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

Presentation on theme: "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"— Presentation transcript:

1 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

2 課程大綱 推薦主要參考書 地球大氣的源起與結構:earth atmosphere, structure and evolution
大氣輻射與氣溫: radiation, energy, and temperature 雲與降水：Cloud and precipitation 大氣的運動,氣壓與風: atmospheric motion, pressure and wind 重要天氣現象: important weather phenomena 天氣預報技術: weather forecast 全球氣候與氣候變遷: climate change and general circulation 空氣品質與大氣化學: air quality and atmospheric chemistry 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.

3 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

4 Course syllabus (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

5 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)

6 大氣科學的最新發展 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。

7 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。

8 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 (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

9 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)

10 Vilhelm F. K. Bjerknes (1862-1951) Jacob A.B. Bjerknes (1897-1975)
Pioneers in modern meteorology and climate research 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 ( ), 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 ( ), 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. (BCCR: Bjerknes Center for Climate Research, Norway)

11 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

12 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)

13 Carl-Gustaf Rossby: Long waves in the westerly

14 Early days of NWP

15 Jule Charney’s influence on modern Meteorology/long waves vs polar front (1982, BAMS)

16 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。

17 Journal of the Atmospheric Sciences: Vol. 35, No. 3, pp. 414–432
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

18 Chaos Theory混沌理論 Predictability problem：可預測度問題

19 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)

20 大氣海洋交互作用-聖嬰與南方震盪ENSO

21 Walker circulation-an equatorial belt circulation
Chervin and Druyan 1984 MWR

22 Sea surface temperature anomaly map

23 Walker’s southern oscillation (Bjerknes 1969)

24 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 (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.

25 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 (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.

26 Oscillation of the thermohaline circulation
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.

27 Multiseason climate forecast with coupled model
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. 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.

28 大氣科學的最新發展 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。

29 災變天氣之監測和預報 氣象局表示，民眾對於颱風路徑、風雨預測之機率問題認知，並不夠清楚，颱風來襲期間，若媒體之氣象預報人員未按氣象局提供的資料做說明，很容易讓民眾誤判，所以，氣象局將從資訊收集、研判、時效等方面，加強與媒體人員互動溝通，讓民眾做好防颱準備。

30 Typhoon Aere visible image, wind and rainfall forecast

31 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

32 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.

33 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)

34 US Navy global forecast model output (48hr forecast) Typhoon Aere and Chaba

35 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 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.

36 空氣污染問題 Real time monitoring of North Africa dust storm

37 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, A dust plume surrounds peninsular UAE/Oman and the Straight of Hormuz.

38 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.

39 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.

40 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)

41 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.

42 Decadal annual SST anomalies (°C) from 30-yr (1961–90) climatology: from (a) decade of 1891–1900 to (j) decade of 1981–90

43 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)。

44 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.