This study identifies break events of the South China Sea(SCS)summer monsoon(SCSSM)based on 42 years of data from 1979 to 2020,and investigates their statistical characteristics and associated atmospheric anomalies.A ...This study identifies break events of the South China Sea(SCS)summer monsoon(SCSSM)based on 42 years of data from 1979 to 2020,and investigates their statistical characteristics and associated atmospheric anomalies.A total of 214 break events are identified by examining the convection evolution during each monsoon season.It is found that most events occur between June and September and show a roughly even distribution.Short-lived events(3–7 days)are more frequent,accounting for about two thirds of total events,with the residual one third for long-lived events(8–24 days).The SCSSM break is featured by drastic variations in various atmospheric variables.Particularly,the convection and precipitation change from anomalous enhancement in adjoining periods to a substantial suppression during the break,with the differences being more than 60 W m−2 for outgoing longwave radiation(OLR)and 10 mm d−1 for precipitation.This convection/precipitation suppression is accompanied by an anomalous anticyclone in the lower troposphere,corresponding to a remarkable westward retreat of the monsoon trough from the Philippine Sea to the Indochina Peninsula,which reduces the transportation of water vapor into the SCS.Besides,the pseudo-equivalent potential temperature()declines sharply,mainly attributable to the local specific humidity reduction caused by downward dry advection.Furthermore,it is found that the suppressed convection and anomalous anticyclone responsible for the monsoon break form near the equatorial western Pacific and then propagate northwestward to the SCS.展开更多
During the summer monsoon season, strong coastal upwelling occurs along the southwest coast of India and at the southern tip of India, which cools the surface temperature of the waters around these regions. The summer...During the summer monsoon season, strong coastal upwelling occurs along the southwest coast of India and at the southern tip of India, which cools the surface temperature of the waters around these regions. The summer monsoon current carries the upwelled cold waters into the Bay of Bengal and forms the ‘cold pool of the Bay of Bengal', with its core south of Sri Lanka and over the southcentral Bay of Bengal. The present study focuses on the intrusion of these cold waters into the south of the Bay of Bengal, its interannual variability, and its association with the surface wind during the break phase of the summer monsoon, when strong westerly surface winds flow south of 10°N.The authors hypothesize that the enhanced cooling in the cold pool region during monsoon spells is associated with the strong westerly wind stress there during the break spells of the monsoon.Seven cases of long break monsoon spells that occurred during the nine years from 2001 to 2009 are analyzed, and the results confirm our hypothesis.展开更多
Boreal summer intraseasonal oscillation(BSISO) of lower tropospheric ozone is observed in the Indian summer monsoon(ISM) region on the basis of ERA-Interim reanalysis data and ozonesonde data from the World Ozone and ...Boreal summer intraseasonal oscillation(BSISO) of lower tropospheric ozone is observed in the Indian summer monsoon(ISM) region on the basis of ERA-Interim reanalysis data and ozonesonde data from the World Ozone and Ultraviolet Radiation Data Centre. The 30–60-day intraseasonal variation of lower-tropospheric ozone shows a northwest–southeast pattern with northeastward propagation in the ISM region. The most significant ozone variations are observed in the Maritime Continent and western North Pacific. In the tropics, ozone anomalies extend from the surface to 300 hPa; however, in extratropical areas, it is mainly observed under 500 hPa. Precipitation caused by BSISO plays a dominant role in modulating the BSISO of lower-tropospheric ozone in the tropics, causing negative/positive ozone anomalies in phases 1–3/5–6. As the BSISO propagates northeastward to the western North Pacific, horizontal transport becomes relatively more important, increasing/reducing tropospheric ozone via anticyclonic/cyclonic anomalies over the western North Pacific in phases 3–4/7–8.As two extreme conditions of the ISM, most of its active/break events occur in BSISO phases 4–7/1–8 when suppressed/enhanced convection appears over the equatorial eastern Indian Ocean and enhanced/suppressed convection appears over India, the Bay of Bengal, and the South China Sea. As a result, the BSISO of tropospheric ozone shows significant positive/negative anomalies over the Maritime Continent, as well as negative/positive anomalies over India, the Bay of Bengal,and the South China Sea in active/break spells of the ISM. This BSISO of tropospheric ozone is more remarkable in break spells than in active spells of the ISM, due to the stronger amplitude of BSISO in the former.展开更多
Based on ECMWF reanalysis data of 1979-1993 and TBB data of GMS,an analysis on the onset and its activities of the summer monsoon over the South China Sea (SCS) is made.It is found that the mean onset date is around 1...Based on ECMWF reanalysis data of 1979-1993 and TBB data of GMS,an analysis on the onset and its activities of the summer monsoon over the South China Sea (SCS) is made.It is found that the mean onset date is around 16 May,the latest onset is at beginning of June.There is a marked interannual variation of the onset date.There occurs marked southwesterly wind over the SCS in the last dekad of April in some years,but it only persists for a short period,and then,the easterly flow appears again.In the beginning of June,the true onset occurs.From the end of April to the middle of May prior to the onset,strong southwesterly wind appears to the north of 15°N over the SCS,which could not be treated as the onset of the SCS summer monsoon.These strong westerlies are due to the southward propagation of cold front or the strengthening of the subtropical high in the SCS.After the onset,there are active and break periods of the southwesterly summer monsoon,the average break period is about 15 days in one year (from onset of summer monsoon to 20 August).展开更多
Using a low-order spectral model derived from the equatorial equilibrium model, possible physical mechanisms are interpreted by the theory of multiple equilibria states for the active and break phases of the South Asi...Using a low-order spectral model derived from the equatorial equilibrium model, possible physical mechanisms are interpreted by the theory of multiple equilibria states for the active and break phases of the South Asian Monsoon, with consideration of the effects of heating by cumulus heating and cooling by radiation. The result shows that the South Asian Monsoon is active when the cumulus convection intensifies (or the radiation cooling weakens). the monsoon breaks when the convection weakens (or the cooling intensifies). It is consistent with the hypothesis of cloud-radiation by Krishnamurti et al.展开更多
基金supported by the National Natural Science Foundation of China[grant number 42275025]the Youth Innovation Promotion Association of the Chinese Academy of Sciences[grant number 2023084].
基金supported by the National Natural Science Foundation of China(Grant No.42275025).
文摘This study identifies break events of the South China Sea(SCS)summer monsoon(SCSSM)based on 42 years of data from 1979 to 2020,and investigates their statistical characteristics and associated atmospheric anomalies.A total of 214 break events are identified by examining the convection evolution during each monsoon season.It is found that most events occur between June and September and show a roughly even distribution.Short-lived events(3–7 days)are more frequent,accounting for about two thirds of total events,with the residual one third for long-lived events(8–24 days).The SCSSM break is featured by drastic variations in various atmospheric variables.Particularly,the convection and precipitation change from anomalous enhancement in adjoining periods to a substantial suppression during the break,with the differences being more than 60 W m−2 for outgoing longwave radiation(OLR)and 10 mm d−1 for precipitation.This convection/precipitation suppression is accompanied by an anomalous anticyclone in the lower troposphere,corresponding to a remarkable westward retreat of the monsoon trough from the Philippine Sea to the Indochina Peninsula,which reduces the transportation of water vapor into the SCS.Besides,the pseudo-equivalent potential temperature()declines sharply,mainly attributable to the local specific humidity reduction caused by downward dry advection.Furthermore,it is found that the suppressed convection and anomalous anticyclone responsible for the monsoon break form near the equatorial western Pacific and then propagate northwestward to the SCS.
基金a donation from Trond Mohn,c/o Frank Mohn AS,for financing part of the workGrants from the Nansen Scientific Society,EU-FP7[project number 295092],INDOMARECLIM
文摘During the summer monsoon season, strong coastal upwelling occurs along the southwest coast of India and at the southern tip of India, which cools the surface temperature of the waters around these regions. The summer monsoon current carries the upwelled cold waters into the Bay of Bengal and forms the ‘cold pool of the Bay of Bengal', with its core south of Sri Lanka and over the southcentral Bay of Bengal. The present study focuses on the intrusion of these cold waters into the south of the Bay of Bengal, its interannual variability, and its association with the surface wind during the break phase of the summer monsoon, when strong westerly surface winds flow south of 10°N.The authors hypothesize that the enhanced cooling in the cold pool region during monsoon spells is associated with the strong westerly wind stress there during the break spells of the monsoon.Seven cases of long break monsoon spells that occurred during the nine years from 2001 to 2009 are analyzed, and the results confirm our hypothesis.
基金support from the World Meteorological Organization–Global Atmosphere Watch Program/WOUDC (https://www.woudc.org/home.php) with respect to the ozonesonde dataset
文摘Boreal summer intraseasonal oscillation(BSISO) of lower tropospheric ozone is observed in the Indian summer monsoon(ISM) region on the basis of ERA-Interim reanalysis data and ozonesonde data from the World Ozone and Ultraviolet Radiation Data Centre. The 30–60-day intraseasonal variation of lower-tropospheric ozone shows a northwest–southeast pattern with northeastward propagation in the ISM region. The most significant ozone variations are observed in the Maritime Continent and western North Pacific. In the tropics, ozone anomalies extend from the surface to 300 hPa; however, in extratropical areas, it is mainly observed under 500 hPa. Precipitation caused by BSISO plays a dominant role in modulating the BSISO of lower-tropospheric ozone in the tropics, causing negative/positive ozone anomalies in phases 1–3/5–6. As the BSISO propagates northeastward to the western North Pacific, horizontal transport becomes relatively more important, increasing/reducing tropospheric ozone via anticyclonic/cyclonic anomalies over the western North Pacific in phases 3–4/7–8.As two extreme conditions of the ISM, most of its active/break events occur in BSISO phases 4–7/1–8 when suppressed/enhanced convection appears over the equatorial eastern Indian Ocean and enhanced/suppressed convection appears over India, the Bay of Bengal, and the South China Sea. As a result, the BSISO of tropospheric ozone shows significant positive/negative anomalies over the Maritime Continent, as well as negative/positive anomalies over India, the Bay of Bengal,and the South China Sea in active/break spells of the ISM. This BSISO of tropospheric ozone is more remarkable in break spells than in active spells of the ISM, due to the stronger amplitude of BSISO in the former.
基金the State Ministry of Science and Technology under the key project A of SCSMEXthe project of Chinese Academy of Sciences under Contract KZ951-408
文摘Based on ECMWF reanalysis data of 1979-1993 and TBB data of GMS,an analysis on the onset and its activities of the summer monsoon over the South China Sea (SCS) is made.It is found that the mean onset date is around 16 May,the latest onset is at beginning of June.There is a marked interannual variation of the onset date.There occurs marked southwesterly wind over the SCS in the last dekad of April in some years,but it only persists for a short period,and then,the easterly flow appears again.In the beginning of June,the true onset occurs.From the end of April to the middle of May prior to the onset,strong southwesterly wind appears to the north of 15°N over the SCS,which could not be treated as the onset of the SCS summer monsoon.These strong westerlies are due to the southward propagation of cold front or the strengthening of the subtropical high in the SCS.After the onset,there are active and break periods of the southwesterly summer monsoon,the average break period is about 15 days in one year (from onset of summer monsoon to 20 August).
文摘Using a low-order spectral model derived from the equatorial equilibrium model, possible physical mechanisms are interpreted by the theory of multiple equilibria states for the active and break phases of the South Asian Monsoon, with consideration of the effects of heating by cumulus heating and cooling by radiation. The result shows that the South Asian Monsoon is active when the cumulus convection intensifies (or the radiation cooling weakens). the monsoon breaks when the convection weakens (or the cooling intensifies). It is consistent with the hypothesis of cloud-radiation by Krishnamurti et al.
