气象科技专业英语专业英语Unit-7--Monsoon.ppt

,单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,*,单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,*,Unit 7 Monsoon,一、,New words,Apply,vt.,运用,;apply to,把,应用于,;apply for,申请；,application,n.,申请；,application form,申请表,Reversal,n.,逆转；,reverse,vt.,Adjacent,a.,邻近的,;surrounding,周围的,Vigorous,a.,强盛的,Dramatic,a.,引人注目的,Inhabitant,n.,居民；,resident,Inland,a.,内陆,Prolong,vt.,延长,Duration,n.,持续时间；,period,期间,Substantially,ad.,实质的，本质的,Substructure,n.,下部结构；,sub+,亚；次级；下级 （构词法）,Subtropical,亚热带,Subgrid,次网格,Subsystem,分系统,Subdivision;subseasonal.,12.Reside,vi.,驻扎；,resident,居民,13.Southern Oscillation,南方涛动；,North Atlantic Oscillation(NAO),北大西洋涛动,Arctic Oscillation(AO),北极涛动；,Antarctic Oscillation(AAO),南极涛动；,Quasi-Biennial Oscillation(QBO),准两年振荡,Seesaw,翘翘板；,Fluctuation n.,振荡，扰动；,Perturbation n.,扰动,14.Passive,a.,消极的，被动的；,active,a.,主动的,15.Quasi-biennial oscillation,准两年振荡,*,quasi+,准,（,approximate,not exact),For example,quasi-static,准静力；,quasi-geostrophic,准地转的；,quasi-stationary front,准静止锋，,etc.,*biennial,两年一次；,biannual,一年两次,16.Condensation,n.,浓缩，凝结,;condense,vt.,17.Convergence,n.,汇合，辐合；,divergence n.,辐散；散度,18.gradients,n.,梯度；,temperature gradients,pressure gradients,SST gradients,etc.,19.Anomaly n.,不规则，异常；,anomalies,复数,20.Hypothesize,v.,假想；,hypothesis,n.,;hypotheses,复数,21.Instability,n.,不稳定性；,stability,稳定性；,unstable,adj.,不稳定的,in+,否定 （构词法）,inaccurate,不精确，,invisible,不可见，,incompressible,不可压缩,independent,独立；,inhomogeneous,不均匀；,informal,非正式,22.Orographic barrier,地形分界线；,topographic,23.Spatial coherence,空间相干性；,spatial,adj.,空间的；,temporal,adj.,时间的,三、,气象科技英语,900,句,有关,MONSOON,内容,四、课文内容,The term“monsoon”appears to have originated from the Arabic word mausim which means season.,It is most often applied to the seasonal reversals of wind direction along the shores of the Indian Ocean,especially in the Arabian Sea,that blow from the southwest during one half of the year and from the northeast during the other,.,As monsoons have come to be better understood,the definition have been broadened to include almost all of the phenomena,associated with,the annual weather cycle within the tropical and subtropical continents of Asia,Australia,and Africa and the adjacent seas and oceans.,It is,within these regions,that,the most vigorous and dramatic cycles of weather events on the earth take place.,Paragraph 1,The dominant characteristic of the great monsoon systems,the annual cycle itself,has led the inhabitants of the monsoon regions to,divide,their lives,customs,and economics,into,two distinct phases:the“wet”and the“dry”.The“wet”,of course,refers to,the rainy season,during which warm moist and very disturbed winds blow inland from the oceans.The dry refers to the other half of the year,when the wind reverses bringing cool and dry air from the hearts of the winter continents.In some locations,the cold and dry winter air flows across the equator toward the hot continents of the summer hemisphere.In this manner,the dry of the winter monsoon,is tied to,the wet of the summer monsoon,and,vice versa,.,Paragraph 2,Surface winds during northern hemisphere a)summer b)winter,Paragraph 4,Short-term variations,include the individual weather disturbances,（,i.e.,a period of disturbed weather or storms lasting some days),that occur,in rapid succession,during the,so-called,active-monsoon periods,.A prolonged period of one to several weeks marked by an absence of weather disturbances is called a break-monsoon,or more correctly,a break in the active monsoon.During an active phase the weather is unstable with frequent storms that produce the rain deluges traditionally,associated with,the monsoon.But,during a dormant or break phase of the monsoon,the weather is hot,clear,and dry.Monsoon breaks are drought period and,if prolonged,may cause considerable,hardship,and even famine in the monsoon lands.,In the course of the Southwest monsoon,there are periods when the monsoon trough shifts northwards to the foot of the Himalayas,and rains decrease over much of India except along the slopes of the Himalayas and parts of Northeast India,and the Southern peninsula.This synoptic situation is called,break in monsoon,.,The break are most frequent in July and August,and they typically last from a few days to three weeks.,Mean pressure departure,03GMT,in mb,during break in monsoon.From Rao(1976),Fig.3.20 Percentage rainfall departure in peak phase of break in monsoon.Symbols are as follows:cross-hatching excess of+50%or more;simple hatching excess of+1 to 49%;thin dot raster deficit of 1 to 49%;thick dot raster deficit of 50%and beyond.From Rao(1976),Paragraph 5,A variable of the monsoon system,of considerable importance,is the timing of the commencement of the set.This,the,so-called,onset of the monsoon,is usually sudden with the weather,changing,abruptly,from,the premonsoon heat(similar to the torrid climate of the break-monsoon),to,the weather disturbances,storms,and intense rainfall of an active period.For a farmer knowledge of when the onset will occur is critical as with it resides the key,to,the timing of the planting of his crops.The withdrawal of the monsoon(i.e.,the cessation of rainfall over the continents)during the early autumn is a much more gradual transition than the onset.,Paragraph 6,Relationships between the Indian monsoon rainfall and the Southern Oscillation were established by Walker in the beginning of this century and,versions,of them have been used since for operational forecasting of monsoon rainfall.It is,therefore,useful to reexamine the relationship by using the Darwin sea level pressure for the period 1901-1981.Darwin pressure is chosen because its long-term record is considered to be more accurate and more complete than that for any other station in that region.Although Tahiti minus Darwin pressure is considered to be better index of the Southern Oscillation,Tahiti pressure is available only for the period 1935-1981,and for this period the correlation coefficient between the spring Tahiti,Paragraph 6(to be continued),pressure and Indian monsoon rainfall is only 0.01.The summer monsoon rainfall data used in this study is the area weighted average of the percentage departure for each of the 31 subdivisions of India,and,is referred to as,the whole Indian monsoon rainfall anomaly.,Paragraph 8,The most remarkable of Walkers results was his discovery of the control that the Southern Oscillation seemingly,exerted upon,subsequent events and in particular of the fact,that the index for the Southern Oscillation as a whole for the summer quarter June-August,had,a correlation coefficient of 0.8 with the same index for the,following,winter-quarter,though only of 0.2 with the,previous,winter quarter,.,Paragraph 8(to be continued),It is quite,in keeping with,this that the Indian monsoon rainfall has its connections with later,rather than,earlier events.The Indian monsoon therefore,stands out,as an active,not a passive feature in world weather more efficient as a broadcasting tool than as an event to be forecast.,Paragraph 9,During the recent years we have gained a better understanding of large-scale atmospheric phenomena such as El Nino and the Southern Oscillation,the quasi-biennial oscillation and atmospheric blocking.This new knowledge provides a better synoptic and dynamical framework to examine the interannual and long-term variability of monsoon.The El Nino Southern Oscillation seems to be the single most important feature of the ocean-atmosphere systems.Its period is quite large(2-5 years)and therefore it can be of practical value for predicting fluctuations of a seasonal phenomenon like the monsoon.,It is therefore necessary to,document,the main features of the global circulation,including the monsoon,during different phases of the Southern Oscillation.It should,however,be recognized that the fluctuations of the monsoon can also be one of the important factors affecting the Southern Oscillation.,Paragraph 9(to be continued),Paragraph 10,The prospects for long-range forecasting of large-scale,seasonal mean monsoon rainfall appear to be good.There are significant correlations between large-scale seasonal mean Indian,(rainfall),anomalies and low-frequency changes in the Southern Oscillation.There are also significant correlations between seasonal Indian rainfall anomalies and slowly varying boundary conditions of sea surface temperature and snow cover.,Paragraph 11,Tropical and monsoon flows are dominated by the thermally forced planetary scale Hadley and Walker type circulations for which the primary energy source is the latent heat of condensation.The large-scale moisture convergence required for the release of the latent energy is organized by gradients of temperature at the earths surface.Solar heating can produce thermal low-pressure areas over the land which can further deepen,due to,latent-heating if the dynamical circulation,is favorable for,moisture convergence.Therefore fluctuations of soil moisture can influence the intensity of the tropical heat sources over the land.,Paragraph 11(to be continued),Similarly,the tropical heat source over the oceans can be influenced by the anomalies of sea surface temperature.It is therefore reasonable to expect that the changes in the large-scale tropical flows would be related to the changes in the slowly varying boundary conditions at the earths surface.Since dynamical instabilities are not too strong in the tropics,it is also reasonable to hypothesize,that the changes in the large-scale flows are dominated by the changes in the boundary conditions,.Therefore arguments collectively suggest that there is a physical basis for predictability of the large-scale,seasonally averaged monsoon flow and rainfall.,Paragraph 12,If the daily rainfall patterns related to the monsoons high frequency,synoptic scale disturbances were the consequence of dynamical instabilities of the large-scale flow,and if the changes of the large-scale flow itself were caused mainly by its interaction with such unstable?,Forecasting,beyond the limits of deterministic prediction,would not be very good,.Fortunately this does not appear to be the case.While it is indeed true that the rain producing disturbances form only when the structure of the large-scale flow(i.e.,horizontal and vertical gradients of wind,temperature,and moisture)is favorable,the changes in the large-scale flow itself,Paragraph 12(to be continued),appear to be primarily,related to,planetary-scale boundary forcing manifested as tropical heat sources and,to,orographic barriers.This provides a physical basis as well as hope for long-range forecasting of monsoon rainfall.It is also,of interest,that during the monsoon season,even the biweekly and monthly anomalies have significant spatial coherence,which further suggests that the prospects for predicting biweekly and monthly anomalies are also quite good,.,