Based on the monthly NCEP/NCAR reanalysis data, OLR （outgoing longwave radiation） data, and tropical cyclone data from the Typhoon Annual and Tropical Cyclone Annual edited by China Meteorological Administration, th...Based on the monthly NCEP/NCAR reanalysis data, OLR （outgoing longwave radiation） data, and tropical cyclone data from the Typhoon Annual and Tropical Cyclone Annual edited by China Meteorological Administration, the relationship between the number of tropical cyclones （with the strongest wind ≥ 17 m s^-1, including tropical storm, strong tropical storm, and typhoon, simply called typhoon in this paper） engendered over the Northwest Pacific and South China Sea in summer and the associated climate conditions is studied. First, the characteristics and differences of the climatic conditions between the years with more typhoons and those with fewer typhoons are compared. The results show that the summer typhoon has a close relationship with SST （sea surface temperature） and ITCZ （intertropical convergence zone） anomalies in the preceding winter and spring. With a La Nina like SST anomaly （SSTA） pattern in the preceding winter and spring, the ITCZ will move northwestward and be enhanced around 160°E in the equatorial central Pacific from the preceding winter to spring. The activity of the Pacific ITCZ is in general stronger and its location is more northward than usual, especially in the typhoon genesis region in West Pacific. This background is propitious to have more typhoons in summer. On the other hand, an El Nino like SSTA pattern in the preceding winter will be companied with weaker ITCZ activities, and its location is more southward over the equatorial western Pacific from the preceding winter to spring; this background is propitious to have fewer typhoons in summer. In the year with more typhoons, the warm SST over West Pacific in the preceding winter provides a favorable condition for typhoon fromation in the following summer. It enhances the convergence in the troposphere and increases the water vapor supply to the warm SST region. In the following spring, the perturbation of the tropical ITCZ plays a more important role. When the ITCZ moves northward in spring, anomalous convergence will appear over the warm SST region and inspire the positive feedback between the large-scale moisture flux at low levels and the latent heat release in the atmosphere, which benefits the typhoon genesis in summer. Otherwise, if cold SST maintains over the northwestern Pacific during the preceding winter and spring, the convergence in the troposphere is disfavored and the water vapor supply to the cold SST region is reduced, which will bring about weaker ITCZ activities and the perturbation is lacking in the following spring. It then results in fewer summer typhoons.展开更多
A field experiment was conducted during the 2002/2003 cropping season of winter wheat （Triticum aestivum） and spring maize （Zea mays） to evaluate the effect of limited single drip irrigation on the yield and water...A field experiment was conducted during the 2002/2003 cropping season of winter wheat （Triticum aestivum） and spring maize （Zea mays） to evaluate the effect of limited single drip irrigation on the yield and water use of both crops under relay intercropping in a semi-arid area of northwestern China. A controlled 35 mm single irrigation, either early or late, was applied to each crop at a certain growth stage. Soil water, leaf area, final grain yield and yield components such as the thousand-grain weight, length of spike, fertile spikelet number, number of grains per spike, and grain weight per spike were measured, and water use efficiency and leaf area index were calculated for the irrigated and non-irrigated relay intercropping treatments and sole cropping controls. The results showed that yield, yield components, water use efficiency, and leaf area index in the relay intercropping treatments were affected by limited single drip irrigation during various growth stages of wheat and maize. The total yields in the relay intercropping treatment irrigated during the heading stage of wheat and the heading and anthesis stage of maize were the highest among all the treatments, followed by that irrigated during the anthesis stage of wheat and silking stage of maize; so was the water use efficiency. Significant differences occurred in most yield components between the irrigated and non-irrigated relay-intercropping treatments. The dynamics of the leaf area index in the relay-intercropped or solely cropped wheat and maize showed a type of single-peak pattern, whereas that of the relay intercropping treatments showed a type of double-peak pattern. Appropriately, limited single irrigation and controlled soil water content level could result in higher total yield, water use efficiency, and leaf area index, and improved yield components in relay intercropping. This practice saved the amount of water used for irrigation and also increased the yield. Therefore, heading stage of wheat and heading and anthesis stage of maize were suggested to be the optimum limited single irrigation time for relay-intercropped wheat and maize in the semi-arid area.展开更多
基金the National"973"Program of China under Grant No.2006CB403600.
文摘Based on the monthly NCEP/NCAR reanalysis data, OLR （outgoing longwave radiation） data, and tropical cyclone data from the Typhoon Annual and Tropical Cyclone Annual edited by China Meteorological Administration, the relationship between the number of tropical cyclones （with the strongest wind ≥ 17 m s^-1, including tropical storm, strong tropical storm, and typhoon, simply called typhoon in this paper） engendered over the Northwest Pacific and South China Sea in summer and the associated climate conditions is studied. First, the characteristics and differences of the climatic conditions between the years with more typhoons and those with fewer typhoons are compared. The results show that the summer typhoon has a close relationship with SST （sea surface temperature） and ITCZ （intertropical convergence zone） anomalies in the preceding winter and spring. With a La Nina like SST anomaly （SSTA） pattern in the preceding winter and spring, the ITCZ will move northwestward and be enhanced around 160°E in the equatorial central Pacific from the preceding winter to spring. The activity of the Pacific ITCZ is in general stronger and its location is more northward than usual, especially in the typhoon genesis region in West Pacific. This background is propitious to have more typhoons in summer. On the other hand, an El Nino like SSTA pattern in the preceding winter will be companied with weaker ITCZ activities, and its location is more southward over the equatorial western Pacific from the preceding winter to spring; this background is propitious to have fewer typhoons in summer. In the year with more typhoons, the warm SST over West Pacific in the preceding winter provides a favorable condition for typhoon fromation in the following summer. It enhances the convergence in the troposphere and increases the water vapor supply to the warm SST region. In the following spring, the perturbation of the tropical ITCZ plays a more important role. When the ITCZ moves northward in spring, anomalous convergence will appear over the warm SST region and inspire the positive feedback between the large-scale moisture flux at low levels and the latent heat release in the atmosphere, which benefits the typhoon genesis in summer. Otherwise, if cold SST maintains over the northwestern Pacific during the preceding winter and spring, the convergence in the troposphere is disfavored and the water vapor supply to the cold SST region is reduced, which will bring about weaker ITCZ activities and the perturbation is lacking in the following spring. It then results in fewer summer typhoons.
基金the National Key Basic Research Special Foundation (NKBRSF) of China (No.G2000018603)and the National High Technology Research and Development Program (863 Program) of China (No.2002AA2Z4191).
文摘A field experiment was conducted during the 2002/2003 cropping season of winter wheat （Triticum aestivum） and spring maize （Zea mays） to evaluate the effect of limited single drip irrigation on the yield and water use of both crops under relay intercropping in a semi-arid area of northwestern China. A controlled 35 mm single irrigation, either early or late, was applied to each crop at a certain growth stage. Soil water, leaf area, final grain yield and yield components such as the thousand-grain weight, length of spike, fertile spikelet number, number of grains per spike, and grain weight per spike were measured, and water use efficiency and leaf area index were calculated for the irrigated and non-irrigated relay intercropping treatments and sole cropping controls. The results showed that yield, yield components, water use efficiency, and leaf area index in the relay intercropping treatments were affected by limited single drip irrigation during various growth stages of wheat and maize. The total yields in the relay intercropping treatment irrigated during the heading stage of wheat and the heading and anthesis stage of maize were the highest among all the treatments, followed by that irrigated during the anthesis stage of wheat and silking stage of maize; so was the water use efficiency. Significant differences occurred in most yield components between the irrigated and non-irrigated relay-intercropping treatments. The dynamics of the leaf area index in the relay-intercropped or solely cropped wheat and maize showed a type of single-peak pattern, whereas that of the relay intercropping treatments showed a type of double-peak pattern. Appropriately, limited single irrigation and controlled soil water content level could result in higher total yield, water use efficiency, and leaf area index, and improved yield components in relay intercropping. This practice saved the amount of water used for irrigation and also increased the yield. Therefore, heading stage of wheat and heading and anthesis stage of maize were suggested to be the optimum limited single irrigation time for relay-intercropped wheat and maize in the semi-arid area.
