國立台灣大學大氣科學系
大氣科學概論
大氣系一年級必修、三學分
授課老師：周仲島教授
上課時間：星期二 9:10～10:00
星期四10:20～12:10
上課教室：大氣系館B105室
課程大綱
1. 地球大氣的源起與結構:earth atmosphere, structure and evolution
2. 大氣輻射與氣溫: radiation, energy, and temperature
3. 雲與降水：Cloud and precipitation
4. 大氣的運動,氣壓與風: atmospheric motion, pressure and wind
5. 重要天氣現象: important weather phenomena
6. 天氣預報技術: weather forecast
7. 全球氣候與氣候變遷: climate change and general circulation
8. 空氣品質與大氣化學: air quality and atmospheric chemistry
9. 高層大氣與太空天氣: upper atmosphere and space weather
推薦主要參考書
Ahrens, C. D., 2003, Meteorology Today: An Introduction to Weather, Climate, and the
Environment. Seventh edition, Brooks/Cole-Thomson Learning, Pacific Grove, CA,
USA, 544 pages.
課程評估
• 作業（25%）+ 期中考試（25%）+期末書面
口頭報告（25％）＋ 期末考試（25%）
• 作業：氣象網站搜尋+氣象名詞解釋 + 簡易期
刊論文選讀 + 參觀訪問報告
• 參觀中央氣象局: 2004年11月中旬
• 期中考試：2004年10月28日星期四上午
• 期末書面口頭報告：2005年1月4-6-11日
• 期末考試：2005年01月13日星期四上午
Course syllabus
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(Sep) 14, 16 (14) course descrip./require; (16) introduction (0th chap)
21, 23
(21) introduction ; (23) pressure/wind (4th chap) + map
28, 30
(28) no class; (30) pressure/wind continue + map
(Oct) 05, 07 extratropical cyclone and related weathers (5th chap) + map
12, 14
severe storms and related phenomena (5th chap) + map
19, 21
tropical cyclone and weather forecasting (6th chap)
26, 28
(26) summary; (28) midterm exam
(Nov) 02, 04 atmospheric composition and its evolution (1st chap)
09, 11
radiation budget and temperature (2nd chap)
16, 18
radiation budget and temperature continues
23, 25
water vapor and cloud/precipitation (3rd chap)
30, (Dec) 02 water vapor and cloud/precipitation continues
07, 09
energy balance/general circulation and climate (7th chap)
14, 16
energy balance/general circulation and climate continues
21, 23
air quality and atmospheric chemistry (8th chap)
28, 30
upper atmosphere and space weather (9th chap)
(Jan) 04, 06 Term project oral report
11, 13
(11) project oral report, (13) final exam
認識大氣科學的態度與方法
• 自然現象Nature phenomena
• 觀察Observations: qualitatively & quantitatively
description (由定性至定量的描述)
• 詮釋Interpretation; data diagnosis / theoretical and
analytical / numerical modeling (資料診斷; 理論
解析; 數值模擬)
Formation-structure-evolution-interaction and
feedback (生成-發展-演變-影響)
• 實踐Execution (application): forecast /
modification (預報 與 改造)
大氣科學的最新發展
1.
2.
3.
4.
5.
6.
7.
劇烈天氣之即時監測與預報：遙測設備的蓬勃發展以及下游應用。
氣象雷達、氣象衛星、以及氣象飛機等。這方面的研究需要大氣
科學家和下游應用各學門專家的通力合作。
大氣與海洋的交互作用：季風和聖嬰現象的研究，並延伸至短期
氣候變化的預測，這方面的研究關連到大氣科學家與海洋學家的
合力研究。
大氣問題的數值模擬：數值模擬天氣及預報，利用電腦自動計算
結果經人為詮釋來預報天氣。這方面的研究關連到大氣科學家，
應用數學家及電子計算機專家的合作。
空氣污染問題：熱島效應,全球增溫,南極臭氧洞等。這方面的研
究關連到大氣科學家與化學家的通力合作。
探討地球氣候變遷的歷史：這方面的研究牽涉到大氣科學家，地
球化學家，地質學家,海洋學家,及冰河學家們的合作。探討百年
甚至千年氣候變化的原因與未來之可能趨勢，並討論因應對策。
太陽表面擾動所造成地球高層大氣各種特殊現象產生的物理過程：
磁暴/太陽風→通訊、太空天氣預報的計畫。這方面的研究牽涉到
高層大氣物理學家，太陽物理學家及太空物理學家們的通力合作。
其他星球的大氣探索：遙測技術,實地太空觀測（太空船）,近代
物理之輻射理論的發展與應用等。
大氣科學的歷史 (一)
Atmospheric science is the study of the atmosphere and its
phenomena (Meteorology and Climate)
大氣科學是研究大氣與其相關現象的科學
（氣象和氣候）
希臘哲學家 亞里斯多德（340 BC），Meteorologica，和天氣
與氣候相關的知識，並包括天文學、地理學、以及化學。雲、
雨、雪、風、雹、雷、和颶風等。”meteoros”希臘字意指在高
空中。Meteorology一字表示由高空掉落以及在空氣中各種事
務或現象稱之。
希臘哲學家 狄奧佛拉斯塔（287 BC），Book of Signs，第一
本天氣預報的書，利用與天氣變化有關的訊息來預報天氣。
氣象學成為『自然科學』源於利用科學儀器來量度氣象變數。
大氣科學的歷史 (二)
意大利天文學家 伽利略(16世紀)：溫度計。
意大利數學及物理學家 托里賽利(17世紀)：水銀氣壓計。
法國數學及哲學家 帕斯卡和笛卡兒(17世紀)：氣壓隨高度變化。
英國科學家 霍克(17世紀)：風速計。
德國物理學家 華氏(18世紀)：定華氏溫標。
法國化學家 查爾斯(18世紀)：溫度與固定體積空氣的關係。
瑞典天文學家 攝氏(18世紀)：定攝氏溫標。
美國科學家法蘭克林(18世紀)：放風箏入雷暴證明閃電來源。
瑞士地質及氣象學家 笛紹高斯(18世紀)：毛髮濕度計。
氣象參數（溫度，氣壓，風速風向，濕度，閃電）的
度量與天氣現象之關係開始被建立
大氣科學的歷史 (三)
英國氣象學家 哈德里(18世紀)：解釋地球旋轉如何影響赤道的
風向。
1821年 天氣圖被繪製（天氣現象）
法國物理學家 科氏(19世紀)：利用數學證明地球旋轉對大氣運
動的影響。
1842年電報系統發展，長程通訊對氣象事業發展影響深遠
1869年等壓線的繪製（現代天氣圖）
挪威學派 (The Bergen School)
1920年氣團與鋒面的概念開始建立:極鋒理論(polar front
theory)，近代天氣學的開端(Bjerknes, Solberg, Bergeron)
Vilhelm F. K. Bjerknes
(1862-1951)
Jacob A.B. Bjerknes
(1897-1975)
BJERKNES
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Pioneers in modern meteorology and climate research
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Born on the 14th March, 1862 in Oslo (Christiania), Vilhelm Frimann Koren Bjerknes was destined for a career in science.
He obtained a Master’s degree in mathematics and physics in Kristiania 1888 and continued his studies in Paris and Bonn,
where his work together with Heinrich Hertz on electrical resonance resulted in a doctoral thesis in 1892.
While he was professor at the University of Stockholm (1895-1906), Vilhelm Bjerknes worked out a synthesis of
hydrodynamics and thermodynamics, which was applicable to large-scale circulation in the atmosphere and the oceans. Based
on his theorems, he published a programatic paper in 1904 on “The problem of weather forecasting as a problem in mechanics
and physics” (Meteorologische Zeitschrift, Wien 21:1-7) where he postulated the procedure now know as numerical weather
forecasting. Once at the Geophysical Institute in Bergen (1917-1926), he laid the foundations of the Bergen School of
Meteorology. Bjerknes established a network of weather observations in Norway that collected data that would be of great
importance in their later work. Together with his son Jacob, also an acknowledged meteorologist, he put forward the acclaimed
“polar front theory”. In analogy with WWI battlefronts, the meteorological “fronts” form the boundaries between cold and
warm air masses and their theories and models suggested that weather activity is concentrated in these relatively narrow zones,
where mid-latitude cyclones were proposed to form, live, and decay. Today, practically all weather forecasting is based on
Bjerknes principles described in his paper of 1904 and made possible thanks to the enormous computer capabilities of today.
The work by Bjerknes marked a turning point in atmospheric science and remains remarkably unaltered to this day.
Further, Vilhelm and Jacob Bjerknes conducted several studies of the ocean circulation, air-sea exchange, and climate
variability that laid the basis for modern research on climate change and the role of the ocean in the climate system. Jacob
Bjerknes carried out pioneer studies on the North Atlantic Oscillation (NAO), by describing its major features and how it
influences the currents and temperature conditions in the North Atlantic. Nowadays the vision provided by the Bjerknes family
has been taken further by simulating climate variability in models that couple the atmosphere, land, and oceans, in an attempt
to estimate the response of the climate system to driving forces.
The Centre is named is thus named as a tribute to their efforts.
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• (BCCR: Bjerknes Center for Climate Research, Norway)
大氣科學的歷史 (四)
芝加哥學派 (The Chicago School-Dynamical meteorology era)
1940年氣球探空、雷達、氣象飛機，西風噴流，羅士比波
(Rossby waves 西風帶長波的發現)，WMO成立
現代氣象科學的蓬勃發展
1950年馮紐曼與查尼 (J. Charney)，高速電子計算機，建
立準地轉理論（長波與氣旋鋒面），數值天氣預報 (NWP)
1960年氣象衛星（泰洛斯1號），全球天氣監測 (熱帶海洋
氣象)，都卜勒雷達
1970年全球氣候與環境變遷，聖嬰與南方震盪(ENSO)，
南極臭氧洞，全球暖化
1980年剖風儀、雙偏振都卜勒雷達、複雜衛星系統、超大
快速電子計算機
大氣科學的歷史（五）
20世紀氣候學理論研究的十大成就
 20~30年代, 三大氣壓震盪,北大西洋震盪(NAO),北太平洋
震盪(NPO),南方震盪(SO); Walker (1932)
 30年代, 大氣長波理論-羅士比波, Rossby (1939)
 40~50年代, 時間平均環流之長波預測, Namias (1953)
 60年代, 赤道東西向沃克環流, Bjerknes (1969)
 70年代, 溫室效應(doubling CO2), Manabe (1975)
 80年代, 月平均環流預測, Miyakoda (1986)
 80~90年代, ENSO預測, Cane and Zebiak (1986)
 80~90年代, ENSO理論, Suarez (1988), Battisti (1989)
 90年代, 溫鹽環流, Delworth (1993)
 90年代, 季平均環流預測, Ming Ji (1994)
Carl-Gustaf Rossby: Long waves in the westerly
Early days
of NWP
Jule Charney’s influence on modern
Meteorology/long waves vs polar front
(1982, BAMS)
極鋒理論在北半球溫帶氣旋之理想生命周期的連續天氣
示意圖。在其生命期，系統由於動力作用向東移。
Journal of the Atmospheric Sciences: Vol. 35, No. 3, pp. 414–432.
The Life Cycles of Some Nonlinear Baroclinic Waves
Adrian J. Simmons and Brian J. Hoskins
Chaos Theory混沌理論
• Predictability problem：可預測度問題
20世紀氣候學理論研究的十大成就
 20~30年代, 三大氣壓震盪,北大西洋震盪(NAO),北太平洋
震盪(NPO),南方震盪(SO); Walker (1932)
 30年代, 大氣長波理論-羅士比波, Rossby (1939)
 40~50年代, 時間平均環流之長波預測, Namias (1953)
 60年代, 赤道東西向沃克環流, Bjerknes (1969)
 70年代, 溫室效應(doubling CO2), Manabe (1975)
 80年代, 月平均環流預測, Miyakoda (1986)
 80~90年代, ENSO預測, Cane and Zebiak (1986)
 80~90年代, ENSO理論, Suarez (1988), Battisti (1989)
 90年代, 溫鹽環流, Delworth (1993)
 90年代, 季平均環流預測, Ming Ji (1994)
大氣海洋交互作用-聖嬰與南方震盪ENSO
Walker circulation-an equatorial belt circulation
Chervin and Druyan 1984 MWR
Sea surface temperature anomaly map
Walker’s southern oscillation (Bjerknes 1969)
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Journal of the Atmospheric Sciences: Vol. 32, No. 1, pp. 3–15.
The Effects of Doubling the CO2 Concentration on the climate of a General
Circulation Model
Syukuro Manabe and Richard T. Wetherald
Geophysical Fluid Dynamics Laboratory/NOAA, Princeton University, Princeton, N.J.
08540
(Manuscript received 6 June 1974, in final form 8 August 1974)
ABSTRACT
An attempt is made to estimate the temperature changes resulting from doubling the
present CO2 concentration by the use of a simplified three-dimensional general
circulation model. This model contains the following simplications: a limited
computational domain, an idealized topography, no heat transport by ocean currents,
and fixed cloudiness. Despite these limitations, the results from this computation
yield some indication of how the increase of CO2 concentration may affect the
distribution of temperature in the atmosphere. It is shown that the CO2 increase raises
the temperature of the model troposphere, whereas it lowers that of the model
stratosphere. The tropospheric warming is somewhat larger than that expected from a
radiative-convective equilibrium model. In particular, the increase of surface
temperature in higher latitudes is magnified due to the recession of the snow
boundary and the thermal stability of the lower troposphere which limits convective
beating to the lowest layer. It is also shown that the doubling of carbon dioxide
significantly increases the intensity of the hydrologic cycle of the model.
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Monthly Weather Review: Vol. 114, No. 12, pp. 2363–2401.
One-Month Forecast Experiments—without Anomaly Boundary Forcings
K. Miyakoda, J. Sirutis, and J. Ploshay
Geophysical Fluid Dynamics Laboratory/N0AA, Princeton University, Princeton, NJ 08542
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(Manuscript received 17 August 1985, in final form 19 May 1986)
ABSTRACT
A series of one-month forecasts were carried out for eight January cases, using a particular
prediction model and prescribing climatological sea-surface temperature as the boundary
condition. Each forecast is a stochastic prediction that consists of three individual integrations.
These forecasts start with observed initial conditions derived from datasets of three
meteorological centers. The forecast skill was assessed with respect to time means of variables
based on the ensemble average of three forecasts. The time or space filter is essential to suppress
unpredictable components of atmospheric variabilities and thereby to make an attempt at
extending the limit of predictability. The circulation patterns of the three individual integrations
tend to be similar to each other on the one-month time scale, implying that forecasts for the 10
day (or 20 day) means are not fully stochastic. The overall results indicate that the 10-day mean
height prognoses resemble observations very well in the first ten days, and then start to lose
similarity to real states, and yet there is some recognizable skill in the last ten days of the month.
The main interests in this study are the feasibility of one-month forecasts, the adequacy of initial
conditions produced by a particular data assimilation, and the growth of stochastic uncertainty.
An outstanding problem turns out to be a considerable degree of systematic error included in the
prediction model, which is now known to be “climate drift.” Forecast errors are largely due to
the model's systematic bias. Thus, forecast skill scores are substantially raised if the final
prognoses are adjusted for the model's known climatic drift.
Oscillation of the thermohaline circulation
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Journal of Climate: Vol. 6, No. 11, pp. 1993–2011.
Interdecadal Variations of the Thermohaline Circulation in a Coupled
Ocean-Atmosphere Model
T. Delworth, S. Manabe, and R.J. Stouffer
Geophysical Fluid Dynamics Laboratory/N0AA, Princeton University, Princeton,
New Jersey
(Manuscript received 5 September 1992, in final form 26 February 1993)
ABSTRACT
A fully coupled ocean-atmosphere model is shown to have irregular oscillations
of the thermohaline circulation in the North Atlantic Ocean with a time scale of
approximately 50 years. The irregular oscillation appears to be driven by density
anomalies in the sinking region of the thermohaline circulation (approximately
52°N to 72°N) combined with much smaller density anomalies of opposite sign in
the broad, rising region. The spatial pattern of sea surface temperature anomalies
associated with this irregular oscillation bears an encouraging resemblance to a
pattern of observed interdecadal variability in the North Atlantic. The anomalies
of sea surface temperature induce model surface air temperature anomalies over
the northern North Atlantic, Arctic, and northwestern Europe.
http://www.cpc.ncep.noaa.gov/schemm
http://www.emc.ncep.noaa.gov/research/cmb/atm_forecast/images
Multiseason climate forecast with coupled model
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Bulletin of the American Meteorological Society: Vol. 75, No. 4, pp. 569–578.
A Multiseason Climate Forecast System at the National Meteorological Center
Ming Ji, Arun Kumar, and Ants Leetmaa
Coupled Model Project, National Meteorological Center, NOAA/NWS, Washington, D.C.
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ABSTRACT
The Coupled Model Project was established at the National Meteorological
Center(NMC)in January l991 to develop a multiseason forecast system based on
coupled ocean atmosphere general circulation models. This provided a focus to combine
expertise in near real-time ocean modeling and analyses situated in the Climate Analysis
Center (CAC) with expertise in atmospheric modeling and data assimilation in the
Development Division. Since the inception of the project, considerable progress has
been made toward establishing a coupled forecast system. A T40 version of NMC's
operational global medium-range forecast model (MRF) has been modified so as to have
improved response to boundary forcing from the Tropics. In extended simulations,
which are forced with observed historical global sea surface temperature (SST) fields,
the model reproduces much of the observed tropical Pacific and North American rainfall
and temperature variability. An ocean reanalysis has been performed for the Pacific
basin starting from July 1982 to present and uses a dynamical model-based as
assimilation system. This also provides the ocean initial conditions for coupled fore cast
experiments. The current coupled forecast model consists of an active Pacific Ocean
model coupled to the T4Oversion of the NMC's MRF. In the future, a global ocean
model will be used to include climato information from other ocean basins. The initial
experiments focused on forecasting Northern Hemisphere winter SST anomalies in the
tropical Pacific with a lead time of two seasons. The coupled model showed
considerable skill during these experiments. Work is currently under way to quantity the
skill in predicting climatic variability over North America.
大氣科學的最新發展
1.
2.
3.
4.
5.
6.
7.
劇烈天氣之即時監測與預報：遙測設備的蓬勃發展以及下游應用。
氣象雷達、氣象衛星、以及氣象飛機等。這方面的研究需要大氣
科學家和下游應用各學門專家的通力合作。
大氣與海洋的交互作用：季風和聖嬰現象的研究，並延伸至短期
氣候變化的預測，這方面的研究關連到大氣科學家與海洋學家的
合力研究。
大氣問題的數值模擬：數值模擬天氣及預報，利用電腦自動計算
結果經人為詮釋來預報天氣。這方面的研究關連到大氣科學家，
應用數學家及電子計算機專家的合作。
空氣污染問題：熱島效應,全球增溫,南極臭氧洞等。這方面的研
究關連到大氣科學家與化學家的通力合作。
探討地球氣候變遷的歷史：這方面的研究牽涉到大氣科學家，地
球化學家，地質學家,海洋學家,及冰河學家們的合作。探討百年
甚至千年氣候變化的原因與未來之可能趨勢，並討論因應對策。
太陽表面擾動所造成地球高層大氣各種特殊現象產生的物理過程：
磁暴/太陽風→通訊、太空天氣預報的計畫。這方面的研究牽涉到
高層大氣物理學家，太陽物理學家及太空物理學家們的通力合作。
其他星球的大氣探索：遙測技術,實地太空觀測（太空船）,近代
物理之輻射理論的發展與應用等。
災變天氣之監測和預報
動研民按風預氣
溝判眾氣來測象
通、誤象襲之局
，時判局期機表
讓效，提間率示
民等所供，問，
眾方以的若題民
做面，資媒認眾
好，氣料體知對
防加象做之，於
颱強局說氣並颱
準與將明象不風
備媒從，預夠路
。體資很報清徑
人訊容人楚、
員收易員，風
互集讓未颱雨
、
Typhoon Aere visible image,
wind and rainfall forecast
Hurricane Isabel
Synoptic Surveillance
Sept 13 to Sept 17, 2003
Red tracks: AFRES WC-130
Blue tracks: NOAA G-IV 00Z
Green tracks: NOAA G-IV 12Z
TRMM SEES RAIN FROM HURRICANES FALL
AROUND THE WORLD
Since rain and freshwater flooding are the number one causes of death from
hurricanes in the United States over the last 30 years, better understanding of
these storms is vital for insuring public safety. A recent study funded by
NASA and the National Science Foundation offers insight into patterns of
rainfall from tropical storms and hurricanes around the world.
Researchers at the University of Miami's Rosenstiel School of Marine and
Atmospheric Science, Miami, and the National Oceanic and Atmospheric
Administration Atlantic Oceanographic and Meteorological Laboratory's
Hurricane Research Division, Miami, used data from NASA's Tropical
Rainfall Measuring Mission (TRMM) satellite to show how rain falls at
different rates in different areas of a storm. The results were published in the
July issue of the journal Monthly Weather Review.
The results are already being used in a model developed at the Hurricane
Research Division to estimate rainfall accumulation related to tropical
cyclones. The findings are important because they may help in the
development of better forecasts.
數值模擬-數值天氣預報(NWP)
DVj/Dt = Aj =  Fj / m, (Vj = [u, v, w] )
 Fj = gravity, pressure gradient, Coriolis, friction
DT/Dt = H =  Q
 Q = radiation, sensible heat, latent heat
Di /Dt =  Si
 Si = cloud, rain, ice, snow
P = RT
Initial and boundary conditions
Meteorological variables: Vj (u, v, w), P, i, T 
(precipitation)
US Navy global forecast model output (48hr forecast) Typhoon Aere and Chaba
NASA DATA SHOWS HURRICANES HELP PLANTS BLOOM IN
"OCEAN DESERTS"
• Whenever a hurricane races across the Atlantic Ocean, chances are
phytoplankton will bloom behind it. According to a new study using NASA
satellite data, these phytoplankton blooms may also affect the Earth's
climate and carbon cycle.
• Dr. Steven Babin, a researcher at the Johns Hopkins University Applied
Physics Laboratory in Laurel, Md., studied 13 North Atlantic hurricanes
between 1998 and 2001. Ocean color data from the SeaWiFS instrument on
the SeaStar satellite were used to analyze levels of chlorophyll, the green
pigment in plants. The satellite images showed tiny microscopic ocean
plants, called phytoplankton, bloomed following the storms.
• "Some parts of the ocean are like deserts, because there isn't enough food
for many plants to grow. A hurricane's high winds stir up the ocean waters
and help bring nutrients and phytoplankton to the surface, where they get
more sunlight, allowing the plants to bloom," Babin said.
http://www.gsfc.nasa.gov/topstory/2004/0602hurricanebloom.html
空氣污染問題
Real time monitoring of North Africa dust storm
The United Arab Emirates Unified Aerosol Experiment mission runs from August 5 through
September 30. Scientists are using satellites, computer models and ground stations to understand
the unique "mixing bowl" of desert dust, smoke and other aerosols created by the complex
atmospheric circulations.
This is a true color image of the United
Arab Emirates taken from Aqua-MODIS
on August 10, 2004. A dust plume
surrounds peninsular UAE/Oman and the
Straight of Hormuz.
Scientists Study Desert Air to Understand
Weather and Climate
NASA, Naval Research Laboratory and Scripps Institution of Oceanography scientists have assembled in the Arabian Desert to study
tiny airborne particles called aerosols and their effect on weather and climate. The scientists are collaborating with researchers
from the United Arab Emirates Department of Water Resources Studies and 20 other U.S., European and South African research
laboratories to decipher the complex processes controlling the area climate.
The United Arab Emirates Unified Aerosol Experiment mission runs from August 5 through September 30. Scientists are using
satellites, computer models and ground stations to understand the unique "mixing bowl" of desert dust, smoke and other aerosols
created by the complex atmospheric circulations.
"Man-made emissions, smoke from the Indian subcontinent and desert dust combine in the air to make a unique aerosol laboratory,"
said Hal Maring of NASA Headquarters, Washington.
"We have the most intensely monitored remote-sensing aerosol network ever assembled, including two radiation and aerosol super
sites, 10 satellite instruments, six computer models, a research aircraft and a research vessel," said Jeff Reid, mission scientist
from the Naval Research Laboratory in Monterey, Calif. "There are 70 scientists participating, 40 of them working in the field,
from over a dozen institutions, including the large South African and Colorado-based National Center for Atmospheric Research
weather modification teams," he added.
Aerosols have always been an interesting puzzle piece in learning how climate works. Lighter aerosols reflect heat
and sunlight and have cooling properties. Darker aerosols absorb heat and light, warming the atmosphere. This
mission will measure aerosol properties, where aerosols move, and whether they add or remove warmth.
Scientists also hope to model and explain complicated weather patterns in the coastal regions of the Arabian
Gulf and the Gulf of Oman.
By obtaining more accurate data about aerosols and their behavior, scientists will improve computer climate models and predictions of
climate behavior in response to changes in aerosol concentrations. To accomplish this task, NASA will start from space, using
primarily its Terra and Aqua satellites, but other satellites as well. Aboard Terra, the Multi-angle Imaging SpectroRadiometer
instrument, built and managed by NASA's Jet Propulsion Laboratory, Pasadena, Calif., will provide an independent measure of
aerosol size and concentration, as well as altitude in some cases. That instrument observes aerosols over both land and ocean.
These satellite data will be compared to ground-based remote sensing measurements of mineral dust and pollutant aerosols gathered
by 15 Aerosol Robotic Network instruments over land and water, the Naval Research Laboratory Mobile Atmospheric Aerosol
and Radiation Characterization Observatory and NASA's Surface-sensing Measurements for Atmospheric Radiative Transfer.
When it Rains, it Pours — Even for the Drops that Lead to Drizzle
New theory on drizzle formation says a few big drops get all the water
UPTON, NY - In research that could lead to more accurate weather forecasts and climate models, scientists at the U.S. Department of
Energy’s Brookhaven National Laboratory say a physical limit on the number of cloud droplets that grow big enough to form drizzle
paradoxically makes drizzle form faster. That’s because those few droplets that cross the drizzle “barrier” readily collect enough
surrounding droplets to fall — instead of staying stuck in the clouds competing for a limited water supply and never getting quite big
enough.
Atmospheric physical chemist Bob McGraw with cloud physicist and co-author Yangang Liu. (Click image for hi-res, 300-dpi
verison)Atmospheric physical chemist Robert McGraw, lead author of the Brookhaven study, will present this research on Thursday,
August 26, 2004, at the 228th national meeting of the American Chemical Society in Philadelphia, Pennsylvania (Pennsylvania
Convention Center, Room 103A, 9:40 a.m. Eastern Time) together with Brookhaven cloud physicist and co-author Yangang Liu. The
research will also be published in an upcoming edition of Physical Review E.
“Drizzle is an important cloud process that plays a crucial role in regulating Earth’s energy balance and water cycle, because drizzle affects
how long clouds persist,” says McGraw. “So understanding drizzle formation will help scientists predict both local weather and the
effects of clouds on global climate.”
Older theories of drizzle formation left scientists with a puzzle: None explained how drizzle could form within the typical cloud lifetime.
In these earlier models, droplets simply coagulated with each other to reach larger size. In this process, many droplets are free to
begin growing, but they all end up competing for the available cloud water at the same time. This competition prevents any of them
from quickly reaching a size large enough to begin falling as drizzle.
The new theory resolves the puzzle through the discovery of a statistical barrier to the number of drops that achieve drizzle size, a barrier
that paradoxically speeds up drizzle formation.
Under the new theory, the rate of drizzle drop formation is dependent on the cloud liquid water content, the droplet concentration, and
turbulence. Atmospheric turbulence causes fluctuations in the rates of droplet growth and evaporation in clouds. Once a drop grows
large enough to fall under gravity, it begins to collect the smaller cloud droplets that surround it.
This process is called collection and it refers to the volumetric gain of a specified drop large enough to have a significant gravitational fall
velocity so as to accrete the smaller, slower falling droplets that typify the main population of the cloud. Collection is thus an
additional growth mechanism that, following the axiom ‘the rich get richer,’ or, ‘when it rains, it pours,’ becomes available to those
relatively few droplets that, through chance fluctuations, reach fall velocity size.
“Those few droplets that do cross the barrier experience less competition for available cloud water and, thus, rapidly reach collection size,”
McGraw says.
“Of course, if the barrier is too high — as it often is in polluted clouds with high droplet concentrations — then no droplets can cross and
drizzle can’t form,” he adds. “Other things being equal, such drizzle suppression tends to increase the lifetimes of clouds formed in
polluted areas, as compared to those formed in unpolluted areas, such as over the ocean.” This could have important implications for
understanding the climate effects of aerosol pollutants via their influence on cloud lifetime and cloud cover.
Early Arctic Thaw Could Have Chilling Effect
Spring will be coming early next year to the great forests and tundra of the Arctic. Good for the vegetation, but perhaps not so good for the
atmosphere.
Spring in the high latitudes has been coming earlier in the past few decades. The early thaw means a longer growing season for the Arctic and
the boreal forest, the ring of mostly evergreen trees that stretches across the northern reaches of North America and Eurasia. It also means
that more carbon, now stored in the region's usually frozen soils, may be released into the air.
"The spring thaw date in boreal North America has been advancing almost one day a year since 1988," says JPL research scientist Dr. Kyle
McDonald. He and his colleagues are using data from NASA's Quikscat and Japan's Midori 2 satellites to determine exactly when and
where the thaw occurs. The satellites' radar instrument, the Seawinds scatterometer, can detect changes in water across the landscape
from its frozen to liquid state. They used data from previous microwave missions to piece together a historical record of the spring thaw
in this large, remote area where few ground measurements exist.
The boreal forest, called the taiga in Russian, is the second largest forest ecosystem on Earth, second only to the tropical rain forest in size. In
North America it covers almost 28 percent of the land north of Mexico, covering much of northern Canada and reaching into Alaska.
Scientists are interested in monitoring thaw events in the Arctic and the boreal forest for several reasons. The region is extremely sensitive to
change in temperature. "If global climate change is happening, here's where you would expect to see it," McDonald says. The region also
plays a major role in Earth's carbon cycle.
For most of the year, the temperature of the ground in the Arctic tundra and boreal forest is below 0 degrees Centigrade (32 degrees Fahrenheit)
and the vegetation is dormant. But a little bit of warming has a big effect. Once surface soil temperatures edge over freezing, plants
rapidly spring into action. "There's a very abrupt change from dormant to productive associated with the spring thaw," says Dr. John
Kimball, a research assistant professor at the University of Montana's Flathead Lake Biological Station. "It is like a natural on and off
switch."
Over the centuries, this huge area of tundra and forest has taken great quantities of the greenhouse gas carbon dioxide out of the air, released
oxygen back into the atmosphere and stored the remaining carbon in vegetation. Eventually plants decompose and the carbon ends up in
the soil. "The high latitudes hold roughly 40 percent of the world's soil carbon," says Kimball.
Earlier springs in the boreal forest and Arctic tundra mean a longer growing season with more vegetation taking more carbon out of the
atmosphere for longer periods. However, the same warming that releases water and nitrogen in the soil enabling plants to grow is also
good for microbes that unleash the carbon stored in the soil back into the atmosphere.
"Frozen soil can store carbon dioxide for thousands of years," says Kimball. "Trees and other vegetation can only store it for up to a few
hundred years or less. The residence time is much shorter and more unstable." He also points out that since the 1960s the number of
forest fires in the region has increased dramatically, decreasing the length of time that trees and other plants hang on to their stored
carbon before releasing it back into the atmosphere.
Could the boreal forest and Arctic tundra change from being a carbon sink, a place where carbon is stored, to a carbon source? That's the big,
yet unanswered, question.
In the '50s horror movie "The Thing," warming up a frozen creature discovered in the Arctic brought a monster to life. It may turn out that
some other things are better kept frozen.
Written by Rosemary Sullivant Media Contact: Alan Buis (818) 354-0474
氣候
變遷
UK
The contribution to each winter's total precipitation made from "heavy"
precipitation days, indicated by red (below average) and blue (above average)
bars. A black smoothing line to highlight decadal variations has been overlaid.
Decadal annual SST anomalies (°C)
from 30-yr (1961–90) climatology:
from (a) decade of 1891–1900 to (j)
decade of 1981–90
太陽表面擾動
(左)太陽表面粒斑化特徵圖, 包括太陽黑子[sunspots],光斑
[faculae], 和光焰[flares]。(右)日全蝕下的日冕[corona]。太陽活
耀年時(1958) 太陽表面的黑子、光斑、及光焰數目非常多。反
之，稱為太陽安靜年(1964)。
Between Sun and Earth
Since 1965, the Mauna Loa Solar
Observatory has collected solar data from
Hawaii's second- highest peak. The site
now hosts the Advanced Coronal
Observing System.
This sequence of images
shows the change in
electron densities through
Earth's atmosphere,
primarily in the ionosphere,
during a solar storm on 10
January 1997.