《气象科技英语》课件：专业英语Unit 7 Monsoon

《气象科技英语》课件：专业英语Unit 7 Monsoon

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 二、 Meteology Today 有关 MONSOON 内容 三、 《 气象科技英语 900 句 》 有关 MONSOON 内容 四、课文内容 ① The term “monsoon” appears to have originated from the Arabic word mausim which means season. ② 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 . ③ 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. ④ It is within these regions that the most vigorous and dramatic cycles of weather events on the earth take place. Paragraph 1 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”. ②The “wet”, of course, refers to the rainy season, during which warm moist and very disturbed winds blow inland from the oceans. ③The 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. ④ In some locations, the cold and dry winter air flows across the equator toward the hot continents of the summer hemisphere. ⑤ 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 ①In this article, we shall concentrate mainly on the annual cycle of the monsoon. ② However, it is incorrect to think of summer and winter phases of the monsoon as just prolonged periods of rain or drought, each of some months duration. ③ There are also significant variations that exist on time scales ranging from days to weeks. ④Thus , while the monsoon appears to have a well-defined annual cycle, closer inspection shows that the monsoon varies substantially and that within the cycles a significant substructure exists that becomes evident as the intensity of the monsoon rains wax and wane through the wet season. Paragraph 3 Paragraph 4 ① 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 . ②A 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. ③During an active phase the weather is unstable with frequent storms that produce the rain deluges traditionally associated with the monsoon. ④ But , during a dormant or break phase of the monsoon, the weather is hot, clear, and dry. ⑤Monsoon 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 ① A variable of the monsoon system of considerable importance is the timing of the commencement of the set. ②This , 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. ③ 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. ④The 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. Das(1984) describes the following working rules used to define the onset of the monsoon over Kerala: (i) starting with 10 May, if at least 5 out 10 stations in Kerala report 24 hour rainfall totals of >1 mm for two consecutive （连续的） days, an onset is declared on the second day; (ii) if >3 out of 7 stations in Kerala report no rainfall for the next 3 days, indication are given for a recession （撤回） of the monsoon; (iii) after the monsoon has advanced North of 13°N even a temporary recession is a rare event. Das futher mentions that there are similar working rules for other parts of India. Normal dates of (a) onset, and (b) withdrawal of Southwest monsoon over India. From Rao (1976) (copyright by the Government of India). Onset and withdrawal of monsoon over India Onset Withdrawal Paragraph 6 ①Relationships 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. ②It is, therefore, useful to reexamine the relationship by using the Darwin sea level pressure for the period 1901-1981. ③Darwin 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. ④Although 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. ⑤The 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 7 and 8 ① If one is going to predict monsoon rain, it is necessary to examine the Southern Oscillation before the monsoon. ②However, it should be recalled that one of Walker’s most important findings was that monsoon rainfall has very significant correlations with the subsequent global circulation . Paragraph 8 ①The most remarkable of Walker’s 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) ②It is quite in keeping with this that the Indian monsoon rainfall has its connections with later rather than earlier events. ③The 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 ① 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. ②This new knowledge provides a better synoptic and dynamical framework to examine the interannual and long-term variability of monsoon. ③The El Nino –Southern Oscillation seems to be the single most important feature of the ocean-atmosphere systems. ④Its 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. ⑤ It is therefore necessary to document the main features of the global circulation, including the monsoon, during different phases of the Southern Oscillation. ⑥It 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 ① The prospects for long-range forecasting of large-scale, seasonal mean monsoon rainfall appear to be good. ②There are significant correlations between large-scale seasonal mean Indian (rainfall) anomalies and low-frequency changes in the Southern Oscillation. ③There are also significant correlations between seasonal Indian rainfall anomalies and slowly varying boundary conditions of sea surface temperature and snow cover. Paragraph 11 ① 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. ②The large-scale moisture convergence required for the release of the latent energy is organized by gradients of temperature at the earth’s surface. ③Solar 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. ④Therefore fluctuations of soil moisture can influence the intensity of the tropical heat sources over the land. Paragraph 11 (to be continued) ⑤Similarly, the tropical heat source over the oceans can be influenced by the anomalies of sea surface temperature. ⑥It 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 earth’s surface. ⑦Since 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 . ⑧Therefore arguments collectively suggest that there is a physical basis for predictability of the large-scale,seasonally averaged monsoon flow and rainfall. Paragraph 12 ①If the daily rainfall patterns related to the monsoon’s 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? ② Forecasting beyond the limits of deterministic prediction would not be very good . ③Fortunately this does not appear to be the case. ④While 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. ⑤This provides a physical basis as well as hope for long-range forecasting of monsoon rainfall. ⑥It 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 .