Seasonal march and its spatial difference of rainfall in the Philippines

Akasaka, Ikumi; Morishima, Wataru; Mikami, Taisei

doi:10.1002/joc.1428

Cited by 47 publications

(68 citation statements)

References 9 publications

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“…The onset of the WNP summer monsoon, including that in the Philippine region, has been the focus of several studies. Rainfall data were used to define the Asian monsoon onset (Matsumoto 1997;Akasaka et al 2007). Some studies (Tanaka 1992;Lau and Yang 1997;Wang and LinHo 2002) used satellite data of outgoing longwave radiation (OLR) to define an index of convective activity.…”

Section: Introductionmentioning

confidence: 99%

Tropical cyclone influence on the long-term variability of Philippine summer monsoon onset

Kubota

Shirooka

Matsumoto

et al. 2017

Prog Earth Planet Sci

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The long-term variability of Philippine summer monsoon onset from 1903 to 2013 was investigated. The onset date is defined by daily rainfall data at eight stations in the northwestern Philippines. Summer monsoons tended to start earlier in May after the mid-1990s. Other early onset periods were found during the 1900s, 1920s, and 1930s, and an interdecadal variability of summer monsoon onset was identified. Independent surface wind data observed by ships in the South China Sea (SCS) revealed prevailing westerly wind in May during the early monsoon onset period. To identify atmospheric structures that trigger Philippine summer monsoon onset, we focused on the year 2013, conducting intensive upper-air observations. Tropical cyclone (TC) Yagi traveled northward in the Philippine Sea (PS) in 2013 and triggered the Philippine monsoon onset by intensifying moist low-level southwesterly wind in the southwestern Philippines and intensifying low-level southerly wind after the monsoon onset in the northwestern Philippines. The influence of TC was analyzed by the probability of the existence of TC in the PS and the SCS since 1951, which was found to be significantly correlated with the Philippine summer monsoon onset date. After the mid-1990s, early monsoon onset was influenced by active TC formation in the PS and the SCS. However, the role of TC activity decreased during the late summer monsoon periods. In general, it was found that TC activity in the PS and the SCS plays a key role in initiating Philippine summer monsoon onset.

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Section: Introductionmentioning

confidence: 99%

Tropical cyclone influence on the long-term variability of Philippine summer monsoon onset

Kubota

Shirooka

Matsumoto

et al. 2017

Prog Earth Planet Sci

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“…The strong southwesterlies are said to be a result of the combination of the monsoon southwesterlies and the westerlies generated by TCs present in the vicinity of Luzon Island. During the rainy season, rainfall amount on the west coasts of the Philippines peaks when southwesterlies are strongest (Akasaka et al 2007). The strength of these westerlies is modulated by the position of the northward propagating 30-60 day monsoon trough and western north Pacific anticyclone (Chen et al 2000;Chen and Murakami 1988).…”

Section: Introductionmentioning

confidence: 99%

The Effect of Tropical Cyclones on Southwest Monsoon Rainfall in the Philippines

Cayanan¹,

Chen

Argete

et al. 2011

Journal of the Meteorological Society of Japan

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Intense southwest monsoon (SWM) rainfall events causing massive landslides and flash floods along the western sections of the Philippines were studied. These rainfall events, are not directly coming from the tropical cyclones (TCs) for they are situated far north to northeast of Luzon Island. The heavy rainfall is hypothesized as caused by the interaction of strong westerlies with the mountain ranges along the west coast of Luzon that produces strong vertical motion and consequently generates heavy rainfall. Four of heavy SWM rainfall cases were examined to determine how the presence and position of tropical cyclones in the Philippine vicinity a¤ect these SWM rainfall events; three cases with TC of varying positions within the Philippine area of responsibility (PAR) and the fourth case without TC. Using a spatial Fourier decomposition approach, the total streamfunction is decomposed into two flow regimes: monsoon basic flow (Waves 0-1) and tropical cyclone perturbation flow (Waves 2-23) over a domain of (20 E-140 W, 5 S-35 N). The purpose of this flow decomposition is to determine the latter's e¤ect on or contribution to the monsoon activity. The analysis utilized the NCEP Final (FNL) data with 1 long. Â 1 lat. resolution. Results show that the tropical cyclones over the Pacific Ocean located northeast of Luzon generate strong southwesterly winds over the west coast of Luzon. These in addition to the southwesterlies from the basic flow strengthened the southwest winds that interact with the high Cordillera Mountain ranges Corresponding author: Esperanza O. Cayanan, Philippine Atmospheric, Geophysical and Astronomical Services Administration (PAGASA), Science Garden, Agham Road, Diliman, Quezon City 1100, Philippines. E-mail: eocayanan@gmail.com 6 2011, Meteorological Society of Japan along the west coast of Luzon. When the tropical cyclone is located north or north-northwest of Luzon, it generates northwesterlies which converge with the southwesterlies from the basic flow. This results to enhancement of rising motion over western Luzon. The much stronger westerlies are then forced to rise above the mountains resulting to strong vertical motion that brings about heavy rainfall.

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“…These characteristics appear particularly in the western part around 10°N-16°N, where the windward side of the southwest monsoon is located. Lower factor loadings of less than 0.5 appeared in the southeastern part of the Philippines, corresponding to the area where it has the rainfall peak for November-January by the northeast monsoon and the orographic effect as shown by Akasaka et al (2007). That is, EOF1 mainly shows consecutive rainfall variations from late May to mid-December, which are characterized by the onset and withdrawal of the southwest monsoon.…”

Section: Resultsmentioning

confidence: 99%

“…Kubota and Wang (2009) estimated that the tropical-cyclone-induced rainfall ratio from July to October exceeds 50% in northern Luzon. Moreover, the mean seasonal march of rainfall amount clearly differs between the western and eastern coastal regions of the Philippines because of the Asian monsoon and the orographic effect, as shown by station rainfall data reported by Akasaka et al (2007) and by the satellite data by Chang et al (2005). Both the rainfall amount and the seasonality of rainfall are important factors for the agriculture and economics of the Philippines.…”

Section: Introductionmentioning

confidence: 99%

Seasonal march patterns of the summer rainy season in the Philippines and their long-term variability since the late twentieth century

Akasaka

Kubota

Matsumoto

et al. 2018

Prog Earth Planet Sci

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This study investigates the seasonal march patterns of rainfall in the Philippines from 1951 to 2012 and their long-term variability. In order to clarify the dominant patterns in the seasonal march of rainfall, an empirical orthogonal function (EOF) analysis was applied to pentad rainfall data of 30 stations. For the first EOF mode (EOF1), we obtained a pattern related to the summer rainy season. We then applied cluster analysis to the time coefficients of EOF1 in each year to classify the seasonal patterns of the summer rainy season. As a result, the patterns were classified into six clusters. We found a long-term change in the pattern appearances with three anomalous patterns frequently observed since the 1990s: (1) a pattern that has an indistinct dry season and a prolonged peak rainfall, (2) a pattern that has a distinct dry season and an earlier withdrawal of the summer rainy season, resulting in a shortened rainy season, and (3) a pattern with a distinct dry season as well as delayed onset and withdrawal of the summer rainy season. This study also shows the relations between these three patterns and the lower atmospheric circulation at the 850 hPa level around the Philippines. Consequently, large positive and negative anomalies in geopotential height were observed around the Philippines for the distinct and indistinct dry seasons, respectively. The duration and condition of the dry season were greatly affected by the strength and location of the subtropical high especially for February-March. It is also noteworthy that the timing of the onset (withdrawal) of the summer rainy season is clearly related to that of the onset of the westerly (northerly) wind in the zonal (meridional) component around the Philippines. Further, the duration and amount of peak rainfall were directly influenced by the strength of the westerly winds in the zonal component. These three anomalous patterns tended to appear in the years when the warm or cold event of the El Niño-Southern Oscillation (ENSO) occurred. This study suggests that the long-term variability in the seasonal march of rainfall is considerably influenced by the variability in ENSO.

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Seasonal march and its spatial difference of rainfall in the Philippines

Cited by 47 publications

References 9 publications

Tropical cyclone influence on the long-term variability of Philippine summer monsoon onset

Tropical cyclone influence on the long-term variability of Philippine summer monsoon onset

The Effect of Tropical Cyclones on Southwest Monsoon Rainfall in the Philippines

Seasonal march patterns of the summer rainy season in the Philippines and their long-term variability since the late twentieth century

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