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2005 Vol. 22, No. 3

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A Preliminary Study on the Relationship Between Arctic Oscillation and Daily SLP Variance in the Northern Hemisphere During Wintertime
GONG Daoyi, Helge DRANGE
2005, 22(3): 313-327. doi: 10.1007/BF02918745
In the present study, the authors investigated the relationship between the Arctic Oscillation (AO) and the high-frequency variability of daily sea level pressures in the Northern Hemisphere in winter (November through March), using NCEP/NCAR reanalysis datasets for the time period of 1948/49-2000/01.High-frequency signals are defined as those with timescales shorter than three weeks and measured in terms of variance, for each winter for each grid. The correlations between monthly mean AO index and high-frequency variance are conducted. A predominant feature is that several regional centers with high correlation show up in the middle to high latitudes. Significant areas include mid- to high-latitude Asia centered at Siberia, northern Europe and the middle-latitude North Atlantic east of northern Africa. Their strong correlations can also be confirmed by the singular value decomposition analysis of covariance between mean SLP and high-frequency variance. This indicates that the relationship of AO with daily Sea Level Pressure (SLP) is confined to some specific regions in association with the inherent atmospheric dynamics. In middle-latitude Asia, there is a significant (at the 95% level) trend of variance of-2.26% (10yr)-1. Another region that displays a strong trend is the northwestern Pacific with a significant rate of change of 0.80% (10 yr)-1. If the winter of 1948/49, an apparent outlier, is excluded, a steady linear trend of +1.51% (10 yr)-1 shows up in northern Europe. The variance probability density functions (PDFs) are found to change in association with different AO phases. The changes corresponding to high and low AO phases, however, are asymmetric in these regions. Some regions such as northern Europe display much stronger changes in high AO years, whereas some other regions such as Siberia show a stronger connection to low AO conditions. These features are supported by ECMWF reanalysis data. However, the dynamical mechanisms involved in the AO-high frequency SLP variance connection have not been well understood,and this needs further study.
Study on Size Distributions of Airborne Particles by Aircraft Observation in Spring over Eastern Coastal Areas of China
WANG Wei, LIU Hongjie, YUE Xin, LI Hong, CHEN Jianhua, TANG Dagang
2005, 22(3): 328-336. doi: 10.1007/BF02918746
The authors studied the size distributions of particles at an altitude of 2000 m by aircraft observation over eastern costal areas of China from Zhuhai, Guangdong to Dalian, Liaoning (0.47-30 μm, 57 channels,including number concentration distribution, surface area concentration distribution and mass concentration distribution). In these cities, the average daily concentrations of PM10 are very high. They are among the most heavily polluted cities in China. The main pollution sources are anthropogenic activities such as wood, coal and oil burning. The observed size distributions show a broad spectrum and unique multi-peak characteristics, indicating no significant impacts of individual sources from urban areas. These results are far different from the distribution type at ground level. It may reflect the comprehensive effect of the regional pollution characteristics. Monitoring results over big cities could to some extent reflect their pollution characteristics.
A Nonlinear Coupled Soil Moisture-Vegetation Model
LIU Shikuo, LIU Shida, FU Zuntao, SUN Lan
2005, 22(3): 337-342. doi: 10.1007/BF02918747
Based on the physical analysis that the soil moisture and vegetation depend mainly on the precipitation and evaporation as well as the growth, decay and consumption of vegetation a nonlinear dynamic coupled system of soil moisture-vegetation is established. Using this model, the stabilities of the steady states of vegetation are analyzed. This paper focuses on the research of the vegetation catastrophe point which represents the transition between aridness and wetness to a great extent. It is shown that the catastrophe point of steady states of vegetation depends mainly on the rainfall P and saturation value v0, which is selected to balance the growth and decay of vegetation. In addition, when the consumption of vegetation remains constant, the analytic solution of the vegetation equation is obtained.
Impact of Land Use Changes on Surface Warming in China
ZHANG Jingyong, DONG Wenjie, WU Lingyun, WEI Jiangfeng, CHEN Peiyan, Dong-Kyou LEE
2005, 22(3): 343-348. doi: 10.1007/BF02918748
Land use changes such as urbanization, agriculture, pasturing, deforestation, desertification and irrigation can change the land surface heat flux directly, and also change the atmospheric circulation indirectly, and therefore affect the local temperature. But it is difficult to separate their effects from climate trends such as greenhouse-gas effects. Comparing the decadal trends of the observation station data with those of the NCEP/NCAR Reanalysis (NNR) data provides a good method to separate the effects because the NNR is insensitive to land surface changes. The effects of urbanization and other land use changes over China are estimated by using the difference between the station and the NNR surface temperature trends. Our results show that urbanization and other land use changes may contribute to the observed 0.12℃ (10 yr)- 1 increase for daily mean surface temperature, and the 0.20℃ (10 yr)- 1 and 0.03℃ (10 yr)-1 increases for the daily minimum and maximum surface temperatures, respectively. The urban heat island effect and the effects of other land-use changes mayalso play an important role in the diurnal temperature range change. The spatial pattern of the differences in trends shows a marked heterogeneity.The land surface degradation such as deforestation and desertification due to human activities over northern China, and rapidly-developed urbanization over southern China, may have mostly contributed to the increases at stations north of about 38°N and in Southeast China, respectively. Furthermore, the vegetation cover increase due to irrigation and fertilization may have contributed to the decreasing trend of surface temperature over the lower Yellow River Basin. The study illustrates the possible impacts of land use changes on surface temperature over China.
Wind-Driven Ocean Circulation in Shallow Water Lattice Boltzmann Model
ZHONG Linhao, FENG Shide, GAO Shouting
2005, 22(3): 349-358. doi: 10.1007/BF02918749
A lattice Boltzmann (LB) model with overall second-order accuracy is applied to the 1.5-layer shallow water equation for a wind-driven double-gyre ocean circulation. By introducing the second-order integral approximation for the collision operator, the model becomes fully explicit. In this case, any iterative technique is not needed. The Coriolis force and other external forces are included in the model with second-order accuracy, which is consistent with the discretized accuracy of the LB equation. The numerical results show correct physics of the ocean circulation driven by the double-gyre wind stress with different Reynolds numbers and different spatial resolutions. An intrinsic low-frequency variability of the shallow water model is also found. The wind-driven ocean circulation exhibits subannual and interannual oscillations, which are comparable to those of models in which the conventional numerical methods are used.
27.3-day and 13.6-day Atmospheric Tide and Lunar Forcing on Atmospheric Circulation
LI Guoqing
2005, 22(3): 359-374. doi: 10.1007/BF02918750
An analysis of time variations of the earth's length of day (LOD) versus atmospheric geopotential height fields and lunar phase is presented. A strong correlation is found between LOD and geopotential height from which a close relationship is inferred and found between atmospheric circulation and the lunar cycle around the earth. It is found that there is a 27.3-day and 13.6-day east-west oscillation in the atmospheric circulation following the lunar phase change. The lunar revolution around the earth strongly influences the atmospheric circulation. During each lunar cycle around the earth there is, on average, an alternating change of 6.8-day-decrease, 6.8-day-increase, 6.8-day-decrease and 6.8-day-increase in atmospheric zonal wind, atmospheric angular momentum and LOD. The dominant factor producing such an oscillation in atmospheric circulation is the periodic change of lunar declination during the lunar revolution around the earth. The 27.3- day and 13.6-day atmospheric oscillatory phenomenon is akin to a strong atmospheric tide, which is different from the weak atmospheric tides, diurnal and semidiurnal, previously documented in the literature. Also it is different from the tides in the ocean in accordance with their frequency and date of occurrence. Estimation shows that the 27.3-day lunar forcing produces a 1-2 m s-1 change in atmospheric zonal wind. Therefore, it should be considered in models of atmospheric circulation and short and middle term weather forecasting. The physical mechanism and dynamic processes in lunar forcing on atmospheric circulation are discussed.
A Diagnostic Study of Heavy Rainfall in Karachi Due to Merging of a Mesoscale Low and a Diffused Tropical Depression during South Asian Summer Monsoon
Ghulam RASUL, Qamar-uz-Zaman CHAUDHRY, ZHAO Sixiong, ZENG Qingcun, QI Linlin, ZHANG Gaoying
2005, 22(3): 375-391. doi: 10.1007/BF02918751
This paper presents the results of a diagnostic study of a typical case of very heavy rainfall during the South Asian summer monsoon when a mesoscale low in a desert climate merged with a diffused tropical depression. The former low was located over Pakistan's desert region and the latter depression originated over the Bay of Bengal. Surface and NCEP reanalysis data supported by satellite and radar images were incorporated in the diagnosis. The relationship between the heavy precipitation process and large-scale circulations such as monsoon trough, subtropical high, westerly jet, low level jet and water vapor transport were investigated to further understand the mechanism of this peculiar interaction. It was found that: (1)the mesoscale low developed as a result of cold air advection aloft from northern latitudes and strong convection over the region of humidity convergence on 24 July 2003 over the Indian Rajistan area. (2) On the same day, a low that formed over the Bay of Bengal was transformed into a monsoon depression and moved westward to the mesoscale low which existed over southwest India and the adjoining southeastern parts of Pakistan. (3) Initially, the mesoscale low received moisture supply from both the Bay of Bengal as well as the Arabian Sea, whereas the Bay of Bengal maintained the continuous supply of moisture to the monsoon depression. (4) After the depression crossed central India, the Bay's moisture supply was cut off and the Arabian Sea became the only source of moisture to both the closely located systems. On 27July, both of the systems merged together and the merger resulted in a heavy downpour in the Karachi metropolitan and in its surroundings. (5) With the intensification as well as the southeastward extension of the subtropical high and the shift of the monsoon trough axis from southwest-west to northeast-east,the monsoon depression moved southwestward. In this situation, there existed a very favourable condition for a merger of the two systems in the presence of cross-latitude influence. (6) A number of convective cloud clusters were developed and organized in the mesoscale low. Probably, interactions existed among the multi-scale systems.
The Characteristics of Longitudinal Movement of the Subtropical High in the Western Pacific in the Pre-rainy Season in South China
YANG Hui, SUN Shuqing
2005, 22(3): 392-400. doi: 10.1007/BF02918752
Using the NCEP/NCAR reanalysis data, the China rainfall data of the China Meteorological Administration, and the sea surface temperature (SST) data of NOAA from 1951-2000, the features of theanomalous longitudinal position of the subtropical high in the western Pacific (SHWP) in the pre-rainyseason in South China and associated circulation and precipitation are studied. Furthermore, the relationship between SHWP and SST and the eastern Asian winter monsoon is also investigated. Associatedwith the anomalous longitudinal position of SHWP in the pre-rainy season in South China, the flow patterns in both the middle and lower latitudes are different. The circulation anomalies greatly influence theprecipitation in the pre-rainy season in South China. When the SHWP is in a west position (WP), theSouth China quasi-stationary front is stronger with more abundant precipitation there. However, whenthe SHWP is in an east position (EP), a weaker front appears with a shortage of precipitation there. Thereexists a good relationship between the longitudinal position of SHWP and SST in the tropical region. Anegative correlation can be found both in the central and eastern tropical Pacific and the Indian Ocean.This means that the higher (lower) SST there corresponds to a west (east) position of SHWP. This closerelationship can be found even in the preceding autumn and winter. A positive correlation appears in thewestern and northern Pacific and large correlation coefficient values also occur in the preceding autumnand winter. A stronger eastern Asian winter monsoon will give rise to cooler SSTs in the Kuroshio and theSouth China Sea regions and it corresponds to negative SST anomaly (SSTA) in the central and easternPacific and positive SSTA in the western Pacific in winter and the following spring. The whole tropicalSSTA pattern, that is, positive (negative) SSTA in the central and eastern Pacific and negative (positive)SSTA in the western Pacific, is favorable to the WP (EP) of SHWP.
Seasonal Variations of Number Size Distributions and Mass Concentrations of Atmospheric Particles in Beijing
YU Jianhua, Benjamin GUINOT, YU Tong, WANG Xin, LIU Wenqing
2005, 22(3): 401-407. doi: 10.1007/BF02918753
Particle number and mass concentrations were measured in Beijing during the winter and summer periods in 2003, together with some other parameters including black carbon (BC) and meteorological conditions. Particle mass concentrations exhibited low seasonality, and the ratio of PM2.5/PM10 in winter was higher than that in summer. Particle number size distribution (PSD) was characterized by four modes and exhibited low seasonality. BC was well correlated with the number and mass concentrations of accumulation and coarse particles, indicating these size particles are related to anthropogenic activities.Particle mass and number concentrations (except ultra-fine and nucleation particles) followed well the trends of BC concentration for the majority of the day, indicating that most particles were associated with primary emissions. The diurnal number distributions of accumulation and coarse mode particles were characterized by two peaks.
Study of the Optimal Precursors for Blocking Events
JIANG Zhina, LUO Dehai
2005, 22(3): 408-414. doi: 10.1007/BF02918754
The precursors of dipole blocking are obtained by a numerical approach based upon a quasi-geostrophic barotropic planetary- to synoptic-scale interaction model without topography and with a localized synopticscale wave-maker. The optimization problem related to the precursors of blocking is formulated and the nonlinear optimization method is used to examine the optimal synoptic-scale initial field successfully. The results show that the prominent characteristics of the optimal synoptic-scale initial field are that the synoptic-scale wave train structures exist upstream of the incipient blocking. In addition, the large-scale low/high eddy-forcing pattern upstream of the incipient blocking is an essential precondition for the onset of dipole blocking.
Assimilation and Simulation of Typhoon Rusa (2002) Using the WRF System
GU Jianfeng, Qingnong XIAO, Ying-Hwa KUO, Dale M. BARKER, XUE Jishan, MA Xiaoxing
2005, 22(3): 415-427. doi: 10.1007/BF02918755
Using the recently developed Weather Research and Forecasting (WRF) 3DVAR and the WRF model, numerical experiments are conducted for the initialization and simulation of typhoon Rusa (2002).The observational data used in the WRF 3DVAR are conventional Global Telecommunications System (GTS) data and Korean Automatic Weather Station (AWS) surface observations. The Background Error Statistics (BES) via the National Meteorological Center (NMC) method has two different resolutions, that is, a 210-km horizontal grid space from the NCEP global model and a 10-kn horizontal resolution from Korean operational forecasts. To improve the performance of the WRF simulation initialized from the WRF 3DVAR analyses, the scale-lengths used in the horizontal background error covariances via recursive filter are tuned in terms of the WRF 3DVAR control variables, streamfunction, velocity potential, unbalanced pressure and specific humidity. The experiments with respect to different background error statistics and different observational data indicate that the subsequent 24-h the WRF model forecasts of typhoon Rusa's track and precipitation are significantly impacted upon the initial fields. Assimilation of the AWS data with the tuned background error statistics obtains improved predictions of the typhoon track and its precipitation.
A Short-Term Climate Prediction Model Based on a Modular Fuzzy Neural Network
JIN Long, JIN Jian, YAO Cai
2005, 22(3): 428-435. doi: 10.1007/BF02918756
In terms of the modular fuzzy neural network (MFNN) combining fuzzy c-mean (FCM) cluster and single-layer neural network, a short-term climate prediction model is developed. It is found from modeling results that the MFNN model for short-term climate prediction has advantages of simple structure, no hidden layer and stable network parameters because of the assembling of sound functions of the selfadaptive learning, association and fuzzy information processing of fuzzy mathematics and neural network methods. The case computational results of Guangxi flood season (JJA) rainfall show that the mean absolute error (MAE) and mean relative error (MRE) of the prediction during 1998-2002 are 68.8 mm and 9.78%, and in comparison with the regression method, under the conditions of the same predictors and period they are 97.8 mm and 12.28% respectively. Furthermore, it is also found from the stability analysis of the modular model that the change of the prediction results of independent samples with training times in the stably convergent interval of the model is less than 1.3 mm. The obvious oscillation phenomenon of prediction results with training times, such as in the common back-propagation neural network (BPNN)model, does not occur, indicating a better practical application potential of the MFNN model.
A Case Study on a Strong Tropical Disturbance and Record Heavy Rainfall in Hat Yai, Thailand during the Winter Monsoon
Angkool WANGWONGCHAI, ZHAO Sixiong, ZENG Qingcun
2005, 22(3): 436-450. doi: 10.1007/BF02918757
The evolutionary process and structural characteristics of the atmospheric circulation and synoptic situation which caused the record heavy rainfall with a precipitation amount of 550 mm in Hat Yai,Thailand from 20 to 23 November 2000 is studied. In the study, the modern three dimensional observational data were collected as completely as possible, and detailed analyses were made. It is revealed that the cold surges of the Asian winter monsoon that originate from Siberia can arrive at the lower latitudes, including South Thailand, Malaysia, Indonesia, cause strong heavy rainfall there, and interact with weather systems in the near-equatorial regions of the Southern Hemisphere. This is strongly supported by Chinese scientist's original finding in 1930s. The strong convective cloud clusters in the above areas are generated by the direct influence of the cold surges, and are related with the South China Sea disturbances in the lower troposphere. The maximum of the convergence of total moisture flux near South Thailand in the situation under study implies that the water vapour supply is abundant and very favorable to the occurrence of the heavy rainfall. The release of latent heat enhances the Hadley Circulation also. The feedback of the strong severe weather on climate indeed exists, and there are pronounced interactions between the multi-scale systems and between both hemispheres.
On the Mechanism of the Seasonal Variability of SST in the Tropical Indian Ocean
HU Ruijin, LIU Qinyu, MENG Xiangfeng, J. Stuart GODFREY
2005, 22(3): 451-462. doi: 10.1007/BF02918758
A general form of an equation that "explicitly" diagnoses SST change is derived. All other equations in wide use are its special case. Combining with the data from an ocean general circulation model (MOM2)with an integration of 10 years (1987-1996), the relative importances of various processes that determine seasonal variations of SST in the tropical Indian Ocean are compared mainly for January, April, July and October. The main results are as follows. (1) The net surface heat flux is the most important factor affecting SST over the Arabian Sea, the Bay of Bengal and the region south of the equator in January; in April, its influence covers almost the whole region studied; whereas in July and October, this term shows significance only in the regions south of 10°S and north of the equator, respectively. (2) The horizontal advection dominates in the East African-Arabian coast and the region around the equator in January and July; in October, the region is located south of 10°S. (3) The entrainment is significant only in a narrow band centered on 10°S in April and the coastal region around the Arabian Sea and the equator in July. (4)As for SST, it decreases in January and July but increases in April and October in the Arabian Sea and the Bay of Bengal, showing a (asymmetrical) semiannual variability; by contrast, the SST in the region south of the equator has an annual variability, decreasing in April and July and increasing in October and January.
The Circum-Pacific Teleconnection Pattern in Meridional Wind in the High Troposphere
WANG Huijun
2005, 22(3): 463-466. doi: 10.1007/BF02918759
The Circum-Pacific Teleconnection Pattern (CPTP) is revealed in the meridional wind in the high troposphere via an emprirical orthogonal function (EOF) and correlation analysis on NCEP/NCAR reanalysis data. The CPTP is found to be composed of the North Pacific-North American teleconnection pattern (PNA), the South Pacific-South American teleconnection pattern (PSA), and the teleconnection patterns over the tropical western Pacific and the tropical eastern Pacific (or, Central America, or, tropical Atlantic). There is substantial interannual variability of the CPTP and a typical CPTP can be detected in some years. It is speculated that the zonal wind anomalies over the equatorial region in the western and eastern sides of the Pacific may play a role in linking the two hemispheres. The anomalous convection activities in the Tropics are plausible triggering factors for the zonal wind anomalies that are responsible for the composition of the CPTP.