「大氣科學」第三十一期第四號（Atmospheric Sciences Vol.31 No.04）P. 307~306
台灣與全球雨量長期變化研究(二)：
亞澳季風區一至三月雨量年際變化
盧孟明 麥如俊
中央氣象局氣象科技中心
（中華民國九十一年八月二十六日投稿；中華民國九十二年九月一日定稿）
摘 要
分析了Dai全球陸上降水格點資料(1920-95)我們發現台灣一至三月降雨的年際變化和西太平洋群島(關島附近)與澳洲西北部的降雨變化顯著相關。藉由NCEP/NCAR重分析資料的可降水量之佐證，我們歸納出三種降雨類型：類型一是台灣偏濕，菲律賓海與熱帶西太平洋和澳洲西北偏乾；類型二則是台灣偏乾，另兩地偏濕；類型七是台灣和澳洲西北偏乾，菲律賓海與熱帶西太平洋偏濕。環流分析結果指出，類型一的出現主要是El Niño造成的，而類型二與類型七都發生在菲律賓海與熱帶西北太平洋上對流運動比較活躍的時候，有二分之一的個案發生在La Niña年。伴隨類型二的重要低層環流特徵為從東亞與中緯度西北太平洋伸入菲律賓海和赤道西太平洋的低壓深槽，此深槽可加強跨赤道流。和類型二相比，類型七在菲律賓海上也有低壓環流，然而尺度較小。
亞澳季風區海平面氣壓場的EOF分析結果顯示赤道太平洋海溫的年際與年代際變化對這個區域的大氣有不同的影響。伴隨ENSO年代際變化，赤道西太平洋和澳洲東部的海平面氣壓場有升高的趨勢，下沉氣流增強。此一趨勢對於類型一的出現頻率影響並不大，對於類型二、七的出現影響也有限。顯示形成類型一雨型的主要因子仍是ENSO的年際變化，而La Niña不是類型二、七的形成主因。類型二、七雨型的形成可能決定於菲律賓海和赤道西太平洋上低層低壓環流的尺度大小。
關鍵詞： 台灣冬雨，台灣冬雨與聖嬰現象，亞澳季風系統
The January-March
Precipitation in the Region
of Asian-Australian
Monsoon
Mong-Ming Lu Ru-Jun May
（Manuscript received 26 August 2002；in final form 01 September 2003）
ABSTRACT
The 1920-95 grid precipitation
over the land prepared by Dai et al. (1997) has been analyzed for studying the
relationship between
Based on the results of EOF
analysis of the sea-level pressure over the Asian-Australian monsoon region, it
is suggested that the atmosphere is affected by the equatorial SST anomalies in
two different time scales of interannual and interdecadal scales. In the
interdecadal time scale, the sea-level pressure over the western Pacific and
eastern Australia in the decade after 1977 became higher than the decade before
1977. The increase in sea level pressure does not have clear impact on the
occurrence frequency of the three rainfall types. These findings support the
conclusion that the Type-1 pattern results from El Niño, while neither Type-2
nor Type-7 is primarily caused by remote SST anomalies.
Key words:
Taiwan winter precipitation, Taiwan precipitation and ENSO, Asian - Australian
Monsoon System
「大氣科學」第三十一期第四號（Atmospheric Sciences Vol.31 No.04）P. 307~306
北台灣夏季雹暴之雙都卜勒雷達分析
林品芳 周仲島 游政谷
國立台灣大學大氣科學研究所
（中華民國九十二年六月九日收稿；中華民國九十二年九月十八日定稿）
摘 要
冰雹事件於副熱帶地區相當罕見，根據過去台灣地區38年(1961~1999)地面測站紀錄顯示，只有6次發生於夏季，其中在1999年8月28日至8月31日連續四日於台北地區午後降下冰雹。這些雷暴系統先在台北南方的斜坡山區形成，而後發展成具組織性之多胞對流系統，到達平地時降下冰雹。本文針對8月29日之雹暴個案，利用台灣北部中央氣象局五分山都卜勒雷達及民用航空局中正機場都卜勒雷達資料進行雙都卜勒風場反演，探討此雹暴之運動場及降水結構特徵。
綜觀環境顯示在台灣東方有一高層冷心低壓，伴隨高層較強東北風，具環境風切隨高度順轉之綜觀環境條件與美國中西大平原類似，有利劇烈風暴發展。除此之外，融解層較台灣地區相同季節之氣候值5200公尺低約350公尺。
回波資料顯示大於55 dBZ之回波值初始發生於高度5~6公里，於30分鐘之內先向上發展至高度10公里，然後往下延伸至近地面。回波拱腔(vault)及胚核簾(embryo curtain)特徵位於雹暴移動方向之前緣。由雙都卜勒風場分析得知，上衝流位於系統移動方向的前緣，此傾斜上衝流之最大垂直速度位於高度7公里處，達18
。藉由地面觀測資料指出，此上衝流是由局部環流之海風及因降水之下衝流配合地形所形成的下坡冷外流之輻合所維持。
關鍵詞：雹暴、都卜勒雷達、回波拱腔、胚核簾、局部環流、地形效應。
Summer
Hailstorm Observed by Doppler Radars
in Northern Taiwan
Pin-Fang Lin Ben Jong-Dao Jou Cheng-Ku Yu
Department of Atmospheric Sciences, National Taiwan
University
（Manuscript
received 09 June 2003；in final form 18 September
2003）
ABSTRACT
Occurrence of hailstorm in
subtropical oceanic region is unusual. According to the surface station record,
in the past 38 years (1961~1999), there was only 6 hail events occurring in
Taiwan in summer time. During 28-31 August 1999,
hailstorms occurred in Taipei every afternoon. Thunderstorms over the sloping
area south of Taipei organized into a multicell convective system and produced
hails while reached foothill and plain area. In this study, the kinematic and
precipitation structure of the hailstorm occurring on August 29 is examined by
using data taken from the dual-Doppler radar network operated by Central
Weather Bureau and Civil Aeronautic Administration of Taiwan.
The synoptic conditions
showed a cold-core low existed on the east of Taiwan and associated with an
upper level northeasterly jet streak. The veering of the wind with pronounced
vertical wind shear suggested an environment similar to that of severe storms
developing in west plain of US. In addition, the melting layer was about 350
meters(i.e. 4.8 km) lower than the climatological value in the same season.
The reflectivity data showed
echoes greater than 55 dBZ occurred first at 5-6 km height and penetrated
upward to 10 km, and then developed downward to the ground within 30 minutes. The
signature of the vault and embryo curtain were identified near the leading edge
of the storm. From dual-Doppler wind analysis, a pronounced updraft was found at
the leading edge of the storm. The tilting updraft possessed its maximum value
of 18 m s-1 at 7 km height. With the help of the surface mesonet
observations, near-surface dual-Doppler wind analysis indicated the
leading-edge updraft was maintained by the convergence between the upslope sea
breeze and the down slope precipitation cold outflow.
Key
words：Hailstorm,
Doppler radar, Vault, Embryo curtain, Sea breeze, Terrain effect
「大氣科學」第三十一期第四號（Atmospheric Sciences Vol.31 No.04）P. 307~306
CWB GFS模擬亞洲夏季季風環流
之可預報度、準確度與海溫變化之關係
陳昭銘1 陳仁曾1 呂芳川2 郭漱泠2 胡志文1
1中央氣象局 科技中心
2國防大學中正理工學院 應用物理系
（中華民國九十二年六月九日收稿；中華民國九十二年十月十五日定稿）
摘
要
本文以中央氣象局全球預報模式(GFS)所執行之10個1950-99年氣候系集實驗為分析對象，探討GFS對亞洲夏季季風環流之模擬能力，即GFS之可預報度與準確度特性，及上述二特性與外作用力海溫變化之對應關係。
可預報度的分析結果顯示，可預報度的高低與熱帶海溫變化強度有關，高可預報度年傾向發生於熱帶海溫變化強度明顯增強的ENSO時期，低可預報度年傾向發生於非ENSO時期。當熱帶海溫變化強度於高可預報度年增強，搭配東、西太平洋呈現相反相位變化，促使熱帶西太平洋區降雨顯著變化，形成穩定熱源距平，激發穩定且強盛的亞洲夏季季風環流變化，使可預報度提高；於低可預報度年，熱帶海溫距平無明顯水平對比，且變化強度微弱，無法產生明顯熱帶熱源變化，季風環流變化隨之轉弱且不穩定，可預報度於是降低。
在準確度方面，影響季風環流年際變化模擬準確度的重要因素為熱帶海溫距平之水平梯度變化。當熱帶海溫有強烈變化時(如聖嬰現象)，若印度洋、熱帶東太平洋二區海溫距平與熱帶西太平洋海溫距平之水平梯度增大，西太平洋區產生強烈熱源變化，易使GFS模擬夏季環流強度過強的系統性誤差增強，而降低模擬亞洲夏季季風環流長波分量年際變化之準確性；反之，較小的海溫距平水平梯度可避免強化系統性誤差，於是GFS之準確度提高。在另一種氣候類型，即熱帶海溫變化不顯著時(如非ENSO之正常時期)，微弱海溫距平不足以強化GFS環流強度過強之系統性誤差，若伴隨較小熱帶海溫距平水平梯度變化，無足夠明顯的熱帶熱源變化，使GFS難以反應海溫變化的效應，對亞洲季風環流長波分量年際變化之模擬準確性於是降低；反之，海溫距平水平梯度比較明顯時，有助強化熱帶熱源，GFS較易反應海溫變化之效應，模擬亞洲夏季季風環流長波分量年際變化之準確度便會提高。
關鍵詞：系集實驗，可預報度，準確度，海溫變化
Predictability
and Simulation Accuracy of the Asian Summer Monsoon Circulation in Relation to
SST Anomalies Depicted by the CWB GFS
Jau-Ming Chen1 Ren-Jen Chen1 Fang-Chuan Lu2
Shu-Lin
Kuo2 Jyh-Wen Hwu1
1 Research and
Development Center, Central Weather Bureau
2 Dept. of Applied
Physics, Chung-Cheng Institute of Technology
（Manuscript
received 09 June 2003；in final form 15 October 2003）
ABSTRACT
Using
the CWB GFS (T42L18) model, a 10-member ensemble climate (1950-99) simulation
was performed and analyzed to study the predictability and simulation accuracy
of the Asian summer monsoon circulation (ASMC) anomalies delineated by the GFS
and their relationships with SST anomalies. Major findings of this study are as
follows.
Regarding the
predictability, degree of predictability of the ASMC anomalies is associated
with the strength of tropical SST variability. Cases of high (low) ASMC predictability
tend to occur in the ENSO (non-ENSO) phase. During the ENSO phases with high
ASMC predictability in the GFS simulation, increase in the strength of tropical
SST anomalies induces pronounced changes in precipitation and tropical heating
in the western Pacific, which in turn maintain strong and steady ASMC anomalies
and result in high ASMC predictability. On the other hand, weak SST anomalies
in the non-ENSO phases with low ASMC predictability lead to weak tropical
heating variability in the western Pacific, as well as weak and unsteady ASMC
anomalies. ASMC predictability in the GFS simulation thus deceases.
Regarding the
degree of simulation accuracy, it is most affected by the variability of
horizontal gradient of tropical SST anomalies, rather than the occurrence of
ENSO event. For cases with significant tropical SST anomalies, such as the El
Nino event, significant (moderate) increase in the horizontal gradient of
tropical SST anomalies provide strong (moderate) extern forcing, which should
(should not) intensify the systematic bias of GFS and lead to decrease
(increase) in the degree of simulation accuracy for the long wave components
(wavenumbers 1-4) of the interannual ASMC anomalies. For cases with weak
tropical SST variability, such as the non-ENSO event, horizontal gradient of
tropical SST anomalies is not strong enough to form a strong external forcing
to intensify the systematic bias of the GFS. Under this condition, stronger (weaker)
SST gradient is able to form a more (less) noticeable forcing to drive the ASMC
change, leading to increase (decrease) in the degree of accuracy of the long
wave components of the interannual ASMC anomalies in the GFS simulation.
Key
words：Ensemble simulation，Predictability，Accuracy，SST
variability
「大氣科學」第三十一期第四號（Atmospheric Sciences Vol.31 No.04）P. 307~306
TAMEX IOP3期間華南地區長時間
持續性豪雨事件之位渦診斷分析
侯喜真1 陳泰然2
1私立興國管理學院通識中心
2國立臺灣大學大氣科學系
（中華民國九十一年五月二十七日收稿；中華民國九十二年十月二十一日定稿）
摘 要
本文選取1987年TAMEX IOP3期間5月20~22日發生於華南沿岸地區的持續性豪雨事件，針對降雨區的低壓擾動進行位渦診斷分析，以探討發生豪雨的環境特徵與持續降雨的動力機制。在長達三天的豪雨事件中，雨區低對流層存在一準滯留鋒面，其中雨區範圍之平均位渦呈現三波的增強趨勢。
以此平均位渦三波之變化將整個降雨時期區分為三個階段，各階段並分別伴隨不同的位渦垂直結構。片段位渦反演求取的垂直速度場顯示，不同階段上升運動的來源不同。在第一階段，中、高對流層皆出現低壓槽，幾位於低對流層槽線上方，此階段低層位渦增強屬於垂直重疊型，反演結果顯示高層位渦與中層濕位渦提供幾近相同的上升運動，中層乾位渦對上升運動貢獻較小，低邊界層效應則提供下降運動；在第二階段，中、高對流層並無槽線系統通過，低層位渦之增強屬於中低層擾動型，垂直運動主要來自中層濕位渦的貢獻，即由潛熱釋放主宰；在第三階段，青藏高原東側之西南渦東移，併入原滯留於華南的鋒面，此時中、高對流層分別有一低壓槽由西向東移至雨區附近，與低層鋒面系統形成隨高度向西傾斜的深厚斜壓結構，低層位渦增強屬於垂直偶合型，中層潛熱釋放仍主宰上升運動，而高層與中層乾位渦對上升運動的貢獻雖較潛熱釋放的效應為小，但較前期增大，低邊界層效應則仍為負貢獻。
導致豪雨的另一條件為水氣的供給，配合三波位渦增強的時段，雨區水氣通量輻合亦呈現三波的增強趨勢。經由水氣通量輻散的收支計算，發現速度輻合是導致雨區水氣有效匯聚的主要因素，即西南氣流在雨區所產生的速度輻合是此次豪雨事件得以長時間維持的重要關鍵。其中，雨區的速度輻合與源自青藏高原東側且沿著雨區北側東移的西南渦相關，其低壓擾動環流疊加在盛行於華南一帶的西南風上，使得雨區東側產生明顯的低層噴流，且西南氣流於低壓擾動東側轉為東南風，導致雨區產生明顯的速度輻合。另外，西南氣流亦攜帶大量南來的暖濕空氣，增加大氣的潛在不穩度，亦有利豪雨系統的發展。
關鍵詞：豪雨、位渦、潛熱釋放、垂直偶合、垂直重疊、低層噴流
Potential
Vorticity Diagnostics of a Long-Lived Heavy
Rainfall
Event in Southern China during TAMEX IOP 3
Shi-Chen
Hou 1
Goeorge Tai-Jen Chen2
1Center for General Education, Hsing-Kuo University
2Department of Atmospheric Sciences, National
Taiwan University
（Manuscript
received 27 May 2002；in final form 21 October 2003）
ABSTRACT
A
long-lived heavy rainfall event occurred along the southeastern coastal China
over 20~22 May 1987 during TAMEX (Taiwan Area Mesoscale Experiment) IOP3. The potential
vorticity (PV) diagnostic system was used to analyze the development of
disturbances over rainfall region in order to understand the synoptic situation
and dynamical mechanism responsible for the heavy rainfall, which was observed
along and over the area to the south of the quasi-stationary Mei-Yu front. During
the heavy rainfall period, the PV over the rainfall area exhibited three
periods of enhancement with three relative maxima.
Based
on the PV tendency, the entire long-lived rainfall event was divided into three
periods, each with distinctly different vertical PV structure. The piecewise PV
inversion technique was used to shed light on the evolution of vertical motion
and its contributing processes. During the first period, an eastward moving
upper-level trough approached and affected the low-level system through the
"vertical superposition" process. The upper-level trough, as well as
latent heat release and unsaturated PV anomaly at mid-levels all provided
positive contribution toward the upward motion. In the second period, 500-hPa
short wave trough and 850-hPa quasi-stationary front were found to be
responsible for the development of the low-level disturbance, without the
presence of any upper-level system. The latent heat release was the major
contributor to the upward motion. During the third period, another eastward
upper-level trough approached and affected the low-level system through the
"vertical coupling" process. In addition to the important role played
by the latent heat release, positive contribution from the upper-level trough
and unsaturated PV anomaly in middle levels also increased.
The
strong low-level warm and moist southwesterly flow provided moisture flux
convergence such that heavy rainfall occurred consecutively over the same area
for several days. During the entire rainfall period, the moisture flux
convergence was largely due to velocity convergence, which was the key to
maintain the heavy rainfall for a long time. The velocity convergence was
related to the southwest vortex developed to the lee of Tibetan Plateau and
moved eastward subsequently. The low-level jet was a result from adding the
circulation of the vortex to the prevailing southwesterlies over the southern
China. As the southwesterly turned into southeasterlies to the east of the vortex,
strong. velocity convergence over the rainfall region was produced. In
addition, the southwesterlies brought abundant warmth and moisture from the
south, enhancing the potential instability of the atmosphere, and supported the
development of heavy rainfall.
Key words：Heavy rainfall, Potential vorticity, Latent heat
release, Vertical coupling, Vertical superposition, LLJ.
「大氣科學」第三十一期第四號（Atmospheric Sciences Vol.31 No.04）P. 307~306
1998年夏季季風肇始期間
南海地區之熱力與水氣分析
林松錦1 施佩君2 郭勉之2
1國立中央大學大氣物理研究所
2中央氣象局
（中華民國九十二年八月二十八日收稿；中華民國九十二年十一月十一日定稿）
摘 要
本研究利用1998年南海季風實驗所提供的1° ×1°經緯度網格資料，將1998年夏季季風的肇始過程分成三個階段，經由熱力與水氣變數場的分析，來了解南海地區夏季季風肇始的過程，以及季風肇始發展期間南海南北部的環流特徵與差異。
分析結果顯示，在1998年南海夏季季風肇始發展過程中，南海北部的大氣大多呈現對流不穩定的形勢，第一階段鋒前西南氣流造成低層強烈的水氣輻合，第二階段之後鋒面遠離且太平洋副熱帶高壓東退，來自孟加拉灣的西南氣流夾帶大量暖濕水氣使得南海北部在整個季風肇始期間都是有利於對流的狀況。而在南海南部，不同的是在第一與第二個階段，因水氣量的不足，造成夏季季風已在南海北部盛行時，南海南部地區卻沒有較明顯的變化。一直到第三個階段，太平洋副熱帶高壓完全退出南海，而華南低壓中心移入南海北部的低壓帶，與強盛的熱帶西南氣流結合，在南海南部形成強烈的西風與大量的水氣集結，低層對流不穩定度快速增加，以致於產生旺盛的對流。顯示南海南北部在肇始期間最主要的差異即在於水氣的多寡與到達的時間。
關鍵詞：夏季季風肇始，南海季風實驗，熱力與水氣分析
Thermodynamic
and Moisture Analyses over
The
South China Sea during
the
Summer Monsoon Onset in 1998
Song-Chin
Lin1 Pei-Chun Shih2 Mien-Tze Kueh2
1 Institute of
Atmospheric Physics, National Central University
2 Central Weather Bureau
（Manuscript
received 28 August 2003；in final form 11 November
2003）
ABSTRACT
By dividing the whole
evolution of the 1998 summer monsoon onset process into three stages and
using 1° ×1°grid observations
provided by the SCSMEX (South China Sea Monsoon Experiment) Data Center, this
study performs thermodynamic and moisture analyses to investigate the
differences in the circulation features over the northern and the southern
South China Sea (SCS).
Over the northern SCS,
analysis results find the lower troposphere is convectively unstable during the
entire onset period. The favorable
atmospheric conditions for convection are attributed to low-level moisture
convergence caused by the frontal southwesterly flow during the first stage,
and the retreat of western Pacific subtropical high and warm-moist
southwesterly flow from the Bay of Bengal during the later stages. While summer monsoon are prevailing over
the northern SCS during the early two stages, the lower tropospheric conditions
are still not favorable for the development of convection over the southern SCS
due to lack of moisture. Until the
third stage, when subtropical high retreats completely from the SCS and the low
pressure system over southern China moves southeastward and embeds itself in
the low pressure zone over the northern SCS, strong tropical southwesterly flow
brings in ample amount of moisture and causes moisture convergence over the
southern SCS under the influences of the low pressure zone. Deep convections
bloom due to sudden increase of low-level convective instability. The major factors that influence the
onset process over the northern and the southern SCS seem to be the amount of
moisture and the time of the arrival of moisture.
Key words：Summer monsoon onset, South China Sea Monsoon Experiment, Thermodynamic
and moisture analyses