西南氣流 (Southwest Monsoon, SWM) ，每年為菲律賓帶來近過半的降雨，過往有許多相關研究，然而降雨中的微物理卻未被探索。本研究使用2018年六至九月期間，PARSIVEL 雨滴譜儀的觀測，以及位於Tagaytay的 C波段雙偏極化氣象雷達的資料，分析菲律賓南方呂宋島 (South Luzon) 降雨的微物理特徵。將降水分為四種型態：大範圍強對流 (SWC) 、獨立強對流 (SIC) 、淺對流 (WC) 與層狀 (WS) 降水。利用主成份分析法 (PCA) 分析雨滴粒徑分布 (Drop Size Distribution, DSD) 和降雨積分參數 (integral rain parameters) ，客觀地將DSD分群 (PCA Groups, PGs) 以分析和不同微物理過程的關聯。
　　透過比對PGs和雷達參數，如：回波 (ZH)、差異反射率 (ZDR) 、比差異相位差 (KDP) 與相關係數 (ρ_HV) 時間序列剖面圖，顯示雷達參數垂直分佈與時序變化和微物理過程特徵一致。SIC由高濃度的中至大雨滴組成，伴隨高ZH、ZDR與KDP數值，且發展達高度10公里，觀測到以冰相為基礎的PG對流分群，並伴隨降雨率 (R)、液態水含量 (LWC) 和ZH的極值，也解釋地面觀測到大雨滴的現象。SWC有較廣的雨滴粒徑分布區間，且許多分群會隨系統轉移，其log10Nw (雨滴濃度 參數)、Dm (質量權重平均粒滴直徑) 與LWC可與SIC相當，卻伴隨較弱降雨率。WC通常可見高濃度小雨滴的淺對流，強回波 (ZH > 35 dBZ) 不超過6公里高。WS主要由小至中型雨滴組成，低降雨率，有明顯亮帶訊號，其DSDs緊密分布於對流/層狀分界線以下。
　　本研究近一步使用CFAD (Contoured frequency by altitude diagrams) 找出雷達參數垂直結構與PGs的關係。常態對流 (PG1) 與以冰相為主的對流 (PG6) 在各雷達參數均有較高數值，PG6的回波值可達40dBZ，且出現顯著柱狀ZH、ZDR與KDP。至於淺對流 (PG3) 的強回波在5公里以下。在CFADs對層狀的分群中，弱層狀 (PG2) 與中度層狀 (PG4) 高頻率地出現低ZH、ZDR與KDP數值，中度層狀因為更強的融解作用，稍微有著更高的數值，較大的雨滴會反映在ZDR CFAD中。上述發現對於菲律賓過往降雨事件研究中未提及的部分，提供了更詳盡的觀點。

The Southwest Monsoon (SWM), which brings nearly half of the Philippines' annual rainfall, has been extensively studied; however, its rainfall microphysics remain largely unexplored. This study investigates the microphysical characteristics of rainfall in South Luzon, Philippines, during the 2018 SWM season (June to September), using data from a PARSIVEL disdrometer and the Tagaytay C-band dual-polarization weather radar.
Four precipitation types are presented: strong widespread convection (SWC), strong isolated convection (SIC), weak shallow convection (WC), and weak stratiform (WS). Applying principal component analysis (PCA) to the drop size distribution (DSD) and integral rain parameters, PCA groups (PGs) are identified and linked to dominant microphysical processes. PGs and the averaged time-height plots of reflectivity (ZH), differential reflectivity (ZDR), specific differential phase (KDP), and co-polar cross-correlation coefficient (ρHV) were time-matched to reveal these processes. SIC exhibited high concentrations of mid-to-large drops and with high ZH, ZDR, and KDP values reaching heights up to 10 km ¬¬¬—typical for deep convective systems. Most ice-based convection DSDs (PG6) were observed after the peak rainfall rate (R), liquid water content (LWC), and ZH, explaining the large drops observed at the surface. SWC showed wider range of drop diameters with multiple PGs observed showing the transitions within the system. The values of normalized intercept parameter (log10Nw), mass-weighted mean diameter (Dm) and LWC are comparable to SIC, but with lower R. High concentrations of small drops were typically observed in WC, but convective reflectivities (>35 dBZ) were confined at the lower levels, hence the shallow classification. Meanwhile, in WS, small to mid-sized drops dominate, with low R, with an evident bright band signature and DSDs are tightly clustered below the convective-stratiform (CS) separation line.
Contoured frequency by altitude diagrams (CFAD) were used to relate radar vertical profiles to specific PGs. Both normal convection DSD group (PG1) and PG6 have high values of the same radar parameters. However, reflectivity values for PG6 are centered around 40 dBZ and usually show pronounced columns of ZH, ZDR and KDP. For shallow convection (PG3), high values of ZH (≥35 dBZ) are confined below 5 km suggesting the less intense and shallow nature of this convection compared to other convective groups. CFADs for stratiform groups—weak (PG2) and moderate (PG4) — revealed high frequencies of low ZH, ZDR and KDP values. PG4 has slightly higher values, likely due to more intense melting, which produces larger drops as reflected in the ZDR CFAD. These findings provide a more detailed perspective on Philippine precipitation systems which were not presented in previous literature.

Abon, C. C., Kneis, D., Crisologo, I., Bronstert, A., David, C. P., & Heistermann, M. (2016). Evaluating the potential of radar-based rainfall estimates for streamflow and flood simulations in the Philippines. Geomatics, Natural Hazards and Risk, 1390-1405. https://doi.org/http://dx.doi.org/10.1080/19475705.2015.1058862
Aragon, L. G., Ibanez, M. P., Ordinario, R. C., Simpas, J. B., Cambaliza, M. O., Dado, J. M., Maquiling, J. T., & Reid, E. A. (2024). Seasonal characteristics of raindrop size distribution and implication for radar rainfall retrievals in Metro Manila, Philippines. Atmospheric Research. https://doi.org/https://doi.org/10.1016/j.atmosres.2024.107669
Asuncion, J. F., & Jose, A. M. (1980). A study of the characteristics of the northeast and southwest monsoons in the Philippines. NRCP Assisted Project.
Bagtasa, G. (2017). Contribution of Tropical Cyclones to Rainfall in the Philippines. Journal of Climate, 3621-3633. https://doi.org/https://doi.org/10.1175/JCLI-D-16-0150.1
Bagtasa, G. (2019). Enhancement of Summer Monsoon Rainfall by Tropical Cyclones in Northwestern Philippines. Journal of the Meteorological Society of Japan, 967-976. https://doi.org/10.2151/jmsj.2019-052
Bagtasa, G. (2020). Influence of Madden–Julian Oscillation on the Intraseasonal Variability of Summer and Winter Monsoon Rainfall in the Philippines. Journal of Climate, 9581–9594. https://doi.org/https://doi.org/10.1175/JCLI-D-20-0305.1
Bagtasa, G. (2023). Characterization of the 2012 and 2013 Metro Manila “Enhanced Habagat” Heavy Rainfall Events. Philippine Journal of Science, 123-135.
Bañares, E. N., Narisma, G. T., Simpas, J. B., Cruz, F. T., Lorenzo, G. R., Cambaliza, M. O., & Coronel, R. C. (2021). Seasonal and diurnal variations of observed convective rain events in Metro Manila, Philippines. Atmospheric Research. https://doi.org/https://doi.org/10.1016/j.atmosres.2021.105646
Bang, W., Lee, G., Ryzhkov, A., Schuur, T., & Lim, K.-S. S. (2020). Comparison of Microphysical Characteristics between the Southern Korean Peninsula and Oklahoma Using Two-Dimensional Video Disdrometer Data. Journal of Hydrometeorology, 2675-2690. https://doi.org/10.1175/JHM-D-20-0087.1
Beard, K. V. (1976). Terminal Velocity and Shape of Cloud and Precipitation Drops Aloft. Journal of the Atmospheric Sciences, 851-864. https://doi.org/https://doi.org/10.1175/1520-0469(1976)033<0851:TVASOC>2.0.CO;2
Brandes, E. A., Zhang, G., & Vivekanandan, J. (2002). Experiments in Rainfall Estimation with a Polarimetric Radar in a Subtropical Environment. Journal of Applied Meteorology, 674-685. https://doi.org/https://doi.org/10.1175/1520-0450(2002)041<0674:EIREWA>2.0.CO;2
Bringi, V. N., Chandrasekar, V., Balakrishnan, N., & Zrnic, D. S. (1990). An Examination of Propagation Effects in Rainfall on Radar Measurements at Microwave Frequencies. Journal of Atmospheric and Oceanic Technology, 829-840. https://doi.org/https://doi.org/10.1175/1520-0426(1990)007<0829:AEOPEI>2.0.CO;2
Bringi, V. N., Chandrasekar, V., Hubbert, J., Gorgucci, E., Randeu, W. L., & Schoenhuber, M. (2003). Raindrop Size Distribution in Different Climatic Regimes from Disdrometer and Dual-Polarized Radar Analysis. Journal of Atmospheric Sciences, 354-365. https://doi.org/https://doi.org/10.1175/1520-0469(2003)060<0354:RSDIDC>2.0.CO;2
Bringi, V. N., Williams, C. R., Thurai, M., & May, P. T. (2009). Using Dual-Polarized Radar and Dual-Frequency Profiler for DSD Characterization: A Case Study from Darwin, Australia. Journal of Atmospheric and Oceanic Technology. https://doi.org/10.1175/2009JTECHA1258.1
Carey, L. D., Rutledge, S. A., & Ahijevych, D. A. (2000). Correcting Propagation Effects in C-Band Polarimetric Radar Observations of Tropical Convection Using Differential Propagation Phase. Journal of Applied Meteorology, 1405-1433. https://doi.org/https://doi.org/10.1175/1520-0450(2000)039<1405:CPEICB>2.0.CO;2
Cayanan, E. O., Chen, T.-C., Argete, J. C., Yen, M.-C., & Nilo, P. D. (2011). The Effect of Tropical Cyclones on Southwest Monsoon Rainfall in the Philippines. Journal of the Meteorological Society of Japan, 123--139. https://doi.org/10.2151/jmsj.2011-A08
Chang, W.-Y., Lee, G., Jou, B. J.-D., Lee, W.-C., Lin, P.-L., & Yu, C.-K. (2020). Uncertainty in Measured Raindrop Size Distributions from Four Types of Collocated Instruments. Remote Sensing. https://doi.org/10.3390/rs12071167
Chang, W.-Y., Vivekanandan, J., & Wang, T.-C. C. (2014). Estimation of X-Band Polarimetric Radar Attenuation and Measurement Uncertainty Using a Variational Method. Journal of Applied Meteorology and Climatology, 1099-1119. https://doi.org/10.1175/JAMC-D-13-0191.1
Chang, W.-Y., Vivekanandan, J., Ikeda, K., & Lin, P.-L. (2016). Quantitative Precipitation Estimation of the Epic 2013 Colorado Flood Event: Polarization Radar-Based Variational Scheme. Journal of Applied Meteorology and Climatology, 1477-1495. https://doi.org/10.1175/JAMC-D-15-0222.1
Chen, B., Yang, J., & Pu, J. (2013). Statistical Characteristics of Raindrop Size Distribution in the Meiyu Season Observed in Eastern China. Journal of the Meteorological Society of Japan, 215-227. https://doi.org/10.2151/jmsj.2013-208
Crisologo, I., Vulpiani, G., Abon, C., David, C., Bronstert, A., & Heistermann, M. (2014). Polarimetric Rainfall Retrieval from a C-Band Weather Radar in a Tropical Environment (The Philippines). Asia-Pac. J. Atmos. Sci. https://doi.org/10.1007/s13143-014-0049-y
Dolan, B., Fuchs, B., Rutledge, S. A., Barnes, E. A., & Thompson, E. J. (2018). Primary Modes of Global Drop Size Distributions. Journal of Atmospheric Sciences, 1453-1476. https://doi.org/10.1175/JAS-D-17-0242.1
DOST-PAGASA. (n.d.). https://www.pagasa.dost.gov.ph/climate/climate-data
Flores, J., & Balagot, V. (1969). Climate of the Philippines. In H. Arakawa, Climates of Northern and Eastern Asia, World Survey of Climatology (pp. 159-213). Amsterdam, New York: Elsevier.
Heistermann, M., Crisologo, I., Abon, C. C., Racoma, B. A., Jacobi, S., Servando, N. T., David, C. P., & Bronstert, A. (2013). Brief communication “Using the new Philippine radar network to reconstruct the Habagat of August 2012 monsoon event around Metropolitan Manila". Natural Hazards and Earth System Sciences, 653-657. https://doi.org/10.5194/nhess-13-653-2013
Huang, X., Bai, L., Yu, Z., Chan, J. C., Yu, H., Tang, J., Guo, R., & Wan, R. (2024). Tropical cyclone activities in the Western North Pacific in 2022. Tropical Cyclone Research and Review, 125-135. https://doi.org/https://doi.org/10.1016/j.tcrr.2024.05.002
Ibañez, M. P., Martirez, S. C., Pura, A. G., Sajulga, R. A., Cayanan, E. O., Jou, B. J. D., & Chang, W. Y. (2023). Development of quantitative precipitation estimation (QPE) relations for dual-polarization radars based on raindrop size distribution measurements in Metro Manila, Philippines. Terrestrial, Atmospheric and Oceanic Sciences. https://doi.org/https://doi.org/10.1007/s44195-023-00056-0
Ibañez, M. P., Pura, A. G., Sajulga, R. A., & David, S. J. (2022). Raindrop Size Distribution (RSD) Characteristics during the Southwest Monsoon Period in Western Luzon, Philippines. Philippine Journal of Science, 1-16.
Jameson, A. R. (1991). Polarization Radar Measurements in Rain at 5 and 9 GHz. Journal of Applied Meteorology, 1500-1513. https://doi.org/https://doi.org/10.1175/1520-0450(1991)030<1500:PRMIRA>2.0.CO;2
Jameson, A. R. (1992). The Effect of Temperature on Attenuation-Correction Schemes in Rain Using Polarization Propagation Differential Phase Shift. Journal of Applied Meteorology and Climatology, 1106-1118. https://doi.org/https://doi.org/10.1175/1520-0450(1992)031<1106:TEOTOA>2.0.CO;2
Kottek, M., Grieser, J., Beck, C., Rudolf, B., & Rubel, F. (2006). World Map of the Köppen-Geiger climate classification updated. Meteorologische Zeitschrift, 259-263. https://doi.org/10.1127/0941-2948/2006/0130
Krajewski, W. F., & Smith, J. A. (2002). Radar hydrology: rainfall estimation. Advances in Water Resources, 1387-1394. https://doi.org/https://doi.org/10.1016/S0309-1708(02)00062-3
Lin, P.-F., Lagrimas, L. K., Wang, J.-B., Chang, P.-L., Fang, W.-T., Almario, J. G., Jou, B. J.-D., & Cayanan, E. O. (2021). Removing interference echoes in Philippine radars using a fuzzy logic approach. Terr. Atmos. Ocean. Sci., 755-776. https://doi.org/10.3319/TAO.2021.12.20.01
Löffler-Mang, M., & Joss, J. (2000). An Optical Disdrometer for Measuring Size and Velocity of Hydrometeors. Journal of Atmospheric and Oceanic Technology, 130-139. https://doi.org/https://doi.org/10.1175/1520-0426(2000)017<0130:AODFMS>2.0.CO;2
Loh, J. L., Chang, W.-Y., Hsu, H.-W., Lin, P.-F., Chang, P.-L., Teng, Y.-L., & Liou, Y.-C. (2022). Long-Term Assessment of the Reflectivity Biases and Wet-Radome Effect Using Collocated Operational S- and C-Band Dual-Polarization Radars. IEEE Transactions on Geoscience and Remote Sensing, Vol. 60. https://doi.org/10.1109/TGRS.2022.3170609
Macuroy, J. T., Chang, W.-Y., Faustino-Eslava, D. V., Sanchez, P. A., Jr., C. L., & Jou, B. J.-D. (2021). Evaluations on radar QPE using raindrop size distribution in Southern Luzon, Philippines. Terr. Atmos. Ocean. Sci., 693-724. https://doi.org/10.3319/TAO.2021.02.22.01
McFarquhar, G. M., Hsieh, T.-L., Freer, M., Mascio, J., & Jewett, B. F. (2015). The Characterization of Ice Hydrometeor Gamma Size Distributions as Volumes in N0–λ–μ Phase Space: Implications for Microphysical Process Modeling. Journal of Atmospheric Sciences, 892–909. https://doi.org/https://doi.org/10.1175/JAS-D-14-0011.1
NASA Shuttle Radar Topography Mission (SRTM). (2013). Shuttle Radar Topography Mission (SRTM) Global. https://doi.org/10.5069/G9445JDF
Ryzhkov, A., & Zrnic, D. (1996). Assessment of Rainfall Measurement That Uses Specific Differential Phase. Journal of Applied Meteorology, 2080-2090. https://doi.org/https://doi.org/10.1175/1520-0450(1996)035<2080:AORMTU>2.0.CO;2
Seela, B. K., Janapati, J., Lin, P.-L., Reddy, K. K., Shirooka, R., & Wang, P. K. (2017). A Comparison Study of Summer Season Raindrop Size Distribution Between Palau and Taiwan, Two Islands in Western Pacific. Journal of Geophysical Research: Atmospheres, 11,787–11,805. https://doi.org/https://doi.org/10.1002/2017JD026816
Sekhon, R. S., & Srivastana, R. C. (1971). Doppler Radar Observations of Drop-Size Distributions in a Thunderstorm. Journal of Atmospheric Sciences, 983-994. https://doi.org/https://doi.org/10.1175/1520-0469(1971)028<0983:DROODS>2.0.CO;2
Smyth, T. J., & Illingworth, A. J. (1998). Correction for attenuation of radar reflectivity using polarization data. Quarterly Journal of the Royal Meteorological Society, 2393-2415. https://doi.org/ https://doi.org/10.1002/qj.49712455111
Testud, J., Oury, S., Black, R. A., Amayenc, P., & Dou, X. (2001). The Concept of ‘‘Normalized’’ Distribution to Describe Raindrop Spectra: A Tool for Cloud Physics and Cloud Remote Sensing. Journal of Applied Meteorology, 1118-1140. https://doi.org/https://doi.org/10.1175/1520-0450(2001)040<1118:TCONDT>2.0.CO;2
Thompson, E. J., Rutledge, S. A., Dolan, B., & Thurai, M. (2015). Drop size distributions and radar observations of convective and stratiform rain over the equatorial Indian and West Pacific Oceans. Journal of the Atmospheric Sciences, 72(11), 4091–4125. https://doi.org/https://doi.org/10.1175/jas-d-14-0206.1
Ulbrich, C. W. (1983). Natural Variations in the Analytical Form of the Raindrop Size Distribution. Journal of Climate and Applied Meteorology, 1764-1775. https://doi.org/https://doi.org/10.1175/1520-0450(1983)022<1764:NVITAF>2.0.CO;2
Vivekanandan, J., Zhang, G., Ellis, S. M., Rajopadhyaya, D., & Avery, S. K. (2003). Radar reflectivity calibration using differential propagation phase measurement. Radio Science. https://doi.org/10.1029/2002RS002676
Vulpiani, G., Montopoli, M., Passeri, L. D., Gioia, A. G., Giordano, P., & Marzano, F. S. (2012). On the Use of Dual-Polarized C-Band Radar for Operational Rainfall Retrieval in Mountainous Areas. Journal of Applied Meteorology and Climatology, 405-425. https://doi.org/10.1175/JAMC-D-10-05024.1
Waterman, P. C. (1971). Symmetry, unitarity, and geometry in electromagnetic scattering. Phys. Rev. D, 825-839. https://doi.org/https://doi.org/10.1103/PhysRevD.3.825
Williams, C. R., Bringi, V. N., Carey, L. D., Chandrasekar, V., Gatlin, P. N., Haddad, Z. S., Meneghini, R., Munchak, S. J., Nesbitt, S. W., Petersen, W. A., Tanelli, S., Tokay, A., Wilson, A., & Wolff, D. B. (2014). Describing the Shape of Raindrop Size Distributions Using Uncorrelated Raindrop Mass Spectrum Parameters. Journal of Applied Meteorology and Climatology, 1282-1296. https://doi.org/10.1175/JAMC-D-13-076.1
Willis, P. T. (1984). Functional Fits to Some Observed Drop size Distributions and Parameterization of Rain. Journal of Atmopsheric Sciences, 1648-1661. https://doi.org/https://doi.org/10.1175/1520-0469(1984)041<1648:FFTSOD>2.0.CO;2
Yuter, S. E., & Houze, R. J. (1997). Measurements of Raindrop Size Distributions over the Pacific Warm Pool and Implications for Z–R Relations. Journal of Applied Meteorology, 847-867. https://doi.org/https://doi.org/10.1175/1520-0450(1997)036<0847:MORSDO>2.0.CO;2