Numerical Simulation and Comparison Study of the Atmospheric Intraseasonal Oscillation

Daily mean outputs for 12 yr （1978-1989） from two general circulation models （SAMIL-R42L9 and CAM2.0.2） are analyzed and compared with the corresponding NCEP/NCAR reanalysis dataset, and results in two models show clearly that the root-mean square errors （RMSEs） from the simulation of intraseasonal oscillation can take 30-40 percent of the total RMSE, particularly, the distributions of the RMSE in simulating intraseasonal oscillation are almost identical with that of the total RMSE. The maximum RMSE of intraseasonal oscillation height at 500 hPa is shown in the middle latitude regions, but there are also large RMSEs of intraseasonal oscillation wind over the tropical western Pacific and tropical Indian Oceans. The simulated ISO energy in the tropic has very large difference from the result of the NCEP/NCAR reanalysis dataset which means the simulation of tropical atmospheric ISO still possesses serious insufficiency. Therefore, intraseasonal oscillation in the weather and climate numerical simulation is very important, and thus, how to improve the ability of the GCM to simulate the intraseasonal oscillation becomes very significant.

27.3-day and Average 13.6-day Periodic Oscillations in the Earth’s Rotation Rate and Atmospheric Pressure Fields Due to Celestial Gravitation Forcing

Variation in length of day of the Earth （LOD, equivalent to the Earth＇s rotation rate） versus change in atmospheric geopotential height fields and astronomical parameters were analyzed for the years 1962-2006. This revealed that there is a 27.3-day and an average 13.6-day periodic oscillation in LOD and atmospheric pressure fields following lunar revolution around the Earth. Accompanying the alternating change in celestial gravitation forcing on the Earth and its atmosphere, the Earth＇s LOD changes from minimum to maximum, then to minimum, and the atmospheric geopotential height fields in the tropics oscillate from low to high, then to low. The 27.3-day and average 13.6-day periodic atmospheric oscillation in the tropics is proposed to be a type of strong atmospheric tide, excited by celestial gravitation forcing. A formula for a Tidal Index was derived to estimate the strength of the celestial gravitation forcing, and a high degree of correlation was found between the Tidal Index determined by astronomical parameters, LOD, and atmospheric geopotential height. The reason for the atmospheric tide is periodic departure of the lunar orbit from the celestial equator during lunar revolution around the Earth. The alternating asymmetric change in celestial gravitation forcing on the Earth and its atmosphere produces a ＂modulation＂ to the change in the Earth＇s LOD and atmospheric pressure fields.

强弱南海夏季风活动及大气季节内振荡(英文)

The circulation pattern corresponding to the strong / weak summer monsoon in the South China Sea (SCS) region and the associated characteristics of the abnormal rainfall in Eastern China have been studied by using the NECP reanalysis data and precipitation data in China. The results show that the climate variations in China caused by the strong / weak summer monsoon are completely different (even in opposite phase). The analyses of atmospheric intraseasonal oscillation (ISO) activity showed that the atmospheric ISO at 850 hPa near the SCS region is strong (weak) corresponding to the strong (weak) SCS summer monsoon. And the analyses of the circulation pattern of the atmospheric ISO showed that the strong / weak SCS summer monsoon circulation (200 hPa and 850 hPa) result mainly from abnormal atmospheric ISO. This study also reveals that the atmospheric ISO variability in the South China Sea region is usually at opposite phase with one in the Jiang-huai River basin. For example, strong (weak) atmospheric ISO in the SCS region corresponds to the weak (strong) atmospheric ISO in the Jiang-huai River basin. As to the intensity of atmospheric ISO, it is generally exhibits the local exciting characteristics, the longitudinal propagation is weak. Key words The SCS summer monsoon - Atmospheric intraseasonal oscillation - Circulation pattern This was supported by National Key Basic Science Program in China (G1998040903) and State Key Project-SCSMEX.

INFLUENCE OF INTRASEASONAL OSCILLATION ON EAST-ASIAN SUMMER MONSOON

The impact of intraseasonal oscillation on the onset of summer monsoon in the South China Sea (SCS) region is studied by using NCEP reanalysis data,the SCSMEX data and precipitation data in China.It is shown that the onset of summer monsoon in the South China Sea region is closely related to the activity of intraseasonal oscillation.Particularly,the existence of low frequency cyclone over the east of Philippines and its expanding into the South China Sea play an important role in the onset of the SCS summer monsoon.The analyses of the circulation pattern and summer rainfall showed that the climate variations in China caused by the strong and weak summer monsoons are completely different,even are out of the phase.Analyzing the activity of atmospheric intraseasonal oscillation (ISO),we found that the atmospheric ISO at 850 hPa over the SCS and neighboring regions is strong (weak) corresponding to strong (weak) SCS summer monsoon.The comparison of the atmospheric circulation pattern with the circulation pattern of atmospheric ISO showed that strong and weak East-Asian summer monsoon circulations (200 hPa and 850 hPa) should mainly result from the abnormal activity of atmospheric ISO.