The daily outgoing longwave radiation(OLR)field in boreal summer shows significant power spectrum peaks on quasi-biweekly(10–20-day)and intraseasonal(20–80-day)timescales over the Indo–western Pacific warm pool,esp...The daily outgoing longwave radiation(OLR)field in boreal summer shows significant power spectrum peaks on quasi-biweekly(10–20-day)and intraseasonal(20–80-day)timescales over the Indo–western Pacific warm pool,especially over the South China Sea and Bay of Bengal.The quasi-biweekly oscillation(QBWO)originates from offequatorial western North Pacific,and is characterized by a northwest–southeast oriented wave train pattern,propagating northwestward.The intraseasonal oscillation(ISO),on the other hand,originates from the equatorial Indian Ocean and propagates eastward and northward.Why the equatorial mode possesses a 20–80-day periodicity while the off-equatorial mode favors a 10–20-day periodicity is investigated through idealized numerical experiments with a 2.5-layer atmospheric model.In the off-equatorial region,the model simulates,under a realistic three-dimensional summer mean flow,the most unstable mode that has a wave train pattern with a typical zonal wavelength of 6000 km and a period of 10–20 days,propagating northwestward.This is in contrast to the equatorial region,where a Madden–Julian oscillation(MJO)like mode with a planetary(wavenumber-1)zonal scale and a period ranging from 20 to 80 days is simulated.Sensitivity experiments with different initial conditions indicate that the QBWO is an intrinsic mode of the atmosphere in boreal summer in the off-equatorial Indo–western Pacific region under the summer mean state,while the MJO is the most unstable mode in the equatorial region.展开更多
Shanghai experienced the longest rainy days in 2018/2019 winter since 1988. The physical cause of such an unusual climate condition was investigated through the diagnosis of observational data. From a seasonal perspec...Shanghai experienced the longest rainy days in 2018/2019 winter since 1988. The physical cause of such an unusual climate condition was investigated through the diagnosis of observational data. From a seasonal perspective, a long persistent rainy winter was often associated with an El Ni?o condition in the equatorial Pacific. This abnormal oceanic condition induces a remote teleconnection pattern with pronounced low-level southerly anomalies over East China.The wind anomalies transported moisture from tropical oceans and caused persistent rainfall in East Asia. Meanwhile, the local rainfall time series exhibited a strong quasi-biweekly oscillation (QBWO). Three persistent rainy events were identified in the 2018/2019 winter and they all occurred during the active phase of the QBWO. The first two events were associated with a low pressure anomaly west of Shanghai. Southerly anomalies associated with the low pressure system advected high mean moisture into central eastern China, leading to the persistent rainfall there.The third event was associated with a high pressure anomaly in lower troposphere to the east of Shanghai, which induced anomalous southerlies to its west, favoring the occurrence of rainfall in Shanghai. The result suggests the importance of high-frequency variability in affecting seasonal rainfall anomalies.展开更多
基金Supported by the National Key Research and Development Program of China(2018YFC1505805)US NOAA(NA18OAR4310298)+2 种基金US NSF(AGS-1643297)National Natural Science Foundation of China(41875069,41575052,and 41575043)Fund for Collaborative Innovation of Meteorological Science in East China(QYHZ201608).
文摘The daily outgoing longwave radiation(OLR)field in boreal summer shows significant power spectrum peaks on quasi-biweekly(10–20-day)and intraseasonal(20–80-day)timescales over the Indo–western Pacific warm pool,especially over the South China Sea and Bay of Bengal.The quasi-biweekly oscillation(QBWO)originates from offequatorial western North Pacific,and is characterized by a northwest–southeast oriented wave train pattern,propagating northwestward.The intraseasonal oscillation(ISO),on the other hand,originates from the equatorial Indian Ocean and propagates eastward and northward.Why the equatorial mode possesses a 20–80-day periodicity while the off-equatorial mode favors a 10–20-day periodicity is investigated through idealized numerical experiments with a 2.5-layer atmospheric model.In the off-equatorial region,the model simulates,under a realistic three-dimensional summer mean flow,the most unstable mode that has a wave train pattern with a typical zonal wavelength of 6000 km and a period of 10–20 days,propagating northwestward.This is in contrast to the equatorial region,where a Madden–Julian oscillation(MJO)like mode with a planetary(wavenumber-1)zonal scale and a period ranging from 20 to 80 days is simulated.Sensitivity experiments with different initial conditions indicate that the QBWO is an intrinsic mode of the atmosphere in boreal summer in the off-equatorial Indo–western Pacific region under the summer mean state,while the MJO is the most unstable mode in the equatorial region.
基金Supported by the National Key Research and Development Program of China(2018YFC1505806)US NOAA(NA18OAR4310298)+4 种基金US NSF(AGS-1643297)National Natural Science Foundation of China(41875069,41575052,and 41575043)University of Hawaii SOEST(10867)IPRC(1418)National Key Research and Development Program of China Health Risk Assessment Program(2018YFA0606203)。
文摘Shanghai experienced the longest rainy days in 2018/2019 winter since 1988. The physical cause of such an unusual climate condition was investigated through the diagnosis of observational data. From a seasonal perspective, a long persistent rainy winter was often associated with an El Ni?o condition in the equatorial Pacific. This abnormal oceanic condition induces a remote teleconnection pattern with pronounced low-level southerly anomalies over East China.The wind anomalies transported moisture from tropical oceans and caused persistent rainfall in East Asia. Meanwhile, the local rainfall time series exhibited a strong quasi-biweekly oscillation (QBWO). Three persistent rainy events were identified in the 2018/2019 winter and they all occurred during the active phase of the QBWO. The first two events were associated with a low pressure anomaly west of Shanghai. Southerly anomalies associated with the low pressure system advected high mean moisture into central eastern China, leading to the persistent rainfall there.The third event was associated with a high pressure anomaly in lower troposphere to the east of Shanghai, which induced anomalous southerlies to its west, favoring the occurrence of rainfall in Shanghai. The result suggests the importance of high-frequency variability in affecting seasonal rainfall anomalies.
