DSpace collection: 博碩士論文

TAHOPE IOP3及IOP10中水氣對融化層厚度和降水的影響;The Impact of the Melting Layer Thickness and Precipitation from Precipitable Water in TAHOPE IOP3 and IOP10

title: TAHOPE IOP3及IOP10中水氣對融化層厚度和降水的影響;The Impact of the Melting Layer Thickness and Precipitation from Precipitable Water in TAHOPE IOP3 and IOP10 abstract: 融化層(ML, Melting Layer)是層狀降水的重要特徵，融化層的頂部接近0°C等溫線的高度，與雪花或冰晶的融化有關，並且融化層的底部指示了液體降水的垂直範圍。偵測融化層其中一項目的是為了改善定量降水估計(QPE, Quantitative Precipitation Estimation)。本研究探討2022年TAHOPE IOP3及IOP10中，高或低可降水量(Precipitable Water, PW)影響融化層厚度與否，進而分析融化層之上或之下雲微物理過程差異，並比較不同可降水量條件下的雷達回波、降雨量與降雨特性。依據地基GPS大氣觀測站北臺灣區域的每小時平均可降水量資料分類高、低可降水量時間區間，並根據Giangrande等人在2008提出計算融化層厚度的方法，找出雷達回波(radar reflectivity, ZH)、差異反射率(differential reflectivity, ZDR)的最大值和降水相關係數(cross-correlation coefficient, ρhv)的最小值區間，分析在水氣多寡情況下S-Pol雷達RHI掃描垂直剖面中融化層厚度差異以及雙偏極化參數垂直剖面雲微物理過程。融化層厚度和ZH最大值(ZH peak)以及ZH最大值高度到ρhv最小值(ρhv peak)高度的距離成正比，和探空溫度於 ±0.2°C區間內的環境遞減率以及探空0°C層的平均相對溼度呈負相關。高可降水量個案中，ZH、ZDR與ρhv所對應之融化層厚度中位數與低可降水量個案相當；然而，高可降水量的ZH、ZDR、ρhv與KDP垂直剖面中，可以在ML之上的冰相區域觀察到枝狀冰晶成長層(Dendritic Growth Layer, DGL)，形成較大的雷達回波與較多的地面降水量；相較之下，低可降水量個案呈現發展高度較低的層狀降水及ML之下的蒸發現象，導致地面降水量較少。;The melting layer (ML) provides valuable information into the vertical structure of precipitation. The base of the ML indicates how far liquid precipitation extends downward, while its top is typically near the altitude of the 0°C isotherm. Detecting the ML is essential for quantitative precipitation estimation (QPE), since mixed-phase hydrometeors may contaminate rainfall estimates. This study investigates how high and low precipitable water (PW) and strong and weak radar echoes influence the melting layer thickness during TAHOPE IOP3 and IOP10 in 2022. Furthermore, it examines how these environmental conditions modify the microphysical processes above and below the melting layer and compares the rainfall and characteristics under different PW conditions. Hourly mean PW observations from ground-based GPS atmospheric stations over northern Taiwan were used to classify high- and low-PW periods. Following the algorithm proposed by Giangrande et al. (2008), the ML is identified on polarimetric RHI (Range Height Indicator) scans as the vertical interval where the ZH and ZDR maximum and the minimum of ρhv. The vertical structure of the ML and its associated microphysical processes are then analyzed using RHI scans from the S-Pol radar. The ML thickness is positively correlated with the maximum ZH and the vertical distance between the height of the ZH peak and the minimum ρhv, while it is negatively correlated with the environmental lapse rate within the ±0.2°C temperature interval and the mean relative humidity at the 0°C level derived from soundings. In high PW cases, the median ML thicknesses identified using ZH, ZDR, and ρhv are comparable to those in low PW cases. However, vertical profiles of ZH, ZDR, ρhv, and KDP in high PW cases reveal the presence of a dendritic growth layer (DGL) above the ML, which favors the development of stronger radar echoes and results in larger surface precipitation amounts. In contrast, low PW cases are characterized by shallower stratiform precipitation and evaporation below the ML, leading to reduced surface rainfall.

The Spring Arctic Oscillation as a Modulator of El Ni�o Variability: Mechanisms and Comparative Evaluation

title: The Spring Arctic Oscillation as a Modulator of El Ni�o Variability: Mechanisms and Comparative Evaluation abstract: 聖嬰現象 (El Niño Southern Oscillation，簡稱ENSO) 是一個位於赤道太平洋區域並具有週期性之氣候現象，其不僅對南北半球熱帶區域的天氣發揮一定的調節作用，同時也會對其他地區以及各個氣候因子產生遙相關的影響，因此研究各種可能導致ENSO發生的因子是極具重要性的課題，其有助於藉由提高ENSO的預測能力來精進氣象預報之準確度並以此來影響人類生活。過往研究顯示於春季的北極震盪 (Arctic Oscillation，簡稱AO) 可能會透過綜觀尺度的渦流活動來影響西風產生進而促進ENSO形成，而本篇研究後續將會針對不同相位的春季AO對聖嬰事件造成的差異進行討論，並探索相關的機制。此篇研究發現春季AO在不同相位下可能會透過不同方式激發西風異常，正相位如前人研究會傾向激發低緯度氣旋式異常，並因此引發太平洋經向模態 (Pacific Meridional Mode，簡稱PMM) 相關之機制出現與緯向平流作用增強，對後續成熟期的海面溫度在接近中太平洋之區域影響顯著，然而，負相位會傾向透過向赤道的波列傳播來間接引發西風異常，並主要通過緯向平流作用來使接近中太平洋之區域的海面溫度相對於沒有春季AO的條件下有增暖的情形，此外，不同的春季AO相位對同年度的聖嬰事件於強度以及持續時間上，連同隔一年的聖嬰相位皆會有所差異，由負春季AO相位所引發的聖嬰事件在強度與時間下皆會較正相位時弱，但其有助於隔年的反聖嬰事件接續出現，相對而言，正春季AO雖會傾向形成較強且較久的聖嬰事件，但對接續之聖嬰相位的轉換則相較負相位具有較高的變異性。最後，本篇研究也執行了動力與熱力的收支分析，揭示在春季AO的作用下基本上會由緯向平流作用主導聖嬰的發展，而熱力則會透過短波輻射與潛熱通量的調節主導衰退的進行。 ;El Niño Southern Oscillation (ENSO) is a quasi-periodic climate phenomenon over the equatorial Pacific area. It not only influences the weather in both Northern and Southern tropics, but also affects diverse climatic factors through teleconnections. As a result, examining the factors responsible for the initiation of El Niño is a critical issue. It is conducive to improving ENSO predictability and advancing the accuracy of weather forecasts. Previous studies have illustrated that the spring Arctic Oscillation (AO) initiates the ENSO pattern via synoptic scale eddy feedback that can modulate the equatorial westerly wind anomalies. Therefore, this study will further analyze the varying El Niño responses to the spring AO phases and explore the mechanisms involved. This study reveals that the ways in which the El Niño-like pattern and the westerly wind anomalies are generated under the respective spring AO conditions are contrasting. During the positive spring AO phase, the low-latitude cyclonic circulation anomalies, along with the tropical westerly and southwesterly wind anomalies, tend to form. These anomalies, in turn, trigger the Pacific Meridional Mode (PMM)-related mechanism and enhance the zonal advective feedback. They also reinforce the significant impacts on the sea surface temperature anomalies (SSTA) near the central Pacific at the subsequent mature stage. By contrast, the negative spring AO pattern tends to produce an equatorward wave train-like pattern to modulate the tropical westerly wind anomalies (Deng and Dai, 2024). Of note, compared to the neutral spring AO, the negative spring AO warms the SSTA near the central Pacific predominantly through zonal advective feedback. In addition, the positive spring AO tends to produce stronger and longer El Niño events. However, the induced subsequent ENSO phase associated with the positive spring AO exhibits relatively large variability. During the negative spring AO phase, the occurrence of weaker and shorter El Niño events is more likely. In the subsequent winter, a La Niña event tends to develop. This research also conducts the dynamic and thermodynamic analysis. It suggests that under the effect of spring AO, the development stage of El Niño is dominated by the zonal advective process, whereas the decaying stage is mainly governed by the modulation of shortwave radiation and latent heat fluxes.

以雷達反演資料改善熱動力場結構及梅雨季定量降水預報之研究：以2022年TAHOPE IOP#1為例

title: 以雷達反演資料改善熱動力場結構及梅雨季定量降水預報之研究：以2022年TAHOPE IOP#1為例 abstract: 本研究採用多都卜勒雷達風場合成方法(WInd Synthesis System using DOppler Measurement, WISSDOM)及熱動力反演技術(Terrain-Permitting Thermodynamic Retrieval Scheme, TPTRS)，建立複雜地形上的三維風場、壓力場、溫度場與水氣場，並將其納入WRF模式同化中。以2022年TAHOPE (Taiwan-Area Heavy rain Observation and Prediction Experiment)梅雨鋒面降水個案(#IOP1)為例，探討雷達資料同化後對定量降水預報(Quantitative Precipitation Forecast, QPF)及熱動力場結構模擬的改善情形。研究結果顯示，同化雷達反演資料能使降雨分布的預報更符合實際觀測，但在雨量強度方面仍有低估的情形，且改善效果主要集中在預報前 4 小時。雷達反演後的熱動力初始場及回波分布貼近觀測之外，模式對於近地層鋒面移速的模擬亦較未同化時準確；若進一步加入地面觀測風場，改善效益的持續時間則更為延長。然而，地面氣壓場的誤差改善有限，顯示模式在熱力結構及地表通量的處理上仍存在不足，而近地面氣溫及相對溼度則有些微改善。整體而言，雷達資料的同化有助於提升降雨空間分布及低層風場的模擬品質，同時改善模式對鋒面系統位置與移動速度的掌握。但由於效果仍偏短期，加上降雨量級的低估問題尚未完全解決，後續可從邊界層參數化、水氣場調整或同化策略等方向進一步改進，以提升預報的穩定度與實務應用價值。 ;This study applies the Wind Synthesis System using Doppler Measurements (WISSDOM) and the Terrain-Permitting Thermodynamic Retrieval Scheme (TPTRS) to reconstruct three-dimensional wind, pressure, temperature, and moisture fields over complex terrain, and assimilates these fields into the WRF model. Using the 2022 TAHOPE Mei-yu frontal case (IOP1) as an example, we examine how assimilating radar-derived fields influences quantitative precipitation forecasts (QPF) and the simulation of thermodynamic and dynamic structures. The results show that assimilating radar-retrieved fields improves the spatial distribution of rainfall forecasts, bringing them closer to observations, although the rainfall intensity remains generally underestimated. The improvements are most evident within the first four hours of the forecast. With initial thermodynamic fields and radar echo structures closer to observations, the model better captures the near-surface frontal propagation speed; furthermore, incorporating surface wind observations extends the duration of the positive assimilation impact. However, improvements in surface pressure remain limited and slight improvements are observed in near-surface air temperature and relative humidity, suggesting deficiencies in the model’s representation of thermodynamic structure and surface flux processes.Overall, radar data assimilation enhances the simulation of rainfall distribution and low-level wind fields, and improves the model’s ability to represent frontal position and movement. Nevertheless, the effect diminishes after a short lead time, and the underestimation of rainfall magnitude persists. Future work may benefit from refinements in boundary layer parameterization, moisture adjustment strategies, or assimilation techniques to further improve forecast stability and operational applicability.

從能量學觀點理解MJO的多樣性;Understanding the Diversity of MJO from the Energetics Perspective

title: 從能量學觀點理解MJO的多樣性;Understanding the Diversity of MJO from the Energetics Perspective abstract: 本論文探討熱帶對流能量學如何形塑 Madden–Julian 振盪（MJO）之傳播多樣性。利用現代再分析資料，我們透過整層水氣與乾靜能（DSE）收支，以及一組以物理過程為導向的總濕穩定度（GMS）指標，診斷 MJO 的演變。本研究發展一個受對流準平衡（CQE）約束的 GMS 相位平面，以區分能量再充填–釋放過程與增濕–乾化途徑。此框架提供了一種簡潔的診斷方式，用以視覺化 MJO 生命週期的演變並辨識增強與衰減階段。隨後，我們將此框架應用於大量歷史 MJO 事件，並以 k-means 分群方法分類為駐留型、慢速傳播型與快速傳播型。對每一類型而言，GMS 相位平面揭示其獨特的能量途徑，並釐清垂直與水平過程如何共同促成傳播。各類型所對應的特徵性 GMS 亦提供一項統一不同傳播行為的能量判據。基於水平水氣平流對 MJO 傳播具有關鍵性影響，我們進一步構建一個可解釋的分類方法，利用少量具物理意義的預測因子，實現近即時的 MJO 類型判識。儘管其整體技巧較 k-means 為低，但此方法提供了一種透明且以能量學為基礎的替代方案，可補充更為複雜的機器學習模型。綜合而言，本研究建立了一套一致的能量學觀點，以解釋 MJO 之多樣性，並展示水氣–能量途徑如何支配不同類型 MJO 在印太暖池中的增強、傳播或衰減行為。;This dissertation investigates how the energetics of tropical convection shape the diversity of Madden–Julian Oscillation (MJO) propagation. Using modern reanalysis data, we diagnose MJO evolution through the column moisture and dry static energy (DSE) budgets and a set of process-oriented gross moist stability (GMS) measures. A convective-quasi-equilibrium (CQE) constrained GMS phase plane is developed to separate energetic recharge–discharge processes from moistening–drying pathways. This framework provides a compact diagnostic for visualizing MJO life-cycle evolution and identifying amplification and decay stages. The framework is then applied to a large set of historical MJO events categorized via k-means clustering into standing, slow-propagating, and fast-propagating groups. For each type, the GMS plane reveals distinct energetic pathways and clarifies how vertical and horizontal processes contribute to propagation. A characteristic GMS associated with each archetype acts as an energetic criterion that unifies these behaviors across regimes. Recognizing the pivotal role of horizontal moisture advection for propagation, we further construct an interpretable classification scheme that enables near–real-time identification of MJO regimes using a small set of physically meaningful predictors. Although its overall skill is modest compared with k-means, the scheme offers a transparent, energetically grounded alternative to more complex machine-learning models. Together, these results provide a coherent energetic perspective on MJO diversity and demonstrate how moisture–energy pathways govern the variety of MJO types to amplify, propagate, or decay across the Indo-Pacific warm pool.