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1.
The Relationship between the East Asian Subtropical Westerly Jet and Summer Precipitation over East Asia as Simulated by the IAP AGCM4.0 
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下载免费PDF全文 Based on a 30-year Atmospheric Model Intercomparison Project（AMIP） simulation using IAP AGCM4.0, the relationship between the East Asian subtropical westerly jet（EASWJ） and summer precipitation over East Asia has been investigated, and compared with observation. It was found the meridional displacement of the EASWJ has a closer relationship with the precipitation over East Asia both from model simulation and observation, with an anomalous southward shift of EASWJ being conducive to rainfall over the Yangtze-Huaihe River Valley（YHRV）, and an anomalous northward shift resulting in less rainfall over the YHRV. However, the simulated precipitation anomalies were found to be weaker than observed from the composite analysis, and this would be related to the weakly reproduced mid-upper-level convergence in the mid-high latitudes and ascending motion in the lower latitudes. 相似文献
2.
Land surface heating of the Tibetan Plateau （TP） plays an important role in the Asian Monsoon system. In this study, the interannual variability of the sensible heat flux over the TP and its connection with the summer monsoon intensity and onset date was examined based on the newly released land ＂reanalysis＂ data, produced by NASA Global Land Data Assimilation System. Although correlation analyses don＇t show a significant relevance to the summer monsoon intensity, the interannual anomalies in sensible heating near the south flank of the TP indicate a weak reversal in the relationship with the onset date of the West Pacific East Asian monsoon. A diagnostic study shows that above （below） normal sensible heating over the south flake of the TP will lead to rapid （slow） warming of the upper air column over the TP and early （later） reversal of （overturn） the meridional temperature gradient and the vertical wind shear. This will further lead to an earlier （later） onset of the Asian Monsoon. 相似文献
3.
The first decadal leading mode of East Asian summer rainfall （EASR） is characterized by rainfall anomalies along the East Asian subtropical rain belt. This study focuses on the second decadal leading mode （2DLM）, accounting for 17.3% of rainfall decadal vari- ance, as distinct from the other two neighboring modes of EAMR, based on the state-of-the-art in-situ rainfall data. This mode is characterized by a South-China-wet-Huaihe- River-dry pattern, and is dominated by a quasi-30-yr pe- riod. Further analysis reveals the 2DLM corresponds to an enhanced lower-level monsoon jet, an eastward extension of the western North Pacific subtropical high, and a weakened East Asian upper-level westerly jet flow. The Tibetan Plateau surface temperature and Pacific Decadal Oscillation （PDO） are closely linked with the 2DLM. The regressed SST pattern indicates the PDO-like pattern of sea surface temperature anomalies may have a telecon- nection relationship with the 2DLM of EASR. 相似文献
4.
This paper investigates the variability of the summer （May-September） South Asian Iligh （SAIl） for the period 1979-2012. Results show that the intensity and the area of the summer SAH decreased around 2002 at the decadal scale; and the East Asian westerly jet suppressed at the north edge of the SAH, which is consistent with the SAH variation. The precipitation pattern over eastern China also shifted during the same periods, with increased rainfall in the Huang-Huai River region and South China and decreased rainfall in the Yangtze River region. The relationship between the two variations is evidently strengthened via changes in moisture flux. 相似文献
5.
通过对海温资料和500hPa位势高度、垂直速度、850 hPa的水平风分量资料的分析,探讨ENSO的各不同阶段西太平洋副高和东亚季风的变化特征.结果表明:赤道东太平洋海温与西太平洋副高有密切的关系.Nino 1+2区海温有明显的10年际变化,与西太平洋副高的1O年际变化非常吻合;前期Nino 1+2区为冷、暖水期时西太平洋副高的强度和位置有明显差异,前期为暖水期时夏季西太平洋副高较强,范围向西和向南伸展,冷水期反之,西太平洋副高较弱,位置偏东偏北.西太平洋副高的变化进一步影响东亚季风和我国的降水.这种影响在Nino 1+2区海温变化后4～6个月最明显.因此,前期Nino 1+2区海温的变化可以为东亚季风和我国降水的长期预报提供依据. 相似文献
6.
利用1948—2012年NCEP/NCAR逐日再分析风场资料,对亚洲两个热带夏季风子系统 (南亚夏季风和东亚热带夏季风) 边界进行划分。根据所得出的边界提出了亚洲两大热带夏季风子系统分界域的观点,定义偏向指数来确定两大热带夏季风子系统边界的偏向;通过对比,确定出边界在纬向上的变动较大的区域,并以确定的变动较大的纬度区域来研究亚洲两大热带夏季风分界域的变化规律;最后通过边界指标刻画出季风强度的变化情况,分析其关键环流特征。选取涡度作为边界的确定指标,边界的变动可以分为东部型、中部型、西部型。根据边界的振幅情况选取10°~17.5°N作为主要研究区域,由边界指标定义的夏季风指数得出,亚洲两大热带夏季风子系统强度的一致性变化占主导地位,其次为反相变化。 相似文献
7.
Tides and Wind-Driven Circulation in the Tropical and Southern Atlantic Ocean:The BRAZCOAST System 下载免费PDF全文
下载免费PDF全文 The Brazilian coast is characterized by dif- ferent tidal regimes and distinct meteorological influ- ences. The northern part has larger tidal amplitudes and is permanently affected by trade winds and tropical distur- bances; the southern portion has smaller tidal amplitudes and is frequently influenced by extratropical cyclone ac- tivity. Besides these aspects, many features regarding current structure and behavior are also present, such as the equatorial system of currents, the subtropical gyre and the corresponding western boundary currents, and the Bra- zil-Malvinas confluence region. Within this context, ef- forts were made to develop the BRAZCOAST system, capable of describing the processes that determine the oceanic circulation from large to coastal scales. A cus- tomized version of the Princeton Ocean Model （POM） was implemented in a basin-scale domain covering the whole of the tropical and southern Atlantic Ocean, with 0.5° spatial resolution, as well as three nested grids with （1/12）° resolution covering the different parts of the Bra- zilian shelf, in a one-way procedure. POM was modified to include tidal potential generator terms and a par- tially-clamped boundary condition for tidal elevations. The coarse grid captured large-scale features, while the nested grids detailed local circulations affected by bathymetry and coastal restrictions. An interesting aspect at the coarse grid level was the relevance of the Weddell Sea to the location of the tidal amphidromic systems. 相似文献
8.
The Soil Moisture and Net Primary Production Affected by CO_2 and Climate Change Using a Coupled Model 下载免费PDF全文
下载免费PDF全文 In this paper, a coupled model was used to estimate the responses of soil moisture and net primary production of vegetation （NPP） to increasing atmospheric CO2 concentration and climate change. The analysis uses three experiments simulated by the second-generation Earth System Model （CanESM2） of the Canadian Centre for Climate Modelling and Analysis （CCCma）, which are part of the phase 5 of the Coupled Model Intercomparison Project （CMIP5）. The authors focus on the magnitude and evolution of responses in soil moisture and NPP using simulations modeled by CanESM, in which the individual effects of increasing CO2 concentration and climate change and their combined effect are separately accounted for. When considering only the single effect of climate change, the soil moisture and NPP have a linear trend of 0.03 kg m^-2 yr^-1 and-0.14 gC m^- 2 yr^-2, respec- tively. However, such a reduction in the global NPP results from the decrease of NPP at lower latitudes and in the Southern Hemisphere, although increased NPP has been shown in high northern latitudes. The largest negative trend is located in the Amazon basin at -1.79 gC m^-2 yr^-2. For the individual effect of increasing CO2 concentration, both soil moisture and NPP show increases, with an elevated linear trend of 0.02 kg m^-2 yr^-1 and 0.84 gC m^-2 yr^-2, respectively. Most regions show an increasing NPP, except Alaska. For the combined effect of increasing atmospheric CO2 and climate change, the increased soil moisture and NPP exhibit a linear trend of 0.04 kg m^2 yr^-1 and 0.83 gC m^2 yr^-2 at a global scale. In the Amazon basin, the higher reduction in soil moisture is illustrated by the model, with a linear trend of-0.39 kg m^-2 yr^-1, for the combined effect. Such a change in soil moisture is caused by a weakened Walker circulation simulated by this coupled model, compared with the single effect of increasing CO2 concentration （experiment M2）, and a consequence of the reduction in NPP is also shown in this area, with a linear trend of- 相似文献
9.
Individual Variations of Winter Surface Air Temperature over Northwest and Northeast China and Their Respective Preceding Factors 下载免费PDF全文
下载免费PDF全文 Based on monthly mean surface air temperature （SAT） from 71 stations in northern China and NCEP/ NCAR and NOAA-CIRES （Cooperative Institute for Research in Environmental Sciences） twentieth century reanalysis data, the dominant modes of winter SAT over northem China were explored. The results showed that there are two modes that account for a majority of the total variance over northern China. The first mode is unanimously colder （warmer） over the whole of northern China. The second mode is characterized by a dipole structure that is colder （warmer） over Northwest China （NWC） and warmer （colder） over Northeast China （NEC）, accounting for a fairly large proportion of the total variance. The two components constituting the second mode, the individual variations of winter SAT over NWC and NEC and their respective preceding factors, were further investigated. It was found that the autumn SAT anomalies are closely linked to persistent snow cover anomalies over Eurasia, showing the delayed effects on winter climate over northern China. Specifically, the previous autumn SAT anomalies over the Lake Baikal （LB; 50-60°N, 85-120°E） and Mongolian Plateau （MP; 42-52°N, 80-120°E） regions play an important role in adjusting the variations of winter SAT over NWC and NEC, respectively. The previous autumn SAT anomaly over the MP region may exert an influence on the winter SAT over NEC through modulating the strength and location of the East Asian major trough. The previous autumn SAT over the LB region may modulate winter westerlies at the middle and high latitudes of Asia and accordingly affects the invasion of cold air and associated winter SAT over NWC. 相似文献
10.
Summer Asian-Pacific Oscillation and Its Relationship with Atmospheric Circulation and Monsoon Rainfall 总被引：1，自引：0，他引：1 下载免费PDF全文
下载免费PDF全文 ZHAO Ping CHEN Junming XIAO Dong NAN Sulan ZOU Yan ZHOU Botao 《Acta Meteorologica Sinica》2008,22(4):455-471
Using the ERA-40 data and numerical simulations, this study investigated the teleconnection over the extratropical Asian-Pacific region and its relationship with the Asian monsoon rainfall and the climatological characteristics of tropical cyclones over the western North Pacific, and analyzed impacts of the Tibetan Plateau （TP） heating and Pacific sea surface temperature （SST） on the teleconnection. The Asian-Pacific oscillation （APO） is defined as a zonal seesaw of the tropospheric temperature in the midlatitudes of the Asian-Pacific region. When the troposphere is cooling in the midlatitudes of the Asian continent, it is warming in the midlatitudes of the central and eastern North Pacific; and vice versa. The APO also appears in the stratosphere, but with a reversed phase. Used as an index of the thermal contrast between Asia and the North Pacific, it provides a new way to explore interactions between the Asian and Pacific atmospheric circulations. The APO index exhibits the interannual and interdecadal variability. It shows a downward trend during 1958-2001, indicating a weakening of the thermal contrast, and shows a 5.5-yr oscillation period. The formation of the APO is associated with the zonal vertical circulation caused by a difference in the solar radiative heating between the Asian continent and the North Pacific. The numerical simulations further reveal that the summer TP heating enhances the local tropospheric temperature and upward motion, and then strengthens downward motion and decreases the tropospheric temperature over the central and eastern North Pacific. This leads to the formation of the APO. The Pacific decadal oscillation and El Nino/La Nina over the tropical eastern Pacific do not exert strong influences on the APO. When there is an anomaly in the summer APO, the South Asian high, the westerly jet over Eurasia, the tropical easterly jet over South Asia, and the subtropical high over the North Pacific change significantly, with anomalous Asian monsoon rainfall and tropical cyclon 相似文献
11.
PAN Lunxiang LIU Dongxi QIE Xiushu WANG Dongfang ZHU Runpeng 《Acta Meteorologica Sinica》2013,27(4):591-600
Data from the World Wide Lightning Location Network (WWLLN) for the period 2005-2011 and data composite of the Lightning Imaging Sensor/Optical Transient Detector (LIS/OTD) for 1995-2010 are used to analyze the lightning activity and its diurnal variation over land and ocean of the globe. The Congo basin shows a peak mean annual flash density of 160.7 fl km-2 yr-1 according to the LIS/OTD. The annual mean land to ocean flash ratio is 9.6:1, which confirms the result from Christian et al. in 2003 based on only 5-yr OTD data. The lightning density detected by the WWLLN is in general one order of magnitude lower than that of the LIS/OTD. The diurnal cycle of the lightning activity over land shows a single peak, with the maximum activity occurring around 1400-1900 LT (Local Time) and a minimum in the morning from both datasets. The oceanic diurnal variation has two peaks: the early morning peak between 0100 and 0300 LT and the afternoon peak with a stronger intensity between 1100 and 1400 LT over the Pacific Ocean, as revealed from the WWLLN dataset; whereas the diurnal variation over ocean in the LIS/OTD dataset shows a large fluctuation. 相似文献
12.
13.
Soil Moisture Effects on Sand Saltation and Dust Emission Observed over the Horqin Sandy Land Area in China 总被引：1，自引：1，他引：0 下载免费PDF全文
下载免费PDF全文 In this study, the effects of soil moisture on sand saltation and dust emission over the Horqin Sandy Land area are investigated, based on observations of three dust events in 2010. The minimum friction velocity initiating the motion of surface particles, namely, the threshold friction velocity, is estimated to be 0.34,0.40, and 0.50 m s-1under the very dry, dry, and wet soil conditions, respectively. In comparison with the observations during the dust events under the very dry and dry soil conditions, the dust emission flux during the wet event is smaller, but the saltation activities of sand particles(d 50 μm) are stronger. The size distributions of airborne dust particles(0.1 d 20 μm) show that concentrations of the finer dust particles(0.1 d 0.3 μm) have a secondary peak under dry soil conditions, while they are absent under wet soil conditions. This suggests that the surface soil particle size distribution can be changed by soil moisture. Under wet soil conditions, the particles appear to have a larger size, and hence more potential saltating particles are available. This explains the occurrence of stronger saltation processes observed under wet soil conditions. 相似文献
14.
ZHAO Tian-Bao 《大气和海洋科学快报》2014,(4):369-375
Diurnal temperature range （DTR） is an im- portant measure in studies of climate change and variability. The changes of DTR in different regions are affected by many different factors. In this study, the degree of correlation between the DTR and atmospheric precipitable water （PW） over China is explored using newly homogenized surface weather and sounding observations. The results show that PW changes broadly reflect the geographic patterns of DTR long-term trends over most of China during the period 1970-2012, with significant anticorrelations of trend patterns between the DTR and PW, especially over those regions with higher magnitude DTR trends. PW can largely explain about 40% or more （re 0.40） of the DTR changes, with a d（PW）/d（DTR） slope of -2% to -10% K^-1 over most of northwestern and southeastern China, despite certain seasonal dependencies. For China as whole, the significant anticorrelations between the DTR and PW anomalies range from -0.42 to -0.75, with a d（PW）/d（DTR） slope of-6% to -11% K^-1. This implies that long-term DTR changes are likely to be associated with opposite PW changes, approximately following the Clausius-Clapeyron equation. Furthermore, the relationship is more significant in the warm season than in the cold season. Thus, it is possible that PW can be considered as one potential factor when exploring long-term DTR changes over China. It should be noted that the present study has a largely statistical focus and that the underlying physical processes should therefore be examined in future work. 相似文献
15.
The Combined Effect of Initial Error and Model Error on ENSO Prediction Uncertainty Generated by the Zebiak-Cane Model 下载免费PDF全文
下载免费PDF全文 Initial errors and model errors are the source of prediction errors. In this study, the authors compute the conditional nonlinear optimal perturbation （CNOP）-type initial errors and nonlinear forcing singular vector （NFSV）- type tendency errors of the Zebiak-Cane model with respect to El Nifio events and analyze their combined effect on the prediction errors for E1 Nino events. The CNOP- type initial error （NFSV-type tendency error） represents the initial errors （model errors） that have the largest effect on prediction uncertainties for E1 Nifio events under the perfect model （perfect initial conditions） scenario. How- ever, when the CNOP-type initial errors and the NFSV- type tendency errors are simultaneously considered in the model, the prediction errors caused by them are not am- plified as the authors expected. Specifically, the predic- tion errors caused by the combined mode of CNOP-type initial errors and NFSV-type tendency errors are a little larger than those caused by the NFSV-type tendency er- rors. This fact emphasizes a need to investigate the opti- mal combined mode of initial errors and tendency errors that cause the largest prediction error for E1 Nifio events. 相似文献
16.
This study investigated the relationship be- tween the asymmetry in the duration of El Nifio and La Nina and the length of their decaying phases. The results suggested that the duration asymmetry comes from the long decaying ENSO cases rather than the short decaying ones. The evolutions of short decaying El Nino and La Nina are approximately a mirror image with a rapid decline in the following summer for the warm and cold events. However, a robust asymmetry was found in long decaying cases, with a prolonged and re-intensified La Nina in the following winter. The asymmetry for long decaying cases starts from the westward extension of the zonal wind anomalies in a mature winter, and is further contributed to by the air-sea interaction over the tropical Pacific in the following seasons. 相似文献
17.
The Unprecedented Freezing Disaster in January 2008 in Southern China and Its Possible Association with the Global Warming 总被引：7，自引：0，他引：7 下载免费PDF全文
下载免费PDF全文 The unprecedented disaster of low temperature and persistent rain, snow, and ice storms, causing widespread freezing in the Yangtze River Basin and southern China in January 2008, is not a local or regional event, but a part of the chain events of large-scale low temperature and snow storms in the same period in Asia. The severity and impacts of the southern China 2008 freezing disaster were the most significant among others. This disastrous event was characterized by three major features： （1） snowfall, freezing rain, and rainfall, the three forms of precipitation, coexisted with freezing rain being the dominant producer responsible for the disaster; （2） low temperature, rain and snow, and freezing rain exhibited extremely great intensity, with record-breaking measurements observed for eight meteorological variables based on the statistics made by China National Climate Center and the provincial meteorological services in the Yangtze River Basin and southern China; （3） the disastrous weathers persisted for an exceptionally long time period, unrecorded before in the meteorological observation history of China.
The southern China 2008 freezing disaster may be resulted from multiple different factors that superimpose on and interlink with one another at the right time and place. Among them, the La Nina situation is a climate background that provided conducive conditions for the intrusions of cold air into southern China; the persistent anomaly of the atmospheric circulation in Eurasia is the direct cause for a succession of cold air incursions into southern China; and the northward transport of warm and moist airflows from the Bay of Bengal and South China Sea finally warranted the formation of the freezing rain and snow storms and their prolonged dominance in the southern areas of China.
A preliminary discussion of a possible association of this disastrous event with the global warming is presented. This event may be viewed as a short-term regional perturbation to the global warming. There is no 相似文献
The southern China 2008 freezing disaster may be resulted from multiple different factors that superimpose on and interlink with one another at the right time and place. Among them, the La Nina situation is a climate background that provided conducive conditions for the intrusions of cold air into southern China; the persistent anomaly of the atmospheric circulation in Eurasia is the direct cause for a succession of cold air incursions into southern China; and the northward transport of warm and moist airflows from the Bay of Bengal and South China Sea finally warranted the formation of the freezing rain and snow storms and their prolonged dominance in the southern areas of China.
A preliminary discussion of a possible association of this disastrous event with the global warming is presented. This event may be viewed as a short-term regional perturbation to the global warming. There is no 相似文献
18.
The microphysical ＂three-layer＂ model for stratiform clouds over a midlatitude location in Northwest China is investigated by combining in situ airborne Particle Measuring Systems, Inc. （PMS）, radar measurements, and the NCAR/Penn State Mesoscale Model Version 5 （MM5） simulation with a two-moment microphysics scheme. The coexistence of measured supercooled liquid water and small ice particles produces snow particles below the cloud top in the second layer. Peak number concentration and mean diameter of cloud water and raindrop appear in the third warm layer. A thin dry layer just below the melting layer is also observed. The predicted precipitation is tested by equitable threat score. The melting layer is clearly defined in the radar image and model radar reflectivity output is agreement with the observations. The model results provide features of the microphysical structure for every layer of ＂three-layer＂ model at Yan＇an station. For both observation and model simulation, the ＂three-layer＂ model explains the stratiform precipitation formation completely and comprehensively. 相似文献
19.
Some depression cells with heights lower than their surrounding cells may often be found in Grid-based digital elevation models （DEM） dataset due to sampling errors. The depression-filling algorithm presented by Planchon and Darboux works very quickly compared to other published methods. Despite its simplicity and delicacy, this algorithm remains difficult to understand due to its three complex subroutines and its recursive execution. Another fast algorithm is presented in this article. The main idea of this new algorithm is as follows： first, the DEM dataset is viewed as an island and the outer space as an ocean; when the ocean level increases, the DEM cells on the island＇s boundary will be inundated; when a cell is inundated for the first time, its elevation is increased to the ocean level at that moment; after the ocean has inun- dated the entire DEM, all of the depressions are filled. The depression-removing processing is performed using a priority queue. Theoretically, this new algorithm is a fast algorithm despite the fact that it runs more slowly than Planchon and Darboux＇s method. Its time-complexity in both the worst case and in an average case is O（8nlog2 （m））, which is close to O（n）. The running speed of this algorithm depends mainly on the insertion operation of the priority queue. As shown by the tests, the depres- sion-filling effects of this algorithm are correct and valid, and the overall time consumption of this algorithm is less than twice the time consumed by Planchon ＆ Darboux＇s method for handling a DEM smaller than 2500×2500 cells. More importantly, this new algorithm is simpler and easier to understand than Planchon and Darboux＇s method. This advantage allows the correct program code to be written quickly. 相似文献
20.
Simulation of the Microphysical Processes and Effect of Latent Heat on a Heavy Rainfall Event in Beijing 下载免费PDF全文
下载免费PDF全文 An extraordinary rainstorm that occurred in Beijing on 21 July 2012 was simulated using the Weather Research and Forecasting model. The results showed that：（1） The two precipitation phases were based on a combination of cold cloud processes and warm cloud processes. The accumulated conversion amount and conversion rate of microphysical processes in the warm-area phase were all much larger than those in the cold front phase.（2） 72.6% of rainwater was from the warm-area phase. Rainwater mainly came from the melting of graupel and the melting of snow, while the accretion of cloud water by rain ranked second.（3） The net heating rate with height appeared as an overall warming with two strong heating centers in the lower and middle layers of the troposphere and a minimum heating center around the melting layer. The net heating effect in the warm-area phase was stronger than that in the cold front phase.（4） Warm cloud processes contributed most to latent heat release, and the thermal effect of cold cloud processes on the storm in the cold front phase was enhanced compared to that in the warm-area phase.（5） The melting of graupel and snow contributed most to latent heat absorption, and the effect of the evaporation of rainwater was significantly reduced in the cold front phase. 相似文献