Seasonal changes exhibit climate changes, so models can predict future climate change accurately only if they can reproduce seasonal cycle accu-rately. Further, seasonal changes are much larger than the changes even i...Seasonal changes exhibit climate changes, so models can predict future climate change accurately only if they can reproduce seasonal cycle accu-rately. Further, seasonal changes are much larger than the changes even in long period of centuries. Thus it is unwise to ignore large ones compared to small climate change. In this paper, we determine how accurately a suite of ten coupled general circulation models reproduce the observed seasonal cycle in rainfall of the tropics. The seasonal cycles in rainfall of global tropics are known as monsoons. We found that the models can reasonably reproduce the seasonal cycle in rainfall, thus are useful in climate prediction and simulation of global monsoons.展开更多
The relationships between ENSO and the East Asian-western North Pacific monsoon simulated by the Flexible Global Ocean-Atmosphere-Land System model, Spectral Version 2 （FGOALS-s2）, a state-of-the-art coupled general...The relationships between ENSO and the East Asian-western North Pacific monsoon simulated by the Flexible Global Ocean-Atmosphere-Land System model, Spectral Version 2 （FGOALS-s2）, a state-of-the-art coupled general circulation model （CGCM）, are evaluated. For E1 Nino developing summers, FGOALS-s2 reproduces the anomalous cyclone over the western North Pacific （WNP） and associated negative precipita- tion anomalies in situ. In the observation, the anomalous cyclone is transformed to an anomalous anticyclone over the WNP （WNPAC） during E1 Nifio mature winters. The model reproduces the WNPAC and associated positive precipitation anomalies over southeastern China during winter. However, the model fails to simu- late the asymmetry of the wintertime circulation anomalies over the WNP between E1 Nifio and La Nifia. The simulated anomalous cyclone over the WNP （WNPC） associated with La Nifia is generally symmetric about the WNPAC associated with E1 Nifio, rather than shifted westward as that in the observation. The discrepancy can partially explain why simulated La Nifia events decay much faster than observed. In the observation, the WNPAC maintains throughout the E1 Nifio decaying summer under the combined effects of local forcing of the WNP cold sea surface temperature anomaly （SSTA） and remote forcing from basin- wide warming in the tropical Indian Ocean. FGOALS-s2 captures the two mechanisms and reproduces the WNPAC throughout the summer. However, owing to biases in the mean state, the precipitation anomalies over East Asia, especially those of the Meiyu rain belt, are much weaker than that in the observation.展开更多
Satellite observations of SSTs have revealed the existence of unstable waves in the equatorial eastern Pacific and Atlantic oceans. These waves have a 20-40-day periodicity with westward phase speeds of 0.4-0.6 m s^-1...Satellite observations of SSTs have revealed the existence of unstable waves in the equatorial eastern Pacific and Atlantic oceans. These waves have a 20-40-day periodicity with westward phase speeds of 0.4-0.6 m s^-1 and wavelengths of 1000-2000 km during boreal summer and fall. They are generally called tropical instability waves （TIWs）. This study investigates TIWs simulated by a high-resolution coupled atmosphere-ocean general circulation model （AOGCM）. The horizontal resolution of the model is 120 km in the atmosphere, and 30 km longitude by 20 km latitude in the ocean. Model simulations show good agreement with the observed main features associated with TIWs. The results of energetics analysis reveal that barotropic energy conversion is responsible for providing the main energy source for TIWs by extracting energy from the meridional shear of the climatological-mean equatorial currents in the mixed layer. This deeper and northward-extended wave activity appears to gain its energy through baroclinic conversion via buoyancy work, which further contributes to the asymmetric distribution of TIWs. It is estimated that the strong cooling effect induced by equatorial upwelling is partially （-30%-40%） offset by the equatorward heat flux due to TIWs in the eastern tropical Pacific during the seasons when TIWs are active. The atmospheric mixed layer just above the sea surface responds to the waves with enhanced or reduced vertical mixing. Furthermore, the changes in turbulent mixing feed back to sea surface evaporation, favoring the westward propagation of TIWs. The atmosphere to the south of the Equator also responds to TIWs in a similar way, although TIWs are much weaker south of the Equator.展开更多
We present an overview of the El Ni?o–Southern Oscillation(ENSO) stability simulation using the Chinese Academy of Meteorological Sciences climate system model(CAMS-CSM). The ENSO stability was quantified based on th...We present an overview of the El Ni?o–Southern Oscillation(ENSO) stability simulation using the Chinese Academy of Meteorological Sciences climate system model(CAMS-CSM). The ENSO stability was quantified based on the Bjerknes(BJ) stability index. Generally speaking, CAMS-CSM has the capacity of reasonably representing the BJ index and ENSO-related air–sea feedback processes. The major simulation biases exist in the underestimated thermodynamic damping and thermocline feedbacks. Further diagnostic analysis reveals that the underestimated thermodynamic feedback is due to the underestimation of the shortwave radiation feedback, which arises from the cold bias in mean sea surface temperature(SST) over central–eastern equatorial Pacific(CEEP). The underestimated thermocline feedback is attributed to the weakened mean upwelling and weakened wind–SST feedback(μ_a) in the model simulation compared to observation. We found that the weakened μ_a is also due to the cold mean SST over the CEEP.The study highlights the essential role of reasonably representing the climatological mean state in ENSO simulations.展开更多
Using the ECMWF reanalysis daily 200-hPa wind data during the two 20-yr periods from 1958 to 1977 and from 1980 to 1999, the characteristics and changes of Intraseasonal Oscillations （ISO） in the two periods associa...Using the ECMWF reanalysis daily 200-hPa wind data during the two 20-yr periods from 1958 to 1977 and from 1980 to 1999, the characteristics and changes of Intraseasonal Oscillations （ISO） in the two periods associated with global warming are analyzed and compared in this study. It is found that during the last 20 years, the ISO has weakened in the central equatorial Pacific Ocean, but becomes more active in the central Indian Ocean and the Bay of Bengal; under the background of the global warming, increase in the amplitude of ISO intensity suggests that the ISO has become more active than before, with an obvious seasonal cycle, i.e., strong during winter and spring, but weak during summer and autumn; the energy of the upper tropospheric zonal winds has more concentrated in wave numbers 1-3, and the frequency of ISO tended to increase. Comparison between the results of control experiment and CO2 increase （1% per year） experiment of FGOALS-1.0g （developed at LASG） with the first and second 20-yr observations, is also performed, respectively. The comparative results show that the spatial structure of the ISO was well reproduced, but the strength of ISO was underestimated. On the basis of space-time spectral analysis, it is found that the simulated ISO contains too much high frequency waves, leading to the underestiniation of ISO intensity due to the dispersion of ISO energy. However, FGOALS-1.0g captured the salient features of ISO under the global warming background by two contrast experiments, such as the vitality and frequency-increasing of ISO in the central Indian Ocean and the Bay of Bengal.展开更多
文摘Seasonal changes exhibit climate changes, so models can predict future climate change accurately only if they can reproduce seasonal cycle accu-rately. Further, seasonal changes are much larger than the changes even in long period of centuries. Thus it is unwise to ignore large ones compared to small climate change. In this paper, we determine how accurately a suite of ten coupled general circulation models reproduce the observed seasonal cycle in rainfall of the tropics. The seasonal cycles in rainfall of global tropics are known as monsoons. We found that the models can reasonably reproduce the seasonal cycle in rainfall, thus are useful in climate prediction and simulation of global monsoons.
基金supported by the Chinese Academy of Sciences Strategic Priority Research Program(Grant No.XDA05110305)the National Program on Key Basic Research Project(2010CB951904)+2 种基金the National Natural Science Foundation of China(Grant Nos.41005040,41023002 and 40890054)the National High-Tech Research and Development Plan of China(2010AA012302)the China Meteorological Administration(Grant No.GYHY201006019)
文摘The relationships between ENSO and the East Asian-western North Pacific monsoon simulated by the Flexible Global Ocean-Atmosphere-Land System model, Spectral Version 2 （FGOALS-s2）, a state-of-the-art coupled general circulation model （CGCM）, are evaluated. For E1 Nino developing summers, FGOALS-s2 reproduces the anomalous cyclone over the western North Pacific （WNP） and associated negative precipita- tion anomalies in situ. In the observation, the anomalous cyclone is transformed to an anomalous anticyclone over the WNP （WNPAC） during E1 Nifio mature winters. The model reproduces the WNPAC and associated positive precipitation anomalies over southeastern China during winter. However, the model fails to simu- late the asymmetry of the wintertime circulation anomalies over the WNP between E1 Nifio and La Nifia. The simulated anomalous cyclone over the WNP （WNPC） associated with La Nifia is generally symmetric about the WNPAC associated with E1 Nifio, rather than shifted westward as that in the observation. The discrepancy can partially explain why simulated La Nifia events decay much faster than observed. In the observation, the WNPAC maintains throughout the E1 Nifio decaying summer under the combined effects of local forcing of the WNP cold sea surface temperature anomaly （SSTA） and remote forcing from basin- wide warming in the tropical Indian Ocean. FGOALS-s2 captures the two mechanisms and reproduces the WNPAC throughout the summer. However, owing to biases in the mean state, the precipitation anomalies over East Asia, especially those of the Meiyu rain belt, are much weaker than that in the observation.
基金supported by the Postdoctoral Fellow ship given by the Japan Society for the Promotion of Sciencesupported by the Kyousei and Kakushin Projects of the ministry of Education, Culture,Sports, Science, and Technology of Japan, the Core Research for Evolutional Science and Technology of the Japan Science and Technology Agencythe National Basic Research Program of China (Grant No. 2006CB403606)
文摘Satellite observations of SSTs have revealed the existence of unstable waves in the equatorial eastern Pacific and Atlantic oceans. These waves have a 20-40-day periodicity with westward phase speeds of 0.4-0.6 m s^-1 and wavelengths of 1000-2000 km during boreal summer and fall. They are generally called tropical instability waves （TIWs）. This study investigates TIWs simulated by a high-resolution coupled atmosphere-ocean general circulation model （AOGCM）. The horizontal resolution of the model is 120 km in the atmosphere, and 30 km longitude by 20 km latitude in the ocean. Model simulations show good agreement with the observed main features associated with TIWs. The results of energetics analysis reveal that barotropic energy conversion is responsible for providing the main energy source for TIWs by extracting energy from the meridional shear of the climatological-mean equatorial currents in the mixed layer. This deeper and northward-extended wave activity appears to gain its energy through baroclinic conversion via buoyancy work, which further contributes to the asymmetric distribution of TIWs. It is estimated that the strong cooling effect induced by equatorial upwelling is partially （-30%-40%） offset by the equatorward heat flux due to TIWs in the eastern tropical Pacific during the seasons when TIWs are active. The atmospheric mixed layer just above the sea surface responds to the waves with enhanced or reduced vertical mixing. Furthermore, the changes in turbulent mixing feed back to sea surface evaporation, favoring the westward propagation of TIWs. The atmosphere to the south of the Equator also responds to TIWs in a similar way, although TIWs are much weaker south of the Equator.
基金Supported by the National Natural Science Foundation of China(41606011 and 91637210)National Key Research and Development Program(2016YFE0102400,2016YFA0600602,and 2018YFC1506002)+3 种基金Basic Scientific Research and Operation Funds of the Chinese Academy of Meteorological Sciences(2017Y007)Startup Funds for Introduced Talents of Nanjing University of Information Science&TechnologyOpen Project Funds of the State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid DynamicsOpen Project Funds of the State Key Laboratory of Loess and Quartary Geology
文摘We present an overview of the El Ni?o–Southern Oscillation(ENSO) stability simulation using the Chinese Academy of Meteorological Sciences climate system model(CAMS-CSM). The ENSO stability was quantified based on the Bjerknes(BJ) stability index. Generally speaking, CAMS-CSM has the capacity of reasonably representing the BJ index and ENSO-related air–sea feedback processes. The major simulation biases exist in the underestimated thermodynamic damping and thermocline feedbacks. Further diagnostic analysis reveals that the underestimated thermodynamic feedback is due to the underestimation of the shortwave radiation feedback, which arises from the cold bias in mean sea surface temperature(SST) over central–eastern equatorial Pacific(CEEP). The underestimated thermocline feedback is attributed to the weakened mean upwelling and weakened wind–SST feedback(μ_a) in the model simulation compared to observation. We found that the weakened μ_a is also due to the cold mean SST over the CEEP.The study highlights the essential role of reasonably representing the climatological mean state in ENSO simulations.
基金Supported by the National Natural Science Foundation of China under Grant Nos.90211011 and 40231004the Science and Technology Department"Eleventh Five"programme under Grant No.2001BA611B01.
文摘Using the ECMWF reanalysis daily 200-hPa wind data during the two 20-yr periods from 1958 to 1977 and from 1980 to 1999, the characteristics and changes of Intraseasonal Oscillations （ISO） in the two periods associated with global warming are analyzed and compared in this study. It is found that during the last 20 years, the ISO has weakened in the central equatorial Pacific Ocean, but becomes more active in the central Indian Ocean and the Bay of Bengal; under the background of the global warming, increase in the amplitude of ISO intensity suggests that the ISO has become more active than before, with an obvious seasonal cycle, i.e., strong during winter and spring, but weak during summer and autumn; the energy of the upper tropospheric zonal winds has more concentrated in wave numbers 1-3, and the frequency of ISO tended to increase. Comparison between the results of control experiment and CO2 increase （1% per year） experiment of FGOALS-1.0g （developed at LASG） with the first and second 20-yr observations, is also performed, respectively. The comparative results show that the spatial structure of the ISO was well reproduced, but the strength of ISO was underestimated. On the basis of space-time spectral analysis, it is found that the simulated ISO contains too much high frequency waves, leading to the underestiniation of ISO intensity due to the dispersion of ISO energy. However, FGOALS-1.0g captured the salient features of ISO under the global warming background by two contrast experiments, such as the vitality and frequency-increasing of ISO in the central Indian Ocean and the Bay of Bengal.
