厦门大学海洋科学导论课件水文部分lect19-1226

1、Review: 各种形态海区中潮波潮流特性的比较,0,重点：a)各种海区潮汐、潮流的定性解释 b)计算：窄长半封闭海湾的潮位、潮流计算,4. 如图所示，正规半日潮潮波（波长为）由南向北传入一个等深的窄长海区（长度AC=/6，平均水深H=10米，AB为一海堤），设潮波在该海区中的传播不受科氏力的影响，求： 1)D点的最大潮流流速为1.73米/秒，那么C点的潮差为多大？ 2) 若B点的高潮间隙为1059，那么，D点农历四月初七何时出现最大潮流流速？ 3) E点的最大潮流流速； 4) 若把AB海堤炸掉，建一个足够高的大桥取代之，那么，安全行使水深为8.5米的船通过大桥是否受时间限制，为什么？,/6,

2、C,D,E,潮波,A,B,解：(1) 窄长半封闭海湾的原点设在离湾顶/4处,D点,(2) 出现最大潮流流速为半潮面,D点出现的高潮时,(7-1)0.8+1059=1547 1547+T/4=1547+0306=1853 1547-T/4=1547-0306=1241,D点另一高潮时,1547-1224=0323 0323+T/4=0629 0323-T/4=0017,所以D点农历四月初七出现最大潮流流速时刻为1853、1241、0629、0017,（3） umax=1.0m/s,(4) 不受时间限制，潮波波高为A/2=1米，即使低潮时水深还有9米, The Atmosphere and the

3、 Ocean 大气与海洋,Structure of the Atmosphere地球大气的垂直分层,Layered ( approximate thickness of layers) Troposphere对流层 (weather zone) (15 km) Stratosphere平流层(35 km) Mesosphere中层 (30 km) Thermosphere 热成层(415 km) Exosphere 逸散层( beyond 500 km from Earth) Based on temperature variations,Troposphere(对流层） 温度随高度降低 大气

4、铅直混合强 气象要素水平分布不均 主要天气现象和过程的源地 Stratosphere（平流层） 底层温度变化不大，上部温度随高度增加而明显增高 大气层结稳定，铅直运动很弱,Mesosphere（中层） 温度随高度升高降低得很快 最冷层 Thermosphere（热成层） 温度随高度增加而增加 温度最高的层 温度日变化可达上百度,2. Atmospheric variables（气象要素）,Temperature（气温） Pressure (weight of overlying air, 1in Hg=33.86 mb)- average surface pressure = 1013mb （

5、气压） Water vapor-humidity/dew point/RH（湿度） Wind-speed and direction（风）,3.1 Temperature,Temperature is a measure of the hotness or coldness of a substance. Temperature typically is measured in either Fahrenheit(华氏温标), Celsius(摄氏温标), or Kelvin(开氏温标).,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、 + 273,三种不同温标之间换算,3.2 Atmospheric pressure(气压),观测高度到大气上界单位面积上铅直空气柱的重量 1hPa=1000dyn/cm2 1mb 1mmHg=1.33hPa 1hPa=0.75mmHg,气象学上规定：温度为C，纬度为45度的海平面的气压作为标准大气压，称为1个大气压，其值相当于760mmHg，或相当于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.,水平气压场,3.3 Humidity,Vapor pressure (e,水汽压)：湿空气中，由水汽所引起的那一部分压强 Saturation vapor pressure (E,饱和水汽压)：当温度一定时，若从纯水的水表面逸入空气中的水分与从空气中进入水面的水分在数量上相同，此时水汽所造成的那部分压强温度越高，E越大,Relative H

10、umidity (RH，相对湿度): 空气中实际水气压e与同温度下的饱和水气压E之比 RH=e/E*100% Dew point (Td，露点): 湿空气等压降温达到饱和时的温度,3.4 Wind,Wind is simply the velocity of the air with respect to the earth. （空气相对于地面作水平运动） In meteorology, we refer to the wind direction as the direction from which the wind is blowing.,蒲福风级表,3. The atmosphere

11、in motion（大气运动）,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.,大尺度水平运动基本上是在水平气压梯度力和科氏力相平衡下维持的地转平衡运动。,

14、3.3 平均大气环流的垂直结构,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（三圈环流） are present in each hemisphere.,The Hadley cell(哈得莱环流) extends from the Equator to about 30o latitude. The Ferrel Cell(费雷尔环流) extends from 30 o to about 50 o latitude. The Polar Cell(极地环流) 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 季风 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.,夏季风作用下，天气炎热、湿润、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,冬季风作用下，天气寒冷、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（地形效应） 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(飓风),Tropical storm：热带风暴 Cyclone：气旋 Hurricane：飓风 Typhoon：台风,Not in SA or SP-waters too cold Not within 50 of equator air too still,5.1 Tropical area,推动热带地区大气运动的能量来源不是直接由日照提供，主要由水汽凝结所释放的潜热來提供。,热带地区由于科氏力较小，通常云层零乱，不像高纬度那样有组织,Inter-tropical Convergence Zone（热带辐合带）,七月,Extratropical storms,5.2 Hurricane,Satellite tracking-Hurricane Andrew in 1992 late August,Hot, humid