廈門(mén)大學(xué)海洋科學(xué)導(dǎo)論課件水文部分lect19-1226

1、Review: 各種形態(tài)海區(qū)中潮波潮流特性的比較,0,重點(diǎn)：a)各種海區(qū)潮汐、潮流的定性解釋 b)計(jì)算：窄長(zhǎng)半封閉海灣的潮位、潮流計(jì)算,4. 如圖所示，正規(guī)半日潮潮波（波長(zhǎng)為）由南向北傳入一個(gè)等深的窄長(zhǎng)海區(qū)（長(zhǎng)度AC=/6，平均水深H=10米，AB為一海堤），設(shè)潮波在該海區(qū)中的傳播不受科氏力的影響，求： 1)D點(diǎn)的最大潮流流速為1.73米/秒，那么C點(diǎn)的潮差為多大？ 2) 若B點(diǎn)的高潮間隙為1059，那么，D點(diǎn)農(nóng)歷四月初七何時(shí)出現(xiàn)最大潮流流速？ 3) E點(diǎn)的最大潮流流速； 4) 若把AB海堤炸掉，建一個(gè)足夠高的大橋取代之，那么，安全行使水深為8.5米的船通過(guò)大橋是否受時(shí)間限制，為什么？,/6,

2、C,D,E,潮波,A,B,解：(1) 窄長(zhǎng)半封閉海灣的原點(diǎn)設(shè)在離灣頂/4處,D點(diǎn),(2) 出現(xiàn)最大潮流流速為半潮面,D點(diǎn)出現(xiàn)的高潮時(shí),(7-1)0.8+1059=1547 1547+T/4=1547+0306=1853 1547-T/4=1547-0306=1241,D點(diǎn)另一高潮時(shí),1547-1224=0323 0323+T/4=0629 0323-T/4=0017,所以D點(diǎn)農(nóng)歷四月初七出現(xiàn)最大潮流流速時(shí)刻為1853、1241、0629、0017,（3） umax=1.0m/s,(4) 不受時(shí)間限制，潮波波高為A/2=1米，即使低潮時(shí)水深還有9米, The Atmosphere and the

3、 Ocean 大氣與海洋,Structure of the Atmosphere地球大氣的垂直分層,Layered ( approximate thickness of layers) Troposphere對(duì)流層 (weather zone) (15 km) Stratosphere平流層(35 km) Mesosphere中層 (30 km) Thermosphere 熱成層(415 km) Exosphere 逸散層( beyond 500 km from Earth) Based on temperature variations,Troposphere(對(duì)流層） 溫度隨高度降低 大氣

4、鉛直混合強(qiáng) 氣象要素水平分布不均 主要天氣現(xiàn)象和過(guò)程的源地 Stratosphere（平流層） 底層溫度變化不大，上部溫度隨高度增加而明顯增高 大氣層結(jié)穩(wěn)定，鉛直運(yùn)動(dòng)很弱,Mesosphere（中層） 溫度隨高度升高降低得很快 最冷層 Thermosphere（熱成層） 溫度隨高度增加而增加 溫度最高的層 溫度日變化可達(dá)上百度,2. Atmospheric variables（氣象要素）,Temperature（氣溫） Pressure (weight of overlying air, 1in Hg=33.86 mb)- average surface pressure = 1013mb （

5、氣壓） Water vapor-humidity/dew point/RH（濕度） Wind-speed and direction（風(fēng)）,3.1 Temperature,Temperature is a measure of the hotness or coldness of a substance. Temperature typically is measured in either Fahrenheit(華氏溫標(biāo)), Celsius(攝氏溫標(biāo)), or Kelvin(開(kāi)氏溫標(biāo)).,Fahrenheit (1714, Germany): Freezing of water at sea

6、 level = 32 degrees Fahrenheit Boiling = 212 degrees Fahrenheit The scale is linear. Celsius (1742, Sweden): Freezing = 0 degrees Celsius Boiling = 100 degrees Celsius The scale is linear. Kelvin (1800s, Lord Kelvin) Freezing = 273 Kelvin Boiling = 373 Kelvin The scale is linear. K = degrees Celsius

7、 + 273,三種不同溫標(biāo)之間換算,3.2 Atmospheric pressure(氣壓),觀(guān)測(cè)高度到大氣上界單位面積上鉛直空氣柱的重量 1hPa=1000dyn/cm2 1mb 1mmHg=1.33hPa 1hPa=0.75mmHg,氣象學(xué)上規(guī)定：溫度為C，緯度為45度的海平面的氣壓作為標(biāo)準(zhǔn)大氣壓，稱(chēng)為1個(gè)大氣壓，其值相當(dāng)于760mmHg，或相當(dāng)于1013.25hPa,Meteorologists generally measure air pressure in millibars (mb). Average sea level pressure = 1013 mb The highes

8、t measured sea level pressure on Earth was 1084 mb (Agata, Siberia). The lowest measured sea level pressure on Earth was 870 mb (within a typhoon).,Isobars are in millibars,Low pressure zone is where air density is lower than in surrounding areas because the air is warmer or has a higher moisture co

9、ntent. High pressure zone is where air pressure is higher than in surrounding area because of cooling or lower moisture content.,水平氣壓場(chǎng),3.3 Humidity,Vapor pressure (e,水汽壓)：濕空氣中，由水汽所引起的那一部分壓強(qiáng) Saturation vapor pressure (E,飽和水汽壓)：當(dāng)溫度一定時(shí)，若從純水的水表面逸入空氣中的水分與從空氣中進(jìn)入水面的水分在數(shù)量上相同，此時(shí)水汽所造成的那部分壓強(qiáng)溫度越高，E越大,Relative H

10、umidity (RH，相對(duì)濕度): 空氣中實(shí)際水氣壓e與同溫度下的飽和水氣壓E之比 RH=e/E*100% Dew point (Td，露點(diǎn)): 濕空氣等壓降溫達(dá)到飽和時(shí)的溫度,3.4 Wind,Wind is simply the velocity of the air with respect to the earth. （空氣相對(duì)于地面作水平運(yùn)動(dòng)） In meteorology, we refer to the wind direction as the direction from which the wind is blowing.,蒲福風(fēng)級(jí)表,3. The atmosphere

11、in motion（大氣運(yùn)動(dòng)）,Warm air is less dense than cold air and moist air is less dense than dry air. Low air density results in rising air and low surface pressure High air density results in descending air and high surface pressure.,3.1 Density differences in the atmosphere result in pressure differences

12、 at the surface.,3.2 Atmospheric Processes,Fluids (air and water) flow from areas of high pressure to areas of low pressure. Change in pressure across a horizontal distance is a pressure gradient. Greater the difference in pressure and the shorter the distance between them, the steeper the pressure

13、gradient and the stronger the wind. Movement of air across a pressure gradient parallel to Earths surface is called a wind winds are named for the direction from which they come. In contrast, ocean currents are named for the direction towards which they travel.,大尺度水平運(yùn)動(dòng)基本上是在水平氣壓梯度力和科氏力相平衡下維持的地轉(zhuǎn)平衡運(yùn)動(dòng)。,

14、3.3 平均大氣環(huán)流的垂直結(jié)構(gòu),Simple wind system: surface winds blow from the polar high to the equatorial low The air at the equator heats up, becomes less dense and returns to the poles at the top of the troposphere to complete this convection cell the Northern Hemisphere : north winds at the surface; the South

15、ern Hemisphere: south winds at the surface.,Three major convection cells（三圈環(huán)流） are present in each hemisphere.,The Hadley cell(哈得萊環(huán)流) extends from the Equator to about 30o latitude. The Ferrel Cell(費(fèi)雷爾環(huán)流) extends from 30 o to about 50 o latitude. The Polar Cell(極地環(huán)流) extends from 90 o to about 50o l

16、atitude.,Break the atmospheric circulation pattern into three cells: Lows at 0o and 60o characterized by warm, less dense, rising air Highs at 30o and 90o characterized by cold, more dense, descending air Surface winds blow from highs to lows,Effect of the Coriolis Force Deflect currents or winds Th

17、e equator Characterized by weak winds (“doldrums”) Intertropical Convergence Zone (ITCZ) Zone along which the wind systems of the two hemispheres converge Also the zone of highest sea surface temperatures Not exactly on the equator because of the land/water difference between the N and S Hemispheres

18、,30o to Equator: Trade Winds blow towards the equator (“Easterlies”) Form part of the atmospheric circulation known as Hadley Circulation or Hadley Cells Strictly speaking, the term “Hadley Cell” refers only to the N-S component of the circulation. Because the flow within these cells is deflected by

19、 the Coriolis Force, circulation flows in a spiral pattern in three dimensions. At 30o, weak and variable winds prevail “Horse Latitudes”,Between 30o and 60o, Westerlies prevail Between 60o and 90o, Polar Easterlies prevail Rain is caused by rising air the greatest precipitation is at 0o and 60o,4.M

20、odifying the wind bands,4.1 季風(fēng) Middle latitudes, particularly over land ,experience large seasonal changes in surface temperature Waters high heat capacity and its great mobility combine to minimize the variation of temperature in the oceans. In the Northern Hemisphere , at temperate latitudes, dist

21、inct patterns of high and low atmospheric pressure that change with the seasons. Summer: low-pressure areas over the continents. and high-pressure cells over the water. Winter: the land loses heat much more rapidly than the water, the pattern of high- and low-pressure cells reverses,Atmospheric circ

22、ulation in the Northern Hemisphere clockwise around high pressure cells counterclockwise around low pressure cells In the Southern Hemisphere this is reversed The wind pattern in the Southern Hemisphere exhibits little seasonal variation because there is relatively little land area. the atmospheric

23、circulation is quite similar to that predicted by the model of a water-covered planet,clockwise around high pressure cells, divergence counterclockwise around low pressure cells, convergence,Northern Hemisphere,Along the Pacific coast of the United State, the northerly winds cool the coastal areas i

24、n the summer and the southerly wind warm them in the winter. The eastern United State receives warm, moist air from the low latitudes in the summer, and cold air moves down from the high latitude in the winter.,Average wind for summer Average wind for winter,4.2 Monsoon effect Large seasonal tempera

25、ture variations over land can produce major climatic changes in coastal regions. During summer months, a large low-pressure system forms over India and Southeast Asia in response to the heating of the land. Counterclockwise airflow around this system carries warm, moist air from the Indian Ocean ove

26、r the continent where the moisture condenses as the air rises and cools. This results in a steady, heavy rain over the land that is referred to as the wet or summer monsoon.,夏季風(fēng)作用下，天氣炎熱、濕潤(rùn)、多雨,During winter months, the loss of heat from the land will cool the overlying air, producing a high-pressure

27、system over the continent. Clockwise circulation around this system carries cool, dry air from the interior of the continent over the coastal regions. This is the dry, or winter, monsoon,冬季風(fēng)作用下，天氣寒冷、干燥、少雨,Monsoon,Seasonal influences: Monsoon climate,Seabreeze / Landbreeze,usually strongest in the af

28、ternoon,usually strongest in the late night and early morning hours,4.3 Topographic Effect（地形效應(yīng)） As the wind moves higher above sea level, it will cool and water vapor will begin to condense out of the air. Precipitation(降水) will often fall on the windward side of mountains or islands, while on the

29、opposite, or leeward side, it will remain dry creating a rain shadow. Precipitation patterns caused by changes in topography, or elevation, are called the orographic(地形的) effect.,Precipitation(降水) will often fall on the windward side of mountains or islands, while on the opposite, or leeward side, i

30、t will remain dry creating a rain shadow.,5. Hurricanes(颶風(fēng)),Tropical storm：熱帶風(fēng)暴 Cyclone：氣旋 Hurricane：颶風(fēng) Typhoon：臺(tái)風(fēng),Not in SA or SP-waters too cold Not within 50 of equator air too still,5.1 Tropical area,推動(dòng)熱帶地區(qū)大氣運(yùn)動(dòng)的能量來(lái)源不是直接由日照提供，主要由水汽凝結(jié)所釋放的潛熱來(lái)提供。,熱帶地區(qū)由于科氏力較小，通常云層零亂，不像高緯度那樣有組織,Inter-tropical Convergence Zone（熱帶輻合帶）,七月,Extratropical storms,5.2 Hurricane,Satellite tracking-Hurricane Andrew in 1992 late August,Hot, humid