skills of these two extended-range TC prediction model are lead 20–25 days.A probabilistic map of TC tracks at the extended-range timescale is further predicted by incorporating the climatological probability of track distributions of these TC clusters...