The authors investigate the characteristics of propagation and the influence on tropical precipitation of 9–29-day intraseasonal variation over midlatitude East Asia during boreal winter, and find that the intraseaso...The authors investigate the characteristics of propagation and the influence on tropical precipitation of 9–29-day intraseasonal variation over midlatitude East Asia during boreal winter, and find that the intraseasonal wind signal can propagate both eastward and southward. In the case of eastward propagation, the intraseasonal wind signal is mainly confined to the midlatitudes, featuring eastward migration of anomalous cyclones and anticyclones. In the case of southward propagation, intraseasonal meridional wind perturbations may extend from the mid to the low latitudes, and even the equatorial region. The accompanying wind convergence/divergence induces anomalous precipitation in the near-equatorial regions, forming a north–south dipole precipitation anomaly pattern between the southern South China Sea and the eastern China– Japan region. An anomalous meridional overturning circulation plays an important role in linking tropical and midlatitude intraseasonal wind and precipitation variations.展开更多
Nighttime enhancements in ionospheric electron density at mid- and low-latitudes are investigated by using the critical frequency of the F2-1ayer （foF2） data measured from ionosonde stations at Okinawa （26.3°N...Nighttime enhancements in ionospheric electron density at mid- and low-latitudes are investigated by using the critical frequency of the F2-1ayer （foF2） data measured from ionosonde stations at Okinawa （26.3°N, 127.8°E, Geomagnetic 15.3°N）, Yamagawa （31.2°N, 130.6°E, Geomagnetic 20.4°N）, Kokubunji （35.7°N, 139.5°E, Geomagnetic 25.5°N）, and Wakkanai （45.4°N, 141.7°E, Geomagnetic 35.4°N） in East Asia during several solar cycles. The results show that there are obvious seasonal and solar activity dependencies of the nighttime electron density enhancements. The enhancements are termed pre-midnight enhancement and post-midnight enhancement, according to the local time when the enhancement appeared. The former has a higher occurrence probability in summer months than in winter months. In contrast, the latter has a larger occurrence probability in winter months than in summer months. Moreover, the nighttime enhancements in electron density are more likely to occur at lower solar activity. These seasonal and solar activity variations of the nighttime enhancements in electron density can be explained in terms of the combined effects of downward plasma flux from the plasmasphere and the neutral winds.展开更多
Using observational data, the East Asian-North Indian Ocean index （]EANI）, which reflects a tropospheric thermal contrast, is found to correlate well with the East Asian summer monsoon （EASM） and associated rainfa...Using observational data, the East Asian-North Indian Ocean index （]EANI）, which reflects a tropospheric thermal contrast, is found to correlate well with the East Asian summer monsoon （EASM） and associated rainfall over eastern China. Corresponding to a higher （lower） IEANI, the EASM at mid-latitudes is stronger （weaker）, and there is more （less） rainfall in North China and less （more） rainfall near the Yangtze River valley. To investigate long-term variation in the EASM, we reconstructed the BC 665AD 1985 IEANI based on reconstructed temperatures in Beijing and Tasmania, Australia. Over the past 2000 years, the reconstructed/EANI generally represents centennial-scale variations in the EASM and rainfall over eastem China. The correlation pattern between the reconstructed IEANI and rainfall over eastern China is similar to modem observations, implying that the correlation feature at centennial scales also occurred over the past 2000 years. With respect to longer-scale （several hundreds to one thousand years） IEANI variations and their correlations with rainfall, further verifications should be performed using various paleoclimatic proxy data.展开更多
基金supported by the National Natural Science Foundation of China [grant numbers 41530425,41721004,41475081,and 41775080]
文摘The authors investigate the characteristics of propagation and the influence on tropical precipitation of 9–29-day intraseasonal variation over midlatitude East Asia during boreal winter, and find that the intraseasonal wind signal can propagate both eastward and southward. In the case of eastward propagation, the intraseasonal wind signal is mainly confined to the midlatitudes, featuring eastward migration of anomalous cyclones and anticyclones. In the case of southward propagation, intraseasonal meridional wind perturbations may extend from the mid to the low latitudes, and even the equatorial region. The accompanying wind convergence/divergence induces anomalous precipitation in the near-equatorial regions, forming a north–south dipole precipitation anomaly pattern between the southern South China Sea and the eastern China– Japan region. An anomalous meridional overturning circulation plays an important role in linking tropical and midlatitude intraseasonal wind and precipitation variations.
基金supported by the projects of Chinese Academy of Sciences(Grant No.KZZD-EW-01-3)the National Basic Research Program of China(Grant No.2012CB825604)the National Natural Science Foundation of China(Grant Nos.41231065,41174137,41321003)
文摘Nighttime enhancements in ionospheric electron density at mid- and low-latitudes are investigated by using the critical frequency of the F2-1ayer （foF2） data measured from ionosonde stations at Okinawa （26.3°N, 127.8°E, Geomagnetic 15.3°N）, Yamagawa （31.2°N, 130.6°E, Geomagnetic 20.4°N）, Kokubunji （35.7°N, 139.5°E, Geomagnetic 25.5°N）, and Wakkanai （45.4°N, 141.7°E, Geomagnetic 35.4°N） in East Asia during several solar cycles. The results show that there are obvious seasonal and solar activity dependencies of the nighttime electron density enhancements. The enhancements are termed pre-midnight enhancement and post-midnight enhancement, according to the local time when the enhancement appeared. The former has a higher occurrence probability in summer months than in winter months. In contrast, the latter has a larger occurrence probability in winter months than in summer months. Moreover, the nighttime enhancements in electron density are more likely to occur at lower solar activity. These seasonal and solar activity variations of the nighttime enhancements in electron density can be explained in terms of the combined effects of downward plasma flux from the plasmasphere and the neutral winds.
基金sponsored by National Natural Science Foundation of China (Grant Nos. 40890053 and 40890052)National Basic Research Program of China (Grant No. 2007CB815901)
文摘Using observational data, the East Asian-North Indian Ocean index （]EANI）, which reflects a tropospheric thermal contrast, is found to correlate well with the East Asian summer monsoon （EASM） and associated rainfall over eastern China. Corresponding to a higher （lower） IEANI, the EASM at mid-latitudes is stronger （weaker）, and there is more （less） rainfall in North China and less （more） rainfall near the Yangtze River valley. To investigate long-term variation in the EASM, we reconstructed the BC 665AD 1985 IEANI based on reconstructed temperatures in Beijing and Tasmania, Australia. Over the past 2000 years, the reconstructed/EANI generally represents centennial-scale variations in the EASM and rainfall over eastem China. The correlation pattern between the reconstructed IEANI and rainfall over eastern China is similar to modem observations, implying that the correlation feature at centennial scales also occurred over the past 2000 years. With respect to longer-scale （several hundreds to one thousand years） IEANI variations and their correlations with rainfall, further verifications should be performed using various paleoclimatic proxy data.
