珠江流域秋旱与南海表层海温

秋旱(秋老虎)是威胁珠江流域晚造作物正常生长的严重灾害之一,因此,做好珠江流域秋旱预报是夺取晚造作物丰收的一项有效措施。 珠江流域的秋旱是指8—10月的干旱(广东也称八月旱)。形成秋旱原因较多,诸如:降水分配不均,前汛雨量集中,后汛雨量偏少;8—9月台风少;两广地区受副热带高压(简称副高,下同)或其边缘控制,下沉气流较强,天气晴热;入秋前雨量偏少,加上气温高,蒸     

TBB-REVEALED ANNUAL CYCLE FEATURES OF TROPICAL LFO

In the context of 1980—1992 JMA(Japan Meteorological Agency)GMS TBB gridded dataset,study is undertaken of annual cycle features of FFT-derived window power spectrum averaged overthe record length,with localized space/time characteristics of low-frequency oscillation(LFO)inthe tropical atmosphere investigated alongside possible causes.It turns out that the LFO takes onsurprisingly noticeable annual cycle features marked by a wider variable range of the LFO periodsover northern tropics than the southern counterpart and equatorial vicinity.In addition,on thewhole,the signals are more intense in the Northern Hemisphere during summer/autumn and atequatorial/southern latitudes when northern winter/spring occur as well.Also,not all thesefeatures are identical for different segments at the same latitudes,displaying signatures on a localbasis,and the spatial/temporal locality can be qualitatively interpreted in terms of nonlinearinteraction between tropical waves,and modulation of diabatic heating on the LFO periods.     

CONTOUR DYNAMICS FOR VORTEX MOTION INFLUENCED BY THE CORIOLIS FORCE

The computational formulae are given for single-contour constant-value vortex motion influenced by the Coriolisforce in the framework of contour dynamics,by which four numerical computations are performed,the result exhibitingtheir validity.     

SPECTRAL CHARACTERISTICS OF SURFACE-LAYER TURBULENCE OVER THE SUBURBS OF TIANJIN

The paper computed the spectra of velocity and temperature,and the cospectra of velocity and temperature by theobservational data of July,1990 in the suburbs of Tianjin.The results show that the characteristics of the atmosphericturbulence spectra over the suburbs are basically in accordance with some typical results over the flat terrain.But thescale,on which turbulence can satisfy the isotropic condition,over the suburbs is larger than over the flat terrain.Thespectrum peak frequency range is a bit narrower.The feature of the spectrum range in low frequency(LF)is out ofaccordance with that of the flat terrain either.     

NUMERICAL EXPERIMENTS OF THE EFFECTS OF SEA SURFACE TEMPERATURE ANOMALIES OVER THE PACIFIC ON PRECIPITATION IN 1991

A zonal domain,primitive equation model is used in this paper to study the influences of the main sea surface tem-perature anomaly(SSTA)areas over the Pacific on precipitation in 1991.Some numerical experiments are made and themechanisms of the influences are discussed.The results show that the influences of the SSTA are mainly confined withinthe tropical and the subtropical regions.The direct effect of the SSTA is to change the exchanges of the sensible heat andthe water vapour between the air and the sea,through the consequent changes of temperature and the flow fields and thefeedback process of condensation,the SSTA finally affects precipitation.     

东半球跨赤道气流季节变化及其在EL NINO年的异常

利用1979年1月到1987年12月美国国家气象中心六个层次的月平均风场资料,分析了东半球跨赤道气流的季节变化及其年际异常。得到冬、夏跨赤道气流的输送集中在对流层下部,冬季向南,夏季向北;春、秋跨赤道气流的输送集中在对流层上部,春季向北,秋季向南。低层跨赤道气流位置稳定,南北风方向转换时间为3月和11月;高层跨赤道气流位置变化较大,南北风转换时间为6月和1月。在El Nino年,跨赤道气流出现明显的异常,但表现形式不尽相同。ElNino年,夏季下层跨赤道气流稳定建立的时间比正常年推迟2—3候,且季内变化大,稳定维持时间短。     

EFFECT OF ENERGY DISPERSION ON THE STRUCTURE AND MOTION OF TROPICAL CYCLONE

The energy dispersion of a typhoon vortex and its effect on the typhoon motion are studied using an analyticalmethod of double-Fourier expansion as well as a numerical model in a β-plane nondivergent barotropic framework.The analytic model and the linear version of the numerical model give essentially the same result:the energy dispersionfrom a tropical cyclone can creat an L-H-L wave train to the east of the tropical cyclone.Three numerical experiments,integrated for 7 model days by the nonlinear model,indicate that the closed high in the wave train produces obvious in-fluence on the structure and movement of the tropical cyclone.